PREPARATION OF WORK
Preheating.--The practice of heating the metal around the weld
before applying the torch flame is a desirable one for two reasons. First,
it makes the whole process more economical; second, it avoids the danger of
breakage through expansion and contraction of the work as it is heated and
as it cools.
When it is desired to join two surfaces by welding them, it is, of course,
necessary to raise the metal from the temperature of the surrounding air to
its melting point, involving an increase in temperature of from one
thousand to nearly three thousand degrees. To obtain this entire increase
of temperature with the torch flame is very wasteful of fuel and of the
operator's time. The total amount of heat necessary to put into metal is
increased by the conductivity of that metal because the heat applied at the
weld is carried to other parts of the piece being handled until the whole
mass is considerably raised in temperature. To secure this widely
distributed increase the various methods of preheating are adopted.
As to the second reason for preliminary heating. It is understood that the
metal added to the joint is molten at the time it flows into place. All the
metals used in welding contract as they cool and occupy a much smaller
space than when molten. If additional metal is run between two adjoining
surfaces which are parts of a surrounding body of cool metal, this added
metal will cool while the surfaces themselves are held stationary in the
position they originally occupied. The inevitable result is that the metal
added will crack under the strain, or, if the weld is exceptionally strong,
the main body of the work will he broken by the force of contraction. To
overcome these difficulties is the second and most important reason for
preheating and also for slow cooling following the completion of the weld.
There are many ways of securing this preheating. The work may be brought to
a red heat in the forge if it is cast iron or steel; it may he heated in
special ovens built for the purpose; it may be placed in a bed of charcoal
while suitably supported; it may be heated by gas or gasoline preheating
torches, and with very small work the outer flame of the welding torch
automatically provides means to this end.
The temperature of the parts heated should be gradually raised in all
cases, giving the entire mass of metal a chance to expand equally and to
adjust itself to the strains imposed by the preheating. After the region
around the weld has been brought to a proper temperature the opening to be
filled is exposed so that the torch flame can reach it, while the remaining
surfaces are still protected from cold air currents and from cooling
through natural radiation.
One of the commonest methods and one of the best for handling work of
rather large size is to place the piece to be welded on a bed of fire brick
and build a loose wall around it with other fire brick placed in rows, one
on top of the other, with air spaces left between adjacent bricks in each
row. The space between the brick retaining wall and the work is filled with
charcoal, which is lighted from below. The top opening of the temporary
oven is then covered with asbestos and the fire kept up until the work has
been uniformly raised in temperature to the desired point.
When much work of the same general character and size is to be handled, a
permanent oven may be constructed of fire brick, leaving a large opening
through the top and also through one side. Charcoal may be used in this
form of oven as with the temporary arrangement, or the heat may be secured
from any form of burner or torch giving a large volume of flame. In any
method employing flame to do the heating, the work itself must be protected
from the direct blast of the fire. Baffles of brick or metal should be
placed between the mouth of the torch and the nearest surface of the work
so that the flame will be deflected to either side and around the piece
being heated.
The heat should be applied to bring the point of welding to the highest
temperature desired and, except in the smallest work, the heat should
gradually shade off from this point to the other parts of the piece. In the
case of cast iron and steel the temperature at the point to be welded
should be great enough to produce a dull red heat. This will make the whole
operation much easier, because there will be no surrounding cool metal to
reduce the temperature of the molten material from the welding rod below
the point at which it will join the work. From this red heat the mass of
metal should grow cooler as the distance from the weld becomes greater, so
that no great strain is placed upon any one part. With work of a very
irregular shape it is always best to heat the entire piece so that the
strains will be so evenly distributed that they can cause no distortion or
breakage under any conditions.
The melting point of the work which is being preheated should be kept in
mind and care exercised not to approach it too closely. Special care is
necessary with aluminum in this respect, because of its low melting
temperature and the sudden weakening and flowing without warning. Workmen
have carelessly overheated aluminum castings and, upon uncovering the piece
to make the weld, have been astonished to find that it had disappeared.
Six hundred degrees is about the safe limit for this metal. It is possible
to gauge the exact temperature of the work with a pyrometer, but when this
instrument cannot be procured, it might be well to secure a number of
"temperature cones" from a chemical or laboratory supply house. These cones
are made from material that will soften at a certain heat and in form they
are long and pointed. Placed in position on the part being heated, the
point may be watched, and when it bends over it is sure that the metal
itself has reached a temperature considerably in excess of the temperature
at which that particular cone was designed to soften.
The object in preheating the metal around the weld is to cause it to expand
sufficiently to open the crack a distance equal to the contraction when
cooling from the melting point. In the case of a crack running from the
edge of a piece into the body or of a crack wholly within the body, it is
usually satisfactory to heat the metal at each end of the opening. This
will cause the whole length of the crack to open sufficiently to receive
the molten material from the rod.
