Part 2 out of 3
porous material such as felt is placed in the pipe leading to the torch
lines. As the acetylene gas passes through this filter the particles of
lime dust and other impurities are extracted from it so that danger of
clogging the torch openings is avoided as much as possible.
The gas is also filtered to a large extent by its passage through the water
in the generating chamber, this filtering or "scrubbing" often being
facilitated by the form of piping through which the gas must pass from the
generating chamber into the holder. If the gas passes out of a number of
small openings when going into the holder the small bubbles give a better
washing than large ones would.
_Piping._--Connections from generators to service pipes should
preferably be made with right and left couplings or long thread nipples
with lock nuts. If unions are used, they should be of a type that does not
require gaskets. The piping should be carried and supported so that any
moisture condensing in the lines will drain back toward the generator and
where low points occur they should be drained through tees leading into
drip cups which are permanently closed with screw caps or plugs. No pet
cocks should be used for this purpose.
For the feed pipes to the torch lines the following pipe sizes are
3/8 inch pipe. 26 feet long. 2 cubic feet per hour.
1/2 inch pipe. 30 feet long. 4 cubic feet per hour.
3/4 inch pipe. 50 feet long. 15 cubic feet per hour.
1 inch pipe. 70 feet long. 27 cubic feet per hour.
1-1/4 inch pipe. 100 feet long. 50 cubic feet per hour.
1-1/2 inch pipe. 150 feet long. 65 cubic feet per hour.
2 inch pipe. 200 feet long. 125 cubic feet per hour.
2-1/2 inch pipe. 300 feet long. 190 cubic feet per hour.
3 inch pipe. 450 feet long. 335 cubic feet per hour.
When drainage is possible into a sewer, the generator should not be
connected directly into the sewer but should first discharge into an open
receptacle, which may in turn be connected to the sewer.
No valves or pet cocks should open into the generator room or any other
room when it would be possible, by opening them for draining purposes, to
allow any escape of gas. Any condensation must be removed without the use
of valves or other working parts, being drained into closed receptacles. It
should be needless to say that all the piping for gas must be perfectly
tight at every point in its length.
_Safety Devices._--Good generators are built in such a way that the
operator must follow the proper order of operation in charging and cleaning
as well as in all other necessary care. It has been mentioned that the gas
pressure is released or shut off before it is possible to fill the water
compartment, and this same idea is carried further in making the generator
inoperative and free from gas pressure before opening the residue drain of
the carbide filling opening on top of the hopper. Some machines are made so
that they automatically cease to generate should there be a sudden and
abnormal withdrawal of gas such as would be caused by a bad leak. This
method of adding safety by automatic means and interlocking parts may be
carried to any extent that seems desirable or necessary to the maker.
All generators should be provided with escape or relief pipes of large size
which lead to the open air. These pipes are carried so that condensation
will drain back toward the generator and after being led out of the
building to a point at least twelve feet above ground, they end in a
protecting hood so that no rain or solid matter can find its way into them.
Any escape of gas which might ordinarily pass into the generator room is
led into these escape pipes, all parts of the system being connected with
the pipe so that the gas will find this way out.
Safety blow off valves are provided so that any excess gas which cannot be
contained by the gas holder may be allowed to escape without causing an
undue rise in pressure. This valve also allows the escape of pressure above
that for which the generator was designed. Gas released in this way passes
into the escape pipe just described.
Inasmuch as the pressure of the oxygen is much greater than that of the
acetylene when used in the torch, it will be seen that anything that caused
the torch outlet to become closed would allow the oxygen to force the
acetylene back into the generator and the oxygen would follow it, making a
very explosive mixture. This return of the gas is prevented by a hydraulic
safety valve or back pressure valve, as it is often called.
Mechanical check valves have been found unsuitable for this use and those
which employ water as a seal are now required by the insurance rules. The
valve itself (Figure 13) consists of a large cylinder containing water to a
certain depth, which is indicated on the valve body. Two pipes come into
the upper end of this cylinder and lead down into the water, one being
longer than the other. The shorter pipe leads to the escape pipe mentioned
above, while the longer one comes from the generator. The upper end of the
cylinder has an opening to which is attached the pipe leading to the
[Illustration: Figure 13.--Hydraulic Back-Pressure Valve.
_A_, Acetylene supply line;
_B_, Vent pipe;
_C_, Water filling plug;
_D_, Acetylene service cock;
_E_, Plug to gauge height of water;
_F_, Gas openings under water;
_G_, Return pipe for sealing water;
_H_, Tube to carry gas below water line;
_I_, Tube to carry gas to escape pipe;
_J_, Gas chamber;
_K_, Plug in upper gas chamber;
_L_, High water level;
_M_, Opening through which water returns;
_O_, Bottom clean out casting]
The gas coming from the generator through the longer pipe passes out of the
lower end of the pipe which is under water and bubbles up through the water
to the space in the top of the cylinder. From there the gas goes to the
pipe leading to the torches. The shorter pipe is closed by the depth of
water so that the gas does not escape to the relief pipe. As long as the
gas flows in the normal direction as described there will be no escape to
the air. Should the gas in the torch line return into the hydraulic valve
its pressure will lower the level of water in the cylinder by forcing some
of the liquid up into the two pipes. As the level of the water lowers, the
shorter pipe will be uncovered first, and as this is the pipe leading to
the open air the gas will be allowed to escape, while the pipe leading back
to the generator is still closed by the water seal. As soon as this reverse
flow ceases, the water will again resume its level and the action will
continue. Because of the small amount of water blown out of the escape pipe
each time the valve is called upon to perform this duty, it is necessary to
see that the correct water level is always maintained.
While there are modifications of this construction, the same principle is
used in all types. The pressure escape valve is often attached to this
hydraulic valve body.
_Construction Details._--Flexible tubing (except at torches), swing
pipe joints, springs, mechanical check valves, chains, pulleys and lead or
fusible piping should never be used on acetylene apparatus except where the
failure of those parts will not affect the safety of the machine or permit,
either directly or indirectly, the escape of gas into a room. Floats should
not be used except where failure will only render the machine inoperative.
It should be said that the National Board of Fire Underwriters have
established an inspection service for acetylene generators and any
apparatus which bears their label, stating that that particular model and
type has been passed, is safe to use. This service is for the best
interests of all concerned and looks toward the prevention of accidents.
Such inspection is a very important and desirable feature of any outfit and
should be insisted upon.
_Location of Generators._--Generators should preferably be placed
outside of insured buildings and in properly constructed generator houses.
The operating mechanism should have ample room to work in and there should
be room enough for the attendant to reach the various parts and perform the
required duties without hindrance or the need of artificial light. They
should also be protected from tampering by unauthorized persons.
Generator houses should not be within five feet of any opening into, nor
have any opening toward, any adjacent building, and should be kept under
lock and key. The size of the house should be no greater than called for by
the requirements mentioned above and it should be well ventilated.
The foundation for the generator itself should be of brick, stone, concrete
or iron, if possible. If of wood, they should be extra heavy, located in a
dry place and open to circulation of air. A board platform is not
satisfactory, but the foundation should be of heavy planking or timber to
make a firm base and so that the air can circulate around the wood.
The generator should stand level and no strain should be placed on any of
the pipes or connections or any parts of the generator proper.
_Tank Valves._--The acetylene tank valve is of the needle type, fitted
with suitable stuffing box nuts and ending in an exposed square shank to
which the special wrench may be fitted when the valve is to be opened or
The valve used on Linde oxygen cylinders is also a needle type, but of
slightly more complex construction. The body of the valve, which screws
into the top of the cylinder, has an opening below through which the gas
comes from the cylinder, and another opening on the side through which it
issues to the torch line. A needle screws down from above to close this
lower opening. The needle which closes the valve is not connected directly
to the threaded member, but fits loosely into it. The threaded part is
turned by a small hand wheel attached to the upper end. When this hand
wheel is turned to the left, or up, as far as it will go, opening the
valve, a rubber disc is compressed inside of the valve body and this disc
serves to prevent leakage of the gas around the spindle.
The oxygen valve also includes a safety nut having a small hole through it
closed by a fusible metal which melts at 250 Fahrenheit. Melting of this
plug allows the gas to exert its pressure against a thin copper diaphragm,
this diaphragm bursting under the gas pressure and allowing the oxygen to
escape into the air.
The hand wheel and upper end of the valve mechanism are protected during
shipment by a large steel cap which covers them when screwed on to the end
of the cylinder. This cap should always be in place when tanks are received
from the makers or returned to them.
[Illustration: Figure 14.--Regulating Valve]
_Regulating Valves._--While the pressure in the gas containers may be
anything from zero to 1,800 pounds, and will vary as the gas is withdrawn,
the pressure of the gas admitted to the torch must be held steady and at a
definite point. This is accomplished by various forms of automatic
regulating valves, which, while they differ somewhat in details of
construction, all operate on the same principle.
The regulator body (Figure 14) carries a union which attaches to the side
outlet on the oxygen tank valve. The gas passes through this union,
following an opening which leads to a large gauge which registers the
pressure on the oxygen remaining in the tank and also to a very small
opening in the end of a tube. The gas passes through this opening and into
the interior of the regulator body. Inside of the body is a metal or rubber
diaphragm placed so that the pressure of the incoming gas causes it to
bulge slightly. Attached to the diaphragm is a sleeve or an arm tipped
with a small piece of fibre, the fibre being placed so that it is directly
opposite the small hole through which the gas entered the diaphragm
chamber. The slight movement of the diaphragm draws the fibre tightly over
the small opening through which the gas is entering, with the result that
further flow is prevented.
Against the opposite side of the diaphragm is the end of a plunger. This
plunger is pressed against the diaphragm by a coiled spring. The tension on
the coiled spring is controlled by the operator through a threaded spindle
ending in a wing or milled nut on the outside of the regulator body.
Screwing in on the nut causes the tension on the spring to increase, with a
consequent increase of pressure on the side of the diaphragm opposite to
that on which the gas acts. Inasmuch as the gas pressure acted to close the
small gas opening and the spring pressure acts in the opposite direction
from the gas, it will be seen that the spring pressure tends to keep the
When the nut is turned way out there is of course, no pressure on the
spring side of the diaphragm and the first gas coming through automatically
closes the opening through which it entered. If now the tension on the
spring be slightly increased, the valve will again open and admit gas until
the pressure of gas within the regulator is just sufficient to overcome the
spring pressure and again close the opening. There will then be a pressure
of gas within the regulator that corresponds to the pressure placed on the
spring by the operator. An opening leads from the regulator interior to the
torch lines so that all gas going to the torches is drawn from the
Any withdrawal of gas will, of course, lower the pressure of that remaining
inside the regulator. The spring tension, remaining at the point determined
by the operator, will overcome this lessened pressure of the gas, and the
valve will again open and admit enough more gas to bring the pressure back
to the starting point. This action continues as long as the spring tension
remains at this point and as long as any gas is taken from the regulator.
