SOLDERING, BRAZING AND THERMIT WELDING
SOLDERING
Common solder is an alloy of one-half lead with one-half tin, and is called
"half and half." Hard solder is made with two-thirds tin and one-third
lead. These alloys, when heated, are used to join surfaces of the same or
dissimilar metals such as copper, brass, lead, galvanized iron, zinc,
tinned plate, etc. These metals are easily joined, but the action of solder
with iron, steel and aluminum is not so satisfactory and requires greater
care and skill.
The solder is caused to make a perfect union with the surfaces treated with
the help of heat from a soldering iron. The soldering iron is made from a
piece of copper, pointed at one end and with the other end attached to an
iron rod and wooden handle. A flux is used to remove impurities from the
joint and allow the solder to secure a firm union with the metal surface.
The iron, and in many cases the work, is heated with a gasoline blow torch,
a small gas furnace, an electric heater or an acetylene and air torch.
The gasoline torch which is most commonly used should be filled two-thirds
full of gasoline through the hole in the bottom, which is closed by a screw
plug. After working the small hand pump for 10 to 20 strokes, hold the palm
of your hand over the end of the large iron tube on top of the torch and
open the gasoline needle valve about a half turn. Hold the torch so that
the liquid runs down into the cup below the tube and fills it. Shut the
gasoline needle valve, wipe the hands dry, and set fire to the fuel in the
cup. Just as the gasoline fire goes out, open the gasoline needle valve
about a half turn and hold a lighted match at the end of the iron tube to
ignite the mixture of vaporized gasoline and air. Open or close the needle
valve to secure a flame about 4 inches long.
On top of the iron tube from which the flame issues there is a rest for
supporting the soldering iron with the copper part in the flame. Place the
iron in the flame and allow it to remain until the copper becomes very hot,
not quite red, but almost so.
A new soldering iron or one that has been misused will have to be "tinned"
before using. To do this, take the iron from the fire while very hot and
rub the tip on some flux or dip it into soldering acid. Then rub the tip of
the iron on a stick of solder or rub the solder on the iron. If the solder
melts off the stick without coating the end of the iron, allow a few drops
to fall on a piece of tin plate, then nil the end of the iron on the tin
plate with considerable force. Alternately rub the iron on the solder and
dip into flux until the tip has a coating of bright solder for about half
an inch from the end. If the iron is in very bad shape, it may be necessary
to scrape or file the end before dipping in the flux for the first time.
After the end of the iron is tinned in this way, replace it on the rest of
the torch so that the tinned point is not directly in the flame, turning
the flame down to accomplish this.
_Flux._--The commonest flux, which is called "soldering acid," is made
by placing pieces of zinc in muriatic (hydrochloric) acid contained in a
heavy glass or porcelain dish. There will be bubbles and considerable heat
evolved and zinc should be added until this action ceases and the zinc
remains in the liquid, which is now chloride of zinc.
This soldering acid may be used on any metal to be soldered by applying
with a brush or swab. For electrical work, this acid should be made neutral
by the addition of one part ammonia and one part water to each three parts
of the acid. This neutralized flux will not corrode metal as will the
ordinary acid.
Powdered resin makes a good flux for lead, tin plate, galvanized iron and
aluminum. Tallow, olive oil, beeswax and vaseline are also used for this
purpose. Muriatic acid may be used for zinc or galvanized iron without the
addition of the zinc, as described in making zinc chloride. The addition of
two heaping teaspoonfuls of sal ammoniac to each pint of the chloride of
zinc is sometimes found to improve its action.
_Soldering Metal Parts._--All surfaces to be joined should be fitted
to each other as accurately as possible and then thoroughly cleaned with a
file, emery cloth, scratch bush or by dipping in lye. Work may be cleaned
by dipping it into nitric acid which has been diluted with an equal volume
of water. The work should be heated as hot as possible without danger of
melting, as this causes the solder to flow better and secure a much better
hold on the surfaces. Hard solder gives better results than half and half,
but is more difficult to work. It is very important that the soldering iron
be kept at a high heat during all work, otherwise the solder will only
stick to the surfaces and will not join with them.
Sweating is a form of soldering in which the surfaces of the work are first
covered with a thin layer of solder by rubbing them with the hot iron after
it has been dipped in or touched to the soldering stick. These surfaces are
then placed in contact and heated to a point at which the solder melts and
unites. Sweating is much to be preferred to ordinary soldering where the
form of the work permits it. This is the only method which should ever be
used when a fitting is to be placed over the end of a length of tube.