The judgment of the operator will be called upon to decide just where a
piece of metal should be heated to open the weld properly. It is often
possible to apply the preheating flame to a point some distance from the
point of work if the parts are so connected that the expansion of the
heated part will serve to draw the edges of the weld apart. Whatever part
of the work is heated to cause expansion and separation, this part must
remain hot during the entire time of welding and must then cool slowly at
the same time as the metal in the weld cools.
Image Figure 25.--Preheating at A While Welding at
B. C also May Be Heated.
An example of heating points away from the crack might be found in welding
a lattice work with one of the bars cracked through (Figure 25). If the
strips parallel and near to the broken bar are heated gradually, the work
will be so expanded that the edges of the break are drawn apart and the
weld can be successfully made. In this case, the parallel bars next to the
broken one would be heated highest, the next row not quite so hot and so on
for some distance away. If only the one row were heated, the strains set up
in the next ones would be sufficient to cause a new break to appear.
Image Figure 26.--Cutting Through the Rim of a Wheel (Cut Shown
at A)
If welding is to be done near the central portion of a large piece, the
strains will be brought to bear on the parts farthest away from the center.
Should a fly wheel spoke be broken and made ready to weld, the greatest
strain will come on the rim of the wheel. In cases like this it is often
desirable to cut through at the point of greatest strain with a saw or
cutting torch, allowing free movement while the weld is made at the
original break (Figure 26). After the inside weld is completed, the cut may
be welded without danger, for the reason that it will always be at some
point at which severe strains cannot be set up by the contraction of the
cooling metal.
Image Figure 27.--Using a Wedge While Welding
In materials that will spring to some extent without breakage, that is, in
parts that are not brittle, it may be possible to force the work out of
shape with jacks or wedges (Figure 27) in the same way that it would be
distorted by heating and expanding some portion of it as described. A
careful examination will show whether this method can be followed in such a
way as to force the edges of the break to separate. If the plan seems
feasible, the wedges may be put in place and allowed to remain while the
weld is completed. As soon as the work is finished the wedges should be
removed so that the natural contraction can take place without damage.
It should always be remembered that it is not so much the expansion of the
work when heated as it is the contraction caused by cooling that will do
the damage. A weld may be made that, to all appearances, is perfect and it
may be perfect when completed; but if provision has not been made to allow
for the contraction that is certain to follow, there will be a breakage at
some point. It is not possible to weld the simplest shapes, other than
straight bars, without considering this difficulty and making provision to
take care of it.
The exact method to employ in preheating will always call for good judgment
on the part of the workman, and he should remember that the success or
failure of his work will depend fully as much on proper preparation as on
correct handling of the weld itself. It should be remembered that the outer
flame of the oxy-acetylene torch may be depended on for a certain amount of
preheating, as this flame gives a very large volume of heat, but a heat
that is not so intense nor so localized as the welding flame itself. The
heat of this part of the flame should be fully utilized during the
operation of melting the metal and it should be so directed, when possible,
that it will bring the parts next to be joined to as high a temperature as
possible.
When the work has been brought to the desired temperature, all parts except
the break and the surface immediately surrounding it on both sides should
be covered with heavy sheet asbestos. This protecting cover should remain
in place throughout the operation and should only be moved a distance
sufficient to allow the torch flame to travel in the path of the weld. The
use of asbestos in this way serves a twofold purpose. It retains the heat
in the work and prevents the breakage that would follow if a draught of air
were to strike the heated metal, and it also prevents such a radiation of
heat through the surrounding air as would make it almost impossible for the
operator to perform his work, especially in the case of large and heavy
castings when the amount of heat utilized is large.
Cleaning and Champfering.--A perfect weld can never be made unless
the surfaces to be joined have been properly prepared to receive the new
metal.
All spoiled, burned, corroded and rough particles must positively be
removed with chisel and hammer and with a free application of emery cloth
and wire brush. The metal exposed to the welding flame should be perfectly
clean and bright all over, or else the additional material will not unite,
but will only stick at best.
Image Figure 28.--Tapering the Opening Formed by a Break
Following the cleaning it is always necessary to bevel, or champfer, the
edges except in the thinnest sheet metal. To make a weld that will hold,
the metal must be made into one piece, without holes or unfilled portions
at any point, and must be solid from inside to outside. This can only be
accomplished by starting the addition of metal at one point and gradually
building it up until the outside, or top, is reached. With comparatively
thin plates the molten metal may be started from the side farthest from the
operator and brought through, but with thicker sections the addition is
started in the middle and brought flush with one side and then with the
other.
It will readily be seen that the molten material cannot be depended upon to
flow between the tightly closed surfaces of a crack in a way that can be at
all sure to make a true weld. It will be necessary for the operator to
reach to the farthest side with the flame and welding rod, and to start the
new surfaces there. To allow this, the edges that are to be joined are
beveled from one side to the other (Figure 28), so that when placed
together in approximately the position they are to occupy they will leave a
grooved channel between them with its sides at an angle with each other
sufficient in size to allow access to every point of each surface.