Increasing the spring tension will require a greater gas pressure to close
the valve and the pressure of that in the regulator will be correspondingly
When the regulator is not being used, the hand nut should be unscrewed
until no tension remains on the spring, thus closing the valve. After the
oxygen tank valve is open, the regulator hand nut is slowly screwed in
until the spring tension is sufficient to give the required pressure in the
torch lines. Another gauge is attached to the regulator so that it
communicates with the interior of the diaphragm chamber, this gauge showing
the gas pressure going to the torch. It is customary to incorporate a
safety valve in the regulator which will blow off at a dangerous pressure.
In regulating valves and tank valves, as well as all other parts with which
the oxygen comes in contact, it is not permissible to use any form of oil
or grease because of danger of ignition and explosion. The mechanism of a
regulator is too delicate to be handled in the ordinary shop and should any
trouble or leakage develop in this part of the equipment it should be sent
to a company familiar with this class of work for the necessary repairs.
Gas must never be admitted to a regulator until the hand nut is all the way
out, because of danger to the regulator itself and to the operator as well.
A regulator can only be properly adjusted when the tank valve and torch
valves are fully opened.
[Illustration: Figure 15.--High and Low Pressure Gauges with Regulator]
Acetylene regulators are used in connection with tanks of compressed gas.
They are built on exactly the same lines as the oxygen regulating valve and
operate in a similar way. One gauge only, the low pressure indicator, is
used for acetylene regulators, although both high and low pressure may be
used if desired. (See Figure 15.)
Flame is always produced by the combustion of a gas with oxygen and in no
other way. When we burn oil or candles or anything else, the material of
the fuel is first turned to a gas by the heat and is then burned by
combining with the oxygen of the air. If more than a normal supply of air
is forced into the flame, a greater heat and more active burning follows.
If the amount of air, and consequently oxygen, is reduced, the flame
becomes smaller and weaker and the combustion is less rapid. A flame may be
easily extinguished by shutting off all of its air supply.
The oxygen of the combustion only forms one-fifth of the total volume of
air; therefore, if we were to supply pure oxygen in place of air, and in
equal volume, the action would be several times as intense. If the oxygen
is mixed with the fuel gas in the proportion that burns to the very best
advantage, the flame is still further strengthened and still more heat is
developed because of the perfect combustion. The greater the amount of fuel
gas that can be burned in a certain space and within a certain time, the
more heat will be developed from that fuel.
The great amount of heat contained in acetylene gas, greater than that
found in any other gaseous fuel, is used by leading this gas to the
oxy-acetylene torch and there combining it with just the right amount of
oxygen to make a flame of the greatest power and heat than can possibly be
produced by any form of combustion of fuels of this kind. The heat
developed by the flame is about 6300 Fahrenheit and easily melts all the
metals, as well as other solids.
Other gases have been and are now being used in the torch. None of them,
however, produce the heat that acetylene does, and therefore the
oxy-acetylene process has proved the most useful of all. Hydrogen was used
for many years before acetylene was introduced in this field. The
oxy-hydrogen flame develops a heat far below that of oxy-acetylene, namely
4500 Fahrenheit. Coal gas, benzine gas, blaugas and others have also been
used in successful applications, but for the present we will deal
exclusively with the acetylene fuel.
It was only with great difficulty that the obstacles in the way of
successfully using acetylene were overcome by the development of
practicable controlling devices and torches, as well as generators. At
present the oxy-acetylene process is the most universally adaptable, and
probably finds the most widely extended field of usefulness of any welding
The theoretical proportion of the gases for perfect combustion is two and
one-half volumes of oxygen to one of acetylene. In practice this proportion
is one and one-eighth or one and one-quarter volumes of oxygen to one
volume of acetylene, so that the cost is considerably reduced below what it
would be if the theoretical quantity were really necessary, as oxygen costs
much more than acetylene in all cases.
While the heat is so intense as to fuse anything brought into the path of
the flame, it is localized in the small "welding cone" at the torch tip so
that the torch is not at all difficult to handle without special protection
except for the eyes, as already noted. The art of successful welding may be
acquired by any operator of average intelligence within a reasonable time
and with some practice. One trouble met with in the adoption of this
process has been that the operation looks so simple and so easy of
performance that unskilled and unprepared persons have been tempted to try
welding, with results that often caused condemnation of the process, when
the real fault lay entirely with the operator.
The form of torch usually employed is from twelve to twenty-four inches
long and is composed of a handle at one end with tubes leading from this
handle to the "welding head" or torch proper. At or near one end of the
handle are adjustable cocks or valves for allowing the gases to flow into
the torch or to prevent them from doing so. These cocks are often used for
regulating the pressure and amount of gas flowing to the welding head, but
are not always constructed for this purpose and should not be so used when
it is possible to secure pressure adjustment at the regulators (Figure 16).
Figure 16 shows three different sizes of torches. The number 5 torch is
designed especially for jewelers' work and thin sheet steel welding. It is
eleven inches in length and weighs nineteen ounces. The tips for the number
10 torch are interchangeable with the number 5. The number 10 torch is
adapted for general use on light and medium heavy work. It has six tips and
its length is sixteen inches, with a weight of twenty-three ounces.
The number 15 torch is designed for heavy work, being twenty-five inches in
length, permitting the operator to stand away from the heat of the metal
being worked. These heavy tips are in two parts, the oxygen check being
[Illustration: Figure 16.--Three Sizes of Torches, with Tips]
Figures 17 and 18 show two sizes of another welding torch. Still another
type is shown in Figure 19 with four interchangeable tips, the function of
each being as follows:
No. 1. For heavy castings.
No. 2. Light castings and heavy sheet metal.
No. 3. Light sheet metal.
No. 4. Very light sheet metal and wire.
[Illustration: Figure 17.--Cox Welding Torch (No. 1)]
[Illustration: Figure 18.--Cox Welding Torch (No. 2)]
[Illustration: Figure 19.--Monarch Welding Torch]
At the side of the shut off cock away from the torch handle the gas tubes
end in standard forms of hose nozzles, to which the rubber hose from the
gas supply tanks or generators can be attached. The tubes from the handle
to the head may be entirely separate from each other, or one may be
contained within the other. As a general rule the upper one of two
separate tubes carries the oxygen, while this gas is carried in the inside
tube when they are concentric with each other.
In the welding head is the mixing chamber designed to produce an intimate
mixture of the two gases before they issue from the nozzle to the flame.
The nozzle, or welding tip, of a suitable size are design for the work to
be handled and the pressure of gases being used, is attached to the welding
head and consists essentially of the passage at the outer end of which the
The torch body and tubes are usually made of brass, although copper is
sometimes used. The joint must be very strong, and are usually threaded and
soldered with silver solder. The nozzle proper is made from copper, because
it withstands the heat of the flame better than other less suitable metals.
The torch must be built in such a way that it is not at all liable to come
apart under the influence of high temperatures.
All torches are constructed in such a way that it is impossible for the
gases to mix by any possible chance before they reach the head, and the
amount of gas contained in the head and tip after being mixed is made as
small as possible. In order to prevent the return of the flame through the
acetylene tube under the influence of the high pressure oxygen some form of
back flash preventer is usually incorporated in the torch at or near the
point at which the acetylene enters. This preventer takes the form of some
porous and heat absorbing material, such as aluminum shavings, contained in
a small cavity through which the gas passes on its way to the head.
_High Pressure Torches._--Torches are divided into the same classes as
are the generators; that is, high pressure, medium pressure and low
pressure. As mentioned before, the medium pressure is usually called the
high pressure, because there are very few true high pressure systems in
use, and comparatively speaking the medium pressure type is one of high
[Illustration: Figure 20.--High Pressure Torch Head]
With a true high pressure torch (Figure 20) the gases are used at very
nearly equal heads so that the mixing before ignition is a simple matter.
This type admits the oxygen at the inner end of a straight passage leading
to the tip of the nozzle. The acetylene comes into this same passage from
openings at one side and near the inner end. The difference in direction of
the two gases as they enter the passage assists in making a homogeneous
mixture. The construction of this nozzle is perfectly simple and is easily
understood. The true high pressure torch nozzle is only suited for use with
compressed and dissolved acetylene, no other gas being at a sufficient
pressure to make the action necessary in mixing the gases.
_Medium Pressure Torches._--The medium pressure (usually called high
pressure) torch (Figure 21) uses acetylene from a medium pressure generator
or from tanks of compressed gas, but will not take the acetylene from low
[Illustration: Figure 21.--Medium Pressure Torch Head]
The construction of the mixing chamber and nozzle is very similar to that
of the high pressure torch, the gases entering in the same way and from the
same positions of openings. The pressure of the acetylene is but little
lower than that of the oxygen, and the two gases, meeting at right angles,
form a very intimate mixture at this point of juncture. The mixture in its
proportions of gases depends entirely on the sizes of the oxygen and
acetylene openings into the mixing chamber and on the pressures at which
the gases are admitted. There is a very slight injector action as the fast
moving stream of oxygen tends to draw the acetylene from the side openings
into the chamber, but the operation of the torch does not depend on this
action to any extent.
_Low Pressure Torches._--The low pressure torch (Figure 22) will use
gas from low pressure generators from medium pressure machines or from
tanks in which it has been compressed and dissolved. This type depends for
a perfect mixture of gas upon the principle of the injector just as it is
applied in steam boiler practice.
[Illustration: Figure 22.--Low Pressure Torch with Separate Injector
The oxygen enters the head at considerable pressure and passes through its
tube to a small jet within the head. The opening of this jet is directly
opposite the end of the opening through the nozzle which forms the mixing
chamber and the path of the gases to the flame. A small distance remains
between the opening from which the oxygen issues and the inner opening into
the mixing passage. The stream of oxygen rushes across this space and
enters the mixing chamber, being driven by its own pressure.
