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Lube-Tech


are sheared off under the high pressure. Wear of the metal surfaces is delayed in this way. An unwanted side effect of the use of EP additives though can be an increase in long-term wear since metal is lost from the surface of materials due to the resulting metal bond. This negative side effect can be reduced by using a suitable Base Oil: The use of a Base Oil with its own very good wear properties can reduce the amount of EP additive needed without affecting the wear properties of the end product.


Figure 6 shows the characteristic wear values of an unsaturated complex ester, a saturated complex ester and an estolide measured according to DIN 51350-3.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.131 page 4 Evaporation loss


The evaporation loss of a lubricant is caused by highly volatile components but also by the thermal decomposition resulting in formation of short-chain components. The evaporation loss is measured using the Noack method at 250°C for a period of one hour under a constant flow of air. Engine oils for which the test was originally designed recorded a loss certainly in the double-digit percentage range.


Figure 7: Results of evaporation loss according to the Noack method Figure 6: Results of the characteristic wear values according to DIN 51350-3


The saturated complex ester exhibits better values than the unsaturated one due to the shorter aliphatic chains of the fatty acids. The good resistance to oxidation of this ester is also of significance in the long test runs. The additional polarity of the double bond of the unsaturated variant cannot compensate for this.


The tested estolide exhibited slightly better values in this case as well. This result is consistent with research work on the wear properties of karanja oil and the estolides extracted from it (Vetticad, et al., 2016). The authors attribute the improved wear properties to the hydrodynamic boundary film at the contact surfaces.


As Figure 7 shows the ester compounds generally exhibit lower values. The unsaturated complex ester performs far better than the saturated one. This result is based, inter alia, on the far higher flash point of the unsaturated variants. This may be due to the higher polarity because of the double bonds but also the higher molecular mass may correspondingly affect the residual amount of free monocarboxylic acid. This might also be the reason why the estolide value comes out slightly higher than that of the unsaturated complex ester. Despite this, the values for the estolide still lie well below those measured for linear ethylhexyl estolides by Cermak et al. (Cermak, et al., 2007).


Seal compatibility Elastomers are used as seals in fluid technology systems. An elastomer refers to any substance that has the ability to return to its original size and shape following deformation. External influences though


LUBE MAGAZINE NO.160 DECEMBER 2020 29


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