_Soldering Holes._--Clean the surfaces for some distance around the
hole until they are bright, and apply flux while holding the hot iron near
the hole. Touch the tip of the iron to some solder until the solder is
picked up on the iron, and then place this solder, which was just picked
up, around the edge of the hole. It will leave the soldering iron and stick
to the metal. Keep adding solder in this way until the hole has been closed
up by working from the edges and building toward the center. After the hole
is closed, apply more flux to the job and smooth over with the hot iron
until there are no rough spots. Should the solder refuse to flow smoothly,
the iron is not hot enough.
_Soldering Seams._--Clean back from the seam or split for at least
half an inch all around and then build up the solder in the same way as was
done with the hole. After closing the opening, apply more flux to the work
and run the hot iron lengthwise to smooth the job.
_Soldering Wires._--Clean all insulation from the ends to be soldered
and scrape the ends bright. Lay the ends parallel to each other and,
starting at the middle of the cleaned portion, wrap the ends around each
other, one being wrapped to the right, the other to the left. Hold the hot
iron under the twisted joint and apply flux to the wire. Then dip the iron
in the solder and apply to the twisted portion until the spaces between the
wires are filled with solder. Finish by smoothing the joint and cleaning
away all excess metal by rubbing the hot iron lengthwise. The joint should
now be covered with a layer of rubber tape and this covered with a layer of
ordinary friction tape.
_Steel and Iron._--Steel surfaces should be cleaned, then covered with
clear muriatic acid. While the acid is on the metal, rub with a stick of
zinc and then tin the surfaces with the hot iron as directed. Cast iron
should be cleaned and dipped in strong lye to remove grease. Wash the lye
away with clean water and cover with muriatic acid as with steel. Then rub
with a piece of zinc and tin the surfaces by using resin as a flux.
It is very difficult to solder aluminum with ordinary solder. A special
aluminum solder should be secured, which is easily applied and makes a
strong joint. Zinc or phosphor tin may be used in place of ordinary solder
to tin the surfaces or to fill small holes or cracks. The aluminum must be
thoroughly heated before attempting to solder and the flux may be either
resin or soldering acid. The aluminum must be thoroughly cleaned with
dilute nitric acid and kept hot while the solder is applied by forcible
rubbing with the hot iron.
BRAZING
This is a process for joining metal parts, very similar to soldering,
except that brass is used to make the joint in place of the lead and zinc
alloys which form solder. Brazing must not be attempted on metals whose
melting point is less than that of sheet brass.
Two pieces of brass to be brazed together are heated to a temperature at
which the brass used in the process will melt and flow between the
surfaces. The brass amalgamates with the surfaces and makes a very strong
and perfect joint, which is far superior to any form of soldering where the
work allows this process to be used, and in many cases is the equal of
welding for the particular field in which it applies.
_Brazing Heat and Tools._--The metal commonly used for brazing will
melt at heats between 1350° and 1650° Fahrenheit. To bring the parts to
this temperature, various methods are in use, using solid, liquid or
gaseous fuels. While brazing may be accomplished with the fire of the
blacksmith forge, this method is seldom satisfactory because of the
difficulty of making a sufficiently clean fire with smithing coal, and it
should not be used when anything else is available. Large jobs of brazing
may be handled with a charcoal fire built in the forge, as this fuel
produces a very satisfactory and clean fire. The only objection is in the
difficulty of confining the heat to the desired parts of the work.
The most satisfactory fire is that from a fuel gas torch built for this
work. These torches are simply forms of Bunsen burners, mixing the proper
quantity of air with the gas to bring about a perfect combustion. Hose
lines lead to the mixing tube of the gas torch, one line carrying the gas
and the other air under a moderate pressure. The air line is often
dispensed with, allowing the gas to draw air into the burner on the
injector principle, much the same as with illuminating gas burners for use
with incandescent mantles. Valves are provided with which the operator may
regulate the amount of both gas and air, and ordinarily the quality and
intensity of the flame.
When gas is not available, recourse may be had to the gasoline torch made
for brazing. This torch is built in the same way as the small portable
gasoline torches for soldering operations, with the exception that two
regulating needle valves are incorporated in place of only one.
The torches are carried on a framework, which also supports the work being
handled. Fuel is forced to the torch from a large tank of gasoline into
which air pressure is pumped by hand. The torches are regulated to give
the desired flame by means of the needle valves in much the same way as
with any other form of pressure torch using liquid fuel.
