The use of pour point depressants to lower the pour point of engine oils is well known in the literature and the types of pour points depressants are varied. Typically these highly viscous or solid polymers are delivered in oils or some other type of solvent. They are extremely effective in modifying the pour point of oils with treat rates generally less than 0.5 per cent by weight. However, the amount of pour point depressant used will vary according to the base oil type, concentration of the polymer in the oil, the type of polymer and the degree of pour point correction desired. Greases are also required to operate at extreme temperatures and due to their rheology, low temperatures can have a profound effect on their ability to properly function. Greases that meet the NLGI GC/LB specification for the D4693 (Standard Test Method for Low-Temperature Torque of Grease-Lubricated Wheel Bearings) must pass the low temperature torque test at -40°C. The majority of manufactured greases are made with mineral oils that are thickened with lithium 12-hydroxystearate or lithium stearate and they may not pass this test. One method to improve the low temperature properties for these greases is to use synthetic polyalphaolefin (PAO) base stocks. However, the disadvantage of using PAOs is they add cost to the finished grease. Typically, paraffinic mineral oils are the least expensive of oils to use, and therefore, are preferred for their cost savings, but they aggravate this low temperature problem. There have been questions whether the addition of pour point depressants to lithium stearate type greases, which contain high VI paraffinic base oils, would improve the low temperature performance of the grease while still maintaining its cost effectiveness by using the paraffinic oil. This paper will present the results of our study on the effects that three types of pour point depressants had on paraffinic and naphthenic oil based greases when they were evaluated in a Low Temperature Oscillation Rheometry Test. The results will show that the pour point depressant has no effect on the low temperature properties of paraffinic oil based greases regardless of grease grade. Changing from a paraffinic to naphthenic base oil had more effect on the low temperature properties of the finished grease than by the addition of pour point depressants.
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