The acetylene enters the head in an annular space surrounding the oxygen
tube. The space between oxygen jet and mixing chamber opening is at one end
of this acetylene space and the stream of oxygen seizes the acetylene and
under the injector action draws it into the mixing chamber, it being
necessary only to have a sufficient supply of acetylene flowing into the
head to allow the oxygen to draw the required proportion for a proper
The volume of gas drawn into the mixing chamber depends on the size of the
injector openings and the pressure of the oxygen. In practice the oxygen
pressure is not altered to produce different sized flames, but a new nozzle
is substituted which is designed to give the required flame. Each nozzle
carries its own injector, so that the design is always suited to the
conditions. While torches are made having the injector as a permanent part
of the torch body, the replaceable nozzle is more commonly used because it
makes the one torch suitable for a large range of work and a large number
of different sized flames. With the replaceable head a definite pressure of
oxygen is required for the size being used, this pressure being the one for
which the injector and corresponding mixing chamber were designed in
producing the correct mixture.
_Adjustable Injectors._-Another form of low pressure torch operates on
the injector principle, but the injector itself is a permanent part of the
torch, the nozzle only being changed for different sizes of work and flame.
The injector is placed in or near the handle and its opening is the largest
required by any work that can be handled by this particular torch. The
opening through the tip of the injector through which the oxygen issues on
its way to the mixing chamber may be wholly or partly closed by a needle
valve which may be screwed into the opening or withdrawn from it, according
to the operator's judgment. The needle valve ends in a milled nut outside
the torch handle, this being the adjustment provided for the different
_Torch Construction._--A well designed torch is so designed that the
weight distribution is best for holding it in the proper position for
welding. When a torch is grasped by its handle with the gas hose attached,
it should balance so that it does not feel appreciably heavier on one end
than on the other.
The head and nozzle may be placed so that the flame issues in a line at
right angles with the torch body, or they may be attached at an angle
convenient for the work to be done. The head set at an angle of from 120 to
170 degrees with the body is usually preferred for general work in welding,
while the cutting torch usually has its head at right angles to the body.
Removable nozzles have various size openings through them and the different
sizes are designated by numbers from 1 up. The same number does not always
indicate the same size opening in torches of different makes, nor does it
indicate a nozzle of the same capacity.
The design of the nozzle, the mixing chamber, the injector, when one is
used, and the size of the gas openings must be such that all these things
are suited to each other if a proper mixture of gas is to be secured. Parts
that are not made to work together are unsafe if used because of the danger
of a flash back of the flame into the mixing chamber and gas tubes. It is
well known that flame travels through any inflammable gas at a certain
definite rate of speed, depending on the degree of inflammability of the
gas. The easier and quicker the gas burns, the faster will the flame travel
If the gas in the nozzle and mixing chamber stood still, the flame would
immediately travel back into these parts and produce an explosion of more
or less violence. The speed with which the gases issue from the nozzle
prevent this from happening because the flame travels back through the gas
at the same speed at which the gas issues from the torch tip. Should the
velocity of the gas be greater than the speed of flame propagation through
it, it will be impossible to keep the flame at the tip, the tendency being
for a space of unburned gas to appear between tip and flame. On the other
hand, should the speed of the flame exceed the velocity with which the gas
comes from the torch there will result a flash back and explosion.
_Care of Torches._--An oxy-acetylene torch is a very delicate and
sensitive device, much more so that appears on the surface. It must be
given equally as good care and attention as any other high-priced piece of
machinery if it is to be maintained in good condition for use.
It requires cleaning of the nozzles at regular intervals if used regularly.
This cleaning is accomplished with a piece of copper or brass wire run
through the opening, and never with any metal such as steel or iron that is
harder than the nozzle itself, because of the danger of changing the size
of the openings. The torch head and nozzle can often be cleaned by allowing
the oxygen to blow through at high pressure without the use of any tools.
In using a torch a deposit of carbon will gradually form inside of the
head, and this deposit will be more rapid if the operator lights the stream
of acetylene before turning any oxygen into the torch. This deposit may be
removed by running kerosene through the nozzle while it is removed from the
torch, setting fire to the kerosene and allowing oxygen to flow through
while the oil is burning.
Should a torch become clogged in the head or tubes, it may usually be
cleaned by removing the oxygen hose from the handle end, closing the
acetylene cock on the torch, placing the end of the oxygen hose over the
opening in the nozzle and turning on the oxygen under pressure to blow the
obstruction back through the passage that it has entered. By opening the
acetylene cock and closing the oxygen cock at the handle, the acetylene
passages may then be cleaned in the same way. Under no conditions should a
torch be taken apart any more than to remove the changeable nozzle, except
in the hands of those experienced in this work.
_Nozzle Sizes._--The size of opening through the nozzle is determined
according to the thickness and kind of metal being handled. The following
sizes are recommended for steel:
Davis-Bournonville. Oxweld Low
Thickness of Metal (Medium Pressure.) Pressure
1/32 Tip No. 1 Head No. 2
3/32 3 4
3/8 4 5
3/16 5 6
1/4 6 7
3/8 8 8
1/2 9 10
5/8 10 12
3/4 11 15
Very heavy 12 15
_Cutting Torches._--Steel may be cut with a jet of oxygen at a rate of
speed greater than in any other practicable way under usual conditions. The
action consists of burning away a thin section of the metal by allowing a
stream of oxygen to flow onto it while the gas is at high pressure and the
metal at a white heat.
[Illustration: Figure 23.--Cutting Torch]
The cutting torch (Figure 23) has the same characteristics as the welding
torch, but has an additional nozzle or means for temporarily using the
welding opening for the high pressure oxygen. The oxygen issues from the
opening while cutting at a pressure of from ten to 100 pounds to the square
The work is first heated to a white heat by adjusting the torch for a
welding flame. As soon as the metal reaches this temperature, the high
pressure oxygen is turned on to the white-hot portion of the steel. When
the jet of gas strikes the metal it cuts straight through, leaving a very
narrow slot and removing but little metal. Thicknesses of steel up to ten
inches can be economically handled in this way.
The oxygen nozzle is usually arranged so that it is surrounded by a number
of small jets for the heating flame. It will be seen that this arrangement
makes the heating flame always precede the oxygen jet, no matter in which
direction the torch is moved.
The torch is held firmly, either by hand or with the help of special
mechanism for guiding it in the desired path, and is steadily advanced in
the direction it is desired to extend the cut, the rate of advance being
from three inches to two feet per minute through metal from nine inches
down to one-quarter of an inch in thickness.
The following data on cutting is given by the Davis-Bournonville Company:
Feet Cost of
Thickness of Gas Inches Gases
of Cutting Heating per Foot Oxygen Cut per per Foot
Steel Oxygen Oxygen of Cut Acetylene Min. of Cut
1/4 10 lbs. 4 lbs. .40 .086 24 $ .013
1/2 20 4 .91 .150 15 .029
3/4 30 4 1.16 .150 15 .036
1 30 4 1.45 .172 12 .045
1 1/2 30 5 2.40 .380 12 .076
2 40 5 2.96 .380 12 .093
4 50 5 9.70 .800 7 .299
6 70 6 21.09 1.50 4 .648
9 100 6 43.20 2.00 3 1.311
_Acetylene-Air Torch._--A form of torch which burns the acetylene after
mixing it with atmospheric air at normal pressure rather than with the
oxygen under higher pressures has been found useful in certain pre-heating,
brazing and similar operations. This torch (Figure 24) is attached by a
rubber gas hose to any compressed acetylene tank and is regulated as to
flame size and temperature by opening or closing the tank valve more or
After attaching the torch to the tank, the gas is turned on very slowly and
is lighted at the torch tip. The adjustment should cause the presence of a
greenish-white cone of flame surrounded by a larger body of burning gas,
the cone starting at the mouth of the torch.
[Illustration: Figure 24.--Acetylene-Air Torch]
By opening the tank valve more, a longer and hotter flame is produced, the
length being regulated by the tank valve also. This torch will give
sufficient heat to melt steel, although not under conditions suited to
welding. Because of the excess of acetylene always present there is no
danger of oxidizing the metal being heated.
The only care required by this torch is to keep the small air passages at
the nozzle clean and free from carbon deposits. The flame should be
extinguished when not in use rather than turned low, because this low flame
rapidly deposits large quantities of soot in the burner.
OXY-ACETYLENE WELDING PRACTICE
PREPARATION OF WORK
_Preheating._--The practice of heating the metal around the weld
before applying the torch flame is a desirable one for two reasons. First,
it makes the whole process more economical; second, it avoids the danger of
breakage through expansion and contraction of the work as it is heated and
as it cools.
When it is desired to join two surfaces by welding them, it is, of course,
necessary to raise the metal from the temperature of the surrounding air to
its melting point, involving an increase in temperature of from one
thousand to nearly three thousand degrees. To obtain this entire increase
of temperature with the torch flame is very wasteful of fuel and of the
operator's time. The total amount of heat necessary to put into metal is
increased by the conductivity of that metal because the heat applied at the
weld is carried to other parts of the piece being handled until the whole
mass is considerably raised in temperature. To secure this widely
distributed increase the various methods of preheating are adopted.
As to the second reason for preliminary heating. It is understood that the
metal added to the joint is molten at the time it flows into place. All the
metals used in welding contract as they cool and occupy a much smaller
space than when molten. If additional metal is run between two adjoining
surfaces which are parts of a surrounding body of cool metal, this added
metal will cool while the surfaces themselves are held stationary in the
position they originally occupied. The inevitable result is that the metal
added will crack under the strain, or, if the weld is exceptionally strong,
the main body of the work will he broken by the force of contraction. To
overcome these difficulties is the second and most important reason for
preheating and also for slow cooling following the completion of the weld.
There are many ways of securing this preheating. The work may be brought to
a red heat in the forge if it is cast iron or steel; it may he heated in
special ovens built for the purpose; it may be placed in a bed of charcoal
while suitably supported; it may be heated by gas or gasoline preheating
torches, and with very small work the outer flame of the welding torch
automatically provides means to this end.
The temperature of the parts heated should be gradually raised in all
cases, giving the entire mass of metal a chance to expand equally and to
adjust itself to the strains imposed by the preheating. After the region
around the weld has been brought to a proper temperature the opening to be
filled is exposed so that the torch flame can reach it, while the remaining
surfaces are still protected from cold air currents and from cooling
through natural radiation.
