Brazing is a process of joining two pieces of metal by the use of
another metal, such as brass or copper. The use of solder has been
explained in the article on soldering. This article will tell about
brazing of wrought iron, cast-iron, and steel in the forge fire.
One must bear in mind that when a forge fire is used for brazing,
the fire should be free from green coal on account of the presence
of sulphur. A reducing fire is best for that purpose. It is well to
mention here that a forge fire that has been used for brazing must
be thoroughly cleaned before it can be used again for any welding
purposes. The brass will run down and clog the tuyere. If the least
bit of smelter is left on the forge it is apt to mix with the coals.
In that case it would find its way into the fire, melt, and collect on
any iron that may be in the fire heating. The success of any of these
operations depends absolutely upon a clean fire and a clean piece of
work to be done.
_To prepare the pieces to be brazed:_ All parts to be brazed should
be free from any foreign matter. They should be filed or polished
with emery cloth or sand-paper. This refers not only to the parts
that come into contact with each other, but both sides of the contact
edge for the depth of at least 1/2 in. When the parts are clean, put
them together. See that the joints fit. Paint the joints with a flux
made of boracic acid. Mix one part boiling water with one part borax
and two parts boracic acid. Keep it pasty so that it can be handled
with a brush. Ordinary borax can be used if the other is not at hand.
The smelter (brass) can be bought at supply stores. However, brass
filings, common sheet brass, or brass wire is just as good. If brass
filings are used these should be mixed with the flux. Any old tin can
will do for the mixing. A spoon for dipping the flux out when wanted
can be made on the end of a rod 1/4 in. in diameter, about 20 ins.
long, by flattening out an inch of the end, drawn out quite thin and
fashioned spoon shaped. Place the parts to be brazed in the fire and
heat till they are red hot. Dip the spoon into the brazing material
and put a little of the smelter on the joints. Increase the heat. When
the smelter begins to run add more. When it shows a bright streak all
around the parts to be joined shut off the blast and let it cool before
removing it from the fire. When it is black hot remove it from the
fire and file into shape. Be very careful to see that the pieces to be
brazed are so fastened together that they will not move apart when once
put into place. This can be done by packing brick or clay around them
or by clamping them in place. Do not put any weight that would cause
any strain upon them, for when heated this would change the position
and might cause a bend in the brazed parts.
_Brazing of cast-iron:_ Cast-iron is prepared for brazing in the same
way as steel or iron is prepared. The flux, however, is not the same.
It is made up of boric acid, 8 oz.; pulverized chlorate of potash, 4
oz.; carbonate of iron, 3 oz. Mix these together thoroughly, breaking
up all lumps that may be there. Keep this mixture in a glass jar.
Place the pieces to be brazed in a fire as you did the iron and steel.
Heat it all red hot. Mix the flux with the smelter and put it on. Do
not put this on at any time before the metal is red hot. Increase the
heat and add more flux and smelter. When the brass has flowed into
the joints, shut off the heat and let the metal cool off in the fire.
Cast-iron requires a higher temperature for brazing than iron or steel.
If a brass rod is used in place of the smelter, push the end of the rod
in the joint to be brazed. It will melt off as fast as it is pushed
in. When brazing some cast-iron, the break should be reinforced on the
unexposed side by a plate of wrought iron or steel. If this is cleaned
off thoroughly and placed against the break the smelter will not only
fill up the break but it will hold this piece of metal fast.
_Brazing steel band saws:_ Band saws break very often while in use.
They can be repaired only by brazing the broken ends together. Do so
by filing each end of the broken pieces, tapering to a very sharp edge
3/4 in. in length for lapping over. The length of this lapping depends
upon the width of the teeth of the saw. When the ends are filed, place
them in a vise that can be bought for this purpose. If no vise is at
hand two wood clamps, or iron clamps, or an ordinary shop vise will
answer the purpose. Put the two ends overlapping in place, and clamp
close enough to these ends to keep them in a straight line and, also,
for shifting while brazing. Paint the joint with flux, using the first
flux mentioned in the article. Put a piece of silver solder between the
laps. Now heat the jaws of a pair of close tongs white hot, and grasp
the joints between the hot jaws, and pinch them together. The heat in
the tongs will melt the silver and braze the two parts. Hold the tongs
steady; if not, they will bend, and the saw will be rather hard to
straighten when the tongs are removed. Do not remove the tongs until
they are black hot. Now place the saw in a vise and file the teeth to
correspond to those on either side of the joint. Smooth the roughness
from the joint.
_The value of brazing:_ A knowledge of how to braze is most useful to
any one working with the metals. Many things break that can be repaired
only by this process. For instance, tubing, automobile parts, very
complex parts of machinery, etc., when broken cannot be welded; they
must be mended by brazing. The success of the process depends upon the
care taken to make the parts perfectly clean and well fitted together.
If this is well done the brazing material will find its way to the
closest joints and fix them.