Oxy-Acetylene Welding and Cutting
by
Harold P. Manly
Part 3 out of 3
drawing it away quickly. If no sparking is produced, the secondary circuit
is free from ground, and you will then look for a broken connection in the
circuit. Some caution must be used in making the above test, as in case one
terminal is heavily grounded the testing wire may be fused if allowed to
stay in contact with the die.
_The Remedy._--Clean the slides, dies and terminal blocks thoroughly
and dry out the fibre insulation if it is damp. See that no scale or metal
has worked under the sliding parts, and that the secondary leads do not
touch the frame. If the ground is very heavy it may be necessary to remove
the slides in order to facilitate the examination and removal of the
ground. Insulation, where torn or worn through, must be carefully replaced
or taped. If the transformer coils are grounded to the iron core of the
transformer or to the secondary, it may be necessary to remove the coils
and reinsulate them at the points of contact. A short circuited coil will
heat excessively and eventually burn out. This may mean a new coil if you
are unable to repair the old one. In all cases the transformer windings
should be protected from mechanical injury or dampness. Unless excessively
overloaded, transformers will last for years without giving a moment's
trouble, if they are not exposed to moisture or are not injured
mechanically.
The most common trouble arises from poor electrical contacts, and they are
the cause of endless trouble and annoyance. See that all connections are
clean and bright. Take out the dies every day or two and see that there is
no scale, grease or dirt between them and the holders. Clean them
thoroughly before replacing. Tighten the bolts running from the transformer
leads to the work jaws.
ELECTRIC ARC WELDING
This method bears no relation to the one just considered, except that the
source of heat is the same in both cases. Arc welding makes use of the
flame produced by the voltaic arc in practically the same way that
oxy-acetylene welding uses the flame from the gases.
If the ends of two pieces of carbon through which a current of electricity
is flowing while they are in contact are separated from each other quite
slowly, a brilliant arc of flame is formed between them which consists
mainly of carbon vapor. The carbons are consumed by combination with the
oxygen in the air and through being turned to a gas under the intense heat.
The most intense action takes place at the center of the carbon which
carries the positive current and this is the point of greatest heat. The
temperature at this point in the arc is greater than can be produced by any
other means under human control.
An arc may be formed between pieces of metal, called electrodes, in the
same way as between carbon. The metallic arc is called a flaming arc and as
the metal of the electrode burns with the heat, it gives the flame a color
characteristic of the material being used. The metallic arc may be drawn
out to a much greater length than one formed between carbon electrodes.
Arc Welding is carried out by drawing a piece of carbon which is of
negative polarity away from the pieces of metal to be welded while the
metal is made positive in polarity. The negative wire is fastened to the
carbon electrode and the work is laid on a table made of cast or wrought
iron to which the positive wire is made fast. The direction of the flame is
then from the metal being welded to the carbon and the work is thus
prevented from being saturated with carbon, which would prove very
detrimental to its strength. A secondary advantage is found in the fact
that the greatest heat is at the metal being welded because of its being
the positive electrode.
The carbon electrode is usually made from one quarter to one and a half
inches in diameter and from six to twelve inches in length. The length of
the arc may be anywhere from one inch to four inches, depending on the size
of the work being handled.
While the parts are carefully insulated to avoid danger of shock, it is
necessary for the operator to wear rubber gloves as a further protection,
and to wear some form of hood over the head to shield him against the
extreme heat liberated. This hood may be made from metal, although some
material that does not conduct electricity is to be preferred. The work is
watched through pieces of glass formed with one sheet, which is either blue
or green, placed over another which is red. Screens of glass are sometimes
used without the head protector. Some protection for the eyes is absolutely
necessary because of the intense white light.
It is seldom necessary to preheat the work as with the gas processes,
because the heat is localized at the point of welding and the action is so
rapid that the expansion is not so great. The necessity of preheating,
however, depends entirely on the material, form and size of the work being
handled. The same advice applies to arc welding as to the gas flame method
but in a lesser degree. Filling rods are used in the same way as with any
other flame process.
It is the purpose of this explanation to state the fundamental principles
of the application of the electric arc to welding metals, and by applying
the principles the following questions will be answered:
What metals can be welded by the electric arc?
What difficulties are to be encountered in applying the electric arc to
welding?
What is the strength of the weld in comparison with the original piece?
What is the function of the arc welding machine itself?
What is the comparative application of the electric arc and the
oxy-acetylene method and others of a similar nature?
The answers to these questions will make it possible to understand the
application of this process to any work. In a great many places the use of
the arc is cutting the cost of welding to a very small fraction of what it
would be by any other method, so that the importance of this method may be
well understood.
Any two metals which are brought to the melting temperature and applied to
each other will adhere so that they are no more apt to break at the weld
than at any other point outside of the weld. It is the property of all
metals to stick together under these conditions. The electric arc is used
in this connection merely as a heating agent. This is its only function in
the process.
It has advantages in its ease of application and the cheapness with which
heat can be liberated at any given point by its use. There is nothing in
connection with arc welding that the above principles will not answer; that
is, that metals at the melting point will weld and that the electric arc
will furnish the heat to bring them to this point. As to the first
question, what metals can be welded, all metals can be welded.
The difficulties which are encountered are as follows:
In the case of brass or zinc, the metals will be covered with a coat of
zinc oxide before they reach a welding heat. This zinc oxide makes it
impossible for two clean surfaces to come together and some method has to
be used for eliminating this possibility and allowing the two surfaces to
join without the possibility of the oxide intervening. The same is true of
aluminum, in which the oxide, alumina, will be formed, and with several
other alloys comprising elements of different melting points.
In order to eliminate these oxides, it is necessary in practical work, to
puddle the weld; this is, to have a sufficient quantity of molten metal at
the weld so that the oxide is floated away. When this is done, the two
surfaces which are to be joined are covered with a coat of melted metal on
which floats the oxide and other impurities. The two pieces are thus
allowed to join while their surfaces are protected. This precaution is not
necessary in working with steel except in extreme cases.
Another difficulty which is met with in the welding of a great many metals
is their expansion under heat, which results in so great a contraction when
the weld cools that the metal is left with a considerable strain on it. In
extreme cases this will result in cracking at the weld or near it. To
eliminate this danger it is necessary to apply heat either all over the
piece to be welded or at certain points. In the case of cast iron and
sometimes with copper it is necessary to anneal after welding, since
otherwise the welded pieces will be very brittle on account of the
chilling. This is also true of malleable iron.
Very thin metals which are welded together and are not backed up by
something to carry away the excess heat, are very apt to burn through,
leaving a hole where the weld should be. This difficulty can be eliminated
by backing up the weld with a metal face or by decreasing the intensity of
the arc so that this melting through will not occur. However, the practical
limit for arc welding without backing up the work with a metal face or
decreasing the intensity of the arc is approximately 22 gauge, although
thinner metal can be welded by a very skillful and careful operator.
One difficulty with arc welding is the lack of skillful operators. This
method is often looked upon as being something out of the ordinary and
governed by laws entirely different from other welding. As a matter of
fact, it does not take as much skill to make a good arc weld as it does to
make a good weld in a forge fire as the blacksmith does it. There are few
jobs which cannot be handled successfully by an operator of average
intelligence with one week's instructions, although his work will become
better and better in quality as he continues to use the arc.
Now comes the question of the strength of the weld after it has been made.
This strength is equally as great as that of the metal that is used to make
the weld. It should be remembered, however, that the metal which goes into
the weld is put in there as a casting and has not been rolled. This would
make the strength of the weld as great as the same metal that is used for
filling if in the cast form.