Image Figure 29.--Beveling for Thin Work
Image Figure 30.--Beveling for Thick Work
With work less than one-fourth inch thick, this angle should be forty-five
degrees on each piece (Figure 29), so that when they are placed together
the extreme edges will meet at the bottom of a groove whose sides are
square, or at right angles, to each other. This beveling should be done so
that only a thin edge is left where the two parts come together, just
enough points in contact to make the alignment easy to hold. With work of a
thickness greater than a quarter of an inch, the angle of bevel on each
piece may be sixty degrees (Figure 30), so that when placed together the
angle included between the sloping sides will also be sixty degrees. If the
plate is less than one-eighth of an inch thick the beveling is not
necessary, as the edges may be melted all the way through without danger of
leaving blowholes at any point.
Image Figure 31.--Beveling Both Sides of a Thick Piece
Image Figure 32.--Beveling the End of a Pipe
This beveling may be done in any convenient way. A chisel is usually most
satisfactory and also quickest. Small sections may be handled by filing,
while metal that is too hard to cut in either of these ways may be shaped
on the emery wheel. It is not necessary that the edges be perfectly
finished and absolutely smooth, but they should be of regular outline and
should always taper off to a thin edge so that when the flame is first
applied it can be seen issuing from the far side of the crack. If the work
is quite thick and is of a shape that will allow it to be turned over, the
bevel may be brought from both sides (Figure 31), so that there will be two
grooves, one on each surface of the work. After completing the weld on one
side, the piece is reversed and finished on the other side. Figure 32 shows
the proper beveling for welding pipe. Figure 33 shows how sheet metal may
be flanged for welding.
Welding should not be attempted with the edges separated in place of
beveled, because it will be found impossible to build up a solid web of new
metal from one side clear through to the other by this method. The flame
cannot reach the surfaces to make them molten while receiving new material
from the rod, and if the flame does not reach them it will only serve to
cause a few drops of the metal to join and will surely cause a weak and
defective weld.
Image Figure 33.--Flanging Sheet Metal for Welding
Supporting Work.--During the operation of welding it is necessary
that the work be well supported in the position it should occupy. This may
be done with fire brick placed under the pieces in the correct position,
or, better still, with some form of clamp. The edges of the crack should
touch each other at the point where welding is to start and from there
should gradually separate at the rate of about one-fourth inch to the foot.
This is done so that the cooling of the molten metal as it is added will
draw the edges together by its contraction.
Care must be used to see that the work is supported so that it will
maintain the same relative position between the parts as must be present
when the work is finished. In this connection it must be remembered that
the expansion of the metal when heated may be great enough to cause serious
distortion and to provide against this is one of the difficulties to be
overcome.
Perfect alignment should be secured between the separate parts that are to
be joined and the two edges must be held up so that they will be in the
same plane while welding is carried out. If, by any chance, one drops
below the other while molten metal is being added, the whole job may have
to be undone and done over again. One precaution that is necessary is that
of making sure that the clamping or supporting does not in itself pull the
work out of shape while melted.
TORCH PRACTICE
Image Figure 34.--Rotary Movement of Torch in Welding
The weld is made by bringing the tip of the welding flame to the edges of
the metals to be joined. The torch should be held in the right hand and
moved slowly along the crack with a rotating motion, traveling in small
circles (Figure 34), so that the Welding flame touches first on one side of
the crack and then on the other. On large work the motion may be simply
back and forth across the crack, advancing regularly as the metal unites.
It is usually best to weld toward the operator rather than from him,
although this rule is governed by circumstances. The head of the torch
should be inclined at an angle of about 60 degrees to the surface of the
work. The torch handle should extend in the same line with the break
(Figure 35) and not across it, except when welding very light plates.
Image Figure 35.--Torch Held in Line with the Break
If the metal is 1/16 inch or less in thickness it is only necessary to
circle along the crack, the metal itself furnishing enough material to
complete the weld without additions. Heat both sides evenly until they flow
together.
Material thicker than the above requires the addition of more metal of the
same or different kind from the welding rod, this rod being held by the
left hand. The proper size rod for cast iron is one having a diameter equal
to the thickness of metal being welded up to a one-half inch rod, which is
the largest used. For steel the rod should be one-half the thickness of the
metal being joined up to one-fourth inch rod. As a general rule, better
results will be obtained by the use of smaller rods, the very small sizes
being twisted together to furnish enough material while retaining the free
melting qualities.
Image Figure 36.--The Welding Rod Should Be Held in the Molten
Metal
The tip of the rod must at all times be held in contact with the pieces
being welded and the flame must be so directed that the two sides of the
crack and the end of the rod are melted at the same time (Figure 36).
Before anything is added from the rod, the sides of the crack are melted
down sufficiently to fill the bottom of the groove and join the two sides.
Afterward, as metal comes from the rod in filling the crack, the flame is
circled along the joint being made, the rod always following the flame.