One of the commonest methods and one of the best for handling work of
rather large size is to place the piece to be welded on a bed of fire brick
and build a loose wall around it with other fire brick placed in rows, one
on top of the other, with air spaces left between adjacent bricks in each
row. The space between the brick retaining wall and the work is filled with
charcoal, which is lighted from below. The top opening of the temporary
oven is then covered with asbestos and the fire kept up until the work has
been uniformly raised in temperature to the desired point.
When much work of the same general character and size is to be handled, a
permanent oven may be constructed of fire brick, leaving a large opening
through the top and also through one side. Charcoal may be used in this
form of oven as with the temporary arrangement, or the heat may be secured
from any form of burner or torch giving a large volume of flame. In any
method employing flame to do the heating, the work itself must be protected
from the direct blast of the fire. Baffles of brick or metal should be
placed between the mouth of the torch and the nearest surface of the work
so that the flame will be deflected to either side and around the piece
The heat should be applied to bring the point of welding to the highest
temperature desired and, except in the smallest work, the heat should
gradually shade off from this point to the other parts of the piece. In the
case of cast iron and steel the temperature at the point to be welded
should be great enough to produce a dull red heat. This will make the whole
operation much easier, because there will be no surrounding cool metal to
reduce the temperature of the molten material from the welding rod below
the point at which it will join the work. From this red heat the mass of
metal should grow cooler as the distance from the weld becomes greater, so
that no great strain is placed upon any one part. With work of a very
irregular shape it is always best to heat the entire piece so that the
strains will be so evenly distributed that they can cause no distortion or
breakage under any conditions.
The melting point of the work which is being preheated should be kept in
mind and care exercised not to approach it too closely. Special care is
necessary with aluminum in this respect, because of its low melting
temperature and the sudden weakening and flowing without warning. Workmen
have carelessly overheated aluminum castings and, upon uncovering the piece
to make the weld, have been astonished to find that it had disappeared.
Six hundred degrees is about the safe limit for this metal. It is possible
to gauge the exact temperature of the work with a pyrometer, but when this
instrument cannot be procured, it might be well to secure a number of
"temperature cones" from a chemical or laboratory supply house. These cones
are made from material that will soften at a certain heat and in form they
are long and pointed. Placed in position on the part being heated, the
point may be watched, and when it bends over it is sure that the metal
itself has reached a temperature considerably in excess of the temperature
at which that particular cone was designed to soften.
The object in preheating the metal around the weld is to cause it to expand
sufficiently to open the crack a distance equal to the contraction when
cooling from the melting point. In the case of a crack running from the
edge of a piece into the body or of a crack wholly within the body, it is
usually satisfactory to heat the metal at each end of the opening. This
will cause the whole length of the crack to open sufficiently to receive
the molten material from the rod.
The judgment of the operator will be called upon to decide just where a
piece of metal should be heated to open the weld properly. It is often
possible to apply the preheating flame to a point some distance from the
point of work if the parts are so connected that the expansion of the
heated part will serve to draw the edges of the weld apart. Whatever part
of the work is heated to cause expansion and separation, this part must
remain hot during the entire time of welding and must then cool slowly at
the same time as the metal in the weld cools.
[Illustration: Figure 25.--Preheating at _A_ While Welding at
_B_. _C_ also May Be Heated.]
An example of heating points away from the crack might be found in welding
a lattice work with one of the bars cracked through (Figure 25). If the
strips parallel and near to the broken bar are heated gradually, the work
will be so expanded that the edges of the break are drawn apart and the
weld can be successfully made. In this case, the parallel bars next to the
broken one would be heated highest, the next row not quite so hot and so on
for some distance away. If only the one row were heated, the strains set up
in the next ones would be sufficient to cause a new break to appear.
[Illustration: Figure 26.--Cutting Through the Rim of a Wheel (Cut Shown
If welding is to be done near the central portion of a large piece, the
strains will be brought to bear on the parts farthest away from the center.
Should a fly wheel spoke be broken and made ready to weld, the greatest
strain will come on the rim of the wheel. In cases like this it is often
desirable to cut through at the point of greatest strain with a saw or
cutting torch, allowing free movement while the weld is made at the
original break (Figure 26). After the inside weld is completed, the cut may
be welded without danger, for the reason that it will always be at some
point at which severe strains cannot be set up by the contraction of the
[Illustration: Figure 27.--Using a Wedge While Welding]
In materials that will spring to some extent without breakage, that is, in
parts that are not brittle, it may be possible to force the work out of
shape with jacks or wedges (Figure 27) in the same way that it would be
distorted by heating and expanding some portion of it as described. A
careful examination will show whether this method can be followed in such a
way as to force the edges of the break to separate. If the plan seems
feasible, the wedges may be put in place and allowed to remain while the
weld is completed. As soon as the work is finished the wedges should be
removed so that the natural contraction can take place without damage.
It should always be remembered that it is not so much the expansion of the
work when heated as it is the contraction caused by cooling that will do
the damage. A weld may be made that, to all appearances, is perfect and it
may be perfect when completed; but if provision has not been made to allow
for the contraction that is certain to follow, there will be a breakage at
some point. It is not possible to weld the simplest shapes, other than
straight bars, without considering this difficulty and making provision to
take care of it.
The exact method to employ in preheating will always call for good judgment
on the part of the workman, and he should remember that the success or
failure of his work will depend fully as much on proper preparation as on
correct handling of the weld itself. It should be remembered that the outer
flame of the oxy-acetylene torch may be depended on for a certain amount of
preheating, as this flame gives a very large volume of heat, but a heat
that is not so intense nor so localized as the welding flame itself. The
heat of this part of the flame should be fully utilized during the
operation of melting the metal and it should be so directed, when possible,
that it will bring the parts next to be joined to as high a temperature as
When the work has been brought to the desired temperature, all parts except
the break and the surface immediately surrounding it on both sides should
be covered with heavy sheet asbestos. This protecting cover should remain
in place throughout the operation and should only be moved a distance
sufficient to allow the torch flame to travel in the path of the weld. The
use of asbestos in this way serves a twofold purpose. It retains the heat
in the work and prevents the breakage that would follow if a draught of air
were to strike the heated metal, and it also prevents such a radiation of
heat through the surrounding air as would make it almost impossible for the
operator to perform his work, especially in the case of large and heavy
castings when the amount of heat utilized is large.
_Cleaning and Champfering._--A perfect weld can never be made unless
the surfaces to be joined have been properly prepared to receive the new
All spoiled, burned, corroded and rough particles must positively be
removed with chisel and hammer and with a free application of emery cloth
and wire brush. The metal exposed to the welding flame should be perfectly
clean and bright all over, or else the additional material will not unite,
but will only stick at best.
[Illustration: Figure 28.--Tapering the Opening Formed by a Break]
Following the cleaning it is always necessary to bevel, or champfer, the
edges except in the thinnest sheet metal. To make a weld that will hold,
the metal must be made into one piece, without holes or unfilled portions
at any point, and must be solid from inside to outside. This can only be
accomplished by starting the addition of metal at one point and gradually
building it up until the outside, or top, is reached. With comparatively
thin plates the molten metal may be started from the side farthest from the
operator and brought through, but with thicker sections the addition is
started in the middle and brought flush with one side and then with the
It will readily be seen that the molten material cannot be depended upon to
flow between the tightly closed surfaces of a crack in a way that can be at
all sure to make a true weld. It will be necessary for the operator to
reach to the farthest side with the flame and welding rod, and to start the
new surfaces there. To allow this, the edges that are to be joined are
beveled from one side to the other (Figure 28), so that when placed
together in approximately the position they are to occupy they will leave a
grooved channel between them with its sides at an angle with each other
sufficient in size to allow access to every point of each surface.
[Illustration: Figure 29.--Beveling for Thin Work]
[Illustration: Figure 30.--Beveling for Thick Work]
With work less than one-fourth inch thick, this angle should be forty-five
degrees on each piece (Figure 29), so that when they are placed together
the extreme edges will meet at the bottom of a groove whose sides are
square, or at right angles, to each other. This beveling should be done so
that only a thin edge is left where the two parts come together, just
enough points in contact to make the alignment easy to hold. With work of a
thickness greater than a quarter of an inch, the angle of bevel on each
piece may be sixty degrees (Figure 30), so that when placed together the
angle included between the sloping sides will also be sixty degrees. If the
plate is less than one-eighth of an inch thick the beveling is not
necessary, as the edges may be melted all the way through without danger of
leaving blowholes at any point.
[Illustration: Figure 31.--Beveling Both Sides of a Thick Piece]
[Illustration: Figure 32.--Beveling the End of a Pipe]
This beveling may be done in any convenient way. A chisel is usually most
satisfactory and also quickest. Small sections may be handled by filing,
while metal that is too hard to cut in either of these ways may be shaped
on the emery wheel. It is not necessary that the edges be perfectly
finished and absolutely smooth, but they should be of regular outline and
should always taper off to a thin edge so that when the flame is first
applied it can be seen issuing from the far side of the crack. If the work
is quite thick and is of a shape that will allow it to be turned over, the
bevel may be brought from both sides (Figure 31), so that there will be two
grooves, one on each surface of the work. After completing the weld on one
side, the piece is reversed and finished on the other side. Figure 32 shows
the proper beveling for welding pipe. Figure 33 shows how sheet metal may
be flanged for welding.
Welding should not be attempted with the edges separated in place of
beveled, because it will be found impossible to build up a solid web of new
metal from one side clear through to the other by this method. The flame
cannot reach the surfaces to make them molten while receiving new material
from the rod, and if the flame does not reach them it will only serve to
cause a few drops of the metal to join and will surely cause a weak and
[Illustration: Figure 33.--Flanging Sheet Metal for Welding]
_Supporting Work._--During the operation of welding it is necessary
that the work be well supported in the position it should occupy. This may
be done with fire brick placed under the pieces in the correct position,
or, better still, with some form of clamp. The edges of the crack should
touch each other at the point where welding is to start and from there
should gradually separate at the rate of about one-fourth inch to the foot.
This is done so that the cooling of the molten metal as it is added will
draw the edges together by its contraction.
Care must be used to see that the work is supported so that it will
maintain the same relative position between the parts as must be present
when the work is finished. In this connection it must be remembered that
the expansion of the metal when heated may be great enough to cause serious
distortion and to provide against this is one of the difficulties to be
Perfect alignment should be secured between the separate parts that are to
be joined and the two edges must be held up so that they will be in the
same plane while welding is carried out. If, by any chance, one drops
below the other while molten metal is being added, the whole job may have
to be undone and done over again. One precaution that is necessary is that
of making sure that the clamping or supporting does not in itself pull the
work out of shape while melted.