Two pieces of steel could be welded together having a tensile strength at
the weld of 50,000 pounds. Higher strengths than this can be obtained by
the use of special alloys for the filling material or by rolling. Welds
with a tensile strength as great as mentioned will give a result which is
perfectly satisfactory in almost all cases.
There are a great many jobs where it is possible to fill up the weld, that
is, make the section at the point of the weld a little larger than the
section through the rest of the piece. By doing this, the disadvantages
of the weld being in the form of a casting in comparison with the rest of
the piece being in the form of rolled steel can be overcome, and make the
weld itself even stronger than the original piece.
The next question is the adaptability of the electric arc in comparison
with forge fire, oxy-acetylene or other method. The answer is somewhat
difficult if made general. There are no doubt some cases where the use of a
drop hammer and forge fire or the use of the oxy-acetylene torch will make,
all things being considered, a better job than the use of the electric arc,
although a case where this is absolutely proved is rare.
The electric arc will melt metal in a weld for less than the same metal can
be melted by the use of the oxy-acetylene torch, and, on account of the
fact that the heat can be applied exactly where it is required and in the
amount required, the arc can in almost all cases supply welding heat for
less cost than a forge fire or heating furnace.
The one great advantage of the oxy-acetylene method in comparison with
other methods of welding is the fact that in some cases of very thin sheet,
the weld can be made somewhat sooner than is possible otherwise. With metal
of 18 gauge or thicker, this advantage is eliminated. In cutting steel, the
oxy-acetylene torch is superior to almost any other possible method.
_Arc Welding Machines._--A consideration of the function and purpose
of the various types of arc welding machines shows that the only reason for
the use of any machine is either for conversion of the current from
alternating to direct, or, if the current is already direct, then the
saving in the application of this current in the arc.
It is practically out of the question to apply an alternating current arc
to welding for the reason that in any arc practically all the heat is
liberated at the positive electrode, which means that, in alternating
current, half the heat is liberated at each electrode as the current
changes its direction of flow or alternates. Another disadvantage of the
alternating arc is that it is difficult of control and application.
In all arc welding by the use of the carbon arc, the positive electrode is
made the piece to be welded, while in welding with metallic electrodes this
may be either the piece to be welded of the rod that is used as a filler.
The voltage across the arc is a variable quantity, depending on the length
of the flame, its temperature and the gases liberated in the arc. With a
carbon electrode the voltage will vary from zero to forty-five volts. With
the metallic electrode the voltage will vary from zero to thirty volts. It
is, therefore, necessary for the welding machine to be able to furnish to
the arc the requisite amount of current, this amount being varied, and
furnish it at all times at the voltage required.
The simplest welding apparatus is a resistance in series with the arc. This
is entirely satisfactory in every way except in cost of current. By the use
of resistance in series with the arc and using 220 volts as the supply,
from eighty to ninety per cent of the current is lost in heat at the
resistance. Another disadvantage is the fact that most materials change
their resistance as their temperature changes, thus making the amount of
current for the arc a variable quantity, depending on the temperature of
the resistance.
There have been various methods originated for saving the power mentioned
and a good many machines have been put on the market for this purpose. All
of them save some power over what a plain resistance would use. Practically
all arc welding machines at the present time are motor generator sets, the
motor of which is arranged for the supply voltage and current, this motor
being direct connected to a compound wound generator delivering
approximately seventy-five volts direct current. Then by the use of a
resistance, this seventy-five volt supply is applied to the arc. Since the
voltage across the arc will vary from zero to fifty volts, this machine
will save from zero up to seventy per cent of the power that the machine
delivers. The rest of the power, of course, has to be dissipated in the
resistance used in series with the arc.
A motor generator set which can be purchased from any electrical company,
with a long piece of fence wire wound around a piece of asbestos, gives
results equally as good and at a very small part of the first cost.
It is possible to construct a machine which will eliminate all losses in
the resistance; in other words, eliminate all resistance in series with the
arc. A machine of this kind will save its cost within a very short time,
providing the welder is used to any extent.
Putting it in figures, the results are as follows for average conditions.
Current at 2c per kilowatt hour, metallic electrode arc of 150 amperes,
carbon arc 500 amperes; voltage across the metallic electrode arc 20,
voltage across the carbon arc 35. Supply current 220 volts, direct. In the
case of the metallic electrode, if resistance is used, the cost of running
this arc is sixty-six cents per hour. With the carbon electrode, $2.20 per
hour. If a motor generator set with a seventy volt constant potential
machine is used for a welder, the cost will be as follows:
Metallic electrode 25.2c. Carbon electrode 84c per hour. With a machine
which will deliver the required voltage at the arc and eliminate all the
resistance in series with the arc, the cost will be as follows: Metallic
electrode 7.2c per hour; carbon electrode 42c per hour. This is with the
understanding that the arc is held constant and continuously at its full
value. This, however, is practically impossible and the actual load factor
is approximately fifty per cent, which would mean that operating a welder
as it is usually operated, this result will be reduced to one-half of that
stated in all cases.
CHAPTER VII
HAND FORGING AND WELDING
Smithing, or blacksmithing, is the process of working heated iron, steel or
other metals by forging, bending or welding them.
_The Forge._--The metal is heated in a forge consisting of a shallow
pan for holding the fire, in the center of which is an opening from below
through which air is forced to make a hot fire.
[Illustration: Figure 48.--Tuyere Construction on a Forge]
Air is forced through this hole, called a "tuyere" (Figure 48) by means of
a hand bellows, a rotary fan operated with crank or lever, or with a fan
driven from an electric motor. The harder the air is driven into the fire
above the tuyere the more oxygen is furnished and the hotter the fire
becomes.
Directly below the tuyere is an opening through which the ashes that drop
from the fire may be cleaned out.
_The Fire._--The fire is made by placing a small piece of waste soaked
in oil, kerosene or gasoline, over the tuyere, lighting the waste, then
starting the fan or blower slowly. Gradually cover the waste, while it is
burning brightly, with a layer of soft coal. The coal will catch fire and
burn after the waste has been consumed. A piece of waste half the size of a
person's hand is ample for this purpose.
The fuel should be "smithing coal." A lump of smithing coal breaks easily,
shows clean and even on all sides and should not break into layers. The
coal is broken into fine pieces and wet before being used on the fire.
The fire should be kept deep enough so that there is always three or four
inches of fire below the piece of metal to be heated and there should be
enough fire above the work so that no part of the metal being heated comes
in contact with the air. The fire should be kept as small as possible while
following these rules as to depth.
To make the fire larger, loosen the coal around the edges. To make the fire
smaller, pack wet coal around the edges in a compact mass and loosen the
fire in the center. Add fresh coal only around the edges of the fire. It
will turn to coke and can then be raked onto the fire. Blow only enough air
into the fire to keep it burning brightly, not so much that the fire is
blown up through the top of the coal pack. To prevent the fire from going
out between jobs, stick a piece of soft wood into it and cover with fresh
wet coal.
_Tools._--The _hammer_ is a ball pene, or blacksmith's hammer,
weighing about a pound and a half.
The _sledge_ is a heavy hammer, weighing from 5 to 20 pounds and
having a handle 30 to 36 inches long.
The _anvil_ is a heavy piece of wrought iron (Figure 49), faced with
steel and having four legs. It has a pointed horn on one end, an
overhanging tail on the other end and a flat top. In the tail there is a
square hole called the "hardie" hole and a round one called the "spud"
hole.