Image Figure 37.--Welding Pieces of Unequal Thickness
Figure 37 illustrates the welding of pieces of unequal thickness.
Figure 38 illustrates welding at an angle.
The molten metal may be directed as to where it should go by the tip of the
welding flame, which has considerable force, but care must be taken not to
blow melted metal on to cooler surfaces which it cannot join. If, while
welding, a spot appears which does not unite with the weld, it may be
handled by heating all around it to a white heat and then immediately
welding the bad place.
Image Figure 38.--Welding at an Angle
Never stop in the middle of a weld, as it is extremely difficult to
continue smoothly when resuming work.
The Flame.--The welding flame must have exactly the right
proportions of each gas. If there is too much oxygen, the metal will be
burned or oxidized; the presence of too much acetylene carbonizes the
metal; that is to say, it adds carbon and makes the work harder. Just the
right mixture will neither burn nor carbonize and is said to be a "neutral"
flame. The neutral flame, if of the correct size for the work, reduces the
metal to a melted condition, not too fluid, and for a width about the same
as the thickness of the metal being welded.
When ready to light the torch, after attaching the right tip or head as
directed in accordance with the thickness of metal to be handled, it will
be necessary to regulate the pressure of gases to secure the neutral flame.
The oxygen will have a pressure of from 2 to 20 pounds, according to the
nozzle used. The acetylene will have much less. Even with the compressed
gas, the pressure should never exceed 10 pounds for the largest work, and
it will usually be from 4 to 6. In low pressure systems, the acetylene will
be received at generator pressure. It should first be seen that the
hand-screws on the regulators are turned way out so that the springs are
free from any tension. It will do no harm if these screws are turned back
until they come out of the threads. This must be done with both oxygen and
acetylene regulators.
Next, open the valve from the generator, or on the acetylene tank, and
carefully note whether there is any odor of escaping gas. Any leakage of
this gas must be stopped before going on with the work.
The hand wheel controlling the oxygen cylinder valve should now be turned
very slowly to the left as far as it will go, which opens the valve, and
it should be borne in mind the pressure that is being released. Turn in the
hand screw on the oxygen regulator until the small pressure gauge shows a
reading according to the requirements of the nozzle being used. This oxygen
regulator adjustment should be made with the cock on the torch open, and
after the regulator is thus adjusted the torch cock may be closed.
Open the acetylene cock on the torch and screw in on the acetylene
regulator hand-screw until gas commences to come through the torch. Light
this flow of acetylene and adjust the regulator screw to the pressure
desired, or, if there is no gauge, so that there is a good full flame. With
the pressure of acetylene controlled by the type of generator it will only
be necessary to open the torch cock.
With the acetylene burning, slowly open the oxygen cock on the torch and
allow this gas to join the flame. The flame will turn intensely bright and
then blue white. There will be an outer flame from four to eight inches
long and from one to three inches thick. Inside of this flame will be two
more rather distinctly defined flames. The inner one at the torch tip is
very small, and the intermediate one is long and pointed. The oxygen should
be turned on until the two inner flames unite into one blue-white cone from
one-fourth to one-half inch long and one-eighth to one-fourth inch in
diameter. If this single, clearly defined cone does not appear when the
oxygen torch cock has been fully opened, turn off some of the acetylene
until it does appear.
If too much oxygen is added to the flame, there will still be the central
blue-white cone, but it will be smaller and more or less ragged around the
edges (Figure 39). When there is just enough oxygen to make the single
cone, and when, by turning on more acetylene or by turning off oxygen, two
cones are caused to appear, the flame is neutral (Figure 40), and the small
blue-white cone is called the welding flame.
Image Figure 39.--Oxidizing Flame--Too Much Oxygen
Image Figure 40.--Neutral Flame
Image Figure 41.--Reducing Flame--Showing an Excess of Acetylene
While welding, test the correctness of the flame adjustment occasionally by
turning on more acetylene or by turning off some oxygen until two flames or
cones appear. Then regulate as before to secure the single distinct cone.
Too much oxygen is not usually so harmful as too much acetylene, except
with aluminum. (See Figure 41.) An excessive amount of sparks coming from
the weld denotes that there is too much oxygen in the flame. Should the
opening in the tip become partly clogged, it will be difficult to secure a
neutral flame and the tip should be cleaned with a brass or copper
wire--never with iron or steel tools or wire of any kind. While the torch
is doing its work, the tip may become excessively hot due to the heat
radiated from the molten metal. The tip may be cooled by turning off the
acetylene and dipping in water with a slight flow of oxygen through the
nozzle to prevent water finding its way into the mixing chamber.
The regulators for cutting are similar to those for welding, except that
higher pressures may be handled, and they are fitted with gauges reading up
to 200 or 250 pounds pressure.
In welding metals which conduct the heat very rapidly it is necessary to
use a much larger nozzle and flame than for metals which have not this
property. This peculiarity is found to the greatest extent in copper,
aluminum and brass.