[Illustration: Figure 34.--Rotary Movement of Torch in Welding]
The weld is made by bringing the tip of the welding flame to the edges of
the metals to be joined. The torch should be held in the right hand and
moved slowly along the crack with a rotating motion, traveling in small
circles (Figure 34), so that the Welding flame touches first on one side of
the crack and then on the other. On large work the motion may be simply
back and forth across the crack, advancing regularly as the metal unites.
It is usually best to weld toward the operator rather than from him,
although this rule is governed by circumstances. The head of the torch
should be inclined at an angle of about 60 degrees to the surface of the
work. The torch handle should extend in the same line with the break
(Figure 35) and not across it, except when welding very light plates.
[Illustration: Figure 35.--Torch Held in Line with the Break]
If the metal is 1/16 inch or less in thickness it is only necessary to
circle along the crack, the metal itself furnishing enough material to
complete the weld without additions. Heat both sides evenly until they flow
Material thicker than the above requires the addition of more metal of the
same or different kind from the welding rod, this rod being held by the
left hand. The proper size rod for cast iron is one having a diameter equal
to the thickness of metal being welded up to a one-half inch rod, which is
the largest used. For steel the rod should be one-half the thickness of the
metal being joined up to one-fourth inch rod. As a general rule, better
results will be obtained by the use of smaller rods, the very small sizes
being twisted together to furnish enough material while retaining the free
[Illustration: Figure 36.--The Welding Rod Should Be Held in the Molten
The tip of the rod must at all times be held in contact with the pieces
being welded and the flame must be so directed that the two sides of the
crack and the end of the rod are melted at the same time (Figure 36).
Before anything is added from the rod, the sides of the crack are melted
down sufficiently to fill the bottom of the groove and join the two sides.
Afterward, as metal comes from the rod in filling the crack, the flame is
circled along the joint being made, the rod always following the flame.
[Illustration: Figure 37.--Welding Pieces of Unequal Thickness]
Figure 37 illustrates the welding of pieces of unequal thickness.
Figure 38 illustrates welding at an angle.
The molten metal may be directed as to where it should go by the tip of the
welding flame, which has considerable force, but care must be taken not to
blow melted metal on to cooler surfaces which it cannot join. If, while
welding, a spot appears which does not unite with the weld, it may be
handled by heating all around it to a white heat and then immediately
welding the bad place.
[Illustration: Figure 38.--Welding at an Angle]
Never stop in the middle of a weld, as it is extremely difficult to
continue smoothly when resuming work.
_The Flame._--The welding flame must have exactly the right
proportions of each gas. If there is too much oxygen, the metal will be
burned or oxidized; the presence of too much acetylene carbonizes the
metal; that is to say, it adds carbon and makes the work harder. Just the
right mixture will neither burn nor carbonize and is said to be a "neutral"
flame. The neutral flame, if of the correct size for the work, reduces the
metal to a melted condition, not too fluid, and for a width about the same
as the thickness of the metal being welded.
When ready to light the torch, after attaching the right tip or head as
directed in accordance with the thickness of metal to be handled, it will
be necessary to regulate the pressure of gases to secure the neutral flame.
The oxygen will have a pressure of from 2 to 20 pounds, according to the
nozzle used. The acetylene will have much less. Even with the compressed
gas, the pressure should never exceed 10 pounds for the largest work, and
it will usually be from 4 to 6. In low pressure systems, the acetylene will
be received at generator pressure. It should first be seen that the
hand-screws on the regulators are turned way out so that the springs are
free from any tension. It will do no harm if these screws are turned back
until they come out of the threads. This must be done with both oxygen and
Next, open the valve from the generator, or on the acetylene tank, and
carefully note whether there is any odor of escaping gas. Any leakage of
this gas must be stopped before going on with the work.
The hand wheel controlling the oxygen cylinder valve should now be turned
very slowly to the left as far as it will go, which opens the valve, and
it should be borne in mind the pressure that is being released. Turn in the
hand screw on the oxygen regulator until the small pressure gauge shows a
reading according to the requirements of the nozzle being used. This oxygen
regulator adjustment should be made with the cock on the torch open, and
after the regulator is thus adjusted the torch cock may be closed.
Open the acetylene cock on the torch and screw in on the acetylene
regulator hand-screw until gas commences to come through the torch. Light
this flow of acetylene and adjust the regulator screw to the pressure
desired, or, if there is no gauge, so that there is a good full flame. With
the pressure of acetylene controlled by the type of generator it will only
be necessary to open the torch cock.
With the acetylene burning, slowly open the oxygen cock on the torch and
allow this gas to join the flame. The flame will turn intensely bright and
then blue white. There will be an outer flame from four to eight inches
long and from one to three inches thick. Inside of this flame will be two
more rather distinctly defined flames. The inner one at the torch tip is
very small, and the intermediate one is long and pointed. The oxygen should
be turned on until the two inner flames unite into one blue-white cone from
one-fourth to one-half inch long and one-eighth to one-fourth inch in
diameter. If this single, clearly defined cone does not appear when the
oxygen torch cock has been fully opened, turn off some of the acetylene
until it does appear.
If too much oxygen is added to the flame, there will still be the central
blue-white cone, but it will be smaller and more or less ragged around the
edges (Figure 39). When there is just enough oxygen to make the single
cone, and when, by turning on more acetylene or by turning off oxygen, two
cones are caused to appear, the flame is neutral (Figure 40), and the small
blue-white cone is called the welding flame.
[Illustration: Figure 39.--Oxidizing Flame--Too Much Oxygen]
[Illustration: Figure 40.--Neutral Flame]
[Illustration: Figure 41.--Reducing Flame--Showing an Excess of Acetylene]
While welding, test the correctness of the flame adjustment occasionally by
turning on more acetylene or by turning off some oxygen until two flames or
cones appear. Then regulate as before to secure the single distinct cone.
Too much oxygen is not usually so harmful as too much acetylene, except
with aluminum. (See Figure 41.) An excessive amount of sparks coming from
the weld denotes that there is too much oxygen in the flame. Should the
opening in the tip become partly clogged, it will be difficult to secure a
neutral flame and the tip should be cleaned with a brass or copper
wire--never with iron or steel tools or wire of any kind. While the torch
is doing its work, the tip may become excessively hot due to the heat
radiated from the molten metal. The tip may be cooled by turning off the
acetylene and dipping in water with a slight flow of oxygen through the
nozzle to prevent water finding its way into the mixing chamber.
The regulators for cutting are similar to those for welding, except that
higher pressures may be handled, and they are fitted with gauges reading up
to 200 or 250 pounds pressure.
In welding metals which conduct the heat very rapidly it is necessary to
use a much larger nozzle and flame than for metals which have not this
property. This peculiarity is found to the greatest extent in copper,
aluminum and brass.
Should a hole be blown through the work, it may be closed by withdrawing
the flame for a few seconds and then commencing to build additional metal
around the edges, working all the way around and finally closing the small
opening left at the center with a drop or two from the welding rod.
WELDING VARIOUS METALS
Because of the varying melting points, rates of expansion and contraction,
and other peculiarities of different metals, it is necessary to give
detailed consideration to the most important ones.
_Characteristics of Metals._--The welder should thoroughly understand
the peculiarities of the various metals with which he has to deal. The
metals and their alloys are described under this heading in the first
chapter of this book and a tabulated list of the most important points
relating to each metal will be found at the end of the present chapter.
All this information should be noted by the operator of a welding
installation before commencing actual work.
Because of the nature of welding, the melting point of a metal is of great
importance. A metal melting at a low temperature should have more careful
treatment to avoid undesired flow than one which melts at a temperature
which is relatively high. When two dissimilar metals are to be joined, the
one which melts at the higher temperature must be acted upon by the flame
first and when it is in a molten condition the heat contained in it will in
many cases be sufficient to cause fusion of the lower melting metal and
allow them to unite without playing the flame on the lower metal to any
The heat conductivity bears a very important relation to welding, inasmuch
as a metal with a high rate of conductance requires more protection from
cooling air currents and heat radiation than one not having this quality to
such a marked extent. A metal which conducts heat rapidly will require a
larger volume of flame, a larger nozzle, than otherwise, this being
necessary to supply the additional heat taken away from the welding point
by this conductance.
The relative rates of expansion of the various metals under heat should be
understood in order that parts made from such material may have proper
preparation to compensate for this expansion and contraction. Parts made
from metals having widely varying rates of expansion must have special
treatment to allow for this quality, otherwise breakage is sure to occur.
_Cast Iron._--All spoiled metal should he cut away and if the work is
more than one-eighth inch in thickness the sides of the crack should be
beveled to a 45 degree angle, leaving a number of points touching at the
bottom of the bevel so that the work may be joined in its original
The entire piece should be preheated in a bricked-up oven or with charcoal
placed on the forge, when size does not warrant building a temporary oven.
The entire piece should be slowly heated and the portion immediately
surrounding the weld should be brought to a dull red. Care should be used
that the heat does not warp the metal through application to one part more
than the others. After welding, the work should be slowly cooled by
covering with ashes, slaked lime, asbestos fibre or some other
non-conductor of heat. These precautions are absolutely essential in the
case of cast iron.
A neutral flame, from a nozzle proportioned to the thickness of the work,
should be held with the point of the blue-white cone about one-eighth inch
from the surface of the iron.
A cast iron rod of correct diameter, usually made with an excess of
silicon, is used by keeping its end in contact with the molten metal and
flowing it into the puddle formed at the point of fusion. Metal should be
added so that the weld stands about one-eighth inch above the surrounding
surface of the work.
Various forms of flux may be used and they are applied by dipping the end
of the welding rod into the powder at intervals. These powders may contain
borax or salt, and to prevent a hard, brittle weld, graphite or
ferro-silicon may be added. Flux should be added only after the iron is
molten and as little as possible should be used. No flux should be used
just before completion of the work.
The welding flame should be played on the work around the crack and
gradually brought to bear on the work. The bottom of the bevel should be
joined first and it will be noted that the cast iron tends to run toward
the flame, but does not stick together easily. A hard and porous weld
should be carefully guarded against, as described above, and upon
completion of the work the welded surface should be scraped with a file,
while still red hot, in order to remove the surface scale.
_Malleable Iron._--This material should be beveled in the same way
that cast iron is handled, and preheating and slow cooling are equally
desirable. The flame used is the same as for cast iron and so is the flux.
