Part 1 out of 3
Produced by Juliet Sutherland, John Argus, Tonya Allen,
Charles Franks and the Online Distributed Proofreading Team.
Oxy-Acetylene Welding and Cutting
Electric, Forge and Thermit Welding
Together with Related Methods and Materials Used in Metal Working
The Oxygen Process for Removal of Carbon
HAROLD P. MANLY
In the preparation of this work, the object has been to cover not only the
several processes of welding, but also those other processes which are so
closely allied in method and results as to make them a part of the whole
subject of joining metal to metal with the aid of heat.
The workman who wishes to handle his trade from start to finish finds that
it is necessary to become familiar with certain other operations which
precede or follow the actual joining of the metal parts, the purpose of
these operations being to add or retain certain desirable qualities in the
materials being handled. For this reason the following subjects have been
included: Annealing, tempering, hardening, heat treatment and the
restoration of steel.
In order that the user may understand the underlying principles and the
materials employed in this work, much practical information is given on the
uses and characteristics of the various metals; on the production, handling
and use of the gases and other materials which are a part of the equipment;
and on the tools and accessories for the production and handling of these
An examination will show that the greatest usefulness of this book lies in
the fact that all necessary information and data has been included in one
volume, making it possible for the workman to use one source for securing a
knowledge of both principle and practice, preparation and finishing of the
work, and both large and small repair work as well as manufacturing methods
used in metal working.
An effort has been made to eliminate all matter which is not of direct
usefulness in practical work, while including all that those engaged in
this trade find necessary. To this end, the descriptions have been limited
to those methods and accessories which are found in actual use today. For
the same reason, the work includes the application of the rules laid down
by the insurance underwriters which govern this work as well as
instructions for the proper care and handling of the generators, torches
and materials found in the shop.
Special attention has been given to definite directions for handling the
different metals and alloys which must be handled. The instructions have
been arranged to form rules which are placed in the order of their use
during the work described and the work has been subdivided in such a way
that it will be found possible to secure information on any one point
desired without the necessity of spending time in other fields.
The facts which the expert welder and metalworker finds it most necessary
to have readily available have been secured, and prepared especially for
this work, and those of most general use have been combined with the
chapter on welding practice to which they apply.
The size of this volume has been kept as small as possible, but an
examination of the alphabetical index will show that the range of subjects
and details covered is complete in all respects. This has been accomplished
through careful classification of the contents and the elimination of all
repetition and all theoretical, historical and similar matter that is not
Free use has been made of the information given by those manufacturers who
are recognized as the leaders in their respective fields, thus insuring
that the work is thoroughly practical and that it represents present day
methods and practice.
METALS AND ALLOYS--HEAT TREATMENT:--The Use and Characteristics of the
Industrial Alloys and Metal Elements--Annealing, Hardening, Tempering and
Case Hardening of Steel
WELDING MATERIALS:--Production, Handling and Use of the Gases, Oxygen and
Acetylene--Welding Rods--Fluxes--Supplies and Fixtures
ACETYLENE GENERATORS:--Generator Requirements and Types--Construction--Care
and Operation of Generators.
WELDING INSTRUMENTS:--Tank and Regulating Valves and Gauges--High, Low and
Medium Pressure Torches--Cutting Torches--Acetylene-Air Torches
OXY-ACETYLENE WELDING PRACTICE:--Preparation of Work--Torch Practice--
Control of the Flame--Welding Various Metals and Alloys--Tables of
Information Required in Welding Operations
ELECTRIC WELDING:--Resistance Method--Butt, Spot and Lap Welding--Troubles
and Remedies--Electric Arc Welding
HAND FORGING AND WELDING:--Blacksmithing, Forging and Bending--Forge
SOLDERING, BRAZING AND THERMIT WELDING:--Soldering Materials and Practice--
OXYGEN PROCESS FOR REMOVAL OF CARBON
OXY-ACETYLENE WELDING AND CUTTING, ELECTRIC AND THERMIT WELDING
METALS AND THEIR ALLOYS--HEAT TREATMENT
_Iron._--Iron, in its pure state, is a soft, white, easily worked
metal. It is the most important of all the metallic elements, and is, next
to aluminum, the commonest metal found in the earth.
Mechanically speaking, we have three kinds of iron: wrought iron, cast iron
and steel. Wrought iron is very nearly pure iron; cast iron contains carbon
and silicon, also chemical impurities; and steel contains a definite
proportion of carbon, but in smaller quantities than cast iron.
Pure iron is never obtained commercially, the metal always being mixed with
various proportions of carbon, silicon, sulphur, phosphorus, and other
elements, making it more or less suitable for different purposes. Iron is
magnetic to the extent that it is attracted by magnets, but it does not
retain magnetism itself, as does steel. Iron forms, with other elements,
many important combinations, such as its alloys, oxides, and sulphates.
[Illustration: Figure 1.--Section Through a Blast Furnace]
_Cast Iron._--Metallic iron is separated from iron ore in the blast
furnace (Figure 1), and when allowed to run into moulds is called cast
iron. This form is used for engine cylinders and pistons, for brackets,
covers, housings and at any point where its brittleness is not
objectionable. Good cast iron breaks with a gray fracture, is free from
blowholes or roughness, and is easily machined, drilled, etc. Cast iron is
slightly lighter than steel, melts at about 2,400 degrees in practice, is
about one-eighth as good an electrical conductor as copper and has a
tensile strength of 13,000 to 30,000 pounds per square inch. Its
compressive strength, or resistance to crushing, is very great. It has
excellent wearing qualities and is not easily warped and deformed by heat.
Chilled iron is cast into a metal mould so that the outside is cooled
quickly, making the surface very hard and difficult to cut and giving great
resistance to wear. It is used for making cheap gear wheels and parts that
must withstand surface friction.
_Malleable Cast Iron._--This is often called simply malleable iron. It
is a form of cast iron obtained by removing much of the carbon from cast
iron, making it softer and less brittle. It has a tensile strength of
25,000 to 45,000 pounds per square inch, is easily machined, will stand a
small amount of bending at a low red heat and is used chiefly in making
brackets, fittings and supports where low cost is of considerable
importance. It is often used in cheap constructions in place of steel
forgings. The greatest strength of a malleable casting, like a steel
forging, is in the surface, therefore but little machining should be done.
_Wrought Iron._--This grade is made by treating the cast iron to
remove almost all of the carbon, silicon, phosphorus, sulphur, manganese
and other impurities. This process leaves a small amount of the slag from
the ore mixed with the wrought iron.
Wrought iron is used for making bars to be machined into various parts. If
drawn through the rolls at the mill once, while being made, it is called
"muck bar;" if rolled twice, it is called "merchant bar" (the commonest
kind), and a still better grade is made by rolling a third time. Wrought
iron is being gradually replaced in use by mild rolled steels.
Wrought iron is slightly heavier than cast iron, is a much better
electrical conductor than either cast iron or steel, has a tensile strength
of 40,000 to 60,000 pounds per square inch and costs slightly more than
steel. Unlike either steel or cast iron, wrought iron does not harden when
cooled suddenly from a red heat.
_Grades of Irons._--The mechanical properties of cast iron differ
greatly according to the amount of other materials it contains. The most
important of these contained elements is carbon, which is present to a
degree varying from 2 to 5-1/2 per cent. When iron containing much carbon
is quickly cooled and then broken, the fracture is nearly white in color
and the metal is found to be hard and brittle. When the iron is slowly
cooled and then broken the fracture is gray and the iron is more malleable
and less brittle. If cast iron contains sulphur or phosphorus, it will show
a white fracture regardless of the rapidity of cooling, being brittle and
less desirable for general work.
_Steel._--Steel is composed of extremely minute particles of iron and
carbon, forming a network of layers and bands. This carbon is a smaller
proportion of the metal than found in cast iron, the percentage being from
3/10 to 2-1/2 per cent.
Carbon steel is specified according to the number of "points" of carbon, a
point being one one-hundredth of one per cent of the weight of the steel.
Steel may contain anywhere from 30 to 250 points, which is equivalent to
saying, anywhere from 3/10 to 2-1/2 per cent, as above. A 70-point steel
would contain 70/100 of one per cent or 7/10 of one per cent of carbon by
weight. The percentage of carbon determines the hardness of the steel, also
many other qualities, and its suitability for various kinds of work. The
more carbon contained in the steel, the harder the metal will be, and, of
course, its brittleness increases with the hardness. The smaller the grains
or particles of iron which are separated by the carbon, the stronger the
steel will be, and the control of the size of these particles is the object
of the science of heat treatment.
In addition to the carbon, steel may contain the following:
Silicon, which increases the hardness, brittleness, strength and difficulty
of working if from 2 to 3 per cent is present.
Phosphorus, which hardens and weakens the metal but makes it easier to
cast. Three-tenths per cent of phosphorus serves as a hardening agent and
may be present in good steel if the percentage of carbon is low. More
than this weakens the metal.
Sulphur, which tends to make the metal hard and filled with small holes.
Manganese, which makes the steel so hard and tough that it can with
difficulty be cut with steel tools. Its hardness is not lessened by
annealing, and it has great tensile strength.
Alloy steel has a varying but small percentage of other elements mixed with
it to give certain desired qualities. Silicon steel and manganese steel are
sometimes classed as alloy steels. This subject is taken up in the latter
part of this chapter under _Alloys_, where the various combinations
and their characteristics are given consideration.
Steel has a tensile strength varying from 50,000 to 300,000 pounds per
square inch, depending on the carbon percentage and the other alloys
present, as well as upon the texture of the grain. Steel is heavier than
cast iron and weighs about the same as wrought iron. It is about one-ninth
as good a conductor of electricity as copper.
Steel is made from cast iron by three principal processes: the crucible,
Bessemer and open hearth.
_Crucible steel_ is made by placing pieces of iron in a clay or
graphite crucible, mixed with charcoal and a small amount of any desired
alloy. The crucible is then heated with coal, oil or gas fires until the
iron melts, and, by absorbing the desired elements and giving up or
changing its percentage of carbon, becomes steel. The molten steel is then
poured from the crucible into moulds or bars for use. Crucible steel may
also be made by placing crude steel in the crucibles in place of the iron.
This last method gives the finest grade of metal and the crucible process
in general gives the best grades of steel for mechanical use.
[Illustration: Figure 2.--A Bessemer Converter]
_Bessemer steel_ is made by heating iron until all the undesirable
elements are burned out by air blasts which furnish the necessary oxygen.