Should a hole be blown through the work, it may be closed by withdrawing
the flame for a few seconds and then commencing to build additional metal
around the edges, working all the way around and finally closing the small
opening left at the center with a drop or two from the welding rod.
WELDING VARIOUS METALS
Because of the varying melting points, rates of expansion and contraction,
and other peculiarities of different metals, it is necessary to give
detailed consideration to the most important ones.
Characteristics of Metals.--The welder should thoroughly understand
the peculiarities of the various metals with which he has to deal. The
metals and their alloys are described under this heading in the first
chapter of this book and a tabulated list of the most important points
relating to each metal will be found at the end of the present chapter.
All this information should be noted by the operator of a welding
installation before commencing actual work.
Because of the nature of welding, the melting point of a metal is of great
importance. A metal melting at a low temperature should have more careful
treatment to avoid undesired flow than one which melts at a temperature
which is relatively high. When two dissimilar metals are to be joined, the
one which melts at the higher temperature must be acted upon by the flame
first and when it is in a molten condition the heat contained in it will in
many cases be sufficient to cause fusion of the lower melting metal and
allow them to unite without playing the flame on the lower metal to any
great extent.
The heat conductivity bears a very important relation to welding, inasmuch
as a metal with a high rate of conductance requires more protection from
cooling air currents and heat radiation than one not having this quality to
such a marked extent. A metal which conducts heat rapidly will require a
larger volume of flame, a larger nozzle, than otherwise, this being
necessary to supply the additional heat taken away from the welding point
by this conductance.
The relative rates of expansion of the various metals under heat should be
understood in order that parts made from such material may have proper
preparation to compensate for this expansion and contraction. Parts made
from metals having widely varying rates of expansion must have special
treatment to allow for this quality, otherwise breakage is sure to occur.
Cast Iron.--All spoiled metal should he cut away and if the work is
more than one-eighth inch in thickness the sides of the crack should be
beveled to a 45 degree angle, leaving a number of points touching at the
bottom of the bevel so that the work may be joined in its original
relation.
The entire piece should be preheated in a bricked-up oven or with charcoal
placed on the forge, when size does not warrant building a temporary oven.
The entire piece should be slowly heated and the portion immediately
surrounding the weld should be brought to a dull red. Care should be used
that the heat does not warp the metal through application to one part more
than the others. After welding, the work should be slowly cooled by
covering with ashes, slaked lime, asbestos fiber or some other
non-conductor of heat. These precautions are absolutely essential in the
case of cast iron.
A neutral flame, from a nozzle proportioned to the thickness of the work,
should be held with the point of the blue-white cone about one-eighth inch
from the surface of the iron.
A cast iron rod of correct diameter, usually made with an excess of
silicon, is used by keeping its end in contact with the molten metal and
flowing it into the puddle formed at the point of fusion. Metal should be
added so that the weld stands about one-eighth inch above the surrounding
surface of the work.
Various forms of flux may be used and they are applied by dipping the end
of the welding rod into the powder at intervals. These powders may contain
borax or salt, and to prevent a hard, brittle weld, graphite or
ferro-silicon may be added. Flux should be added only after the iron is
molten and as little as possible should be used. No flux should be used
just before completion of the work.
The welding flame should be played on the work around the crack and
gradually brought to bear on the work. The bottom of the bevel should be
joined first and it will be noted that the cast iron tends to run toward
the flame, but does not stick together easily. A hard and porous weld
should be carefully guarded against, as described above, and upon
completion of the work the welded surface should be scraped with a file,
while still red hot, in order to remove the surface scale.
Malleable Iron.--This material should be beveled in the same way
that cast iron is handled, and preheating and slow cooling are equally
desirable. The flame used is the same as for cast iron and so is the flux.
The welding rod may be of cast iron, although better results are secured
with Norway iron wire or else a mild steel wire wrapped with a coil of
copper wire.
It will be understood that malleable iron turns to ordinary cast iron when
melted and cooled. Welds in malleable iron are usually far from
satisfactory and a better joint is secured by brazing the edges together
with bronze. The edges to be joined are brought to a heat just a little
below the point at which they will flow and the opening is then
quickly-filled from a rod of Tobin bronze or manganese bronze, a brass or
bronze flux being used in this work.
Wrought Iron or Semi-Steel.--This metal should be beveled and heated
in the same way as described for cast iron. The flame should be neutral, of
the same size as for steel, and used with the tip of the blue-white cone
just touching the work. The welding rod should be of mild steel, or, if
wrought iron is to be welded to steel, a cast iron rod may be used. A cast
iron flux is well suited for this work. It should be noted that wrought
iron turns to ordinary cast iron if kept heated for any length of time.
Steel.--Steel should be beveled if more than one-eighth inch in
thickness. It requires only a local preheating around the point to be
welded. The welding flame should be absolutely neutral, without excess of
either gas. If the metal is one-sixteenth inch or less in thickness, the
tip of the blue-white cone must be held a short distance from the surface
of the work; in all other cases the tip of this cone is touched to the
metal being welded.
