Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 511-515 Mochida, I.; Matsuoka, H.; Koral, Y.; FuJltsu. H.; Takeshlta, K. fuel 1982, in press. Mochida, I.; Takeshlta, Y.; Korai, Y.; Fujltsu, H.; Takeshlta, K. I n d . Eng. Chem. Prod. Res. Dev. 1982, 21, 315. Neavel, R. C. Fuel 1978, 55, 237. Takeuchi, C.; Nakamura, M.; Shiroto, Y. Prepr. Dlv. Pet. Chem., Am.
511
Chem. SOC. 1979, 24, 666. Yen, T. F. Prepr. Dlv. Pet. Chem., Am. Chem. SOC. 1972, 17, 103.
Received for reuiew July 23, 1981 Accepted March 4, 1982
Bench, Bearing, and Engine Tests on a Polyphenyl Thioether Lubricant Frank S. Clark Monsanto Industrial Chemicals Company, Si. Louls, Mlssouri 63167
This paper describes some advanced testing of a polyphenyl thioether jet engine lubricant. Fatigue tests lasting 2000 h showed that the thioether had a longer B-10 fatigue life at 149 "C than hindered esters at 121 "C. This synthetic fluid also completed a 1004 run in a commercial jet engine without mishap under conditions which caused frequent fires with an ester oil. Finally, in bearing tests on custom bearings at bulk temperatures of 260 "C, lubrication additives extended bearing life from about 1 h to over 90 h in three instances. However, wear was not totally eliminated, and the bearings were not as clean as those run on esters at lower temperatures. A following section gives typical results from two bench tests used on this fluid: a slow-speed ball-ondisk wear test and a thin-film oxidation test.
Introduction The past century has witnessed the invention and development of many new synthetic lubricants. This research mainly sought products with unique operational properties. The resulting fluids have outperformed petroleum oils in such important areas as fire resistance, highand low-temperature stability, and radiation stability. Some of the chemical classes used included phosphate esters, polyacid esters, hindered esters, fluorocarbons, silicones, and polyphenyl ethers. The polyphenyl ethers consist of benzene rings joined by oxygen atoms. Substitution of sulfur for the connecting oxygen atom of the ethers gives polyphenyl thioethers, a class of lubricants previously designated as C-ethers or modified polyphenyl ethers (McHugh and Stark, 1966). Figure 1 shows the structures of these fluids. The base fluid described in this article, a polyphenyl thioether, contains a small amount of oxyether linkages. Table I compares some properties of this polyphenyl thioether with a polyphenyl ether and a formulated hindered ester. Like many other aromatic chemicals, the oxy and thioethers possess inherent thermal and oxidative stability, i.e., great inertness. Thus, the oxyethers survive oxidation-corrosion tests up to 316 "C. The thioethers survive such tests up to 260 "C and perform very well in the absence of copper up to 316 "C. These aromatics also possess higher autoignition temperatures than aliphatic fluids. This property together with their stability allows their use at temperatures well above those of nonaromatic fluids, for example in high-temperature jet engines whose temperature environments would prove destructive to other lubricants. As a rule, the aromatics have lower viscosities and higher pour points than hindered esters. The thioether oil has a lower pour point than the oxyether partly because of its lower number of rings. In this paper we will summarize some advanced testing of the thioether fluid of Table I: specifically, ten 2000-h bearing fatigue tests; a 100-h run in a commercial jet engine; and tests on custom bearings at 260 OC bulk fluid temperature. The results demonstrated some of the 0196-4321/82/1221-0511$01.25/0
aforementioned properties and showed some advantages for the aromatic fluid. In conclusion, there is a brief outline of some bench screening methods used on this product. Two Thousand Hour Bearing Fatigue Tests (Miner, 1970) The entire test rig consisted of ten Pratt & Whitney bearings, specifically M5O-CVM JT3 number 4 size bearings. These are made of M50 races and silvered AMS 6415 steel retainers. Figure 2 shows a simplified schematic of one bearing test stand. Table I1 gives the test temperatures for the thioether lubricant. For comparison, it includes temperatures on six ester oils, all with operating engine experience. The temperatures for the thioether averaged about 28 "C higher, but speed and loads were equal for all tests. After 2000 h, eight of ten bearings survived the test without fatigue failure; two other bearings failed at 1084 and 1863 h, respectively. The calculated B-10 life for the thioether (1300 h) exceeded that of the most fully tested type I1 ester (1050 h). Moreover, this small difference presumably would be increased were it possible to factor the temperature difference into the results. These results confirmed superior fatigue life for the thioether first predicted by various bench tests (rolling contact, one-ball, and Ryder gear) on M50 steel. The bulk properties of the used fluid reflected the relatively mild temperatures of this test. The increases in total acid number and 37.8 OC viscosity amounted to only 0.02 mg KOH/g and 2%, respectively. One Hundred Hour Engine Test The test engine, a commercial engine consisting of two thrust bearings and six roller bearings, ran at temperatures roughly those of Table 11, that is, about 25 "C above those often used for esters. Repeated fires took place with the original ester test oil forcing replacement of the ester with the C-ether. This led to trouble-free lubrication for the next 100 h. (Actually, two thioether blends were used differing only in their additive packages. The first ran for about 30 h, the second for ca. 70 h.) 0 1982 American Chemical Society
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Table I. Properties of Base Stocks poly phenyl ether (5P4E)
C-ether viscosity, cSt 37.8 "C 98.9 "C 260 "C thermal decomposition, "C autoignition temperature, "C pour point, "C evaporation loss, % (204 "C, 6.5 h ) surface tension, dyn/cm a t 23.9 "C isotherm secant bulk modulus, psi a t 37.8"C
28 5.5
25.2 4.1 0.81 367 504 -29 10
363 13.1 1.2 453 559 +5