The welding rod may be of cast iron, although better results are secured
with Norway iron wire or else a mild steel wire wrapped with a coil of
It will be understood that malleable iron turns to ordinary cast iron when
melted and cooled. Welds in malleable iron are usually far from
satisfactory and a better joint is secured by brazing the edges together
with bronze. The edges to be joined are brought to a heat just a little
below the point at which they will flow and the opening is then
quickly-filled from a rod of Tobin bronze or manganese bronze, a brass or
bronze flux being used in this work.
_Wrought Iron or Semi-Steel._--This metal should be beveled and heated
in the same way as described for cast iron. The flame should be neutral, of
the same size as for steel, and used with the tip of the blue-white cone
just touching the work. The welding rod should be of mild steel, or, if
wrought iron is to be welded to steel, a cast iron rod may be used. A cast
iron flux is well suited for this work. It should be noted that wrought
iron turns to ordinary cast iron if kept heated for any length of time.
_Steel._--Steel should be beveled if more than one-eighth inch in
thickness. It requires only a local preheating around the point to be
welded. The welding flame should be absolutely neutral, without excess of
either gas. If the metal is one-sixteenth inch or less in thickness, the
tip of the blue-white cone must be held a short distance from the surface
of the work; in all other cases the tip of this cone is touched to the
metal being welded.
The welding rod may be of mild, low carbon steel or of Norway iron. Nickel
steel rods may be used for parts requiring great strength, but vanadium
alloys are very difficult to handle. A very satisfactory rod is made by
twisting together two wires of the required material. The rod must be kept
constantly in contact with the work and should not be added until the edges
are thoroughly melted. The flux may or may not be used. If one is wanted,
it may be made from three parts iron filings, six parts borax and one part
It will be noticed that the steel runs from the flame, but tends to hold
together. Should foaming commence in the molten metal, it shows an excess
of oxygen and that the metal is being burned.
High carbon steels are very difficult to handle. It is claimed that a drop
or two of copper added to the weld will assist the flow, but will also
harden the work. An excess of oxygen reduces the amount of carbon and
softens the steel, while an excess of acetylene increases the proportion of
carbon and hardens the metal. High speed steels may sometimes be welded if
first coated with semi-steel before welding.
_Aluminum._--This is the most difficult of the commonly found metals
to weld. This is caused by its high rate of expansion and contraction and
its liability to melt and fall away from under the flame. The aluminum
seems to melt on the inside first, and, without previous warning, a portion
of the work will simply vanish from in front of the operator's eyes. The
metal tends to run from the flame and separate at the same time. To keep
the metal in shape and free from oxide, it is worked or puddled while in a
plastic condition by an iron rod which has been flattened at one end.
Several of these rods should be at hand and may be kept in a jar of salt
water while not being used. These rods must not become coated with aluminum
and they must not get red hot while in the weld.
The surfaces to be joined, together with the adjacent parts, should be
cleaned thoroughly and then washed with a 25 per cent solution of nitric
acid in hot water, used on a swab. The parts should then be rinsed in clean
water and dried with sawdust. It is also well to make temporary fire clay
moulds back of the parts to be heated, so that the metal may be flowed into
place and allowed to cool without danger of breakage.
Aluminum must invariably be preheated to about 600 degrees, and the whole
piece being handled should be well covered with sheet asbestos to prevent
excessive heat radiation.
The flame is formed with an excess of acetylene such that the second cone
extends about an inch, or slightly more, beyond the small blue-white point.
The torch should be held so that the end of this second cone is in contact
with the work, the small cone ordinarily used being kept an inch or an inch
and a half from the surface of the work.
Welding rods of special aluminum are used and must be handled with their
end submerged in the molten metal of the weld at all times.
When aluminum is melted it forms alumina, an oxide of the metal. This
alumina surrounds small masses of the metal, and as it does not melt at
temperatures below 5000 degrees (while aluminum melts at about 1200), it
prevents a weld from being made. The formation of this oxide is retarded
and the oxide itself is dissolved by a suitable flux, which usually
contains phosphorus to break down the alumina.
_Copper._--The whole piece should be preheated and kept well covered
while welding. The flame must be much larger than for the same thickness of
steel and neutral in character. A slight excess of acetylene would be
preferable to an excess of oxygen, and in all cases the molten metal should
be kept enveloped with the flame. The welding rod is of copper which
contains phosphorus; and a flux, also containing phosphorus, should be
spread for about an inch each side of the joint. These assist in preventing
oxidation, which is sure to occur with heated copper.
Copper breaks very easily at a heat slightly under the welding temperature
and after cooling it is simply cast copper in all cases.
_Brass and Bronze._--It is necessary to preheat these metals, although
not to a very high temperature. They must be kept well covered at all times
to prevent undue radiation. The flame should be produced with a nozzle one
size larger than for the same thickness of steel and the small blue-white
cone should be held from one-fourth to one-half inch above the surface of
the work. The flame should be neutral in character.
A rod or wire of soft brass containing a large percentage of zinc is
suitable for adding to brass, while copper requires the use of copper or
manganese bronze rods. Special flux or borax may be used to assist the
The emission of white smoke indicates that the zinc contained in these
alloys is being burned away and the heat should immediately be turned away
or reduced. The fumes from brass and bronze welding are very poisonous and
should not be breathed.
RESTORATION OF STEEL
The result of the high heat to which the steel has been subjected is that
it is weakened and of a different character than before welding. The
operator may avoid this as much as possible by first playing the outer
flame of the torch all over the surfaces of the work just completed until
these faces are all of uniform color, after which the metal should be well
covered with asbestos and allowed to cool without being disturbed. If a
temporary heating oven has been employed, the work and oven should be
allowed to cool together while protected with the sheet asbestos. If the
outside air strikes the freshly welded work, even for a moment, the result
will be breakage.
A weld in steel will always leave the metal with a coarse grain and with
all the characteristics of rather low grade cast steel. As previously
mentioned in another chapter, the larger the grain size in steel the weaker
the metal will be, and it is the purpose of the good workman to avoid, as
far as possible, this weakening.
The structure of the metal in one piece of steel will differ according to
the heat that it has under gone. The parts of the work that have been at
the melting point will, therefore, have the largest grain size and the
least strength. Those parts that have not suffered any great rise in
temperature will be practically unaffected, and all the parts between these
two extremes will be weaker or stronger according to their distance from
the weld itself. To restore the steel so that it will have the best grain
size, the operator may resort to either of two methods: (1) The grain may
be improved by forging. That means that the metal added to the weld and the
surfaces that have been at the welding heat are hammered much as a
blacksmith would hammer his finished work to give it greater strength. The
hammering should continue from the time the metal first starts to cool
until it has reached the temperature at which the grain size is best for
strength. This temperature will vary somewhat with the composition of the
metal being handled, but in a general way, it may be stated that the
hammering should continue without intermission from the time the flame is
removed from the weld until the steel just begins to show attraction for a
magnet presented to it. This temperature of magnetic attraction will always
be low enough and the hammering should be immediately discontinued at this
point. (2) A method that is more satisfactory, although harder to apply, is
that of reheating the steel to a certain temperature throughout its whole
mass where the heat has had any effect, and then allowing slow and even
cooling from this temperature. The grain size is affected by the
temperature at which the reheating is stopped, and not by the cooling, yet
the cooling should be slow enough to avoid strains caused by uneven
After the weld has been completed the steel must be allowed to cool until
below 1200 Fahrenheit. The next step is to heat the work slowly until all
those parts to be restored have reached a temperature at which the magnet
just ceases to be attracted. While the very best temperature will vary
according to the nature and hardness of the steel being handled, it will be
safe to carry the heating to the point indicated by the magnet in the
absence of suitable means of measuring accurately these high temperatures.
In using a magnet for testing, it will be most satisfactory if it is an
electromagnet and not of the permanent type. The electric current may be
secured from any small battery and will be the means of making sure of the
test. The permanent magnet will quickly lose its power of attraction under
the combined action of the heat and the jarring to which it will be
In reheating the work it is necessary to make sure that no part reaches a
temperature above that desired for best grain size and also to see that all
parts are brought to this temperature. Here enters the greatest difficulty
in restoring the metal. The heating may be done so slowly that no part of
the work on the outside reaches too high a temperature and then keeps the
outside at this heat until the entire mass is at the same temperature. A
less desirable way is to heat the outside higher than this temperature and
allow the conductivity of the metal to distribute the excess to the inside.
The most satisfactory method, where it can be employed, is to make use of a
bath of some molten metal or some chemical mixture that can be kept at the
exact heat necessary by means of gas fires that admit of close regulation.
The temperature of these baths may be maintained at a constant point by
watching a pyrometer, and the finished work may be allowed to remain in the
bath until all parts have reached the desired temperature.
The following tables include much of the information that the operator must
use continually to handle the various metals successfully. The temperature
scales are given for convenience only. The composition of various alloys
will give an idea of the difficulties to be contended with by consulting
the information on welding various metals. The remaining tables are of
self-evident value in this work.
