PART ONE.--ALUMINUM WELDING
(=117=) So far as the actual fusion of aluminum is concerned, it is
probably more easily learned than any other metal, but on account of
the rapid conductivity of heat and the loss of most of its strength
when heated, aluminum has caused much concern among oxy-acetylene
welders.
(=118=) There are two methods used in welding aluminum, the flux
method and the puddle method. The puddle system gets its name from
the use of a puddle stick or spoon-like rod which is used to stir the
metal together, and is very satisfactorily used on all cast aluminum.
The flux method is applied to both cast and sheet aluminum and it is
so-called because a flux is used to break up the oxide along the line
of weld. The discussion to follow applies only to cast aluminum. It
is in this metal that most interest is centered, as the welding of
sheet aluminum, such as is found in automobile bodies and some cooking
utensils, is not encountered in the ordinary run of work.
[Illustration:
(_Courtesy of the Torchweld Equipment Co._)
FIG. 76.--Showing Aluminum Crank Cases Before and After Welding.]
(=119=) When working with the flux method about the same sized tip is
used as when working on cast iron. This is applied to the line of weld
and held there until the oxide on the surface commences to wrinkle
and small globules of a mercury-like appearance form on the surface.
When heat is introduced in aluminum it is transmitted throughout the
piece in the same manner as occurs in copper and brass, therefore it
will require much more time to heat the work than the same sized piece
of cast iron or steel. As soon as the weld assumes the condition
mentioned, fast work is necessary or the metal will collapse, for it
loses most of its strength when heated to this condition. The end
of the filler-rod bearing the flux is brought down on the metal and
immediately the surfaces will clear up and run together, like so much
mercury. The torch is instantly jerked away and applied farther along
the weld. The theory of this reaction is that the heavy aluminum
oxide is the only thing which prevents the metal flowing together
when heated, and as soon as the flux is introduced this oxide will be
destroyed along the line of weld and a fusion of the metal effected.
This actually takes place, providing enough heat has been introduced
to permit this reaction to penetrate the depth of the weld. The
flux contains the chemicals necessary to cause this reaction if the
metal is in the right condition. There are many welders who do not
use sufficient heat and blame the faulty results upon the flux. On
the other hand, there are many fluxes which are absolutely useless
in performing a function of this kind. The chemicals necessary in
compounding a good flux for this class of work are expensive and
therefore this flux cannot be procured at a low price. When the weld
is finished and cooled the surface should be scrubbed with soap and
water to remove all traces of the flux, otherwise a corrosion may occur
a month or so afterwards, and while it may not affect the weld in any
degree, the owner of the piece may not be pleased at the sight. It is
therefore advisable to remove all traces of flux used on aluminum work.
(=120=) The puddle system differs from that of the flux, insomuch
that when the metal has been brought to the same heat, where the flux
has been applied it will be found that the metal is really in a pasty
condition. It can be stirred together and the break entirely eliminated
by the use of a puddle stick, either of a pointed or a flat spoon-shape
design, as shown in Fig. 77. During this puddling stage, the torch
is usually held in the left hand with the flame some distance away
from the work, only introducing enough heat to keep the puddle pasty.
The puddle stick is handled by the right hand and when extra metal
is needed the puddle stick is laid aside and the aluminum filler-rod
is picked up and worked into the weld. When sufficient metal has
been added the puddle stick again comes into play and can be used in
stirring the metal together and finishing it off in the desired manner.
Reinforcing the weld will apply to aluminum the same as every other
metal, and a very neat job can be made after a little practice with the
puddle stick. At times some of the aluminum may adhere to the stick,
which is made from a quarter-inch piece of steel filler-rod, but this
can be removed by scraping it upon the fire bricks which should be in
the vicinity of the weld.
[Illustration: FIG. 77.--“Puddle-sticks” for Welding Aluminum.]
(=121=) There are two kinds of filler-rods used in aluminum welding.
Both are aluminum, but one is cast and the other is a drawn rod. This
same difference will also be noticed in bronze filler-rods, and there
has been much discussion as to which is the desirable one to use.
Neither of them is supposed to be 100 per cent pure aluminum, as such a
filler-rod does not give the desired results under the action of the
flame. A matter of from 90 to 95 per cent aluminum, with 5 per cent to
10 per cent of copper present as an alloy, is found to make a stronger
and more successful weld. It is recommended, if possible, to use the
drawn rods whenever available; for a weld at best is only a casting,
and if this casting can be made from virgin metal, rather than recast
from metal which has been cast many times and the contents not known,
it is thought that the results will be far more satisfactory. A weld
made with such a filler-rod, care being taken to work out the oxides,
will compare very favorably with the strength of the original metal and
in many instances a reinforcement will make it much stronger.