[Illustration: Figure 49.--Anvil, Showing Horn, Tail, Hardie Hole and Spud
Hole]
_Tongs_, with handles about one foot long and jaws suitable for
holding the work, are used. To secure a firm grip on the work, the jaws may
be heated red hot and hammered into shape over the piece to be held, thus
giving a properly formed jaw. Jaws should touch the work along their entire
length.
The _set hammer_ is a hammer, one end of whose head is square and
flat, and from this face the head tapers evenly to the other face. The
large face is about 1-1/4 inches square.
The _flatter_ is a hammer having one face of its head flat and about
2-1/2 inches square.
_Swages_ are hammers having specially formed faces for finishing
rounds, squares, hexagons, ovals, tapers, etc.
_Fullers_ are hammers having a rounded face, long in one direction.
They are used for spreading metal in one direction only.
The _hardy_ is a form of chisel with a short, square shank which may
be set into the hardie hole for cutting off hot bars.
_Operations._--Blacksmithing consists of bending, drawing or upsetting
with the various hammers, or in punching holes.
Bending is done over the square corners of the anvil if square cornered
bends are desired, or over the horn of the anvil if rounding bends, eyes,
hooks, etc., are wanted.
To bend a ring or eye in the end of a bar, first figure the length of stock
needed by multiplying the diameter of the hole by 31/7, then heat the piece
to a good full red at a point this distance back from the end. Next bend
the iron over at a 90 degree angle (square) at this point. Next, heat the
iron from the bend just made clear to the point and make the eye by laying
the part that was bent square over the horn of the anvil and bending the
extreme tip into part of a circle. Keep pushing the piece farther and
farther over the horn of the anvil, bending it as you go. Do not hammer
directly over the horn of the anvil, but on the side where you are doing
the bending.
To make the outside of a bend square, sharp and full, rather than slightly
rounding, the bent piece must be laid edgewise on the face of the anvil.
That is, after making the bend over the corner of the anvil, lay the piece
on top of the anvil so that its edge and not the flat side rests on the
anvil top. With the work in this position, strike directly against the
corner with the hammer so that the blows come in line, first with one leg
of the work, then the other, and always directly on the corner of the
piece. This operation cannot be performed by laying the work so that one
leg hangs over the anvil's corner.
To make a shoulder on a rod or bar, heat the work and lay flat across the
top of the anvil with the point at which the shoulder is desired at the
edge of the anvil. Then place the set hammer on top of the piece, with the
outside edge of the set hammer directly over the edge of the anvil. While
hammering in this position keep the work turning continually.
To draw stock means to make it longer and thinner by hammering. A piece to
be drawn out is usually laid across the horn of the anvil while being
struck with the hammer. The metal is then spread in only one direction in
place of being spread in every direction, as it would be if laid on the
anvil face. To draw the work, heat it to as high a temperature as it will
stand without throwing sparks and burning. The fuller may be used for
drawing metal in place of laying the work over the horn of the anvil.
When drawing round stock, it should be first drawn out square, and when
almost down to size it may be rounded. When pointing stock, the same rule
of first drawing out square applies.
Upsetting means to make a piece shorter in length and greater in thickness
or width, or both shorter and thicker. To upset short pieces, heat to a
bright red at the place to be upset, then stand on end on the anvil face
and hammer directly down on top until of the right form. Longer pieces may
be swung against the anvil or placed upright on a heavy piece of metal
lying on the floor or that is sunk into the floor. While standing on this
heavy piece the metal may be upset by striking down on the end with a heavy
hammer or the sledge. If a bend appears while upsetting, it should be
straightened by hammering back into shape on the anvil face.
Light blows affect the metal for only a short distance from the point of
striking, but heavy blows tend to swell the metal more equally through its
entire length. In driving rivets that should fill the holes, heavy blows
should be struck, but to shape the end of a rivet or to make a head on a
rod, light blows should be used.
The part of the piece that is heated most will upset the most.
To punch a hole through metal, use a tool steel punch with its end slightly
tapering to a size a little smaller than the hole to be punched. The end of
the punch must be square across and never pointed or rounded.
First drive the punch part way through from one side and then turn the work
over. When you turn it over, notice where the bulge appears and in that way
locate the hole and drive the punch through from the second side. This
makes a cleaner and more even hole than to drive completely through from
one side. When the punch is driven in from the second side, the place to be
punched through should be laid over the spud hole in the tail of the anvil
and the piece driven out of the work.
Work when hot is larger than it will be after cooling. This must be
remembered when fitting parts or trouble will result. A two-foot bar of
steel will be 1/4 inch longer when red hot than when cold.
The temperatures of iron correspond to the following colors:
Dullest red seen in the dark... 878
Dullest red seen in daylight... 887
Dull red....................... 1100
Full red....................... 1370
Light red...................... 1550
Orange......................... 1650
Light orange................... 1725
Yellow......................... 1825
Light yellow................... 1950
_Bending Pipes and Tubes._--It is difficult to make bends or curves in
pipes and tubing without leaving a noticeable bulge at some point of the
work. Seamless steel tubing may be handled without very great danger of
this trouble if care is used, but iron pipe, having a seam running
lengthwise, must be given special attention to avoid opening the seam.
Bends may be made without kinking if the tube or pipe is brought to a full
red heat all the way around its circumference and at the place where the
bend is desired. Hold the cool portion solidly in a vise and, by taking
hold of the free end, bend very slowly and with a steady pull. The pipe
must be kept at full red heat with the flames from one or more torches and
must not be hammered to produce the bend. If a sufficient purchase cannot
be secured on the free end by the hand, insert a piece of rod or a smaller
pipe into the opening.
While making the bend, should small bulges appear, they may be hammered
back into shape before proceeding with the work.
Tubing or pipes may be bent while being held between two flat metal
surfaces while at a bright red heat. The metal plates at each side of the
work prevent bulging.
Another method by which tubing may be bent consists of filling completely
with tightly packed sand and fitting a solid cap or plug at each end.
Thin brass tubing may be filled with melted resin and may be bent after the
resin cools. To remove the resin it is necessary to heat the tube, allowing
it to run out.
Large jobs of bending should be handled in special pipe bending machines in
which the work is forced through formed rolls which prevent its bulging.
WELDING
Welding with the heat of a blacksmith forge fire, or a coal or illuminating
gas fire, can only be performed with iron and steel because of the low heat
which is not localized as with the oxy-acetylene and electric processes.
Iron to be welded in this manner is heated until it reaches the temperature
indicated by an orange color, not white, as is often stated, this orange
color being slightly above 3600 degrees Fahrenheit. Steel is usually welded
at a bright red heat because of the danger of oxidizing or burning the
metal if the temperature is carried above this point.
_The Fire._--If made in a forge, the fire should be built from good
smithing coal or, better still, from coke. Gas fires are, of course,
produced by suitable burners and require no special preparation except
adjustment of the heat to the proper degree for the size and thickness of
the metal being welded so that it will not be burned.
A coal fire used for ordinary forging operations should not be used for
welding because of the impurities it contains. A fresh fire should be built
with a rather deep bed of coal, four to eight inches being about right for
work ordinarily met with. The fire should be kept burning until the coal
around the edges has been thoroughly coked and a sufficient quantity of
fuel should be on and around the fire so that no fresh coal will have to
be added while working.
After the coking process has progressed sufficiently, the edges should be
packed down and the fire made as small as possible while still surrounding
the ends to be joined. The fire should not be altered by poking it while
the metal is being heated. The best form of fire to use is one having
rather high banks of coked coal on each side of the mass, leaving an
opening or channel from end to end. This will allow the added fuel to be
brought down on top of the fire with a small amount of disturbance.