The welding rod may be of mild, low carbon steel or of Norway iron. Nickel
steel rods may be used for parts requiring great strength, but vanadium
alloys are very difficult to handle. A very satisfactory rod is made by
twisting together two wires of the required material. The rod must be kept
constantly in contact with the work and should not be added until the edges
are thoroughly melted. The flux may or may not be used. If one is wanted,
it may be made from three parts iron filings, six parts borax and one part
sal ammoniac.
It will be noticed that the steel runs from the flame, but tends to hold
together. Should foaming commence in the molten metal, it shows an excess
of oxygen and that the metal is being burned.
High carbon steels are very difficult to handle. It is claimed that a drop
or two of copper added to the weld will assist the flow, but will also
harden the work. An excess of oxygen reduces the amount of carbon and
softens the steel, while an excess of acetylene increases the proportion of
carbon and hardens the metal. High speed steels may sometimes be welded if
first coated with semi-steel before welding.
Aluminum.--This is the most difficult of the commonly found metals
to weld. This is caused by its high rate of expansion and contraction and
its liability to melt and fall away from under the flame. The aluminum
seems to melt on the inside first, and, without previous warning, a portion
of the work will simply vanish from in front of the operator's eyes. The
metal tends to run from the flame and separate at the same time. To keep
the metal in shape and free from oxide, it is worked or puddled while in a
plastic condition by an iron rod which has been flattened at one end.
Several of these rods should be at hand and may be kept in a jar of salt
water while not being used. These rods must not become coated with aluminum
and they must not get red hot while in the weld.
The surfaces to be joined, together with the adjacent parts, should be
cleaned thoroughly and then washed with a 25 per cent solution of nitric
acid in hot water, used on a swab. The parts should then be rinsed in clean
water and dried with sawdust. It is also well to make temporary fire clay
moulds back of the parts to be heated, so that the metal may be flowed into
place and allowed to cool without danger of breakage.
Aluminum must invariably be preheated to about 600 degrees, and the whole
piece being handled should be well covered with sheet asbestos to prevent
excessive heat radiation.
The flame is formed with an excess of acetylene such that the second cone
extends about an inch, or slightly more, beyond the small blue-white point.
The torch should be held so that the end of this second cone is in contact
with the work, the small cone ordinarily used being kept an inch or an inch
and a half from the surface of the work.
Welding rods of special aluminum are used and must be handled with their
end submerged in the molten metal of the weld at all times.
When aluminum is melted it forms alumina, an oxide of the metal. This
alumina surrounds small masses of the metal, and as it does not melt at
temperatures below 5000 degrees (while aluminum melts at about 1200), it
prevents a weld from being made. The formation of this oxide is retarded
and the oxide itself is dissolved by a suitable flux, which usually
contains phosphorus to break down the alumina.
Copper.--The whole piece should be preheated and kept well covered
while welding. The flame must be much larger than for the same thickness of
steel and neutral in character. A slight excess of acetylene would be
preferable to an excess of oxygen, and in all cases the molten metal should
be kept enveloped with the flame. The welding rod is of copper which
contains phosphorus; and a flux, also containing phosphorus, should be
spread for about an inch each side of the joint. These assist in preventing
oxidation, which is sure to occur with heated copper.
Copper breaks very easily at a heat slightly under the welding temperature
and after cooling it is simply cast copper in all cases.
Brass and Bronze.--It is necessary to preheat these metals, although
not to a very high temperature. They must be kept well covered at all times
to prevent undue radiation. The flame should be produced with a nozzle one
size larger than for the same thickness of steel and the small blue-white
cone should be held from one-fourth to one-half inch above the surface of
the work. The flame should be neutral in character.
A rod or wire of soft brass containing a large percentage of zinc is
suitable for adding to brass, while copper requires the use of copper or
manganese bronze rods. Special flux or borax may be used to assist the
flow.
The emission of white smoke indicates that the zinc contained in these
alloys is being burned away and the heat should immediately be turned away
or reduced. The fumes from brass and bronze welding are very poisonous and
should not be breathed.
RESTORATION OF STEEL
The result of the high heat to which the steel has been subjected is that
it is weakened and of a different character than before welding. The
operator may avoid this as much as possible by first playing the outer
flame of the torch all over the surfaces of the work just completed until
these faces are all of uniform color, after which the metal should be well
covered with asbestos and allowed to cool without being disturbed. If a
temporary heating oven has been employed, the work and oven should be
allowed to cool together while protected with the sheet asbestos. If the
outside air strikes the freshly welded work, even for a moment, the result
will be breakage.
A weld in steel will always leave the metal with a coarse grain and with
all the characteristics of rather low grade cast steel. As previously
mentioned in another chapter, the larger the grain size in steel the weaker
the metal will be, and it is the purpose of the good workman to avoid, as
far as possible, this weakening.
