Electric, Forge and Thermit Welding
Together with Related Methods and Materials Used in Metal Working
And
The Oxygen Process for Removal of Carbon
By
HAROLD P. MANLY
CONTENTS
CHAPTER I
METALS AND ALLOYS--HEAT TREATMENT:--The Use and Characteristics of the
Industrial Alloys and Metal Elements--Annealing, Hardening, Tempering and
Case Hardening of Steel
CHAPTER II
WELDING MATERIALS:--Production, Handling and Use of the Gases, Oxygen and
Acetylene--Welding Rods--Fluxes--Supplies and Fixtures
CHAPTER III
ACETYLENE GENERATORS:--Generator Requirements and Types--Construction--Care
and Operation of Generators.
CHAPTER IV
WELDING INSTRUMENTS:--Tank and Regulating Valves and Gauges--High, Low and
Medium Pressure Torches--Cutting Torches--Acetylene-Air Torches
CHAPTER V
OXY-ACETYLENE WELDING PRACTICE:--Preparation of Work--Torch Practice--
Control of the Flame--Welding Various Metals and Alloys--Tables of
Information Required in Welding Operations
CHAPTER VI
ELECTRIC WELDING:--Resistance Method--Butt, Spot and Lap Welding--Troubles
and Remedies--Electric Arc Welding
CHAPTER VII
HAND FORGING AND WELDING:--Blacksmithing, Forging and Bending--Forge
Welding Methods
CHAPTER VIII
SOLDERING, BRAZING AND THERMIT WELDING:--Soldering Materials and Practice--
Brazing--Thermit Welding
CHAPTER IX
OXYGEN PROCESS FOR REMOVAL OF CARBON
INDEX
OXY-ACETYLENE WELDING AND CUTTING, ELECTRIC AND THERMIT WELDING
OXY-ACETYLENE WELDING PRACTICE
PREPARATION OF WORK
Preheating.--The practice of heating the metal around the weld
before applying the torch flame is a desirable one for two reasons. First,
it makes the whole process more economical; second, it avoids the danger of
breakage through expansion and contraction of the work as it is heated and
as it cools.
When it is desired to join two surfaces by welding them, it is, of course,
necessary to raise the metal from the temperature of the surrounding air to
its melting point, involving an increase in temperature of from one
thousand to nearly three thousand degrees. To obtain this entire increase
of temperature with the torch flame is very wasteful of fuel and of the
operator's time. The total amount of heat necessary to put into metal is
increased by the conductivity of that metal because the heat applied at the
weld is carried to other parts of the piece being handled until the whole
mass is considerably raised in temperature. To secure this widely
distributed increase the various methods of preheating are adopted.
As to the second reason for preliminary heating. It is understood that the
metal added to the joint is molten at the time it flows into place. All the
metals used in welding contract as they cool and occupy a much smaller
space than when molten. If additional metal is run between two adjoining
surfaces which are parts of a surrounding body of cool metal, this added
metal will cool while the surfaces themselves are held stationary in the
position they originally occupied. The inevitable result is that the metal
added will crack under the strain, or, if the weld is exceptionally strong,
the main body of the work will he broken by the force of contraction. To
overcome these difficulties is the second and most important reason for
preheating and also for slow cooling following the completion of the weld.
There are many ways of securing this preheating. The work may be brought to
a red heat in the forge if it is cast iron or steel; it may he heated in
special ovens built for the purpose; it may be placed in a bed of charcoal
while suitably supported; it may be heated by gas or gasoline preheating
torches, and with very small work the outer flame of the welding torch
automatically provides means to this end.
The temperature of the parts heated should be gradually raised in all
cases, giving the entire mass of metal a chance to expand equally and to
adjust itself to the strains imposed by the preheating. After the region
around the weld has been brought to a proper temperature the opening to be
filled is exposed so that the torch flame can reach it, while the remaining
surfaces are still protected from cold air currents and from cooling
through natural radiation.