(=122=) To combine the two methods of welding aluminum is not
recommended. If the flux were stirred up inside the weld with a puddle
stick an unsatisfactory weld would result, so they are to be kept
entirely separate. It is not necessary to “V” out aluminum for the
same reason as other metals are “V-ed” out. When it is in workable
condition it can be puddled and stirred about as desired. It is well,
however, to “V” out slightly for the sake of marking the line of weld.
When aluminum is heated up, the expansion which occurs may close up
the crack, which was previously quite visible, in such a manner that
it cannot be located without much loss of time. Ordinary chalk or
soapstone, if available, may be used to mark any preheated work, but
the use of a chisel along the line of weld is the most reliable method.
PART TWO.--ALUMINUM WELDING
(=123=) It will be noticed, when welding aluminum, that bright surfaces
will oxidize immediately when exposed to the air. This action occurs
perhaps faster on aluminum than on any other metal. With this oxide
or scale present the metal will not run together nor fuse, no matter
how much heat is applied. The metal may be molten on each side of an
oxidized crack and at times will cause the line of fracture to even
float, but if the oxide is not destroyed the metal will not fuse.
As has been noted previously, two methods are used to destroy this
oxide, namely, the flux method and the puddle system. On account of
this exceedingly rapid oxidation, it will be found to the operator’s
advantage to complete his aluminum welds as quickly as possible in
order that he will have less of this oxide to combat. It will be found
in using the puddle system that greater haste can be made by using the
torch in the left hand, leaving the right free to do the puddling and
to add whatever metal is necessary. In this method most of the success
depends upon the operator’s skill in handling his puddle stick and
puddling in additional metal. Generally the right hand can do this more
rapidly than the left.
(=124=) It is well to learn how to make a successful weld from one
side of the metal only, and while this will apply to all metals, it is
especially advantageous in working aluminum. Where a small layer of
metal has been added to one side of an aluminum job, such as a crank
case, and it does not penetrate the entire thickness of the metal, when
the other side is turned, and the flame applied to it, a difference in
temperature and the loss of strength in this metal when heated will
cause the first side welded to crack unless the operator is extremely
cautious. Therefore it is always well to learn how to penetrate the
entire thickness of the metal from one side and make a satisfactory
weld in this manner.
(=125=) As previously stated, aluminum when melted loses most of its
strength, and if not supported by some means or other the metal will
collapse. On account of this it is advisable to back up aluminum work,
when possible, whether the job is to be done cold or in preheated
condition. The most successful manner of backing up is shown in Fig.
78, wherein _A_ represents a thin sheet of copper which has been fitted
to the work, and daubs of asbestos cement shown at _B_ will aid to some
extent in holding the plate in position, but this alone should not be
depended upon. A prop or fire brick, upon the top of which has been
placed a cushion of cement, will serve as a good backing, but where
this cannot be accomplished filler-rods may be bent in the manner shown
in Fig. 78. These filler-rods are not of the springy type, but are of
soft wire and the loop as shown is not for a spring effect, but merely
to take care of the contraction and expansion of the wire. Copper is
given a preference over most of the other sheet metals, because it
can be peened with a hammer to any shape desired, and many odd shaped
additions can be formed by its use.
[Illustration: FIG. 78.--One Method Used to “Back Up” Aluminum Work,
when Welding. _A_ Represents a Sheet of Copper; _B_, Asbestos Cement.]
(=126=) The use of clamps, when working on aluminum, is not recommended
on account of the great conductivity of heat and the weakening of the
metal as it approaches the melting-point. Pressure of any kind is not
desired and the operators who attempt to use clamps will regret it
sooner or later.
(=127=) In aluminum work contraction and expansion take place the
same as in other metals, only to a much greater extent, and greater
allowances must be made. However, the same rules can be applied when
determining whether work should be preheated or not, for if the
ends are free to move, the work can usually be accomplished without
preheating, whereas if confined, it will be necessary. When preheating
is necessary the whole piece must be treated in the same way,
regardless of the size. If only part of the work were preheated and the
balance left exposed, it would be almost impossible to avoid warpage
and shrinkage strains, which would render the work useless. Always
preheat the entire piece if any portion requires it.
(=128=) Great care must be exercised when setting up aluminum work
for preheating. Its weight should be distributed equally on whatever
support is used, so that there will be no danger of any one part
sagging, thereby throwing the whole piece out of alignment. A good way
of accomplishing this is to lay fire bricks on their flat side, in such
a manner that the weight of the work will be fairly well distributed.