The iron is placed in a large retort called a converter, being poured,
while at a melting heat, directly from the blast furnace into the
converter. While the iron in the converter is molten, blasts of air are
forced through the liquid, making it still hotter and burning out the
impurities together with the carbon and manganese. These two elements are
then restored to the iron by adding spiegeleisen (an alloy of iron, carbon
and manganese). A converter holds from 5 to 25 tons of metal and requires
about 20 minutes to finish a charge. This makes the cheapest steel.
[Illustration: Figure 3.--An Open Hearth Furnace]
_Open hearth steel_ is made by placing the molten iron in a receptacle
while currents of air pass over it, this air having itself been highly
heated by just passing over white hot brick (Figure. 3). Open hearth steel
is considered more uniform and reliable than Bessemer, and is used for
springs, bar steel, tool steel, steel plates, etc.
_Aluminum_ is one of the commonest industrial metals. It is used for
gear cases, engine crank cases, covers, fittings, and wherever lightness
and moderate strength are desirable.
Aluminum is about one-third the weight of iron and about the same weight as
glass and porcelain; it is a good electrical conductor (about one-half as
good as copper); is fairly strong itself and gives great strength to other
metals when alloyed with them. One of the greatest advantages of aluminum
is that it will not rust or corrode under ordinary conditions. The granular
formation of aluminum makes its strength very unreliable and it is too soft
to resist wear.
_Copper_ is one of the most important metals used in the trades, and
the best commercial conductor of electricity, being exceeded in this
respect only by silver, which is but slightly better. Copper is very
malleable and ductile when cold, and in this state may be easily worked
under the hammer. Working in this way makes the copper stronger and harder,
but less ductile. Copper is not affected by air, but acids cause the
formation of a green deposit called verdigris.
Copper is one of the best conductors of heat, as well as electricity, being
used for kettles, boilers, stills and wherever this quality is desirable.
Copper is also used in alloys with other metals, forming an important part
of brass, bronze, german silver, bell metal and gun metal. It is about
one-eighth heavier than steel and has a tensile strength of about 25,000 to
50,000 pounds per square inch.
_Lead._--The peculiar properties of lead, and especially its quality
of showing but little action or chemical change in the presence of other
elements, makes it valuable under certain conditions of use. Its principal
use is in pipes for water and gas, coverings for roofs and linings for vats
and tanks. It is also used to coat sheet iron for similar uses and as an
important part of ordinary solder.
Lead is the softest and weakest of all the commercial metals, being very
pliable and inelastic. It should be remembered that lead and all its
compounds are poisonous when received into the system. Lead is more than
one-third heavier than steel, has a tensile strength of only about 2,000
pounds per square inch, and is only about one-tenth as good a conductor of
electricity as copper.
_Zinc._--This is a bluish-white metal of crystalline form. It is
brittle at ordinary temperatures and becomes malleable at about 250 to 300
degrees Fahrenheit, but beyond this point becomes even more brittle than at
ordinary temperatures. Zinc is practically unaffected by air or moisture
through becoming covered with one of its own compounds which immediately
resists further action. Zinc melts at low temperatures, and when heated
beyond the melting point gives off very poisonous fumes.
The principal use of zinc is as an alloy with other metals to form brass,
bronze, german silver and bearing metals. It is also used to cover the
surface of steel and iron plates, the plates being then called galvanized.
Zinc weighs slightly less than steel, has a tensile strength of 5,000
pounds per square inch, and is not quite half as good as copper in
_Tin_ resembles silver in color and luster. Tin is ductile and
malleable and slightly crystalline in form, almost as heavy as steel, and
has a tensile strength of 4,500 pounds per square inch.
The principal use of tin is for protective platings on household utensils
and in wrappings of tin-foil. Tin forms an important part of many alloys
such as babbitt, Britannia metal, bronze, gun metal and bearing metals.
_Nickel_ is important in mechanics because of its combinations with
other metals as alloys. Pure nickel is grayish-white, malleable, ductile
and tenacious. It weighs almost as much as steel and, next to manganese, is
the hardest of metals. Nickel is one of the three magnetic metals, the
others being iron and cobalt. The commonest alloy containing nickel is
german silver, although one of its most important alloys is found in nickel
steel. Nickel is about ten per cent heavier than steel, and has a tensile
strength of 90,000 pounds per square inch.
_Platinum._--This metal is valuable for two reasons: it is not
affected by the air or moisture or any ordinary acid or salt, and in
addition to this property it melts only at the highest temperatures. It is
a fairly good electrical conductor, being better than iron or steel. It is
nearly three times as heavy as steel and its tensile strength is 25,000
pounds per square inch.
An alloy is formed by the union of a metal with some other material, either
metal or non-metallic, this union being composed of two or more elements
and usually brought about by heating the substances together until they
melt and unite. Metals are alloyed with materials which have been found to
give to the metal certain characteristics which are desired according to
the use the metal will be put to.
The alloys of metals are, almost without exception, more important from an
industrial standpoint than the metals themselves. There are innumerable
possible combinations, the most useful of which are here classed under the
head of the principal metal entering into their composition.
_Steel._--Steel may be alloyed with almost any of the metals or
elements, the combinations that have proven valuable numbering more than a
score. The principal ones are given in alphabetical order, as follows:
Aluminum is added to steel in very small amounts for the purpose of
preventing blow holes in castings.
Boron increases the density and toughness of the metal.
Bronze, added by alloying copper, tin and iron, is used for gun metal.
Carbon has already been considered under the head of steel in the section
devoted to the metals. Carbon, while increasing the strength and hardness,
decreases the ease of forging and bending and decreases the magnetism and
electrical conductivity. High carbon steel can be welded only with
difficulty. When the percentage of carbon is low, the steel is called "low
carbon" or "mild" steel. This is used for rods and shafts, and called
"machine" steel. When the carbon percentage is high, the steel is called
"high carbon" steel, and it is used in the shop as tool steel. One-tenth
per cent of carbon gives steel a tensile strength of 50,000 to 65,000
pounds per square inch; two-tenths per cent gives from 60,000 to 80,000;
four-tenths per cent gives 70,000 to 100,000, and six-tenths per cent
gives 90,000 to 120,000.
Chromium forms chrome steel, and with the further addition of nickel is
called chrome nickel steel. This increases the hardness to a high degree
and adds strength without much decrease in ductility. Chrome steels are
used for high-speed cutting tools, armor plate, files, springs, safes,
Manganese has been mentioned under _Steel_. Its alloy is much used for
high-speed cutting tools, the steel hardening when cooled in the air and
being called self-hardening.
Molybdenum is used to increase the hardness to a high degree and makes the
steel suitable for high-speed cutting and gives it self-hardening
Nickel, with which is often combined chromium, increases the strength,
springiness and toughness and helps to prevent corrosion.
Silicon has already been described. It suits the metal for use in
Silver added to steel has many of the properties of nickel.
Tungsten increases the hardness without making the steel brittle. This
makes the steel well suited for gas engine valves as it resists corrosion
and pitting. Chromium and manganese are often used in combination with
tungsten when high-speed cutting tools are made.
Vanadium as an alloy increases the elastic limit, making the steel
stronger, tougher and harder. It also makes the steel able to stand much
bending and vibration.
_Copper._--The principal copper alloys include brass, bronze, german
silver and gun metal.
Brass is composed of approximately one-third zinc and two-thirds copper. It
is used for bearings and bushings where the speeds are slow and the loads
rather heavy for the bearing size. It also finds use in washers, collars
and forms of brackets where the metal should be non-magnetic, also for many
highly finished parts.
Brass is about one-third as good an electrical conductor as copper, is
slightly heavier than steel and has a tensile strength of 15,000 pounds
when cast and about 75,000 to 100,000 pounds when drawn into wire.
Bronze is composed of copper and tin in various proportions, according to
the use to which it is to be put. There will always be from six-tenths to
nine-tenths of copper in the mixture. Bronze is used for bearings,
bushings, thrust washers, brackets and gear wheels. It is heavier than
steel, about 1/15 as good an electrical conductor as pure copper and has a
tensile strength of 30,000 to 60,000 pounds.
Aluminum bronze, composed of copper, zinc and aluminum has high tensile
strength combined with ductility and is used for parts requiring this
Bearing bronze is a variable material, its composition and proportion
depending on the maker and the use for which it is designed. It usually
contains from 75 to 85 per cent of copper combined with one or more
elements, such as tin, zinc, antimony and lead.
White metal is one form of bearing bronze containing over 80 per cent of
zinc together with copper, tin, antimony and lead. Another form is made
with nearly 90 per cent of tin combined with copper and antimony.
Gun metal bronze is made from 90 per cent copper with 10 per cent of tin
and is used for heavy bearings, brackets and highly finished parts.
Phosphor bronze is used for very strong castings and bearings. It is
similar to gun metal bronze, except that about 1-1/2 per cent of phosphorus
has been added.
Manganese bronze contains about 1 per cent of manganese and is used for
parts requiring great strength while being free from corrosion.
German silver is made from 60 per cent of copper with 20 per cent each of
zinc and nickel. Its high electrical resistance makes it valuable for
regulating devices and rheostats.
_Tin_ is the principal part of _babbitt_ and _solder_. A
commonly used babbitt is composed of 89 per cent tin, 8 per cent antimony
and 3 per cent of copper. A grade suitable for repairing is made from
80 per cent of lead and 20 per cent antimony. This last formula should not
be used for particular work or heavy loads, being more suitable for
spacers. Innumerable proportions of metals are marketed under the name of
Solder is made from 50 per cent tin and 50 per cent lead, this grade being
called "half-and-half." Hard solder is made from two-thirds tin and
Aluminum forms many different alloys, giving increased strength to whatever
metal it unites with.
Aluminum brass is composed of approximately 65 per cent copper, 30 per cent
zinc and 5 per cent aluminum. It forms a metal with high tensile strength
while being ductile and malleable.
Aluminum zinc is suitable for castings which must be stiff and hard.
Nickel aluminum has a tensile strength of 40,000 pounds per square inch.
Magnalium is a silver-white alloy of aluminum with from 5 to 20 per cent of
magnesium, forming a metal even lighter than aluminum and strong enough to
be used in making high-speed gasoline engines.