_Preparing to Weld._--If the operator is not familiar with the metal
to be handled, it is best to secure a test piece if at all possible and try
heating it and joining the ends. Various grades of iron and steel call for
different methods of handling and for different degrees of heat, the proper
method and temperature being determined best by actual test under the
hammer.
The form of the pieces also has a great deal to do with their handling,
especially in the case of a more or less inexperienced workman. If the
pieces are at all irregular in shape, the motions should be gone through
with before the metal is heated and the best positions on the anvil as well
as in the fire determined with regard to the convenience of the workman and
speed of handling the work after being brought to a welding temperature.
Unnatural positions at the anvil should be avoided as good work is most
difficult of performance under these conditions.
_Scarfing._--While there are many forms of welds, depending on the
relative shape of the pieces to be joined, the portions that are to meet
and form one piece are always shaped in the same general way, this shape
being called a "scarf." The end of a piece of work, when scarfed, is
tapered off on one side so that the extremity comes to a rather sharp edge.
The other side of the piece is left flat and a continuation in the same
straight plane with its side of the whole piece of work. The end is then in
the form of a bevel or mitre joint (Figure 50).
[Illustration: Figure 50.--Scarfing Ends of Work Ready for Welding]
Scarfing may be produced in any one of several ways. The usual method is to
bring the ends to a forging heat, at which time they are upset to give a
larger body of metal at the ends to be joined. This body of metal is then
hammered down to the taper on one side, the length of the tapered portion
being about one and a half times the thickness of the whole piece being
handled. Each piece should be given this shape before proceeding farther.
The scarf may be produced by filing, sawing or chiseling the ends, although
this is not good practice because it is then impossible to give the desired
upset and additional metal for the weld. This added thickness is called for
by the fact that the metal burns away to a certain extent or turns to
scale, which is removed before welding.
When the two ends have been given this shape they should not fit as closely
together as might be expected, but should touch only at the center of the
area to be joined (Figure 51). That is to say, the surface of the beveled
portion should bulge in the middle or should be convex in shape so that the
edges are separated by a little distance when the pieces are laid together
with the bevels toward each other. This is done so that the scale which is
formed on the metal by the heat of the fire can have a chance to escape
from the interior of the weld as the two parts are forced together.
[Illustration: Figure 51.--Proper Shape of Scarfed Ends]
If the scarf were to be formed with one or more of the edges touching each
other at the same time or before the centers did so, the scale would be
imprisoned within the body of the weld and would cause the finished work to
be weak, while possibly giving a satisfactory appearance from the outside.
_Fluxes._--In order to assist in removing the scale and other
impurities and to make the welding surfaces as clean as possible while
being joined, various fluxing materials are used as in other methods of
welding.
For welding iron, a flux of white sand is usually used, this material being
placed on the metal after it has been brought to a red heat in the fire.
Steel is welded with dry borax powder, this flux being applied at the same
time as the iron flux just mentioned. Borax may also be used for iron
welding and a mixture of borax with steel borings may also be used for
either class of work. Mixtures of sal ammoniac with borax have been
successfully used, the proportions being about four parts of borax to one
of sal ammoniac. Various prepared fluxing powders are on the market for
this work, practically all of them producing satisfactory results.
After the metal has been in the fire long enough to reach a red heat, it is
removed temporarily and, if small enough in size, the ends are dipped into
a box of flux. If the pieces are large, they may simply be pulled to the
edge of the fire and the flux then sprinkled on the portions to be joined.
A greater quantity of flux is required in forge welding than in electric or
oxy-acetylene processes because of the losses in the fire. After the powder
has been applied to the surfaces, the work is returned to the fire and
heated to the welding temperature.
_Heating the Work._--After being scarfed, the two pieces to be welded
are placed in the fire and brought to the correct temperature. This
temperature can only be recognized by experiment and experience. The metal
must be just below that point at which small sparks begin to be thrown out
of the fire and naturally this is a hard point to distinguish. At the
welding heat the metal is almost ready to flow and is about the consistency
of putty. Against the background of the fire and coal the color appears to
be a cream or very light yellow and the work feels soft as it is handled.
It is absolutely necessary that both parts be heated uniformly and so that
they reach the welding temperature at the same time. For this reason they
should be as close together in the fire as possible and side by side. When
removed to be hammered together, time is saved if they are picked up in
such a way that when laid together naturally the beveled surfaces come
together. This makes it necessary that the workman remember whether the
scarfed side is up or down, and to assist in this it is a good thing to
mark the scarfed side with chalk or in some other noticeable manner, so
that no mistake will be made in the hurry of placing the work on the anvil.
The common practice in heating allows the temperature to rise until the
small white sparks are seen to come from the fire. Any heating above this
point will surely result in burning that will ruin the iron or steel being
handled. The best welding heat can be discerned by the appearance of the
metal and its color after experience has been gained with this particular
material. Test welds can be made and then broken, if possible, so that the
strength gained through different degrees of heat can be known before
attempting more important work.
_Welding._--When the work has reached the welding temperature after
having been replaced in the fire with the flux applied, the two parts are
quickly tapped to remove the loose scale from their surfaces. They are then
immediately laid across the top of the anvil, being placed in a diagonal
position if both pieces are straight. The lower piece is rested on the
anvil first with the scarf turned up and ready to receive the top piece in
the position desired. The second piece must be laid in exactly the position
it is to finally occupy because the two parts will stick together as soon
as they touch and they cannot well be moved after having once been allowed
to come in contact with each other. This part of the work must be done
without any unnecessary loss of time because the comparatively low heat at
which the parts weld allows them to cool below the working temperature in
a few seconds.
The greatest difficulty will be experienced in withdrawing the metal from
the fire before it becomes burned and in getting it joined before it cools
below this critical point. The beveled edges of the scarf are, of course,
the first parts to cool and the weld must be made before they reach a point
at which they will not join, or else the work will be defective in
appearance and in fact.
If the parts being handled are of such a shape that there is danger of
bending a portion back of the weld, this part may be cooled by quickly
dipping it into water before laying the work on the anvil to be joined.
The workman uses a heavy hand hammer in making the joint, and his helper,
if one is employed, uses a sledge. With the two parts of the work in place
on the anvil, the workman strikes several light blows, the first ones being
at a point directly over the center of the weld, so that the joint will
start from this point and be worked toward the edges. After the pieces have
united the helper strikes alternate blows with his sledge, always striking
in exactly the same place as the last stroke of the workman. The hammer
blows are carried nearer and nearer to the edges of the weld and are made
steadily heavier as the work progresses.
The aim during the first part of the operation should be to make a perfect
joint, with every part of the surfaces united, and too much attention
should not be paid to appearance, at least not enough to take any chance
with the strength of the work.
It will be found, after completion of the weld, that there has been a loss
in length equal to one-half the thickness of the metal being welded. This
loss is occasioned by the burned metal and the scale which has been formed.
_Finishing the Weld._--If it is possible to do so, the material should
be hammered into the shape that it should remain with the same heat that
was used for welding. It will usually be found, however, that the metal has
cooled below the point at which it can be worked to advantage. It should
then be replaced in the fire and brought back to a forging heat.
[Illustration: Figure 52.--Upsetting and Scarfing the End of a Rod]
While shaping the work at this forging heat every part that has been at a
red heat should be hammered with uniformly light and even blows as it
cools. This restores the grain and strength of the iron or steel to a great
extent and makes the unavoidable weakness as small as possible.
_Forms of Welds._--The simplest of all welds is that called a "lap
weld." This is made between the ends of two pieces of equal size and
similar form by scarfing them as described and then laying one on top of
the other while they are hammered together.