One of the commonest methods and one of the best for handling work of
rather large size is to place the piece to be welded on a bed of fire brick
and build a loose wall around it with other fire brick placed in rows, one
on top of the other, with air spaces left between adjacent bricks in each
row. The space between the brick retaining wall and the work is filled with
charcoal, which is lighted from below. The top opening of the temporary
oven is then covered with asbestos and the fire kept up until the work has
been uniformly raised in temperature to the desired point.
When much work of the same general character and size is to be handled, a
permanent oven may be constructed of fire brick, leaving a large opening
through the top and also through one side. Charcoal may be used in this
form of oven as with the temporary arrangement, or the heat may be secured
from any form of burner or torch giving a large volume of flame. In any
method employing flame to do the heating, the work itself must be protected
from the direct blast of the fire. Baffles of brick or metal should be
placed between the mouth of the torch and the nearest surface of the work
so that the flame will be deflected to either side and around the piece
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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 fibre or some other
non-conductor of heat. These precautions are absolutely essential in the
case of cast iron.
A neutral flame, from a nozzle proportioned to the thickness of the work,
should be held with the point of the blue-white cone about one-eighth inch
from the surface of the iron.
A cast iron rod of correct diameter, usually made with an excess of
silicon, is used by keeping its end in contact with the molten metal and
flowing it into the puddle formed at the point of fusion. Metal should be
added so that the weld stands about one-eighth inch above the surrounding
surface of the work.
Various forms of flux may be used and they are applied by dipping the end
of the welding rod into the powder at intervals. These powders may contain
borax or salt, and to prevent a hard, brittle weld, graphite or
ferro-silicon may be added. Flux should be added only after the iron is
molten and as little as possible should be used. No flux should be used
just before completion of the work.
The welding flame should be played on the work around the crack and
gradually brought to bear on the work. The bottom of the bevel should be
joined first and it will be noted that the cast iron tends to run toward
the flame, but does not stick together easily. A hard and porous weld
should be carefully guarded against, as described above, and upon
completion of the work the welded surface should be scraped with a file,
while still red hot, in order to remove the surface scale.
Malleable Iron.--This material should be beveled in the same way
that cast iron is handled, and preheating and slow cooling are equally
desirable. The flame used is the same as for cast iron and so is the flux.
The welding rod may be of cast iron, although better results are secured
with Norway iron wire or else a mild steel wire wrapped with a coil of
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
ELECTRIC WELDING
RESISTANCE METHOD
Two distinct forms of electric welding apparatus are in use, one producing
heat by the resistance of the metal being treated to the passage of
electric current, the other using the heat of the electric arc.
The resistance process is of the greatest use in manufacturing lines where
there is a large quantity of one kind of work to do, many thousand pieces
of one kind, for instance. The arc method may be applied in practically any
case where any other form of weld may be made. The resistance process will
be described first.
It is a well known fact that a poor conductor of electricity will offer so
much resistance to the flow of electricity that it will heat. Copper is a
good conductor, and a bar of iron, a comparatively poor conductor, when
placed between heavy copper conductors of a welder, becomes heated in
attempting to carry the large volume of current. The degree of heat depends
on the amount of current and the resistance of the conductor.
In an electric circuit the ends of two pieces of metal brought together
form the point of greatest resistance in the electric circuit, and the
abutting ends instantly begin to heat. The hotter this metal becomes, the
greater the resistance to the flow of current; consequently, as the edges
of the abutting ends heat, the current is forced into the adjacent cooler
parts, until there is a uniform heat throughout the entire mass. The heat
is first developed in the interior of the metal so that it is welded there
as perfectly as at the surface.