HEAT TREATMENT OF STEEL
The processes of heat treatment are designed to suit the steel for various
purposes by changing the size of the grain in the metal, therefore the
strength; and by altering the chemical composition of the alloys in the
metal to give it different physical properties. Heat treatment, as applied
in ordinary shop work, includes the three processes of annealing, hardening
and tempering, each designed to accomplish a certain definite result.
All of these processes require that the metal treated be gradually brought
to a certain predetermined degree of heat which shall be uniform throughout
the piece being handled and, from this point, cooled according to certain
rules, the selection of which forms the difference in the three methods.
_Annealing._--This is the process which relieves all internal strains
and distortion in the metal and softens it so that it may more easily be
cut, machined or bent to the required form. In some cases annealing is used
only to relieve the strains, this being the case after forging or welding
operations have been performed. In other cases it is only desired to soften
the metal sufficiently that it may be handled easily. In some cases both of
these things must be accomplished, as after a piece has been forged and
must be machined. No matter what the object, the procedure is the same.
The steel to be annealed must first be heated to a dull red. This heating
should be done slowly so that all parts of the piece have time to reach the
same temperature at very nearly the same time. The piece may be heated in
the forge, but a much better way is to heat in an oven or furnace of some
type where the work is protected against air currents, either hot or cold,
and is also protected against the direct action of the fire.
[Illustration: Figure 4.--A Gaspipe Annealing Oven]
Probably the simplest of all ovens for small tools is made by placing a
piece of ordinary gas pipe in the fire (Figure 4), and heating until the
inside of the pipe is bright red. Parts placed in this pipe, after one end
has been closed, may be brought to the desired heat without danger of
cooling draughts or chemical change from the action of the fire. More
elaborate ovens may be bought which use gas, fuel oils or coal to produce
the heat and in which the work may be placed on trays so that the fire will
not strike directly on the steel being treated.
If the work is not very important, it may be withdrawn from the fire or
oven, after heating to the desired point, and allowed to cool in the air
until all traces of red have disappeared when held in a dark place. The
work should be held where it is reasonably free from cold air currents. If,
upon touching a pine stick to the piece being annealed, the wood does not
smoke, the work may then be cooled in water.
Better annealing is secured and harder metal may be annealed if the cooling
is extended over a number of hours by placing the work in a bed of
non-heat-conducting material, such as ashes, charred bone, asbestos fibre,
lime, sand or fire clay. It should be well covered with the heat retaining
material and allowed to remain until cool. Cooling may be accomplished by
allowing the fire in an oven or furnace to die down and go out, leaving the
work inside the oven with all openings closed. The greater the time taken
for gradual cooling from the red heat, the more perfect will be the results
of the annealing.
While steel is annealed by slow cooling, copper or brass is annealed by
bringing to a low red heat and quickly plunging into cold water.
_Hardening._--Steel is hardened by bringing to a proper temperature,
slowly and evenly as for annealing, and then cooling more or less quickly,
according to the grade of steel being handled. The degree of hardening is
determined by the kind of steel, the temperature from which the metal is
cooled and the temperature and nature of the bath into which it is plunged
Steel to be hardened is often heated in the fire until at some heat around
600 to 700 degrees is reached, then placed in a heating bath of molten
lead, heated mercury, fused cyanate of potassium, etc., the heating bath
itself being kept at the proper temperature by fires acting on it. While
these baths have the advantage of heating the metal evenly and to exactly
the temperature desired throughout without any part becoming over or under
heated, their disadvantages consist of the fact that their materials and
the fumes are poisonous in most all cases, and if not poisonous, are
The degree of heat that a piece of steel must be brought to in order that
it may be hardened depends on the percentage of carbon in the steel. The
greater the percentage of carbon, the lower the heat necessary to harden.
[Illustration: Figure 5.--Cooling the Test Bar for Hardening]
To find the proper heat from which any steel must be cooled, a simple test
may be carried out provided a sample of the steel, about six inches long
can be secured. One end of this test bar should be heated almost to its
melting point, and held at this heat until the other end just turns red.
Now cool the piece in water by plunging it so that both ends enter at the
same time (Figure 5), that is, hold it parallel with the surface of the
water when plunged in. This serves the purpose of cooling each point along
the bar from a different heat. When it has cooled in the water remove the
piece and break it at short intervals, about 1/2 inch, along its length.
The point along the test bar which was cooled from the best possible
temperature will show a very fine smooth grain and the piece cannot be cut
by a file at this point. It will be necessary to remember the exact color
of that point when taken from the fire, making another test if necessary,
and heat all pieces of this same steel to this heat. It will be necessary
to have the cooling bath always at the same temperature, or the results
cannot be alike.
While steel to be hardened is usually cooled in water, many other liquids
may be used. If cooled in strong brine, the heat will be extracted much
quicker, and the degree of hardness will be greater. A still greater degree
of hardness is secured by cooling in a bath of mercury. Care should be used
with the mercury bath, as the fumes that arise are poisonous.
Should toughness be desired, without extreme hardness, the steel may be
cooled in a bath of lard oil, neatsfoot oil or fish oil. To secure a result
between water and oil, it is customary to place a thick layer of oil on top
of water. In cooling, the piece will pass through the oil first, thus
avoiding the sudden shock of the cold water, yet producing a degree of
hardness almost as great as if the oil were not used.
It will, of course, be necessary to make a separate test for each cooling
medium used. If the fracture of the test piece shows a coarse grain, the
steel was too hot at that point; if the fracture can be cut with a file,
the metal was not hot enough at that point.
When hardening carbon tool steel its heat should be brought to a cherry
red, the exact degree of heat depending on the amount of carbon and the
test made, then plunged into water and held there until all hissing sound
and vibration ceases. Brine may be used for this purpose; it is even better
than plain water. As soon as the hissing stops, remove the work from the
water or brine and plunge in oil for complete cooling.
[Illustration: Figure 6.--Cooling the Tool for Tempering]
In hardening high-speed tool steel, or air hardening steels, the tool
should be handled as for carbon steel, except that after the body reaches
a cherry red, the cutting point must be quickly brought to a white heat,
almost melting, so that it seems ready for welding. Then cool in an oil
bath or in a current of cool air.
Hardening of copper, brass and bronze is accomplished by hammering or
working them while cold.
_Tempering_ is the process of making steel tough after it has been
hardened, so that it will hold a cutting edge and resist cracking.
Tempering makes the grain finer and the metal stronger. It does not affect
the hardness, but increases the elastic limit and reduces the brittleness
of the steel. In that tempering is usually performed immediately after
hardening, it might be considered as a continuation of the former process.
The work or tool to be tempered is slowly heated to a cherry red and the
cutting end is then dipped into water to a depth of 1/2 to 3/4 inch above
the point (Figure 6). As soon as the point cools, still leaving the tool
red above the part in water, remove the work from the bath and quickly rub
the end with a fine emery cloth.
As the heat from the uncooled part gradually heats the point again, the
color of the polished portion changes rapidly. When a certain color is
reached, the tool should be completely immersed in the water until cold.
For lathe, planer, shaper and slotter tools, this color should be a light
Reamers and taps should be cooled from an ordinary straw color.
Drills, punches and wood working tools should have a brown color.
Blue or light purple is right for cold chisels and screwdrivers.
Dark blue should be reached for springs and wood saws.
Darker colors than this, ranging through green and gray, denote that the
piece has reached its ordinary temper, that is, it is partially annealed.
After properly hardening a spring by dipping in lard or fish oil, it should
be held over a fire while still wet with the oil. The oil takes fire and
burns off, properly tempering the spring.
Remember that self-hardening steels must never be dipped in water, and
always remember for all work requiring degrees of heat, that the more
carbon, the less heat.
_Case Hardening._--This is a process for adding more carbon to the
surface of a piece of steel, so that it will have good wear-resisting
qualities, while being tough and strong on the inside. It has the effect of
forming a very hard and durable skin on the surface of soft steel, leaving
the inside unaffected.
The simplest way, although not the most efficient, is to heat the piece to
be case hardened to a red heat and then sprinkle or rub the part of the
surface to be hardened with potassium ferrocyanide. This material is a
deadly poison and should be handled with care. Allow the cyanide to fuse on
the surface of the metal and then plunge into water, brine or mercury.
Repeating the process makes the surface harder and the hard skin deeper
Another method consists of placing the piece to be hardened in a bed of
powdered bone (bone which has been burned and then powdered) and cover with
more powdered bone, holding the whole in an iron tray. Now heat the tray
and bone with the work in an oven to a bright red heat for 30 minutes to an
hour and then plunge the work into water or brine.
OXY-ACETYLENE WELDING AND CUTTING MATERIALS
_Welding._--Oxy-acetylene welding is an autogenous welding process, in
which two parts of the same or different metals are joined by causing the
edges to melt and unite while molten without the aid of hammering or
compression. When cool, the parts form one piece of metal.
The oxy-acetylene flame is made by mixing oxygen and acetylene gases in a
special welding torch or blowpipe, producing, when burned, a heat of 6,300
degrees, which is more than twice the melting temperature of the common
metals. This flame, while being of intense heat, is of very small size.
_Cutting._--The process of cutting metals with the flame produced from
oxygen and acetylene depends on the fact that a jet of oxygen directed upon
hot metal causes the metal itself to burn away with great rapidity,
resulting in a narrow slot through the section cut. The action is so fast
that metal is not injured on either side of the cut.
_Carbon Removal._--This process depends on the fact that carbon will
burn and almost completely vanish if the action is assisted with a supply
of pure oxygen gas. After the combustion is started with any convenient
flame, it continues as long as carbon remains in the path of the jet of
_Materials._--For the performance of the above operations we require
the two gases, oxygen and acetylene, to produce the flames; rods of metal
which may be added to the joints while molten in order to give the weld
sufficient strength and proper form, and various chemical powders, called
fluxes, which assist in the flow of metal and in doing away with many of
the impurities and other objectionable features.
_Instruments._--To control the combustion of the gases and add to the
convenience of the operator a number of accessories are required.
The pressure of the gases in their usual containers is much too high for
their proper use in the torch and we therefore need suitable valves which
allow the gas to escape from the containers when wanted, and other
specially designed valves which reduce the pressure. Hose, composed of
rubber and fabric, together with suitable connections, is used to carry the
gas to the torch.