A butt weld (Figure 52) is made between the ends of two pieces of shaft or
other bar shapes by upsetting the ends so that they have a considerable
flare and shaping the face of the end so that it is slightly higher in the
center than around the edges, this being done to make the centers come
together first. The pieces are heated and pushed into contact, after which
the hammering is done as with any other weld.
[Illustration: Figure 53.--Scarfing for a T Weld]
A form similar to the butt weld in some ways is used for joining the end of
a bar to a flat surface and is called a jump weld. The bar is shaped in the
same way as for a butt weld. The flat plate may be left as it is, but if
possible a depression should be made at the point where the shaft is to be
placed. With the two parts heated as usual, the bar is dropped into
position and hammered from above. As soon as the center of the weld has
been made perfect, the joint may be finished with a fuller driven all the
way around the edge of the joint.
When it is required to join a bar to another bar or to the edge of any
piece at right angles the work is called a "T" weld from its shape when
complete (Figure 53). The end of the bar is scarfed as described and the
point of the other bar or piece where the weld is to be made is hammered so
that it tapers to a thin edge like one-half of a circular depression. The
pieces are then laid together and hammered as for a lap weld.
The ends of heavy bar shapes are often joined with a "V," or cleft, weld.
One bar end is shaped so that it is tapering on both sides and comes to a
broad edge like the end of a chisel. The other bar is heated to a forging
temperature and then slit open in a lengthwise direction so that the
V-shaped opening which is formed will just receive the pointed edge of the
first piece. With the work at welding heat, the two parts are driven
together by hammering on the rear ends and the hammering then continues as
with a lap weld, except that the work is turned over to complete both sides
of the joint.
[Illustration: Figure 54.-Splitting Ends to Be Welded in Thin Work]
The forms so far described all require that the pieces be laid together in
the proper position after removal from the fire, and this always causes a
slight loss of time and a consequent lowering of the temperature. With very
light stock, this fall of temperature would be so rapid that the weld would
be unsuccessful, and in this case the "lock" weld is resorted to. The ends
of the two pieces to be joined are split for some distance back, and
one-half of each end is bent up and the other half down (Figure 54). The
two are then pushed together and placed in the fire in this position. When
the welding heat is reached, it is only necessary to take the work out of
the fire and hammer the parts together, inasmuch as they are already in the
correct position.
Other forms of welds in which the parts are too small to retain their heat,
can be made by first riveting them together or cutting them so that they
can be temporarily fastened in any convenient way when first placed in the
fire.
CHAPTER VIII
SOLDERING, BRAZING AND THERMIT WELDING
SOLDERING
Common solder is an alloy of one-half lead with one-half tin, and is called
"half and half." Hard solder is made with two-thirds tin and one-third
lead. These alloys, when heated, are used to join surfaces of the same or
dissimilar metals such as copper, brass, lead, galvanized iron, zinc,
tinned plate, etc. These metals are easily joined, but the action of solder
with iron, steel and aluminum is not so satisfactory and requires greater
care and skill.
The solder is caused to make a perfect union with the surfaces treated with
the help of heat from a soldering iron. The soldering iron is made from a
piece of copper, pointed at one end and with the other end attached to an
iron rod and wooden handle. A flux is used to remove impurities from the
joint and allow the solder to secure a firm union with the metal surface.
The iron, and in many cases the work, is heated with a gasoline blow torch,
a small gas furnace, an electric heater or an acetylene and air torch.
The gasoline torch which is most commonly used should be filled two-thirds
full of gasoline through the hole in the bottom, which is closed by a screw
plug. After working the small hand pump for 10 to 20 strokes, hold the palm
of your hand over the end of the large iron tube on top of the torch and
open the gasoline needle valve about a half turn. Hold the torch so that
the liquid runs down into the cup below the tube and fills it. Shut the
gasoline needle valve, wipe the hands dry, and set fire to the fuel in the
cup. Just as the gasoline fire goes out, open the gasoline needle valve
about a half turn and hold a lighted match at the end of the iron tube to
ignite the mixture of vaporized gasoline and air. Open or close the needle
valve to secure a flame about 4 inches long.
On top of the iron tube from which the flame issues there is a rest for
supporting the soldering iron with the copper part in the flame. Place the
iron in the flame and allow it to remain until the copper becomes very hot,
not quite red, but almost so.
A new soldering iron or one that has been misused will have to be "tinned"
before using. To do this, take the iron from the fire while very hot and
rub the tip on some flux or dip it into soldering acid. Then rub the tip of
the iron on a stick of solder or rub the solder on the iron. If the solder
melts off the stick without coating the end of the iron, allow a few drops
to fall on a piece of tin plate, then nil the end of the iron on the tin
plate with considerable force. Alternately rub the iron on the solder and
dip into flux until the tip has a coating of bright solder for about half
an inch from the end. If the iron is in very bad shape, it may be necessary
to scrape or file the end before dipping in the flux for the first time.
After the end of the iron is tinned in this way, replace it on the rest of
the torch so that the tinned point is not directly in the flame, turning
the flame down to accomplish this.
_Flux._--The commonest flux, which is called "soldering acid," is made
by placing pieces of zinc in muriatic (hydrochloric) acid contained in a
heavy glass or porcelain dish. There will be bubbles and considerable heat
evolved and zinc should be added until this action ceases and the zinc
remains in the liquid, which is now chloride of zinc.
This soldering acid may be used on any metal to be soldered by applying
with a brush or swab. For electrical work, this acid should be made neutral
by the addition of one part ammonia and one part water to each three parts
of the acid. This neutralized flux will not corrode metal as will the
ordinary acid.
Powdered resin makes a good flux for lead, tin plate, galvanized iron and
aluminum. Tallow, olive oil, beeswax and vaseline are also used for this
purpose. Muriatic acid may be used for zinc or galvanized iron without the
addition of the zinc, as described in making zinc chloride. The addition of
two heaping teaspoonfuls of sal ammoniac to each pint of the chloride of
zinc is sometimes found to improve its action.
_Soldering Metal Parts._--All surfaces to be joined should be fitted
to each other as accurately as possible and then thoroughly cleaned with a
file, emery cloth, scratch bush or by dipping in lye. Work may be cleaned
by dipping it into nitric acid which has been diluted with an equal volume
of water. The work should be heated as hot as possible without danger of
melting, as this causes the solder to flow better and secure a much better
hold on the surfaces. Hard solder gives better results than half and half,
but is more difficult to work. It is very important that the soldering iron
be kept at a high heat during all work, otherwise the solder will only
stick to the surfaces and will not join with them.
Sweating is a form of soldering in which the surfaces of the work are first
covered with a thin layer of solder by rubbing them with the hot iron after
it has been dipped in or touched to the soldering stick. These surfaces are
then placed in contact and heated to a point at which the solder melts and
unites. Sweating is much to be preferred to ordinary soldering where the
form of the work permits it. This is the only method which should ever be
used when a fitting is to be placed over the end of a length of tube.
_Soldering Holes._--Clean the surfaces for some distance around the
hole until they are bright, and apply flux while holding the hot iron near
the hole. Touch the tip of the iron to some solder until the solder is
picked up on the iron, and then place this solder, which was just picked
up, around the edge of the hole. It will leave the soldering iron and stick
to the metal. Keep adding solder in this way until the hole has been closed
up by working from the edges and building toward the center. After the hole
is closed, apply more flux to the job and smooth over with the hot iron
until there are no rough spots. Should the solder refuse to flow smoothly,
the iron is not hot enough.
