CHAPTER 4
THE BLACKSMITH'S WORK
Blacksmithing consists of working or forging iron and steel at the right heat into the required shape by means of hammer blows delivered either directly onto the metal or transmitted through tools. Parts II, III and IV explain and illustrate in detail each forging operation which may be done singly or in combination. The various processes used are summarized as follows:
It is very important that the smith should know the signs and the effect
of burning iron and that he should be able to recognize instantly the correct
degree of temperature which he requires for a particular operation.
The instruction 'Take a BRIGHT RED heat' or 'Take a FULL WELDING heat'
will be found throughout the lessons and a beginner cannot do better than
practice with a bar of iron so that he is able to' judge by eye the heat required
for a specific purpose.
Always look at the iron in ordinary daylight. Take care by the arrangement
of the windows, that the sun's rays cannot fall directly on either the hearth
or the anvil as this makes it very difficult to judge the heat of the metal.
WARM HEAT is taken by passing the metal slowly through the
fire until it is just too hot to be touched safely by the hand. This is the
correct heat for 'setting up' springs without removing the temper.
BLACK HEAT. No red colour is visible in daylight, but the
metal will glow faintly red in the dark. This temperature is not used in any
smithing operation, but may be used for obtaining an oil or matt black finish
on ornamental ironwork.
DULL RED OR BLOOD RED HEAT is used for easy bends on mild steel and for forging carbon steel. It is a little above the temperature required before
quenching carbon steel to obtain the maximum hardness.
BRIGHT RED HEAT. Simple forging operations on mild steel
are carried out at this temperature: for example, bending over the anvil,
light punching and hot chiselling.
BRIGHT YELLOW OR NEAR WELDING HEAT. The principal forging
operations on mild steel and wrought iron are carried out at this temperature,
including drawing down, upsetting, preparing scarfs and punching on heavy
work. This is the correct temperature for forging high-speed steel but carbon
steel should not be made so hot.
LIGHT WELDING, SWEATING OR SLIPPERY HEAT. While this is not
hot enough for welding many grades of mild steel, it is sometimes used successfully
if difficulty is experienced at higher temperatures. Considerable skill is
needed to weld mild steel with a slippery heat.
Wrought iron can be forged at this heat.
FULL WELDING HEAT.If the blast is correct, and the fire has a good heart, a few white bursting sparks will begin to appear among the red sparks from the fire. This is the correct temperature for welding most types of mild steel. A hollow fire and insufficient blast will produce white sparks, but in this case the surface of the metal is being burnt without attaining the correct welding heat.
WHITE OR SNOWBALL HEAT is too high for welding mild steel but is the correct heat for welding good quality wrought iron. Wrought iron has a spongy texture at this temperature but will be restored to normal condition by correct forging.
DRAWING DOWN
Drawing down needs a NEAR WELDING heat and is the process of increasing the length of a piece of metal and at the same time reducing its cross section. The simplest example is the formation of a point on a round or square bar by hammering which is described in Lesson 1. On heavy work the drawing down can be done quicker by fullering between top and bottom tools or by using the bick of the anvil as shown in Lesson 9 C.
BENDING
This can sometimes be carried out cold, but it is preferably done at a BRIGHT RED heat. Bends can be made over the anvil or bick, as shown in Lessons 2, 3 and 4, or sometimes on the swage block. The metal on the outside of a bend is subjected to a stretching action while the inside is upset. This is why the square outside corner bend described in Lesson 29 must always be formed by first upsetting the metal to provide the extra material required on the outside.
UPSETTING OR JUMPING UP
This operation, carried out at a NEAR WELDING heat, is for swelling or increasing the cross section of a bar of metal in one particular place, its overall length being reduced at the same time. Considerable practice is required to upset metal exactly in the place where the swelling is needed and the beginner is advised to do the job in easy stages by cooling off the bar with water, leaving just sufficient at the right heat for the first swelling. The bar should be re-heated and upsetting continued to the required amount.
HOT CUTTING
Hot cutting is done with hot chisels and sets; portions of the metal are either cut away completely or, in some cases, a split is made and opened out to receive another piece for welding, as shown in Lessons 5, 20, 31 and 32. A BRIGHT RED heat is best for hot cutting. Cold cutting is described on part II.
PUNCHING AND DRIFTING
These operations are best carried out with the work at a NEAR WELDING heat. If the hole is deep, the metal tends to contract round the punch which should be withdrawn after every three or four blows and quenched in water. Drifts are used to finish holes that have been punched smaller than the required size and it may be necessary to take two or more heats to complete the job satisfactorily; this is described in Lesson 16. When punching deep holes sprinkle a few grains of fuel into the hole before replacing the punch. The gas formed when the punch is next driven in will blow it out again quickly, saving both time and trouble.
FIRE WELDING
Fire welding is the operation whereby two pieces of metal are joined together while in a plastic state by hammering. Different types of welds are explained in the lessons and considerable practice is required before the simplest fire weld is mastered and even then, some grades of mild steel present difficulties which call for ingenuity in using the right technique. The essential conditions for fire welding are as follows:
(a) Metal properly prepared to suit the type of weld required.
(b) A clinker-free clean fire with a good heart.
(c) Accurate judgment by eye of the correct welding heat which varies from
a LIGHT WELDING heat to a WHITE heat with different types of steel and iron.