The torches for welding and cutting form a class of highly developed
instruments of the greatest accuracy in manufacture, and must be thoroughly
understood by the welder. Tables, stands and special supports are provided
for holding the work while being welded, and in order to handle the various
metals and allow for their peculiarities while heated use is made of ovens
and torches for preheating. The operator requires the protection of
goggles, masks, gloves and appliances which prevent undue radiation of the
_Torch Practice._--The actual work of welding and cutting requires
preliminary preparation in the form of heat treatment for the metals,
including preheating, annealing and tempering. The surfaces to be joined
must be properly prepared for the flame, and the operation of the torches
for best results requires careful and correct regulation of the gases and
the flame produced.
Finally, the different metals that are to be welded require special
treatment for each one, depending on the physical and chemical
characteristics of the material.
It will thus be seen that the apparently simple operations of welding and
cutting require special materials, instruments and preparation on the part
of the operator and it is a proved fact that failures, which have been
attributed to the method, are really due to lack of these necessary
Oxygen, the gas which supports the rapid combustion of the acetylene in the
torch flame, is one of the elements of the air. It is the cause and the
active agent of all combustion that takes place in the atmosphere. Oxygen
was first discovered as a separate gas in 1774, when it was produced by
heating red oxide of mercury and was given its present name by the famous
Oxygen is prepared in the laboratory by various methods, these including
the heating of chloride of lime and peroxide of cobalt mixed in a retort,
the heating of chlorate of potash, and the separation of water into its
elements, hydrogen and oxygen, by the passage of an electric current. While
the last process is used on a large scale in commercial work, the others
are not practical for work other than that of an experimental or temporary
This gas is a colorless, odorless, tasteless element. It is sixteen times
as heavy as the gas hydrogen when measured by volume under the same
temperature and pressure. Under all ordinary conditions oxygen remains in
a gaseous form, although it turns to a liquid when compressed to 4,400
pounds to the square inch and at a temperature of 220 below zero.
Oxygen unites with almost every other element, this union often taking
place with great heat and much light, producing flame. Steel and iron will
burn rapidly when placed in this gas if the combustion is started with a
flame of high heat playing on the metal. If the end of a wire is heated
bright red and quickly plunged into a jar containing this gas, the wire
will burn away with a dazzling light and be entirely consumed except for
the molten drops that separate themselves. This property of oxygen is used
in oxy-acetylene cutting of steel.
The combination of oxygen with other substances does not necessarily cause
great heat, in fact the combination may be so slow and gradual that the
change of temperature can not be noticed. An example of this slow
combustion, or oxidation, is found in the conversion of iron into rust as
the metal combines with the active gas. The respiration of human beings
and animals is a form of slow combustion and is the source of animal heat.
It is a general rule that the process of oxidation takes place with
increasing rapidity as the temperature of the body being acted upon rises.
Iron and steel at a red heat oxidize rapidly with the formation of a scale
and possible damage to the metal.
_Air._--Atmospheric air is a mixture of oxygen and nitrogen with
traces of carbonic acid gas and water vapor. Twenty-one per cent of the
air, by volume, is oxygen and the remaining seventy-nine per cent is the
inactive gas, nitrogen. But for the presence of the nitrogen, which deadens
the action of the other gas, combustion would take place at a destructive
rate and be beyond human control in almost all cases. These two gases exist
simply as a mixture to form the air and are not chemically combined. It is
therefore a comparatively simple matter to separate them with the processes
_Water._--Water is a combination of oxygen and hydrogen, being
composed of exactly two volumes of hydrogen to one volume of oxygen. If
these two gases be separated from each other and then allowed to mix in
these proportions they unite with explosive violence and form water. Water
itself may be separated into the gases by any one of several means, one
making use of a temperature of 2,200 to bring about this separation.
[Illustration: Figure 7.--Obtaining Oxygen by Electrolysis]
The easiest way to separate water into its two parts is by the process
called electrolysis (Figure 7). Water, with which has been mixed a small
quantity of acid, is placed in a vat through the walls of which enter the
platinum tipped ends of two electrical conductors, one positive and the
Tubes are placed directly above these wire terminals in the vat, one tube
being over each electrode and separated from each other by some distance.
With the passage of an electric current from one wire terminal to the
other, bubbles of gas rise from each and pass into the tubes. The gas that
comes from the negative terminal is hydrogen and that from the positive
pole is oxygen, both gases being almost pure if the work is properly
conducted. This method produces electrolytic oxygen and electrolytic
_The Liquid Air Process._--While several of the foregoing methods of
securing oxygen are successful as far as this result is concerned, they are
not profitable from a financial standpoint. A process for separating oxygen
from the nitrogen in the air has been brought to a high state of perfection
and is now supplying a major part of this gas for oxy-acetylene welding. It
is known as the Linde process and the gas is distributed by the Linde Air
Products Company from its plants and warehouses located in the large cities
of the country.
The air is first liquefied by compression, after which the gases are
separated and the oxygen collected. The air is purified and then compressed
by successive stages in powerful machines designed for this purpose until
it reaches a pressure of about 3,000 pounds to the square inch. The large
amount of heat produced is absorbed by special coolers during the process
of compression. The highly compressed air is then dried and the
temperature further reduced by other coolers.
The next point in the separation is that at which the air is introduced
into an apparatus called an interchanger and is allowed to escape through a
valve, causing it to turn to a liquid. This liquid air is sprayed onto
plates and as it falls, the nitrogen return to its gaseous state and leaves
the oxygen to run to the bottom of the container. This liquid oxygen is
then allowed to return to a gas and is stored in large gasometers or tanks.
The oxygen gas is taken from the storage tanks and compressed to
approximately 1,800 pounds to the square inch, under which pressure it is
passed into steel cylinders and made ready for delivery to the customer.
This oxygen is guaranteed to be ninety-seven per cent pure.
Another process, known as the Hildebrandt process, is coming into use in
this country. It is a later process and is used in Germany to a much
greater extent than the Linde process. The Superior Oxygen Co. has secured
the American rights and has established several plants.
_Oxygen Cylinders_.--Two sizes of cylinders are in use, one containing
100 cubic feet of gas when it is at atmospheric pressure and the other
containing 250 cubic feet under similar conditions. The cylinders are made
from one piece of steel and are without seams. These containers are tested
at double the pressure of the gas contained to insure safety while
One hundred cubic feet of oxygen weighs nearly nine pounds (8.921), and
therefore the cylinders will weigh practically nine pounds more when full
than after emptying, if of the 100 cubic feet size. The large cylinders
weigh about eighteen and one-quarter pounds more when full than when empty,
making approximately 212 pounds empty and 230 pounds full.
The following table gives the number of cubic feet of oxygen remaining in
the cylinders according to various gauge pressures from an initial pressure
of 1,800 pounds. The amounts given are not exactly correct as this would
necessitate lengthy calculations which would not make great enough
difference to affect the practical usefulness of the table:
Cylinder of 100 Cu. Ft. Capacity at 68 Fahr.
Gauge Volume Gauge Volume
Pressure Remaining Pressure Remaining
1800 100 700 39
1620 90 500 28
1440 80 300 17
1260 70 100 6
1080 60 18 1
900 50 9 1/2
Cylinder of 250 Cu. Ft. Capacity at 68 Fahr.
Gauge Volume Gauge Volume
Pressure Remaining Pressure Remaining
1800 250 700 97
1620 225 500 70
1440 200 300 42
1260 175 100 15
1080 150 18 8
900 125 9 1-1/4
The temperature of the cylinder affects the pressure in a large degree, the
pressure increasing with a rise in temperature and falling with a fall in
temperature. The variation for a 100 cubic foot cylinder at various
temperatures is given in the following tabulation:
At 150 Fahr........................ 2090 pounds.
At 100 Fahr........................ 1912 pounds.
At 80 Fahr........................ 1844 pounds.
At 68 Fahr........................ 1800 pounds.
At 50 Fahr........................ 1736 pounds.
At 32 Fahr........................ 1672 pounds.
At 0 Fahr........................ 1558 pounds.
At -10 Fahr........................ 1522 pounds.
_Chlorate of Potash Method._--In spite of its higher cost and the
inferior gas produced, the chlorate of potash method of producing oxygen is
used to a limited extent when it is impossible to secure the gas in
[Illustration: Figure 8.--Oxygen from Chlorate of Potash]
An iron retort (Figure 8) is arranged to receive about fifteen pounds of
chlorate of potash mixed with three pounds of manganese dioxide, after
which the cylinder is closed with a tight cap, clamped on. This retort is
carried above a burner using fuel gas or other means of generating heat and
this burner is lighted after the chemical charge is mixed and compressed in
The generation of gas commences and the oxygen is led through water baths
which wash and cool it before storing in a tank connected with the plant.
From this tank the gas is compressed into portable cylinders at a pressure
of about 300 pounds to the square inch for use as required in welding
Each pound of chlorate of potash liberates about three cubic feet of
oxygen, and taking everything into consideration, the cost of gas produced
in this way is several times that of the purer product secured by the
liquid air process.
These chemical generators are oftentimes a source of great danger,
especially when used with or near the acetylene gas generator, as is
sometimes the case with cheap portable outfits. Their use should not be
tolerated when any other method is available, as the danger from accident
alone should prohibit the practice except when properly installed and
cared for away from other sources of combustible gases.
In 1862 a chemist, Woehler, announced the discovery of the preparation of
acetylene gas from calcium carbide, which he had made by heating to a high
temperature a mixture of charcoal with an alloy of zinc and calcium. His
product would decompose water and yield the gas. For nearly thirty years
these substances were neglected, with the result that acetylene was
practically unknown, and up to 1892 an acetylene flame was seen by very few
persons and its possibilities were not dreamed of. With the development of
the modern electric furnace the possibility of calcium carbide as a
commercial product became known.
In the above year, Thomas L. Willson, an electrical engineer of Spray,
North Carolina, was experimenting in an attempt to prepare metallic
calcium, for which purpose he employed an electric furnace operating on a
mixture of lime and coal tar with about ninety-five horse power. The result
was a molten mass which became hard and brittle when cool. This apparently
useless product was discarded and thrown in a nearby stream, when, to the
astonishment of onlookers, a large volume of gas was immediately
liberated, which, when ignited, burned with a bright and smoky flame and
gave off quantities of soot. The solid material proved to be calcium
carbide and the gas acetylene.
Thus, through the incidental study of a by-product, and as the result of an
accident, the possibilities in carbide were made known, and in the spring
of 1895 the first factory in the world for the production of this substance
was established by the Willson Aluminum Company.