_Soldering Seams._--Clean back from the seam or split for at least
half an inch all around and then build up the solder in the same way as was
done with the hole. After closing the opening, apply more flux to the work
and run the hot iron lengthwise to smooth the job.
_Soldering Wires._--Clean all insulation from the ends to be soldered
and scrape the ends bright. Lay the ends parallel to each other and,
starting at the middle of the cleaned portion, wrap the ends around each
other, one being wrapped to the right, the other to the left. Hold the hot
iron under the twisted joint and apply flux to the wire. Then dip the iron
in the solder and apply to the twisted portion until the spaces between the
wires are filled with solder. Finish by smoothing the joint and cleaning
away all excess metal by rubbing the hot iron lengthwise. The joint should
now be covered with a layer of rubber tape and this covered with a layer of
ordinary friction tape.
_Steel and Iron._--Steel surfaces should be cleaned, then covered with
clear muriatic acid. While the acid is on the metal, rub with a stick of
zinc and then tin the surfaces with the hot iron as directed. Cast iron
should be cleaned and dipped in strong lye to remove grease. Wash the lye
away with clean water and cover with muriatic acid as with steel. Then rub
with a piece of zinc and tin the surfaces by using resin as a flux.
It is very difficult to solder aluminum with ordinary solder. A special
aluminum solder should be secured, which is easily applied and makes a
strong joint. Zinc or phosphor tin may be used in place of ordinary solder
to tin the surfaces or to fill small holes or cracks. The aluminum must be
thoroughly heated before attempting to solder and the flux may be either
resin or soldering acid. The aluminum must be thoroughly cleaned with
dilute nitric acid and kept hot while the solder is applied by forcible
rubbing with the hot iron.
BRAZING
This is a process for joining metal parts, very similar to soldering,
except that brass is used to make the joint in place of the lead and zinc
alloys which form solder. Brazing must not be attempted on metals whose
melting point is less than that of sheet brass.
Two pieces of brass to be brazed together are heated to a temperature at
which the brass used in the process will melt and flow between the
surfaces. The brass amalgamates with the surfaces and makes a very strong
and perfect joint, which is far superior to any form of soldering where the
work allows this process to be used, and in many cases is the equal of
welding for the particular field in which it applies.
_Brazing Heat and Tools._--The metal commonly used for brazing will
melt at heats between 1350 and 1650 Fahrenheit. To bring the parts to
this temperature, various methods are in use, using solid, liquid or
gaseous fuels. While brazing may be accomplished with the fire of the
blacksmith forge, this method is seldom satisfactory because of the
difficulty of making a sufficiently clean fire with smithing coal, and it
should not be used when anything else is available. Large jobs of brazing
may be handled with a charcoal fire built in the forge, as this fuel
produces a very satisfactory and clean fire. The only objection is in the
difficulty of confining the heat to the desired parts of the work.
The most satisfactory fire is that from a fuel gas torch built for this
work. These torches are simply forms of Bunsen burners, mixing the proper
quantity of air with the gas to bring about a perfect combustion. Hose
lines lead to the mixing tube of the gas torch, one line carrying the gas
and the other air under a moderate pressure. The air line is often
dispensed with, allowing the gas to draw air into the burner on the
injector principle, much the same as with illuminating gas burners for use
with incandescent mantles. Valves are provided with which the operator may
regulate the amount of both gas and air, and ordinarily the quality and
intensity of the flame.
When gas is not available, recourse may be had to the gasoline torch made
for brazing. This torch is built in the same way as the small portable
gasoline torches for soldering operations, with the exception that two
regulating needle valves are incorporated in place of only one.
The torches are carried on a framework, which also supports the work being
handled. Fuel is forced to the torch from a large tank of gasoline into
which air pressure is pumped by hand. The torches are regulated to give
the desired flame by means of the needle valves in much the same way as
with any other form of pressure torch using liquid fuel.
Another very satisfactory form of torch for brazing is the acetylene-air
combination described in the chapter on welding instruments. This torch
gives the correct degree of heat and may be regulated to give a clean and
easily controlled flame.
Regardless of the source of heat, the fire or flame must be adjusted so
that no soot is deposited on the metal surfaces of the work. This can only
be accomplished by supplying the exact amounts of gas and air that will
produce a complete burning of the fuel. With the brazing torches in common
use two heads are furnished, being supplied from the same source of fuel,
but with separate regulating devices. The torches are adjustably mounted in
such a way that the flames may be directed toward each other, heating two
sides of the work at the same time and allowing the pieces to be completely
surrounded with the flame.
Except for the source of heat, but one tool is required for ordinary
brazing operations, this being a spatula formed by flattening one end of a
quarter-inch steel rod. The spatula is used for placing the brazing metal
on the work and for handling the flux that is required in this work as in
all other similar operations.
_Spelter._--The metal that is melted into the joint is called spelter.
While this name originally applied to but one particular grade or
composition of metal, common use has extended the meaning until it is
generally applied to all grades.
Spelter is variously composed of alloys containing copper, zinc, tin and
antimony, the mixture employed depending on the work to be done. The
different grades are of varying hardness, the harder kinds melting at
higher temperatures than the soft ones and producing a stronger joint when
used. The reason for not using hard spelter in all cases is the increased
difficulty of working it and the fact that its melting point is so near to
some of the metals brazed that there is great danger of melting the work as
well as the spelter.
The hardest grade of spelter is made from three-fourths copper with
one-fourth zinc and is used for working on malleable and cast iron and for
steel.
This hard spelter melts at about 1650 and is correspondingly difficult to
handle.
A spelter suitable for working with copper is made from equal parts of
copper and zinc, melting at about 1400 Fahrenheit, 500 below the melting
point of the copper itself. A still softer brazing metal is composed of
half copper, three-eighths zinc and one-eighth tin. This grade is used for
fastening brass to iron and copper and for working with large pieces of
brass to brass. For brazing thin sheet brass and light brass castings, a
metal is used which contains two-thirds tin and one-third antimony. The
low melting point of this last composition makes it very easy to work with
and the danger of melting the work is very slight. However, as might be
expected, a comparatively weak joint is secured, which will not stand any
great strain.
All of the above brazing metals are used in powder form so that they may be
applied with the spatula where the joint is exposed on the outside of the
work. In case it is necessary to braze on the inside of a tube or any deep
recess, the spelter may be placed on a flat rod long enough to reach to
the farthest point. By distributing the spelter at the proper points along
the rod it may be placed at the right points by turning the rod over after
inserting into the recess.
_Flux._--In order to remove the oxides produced under brazing heat and
to allow the brazing metal to flow freely into place, a flux of some kind
must be used. The commonest flux is simply a pure calcined borax powder,
that is, a borax powder that has been heated until practically all the
water has been driven off.
Calcined borax may also be mixed with about 15 per cent of sal ammoniac to
make a satisfactory fluxing powder. It is absolutely necessary to use flux
of some kind and a part of whatever is used should be made into a paste
with water so that it can be applied to the joint to be brazed before
heating. The remainder of the powder should be kept dry for use during the
operation and after the heat has been applied.
_Preparing the Work._--The surfaces to be brazed are first thoroughly
cleaned with files, emery cloth or sand paper. If the work is greasy, it
should be dipped into a bath of lye or hot soda water so that all trace of
oil is removed. The parts are then placed in the relation to each other
that they are to occupy when the work has been completed. The edges to be
joined should make a secure and tight fit, and should match each other at
all points so that the smallest possible space is left between them. This
fit should not be so tight that it is necessary to force the work into
place, neither should it be loose enough to allow any considerable space
between the surfaces. The molten spelter will penetrate between surfaces
that water will flow between when the work and spelter have both been
brought to the proper heat. It is, of course, necessary that the two parts
have a sufficient number of points of contact so that they will remain in
the proper relative position.