The electric welder (Figure 42) is built to hold the parts to be joined
between two heavy copper dies or contacts. A current of three to five
volts, but of very great volume (amperage), is allowed to pass across
these dies, and in going through the metal to be welded, heats the edges
to a welding temperature. It may be explained that the voltage of an
electric current measures the pressure or force with which it is being sent
through the circuit and has nothing to do with the quantity or volume
passing. Amperes measure the rate at which the current is passing through
the circuit and consequently give a measure of the quantity which passes in
any given time. Volts correspond to water pressure measured by pounds to
the square inch; amperes represent the flow in gallons per minute. The low
voltage used avoids all danger to the operator, this pressure not being
sufficient to be felt even with the hands resting on the copper contacts.
Current is supplied to the welding machine at a higher voltage and lower
amperage than is actually used between the dies, the low voltage and high
amperage being produced by a transformer incorporated in the machine
itself. By means of windings of suitable size wire, the outside current may
be received at voltages ranging from 110 to 550 and converted to the low
pressure needed.
The source of current for the resistance welder must be alternating, that
is, the current must first be negative in value and then positive, passing
from one extreme to the other at rates varying from 25 to 133 times a
second. This form is known as alternating current, as opposed to direct
current, in which there is no changing of positive and negative.
The current must also be what is known as single phase, that is, a current
which rises from zero in value to the highest point as a positive current
and then recedes to zero before rising to the highest point of negative
value. Two-phase of three-phase currents would give two or three positive
impulses during this time.
As long as the current is single phase alternating, the voltage and cycles
(number of alternations per second) may be anything convenient. Various
voltages and cycles are taken care of by specifying all these points when
designing the transformer which is to handle the current.
Direct current is not used because there is no way of reducing the voltage
conveniently without placing resistance wires in the circuit and this uses
power without producing useful work. Direct current may be changed to
alternating by having a direct current motor running an alternating current
dynamo, or the change may be made by a rotary converter, although this last
method is not so satisfactory as the first.
The voltage used in welding being so low to start with, it is absolutely
necessary that it be maintained at the correct point. If the source of
current supply is not of ample capacity for the welder being used, it will
be very hard to avoid a fall of voltage when the current is forced to pass
through the high resistance of the weld. The current voltage for various
work is calculated accurately, and the efficiency of the outfit depends to
a great extent on the voltage being constant.
A simple test for fall of voltage is made by connecting an incandescent
electric lamp across the supply lines at some point near the welder. The
lamp should burn with the same brilliancy when the weld is being made as at
any other time. If the lamp burns dim at any time, it indicates a drop in
voltage, and this condition should be corrected.
The dynamo furnishing the alternating current may be in the same building
with the welder and operated from a direct current motor, as mentioned
above, or operated from any convenient shafting or source of power. When
the dynamo is a part of the welding plant it should be placed as close to
the welding machine as possible, because the length of the wire used
affects the voltage appreciably.
In order to hold the voltage constant, the Toledo Electric Welder Company
has devised connections which include a rheostat to insert a variable
resistance in the field windings of the dynamo so that the voltage may be
increased by cutting this resistance out at the proper time. An auxiliary
switch is connected to the welder switch so that both switches act
together. When the welder switch is closed in making a weld, that portion
of the rheostat resistance between two arms determining the voltage is
short circuited. This lowers the resistance and the field magnets of the
dynamo are made stronger so that additional voltage is provided to care for
the resistance in the metal being heated.
A typical machine is shown in the accompanying cut (Figure 43). On top of
the welder are two jaws for holding the ends of the pieces to be welded.
The lower part of the jaws is rigid while the top is brought down on top of
the work, acting as a clamp. These jaws carry the copper dies through which
the current enters the work being handled. After the work is clamped
between the jaws, the upper set is forced closer to the lower set by a long
compression lever. The current being turned on with the surfaces of the
work in contact, they immediately heat to the welding point when added
pressure on the lever forces them together and completes the weld.
The transformer is carried in the base of the machine and on the left-hand
side is a regulator for controlling the voltage for various kinds of work.
The clamps are applied by treadles convenient to the foot of the operator.