When water and calcium carbide are brought together an action takes place
which results in the formation of acetylene gas and slaked lime.
Calcium carbide is a chemical combination of the elements carbon and
calcium, being dark brown, black or gray with sometimes a blue or red
tinge. It looks like stone and will only burn when heated with oxygen.
Calcium carbide may be preserved for any length of time if protected from
the air, but the ordinary moisture in the atmosphere gradually affects it
until nothing remains but slaked lime. It always possesses a penetrating
odor, which is not due to the carbide itself but to the fact that it is
being constantly affected by moisture and producing small quantities of
This material is not readily dissolved by liquids, but if allowed to come
in contact with water, a decomposition takes place with the evolution of
large quantities of gas. Carbide is not affected by shock, jarring or age.
A pound of absolutely pure carbide will yield five and one-half cubic feet
of acetylene. Absolute purity cannot be attained commercially, and in
practice good carbide will produce from four and one-half to five cubic
feet for each pound used.
Carbide is prepared by fusing lime and carbon in the electric furnace under
a heat in excess of 6,000 degrees Fahrenheit. These materials are among the
most difficult to melt that are known. Lime is so infusible that it is
frequently employed for the materials of crucibles in which the highest
melting metals are fused, and for the pencils in the calcium light because
it will stand extremely high temperatures.
Carbon is the material employed in the manufacture of arc light electrodes
and other electrical appliances that must stand extreme heat. Yet these two
substances are forced into combination in the manufacture of calcium
carbide. It is the excessively high temperature attainable in the electric
furnace that causes this combination and not any effect of the electricity
other than the heat produced.
A mixture of ground coke and lime is introduced into the furnace through
which an electric arc has been drawn. The materials unite and form an ingot
of very pure carbide surrounded by a crust of less purity. The poorer crust
is rejected in breaking up the mass into lumps which are graded according
to their size. The largest size is 2 by 3-1/2 inches and is called "lump,"
a medium size is 1/2 by 2 inches and is called "egg," an intermediate size
for certain types of generators is 3/8 by 1-1/4 inches and called "nut,"
and the finely crushed pieces for use in still other types of generators
are 1/12 by 1/4 inch in size and are called "quarter." Instructions as to
the size best suited to different generators are furnished by the makers
of those instruments.
These sizes are packed in air-tight sheet steel drums containing 100 pounds
each. The Union Carbide Company of Chicago and New York, operating under
patents, manufactures and distributes the supply of calcium carbide for the
entire United States. Plants for this manufacture are established at
Niagara Falls, New York, and Sault Ste. Marie, Michigan. This company
maintains a system of warehouses in more than one hundred and ten cities,
where large stocks of all sizes are carried.
The National Board of Fire Underwriters gives the following rules for the
storage of carbide:
Calcium carbide in quantities not to exceed six hundred pounds may be
stored, when contained in approved metal packages not to exceed one hundred
pounds each, inside insured property, provided that the place of storage be
dry, waterproof and well ventilated and also provided that all but one of
the packages in any one building shall be sealed and that seals shall not
be broken so long as there is carbide in excess of one pound in any other
unsealed package in the building.
Calcium carbide in quantities in excess of six hundred pounds must be
stored above ground in detached buildings, used exclusively for the storage
of calcium carbide, in approved metal packages, and such buildings shall be
constructed to be dry, waterproof and well ventilated.
_Properties of Acetylene._--This gas is composed of twenty-four parts
of carbon and two parts of hydrogen by weight and is classed with natural
gas, petroleum, etc., as one of the hydrocarbons. This gas contains the
highest percentage of carbon known to exist in any combination of this form
and it may therefore be considered as gaseous carbon. Carbon is the fuel
that is used in all forms of combustion and is present in all fuels from
whatever source or in whatever form. Acetylene is therefore the most
powerful of all fuel gases and is able to give to the torch flame in
welding the highest temperature of any flame.
Acetylene is a colorless and tasteless gas, possessed of a peculiar and
penetrating odor. The least trace in the air of a room is easily noticed,
and if this odor is detected about an apparatus in operation, it is certain
to indicate a leakage of gas through faulty piping, open valves, broken
hose or otherwise. This leakage must be prevented before proceeding with
the work to be done.
All gases which burn in air will, when mixed with air previous to ignition,
produce more or less violent explosions, if fired. To this rule acetylene
is no exception. One measure of acetylene and twelve and one-half of air
are required for complete combustion; this is therefore the proportion for
the most perfect explosion. This is not the only possible mixture that will
explode, for all proportions from three to thirty per cent of acetylene in
air will explode with more or less force if ignited.
The igniting point of acetylene is lower than that of coal gas, being about
900 degrees Fahrenheit as against eleven hundred degrees for coal gas. The
gas issuing from a torch will ignite if allowed to play on the tip of a
It is still further true that acetylene, at some pressures, greater than
normal, has under most favorable conditions for the effect, been found to
explode; yet it may be stated with perfect confidence that under no
circumstances has anyone ever secured an explosion in it when subjected to
pressures not exceeding fifteen pounds to the square inch.
Although not exploded by the application of high heat, acetylene is injured
by such treatment. It is partly converted, by high heat, into other
compounds, thus lessening the actual quantity of the gas, wasting it and
polluting the rest by the introduction of substances which do not belong
there. These compounds remain in part with the gas, causing it to burn with
a persistent smoky flame and with the deposit of objectionable tarry
substances. Where the gas is generated without undue rise of temperature
these difficulties are avoided.
_Purification of Acetylene._--Impurities in this gas are caused by
impurities in the calcium carbide from which it is made or by improper
methods and lack of care in generation. Impurities from the material will
be considered first.
Impurities in the carbide may be further divided into two classes: those
which exert no action on water and those which act with the water to throw
off other gaseous products which remain in the acetylene. Those impurities
which exert no action on the water consist of coke that has not been
changed in the furnace and sand and some other substances which are
harmless except that they increase the ash left after the acetylene has
An analysis of the gas coming from a typical generator is as follows:
Acetylene ................................ 99.36
Oxygen ................................... .08
Nitrogen ................................. .11
Hydrogen ................................. .06
Sulphuretted Hydrogen .................... .17
Phosphoretted Hydrogen ................... .04
Ammonia .................................. .10
Silicon Hydride .......................... .03
Carbon Monoxide .......................... .01
Methane .................................. .04
The oxygen, nitrogen, hydrogen, methane and carbon monoxide are either
harmless or are present in such small quantities as to be neglected. The
phosphoretted hydrogen and silicon hydride are self-inflammable gases when
exposed to the air, but their quantity is so very small that this
possibility may be dismissed. The ammonia and sulphuretted hydrogen are
almost entirely dissolved by the water used in the gas generator. The
surest way to avoid impure gas is to use high-grade calcium carbide in the
generator and the carbide of American manufacture is now so pure that it
never causes trouble.
The first and most important purification to which the gas is subjected is
its passage through the body of water in the generator as it bubbles to the
top. It is then filtered through felt to remove the solid particles of lime
dust and other impurities which float in the gas.
Further purification to remove the remaining ammonia, sulphuretted hydrogen
and phosphorus containing compounds is accomplished by chemical means. If
this is considered necessary it can be easily accomplished by readily
available purifying apparatus which can be attached to any generator or
inserted between the generator and torch outlets. The following mixtures
have been used.
"_Heratol,_" a solution of chromic acid or sulphuric acid absorbed in
"_Acagine,_" a mixture of bleaching powder with fifteen per cent of
"_Puratylene,_" a mixture of bleaching powder and hydroxide of lime,
made very porous, and containing from eighteen to twenty per cent of active
"_Frankoline,_" a mixture of cuprous and ferric chlorides dissolved in
strong hydrochloric acid absorbed in infusorial earth.
A test for impure acetylene gas is made by placing a drop of ten per cent
solution of silver nitrate on a white blotter and holding the paper in a
stream of gas coming from the torch tip. Blackening of the paper in a short
length of time indicates impurities.
_Acetylene in Tanks._--Acetylene is soluble in water to a very limited
extent, too limited to be of practical use. There is only one liquid that
possesses sufficient power of containing acetylene in solution to be of
commercial value, this being the liquid acetone. Acetone is produced in
various ways, oftentimes from the distillation of wood. It is a
transparent, colorless liquid that flows with ease. It boils at 133
Fahrenheit, is inflammable and burns with a luminous flame. It has a
peculiar but rather agreeable odor.
Acetone dissolves twenty-four times its own bulk of acetylene at ordinary
atmospheric pressure. If this pressure is increased to two atmospheres,
14.7 pounds above ordinary pressure, it will dissolve just twice as much of
the gas and for each atmosphere that the pressure is increased it will
dissolve as much more.
If acetylene be compressed above fifteen pounds per square inch at ordinary
temperature without first being dissolved in acetone a danger is present of
self-ignition. This danger, while practically nothing at fifteen pounds,
increases with the pressure until at forty atmospheres it is very
explosive. Mixed with acetone, the gas loses this dangerous property and is
safe for handling and transportation. As acetylene is dissolved in the
liquid the acetone increases its volume slightly so that when the gas has
been drawn out of a closed tank a space is left full of free acetylene.
This last difficulty is removed by first filling the cylinder or tank with
some porous material, such as asbestos, wood charcoal, infusorial earth,
etc. Asbestos is used in practice and by a system of packing and supporting
the absorbent material no space is left for the free gas, even when the
acetylene has been completely withdrawn.
The acetylene is generated in the usual way and is washed, purified and
dried. Great care is used to make the gas as free as possible from all
impurities and from air. The gas is forced into containers filled with
acetone as described and is compressed to one hundred and fifty pounds to
the square inch. From these tanks it is transferred to the smaller portable
cylinders for consumers' use.
The exact volume of gas remaining in a cylinder at atmospheric temperature
may be calculated if the weight of the cylinder empty is known. One pound
of the gas occupies 13.6 cubic feet, so that if the difference in weight
between the empty cylinder and the one considered be multiplied by 13.6.
the result will be the number of cubic feet of gas contained.
The cylinders contain from 100 to 500 cubic feet of acetylene under
pressure. They cannot be filled with the ordinary type of generator as they
require special purifying and compressing apparatus, which should never be
installed in any building where other work is being carried on, or near
other buildings which are occupied, because of the danger of explosion.