The structure of the metal in one piece of steel will differ according to
the heat that it has under gone. The parts of the work that have been at
the melting point will, therefore, have the largest grain size and the
least strength. Those parts that have not suffered any great rise in
temperature will be practically unaffected, and all the parts between these
two extremes will be weaker or stronger according to their distance from
the weld itself. To restore the steel so that it will have the best grain
size, the operator may resort to either of two methods: (1) The grain may
be improved by forging. That means that the metal added to the weld and the
surfaces that have been at the welding heat are hammered much as a
blacksmith would hammer his finished work to give it greater strength. The
hammering should continue from the time the metal first starts to cool
until it has reached the temperature at which the grain size is best for
strength. This temperature will vary somewhat with the composition of the
metal being handled, but in a general way, it may be stated that the
hammering should continue without intermission from the time the flame is
removed from the weld until the steel just begins to show attraction for a
magnet presented to it. This temperature of magnetic attraction will always
be low enough and the hammering should be immediately discontinued at this
point. (2) A method that is more satisfactory, although harder to apply, is
that of reheating the steel to a certain temperature throughout its whole
mass where the heat has had any effect, and then allowing slow and even
cooling from this temperature. The grain size is affected by the
temperature at which the reheating is stopped, and not by the cooling, yet
the cooling should be slow enough to avoid strains caused by uneven
contraction.
After the weld has been completed the steel must be allowed to cool until
below 1200° Fahrenheit. The next step is to heat the work slowly until all
those parts to be restored have reached a temperature at which the magnet
just ceases to be attracted. While the very best temperature will vary
according to the nature and hardness of the steel being handled, it will be
safe to carry the heating to the point indicated by the magnet in the
absence of suitable means of measuring accurately these high temperatures.
In using a magnet for testing, it will be most satisfactory if it is an
electromagnet and not of the permanent type. The electric current may be
secured from any small battery and will be the means of making sure of the
test. The permanent magnet will quickly lose its power of attraction under
the combined action of the heat and the jarring to which it will be
subjected.
In reheating the work it is necessary to make sure that no part reaches a
temperature above that desired for best grain size and also to see that all
parts are brought to this temperature. Here enters the greatest difficulty
in restoring the metal. The heating may be done so slowly that no part of
the work on the outside reaches too high a temperature and then keeps the
outside at this heat until the entire mass is at the same temperature. A
less desirable way is to heat the outside higher than this temperature and
allow the conductivity of the metal to distribute the excess to the inside.
The most satisfactory method, where it can be employed, is to make use of a
bath of some molten metal or some chemical mixture that can be kept at the
exact heat necessary by means of gas fires that admit of close regulation.
The temperature of these baths may be maintained at a constant point by
watching a pyrometer, and the finished work may be allowed to remain in the
bath until all parts have reached the desired temperature.
WELDING INFORMATION
The following tables include much of the information that the operator must
use continually to handle the various metals successfully. The temperature
scales are given for convenience only. The composition of various alloys
will give an idea of the difficulties to be contended with by consulting
the information on welding various metals. The remaining tables are of
self-evident value in this work.
TEMPERATURE SCALES
Centigrade Fahrenheit Centigrade Fahrenheit
200° 392° 1000° 1832°
225° 437° 1050° 1922°
250° 482° 1100° 2012°
275° 527° 1150° 2102°
300° 572° 1200° 2192°
325° 617° 1250° 2282°
350° 662° 1300° 2372°
375° 707° 1350° 2462°
400° 752° 1400° 2552°
425° 797° 1450° 2642°
450° 842° 1500° 2732°
475° 887° 1550° 2822°
500° 932° 1600° 2912°
525° 977° 1650° 3002°
550° 1022° 1700° 3092°
575° 1067° 1750° 3182°
600° 1112° 1800° 3272°
625° 1157° 1850° 3362°
650° 1202° 1900° 3452°
675° 1247° 2000° 3632°
700° 1292° 2050° 3722°
725° 1337° 2100° 3812°
750° 1382° 2150° 3902°
775° 1427° 2200° 3992°
800° 1472° 2250° 4082°
825° 1517° 2300° 4172°
850° 1562° 2350° 4262°
875° 1607° 2400° 4352°
900° 1652° 2450° 4442°
925° 1697° 2500° 4532°
950° 1742° 2550° 4622°
975° 1787° 2600° 4712°
METAL ALLOYS
(Society of Automobile Engineers)
Babbitt--
Tin........................... 84.00%
Antimony...................... 9.00%
Copper........................ 7.00%
Brass, White--
Copper........................ 3.00% to 6.00%
