The Modern Hardening Room

: HARDENING CARBON STEEL FOR TOOLS
: The Working Of Steel

A hardening room of today means a very

different place from the dirty, dark smithshop in the corner with

the open coal forge. There, when we wanted to be somewhat particular,

we sometimes shoveled the coal cinders to one side and piled a great

pile of charcoal on the forge. We now have a complete equipment;

a gas- or oil-heating furnace, good running water, several sizes

of lead pots, and an oil tank large enough to ho d a barrel of

oil. By running water, we mean a large tank with overflow pipes

giving a constant supply. The ordinary hardening room equipment

should consist of:



Gas or oil muffle furnace for hardening.

Gas or oil forge furnace.

A good size gas or oil furnace for annealing and case-hardening.

A gas or oil furnace to hold lead pots.

Oil tempering tank, gas- or oil-heated.

Pressure blower.

Large oil tank to hold at least a barrel of oil.

Big water tank with screen trays connected with large pipe from bottom

with overflow.

Straightening press.

The furnace should be connected with pyrometers and tempering tank with

a thermometer.



Beside all this you need a good man. It does not make much difference

how completely the hardening department is fitted up, if you expect

good work, a small percentage of loss and to be able to tackle anything

that comes along, you must have a good man, one who understands

the difference between low- and high-carbon steel, who knows when

particular care must be exercised on particular work. In other

words, a man who knows how his work should be done, and has the

intelligence to follow directions on treatments of steel on which

he has had no experience.



Jewelers' tools, especially for silversmith's work, probably have

to stand the greatest punishment of any all-steel tools and to

make a spoon die so hard that it will not sink under a blow from

an 1,800-lb. hammer with a 4-ft. drop, and still not crack, demands

careful treatment.



To harden such dies, first cover the impression on the die with

paste made from bone dust or lampblack and oil. Place face down

in an iron box partly filled with crushed charcoal, leaving back

of die uncovered so that the heat can be seen at all times. Heat

slowly in furnace to a good cherry red. The heat depends on the

quality and the analysis of steel and the recommended actions of

the steel maker should be carefully followed. When withdrawn from

the fire the die should be quenched as shown in Fig. 80 with the

face of die down and the back a short distance out of the water.

When the back is black, immerse all over.






If such a tank is not at hand, it would pay to rig one up at once,

although a barrel of brine may be used, or the back of the die

may be first immersed to a depth of about 1/2 in. When the piece

is immersed, hold die on an angle as in Fig. 81.






This is for the purpose of expelling all steam bubbles as they

form in contact with hot steel. We are aware of the fact that a

great many toolmakers in jewelry shops still cling to the overhead

bath, as in Fig. 82, but more broken pieces and more dies with

soft spots are due to this method than to all the others combined,

as the water strikes one spot in force, contracting the surface

so much faster than the rest of the die that the results are the

same as if an uneven heating had been given the steel.