Centigrade Fahrenheit Centigrade Fahrenheit
200 392 1000 1832
225 437 1050 1922
250 482 1100 2012
275 527 1150 2102
300 572 1200 2192
325 617 1250 2282
350 662 1300 2372
375 707 1350 2462
400 752 1400 2552
425 797 1450 2642
450 842 1500 2732
475 887 1550 2822
500 932 1600 2912
525 977 1650 3002
550 1022 1700 3092
575 1067 1750 3182
600 1112 1800 3272
625 1157 1850 3362
650 1202 1900 3452
675 1247 2000 3632
700 1292 2050 3722
725 1337 2100 3812
750 1382 2150 3902
775 1427 2200 3992
800 1472 2250 4082
825 1517 2300 4172
850 1562 2350 4262
875 1607 2400 4352
900 1652 2450 4442
925 1697 2500 4532
950 1742 2550 4622
975 1787 2600 4712
(Society of Automobile Engineers)
Copper........................ 3.00% to 6.00%
Tin (minimum) ................ 65.00%
Zinc.......................... 28.00% to 30.00%
Brass, Red Cast--
Copper........................ 62.00% to 65.00%
Lead.......................... 2.00% to 4.00%
Zinc.......................... 36.00% to 31.00%
Copper........................ 87.00% to 88.00%
Tin........................... 9.50% to 10.50%
Zinc.......................... 1.50% to 2.50%
Phosphorus.................... .50% to .25%
Copper (approximate) ......... 60.00%
Zinc (approximate) ........... 40.00%
Manganese (variable) ......... small
Copper........................ 88.00% to 89.00%
Tin........................... 11.00% to 12.00%
Aluminum Copper Zinc Manganese
No. 1.. 90.00% 8.5-7.0%
No. 2.. 80.00% 2.0-3.0% 15% Not over 0.40%
No. 3.. 65.00% 35.0%
Gray Iron Malleable
Total carbon........3.0 to 3.5%
Combined carbon.....0.4 to 0.7%
Manganese...........0.4 to 0.7% 0.3 to 0.7%
Phosphorus..........0.6 to 1.0% Not over 0.2%
Sulphur...........Not over 0.1% Not over 0.6%
Silicon............1.75 to 2.25% Not over 1.0%
Carbon Steel (10 Point)--
Carbon........................ .05% to .15%
Manganese..................... .30% to .60%
Phosphorus (maximum).......... .045%
Sulphur (maximum)............. .05%
Carbon........................ .15% to .25%
Manganese..................... .30% to .60%
Phosphorus (maximum).......... .045%
Sulphur (maximum)............. .05%
Manganese..................... .50% to .80%
Carbon........................ .30% to .40%
Phosphorus (maximum).......... .05%
Sulphur (maximum)............. .05%
Carbon........................ .90% to 1.05%
Manganese..................... .25% to .50%
Phosphorus (maximum).......... .04%
Sulphur (maximum)............. .05%
HEATING POWER OF FUEL GASES
(In B.T.U. per Cubic Foot.)
Acetylene....... 1498.99 Ethylene....... 1562.9
Hydrogen........ 291.96 Methane........ 953.6
MELTING POINTS OF METALS
_NOTE.--These melting points are for average compositions and conditions.
The exact proportion of elements entering into the metals affects their
melting points one way or the other in practice._
TENSILE STRENGTH OF METALS
Alloy steels can be made with tensile strengths as high as 300,000 pounds
per square inch. Some carbon steels are given below according to "points":
Pounds per Square Inch
Steel, 10 point................ 50,000 to 65,000
20 point..................... 60,000 to 80,000
40 point..................... 70,000 to 100,000
60 point..................... 90,000 to 120,000
Iron, Cast..................... 13,000 to 30,000
Wrought...................... 40,000 to 60,000
Malleable.................... 25,000 to 45,000
Copper......................... 24,000 to 50,000
Bronze......................... 30,000 to 60,000
Brass, Cast.................... 12,000 to 18,000
Rolled....................... 30,000 to 40,000
Wire......................... 60,000 to 75,000
Aluminum....................... 12,000 to 23,000
Zinc........................... 5,000 to 15,000
Tin............................ 3,000 to 5,000
Lead........................... 1,500 to 2,500
CONDUCTIVITY OF METALS
(Based on the Value of Silver as 100)
Copper.................... 74 99
Aluminum.................. 38 63
Brass..................... 23 22
Zinc...................... 19 29
Tin....................... 14 15
Wrought Iron.............. 12 16
Steel..................... 11.5 12
Cast Iron................. 11 12
Bronze.................... 9 7
Lead...................... 8 9
WEIGHT OF METALS
(Per Cubic Inch)
Lead............ .410 Wrought Iron..... .278
Copper.......... .320 Tin.............. .263
Bronze.......... .313 Cast Iron........ .260
Brass........... .300 Zinc............. .258
Steel........... .283 Aluminum......... .093
EXPANSION OF METALS
(Measured in Thousandths of an Inch per Foot of
Length When Raised 1000 Degrees in Temperature)
Lead............ .188 Brass............ .115
Zinc............ .168 Copper........... .106
Aluminum........ .148 Steel............ .083
Silver.......... .129 Wrought Iron..... .078
Bronze.......... .118 Cast Iron........ .068
Two distinct forms of electric welding apparatus are in use, one producing
heat by the resistance of the metal being treated to the passage of
electric current, the other using the heat of the electric arc.
The resistance process is of the greatest use in manufacturing lines where
there is a large quantity of one kind of work to do, many thousand pieces
of one kind, for instance. The arc method may be applied in practically any
case where any other form of weld may be made. The resistance process will
be described first.
It is a well known fact that a poor conductor of electricity will offer so
much resistance to the flow of electricity that it will heat. Copper is a
good conductor, and a bar of iron, a comparatively poor conductor, when
placed between heavy copper conductors of a welder, becomes heated in
attempting to carry the large volume of current. The degree of heat depends
on the amount of current and the resistance of the conductor.
In an electric circuit the ends of two pieces of metal brought together
form the point of greatest resistance in the electric circuit, and the
abutting ends instantly begin to heat. The hotter this metal becomes, the
greater the resistance to the flow of current; consequently, as the edges
of the abutting ends heat, the current is forced into the adjacent cooler
parts, until there is a uniform heat throughout the entire mass. The heat
is first developed in the interior of the metal so that it is welded there
as perfectly as at the surface.
[Illustration: Figure 42.--Spot Welding Machine]
The electric welder (Figure 42) is built to hold the parts to be joined
between two heavy copper dies or contacts. A current of three to five
volts, but of very great volume (amperage), is allowed to pass across
these dies, and in going through the metal to be welded, heats the edges
to a welding temperature. It may be explained that the voltage of an
electric current measures the pressure or force with which it is being sent
through the circuit and has nothing to do with the quantity or volume
passing. Amperes measure the rate at which the current is passing through
the circuit and consequently give a measure of the quantity which passes in
any given time. Volts correspond to water pressure measured by pounds to
the square inch; amperes represent the flow in gallons per minute. The low
voltage used avoids all danger to the operator, this pressure not being
sufficient to be felt even with the hands resting on the copper contacts.
Current is supplied to the welding machine at a higher voltage and lower
amperage than is actually used between the dies, the low voltage and high
amperage being produced by a transformer incorporated in the machine
itself. By means of windings of suitable size wire, the outside current may
be received at voltages ranging from 110 to 550 and converted to the low
The source of current for the resistance welder must be alternating, that
is, the current must first be negative in value and then positive, passing
from one extreme to the other at rates varying from 25 to 133 times a
second. This form is known as alternating current, as opposed to direct
current, in which there is no changing of positive and negative.
The current must also be what is known as single phase, that is, a current
which rises from zero in value to the highest point as a positive current
and then recedes to zero before rising to the highest point of negative
value. Two-phase of three-phase currents would give two or three positive
impulses during this time.
As long as the current is single phase alternating, the voltage and cycles
(number of alternations per second) may be anything convenient. Various
voltages and cycles are taken care of by specifying all these points when
designing the transformer which is to handle the current.
Direct current is not used because there is no way of reducing the voltage
conveniently without placing resistance wires in the circuit and this uses
power without producing useful work. Direct current may be changed to
alternating by having a direct current motor running an alternating current
dynamo, or the change may be made by a rotary converter, although this last
method is not so satisfactory as the first.
The voltage used in welding being so low to start with, it is absolutely
necessary that it be maintained at the correct point. If the source of
current supply is not of ample capacity for the welder being used, it will
be very hard to avoid a fall of voltage when the current is forced to pass
through the high resistance of the weld. The current voltage for various
work is calculated accurately, and the efficiency of the outfit depends to
a great extent on the voltage being constant.
A simple test for fall of voltage is made by connecting an incandescent
electric lamp across the supply lines at some point near the welder. The
lamp should burn with the same brilliancy when the weld is being made as at
any other time. If the lamp burns dim at any time, it indicates a drop in
voltage, and this condition should be corrected.
The dynamo furnishing the alternating current may be in the same building
with the welder and operated from a direct current motor, as mentioned
above, or operated from any convenient shafting or source of power. When
the dynamo is a part of the welding plant it should be placed as close to
the welding machine as possible, because the length of the wire used
affects the voltage appreciably.
In order to hold the voltage constant, the Toledo Electric Welder Company
has devised connections which include a rheostat to insert a variable
resistance in the field windings of the dynamo so that the voltage may be
increased by cutting this resistance out at the proper time. An auxiliary
switch is connected to the welder switch so that both switches act
together. When the welder switch is closed in making a weld, that portion
of the rheostat resistance between two arms determining the voltage is
short circuited. This lowers the resistance and the field magnets of the
dynamo are made stronger so that additional voltage is provided to care for
the resistance in the metal being heated.
A typical machine is shown in the accompanying cut (Figure 43). On top of
the welder are two jaws for holding the ends of the pieces to be welded.
The lower part of the jaws is rigid while the top is brought down on top of
the work, acting as a clamp. These jaws carry the copper dies through which
the current enters the work being handled. After the work is clamped
between the jaws, the upper set is forced closer to the lower set by a long
compression lever. The current being turned on with the surfaces of the
work in contact, they immediately heat to the welding point when added
pressure on the lever forces them together and completes the weld.
[Illustration: Figure 43--Operating Parts of a Toledo Spot Welder]
[Illustration: Figure 43a.--Method of Testing Electric Welder]
[Illustration: Figure 44.--Detail of Water-Cooled Spot Welding Head]
The transformer is carried in the base of the machine and on the left-hand
side is a regulator for controlling the voltage for various kinds of work.
The clamps are applied by treadles convenient to the foot of the operator.
A treadle is provided which instantly releases both jaws upon the
completion of the weld. One or both of the copper dies may be cooled by a
stream of water circulating through it from the city water mains
(Figure 44). The regulator and switch give the operator control of the
heat, anything from a dull red to the melting point being easily obtained
by movement of the lever (figure 45).
[Illustration: Figure 45.--Welding Head of a Water-Cooled Welder]
_Welding._--It is not necessary to give the metal to be welded any
special preparation, although when very rusty or covered with scale, the
rust and scale should be removed sufficiently to allow good contact of
clean metal on the copper dies. The cleaner and better the stock, the less
current it takes, and there is less wear on the dies. The dies should be
kept firm and tight in their holders to make a good contact. All bolts and
nuts fastening the electrical contacts should be clean and tight at all
The scale may be removed from forgings by immersing them in a pickling
solution in a wood, stone or lead-lined tank.
The solution is made with five gallons of commercial sulphuric acid in
150 gallons of water. To get the quickest and best results from this
method, the solution should be kept as near the boiling point as possible
by having a coil of extra heavy lead pipe running inside the tank and
carrying live steam. A very few minutes in this bath will remove the scale
and the parts should then be washed in running water. After this washing
they should be dipped into a bath of 50 pounds of unslaked lime in 150
gallons of water to neutralize any trace of acid.
