An important application of grease is to provide lubrication in enclosed gearboxes.Motor operated valves is one of these applications.The operation of these valves is typically periodic or standby service.The failure mechanism for greases in this service may be due to a process other than mechanical working of the grease.The monitoring of chemical changes within the grease is likely an important precursor to the effectiveness of the grease and will be considered in this paper.This paper presents the results of research performed to evaluate the change in anti-oxidant chemistry of the greases.The components in a grease are predominantly a base fluid containing specifically designed additives,like antioxidants,corrosion inhibitors and metal de-activators and an agent to thicken the oil into a grease.The anti-oxidant is primarily responsible for protecting the base fluid from oxidative degradation.Typical antioxidant peaks measured in testing come from zinc dialkyl dithio phosphate,phenolic and amine type of antioxidants.Greases were laboratory aged to simulate a service condition of minimal mechanical action with thermal stress.These samples along with a number of grease samples taken from in-service machines were analyzed for their physico-chemical characteristics using both RULER and FTIR.The results showed that for each evaluated method,the antioxidant capacity depleted with time and that the rate of depletion varied depending on type of greases.It is concluded that both technologies can be used to determine chemical changes and/or the change of antioxidant concentration in greases.The relative effectiveness and degree of difficulty in use for these technologies varied with grease type tested.
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