Tin (minimum) ................ 65.00%
Zinc.......................... 28.00% to 30.00%
Brass, Red Cast--
Copper........................ 85.00%
Tin........................... 5.00%
Lead.......................... 5.00%
Zinc.......................... 5.00%
Brass, Yellow--
Copper........................ 62.00% to 65.00%
Lead.......................... 2.00% to 4.00%
Zinc.......................... 36.00% to 31.00%
Bronze, Hard--
Copper........................ 87.00% to 88.00%
Tin........................... 9.50% to 10.50%
Zinc.......................... 1.50% to 2.50%
Bronze, Phosphor--
Copper........................ 80.00%
Tin........................... 10.00%
Lead.......................... 10.00%
Phosphorus.................... .50% to .25%
Bronze, Manganese--
Copper (approximate) ......... 60.00%
Zinc (approximate) ........... 40.00%
Manganese (variable) ......... small
Bronze, Gear--
Copper........................ 88.00% to 89.00%
Tin........................... 11.00% to 12.00%
Aluminum Alloys--
Aluminum Copper Zinc Manganese
No. 1.. 90.00% 8.5-7.0%
No. 2.. 80.00% 2.0-3.0% 15% Not over 0.40%
No. 3.. 65.00% 35.0%
Cast Iron--
Gray Iron Malleable
Total carbon........3.0 to 3.5%
Combined carbon.....0.4 to 0.7%
Manganese...........0.4 to 0.7% 0.3 to 0.7%
Phosphorus..........0.6 to 1.0% Not over 0.2%
Sulphur...........Not over 0.1% Not over 0.6%
Silicon............1.75 to 2.25% Not over 1.0%
Carbon Steel (10 Point)--
Carbon........................ .05% to .15%
Manganese..................... .30% to .60%
Phosphorus (maximum).......... .045%
Sulphur (maximum)............. .05%
(20 Point)--
Carbon........................ .15% to .25%
Manganese..................... .30% to .60%
Phosphorus (maximum).......... .045%
Sulphur (maximum)............. .05%
(35 Point)--
Manganese..................... .50% to .80%
Carbon........................ .30% to .40%
Phosphorus (maximum).......... .05%
Sulphur (maximum)............. .05%
(95 Point)--
Carbon........................ .90% to 1.05%
Manganese..................... .25% to .50%
Phosphorus (maximum).......... .04%
Sulphur (maximum)............. .05%
HEATING POWER OF FUEL GASES
(In B.T.U. per Cubic Foot.)
Acetylene....... 1498.99 Ethylene....... 1562.9
Hydrogen........ 291.96 Methane........ 953.6
Alcohol......... 1501.76
MELTING POINTS OF METALS
Platinum....................3200°
Iron, wrought...............2900°
malleable.................2500°
cast......................2400°
pure......................2760°
Steel, mild.................2700°
Medium....................2600°
Hard......................2500°
Copper......................1950°
Brass.......................1800°
Silver......................1750°
Bronze......................1700°
Aluminum....................1175°
Antimony....................1150°
Zinc........................ 800°
Lead........................ 620°
Babbitt..................500-700°
Solder...................500-575°
Tin......................... 450°
NOTE.--These melting points are for average compositions and conditions.
The exact proportion of elements entering into the metals affects their
melting points one way or the other in practice.
TENSILE STRENGTH OF METALS
Alloy steels can be made with tensile strengths as high as 300,000 pounds
per square inch. Some carbon steels are given below according to "points":
Pounds per Square Inch
Steel, 10 point................ 50,000 to 65,000
20 point..................... 60,000 to 80,000
40 point..................... 70,000 to 100,000
60 point..................... 90,000 to 120,000
Iron, Cast..................... 13,000 to 30,000
Wrought...................... 40,000 to 60,000
Malleable.................... 25,000 to 45,000
Copper......................... 24,000 to 50,000
Bronze......................... 30,000 to 60,000
Brass, Cast.................... 12,000 to 18,000
Rolled....................... 30,000 to 40,000
Wire......................... 60,000 to 75,000
Aluminum....................... 12,000 to 23,000
Zinc........................... 5,000 to 15,000
Tin............................ 3,000 to 5,000
Lead........................... 1,500 to 2,500
CONDUCTIVITY OF METALS
(Based on the Value of Silver as 100)
Heat Electricity
Silver....................100 100
Copper.................... 74 99
Aluminum.................. 38 63
Brass..................... 23 22
Zinc...................... 19 29
Tin....................... 14 15
Wrought Iron.............. 12 16
Steel..................... 11.5 12
Cast Iron................. 11 12
Bronze.................... 9 7
Lead...................... 8 9
WEIGHT OF METALS
(Per Cubic Inch)
Pounds Pounds
Lead............ .410 Wrought Iron..... .278
Copper.......... .320 Tin.............. .263
Bronze.......... .313 Cast Iron........ .260
Brass........... .300 Zinc............. .258
Steel........... .283 Aluminum......... .093
EXPANSION OF METALS
(Measured in Thousandths of an Inch per Foot of
Length When Raised 1000 Degrees in Temperature)
Inch Inch
Lead............ .188 Brass............ .115
Zinc............ .168 Copper........... .106
Aluminum........ .148 Steel............ .083
Silver.......... .129 Wrought Iron..... .078
Bronze.......... .118 Cast Iron........ .068
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