The work is placed on the surface of the brazing table in such a position
that the flame from the torches will strike the parts to be heated, and
with the joint in such a position that the melted spelter will flow down
through it and fill every possible part of the space between the surfaces
under the action of gravity. That means that the edge of the joint must be
uppermost and the crack to be filled must not lie horizontal, but at the
greatest slant possible. Better than any degree of slant would be to have
the line of the joint vertical.
The work is braced up or clamped in the proper position before commencing
to braze, and it is best to place fire brick in such positions that it will
be impossible for cooling draughts of air to reach the heated metal should
the flame be removed temporarily during the process. In case there is a
large body of iron, steel or copper to be handled, it is often advisable to
place charcoal around the work, igniting this with the flame of the torch
before starting to braze so that the metal will be maintained at the
correct heat without depending entirely on the torch.
When handling brass pieces having thin sections there is danger of melting
the brass and causing it to flow away from under the flame, with the result
that the work is ruined. If, in the judgment of the workman, this may
happen with the particular job in hand, it is well to build up a mould of
fire clay back of the thin parts or preferably back of the whole piece, so
that the metal will have the necessary support. This mould may be made by
mixing the fire clay into a stiff paste with water and then packing it
against the piece to be supported tightly enough so that the form will be
retained even if the metal softens.
_Brazing._--With the work in place, it should be well covered with the
paste of flux and water, then heated until this flux boils up and runs over
the surfaces. Spelter is then placed in such a position that it will run
into the joint and the heat is continued or increased until the spelter
melts and flows in between the two surfaces. The flame should surround the
work during the heating so that outside air is excluded as far as is
possible to prevent excessive oxidization.
When handling brass or copper, the flame should not be directed so that its
center strikes the metal squarely, but so that it glances from one side or
the other. Directing the flame straight against the work is often the cause
of melting the pieces before the operation is completed. When brazing two
different metals, the flame should play only on the one that melts at the
higher temperature, the lower melting part receiving its heat from the
other. This avoids the danger of melting one before the other reaches the
brazing point.
The heat should be continued only long enough to cause the spelter to flow
into place and no longer. Prolonged heating of any metal can do nothing but
oxidize and weaken it, and this practice should be avoided as much as
possible. If the spelter melts into small globules in place of flowing, it
may be caused to spread and run into the joint by lightly tapping the work.
More dry flux may be added with the spatula if the tapping does not produce
the desired result.
Excessive use of flux, especially toward the end of the work, will result
in a very hard surface on all the work, a surface which will be extremely
difficult to finish properly. This trouble will be present to a certain
extent anyway, but it may be lessened by a vigorous scraping with a wire
brush just as soon as the work is removed from the fire. If allowed to cool
before cleaning, the final appearance will not be as good as with the
surplus metal and scale removed immediately upon completing the job.
After the work has been cleaned with the brush it may be allowed to cool
and finished to the desired shape, size and surface by filing and
polishing. When filed, a very thin line of brass should appear where the
crack was at the beginning of the work. If it is desired to avoid a square
shoulder and fill in an angle joint to make it rounding, the filling is
best accomplished by winding a coil of very thin brass wire around the part
of the work that projects and then causing this to flow itself or else
allow the spelter to fill the spaces between the layers of wire. Copper
wire may also be used for this purpose, the spaces being filled with
melted spelter.
THERMIT WELDING
The process of welding which makes use of the great heat produced by oxygen
combining with aluminum is known as the Thermit process and was perfected
by Dr. Hans Goldschmidt. The process, which is controlled by the
Goldschmidt Thermit Company, makes use of a mixture of finely powdered
aluminum with an oxide of iron called by the trade name, Thermit.
The reaction is started with a special ignition powder, such as barium
superoxide and aluminum, and the oxygen from the iron oxide combining with
the aluminum, producing a mass of superheated steel at about 5000 degrees
Fahrenheit. After the reaction, which takes from. 30 seconds to a minute,
the molten metal is drawn from the crucible on to the surfaces to be
joined. Its extreme heat fuses the metal and a perfect joint is the result.
This process is suited for welding iron or steel parts of comparatively
large size.
_Preparation._--The parts to be joined are thoroughly cleaned on the
surfaces and for several inches back from the joint, after which they are
supported in place. The surfaces between which the metal will flow are
separated from 1/4 to 1 inch, depending on the size of the parts, but
cutting or drilling part of the metal away. After this separation is made
for allowing the entrance of new metal, the effects of contraction of the
molten steel are cared for by preheating adjacent parts or by forcing the
ends apart with wedges and jacks. The amount of this last separation must
be determined by the shape and proportions of the parts in the same way as
would be done for any other class of welding which heats the parts to a
melting point.
Yellow wax, which has been warmed until plastic, is then placed around the
joint to form a collar, the wax completely filling the space between the
ends and being provided with vent holes by imbedding a piece of stout cord,
which is pulled out after the wax cools.
A retaining mould (Figure 55) made from sheet steel or fire brick is then
placed around the parts. This mould is then filled with a mixture of one
part fire clay, one part ground fire brick and one part fire sand. These
materials are well mixed and moistened with enough water so that they will
pack. This mixture is then placed in the mould, filling the space between
the walls and the wax, and is packed hard with a rammer so that the
material forms a wall several inches thick between any point of the mould
and the wax. The mixture must be placed in the mould in small quantities
and packed tight as the filling progresses.
[Illustration: Figure 55.--Thermit Mould Construction]
Three or more openings are provided through this moulding material by the
insertion of wood or pipe forms. One of these openings will lead from the
lowest point of the wax pattern and is used for the introduction of the
preheating flame. Another opening leads from the top of the mould into this
preheating gate, opening into the preheating gate at a point about one inch
from the wax pattern. Openings, called risers, are then provided from each
of the high points of the wax pattern to the top of the mould, these risers
ending at the top in a shallow basin. The molten metal comes up into these
risers and cares for contraction of the casting, as well as avoiding
defects in the collar of the weld. After the moulding material is well
packed, these gate patterns are tapped lightly and withdrawn, except in the
case of the metal pipes which are placed at points at which it would be
impossible to withdraw a pattern.
_Preheating._--The ends to be welded are brought to a bright red heat
by introducing the flame from a torch through the preheating gate. The
torch must use either gasoline or kerosene, and not crude oil, as the crude
oil deposits too much carbon on the parts. Preheating of other adjacent
parts to care for contraction is done at this time by an additional torch
burner.
The heating flame is started gently at first and gradually increased. The
wax will melt and may be allowed to run out of the preheating gate by
removing the flame at intervals for a few seconds. The heat is continued
until the mould is thoroughly dried and the parts to be joined are brought
to the red heat required. This leaves a mould just the shape of the wax
pattern.
The heating gate should then be plugged with a sand core, iron plug or
piece of fitted fire brick, and backed up with several shovels full of the
moulding mixture, well packed.
[Illustration: Figure 56.--Thermit Crucible Plug.
