FED-STD-791D
Method 6508.2
September 30, 1944
LOAD CARRYING CAPACITY OF LUBRICATING OILS
(Ryder Gear Machine)
1. SCOPE
1.1 This method describes a procedure for determining the load carrying ability
of lubricating oils with reference to gears.
2. SUMMARY
2.1 The test consists of incremental increasing the pressure between gears to
measure the resultant scuffing. The ability of the test oil to impair scuffing is measured
by the maximum pressure when operating at 10,000 rpm.
3. SAMPLE SIZE
3.1 Approximately 2 L of test oil.
4. REFERENCES, STANDARDS, AND APPARATUS
4.1 Test unit. The apparatus used in this method is the Ryder gear-Erdco
universal tester (Figure l), and test gears available from Erdco Engineering Corp.,
Addison, Ill. This tester comprises a special test machine known as the Ryder gear
machine, a drive system, a support and load oil system, a test oil system, and the
necessary instruments and controls. Figure 2 illustrates the control console.
4.1.1 Ryder gear machine. The Ryder gear machine operates on the so called
"four square" principle. As shown in Figure 3, 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 gear and bearings. The slave gears are helical gears made integral to
the shafts, (see Figure 4). The replaceable test gears are spur gears, shown installed on
the shaft in Figure 5. Load on the test gears is obtained through the application of a
controlled oil pressure in two load chambers (Figure 3, Y and Z) which causes an axial
movement of one shaft relative to the other. Because of the integral helical slave gears, a
torsional load is thus applied on the shafts thereby loading the test gears. The relation
between the tooth load on the test gears and the load oil pressure is 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 6260 steel,
case hardened and ground, having 28 teeth, 8.88-cm (3.5-in) pitch diameter, 8 diametral
pitch, 22.5 pressure angle, and zero tip relief. Each set of test gears comprises gears of
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