Dissolved acetylene is manufactured by the Prest-O-Lite Company, the
Commercial Acetylene Company and the Searchlight Gas Company and is
distributed from warehouses in various cities.
These tanks should not be discharged at a rate per hour greater than
one-seventh of their total capacity, that is, from a tank of 100 cubic feet
capacity, the discharge should not be more than fourteen cubic feet per
hour. If discharge is carried on at an excessive rate the acetone is drawn
out with the gas and reduces the heat of the welding flame.
For this reason welding should not be attempted with cylinders designed for
automobile and boat lighting. When the work demands a greater delivery than
one of the larger tanks will give, two or more tanks may be connected with
a special coupler such as may be secured from the makers and distributers
of the gas. These couplers may be arranged for two, three, four or five
tanks in one battery by removing the plugs on the body of the coupler and
attaching additional connecting pipes. The coupler body carries a pressure
gauge and the valve for controlling the pressure of the gas as it flows to
the welding torches. The following capacities should be provided for:
Acetylene Consumption Combined Capacity of
of Torches per Hour Cylinders in Use
Up to 15 feet.......................100 cubic feet
16 to 30 feet.......................200 cubic feet
31 to 45 feet.......................300 cubic feet
46 to 60 feet.......................400 cubic feet
61 to 75 feet.......................500 cubic feet
The best welding cannot be done without using the best grade of materials,
and the added cost of these materials over less desirable forms is so
slight when compared to the quality of work performed and the waste of
gases with inferior supplies, that it is very unprofitable to take any
chances in this respect. The makers of welding equipment carry an
assortment of supplies that have been standardized and that may be relied
upon to produce the desired result when properly used. The safest plan is
to secure this class of material from the makers.
Welding rods, or welding sticks, are used to supply the additional metal
required in the body of the weld to replace that broken or cut away and
also to add to the joint whenever possible so that the work may have the
same or greater strength than that found in the original piece. A rod of
the same material as that being welded is used when both parts of the work
are the same. When dissimilar metals are to be joined rods of a composition
suited to the work are employed.
These filling rods are required in all work except steel of less than 16
gauge. Alloy iron rods are used for cast iron. These rods have a high
silicon content, the silicon reacting with the carbon in the iron to
produce a softer and more easily machined weld than would otherwise be the
case. These rods are often made so that they melt at a slightly lower point
than cast iron. This is done for the reason that when the part being welded
has been brought to the fusing heat by the torch, the filling material can
be instantly melted in without allowing the parts to cool. The metal can be
added faster and more easily controlled.
Rods or wires of Norway iron are used for steel welding in almost all
cases. The purity of this grade of iron gives a homogeneous, soft weld of
even texture, great ductility and exceptionally good machining qualities.
For welding heavy steel castings, a rod of rolled carbon steel is employed.
For working on high carbon steel, a rod of the steel being welded must be
employed and for alloy steels, such as nickel, manganese, vanadium, etc.,
special rods of suitable alloy composition are preferable.
Aluminum welding rods are made from this metal alloyed to give the even
flowing that is essential. Aluminum is one of the most difficult of all the
metals to handle in this work and the selection of the proper rod is of
Brass is filled with brass wire when in small castings and sheets. For
general work with brass castings, manganese bronze or Tobin bronze may be
Bronze is welded with manganese bronze or Tobin bronze, while copper is
filled with copper wire.
These welding rods should always be used to fill the weld when the
thickness of material makes their employment necessary, and additional
metal should always be added at the weld when possible as the joint cannot
have the same strength as the original piece if made or dressed off flush
with the surfaces around the weld. This is true because the metal welded
into the joint is a casting and will never have more strength than a
casting of the material used for filling.
Great care should be exercised when adding metal from welding rods to make
sure that no metal is added at a point that is not itself melted and molten
when the addition is made. When molten metal is placed upon cooler surfaces
the result is not a weld but merely a sticking together of the two parts
without any strength in the joint.
Difficulty would be experienced in welding with only the metal and rod to
work with because of the scale that forms on many materials under heat, the
oxides of other metals and the impurities found in almost all metals. These
things tend to prevent a perfect joining of the metals and some means are
necessary to prevent their action.
Various chemicals, usually in powder form, are used to accomplish the
result of cleaning the weld and making the work of the operator less
difficult. They are called fluxes.
A flux is used to float off physical impurities from the molten metal; to
furnish a protecting coating around the weld; to assist in the removal of
any objectionable oxide of the metals being handled; to lower the
temperature at which the materials flow; to make a cleaner weld and to
produce a better quality of metal in the finished work.
The flux must be of such composition that it will accomplish the desired
result without introducing new difficulties. They may be prepared by the
operator in many cases or may be secured from the makers of welding
apparatus, the same remarks applying to their quality as were made
regarding the welding rods, that is, only the best should be considered.
The flux used for cast iron should have a softening effect and should
prevent burning of the metal. In many cases it is possible and even
preferable to weld cast iron without the use of a flux, and in any event
the smaller the quantity used the better the result should be. Flux should
not be added just before the completion of the work because the heat will
not have time to drive the added elements out of the metal or to
incorporate them with the metal properly.
Aluminum should never be welded without using a flux because of the oxide
formed. This oxide, called alumina, does not melt until a heat of 5,000
Fahrenheit is reached, four times the heat needed to melt the aluminum
itself. It is necessary that this oxide be broken down or dissolved so that
the aluminum may have a chance to flow together. Copper is another metal
that requires a flux because of its rapid oxidation under heat.
While the flux is often thrown or sprinkled along the break while welding,
much better results will be obtained by dipping the hot end of the welding
rod into the flux whenever the work needs it. Sufficient powder will stick
on the end of the rod for all purposes, and with some fluxes too much will
adhere. Care should always be used to avoid the application of excessive
flux, as this is usually worse than using too little.
SUPPLIES AND FIXTURES
_Goggles._--The oxy-acetylene torch should not be used without the
protection to the eyes afforded by goggles. These not only relieve
unnecessary strain, but make it much easier to watch the exact progress of
the work with the molten metal. The difficulty of protecting the sight
while welding is even greater than when cutting metal with the torch.
Acetylene gives a light which is nearest to sunlight of any artificial
illuminant. But for the fact that this gas light gives a little more green
and less blue in its composition, it would be the same in quality and
practically the same in intensity. This light from the gas is almost absent
during welding, being lost with the addition of the extra oxygen needed to
produce the welding heat. The light that is dangerous comes from the molten
metal which flows under the torch at a bright white heat.
Goggles for protection against this light and the heat that goes with it
may be secured in various tints, the darker glass being for welding and
the lighter for cutting. Those having frames in which the metal parts do
not touch the flesh directly are most desirable because of the high
temperature reached by these parts.
_Gloves._--While not as necessary as are the goggles, gloves are a
convenience in many cases. Those in which leather touches the hands
directly are really of little value as the heat that protection is desired
against makes the leather so hot that nothing is gained in comfort. Gloves
are made with asbestos cloth, which are not open to this objection in so
great a degree.
[Illustration: Figure 9.--Frame for Welding Stand]
_Tables and Stands._--Tables for holding work while being welded
(Figure 9) are usually made from lengths of angle steel welded together.
The top should be rectangular, about two feet wide and two and one-half
feet long. The legs should support the working surface at a height of
thirty-two to thirty-six inches from the floor. Metal lattice work may be
fastened or laid in the top framework and used to support a layer of
firebrick bound together with a mixture of one-third cement and two-thirds
fireclay. The piece being welded is braced and supported on this table with
pieces of firebrick so that it will remain stationary during the operation.
Holders for supporting the tanks of gas may be
made or purchased in forms that rest directly on the floor or that are
mounted on wheels. These holders are quite useful where the floor or ground
is very uneven.
_Hose._--All permanent lines from tanks and generators to the torches
are made with piping rigidly supported, but the short distance from the end
of the pipe line to the torch itself is completed with a flexible hose so
that the operator may be free in his movements while welding. An accident
through which the gases mix in the hose and are ignited will burst this
part of the equipment, with more or less painful results to the person
handling it. For that reason it is well to use hose with great enough
strength to withstand excessive pressure.
A poor grade of hose will also break down inside and clog the flow of gas,
both through itself and through the parts of the torch. To avoid outside
damage and cuts this hose is sometimes encased with coiled sheet metal.
Hose may be secured with a bursting strength of more than 1,000 pounds to
the square inch. Many operators prefer to distinguish between the oxygen
and acetylene lines by their color and to allow this, red is used for the
oxygen and black for acetylene.
_Other Materials._--Sheet asbestos and asbestos fibre in flakes are
used to cover parts of the work while preparing them for welding and during
the operation itself. The flakes and small pieces that become detached from
the large sheets are thrown into a bin where the completed small work is
placed to allow slow and even cooling while protected by the asbestos.
Asbestos fibre and also ordinary fireclay are often used to make a backing
or mould into a form that may be placed behind aluminum and some other
metals that flow at a low heat and which are accordingly difficult to
handle under ordinary methods. This forms a solid mould into which the
metal is practically cast as melted by the torch so that the desired shape
is secured without danger of the walls of metal breaking through and
Carbon blocks and rods are made in various shapes and sizes so that they
may be used to fill threaded holes and other places that it is desired to
protect during welding. These may be secured in rods of various diameters
up to one inch and in blocks of several different dimensions.
Acetylene generators used for producing the gas from the action of water on
calcium carbide are divided into three principal classes according to the
pressure under which they operate.
Low pressure generators are designed to operate at one pound or less per
square inch. Medium pressure systems deliver the gas at not to exceed
fifteen pounds to the square inch while high pressure types furnish gas
above fifteen pounds per square inch. High pressure systems are almost
unknown in this country, the medium pressure type being often referred to
as "high pressure."
Another important distinction is formed by the method of bringing the
carbide and water together. The majority of those now in use operate by
dropping small quantities of carbide into a large volume of water, allowing
the generated gas to bubble up through the water before being collected
above the surface. This type is known as the "carbide to water" generator.
A less used type brings a measured and small quantity of water to a
comparatively large body of the carbide, the gas being formed and collected
from the chamber in which the action takes place. This is called the "water
to carbide" type. Another way of expressing the difference in feed is that
of designating the two types as "carbide feed" for the former and "water
feed" for the latter.
A further division of the carbide to water machines is made by mentioning
the exact method of feeding the carbide. One type, called "gravity feed"
operates by allowing the carbide to escape and fall by the action of its
own weight, or gravity; the other type, called "forced feed," includes a
separate mechanism driven by power. This mechanism feeds definite amounts
of the carbide to the water as required by the demands on the generator.