(d) Speed in withdrawing the metal from the fire and placing the pieces
in the correct position on the anvil, followed immediately by rapid and
accurate hammer blows delivered on the heated metal at the proper place
and in the right order.
Much practice is needed to develop and co-ordinate all these essential factors,
the most difficult being the judging of the correct welding heat, which ranges
from a bright sparkling white heat for good quality wrought iron down to a
bright red just changing to white heat for mild steel.
INSTRUCTIONS FOR FIRE WELDING
The following instructions on fire welding should be read and the procedure
thoroughly understood before attempting any of the lessons which include this
operation.
A certain amount of metal is always lost during fire welding, so it is essential
to upset or thicken the ends first. The upset ends are then forged to form
scarfs which must `pair' when laid together. The important factor when shaping
a scarf is to make certain that the point of contact between the two pieces
is in the middle so that when the metal is hammered, any scale or oxide is
squeezed to the outside and not trapped in the centre.
The scarfs should not be so short that they slide apart before they 'take',
neither should they be too long or the lips will burn off before the thickened
parts reach welding heat.
Although welds can be made without using a flux, it is often an advantage
to use either silver sand or one of the preparatory fire welding compounds,
such as 'Lalfite' Welding Plate.
When using silver sand, the pieces to be welded are placed in the fire side
by side with the faces of the scarfs donvnwards and brought to a NEAR WELDING
heat. Each piece in turn is then removed from the fire for a moment and the
face of the scarf sprinkled with a little silver sand which immediately melts
and flows over the iron, fluxing any scale or oxide that may have begun to
form. Both pieces are then returned to the fire still face down and are jockeyed
about a little to get a heat on each evenly.
The following actions have to be done much more quickly than they can he described.
Immediately welding heat is reached the first piece is removed from the fire
still with the scarf face downward. It is tapped over the edge of the anvil
to shake off the melted sand and dirt clinging to it and immediately turned
over and laid face upward on the anvil.
The second piece is also taken from the fire face downward, similarly tapped
over the edge of the anvil to shake off the dirt, and, without turning it
over, placed in position on top of the first piece. The first blow is then
struck in the centre of the weld.
Some experienced smiths can tell from the sound of the first few hammer blows
if the weld has taken or not. A dense or hard ringing note indicates that
the weld has not taken. It is quite permissible to take a second welding heat
to close the ends of the scarfs as these cool off much more quickly than the
thicker section of the metal, particularly the bottom one which is in contact
with the cold anvil face.
If Laffite is used, the procedure is a little different when the prepared
parts are heated to a DULL RED heat they are removed from the fire and a piece
of Laffite plate, a little bigger than the area of the weld, is placed between
the scarfs and squeezed with light hammer blows until it melts and spreads
over the scarf faces which will stick together. The adhering pieces are then
carefully returned to the fire and brought to a LIGHT WELDING heat when they
are lifted out and given a few gentle blows with the hammer to unite them.
They are then returned to the fire for another LIGHT WELDING heat and the
job finished off with ease and certainty.
HEAT TREATMENT
Heat treatment is applied to steel to make it harder, tougher or softer as
required. These qualities depend on the composition of the steel combined
with the heat treatment it receives (see Chapter 5 on Blacksmith's Materials).
Although an open fire is not an ideal method of carrying out all these processes,
there are five types of heat treatment that the blacksmith frequently undertakes
on small articles, and the following brief descriptions are only intended
to explain the meaning of the terms used. (More detailed information should
be available on this site soon.....)
Hardening is carried out by heating medium and high carbon
steels slowly and uniformly to the correct temperature between BLACK and DULL
RED heat and then quenching them suddenly in some suitable cooling medium,
such as water, oil or brine, according to the composition of the steel and
the degree of hardness required.
Tempering. Carbon steel that has been hardened by quenching
as described, is very brittle and in this state is useless for cutting tools,
particularly those which are subjected to blows. Some of this hardness must
be sacrificed to obtain the requisite toughness and this is done by re-heating
the metal to a lower temperature than that required for hardening and cooling
rather more gently in the cooling medium. The degree of temper required is
obtained by controlling the temperature to which the metal is re-heated and
varies from a high or hard temper for small edge tools to a low or soft temper
for certain kinds of springs.
Annealing is a softening process carried out by heating steel
to the correct temperature and then allowing it to cool slowly in a dying
fire or by burying the metal under hot ashes or in dry lime.
Normalizing differs from annealing in that although the metal
is raised to the same temperature, it is allowed to cool off naturally in
the air. It should not be laid on a cold floor or other cold surface or exposed
to draughts when cooling. It is an advantage to normalize any steel which
has been forged or welded, before the article is put into service.
Case Hardening is a process by which a hard skin is obtained
on steel which does not contain enough carbon to make it harden by heating
and quenching. It is carried out by packing the article to be casehardened
in a suitable metal container with a special case hardening compound, such
as 'Kasenit', and then heating the whole container to a RED heat (900°
C) and letting it soak at this temperature for a given period before allowing
it to cool slowly. The carbon in the compound penetrates the skin of the metal
and unites with the steel to produce a dead hard surface when the article
is subsequently hardened by re-heating and rapid quenching.
