FED-STD-791D
thus applied upon the shafts due to the helical slave gears, thereby loading the test gears.
The relation between the tooth load on the test gears and the load-oil pressure can be
obtained by arithmetic calculation, calibration, or both. Arithmetic calculation is used
herein.
4.1.2 Test gears. The test gears are special spur gears, made of AMS 6475 steel,
nitrided and ground, having 28 teeth, 8.89-cm (3.5-in) pitch diameter, 8 diametral pitch,
22.5 pressure angle,0.0000- to 0.00025-cm (0.000- to 0.0001-in) tip relief, and 0.0279-
to 0.0356-cm (0.011- to 0.014-in) backlash. (Sier-Bath Gear Co., Inc., North Bergen,
N.J., 07047, part No. SB-19293-AN, narrow gear; SB-19469-AN, wide gear; or
equivalent.)
NOTE 1:
The working area of the gear teeth is finish ground to the required profile
after nitriding to remove the "white-layer" formed during the nitriding
process.
Each set of test gears comprises gears of two different widths. The narrow
NOTE 2:
test gear is used for rating purposes. The mating gear is wider in order to
maintain a constant contact width between the two gears at different tooth
loads. Both sides of the test gears are used for testing. The "A" side of
the gears refers to the side obtained by installing the test gears with the
serial numbers facing the end cover. The "B" side is obtained by reversing
the gears (serial numbers facing away from the end cover). Test gears can
be used only once on each side and then discarded.
4.1.2.1 The entire web of each side of the narrow test gear must be electroplated
with black chromium. The black chromium rings thus formed, extending from the root
diameter of the gear teeth approximately 0.64 cm (1/4 in) toward the center of the gear,
provides a continuous black body radiation surface for accurate test gear temperature
measurement during test.
4.1.3 Drive system. An Erdco universal drive system, or equivalent, is used to
drive the WADD gear machine. A 50-hp induction motor drives the machine through a
variable speed dynamatic coupling, a step-up gearbox, and an adapter block to which the
WADD gear machine is attached. The only modification required to the drive system is
the relocation of the mounting studs in the end of the adapter block to match the holes in
the WADD gear machine mounting flange. The test gear speed is controlled by adjusting
the field excitation of the dynamatic coupling. By this means accurate speed control can
be obtained at the specified test speed of 10,000 rpm.
4.1.4 Support and load-oil system. The support and load-oil system used with the
WADD gear machine serves two purposes: To provide lubrication to all necessary parts
except the test gears, and to supply load-oil pressure to the load chamber, and thus, the
application of load to the test gears. A schematic dia-gram of the support and load-oil
system is shown on Figure 2.
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