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May, 1925
faces for the upper die. Fig. 9-F is ready for casting
the cement model of the upper die. Fig. 9-G shows
two pairs of dies ready for hardening. The Keller engraving
machine used for cutting the dies, through
a cleverly designed system of electric relays, automatically
transmits each movement of the tracer in
the model to the cutter in the steel die.
Dies Require Frequent Dressing,
Because of the finish and accuracy required on the
finished blades, dies must be frequently dressed, the
number of blades forged per dressing varying between
forging- Stamping - Heat Treating 163
embodying the characteristics of a hand modeled
blade, has the advantage of greater facility in preparing
and maintaining the forging dies. The surfaces
which give the effect of a twist are developed by
planer or shaper cuts, no models nor engraving machine
work for this design being required. These cuts
with non-intersecting axes diverge at the base and
converge at the tip employ suitably shaped form tools
by means of which the required taper and twist are
obtained. Fig. 7-F shows on the left an untrimmed
finished forging adjoining which is a trimmed forg-
FIG. 9 (A)—Contour gauges lined up in base plate for model making. (B)—Blade surfaces generated in modeling clay. (C)—
Plaster cast matrix for casting cement model. (D)—Cement model bottom die. (E)—Partly prepared form for upper die.
(F)—Form ready for casting cement model upper die. (G)—Two pairs of forging dies ready for hardening.
200 and 500. Fig. 4 shows a group of die stands,
equipped with flexible shaft bench grinders.
The selection of die steels has offered numerous
problems due to the tendency of most steels to spall
because of the thin section of the blades cooling rapidly.
Many grades of steels have been tried for drop
forging dies including various alloy steels. Plain high
carbon steel hardened to a scleroscope hardness of
between 80 and 90 has been found most satisfactory.
The dies must take and retain a high finish as the surface
of the blades are not machined.
Modified Type of Warped Blade.
A modified type of warped and tapered blade has
been developed by Westinghouse engineers, while
ing, and to the right are two viewrs of finished machined
blades.
Stationary Reaction Low Pressure Blades of
Manganese Bronze.
A process which lends itself well to the fabrication
of large section, low pressure, stationary blades where
taper, twist and in some instances where a dividing
partition for multiple exhaust are required consists of
casting such blades in manganese bronze and grinding
the surfaces to the required limits of shape and section
thickness. The material has demonstrated its
fitness for the purpose and the process has been
worked out with entire satisfaction.