Another very satisfactory form of torch for brazing is the acetylene-air
combination described in the chapter on welding instruments. This torch
gives the correct degree of heat and may be regulated to give a clean and
easily controlled flame.
Regardless of the source of heat, the fire or flame must be adjusted so
that no soot is deposited on the metal surfaces of the work. This can only
be accomplished by supplying the exact amounts of gas and air that will
produce a complete burning of the fuel. With the brazing torches in common
use two heads are furnished, being supplied from the same source of fuel,
but with separate regulating devices. The torches are adjustably mounted in
such a way that the flames may be directed toward each other, heating two
sides of the work at the same time and allowing the pieces to be completely
surrounded with the flame.
Except for the source of heat, but one tool is required for ordinary
brazing operations, this being a spatula formed by flattening one end of a
quarter-inch steel rod. The spatula is used for placing the brazing metal
on the work and for handling the flux that is required in this work as in
all other similar operations.
_Spelter._--The metal that is melted into the joint is called spelter.
While this name originally applied to but one particular grade or
composition of metal, common use has extended the meaning until it is
generally applied to all grades.
Spelter is variously composed of alloys containing copper, zinc, tin and
antimony, the mixture employed depending on the work to be done. The
different grades are of varying hardness, the harder kinds melting at
higher temperatures than the soft ones and producing a stronger joint when
used. The reason for not using hard spelter in all cases is the increased
difficulty of working it and the fact that its melting point is so near to
some of the metals brazed that there is great danger of melting the work as
well as the spelter.
The hardest grade of spelter is made from three-fourths copper with
one-fourth zinc and is used for working on malleable and cast iron and for
steel.
This hard spelter melts at about 1650° and is correspondingly difficult to
handle.
A spelter suitable for working with copper is made from equal parts of
copper and zinc, melting at about 1400° Fahrenheit, 500° below the melting
point of the copper itself. A still softer brazing metal is composed of
half copper, three-eighths zinc and one-eighth tin. This grade is used for
fastening brass to iron and copper and for working with large pieces of
brass to brass. For brazing thin sheet brass and light brass castings, a
metal is used which contains two-thirds tin and one-third antimony. The
low melting point of this last composition makes it very easy to work with
and the danger of melting the work is very slight. However, as might be
expected, a comparatively weak joint is secured, which will not stand any
great strain.
All of the above brazing metals are used in powder form so that they may be
applied with the spatula where the joint is exposed on the outside of the
work. In case it is necessary to braze on the inside of a tube or any deep
recess, the spelter may be placed on a flat rod long enough to reach to
the farthest point. By distributing the spelter at the proper points along
the rod it may be placed at the right points by turning the rod over after
inserting into the recess.
_Flux._--In order to remove the oxides produced under brazing heat and
to allow the brazing metal to flow freely into place, a flux of some kind
must be used. The commonest flux is simply a pure calcined borax powder,
that is, a borax powder that has been heated until practically all the
water has been driven off.
Calcined borax may also be mixed with about 15 per cent of sal ammoniac to
make a satisfactory fluxing powder. It is absolutely necessary to use flux
of some kind and a part of whatever is used should be made into a paste
with water so that it can be applied to the joint to be brazed before
heating. The remainder of the powder should be kept dry for use during the
operation and after the heat has been applied.
_Preparing the Work._--The surfaces to be brazed are first thoroughly
cleaned with files, emery cloth or sand paper. If the work is greasy, it
should be dipped into a bath of lye or hot soda water so that all trace of
oil is removed. The parts are then placed in the relation to each other
that they are to occupy when the work has been completed. The edges to be
joined should make a secure and tight fit, and should match each other at
all points so that the smallest possible space is left between them. This
fit should not be so tight that it is necessary to force the work into
place, neither should it be loose enough to allow any considerable space
between the surfaces. The molten spelter will penetrate between surfaces
that water will flow between when the work and spelter have both been
brought to the proper heat. It is, of course, necessary that the two parts
have a sufficient number of points of contact so that they will remain in
the proper relative position.
The work is placed on the surface of the brazing table in such a position
that the flame from the torches will strike the parts to be heated, and
with the joint in such a position that the melted spelter will flow down
through it and fill every possible part of the space between the surfaces
under the action of gravity. That means that the edge of the joint must be
uppermost and the crack to be filled must not lie horizontal, but at the
greatest slant possible. Better than any degree of slant would be to have
the line of the joint vertical.