Cast iron cannot be commercially welded, as it is high in carbon and
silicon, and passes suddenly from a crystalline to a fluid state when
brought to the welding temperature. With steel or wrought iron the
temperature must be kept below the melting point to avoid injury to the
metal. The metal must be heated quickly and pressed together with
sufficient force to push all burnt metal out of the joint.
High carbon steel can be welded, but must be annealed after welding to
overcome the strains set up by the heat being applied at one place. Good
results are hard to obtain when the carbon runs as high as 75 points, and
steel of this class can only be handled by an experienced operator. If the
steel is below 25 points in carbon content, good welds will always be the
result. To weld high carbon to low carbon steel, the stock should be
clamped in the dies with the low carbon stock sticking considerably further
out from the die than the high carbon stock. Nickel steel welds readily,
the nickel increasing the strength of the weld.
Iron and copper may be welded together by reducing the size of the copper
end where it comes in contact with the iron. When welding copper and brass
the pressure must be less than when welding iron. The metal is allowed to
actually fuse or melt at the juncture and the pressure must be sufficient
to force the burned metal out. The current is cut off the instant the metal
ends begin to soften, this being done by means of an automatic switch which
opens when the softening of the metal allows the ends to come together. The
pressure is applied to the weld by having the sliding jaw moved by a weight
on the end of an arm.
Copper and brass require a larger volume of current at a lower voltage than
for steel and iron. The die faces are set apart three times the diameter of
the stock for brass and four times the diameter for copper.
Light gauges of sheet steel can be welded to heavy gauges or to solid bars
of steel by "spot" welding, which will be described later. Galvanized iron
can be welded, but the zinc coating will be burned off. Sheet steel can be
welded to cast iron, but will pull apart, tearing out particles of the
Sheet copper and sheet brass may be welded, although this work requires
more experience than with iron and steel. Some grades of sheet aluminum can
be spot-welded if the slight roughness left on the surface under the die
is not objectionable.
_Butt Welding._--This is the process which joins the ends of two
pieces of metal as described in the foregoing part of this chapter. The
ends are in plain sight of the operator at all times and it can easily be
seen when the metal reaches the welding heat and begins to soften (Figure
46). It is at this point that the pressure must be applied with the lever
and the ends forced together in the weld.
[Illustration: Figure 46.--Butt Welder]
The parts are placed in the clamping jaws (Figure 47) with 1/8 to 1/2 inch
of metal extending beyond the jaw. The ends of the metal touch each other
and the current is turned on by means of a switch. To raise the ends to the
proper heat requires from 3 seconds for 1/4-inch rods to 35 seconds for a
This method is applicable to metals having practically the same area of
metal to be brought into contact on each end. When such parts are forced
together a slight projection will be left in the form of a fin or an
enlarged portion called an upset. The degree of heat required for any work
is found by moving the handle of the regulator one way or the other while
testing several parts. When this setting is right the work can continue as
long as the same sizes are being handled.
[Illustration: Figure 47.--Clamping Dies of a Butt Welder]
Copper, brass, tool steel and all other metals that are harmed by high
temperatures must be heated quickly and pressed together with sufficient
force to force all burned metal from the weld.
In case it is desired to make a weld in the form of a capital letter T, it
is necessary to heat the part corresponding to the top bar of the T to a
bright red, then bring the lower bar to the pre-heated one and again turn
on the current, when a weld can be quickly made.
_Spot Welding._--This is a method of joining metal sheets together at
any desired point by a welded spot about the size of a rivet. It is done on
a spot welder by fusing the metal at the point desired and at the same
instant applying sufficient pressure to force the particles of molten metal
together. The dies are usually placed one above the other so that the work
may rest on the lower one while the upper one is brought down on top of the
upper sheet to be welded.
One of the dies is usually pointed slightly, the opposing one being left
flat. The pointed die leaves a slight indentation on one side of the metal,
while the other side is left smooth. The dies may be reversed so that the
outside surface of any work may be left smooth. The current is allowed to
flow through the dies by a switch which is closed after pressure is applied
to the work.
There is a limit to the thickness of sheet metal that can be welded by this
process because of the fact that the copper rods can only carry a certain
quantity of current without becoming unduly heated themselves. Another
reason is that it is difficult to make heavy sections of metal touch at the
welding point without excessive pressure.
_Lap welding_ is the process used when two pieces of metal are caused
to overlap and when brought to a welding heat are forced together by
passing through rollers, or under a press, thus leaving the welded joint
practically the same thickness as the balance of the work.
Where it is desirable to make a continuous seam, a special machine is
required, or an attachment for one of the other types. In this form of work
the stock must be thoroughly cleaned and is then passed between copper
rollers which act in the same capacity as the copper dies.
_Other Applications._--Hardening and tempering can be done by clamping
the work in the welding dies and setting the control and time to bring the
metal to the proper color, when it is cooled in the usual manner.
Brazing is done by clamping the work in the jaws and heating until the
flux, then the spelter has melted and run into the joint. Riveting and
heading of rivets can be done by bringing the dies down on opposite ends of
the rivet after it has been inserted in the hole, the dies being shaped to
form the heads properly.
Hardened steel may be softened and annealed so that it can be machined by
connecting the dies of the welder to each side of the point to be softened.
The current is then applied until the work has reached a point at which it
will soften when cooled.
_Troubles and Remedies._--The following methods have been furnished by
the Toledo Electric Welder Company and are recommended for this class of
work whenever necessary.
To locate grounds in the primary or high voltage side of the circuit,
connect incandescent lamps in series by means of a long piece of lamp cord,
as shown, in Figure 43a. For 110 volts use one lamp, for 220 volts use two
lamps and for 440 volts use four lamps. Attach one end of the lamp cord to
one side of the switch, and close the switch. Take the other end of the
cord in the hand and press it against some part of the welder frame where
the metal is clean and bright. Paint, grease and dirt act as insulators and
prevent electrical contact. If the lamp lights, the circuit is in
electrical contact with the frame; in other words, grounded. If the lamps
do not light, connect the wire to a terminal block, die or slide. If the
lamps then light, the circuit, coils or leads are in electrical contact
with the large coil in the transformer or its connections.
If, however, the lamps do not light in either case, the lamp cord should be
disconnected from the switch and connected to the other side, and the
operations of connecting to welder frame, dies, terminal blocks, etc., as
explained above, should be repeated. If the lamps light at any of these
connections, a "ground" is indicated. "Grounds" can usually be found by
carefully tracing the primary circuit until a place is found where the
insulation is defective. Reinsulate and make the above tests again to make
sure everything is clear. If the ground can not be located by observation,
the various parts of the primary circuit should be disconnected, and the
transformer, switch, regulator, etc., tested separately.
To locate a ground in the regulator or other part, disconnect the lines
running to the welder from the switch. The test lamps used in the previous
tests are connected, one end of lamp cord to the switch, the other end to a
binding post of the regulator. Connect the other side of the switch to some
part of the regulator housing. (This must be a clean connection to a bolt
head or the paint should be scraped off.) Close the switch. If the lamps
light, the regulator winding or some part of the switch is "grounded" to
the iron base or core of the regulator. If the lamps do not light, this
part of the apparatus is clear.
This test can be easily applied to any part of the welder outfit by
connecting to the current carrying part of the apparatus, and to the iron
base or frame that should not carry current. If the lamps light, it
indicates that the insulation is broken down or is defective.
An A.C. voltmeter can, of course, be substituted for the lamps, or a D.C.
voltmeter with D.C. current can be used in making the tests.
A short circuit in the primary is caused by the insulation of the coils
becoming defective and allowing the bare copper wires to touch each other.
This may result in a "burn out" of one or more of the transformer coils, if
the trouble is in the transformer, or in the continued blowing of fuses in
the line. Feel of each coil separately. If a short circuit exists in a coil
it will heat excessively. Examine all the wires; the insulation may have
worn through and two of them may cross, or be in contact with the frame or
other part of the welder. A short circuit in the regulator winding is
indicated by failure of the apparatus to regulate properly, and sometimes,
though not always, by the heating of the regulator coils.
The remedy for a short circuit is to reinsulate the defective parts. It is
a good plan to prevent trouble by examining the wiring occasionally and see
that the insulation is perfect.
_To Locate Grounds and Short Circuits in the Secondary, or Low Voltage
Side._--Trouble of this kind is indicated by the machine acting sluggish
or, perhaps, refusing to operate. To make a test, it will be necessary to
first ascertain the exciting current of your particular transformer. This
is the current the transformer draws on "open circuit," or when supplied
with current from the line with no stock in the welder dies. The following
table will give this information close enough for all practical purposes:
K.W. ----------------- Amperes at ----------------
Rating 110 Volts 220 Volts 440 Volts 550 Volts
3 1.5 .75 .38 .3
5 2.5 1.25 .63 .5
8 3.6 1.8 .9 .72
10 4.25 2.13 1.07 .85
15 6. 3. 1.5 1.2
20 7. 3.5 1.75 1.4
30 9. 4.5 2.25 1.8
35 9.6 4.8 2.4 1.92
50 10. 5. 2.5 2
Remove the fuses from the wall switch and substitute fuses just large
enough to carry the "exciting" current. If no suitable fuses are at hand,
fine strands of copper from an ordinary lamp cord may be used. These
strands are usually No. 30 gauge wire and will fuse at about 10 amperes.
One or more strands should be used, depending on the amount of exciting
current, and are connected across the fuse clips in place of fuse wire.
Place a piece of wood or fibre between the welding dies in the welder as
though you were going to weld them. See that the regulator is on the
highest point and close the welder switch. If the secondary circuit is
badly grounded, current will flow through the ground, and the small fuses
or small strands of wire will burn out. This is an indication that both
sides of the secondary circuit are grounded or that a short circuit exists
in a primary coil. In either case the welder should not be operated until
the trouble is found and removed. If, however, the small fuses do not
"blow," remove same and replace the large fuses, then disconnect wires
running from the wall switch to the welder and substitute two pieces of
No. 8 or No. 6 insulated copper wire, after scraping off the insulation for
an inch or two at each end. Connect one wire from the switch to the frame
of welder; this will leave one loose end. Hold this a foot or so away from
the place where the insulation is cut off; then turn on the current and
strike the free end of this wire lightly against one of the copper dies,