FED-STD-791D
Method 6517
September 30, 1986
HIGH-TEMPERATURE GEAR LOAD-CARRYING CAPACITY OF LUBRICATING
OILS
1. SCOPE
1.1 This method describes a procedure for determining the gear load-carrying
capacity of lubricating oils at controlled test gear temperatures of 220C (428F) through
371C (700F).
2. SUMMARY
2.1 The method consists of subjecting the lubricant to a series of controlled
temperature tests at increasing gear-tooth loads using a set of special spur test gears.
Each tooth of one of the gears is examined to determine the working area scuffed after
each load step. The load-carrying capacity of the lubricant is determined by the load, in
pounds per inch of tooth width, required to produce 22.5% average scuff of the total
working area of the examined test gear.
3. SAMPLE SIZE
3.1 Approximately 2 L of test oil.
4. REFERENCES, STANDARDS, AND APPARATUS
4.1 Test unit. The apparatus in this method is the WADD gear machine, or
equivalent, available from Erdco Engineering Corp., Addison, IL. This apparatus
consists of a WADD gear machine adapted to a modified Erdco universal tester drive
stand, a support and load-oil system, a test-oil system, a radiometer, and induction heater,
and the necessary instruments and controls.
4.1.1 WADD gear machine. The WADD gear machine operates on the same
principle as the Ryder gear machine, the so-called "four-square" principle. However,
improvements in material and design permit its operation at test gear temperatures up to
371C (700F). Double-row roller bearings are used to support the two parallel shafts,
and screw-thread type nonrubbing seals are used to separate the test oil and support oil
chambers. As shown on Figure 1, the two parallel shafts (P and Q) are connected by two
slave gears (R and S) and two test gears (T and U) to form a "Square" so that the power
required to operate the machine is only that required to overcome the friction losses in the
gears and bearings. The slave gears are helical gears and are made as integral parts of the
two shafts; the test gears are spur gears and are replaceable. Load on the test gears is
obtained through the application of a controlled oil pressure in the load chamber (X),
which causes an axial movement of one shaft relative to the other. A torsional load is
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