The work is braced up or clamped in the proper position before commencing
to braze, and it is best to place fire brick in such positions that it will
be impossible for cooling draughts of air to reach the heated metal should
the flame be removed temporarily during the process. In case there is a
large body of iron, steel or copper to be handled, it is often advisable to
place charcoal around the work, igniting this with the flame of the torch
before starting to braze so that the metal will be maintained at the
correct heat without depending entirely on the torch.
When handling brass pieces having thin sections there is danger of melting
the brass and causing it to flow away from under the flame, with the result
that the work is ruined. If, in the judgment of the workman, this may
happen with the particular job in hand, it is well to build up a mould of
fire clay back of the thin parts or preferably back of the whole piece, so
that the metal will have the necessary support. This mould may be made by
mixing the fire clay into a stiff paste with water and then packing it
against the piece to be supported tightly enough so that the form will be
retained even if the metal softens.
_Brazing._--With the work in place, it should be well covered with the
paste of flux and water, then heated until this flux boils up and runs over
the surfaces. Spelter is then placed in such a position that it will run
into the joint and the heat is continued or increased until the spelter
melts and flows in between the two surfaces. The flame should surround the
work during the heating so that outside air is excluded as far as is
possible to prevent excessive oxidization.
When handling brass or copper, the flame should not be directed so that its
center strikes the metal squarely, but so that it glances from one side or
the other. Directing the flame straight against the work is often the cause
of melting the pieces before the operation is completed. When brazing two
different metals, the flame should play only on the one that melts at the
higher temperature, the lower melting part receiving its heat from the
other. This avoids the danger of melting one before the other reaches the
brazing point.
The heat should be continued only long enough to cause the spelter to flow
into place and no longer. Prolonged heating of any metal can do nothing but
oxidize and weaken it, and this practice should be avoided as much as
possible. If the spelter melts into small globules in place of flowing, it
may be caused to spread and run into the joint by lightly tapping the work.
More dry flux may be added with the spatula if the tapping does not produce
the desired result.
Excessive use of flux, especially toward the end of the work, will result
in a very hard surface on all the work, a surface which will be extremely
difficult to finish properly. This trouble will be present to a certain
extent anyway, but it may be lessened by a vigorous scraping with a wire
brush just as soon as the work is removed from the fire. If allowed to cool
before cleaning, the final appearance will not be as good as with the
surplus metal and scale removed immediately upon completing the job.
After the work has been cleaned with the brush it may be allowed to cool
and finished to the desired shape, size and surface by filing and
polishing. When filed, a very thin line of brass should appear where the
crack was at the beginning of the work. If it is desired to avoid a square
shoulder and fill in an angle joint to make it rounding, the filling is
best accomplished by winding a coil of very thin brass wire around the part
of the work that projects and then causing this to flow itself or else
allow the spelter to fill the spaces between the layers of wire. Copper
wire may also be used for this purpose, the spaces being filled with
melted spelter.
THERMIT WELDING
The process of welding which makes use of the great heat produced by oxygen
combining with aluminum is known as the Thermit process and was perfected
by Dr. Hans Goldschmidt. The process, which is controlled by the
Goldschmidt Thermit Company, makes use of a mixture of finely powdered
aluminum with an oxide of iron called by the trade name, Thermit.
The reaction is started with a special ignition powder, such as barium
superoxide and aluminum, and the oxygen from the iron oxide combining with
the aluminum, producing a mass of superheated steel at about 5000 degrees
Fahrenheit. After the reaction, which takes from. 30 seconds to a minute,
the molten metal is drawn from the crucible on to the surfaces to be
joined. Its extreme heat fuses the metal and a perfect joint is the result.
This process is suited for welding iron or steel parts of comparatively
large size.
_Preparation._--The parts to be joined are thoroughly cleaned on the
surfaces and for several inches back from the joint, after which they are
supported in place. The surfaces between which the metal will flow are
separated from 1/4 to 1 inch, depending on the size of the parts, but
cutting or drilling part of the metal away. After this separation is made
for allowing the entrance of new metal, the effects of contraction of the
molten steel are cared for by preheating adjacent parts or by forcing the
ends apart with wedges and jacks. The amount of this last separation must
be determined by the shape and proportions of the parts in the same way as
would be done for any other class of welding which heats the parts to a
melting point.
Yellow wax, which has been warmed until plastic, is then placed around the
joint to form a collar, the wax completely filling the space between the
ends and being provided with vent holes by imbedding a piece of stout cord,
which is pulled out after the wax cools.