A treadle is provided which instantly releases both jaws upon the
completion of the weld. One or both of the copper dies may be cooled by a
stream of water circulating through it from the city water mains
(Figure 44). The regulator and switch give the operator control of the
heat, anything from a dull red to the melting point being easily obtained
by movement of the lever (figure 45).
Welding.--It is not necessary to give the metal to be welded any
special preparation, although when very rusty or covered with scale, the
rust and scale should be removed sufficiently to allow good contact of
clean metal on the copper dies. The cleaner and better the stock, the less
current it takes, and there is less wear on the dies. The dies should be
kept firm and tight in their holders to make a good contact. All bolts and
nuts fastening the electrical contacts should be clean and tight at all times.
The scale may be removed from forgings by immersing them in a pickling
solution in a wood, stone or lead-lined tank.
The solution is made with five gallons of commercial sulphuric acid in
150 gallons of water. To get the quickest and best results from this
method, the solution should be kept as near the boiling point as possible
by having a coil of extra heavy lead pipe running inside the tank and
carrying live steam. A very few minutes in this bath will remove the scale
and the parts should then be washed in running water. After this washing
they should be dipped into a bath of 50 pounds of unslaked lime in 150
gallons of water to neutralize any trace of acid.
Cast iron cannot be commercially welded, as it is high in carbon and
silicon, and passes suddenly from a crystalline to a fluid state when
brought to the welding temperature. With steel or wrought iron the
temperature must be kept below the melting point to avoid injury to the
metal. The metal must be heated quickly and pressed together with
sufficient force to push all burnt metal out of the joint.
High carbon steel can be welded, but must be annealed after welding to
overcome the strains set up by the heat being applied at one place. Good
results are hard to obtain when the carbon runs as high as 75 points, and
steel of this class can only be handled by an experienced operator. If the
steel is below 25 points in carbon content, good welds will always be the
result. To weld high carbon to low carbon steel, the stock should be
clamped in the dies with the low carbon stock sticking considerably further
out from the die than the high carbon stock. Nickel steel welds readily,
the nickel increasing the strength of the weld.
Iron and copper may be welded together by reducing the size of the copper
end where it comes in contact with the iron. When welding copper and brass
the pressure must be less than when welding iron. The metal is allowed to
actually fuse or melt at the juncture and the pressure must be sufficient
to force the burned metal out. The current is cut off the instant the metal
ends begin to soften, this being done by means of an automatic switch which
opens when the softening of the metal allows the ends to come together. The
pressure is applied to the weld by having the sliding jaw moved by a weight
on the end of an arm.
Copper and brass require a larger volume of current at a lower voltage than
for steel and iron. The die faces are set apart three times the diameter of
the stock for brass and four times the diameter for copper.
Light gauges of sheet steel can be welded to heavy gauges or to solid bars
of steel by "spot" welding, which will be described later. Galvanized iron
can be welded, but the zinc coating will be burned off. Sheet steel can be
welded to cast iron, but will pull apart, tearing out particles of the
iron.
Sheet copper and sheet brass may be welded, although this work requires
more experience than with iron and steel. Some grades of sheet aluminum can
be spot-welded if the slight roughness left on the surface under the die
is not objectionable.
Butt Welding.--This is the process which joins the ends of two
pieces of metal as described in the foregoing part of this chapter. The
ends are in plain sight of the operator at all times and it can easily be
seen when the metal reaches the welding heat and begins to soften (Figure
46). It is at this point that the pressure must be applied with the lever
and the ends forced together in the weld.
The parts are placed in the clamping jaws (Figure 47) with 1/8 to 1/2 inch
of metal extending beyond the jaw. The ends of the metal touch each other
and the current is turned on by means of a switch. To raise the ends to the
proper heat requires from 3 seconds for 1/4-inch rods to 35 seconds for a
1-1/2-inch bar.
