a push fit for the hubs. After
this they were pushed on the hubs. By the method now employed,
the first treatment refines the core, and on the second treatment,
the sleeves are pushed on the hub and at the same time hardened.
This method cuts out the internal grinding time, pressing on hubs,
and haulage from one department to another. Also, less work is
lost through splitting of the sleeves.

The machine for pushing the sleeves on is shown in Fig. 64. At
_A_ is the stem on which the hot sleeve _B_ is to be pushed. The
carburized sleeves are heated in an automatic furnace, which takes
them cold at the back and feeds them through to the front, by which
time they are at the correct temperature. The loose mandrel _C_
is provided with a spigot on the lower end, which fits the hole
in the differential-case hub. The upper end is tapered as shown
and acts as a pilot for the ram _D_. The action of pushing on and
quenching is similar to the action of the Gleason tempering machine,
with the exception that water instead of oil is used as a quenching
medium. The speed of operation depends on a number of variables,
but from 350 to 500 can be heated and pressed on in 11 hr.

CYANIDE BATH FOR TOOL STEELS.--All high-carbon tool steels are
heated in a cyanide bath. With this bath, the heat can be controlled
within 3 deg. The steel is evenly heated without exposure to the
air, resulting in work which is not warped and on which there is no
scale. The cyanide bath is, of course, not available for high-speed
steel because of the very high temperatures necessary.

DROP FORGING DIES

The kind of steel used in the die of course influences the heat
treatment it is to receive, but this also depends on the kind of
work the die is to perform. If the die is for a forging which is
machined all over and does not have to be especially close to size,
where a variation of 1/16 in. is not considered excessive, a low
grade steel will be perfectly satisfactory.

In cases of fine work, however, where the variation cannot be over
0.005 to 0.01 in. we must use a fine steel and prevent its going
out of shape in the heating and quenching. A high quality crucible
steel is suggested with about the following analysis: Carbon 0.75
per cent, manganese 0.25 per cent, silicon 0.15 per cent, sulphur
0.015 per cent, and phosphorus 0.015 per cent. Such a steel will
have a decalescent point in the neighborhood of 1,355 deg.F. and for
the size used, probably in a die