A retaining mould (Figure 55) made from sheet steel or fire brick is then
placed around the parts. This mould is then filled with a mixture of one
part fire clay, one part ground fire brick and one part fire sand. These
materials are well mixed and moistened with enough water so that they will
pack. This mixture is then placed in the mould, filling the space between
the walls and the wax, and is packed hard with a rammer so that the
material forms a wall several inches thick between any point of the mould
and the wax. The mixture must be placed in the mould in small quantities
and packed tight as the filling progresses.
[Illustration: Figure 55.--Thermit Mould Construction]
Three or more openings are provided through this moulding material by the
insertion of wood or pipe forms. One of these openings will lead from the
lowest point of the wax pattern and is used for the introduction of the
preheating flame. Another opening leads from the top of the mould into this
preheating gate, opening into the preheating gate at a point about one inch
from the wax pattern. Openings, called risers, are then provided from each
of the high points of the wax pattern to the top of the mould, these risers
ending at the top in a shallow basin. The molten metal comes up into these
risers and cares for contraction of the casting, as well as avoiding
defects in the collar of the weld. After the moulding material is well
packed, these gate patterns are tapped lightly and withdrawn, except in the
case of the metal pipes which are placed at points at which it would be
impossible to withdraw a pattern.
_Preheating._--The ends to be welded are brought to a bright red heat
by introducing the flame from a torch through the preheating gate. The
torch must use either gasoline or kerosene, and not crude oil, as the crude
oil deposits too much carbon on the parts. Preheating of other adjacent
parts to care for contraction is done at this time by an additional torch
burner.
The heating flame is started gently at first and gradually increased. The
wax will melt and may be allowed to run out of the preheating gate by
removing the flame at intervals for a few seconds. The heat is continued
until the mould is thoroughly dried and the parts to be joined are brought
to the red heat required. This leaves a mould just the shape of the wax
pattern.
The heating gate should then be plugged with a sand core, iron plug or
piece of fitted fire brick, and backed up with several shovels full of the
moulding mixture, well packed.
[Illustration: Figure 56.--Thermit Crucible Plug.
_A_, Hard burn magnesia stone;
_B_, Magnesia thimble;
_C_, Refractory sand;
_D_, Metal disc;
_E_, Asbestos washer;
_F_, Tapping pin]
_Thermit Metal._--The reaction takes place in a special crucible lined
with magnesia tar, which is baked at a red heat until the tar is driven off
and the magnesia left. This lining should last from twelve to fifteen
reactions. This magnesia lining ends at the bottom of the crucible in a
ring of magnesia stone and this ring carries a magnesia thimble through
which the molten steel passes on its way to the mould. It will usually be
necessary to renew this thimble after each reaction. This lower opening is
closed before filling the crucible with thermit by means of a small disc or
iron carrying a stem, which is called a tapping pin (Figure 56). This pin,
_F_, is placed in the thimble with the stem extending down through the
opening and exposing about two inches. The top of this pin is covered with
an asbestos, washer, _E_, then with another iron disc. _D_, and
finally with a layer of refractory sand. The crucible is tapped by knocking
the stem of the pin upwards with a spade or piece of flat iron about four
feet long.
The charge of thermit is added by placing a few handfuls over the
refractory sand and then pouring in the balance required. The amount of
thermit required is calculated from the wax used. The wax is weighed before
and after filling _the entire space that the thermit will occupy_.
This does not mean only the wax collar, but the space of the mould with all
gates filled with wax. The number of pounds of wax required for this
filling multiplied by 25 will give the number of pounds of thermit to be
used. To this quantity of thermit should be added I per cent of pure
manganese, 1 per cent nickel thermit and 15 per cent of steel punchings.
It is necessary, when more than 10 pounds of thermit will be used, to mix
steel punchings not exceeding 3/8 inch diameter by 1/8 inch thick with the
powder in order to sufficiently retard the intensity of the reaction.
Half a teaspoonful of ignition powder is placed on top of the thermit
charge and ignited with a storm match or piece of red hot iron. The cover
should be immediately closed on the top of the crucible and the operator
should get away to a safe distance because of the metal that may be thrown
out of the crucible.
After allowing about 30 seconds to a minute for the reaction to take place
and the slag to rise to the top of the crucible, the tapping pin is struck
from below and the molten metal allowed to run into the mould. The mould
should be allowed to remain in place as long as possible, preferably over
night, so as to anneal the steel in the weld, but in no case should it be
disturbed for several hours after pouring. After removing the mould, drill
through the metal left in the riser and gates and knock these sections off.
No part of the collar should be removed unless absolutely necessary.