ation: FIG. 56.--Packing department and special pots.]

After filling to the top with compound, the lid _D_ is luted on.
Ten pots are then placed in a furnace. It will be noted that the
pots to the right are numbered 1, 2, 3, 4, indicating the position
they are to occupy in the furnace.

The cast-iron ball shown at _E_ is small enough to drop through
the pipe _B_, but will not pass through the hole _A_ in the bottom
of the pot. It is used as a valve to plug the bottom of the pot
to prevent the carburizing compound from dropping through when
removing the carburized gears to the quenching bath.

Without detracting from the high quality of the work, the metallurgist
in this plant has succeeded in cutting out one entire operation
and reducing the time in the hardening room by about 24 hr.

Formerly, the work was carburized at about 1,700 deg.F. for 9 hr. The
pots were then run out into the yard and allowed to cool slowly.
When cool, the work was taken out of the pots, reheated and quenched
at 1,600 deg.F. to refine the core. It was again reheated to 1,425 deg.F.
and quenched to refine the case. Finally, it was drawn to the proper
temper.

SHORT METHOD OF TREATMENT.--In the new method, the packed pots are
run into the case-hardening furnaces, which are heated to 1,600 deg.F.
On the insertion of the cold pots, the temperature naturally falls.
The amount of this fall is dependent upon a number of variables,
but it averages nearly 500 deg.F. as shown in the pyrometer chart,
Fig. 61. The work and furnace must be brought to 1,600 deg.F. Within
2-1/2 hr.; otherwise, a longer time will be necessary to obtain
the desired depth of case. On this work, the depth of case required
is designated in thousandths, and on crown gears, the depth in
0.028 in. Having brought the work to a temperature of 1,600 deg.F.
the depth of case mentioned can be obtained in about 5-1/2 hr. by
maintaining this temperature.

As stated before, at the top of each pot are several test pieces
consisting of a whole scrap gear and several sections. After the
pots have been heated at 1,600 deg.F. for about 5-1/4 hr., they are
removed, and a scrap-section test-piece is quenched direct from
the pot in mineral oil at _not more than_ 100 deg.F. The end of a tooth
of this is then ground and etched to ascertain the depth of case.
As these test pieces are of exactly the same cross-section as the
gears themselves, the carburizing action is similar. When the depth
of