FED-STD-791D
6.4.6 Data sheets. The suggested data sheets are shown in Figures 11 and 12.
Note that the gear teeth inspection data sheet (Figure 12) has provision for computing the
average percent of tooth area scuffed. This sheet also contains a column for entering the
results obtained from the examination of the optional photographic records taken at a
load giving approximately 22.5% scuff.
6.4.7 Determination of load carrying ability.
1. Plot the average percent of tooth area scuffed for the narrow test gear versus the
load oil pressure. The use of a semilogarithmic paper is recommended for this
purpose. Figure 13 is a suggested plot and calculations sheet, showing typical
results from tests on both sides of a test gear.
2. Determine from the plotted curve the load oil pressure at which the average
percent of tooth area scuffed is 22.5%. In Figure 13, this condition is
represented by point X for "A" side, and point Y for "B" side of the test gear.
3. Calculate load carrying ability (see 7.2).
6.4.8 Relative rating procedure. This procedure consists of reporting the load
carrying ability of an oil under test as a percentage of the load carrying ability of a
standard reference oil, both ratings being determined by the procedure outlined in 6.4.7.
Details of this comparative procedure are given in the following paragraphs.
NOTE 9:
Standard reference oil can be obtained from Southwest Research Institute,
P.O. Drawer 28510, San Antonio, TX 78228.
6.4.9 Determination of the average rating on standard Ryder gear test reference
oil.
1.
For a new rig, at least eight determinations (four gears) shall be made,
according to the foregoing procedure, on the standard reference oil. If the
high and low values obtained do not differ by more than 1400 N/cm (800
lb/in) the average is taken as the reference oil rating. If the high and low
values differ by more than 1400 N/cm (800 lb/in) four additional
determinations (two gears) shall be made and the average of the 12
determinations taken as the reference oil rating.
2.
After a major overhaul to a rig such as a bearing or shaft replacement, four
determinations (two gears) shall be made on the standard reference oil. If the
average of these ratings does not differ from the average obtained prior to the
overhaul by more than 525 N/cm (300 lb/in) and the high and low values
obtained do not differ by more than 1400 N/cm (800 lb/in) this average will
be taken as the reference oil rating. If the ratings obtained do not meet the
above criteria, four additional determinations (two gears) shall be made and
the average of all eight determinations taken as the reference oil rating.
3.
At least two determinations (one gear) shall be made on the standard
reference oil for each 20 determinations made on oils under test. The
reference oil rating is a progressive rating in that it will consist of the average
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