the furnaceman and placed in
the lower die, surrounding the centering jaws, as shown at _H_ in
Fig. 62 and _C_ in Fig. 63. Air is then turned into the cylinder
_D_, and the piston rod _E_, the die carrier _B_, the top die _F_
and the expander _G_ descend. The pilot _H_ enters a hole in the
center of the lower die, and the expander _G_ enters the centering
jaws _I_, causing them to expand and center the gear _C_ in the
lower die. On further advance of the piston rod _E_, the expander
_G_ is forced upward against the pressure of the springs _J_ and
the upper die _F_ comes in contact with the upper surface of the
gear. Further downward movement of the dies, which now clamp the
work securely, overcomes the resistance of the pressure weight
_K_ (which normally keeps up the plunger _A_), and the gear is
submerged in the oil. The quenching oil is circulated through a
cooling system outside the building and enters the tempering machine
through the inlet pipe _L_. When the machine is in the position
shown, the oil passes out through the ports _M_ in the lower plunger
to the outer reservoir _N_, passing to the cooling system by way of
the overflow _O_. When the lower plunger _A_ is forced downward,
the ports _M_ are automatically closed and the cool quenching oil
from the inlet pipe _L_, having no other means of escape, passes
through the holes in the lower die and the grooves in the upper,
circulating in contact with the surfaces of the gear and passes to
the overflow. When the air pressure is released, the counterweights
return the parts to the positions shown in Fig. 63, and the operator
removes the gear.

[Illustration: FIG. 63.--Gleason tempering machine.]

The gear comes out uniformly hard all over and of the same degree of
hardness as when tempered in an open tank. The output of the machine
depends on the amount of metal to be cooled, but will average from
8 to 16 per hour. Each machine is served by one man, two furnaces
being required to heat the work. A slight excess of oil is used
in the firing of the furnaces to give a reducing atmosphere and
to avoid scale.

[Illustration: FIG. 64.--Hardening and shrinking sleeves.]

CARBURIZING LOW-CARBON SLEEVES.--Low-carbon sleeves are carburized
and pushed on malleable-iron differential-case hubs. Formerly,
these sleeves were given two treatments after carburization in
order to refine the case and the core, and then sent to the grinding
department, where they were ground to