This method is applicable to metals having practically the same area of
metal to be brought into contact on each end. When such parts are forced
together a slight projection will be left in the form of a fin or an
enlarged portion called an upset. The degree of heat required for any work
is found by moving the handle of the regulator one way or the other while
testing several parts. When this setting is right the work can continue as
long as the same sizes are being handled.
Copper, brass, tool steel and all other metals that are harmed by high
temperatures must be heated quickly and pressed together with sufficient
force to force all burned metal from the weld.
In case it is desired to make a weld in the form of a capital letter T, it
is necessary to heat the part corresponding to the top bar of the T to a
bright red, then bring the lower bar to the pre-heated one and again turn
on the current, when a weld can be quickly made.
Spot Welding.--This is a method of joining metal sheets together at
any desired point by a welded spot about the size of a rivet. It is done on
a spot welder by fusing the metal at the point desired and at the same
instant applying sufficient pressure to force the particles of molten metal
together. The dies are usually placed one above the other so that the work
may rest on the lower one while the upper one is brought down on top of the
upper sheet to be welded.
One of the dies is usually pointed slightly, the opposing one being left
flat. The pointed die leaves a slight indentation on one side of the metal,
while the other side is left smooth. The dies may be reversed so that the
outside surface of any work may be left smooth. The current is allowed to
flow through the dies by a switch which is closed after pressure is applied
to the work.
There is a limit to the thickness of sheet metal that can be welded by this
process because of the fact that the copper rods can only carry a certain
quantity of current without becoming unduly heated themselves. Another
reason is that it is difficult to make heavy sections of metal touch at the
welding point without excessive pressure.
Lap welding is the process used when two pieces of metal are caused
to overlap and when brought to a welding heat are forced together by
passing through rollers, or under a press, thus leaving the welded joint
practically the same thickness as the balance of the work.
Where it is desirable to make a continuous seam, a special machine is
required, or an attachment for one of the other types. In this form of work
the stock must be thoroughly cleaned and is then passed between copper
rollers which act in the same capacity as the copper dies.
Other Applications.--Hardening and tempering can be done by clamping
the work in the welding dies and setting the control and time to bring the
metal to the proper color, when it is cooled in the usual manner.
Brazing is done by clamping the work in the jaws and heating until the
flux, then the spelter has melted and run into the joint. Riveting and
heading of rivets can be done by bringing the dies down on opposite ends of
the rivet after it has been inserted in the hole, the dies being shaped to
form the heads properly.
Hardened steel may be softened and annealed so that it can be machined by
connecting the dies of the welder to each side of the point to be softened.
The current is then applied until the work has reached a point at which it
will soften when cooled.
Troubles and Remedies.--The following methods have been furnished by
the Toledo Electric Welder Company and are recommended for this class of
work whenever necessary.
To locate grounds in the primary or high voltage side of the circuit,
connect incandescent lamps in series by means of a long piece of lamp cord,
as shown, in Figure 43a. For 110 volts use one lamp, for 220 volts use two
lamps and for 440 volts use four lamps. Attach one end of the lamp cord to
one side of the switch, and close the switch. Take the other end of the
cord in the hand and press it against some part of the welder frame where
the metal is clean and bright. Paint, grease and dirt act as insulators and
prevent electrical contact. If the lamp lights, the circuit is in
electrical contact with the frame; in other words, grounded. If the lamps
do not light, connect the wire to a terminal block, die or slide. If the
lamps then light, the circuit, coils or leads are in electrical contact
with the large coil in the transformer or its connections.
If, however, the lamps do not light in either case, the lamp cord should be
disconnected from the switch and connected to the other side, and the
operations of connecting to welder frame, dies, terminal blocks, etc., as
explained above, should be repeated. If the lamps light at any of these
connections, a "ground" is indicated. "Grounds" can usually be found by
carefully tracing the primary circuit until a place is found where the
insulation is defective. Reinsulate and make the above tests again to make
sure everything is clear. If the ground can not be located by observation,
the various parts of the primary circuit should be disconnected, and the
transformer, switch, regulator, etc., tested separately.
