case has been found from the etched test pieces to be satisfactory,
the pots are removed. The iron ball then is dropped into the tube
to seal the hole in the bottom of the pot; the cover and the tube
are removed, and the gears quenched direct from the pot in mineral
oil, which is kept at a temperature not higher than 100 deg.F.

THE EFFECT.--The heating at 1,600 deg.F. gives the first heat treatment
which refines the core, which under the former high heat (1,700 deg.F.)
was rendered coarsely crystalline. All the gears, including the
scrap gears, are quenched direct from the pot in this manner.

The gears then go to the reheating furnaces, situated in front of
a battery of Gleason quenching machines. These furnaces accommodate
from 12 to 16 crown gears. The carbon-steel gears are heated in a
reducing atmosphere to about 1,425 deg.F. (depending on the carbon
content) placed in the dies in the Gleason quenching machine, and
quenched between dies in mineral oil at less than 100 deg.F. The test
gear receives exactly the same treatment as the others and is then
broken, giving a record of the condition of both case and core.

AFFINITY OF NICKEL STEEL FOR CARBON.--The carbon- and nickel-steel
gears are carburized separately owing to the difference in time
necessary for their carburization. Practically all printed information
on the subject is to the effect that nickel steel takes longer to
carburize than plain carbon steel. This is directly opposed to
the conditions found at this plant. For the same depth of case,
other conditions being equal, a nickel-steel gear would require
from 20 to 30 min. less than a low carbon-steel gear.

From the quenching machines, the gears go to the sand-blasting
machines, situated in the wing of the heat-treating building, where
they are cleaned. From here they are taken to the testing department.
The tests are simple and at the same time most thorough.

TESTING AND INSPECTION OF HEAT TREATMENT.--The hard parts of the
gear must be so hard that a new mill file does not bite in the
least. Having passed this file test at several points, the gears go
to the center-punch test. The inspector is equipped with a wooden
trough secured to the top of the bench to support the gear, a number
of center punches (made of 3/4-in. hex-steel having points sharpened
to an angle of 120 deg.) and a hammer weighing about 4 oz. With
these simple tools, supplemented by his skill, the inspector can
_feel_ the depth a