_A_, Hard burn magnesia stone;
_B_, Magnesia thimble;
_C_, Refractory sand;
_D_, Metal disc;
_E_, Asbestos washer;
_F_, Tapping pin]
_Thermit Metal._--The reaction takes place in a special crucible lined
with magnesia tar, which is baked at a red heat until the tar is driven off
and the magnesia left. This lining should last from twelve to fifteen
reactions. This magnesia lining ends at the bottom of the crucible in a
ring of magnesia stone and this ring carries a magnesia thimble through
which the molten steel passes on its way to the mould. It will usually be
necessary to renew this thimble after each reaction. This lower opening is
closed before filling the crucible with thermit by means of a small disc or
iron carrying a stem, which is called a tapping pin (Figure 56). This pin,
_F_, is placed in the thimble with the stem extending down through the
opening and exposing about two inches. The top of this pin is covered with
an asbestos, washer, _E_, then with another iron disc. _D_, and
finally with a layer of refractory sand. The crucible is tapped by knocking
the stem of the pin upwards with a spade or piece of flat iron about four
feet long.
The charge of thermit is added by placing a few handfuls over the
refractory sand and then pouring in the balance required. The amount of
thermit required is calculated from the wax used. The wax is weighed before
and after filling _the entire space that the thermit will occupy_.
This does not mean only the wax collar, but the space of the mould with all
gates filled with wax. The number of pounds of wax required for this
filling multiplied by 25 will give the number of pounds of thermit to be
used. To this quantity of thermit should be added I per cent of pure
manganese, 1 per cent nickel thermit and 15 per cent of steel punchings.
It is necessary, when more than 10 pounds of thermit will be used, to mix
steel punchings not exceeding 3/8 inch diameter by 1/8 inch thick with the
powder in order to sufficiently retard the intensity of the reaction.
Half a teaspoonful of ignition powder is placed on top of the thermit
charge and ignited with a storm match or piece of red hot iron. The cover
should be immediately closed on the top of the crucible and the operator
should get away to a safe distance because of the metal that may be thrown
out of the crucible.
After allowing about 30 seconds to a minute for the reaction to take place
and the slag to rise to the top of the crucible, the tapping pin is struck
from below and the molten metal allowed to run into the mould. The mould
should be allowed to remain in place as long as possible, preferably over
night, so as to anneal the steel in the weld, but in no case should it be
disturbed for several hours after pouring. After removing the mould, drill
through the metal left in the riser and gates and knock these sections off.
No part of the collar should be removed unless absolutely necessary.
CHAPTER IX
OXYGEN PROCESS FOR REMOVAL OF CARBON
Until recently the methods used for removing carbon deposits from gas
engine cylinders were very impractical and unsatisfactory. The job meant
dismantling the motor, tearing out all parts, and scraping the pistons and
cylinder walls by hand.
The work was never done thoroughly. It required hours of time to do it, and
then there was always the danger of injuring the inside of the cylinders.
These methods have been to a large extent superseded by the use of oxygen
under pressure. The various devices that are being manufactured are known
as carbon removers, decarbonizers, etc., and large numbers of them are in
use in the automobile and gasoline traction motor industry.
_Outfit._--The oxygen carbon cleaner consists of a high pressure
oxygen cylinder with automatic reducing valve, usually constructed on the
diaphragm principle, thus assuring positive regulation of pressure. This
valve is fitted with a pressure gauge, rubber hose, decarbonizing torch
with shut off and flexible tube for insertion into the chamber from which
the carbon is to be removed.
There should also be an asbestos swab for swabbing out the inside of the
cylinder or other chamber with kerosene previous to starting the operation.
The action consists in simply burning the carbon to a fine dust in the
presence of the stream of oxygen, this dust being then blown out.
_Operation._--The following are instructions for operating the
cleaner:--
(1) Close valve in gasoline supply line and start the motor, letting it run
until the gasoline is exhausted.
(2) If the cylinders be T or L head, remove either the inlet or the exhaust
valve cap, or a spark plug if the cap is tight. If the cylinders have
overhead valves, remove a spark plug. If any spark plug is then remaining
in the cylinder it should be removed and an old one or an iron pipe plug
substituted.
(3) Raise the piston of the cylinder first to be cleaned to the top of the
compression stroke and continue this from cylinder to cylinder as the work
progresses.
(4) In motors where carbon has been burned hard, the cylinder interior
should then be swabbed with kerosene before proceeding. Work the swab,
saturated with kerosene, around the inside of the cylinder until all the
carbon has been moistened with the oil. This same swab may be used to
ignite the gas in the cylinder in place of using a match or taper.
(5) Make all connections to the oxygen cylinder.
(6) Insert the torch nozzle in the cylinder, open the torch valve gradually
and regulate to about two lbs. pressure. Manipulate the nozzle inside the
cylinder and light a match or other flame at the opening so that the carbon
starts to burn. Cover the various points within the cylinder and when there
is no further burning the carbon has been removed. The regulating and
oxygen tank valves are operated in exactly the same way as for welding as
previously explained.
It should be carefully noted that when the piston is up, ready to start the
operation, both valves must be closed. There will be a considerable display
of sparks while this operation is taking place, but they will not set fire
to the grease and oil. Care should be used to see that no gasoline is
about.
INDEX
Acetylene
filtering
generators
in tanks
piping
properties of
purification of
Acetylene-air torches
Air
oxygen from
Alloys
table of
Alloy steel
Aluminum
alloys
welding
Annealing
Anvil
Arc welding, electric
machines
Asbestos, use of, in welding
Babbitt
Bending pipes and tubes
Bessemer steel
Beveling
Brass
welding
Brazing
electric
heat and tools
spelter
Bronze
welding
Butt welding
Calcium carbide
Carbide
storage of, Fire Underwriters' Rules
to water generator
Carbon removal
by oxygen process
Case hardening steel
Cast iron
welding
Champfering
Charging generator
Chlorate of potash oxygen
Conductivity of metals
Copper
alloys
welding
Crucible steel
Cutting, oxy-acetylene
torches
Dissolved acetylene
Electric arc welding
Electric welding
troubles and remedies
Expansion of metals
Flame, welding
Fluxes
for brazing
for soldering
Forge
fire
practice
tools
tuvere construction of
welding
welding preparation
welds, forms of
Forging
Gas holders
Gases, heating power of
Generator, acetylene
carbide to water
construction
Generator
location of
operation and care of
overheating
requirements
water to carbide
German silver
Gloves
Goggles
Hand forging
Hardening steel
Heat treatment of steel
Hildebrandt process
Hose
Injectors, adjuster
Iron
cast
grades of
malleable cast
wrought
Jump weld
Lap welding
Lead
Linde process
Liquid air oxygen
Magnalium
Malleable iron
welding
Melting points of metals
Metal alloys, table of
Metals
characteristics of
conductivity of
expansion of
heat treatment of
melting points of
tensile strength of
weight of
Nickel
Nozzle sizes, torch
Open hearth steel
Oxy-acetylene cutting
welding practice
Oxygen
cylinders
weight of
Pipes, bending
Platinum
Preheating
Removal of carbon by oxygen process
Resistance method of electric welding
Restoration of steel
Rods, welding
Safety devices
Scarfing
Solder
Soldering
flux
holes
seams
steel and iron
wires
Spelter
Spot welding
Steel
alloys
Bessemer
crucible
heat treatment of
open hearth
restoration of
tensile strength of
welding
Strength of metals
Tank valves
Tapering
Tables of welding information
Tempering steel
Thermit metal
preheating
preparation
welding
Tin
Torch
acetylene-air
care
construction
cutting
high pressure
low pressure
medium pressure
nozzles
practice
Valves, regulating
tank
Water
to carbide generator
Welding aluminum
brass
bronze
butt
cast iron
copper
electric
electric arc
flame
forge
information and tables
instruments
lap
malleable iron
materials
practice, oxy-acetylene
rods
spot
steel
table
thermit
torches
various metals
wrought iron
Wrought iron
welding
Zinc
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