To locate a ground in the regulator or other part, disconnect the lines
running to the welder from the switch. The test lamps used in the previous
tests are connected, one end of lamp cord to the switch, the other end to a
binding post of the regulator. Connect the other side of the switch to some
part of the regulator housing. (This must be a clean connection to a bolt
head or the paint should be scraped off.) Close the switch. If the lamps
light, the regulator winding or some part of the switch is "grounded" to
the iron base or core of the regulator. If the lamps do not light, this
part of the apparatus is clear.
This test can be easily applied to any part of the welder outfit by
connecting to the current carrying part of the apparatus, and to the iron
base or frame that should not carry current. If the lamps light, it
indicates that the insulation is broken down or is defective.
An A.C. voltmeter can, of course, be substituted for the lamps, or a D.C.
voltmeter with D.C. current can be used in making the tests.
A short circuit in the primary is caused by the insulation of the coils
becoming defective and allowing the bare copper wires to touch each other.
This may result in a "burn out" of one or more of the transformer coils, if
the trouble is in the transformer, or in the continued blowing of fuses in
the line. Feel of each coil separately. If a short circuit exists in a coil
it will heat excessively. Examine all the wires; the insulation may have
worn through and two of them may cross, or be in contact with the frame or
other part of the welder. A short circuit in the regulator winding is
indicated by failure of the apparatus to regulate properly, and sometimes,
though not always, by the heating of the regulator coils.
The remedy for a short circuit is to reinsulate the defective parts. It is
a good plan to prevent trouble by examining the wiring occasionally and see
that the insulation is perfect.
To Locate Grounds and Short Circuits in the Secondary, or Low Voltage
Side.--Trouble of this kind is indicated by the machine acting sluggish
or, perhaps, refusing to operate. To make a test, it will be necessary to
first ascertain the exciting current of your particular transformer. This
is the current the transformer draws on "open circuit," or when supplied
with current from the line with no stock in the welder dies. The following
table will give this information close enough for all practical purposes:
K.W. ----------------- Amperes at ----------------
Rating 110 Volts 220 Volts 440 Volts 550 Volts
3 1.5 .75 .38 .3
5 2.5 1.25 .63 .5
8 3.6 1.8 .9 .72
10 4.25 2.13 1.07 .85
15 6. 3. 1.5 1.2
20 7. 3.5 1.75 1.4
30 9. 4.5 2.25 1.8
35 9.6 4.8 2.4 1.92
50 10. 5. 2.5 2
Remove the fuses from the wall switch and substitute fuses just large
enough to carry the "exciting" current. If no suitable fuses are at hand,
fine strands of copper from an ordinary lamp cord may be used. These
strands are usually No. 30 gauge wire and will fuse at about 10 amperes.
One or more strands should be used, depending on the amount of exciting
current, and are connected across the fuse clips in place of fuse wire.
Place a piece of wood or fibre between the welding dies in the welder as
though you were going to weld them. See that the regulator is on the
highest point and close the welder switch. If the secondary circuit is
badly grounded, current will flow through the ground, and the small fuses
or small strands of wire will burn out. This is an indication that both
sides of the secondary circuit are grounded or that a short circuit exists
in a primary coil. In either case the welder should not be operated until
the trouble is found and removed. If, however, the small fuses do not
"blow," remove same and replace the large fuses, then disconnect wires
running from the wall switch to the welder and substitute two pieces of
No. 8 or No. 6 insulated copper wire, after scraping off the insulation for
an inch or two at each end. Connect one wire from the switch to the frame
of welder; this will leave one loose end. Hold this a foot or so away from
the place where the insulation is cut off; then turn on the current and
strike the free end of this wire lightly against one of the copper dies,
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.
