Welding Iron and Steel under the Hammer
Iron and steel can be joined by heating until they become plastic and
then consolidating the two members of the joint by hammer blows, the
work being supported on an anvil. Correct heat and cleanliness are the
chief requisites. The “welding heat” corresponds with that temperature
at which the metal is in a state of partial fusion on the surface. The
better the quality of the iron, the higher the temperature it can stand
without being burned and ruined. Iron at a welding heat gives off
dazzling sparks, whereas ordinary cast steel is only an intense yellow,
but few sparks being evolved. Sufficient lap for the proper making of
the joint must always be allowed. When heated in a perfectly clear fire,
the metal may need no treatment prior to hammering; but otherwise it may
be necessary to sprinkle sand or some special flux over the work. At the
proper moment the iron is transferred to the anvil, and the union of the
two members of the joint immediately effected; delay means an imperfect
joint. In lifting the work out of the fire, remove it vertically and so
as not to collect particles of dirt on it. Keep a switch of brushwood at
hand for removing adhering matter.
=Welding of Steel Specially Considered.=--Some steels will “stand the
fire” better than others, which means that they will stand more heat
before they reach the point when they begin to burn.
The different kinds of steel used in a general way may be summed up as
blister, spring, shear, double shear, and cast steel. Blister steel
will, as a rule, stand the most heating before beginning to burn, and
the others follow in the order given. The difference in heating will
vary from nearly a white heat on blister to the yellow heat of cast
steel.
A simple method of ascertaining what heat a steel will stand before
beginning to burn is as follows: Heat the steel to its burning point,
and at various stages, beginning at the yellow stage, lay it on the
anvil and give it a few blows with the hand hammer. Repeat the process
until a heat is reached that will cause the steel, when struck with the
hammer, to give off sparks like small fireworks. When this stage is
reached it will show that the burning point is arrived at.
Careful observations of these points will enable the smith to know just
when to begin to use the flux for welding, which, by the way, must be
just before the steel reaches the burning point.
Another important point is the formation of the scarfs. These should not
be fullered down so thin or left in the same form as the scarfs as when
joining iron, and should be shorter (compare A and B, Fig. 66).
[Illustration: Fig. 66.--Scarfs for Iron and Steel]
In bringing the steel up to its welding point, care must be taken to
have it at a uniform heat throughout at the part for welding; and, to
get this, the blast should not be forced at the start, but used gently.
In some cases the blast should be stopped occasionally, to allow the
steel to soak. Then restart the blast, and gradually force it when
beginning to use the flux, continuing so until the welding point is
reached. Only light blows should be given at the start, just to cause
the two parts to stick together; but when stuck, the harder the blow the
better the weld.
An idea seems prevalent that the flux has a certain influence on the
steel, and converts it into a form that makes it more weldable. The real
use of a flux in this case is simply to retard the heat, and form a coat
or shell on the steel, and so counteract and prevent the burning action
which takes place when heating steel in an ordinary blast fire.
The reason why different fluxes are required for different brands of
steel is no doubt due to the differences in manufacture. As a rule, the
greater the heat the steel will stand before burning, the less it
requires a flux to protect it, so that in a great many cases a flux
consisting of some clean, sharp sand is all that is required; but the
steels that will burn at a lower heat require something more than sand
to protect them. Hence arises the necessity of adding burnt borax,
crushed glass, powdered marble, etc.
The method of welding steel is as follows; but before proceeding to get
the heat make a point of having a shallow tin on the forge large enough
to hold a sufficient quantity of the flux, so that it will cover the
scarfed end when being dipped in same. Have a clean fire and plenty of
firing on the hearth, so that the heat can be well covered. Start with
gentle blast until the heat is nearly up to burning point. If necessary,
stop the blast and let the heat soak for a few seconds so as to ensure a
uniform heat. Gradually force the blast, and keep withdrawing the
“heats” and roll them well in the flux, and so continue until it is
thought that the heat is plastic enough to unite. Place the scarfs in
position, give a few light blows until the parts stick together, then
hammer well home and move smartly so as to ensure the proper joining
together whilst in a plastic state. When welded, do not continue the
hammering or tooling at too low a heat; but if further hammering is
necessary, re-heat the work.
These hints are not applicable to every make of steel. With the special
steels manufacturers issue particular instructions.
A flux for welding cast steel consists of 2 oz. each of powdered chalk,
soda and burnt borax, mixed with 1 lb. of silver sand.
A firm of steel manufacturers recommend a mixture of 21 oz. of sand and
7 oz. of salt, moistened; the steel is to be treated in a fire of
sulphurless coal.