Then put a daub of clay or asbestos cement on each brick and press
the aluminum piece down on this cushion. This will overcome the use
of shims and other methods used for jacking up the work, which are
unreliable.
(=129=) If charcoal is to be used as a preheating fuel, an oven of fire
brick should be built up with draft holes in the bottom layer of brick,
as described in the chapter on Preheating. A layer or two of charcoal
is then ignited. The oven is then covered with asbestos paper or a
piece of sheet metal. Asbestos paper is preferable as the metal becomes
very hot and is apt to burn the operator. After the fire has received
a good start, additional charcoal is added until sufficient heat is
obtained. This can be determined by sprinkling a little sawdust on the
surface of the aluminum, and if it chars readily, the work is ready to
weld. Other methods have been outlined previously, any or all of which
may be used in learning this heat. In executing the weld as little of
the work is exposed to the air as possible, in order to hold a uniform
heat and not permit any part to become chilled. At the completion of
the weld the oven is covered over, the openings in the bottom row of
bricks are stopped up, and the piece allowed to cool with the dying
fire. The charcoal process is the slow but sure method of handling
preheated aluminum work, and is always recommended.
(=130=) When preheating aluminum with torches burning kerosene or gas
a different kind of oven is built, as previously described in the
lecture on Preheating. No openings are left in the lower row of bricks
and the oven is built very much closer to the work being preheated. As
the object is to confine as much heat as possible and have a uniform
temperature throughout, it is not desirable to have such ovens loosely
constructed. If the bricks are irregular, a double wall can be built
with a layer of asbestos between them. Such a procedure is always
recommended if time and bricks permit. A hole is left in one end of
the oven for the preheating torch flame to enter. On aluminum work the
flame is never played directly upon the metal. A baffling plate of
metal or fire brick is used to distribute the flame around the sides of
the piece and very satisfactory results may be obtained by preheating
in this manner.
PART THREE.--ALUMINUM WELDING
(=131=) Many times aluminum crank cases which have large holes punched
in them and parts missing are brought to a welder for repairs. A
question arises as to whether it is best to back up these holes and
fill in the missing parts with a filler-rod as the welding progresses,
or whether these parts should be cast separately or cut out of another
crank case. It will generally depend upon the size of the hole, as to
the desirable procedure in a case of this kind. It must be remembered
that if the casting and welding are to be done at one and the same time
each additional layer of metal must be fused to the last layer and that
in reality a great deal of welding is necessary. In addition this added
metal must be fused to the crank case. On small holes, perhaps two or
three inches in diameter, this method is recommended, but if the hole
is much larger, it is best to cast a piece and then weld it in, for in
this instance there is only one line of weld to look after.
(=132=) On aluminum work it is proper to weld from the closed end of a
crack toward the open, whether the piece has or has not been preheated.
This is true also of all other metals, for if the weld were to be
started at the open end and worked backwards there would certainly be
internal strains set up, which would be undesirable. If it is not clear
which end is the open one, the operator should stop a moment and figure
it out.
(=133=) Were a suspension arm of the U type on an aluminum crank case
to break about three or four inches from the body of the case, it could
be welded in place without dismantling the motor, if handled properly.
Free access must be had to the line of break, so that the operator
can manipulate his flame at whatever angle he thinks best. Due to the
contraction and expansion, which may throw the piece being welded out
of alignment slightly, it is best to blank the bolt hole at the end
of this suspension arm and face it off, before the piece is welded in
position. Later a new hole can be drilled which will line up accurately
with the frame, and the welder will not then have to worry or attempt
to return it exactly to its former position. In order to keep the case
itself as cool as possible, wet asbestos should be packed around it,
near the broken arm, so that too much heat will not be absorbed by it.
The broken end is then tacked in position at two or three places and
the weld started. On such a problem the puddle system will be found
best, for both horizontal and vertical welding are to be done, as
well as some overhead. As flux causes the metal to flow, it is rather
difficult for the beginner to apply it to vertical and overhead work.
The puddle stick should work through the metal its full thickness and
eliminate every possible trace of the break, digging out the old metal
where dirt is found, and adding new metal for reinforcing. When one
side has been welded and reinforced it should not be allowed to cool
while the other side is being worked. The torch should be played upon
it every now and then, in order that the whole line of weld will be at
approximately the same temperature; otherwise, the weld may break in
cooling. The ease with which aluminum is puddled together, which many
welders have likened to the children’s method of making mud pies, seems
so simple to the beginner that he cannot see where the strength comes
from when cooled. On account of this, he invariably works his aluminum
too long. After welding a few test bars of this metal and breaking them
in the line of weld, many old welders will gain confidence upon seeing
the results of their own efforts.