The action of either feed is controlled by the withdrawal of gas from the
generator, the aim being to supply sufficient carbide to maintain a nearly
_Generator Requirements._--The qualities of a good generator are
outlined as follows: [Footnote: See Pond's "Calcium Carbide and
It must allow no possibility of the existence of an explosive mixture in
any of its parts at any time. It is not enough to argue that a mixture,
even if it exists, cannot be exploded unless kindled. It is necessary to
demand that a dangerous mixture can at no time be formed, even if the
machine is tampered with by an ignorant person. The perfect machine must be
so constructed that it shall be impossible at any time, under any
circumstances, to blow it up.
It must insure cool generation. Since this is a relative term, all machines
being heated somewhat during the generation of gas, this amounts to saying
that a machine must heat but little. A pound of carbide decomposed by water
develops the same amount of heat under all circumstances, but that heat
can be allowed to increase locally to a high point, or it can be equalized
by water so that no part of the material becomes heated enough to do
It must be well constructed. A good generator does not need, perhaps, to be
"built like a watch," but it should be solid, substantial and of good
material. It should be built for service, to last and not simply to sell;
anything short of this is to be avoided as unsafe and unreliable.
It must be simple. The more complicated the machine the sooner it will get
out of order. Understand your generator. Know what is inside of it and
beware of an apparatus, however attractive its exterior, whose interior is
filled with pipes and tubes, valves and diaphragms whose functions you do
not perfectly understand.
It should be capable of being cleaned and recharged and of receiving all
other necessary attention without loss of gas, both for economy's sake, and
more particularly to avoid danger of fire.
It should require little attention. All machines have to be emptied and
recharged periodically; but the more this process is simplified and the
more quickly this can be accomplished, the better.
It should be provided with a suitable indicator to designate how low the
charge is in order that the refilling may be done in good season.
It should completely use up the carbide, generating the maximum amount of
_Overheating._--A large amount of heat is liberated when acetylene gas
is formed from the union of calcium carbide and water. Overheating during
this process, that is to say, an intense local heat rather than a large
amount of heat well distributed, brings about the phenomenon of
polymerization, converting the gas, or part of it, into oily matters, which
can do nothing but harm. This tarry mass coming through the small openings
in the torches causes them to become partly closed and alters the
proportions of the gases to the detriment of the welding flame. The only
remedy for this trouble is to avoid its cause and secure cool generation.
Overheating can be detected by the appearance of the sludge remaining after
the gas has been made. Discoloration, yellow or brown, shows that there has
been trouble in this direction and the resultant effects at the torches may
be looked for. The abundance of water in the carbide to water machines
effects this cooling naturally and is a characteristic of well designed
machines of this class. It has been found best and has practically become a
fundamental rule of generation that a gallon of water must be provided for
each pound of carbide placed in the generator. With this ratio and a
generator large enough for the number of torches to be supplied, little
trouble need be looked for with overheating.
_Water to Carbide Generators._--It is, of course, much easier to
obtain a measured and regular flow of water than to obtain such a flow of
any solid substance, especially when the solid substance is in the form of
lumps, as is carbide This fact led to the use of a great many water-feed
generators for all classes of work, and this type is still in common use
for the small portable machines, such, for instance, as those used on motor
cars for the lamps. The water-feed machine is not, however, favored for
welding plants, as is the carbide feed, in spite of the greater
difficulties attending the handling of the solid material.
A water-feed generator is made up of the gas producing part and a holder
for the acetylene after it is made. The carbide is held in a tray formed of
a number of small compartments so that the charge in each compartment is
nearly equal to that in each of the others. The water is allowed to flow
into one of these compartments in a volume sufficient to produce the
desired amount of gas and the carbide is completely used from this one
division. The water then floods the first compartment and finally overflows
into the next one, where the same process is repeated. After using the
carbide in this division, it is flooded in turn and the water passing on to
those next in order, uses the entire charge of the whole tray.
These generators are charged with the larger sizes of carbide and are
easily taken care of. The residue is removed in the tray and emptied,
making the generator ready for a fresh supply of carbide.
_Carbide to Water Generators._--This type also is made up of two
principal parts, the generating chamber and a gas holder, the holder being
part of the generating chamber or a separate device. The generator (Figure
10) contains a hopper to receive the charge of carbide and is fitted with
the feeding mechanism to drop the proper amount of carbide into the water
as required by the demands of the torches. The charge of carbide is of one
of the smaller sizes, usually "nut" or "quarter."
_Feed Mechanisms._--The device for dropping the carbide into the water
is the only part of the machine that is at all complicated. This
complication is brought about by the necessity of controlling the mass of
carbide so that it can never be discharged into the water at an excessive
rate, feeding it at a regular rate and in definite amounts, feeding it
positively whenever required and shutting off the feed just as positively
when the supply of gas in the holder is enough for the immediate needs.
[Illustration: Figure 10.--Carbide to Water Generator. A. Feed motor weight;
B. Carbide feed motor; C. Carbide hopper; D. Water for gas generation;
E. Agitator for loosening residuum; F. Water seal in gas bell; G. Filter;
H. Hydraulic Valve; J. Motor control levers.]
The charge of carbide is unavoidably acted upon by the water vapor in the
generator and will in time become more or less pasty and sticky. This is
more noticeable if the generator stands idle for a considerable length of
time This condition imposes another duty on the feeding mechanism; that is,
the necessity of self-cleaning so that the carbide, no matter in what
condition, cannot prevent the positive action of this part of the device,
especially so that it cannot prevent the supply from being stopped at the
The gas holder is usually made in the bell form so that the upper portion
rises and falls with the addition to or withdrawal from the supply of gas
in the holder. The rise and fall of this bell is often used to control the
feed mechanism because this movement indicates positively whether enough
gas has been made or that more is required. As the bell lowers it sets the
feed mechanism in motion, and when the gas passing into the holder has
raised the bell a sufficient distance, the movement causes the feed
mechanism to stop the fall of carbide into the water. In practice, the
movement of this part of the holder is held within very narrow limits.
_Gas Holders._--No matter how close the adjustment of the feeding
device, there will always be a slight amount of gas made after the fall of
carbide is stopped, this being caused by the evolution of gas from the
carbide with which water is already in contact. This action is called
"after generation" and the gas holder in any type of generator must
provide sufficient capacity to accommodate this excess gas. As a general
rule the water to carbide generator requires a larger gas holder than the
carbide to water type because of the greater amount of carbide being acted
upon by the water at any one time, also because the surface of carbide
presented to the moist air within the generating chamber is greater with
_Freezing._--Because of the rather large body of water contained in
any type of generator, there is always danger of its freezing and
rendering the device inoperative unless placed in a temperature above the
freezing point of the water. It is, of course, dangerous and against the
insurance rules to place a generator in the same room with a fire of any
kind, but the room may be heated by steam or hot water coils from a furnace
in another building or in another part of the same building.
When the generator is housed in a separate structure the walls should be
made of materials or construction that prevents the passage of heat or
cold through them to any great extent. This may be accomplished by the use
of hollow tile or concrete blocks or by any other form of double wall
providing air spaces between the outer and inner facings. The space between
the parts of the wall may be filled with materials that further retard the
loss of heat if this is necessary under the conditions prevailing.
_Residue From Generators._--The sludge remaining in the carbide to
water generator may be drawn off into the sewer if the piping is run at a
slant great enough to give a fall that carries the whole quantity, both
water and ash, away without allowing settling and consequent clogging.
Generators are provided with agitators which are operated to stir the ash
up with the water so that the whole mass is carried off when the drain cock
If sewer connections cannot be made in such a way that the ash is entirely
carried away, it is best to run the liquid mass into a settling basin
outside of the building. This should be in the form of a shallow pit which
will allow the water to pass off by soaking into the ground and by
evaporation, leaving the comparatively dry ash in the pit. This ash which
remains is essentially slaked lime and can often be disposed of to more or
less advantage to be used in mortar, whitewash, marking paths and any other
use for which slaked lime is suited. The disposition of the ash depends
entirely on local conditions. An average analysis of this ash is as
Sand....................... 1.10 per cent.
Carbon..................... 2.72 "
Oxide of iron and alumina.. 2.77 "
Lime....................... 64.06 "
Water and carbonic acid.... 29.35 "
The water for generating purposes is carried in the large tank-like
compartment directly below the carbide chamber. See Figure 11. This water
compartment is filled through a pipe of such a height that the water level
cannot be brought above the proper point or else the water compartment is
provided with a drain connection which accomplishes this same result by
allowing an excess to flow away.
The quantity of water depends on the capacity of the generator inasmuch as
there must be one gallon for each pound of carbide required. The generator
should be of sufficient capacity to furnish gas under working conditions
from one charge of carbide to all torches installed for at least five hours
After calculating the withdrawal of the whole number of torches according
to the work they are to do for this period of five hours the proper
generator capacity may be found on the basis of one cubic foot of gas per
hour for each pound of carbide. Thus if the torches were to use sixty cubic
feet of gas per hour, five hours would call for three hundred cubic feet
and a three hundred pound generator should be installed. Generators are
rated according to their carbide capacity in pounds.
_Charging._--The carbide capacity of the generator should be great
enough to furnish a continuous supply of gas for the maximum operating
time, basing the quantity of gas generated on four and one-half cubic feet
from each pound of lump carbide and on four cubic feet from each pound of
quarter, intermediate sizes being in proportion.
Generators are built in such a way that it is impossible for the acetylene
to escape from the gas holding compartment during the recharging process.
This is accomplished (1) by connecting the water inlet pipe opening with a
shut off valve in such a way that the inlet cannot be uncovered or opened
without first closing the shut off valve with the same movement of the
operator; (2) by incorporating an automatic or hydraulic one-way valve so
that this valve closes and acts as a check when the gas attempts to flow
from the holder back to the generating chamber, or by any other means that
will positively accomplish this result.
In generators having no separate gas holding chamber but carrying the
supply in the same compartment in which it is generated, the gas contained
under pressure is allowed to escape through vent pipes into the outside
air before recharging with carbide. As in the former case, the parts are
so interlocked that it is impossible to introduce carbide or water without
first allowing the escape of the gas in the generator.
