FED-STD-791D
Method 3410.1
September 30, 1986
HIGH TEMPERATURE DEPOSIT AND OIL DEGRADATION
CHARACTERISTICS OF AVIATION TURBINE OILS
1. SCOPE
1.1 This method describes procedures used to evaluate the thermal stability
characteristics of turbojet lubricants under varying levels of severity.
2. SUMMARY
2.1 Sample of the lubricant is subjected to one of the severity levels (type 1, 1-1/2, or 2)
for a controlled number of hours. At periodic intervals during the test and at the end of test,
samples of the oil are examined for both physical and chemical changes when compared to the
sample of new oil. A visual inspection is made at the end of test of the accumulated deposits on
the bearing and bearing housing. A weighted numerical rating system is used for rating
individual areas as well as for obtaining an overall rating. Additional data on relative sludge
forming tendencies on oils are obtained by weighing a 100-mesh filter element and a 40-mesh
filter element.
3. SAMPLE SIZE
4. REFERENCES, STANDARDS AND APPARATUS
4.1 The apparatus used in this method is the Erdco high temperature bearing head
mounted on a suitable drive test stand, similar to the Erdco universal test stand. It is not
mandatory to use the "universal drive" to power the bearing. The support oil system and the test
oil system are separate units and of special design for the Erdco high temperature bearing head.
4.1.1 Erdco high temperature bearing head. The bearing head is divided inter-nally into
two main sections. The front or test section with its separate test oil system houses the
unshielded 100-mm straight roller test bearing. The temperature of the test bearing is controlled
by supplying heat to the outer race of the bearing. The outer race is secured in a bearing mount
assembly containing wound Calrod heating elements packed in aluminum oxide for even heat
distribution. The rear or support section of the bearing head houses the externally loaded, main
shaft support bearing, together with a separate oil system. The test and support sections of the
modified bearing head are separated by a screw thread seal to prevent mixing of the test and
support oil. Details covering the bearing head and screw thread seal assembly are shown in
Figure 1.
4.1.1.1 Test oil jet. A standard No. 60 drill size jet located at 12 o'clock on a 0.13335-m
(5.250-in) diameter should be used. The size of the jet should be checked with a No. 60 drill and
a visual check of axial straightness made with the drill inserted in the jet. Corrections for orifice
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