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
oxygen.
_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
heat.
_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
qualifications.
OXYGEN
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
chemist, Lavoisier.
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
nature.
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
now available.
_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
other negative.
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
hydrogen.
_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
handling.
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
cylinders.
[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 tube.
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
operations.
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.
ACETYLENE
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.
CARBIDE
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
acetylene gas.
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
lighted cigar.
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
been generated.
An analysis of the gas coming from a typical generator is as follows:
Per cent
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
porous earth.
"_Acagine,_" a mixture of bleaching powder with fifteen per cent of
lead chromate.
"_Puratylene,_" a mixture of bleaching powder and hydroxide of lime,
made very porous, and containing from eighteen to twenty per cent of active
chlorine.
"_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
WELDING RODS
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
great importance.
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
used.
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.
FLUXES
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
flowing away.
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.