It is required by the insurance rules that the entire change of carbide
while in the generator be held in such a way that it may be entirely
removed without difficulty in case the necessity should arise.
Generators should be cleaned and recharged at regular stated intervals.
This work should be done during daylight hours only and likewise all
repairs should be made at such a time that artificial light is not needed.
Where it is absolutely necessary to use artificial light it should be
provided only by incandescent electric lamps enclosed in gas tight globes.
In charging generating chambers the old ash and all residue must first be
cleaned out and the operator should be sure that no drain or other pipe has
become clogged. The generator should then be filled with the required
amount of water. In charging carbide feed machines be careful not to place
less than a gallon of water in the water compartment for each pound of
carbide to be used and the water must be brought to, but not above, the
proper level as indicated by the mark or the maker's instructions. The
generating chamber must be filled with the proper amount of water before
any attempt is made to place the carbide in its holder. This rule must
always be followed. It is also necessary that all automatic water seals
and valves, as well as any other water tanks, be filled with clean water
at this time.
Never recharge with carbide without first cleaning the generating chamber
and completely refilling with clean water. Never test the generator or
piping for leaks with any flame, and never apply flame to any open pipe or
at any point other than the torch, and only to the torch after it has a
welding or cutting nozzle attached. Never use a lighted match, lamp,
candle, lantern, cigar or any open flame near a generator. Failure to
observe these precautions is liable to endanger life and property.
_Operation and Care of Generators._--The following instructions apply
especially to the Davis Bournonville pressure generator, illustrated in
Figure 11. The motor feed mechanism is illustrated in Figure 12.
Before filling the machine, the cover should be removed and the hopper
taken out and examined to see that the feeding disc revolves freely; that
no chains have been displaced or broken, and that the carbide displacer
itself hangs barely free of the feeding disc when it is revolved. After
replacing the cover, replace the bolts and tighten them equally, a little
at a time all around the circumference of the cover--not screwing tight in
one place only. Do not screw the cover down any more than is necessary to
make a tight fit.
To charge the generator, proceed as follows: Open the vent valve by turning
the handle which extends over the filling tube until it stands at a right
angle with the generator. Open the valve in the water filling pipe, and
through this fill with water until it runs out of the overflow pipe of the
drainage chamber, then close the valve in the water filling pipe and vent
valve. Remove the carbide filling plugs and fill the hopper with
1-1/4"x3/8" carbide ("nut" size). Then replace the plugs and the
safety-locking lever chains. Now rewind the motor weight. Run the pressure
up to about five pounds by raising the controlling diaphragm valve lever
by hand (Figure 12, lever marked _E_). Then raise the blow-off lever,
allowing the gas to blow off until the gauge shows about two pounds; this
to clear the generator of air mixture. Then run the pressure up to about
eight pounds by raising the controlling valve lever _E_, or until
this controlling lever rests against the upper wing of the fan governor,
and prevents operation of the feed motor. After this is done, the motor
will operate automatically as the gas is consumed.
[Illustration: Figure 11.--Pressure Generator (Davis Bournonville).
_A_, Feed motor weight;
_B_, Carbide feed motor;
_C_, Motor Control diaphragm;
_D_, Carbide hopper;
_E_, Carbide feed disc;
_F_, Overflow pipe;
_G_, Overflow pipe seal;
_H_, Overflow pipe valve;
_J_, Filling funnel;
_K_, Hydraulic valve;
_L_, Expansion chamber;
_M_, Escape pipe;
_N_, Feed pipe;
_O_, Agitator for residuum;
_P_, Residuum valve;
_Q_, Water level]
[Illustration: Figure 12.--Feed Mechanism of Pressure Generator]
Should the pressure rise much above the blow-off point, the safety
controlling diaphragm valve will operate and throw the safety clutch in
interference and thus stop the motor. This interference clutch will then
have to be returned to its former position before the motor will operate,
but cannot be replaced before the pressure has been reduced below the
The parts of the feed mechanism illustrated in Figure 12 are as follows:
_A_, motor drum for weight cable. _B_, carbide filling plugs.
_C_, chains for connecting safety locking lever of motor to pins on
the top of the carbide plugs. _D_, interference clutch of motor.
_E_, lever on feed controlling diaphragm valve. _F_, lever of
interference controlling diaphragm valve that operates interference clutch.
_G_, feed controlling diaphragm valve. _H_, diaphragm valve
controlling operation of interference clutch. _I_, interference pin
to engage emergency clutch. _J_, main shaft driving carbide feeding
disc. _Y_, safety locking lever.
_Recharging Generator._--Turn the agitator handle rapidly for several
revolutions, and then open the residuum valve, having five or six pounds
gas pressure on the machine. If the carbide charge has been exhausted and
the motor has stopped, there is generally enough carbide remaining in the
feeding disc that can be shaken off, and fed by running the motor to
obtain some pressure in the generator. The desirability of discharging
the residuum with some gas pressure is because the pressure facilitates
the discharge and at the same time keeps the generator full of gas,
preventing air mixture to a great extent. As soon as the pressure is
relieved by the withdrawal of the residuum, the vent valve should be
opened, as if the pressure is maintained until all of the residuum is
discharged gas would escape through the discharge valve.
Having opened the vent pipe valve and relieved the pressure, open the
valve in the water filling tube. Close the residuum valve, then run in
several gallons of water and revolve the agitator, after which draw out the
remaining residuum; then again close the residuum valve and pour in water
until it discharges from the overflow pipe of the drainage chamber. It is
desirable in filling the generator to pour the water in rapidly enough to
keep the filling pipe full of water, so that air will not pass in at the
After the generator is cleaned and filled with water, fill with carbide and
proceed in the same manner as when first charging.
_Carbide Feed Mechanism._--Any form of carbide to water machine should
be so designed that the carbide never falls directly from its holder into
the water, but so that it must take a more or less circuitous path. This
should be true, no matter what position the mechanism is in. One of the
commonest types of forced feed machine carries the carbide in a hopper with
slanting sides, this hopper having a large opening in the bottom through
which the carbide passes to a revolving circular plate. As the pieces of
carbide work out toward the edge of the plate under the influence of the
mass behind them, they are thrown off into the water by small stationary
fins or plows which are in such a position that they catch the pieces
nearest the edges and force them off as the plate revolves. This
arrangement, while allowing a free passage for the carbide, prevents an
excess from falling should the machine stop in any position.
When, as is usually the case, the feed mechanism is actuated by the rise
or fall of pressure in the generator or of the level of some part of the
gas holder, it must be built in such a way that the feeding remains
inoperative as long as the filling opening on the carbide holder remains
The feed of carbide should always be shut off and controlled so that under
no condition can more gas be generated than could be cared for by the
relief valve provided. It is necessary also to have the feed mechanism at
least ten inches above the surface of the water so that the parts will
never become clogged with damp lime dust.
_Motor Feed._--The feed mechanism itself is usually operated by power
secured from a slowly falling weight which, through a cable, revolves a
drum. To this drum is attached suitable gearing for moving the feed parts
with sufficient power and in the way desired. This part, called the motor,
is controlled by two levers, one releasing a brake and allowing the motor
to operate the feed, the other locking the gearing so that no more carbide
will be dropped into the water. These levers are moved either by the
quantity of gas in the holder or by the pressure of the gas, depending on
the type of machine.
With a separate gas holder, such as used with low pressure systems, the
levers are operated by the rise and fall of the bell of the holder or
gasometer, alternately starting and stopping the motor as the bell falls
and rises again. Medium pressure generators are provided with a diaphragm
to control the feed motor.
This diaphragm is carried so that the pressure within the generator acts
on one side while a spring, whose tension is under the control of the
operator, acts on the other side. The diaphragm is connected to the brake
and locking device on the motor in such a way that increasing the tension
on the spring presses the diaphragm and moves a rod that releases the brake
and starts the feed. The gas pressure, increasing with the continuation of
carbide feed, acts on the other side and finally overcomes the pressure of
the spring tension, moving the control rod the other way and stopping the
motor and carbide feed. This spring tension is adjusted and checked with
the help of a pressure gauge attached to the generating chamber.
_Gravity Feed._--This type of feed differs from the foregoing in that
the carbide is simply released and is allowed to fall into the water
without being forced to do so. Any form of valve that is sufficiently
powerful in action to close with the carbide passing through is used and is
operated by the power secured from the rise and fall of the gas holder
bell. When this valve is first opened the carbide runs into the water until
sufficient pressure and volume of gas is generated to raise the bell. This
movement operates the arm attached to the carbide shut off valve and slowly
closes it. A fall of the bell occasioned by gas being withdrawn again opens
the valve and more gas is generated.
_Mechanical Feed._--The previously described methods of feeding
carbide to the water have all been automatic in action and do not depend
on the operator for their proper action.
Some types of large generating plants have a power-driven feed, the power
usually being from some kind of motor other than one operated by a weight,
such as a water motor, for instance. This motor is started and stopped by
the operator when, in his judgment, more gas is wanted or enough has been
generated. This type of machine, often called a "non-automatic generator,"
is suitable for large installations and is attached to a gas holder of
sufficient size to hold a day's supply of acetylene. The generator can then
be operated until a quantity of gas has been made that will fill the large
holder, or gasometer, and then allowed to remain idle for some time.
_Gas Holders._--The commonest type of gas container is that known as a
gasometer. This consists of a circular tank partly filled with water, into
which is lowered another circular tank, inverted, which is made enough
smaller in diameter than the first one so that three-quarters of an inch is
left between them. This upper and inverted portion, called the bell,
receives the gas from the generator and rises or falls in the bath of water
provided in the lower tank as a greater or less amount of gas is contained
These holders are made large enough so that they will provide a means of
caring for any after generation and so that they maintain a steady and even
flow. The generator, however, must be of a capacity great enough so that
the gas holder will not be drawn on for part of the supply with all torches
in operation. That is, the holder must not be depended on for a reserve
The bell of the holder is made so that when full of gas its lower edge is
still under a depth of at least nine inches of water in the lower tank. Any
further rise beyond this point should always release the gas, or at least
part of it, to the escape pipe so that the gas will under no circumstances
be forced into the room from, between the bell and tank. The bell is guided
in its rise and fall by vertical rods so that it will not wedge at any
point in its travel.
A condensing chamber to receive the water which condenses from the
acetylene gas in the holder is usually placed under this part and is
provided with a drain so that this water of condensation may be easily
_Filtering._--A small chamber containing some closely packed but