Choosing the right grease
Steel mills, food manufacturing facilities and pulp and paper plants are a just a few industries well known for their high temperature operating environments. As a result, operators require lubricants including greases that are specifically designed to ensure consistent performance and longevity in such conditions.
Choosing the right grease can play an essential role in helping to protect equipment and ensuring a trouble-free operation. However, in selecting a grease which will help to maximize equipment protection and increase productivity, it is vital to not only consider the quality and performance of a product, but also the requirements and challenges of the specific application.
Operations that function at extreme temperatures and under intense pressure pose a number of lubrication challenges which can only be met by technology that is specifically designed to meet such requirements. Factors such as base oil type, viscosity, thickener type, stability of the composition and operating temperature must all be considered in order to ensure that the most appropriate grease is selected.
Grease Formulation
It is important for maintenance professionals to understand how greases are formulated in order to ensure that they select a grease which will deliver the performance required to protect their equipment in the long term.
A simple way to think of grease is to consider it like a sponge soaked with lubricating oil.
Upon application of external stresses, such as heavy loads or high temperatures, the thickener (sponge) releases the oil to lubricate the mechanical parts. When the stress is removed, the thickener re-absorbs a portion of the released oil for later use.
Typically, greases are applied to mechanisms in which a lubricant cannot stay in position, or re-lubrication is infrequent, difficult, or simply not economical. A few examples include - drive shaft couplings, universal joints and fan shaft bearings.
Selecting a Grease for High Temperature Operations
In extreme temperature applications, there is a risk that a grease will perform poorly due to degradation resulting from thickener and base oil oxidation, or due to the loss of base oil from grease bleed and evaporation. One of the driving factors that can limit the ability of a grease to provide lubrication at higher temperatures is proper viscosity and oxidative resistance. Oxidation is a chemical reaction that occurs between oxygen and the in-service lubricant, and is accelerated in high temperatures.
A grease’s oxidation rate generally doubles with every 15°C rise in temperature above 60°C. This rule-of-thumb varies, based on the type of thickener used in the grease, and for soap thickeners, the amount of metal contained in the structure (lithium, calcium, aluminum, etc).
Typically, greases with synthetic base oils can provide a wider operating temperature range than conventional, mineral-based greases. For example, the Mobil SHC Polyrex™ Series is a range of high performance, synthetic bearing greases that uses advanced polyurea thickener technology in order to achieve excellent high temperature performance up to 170°C.
Even at these extreme temperatures, the polyurea thickener technology resists oxidation and loss of structural stability allowing re-lubrication intervals to be extended while maintaining equipment protection when compared to competitor mineral oils. This carefully balanced combination of thickener, base oils, and additives yields a grease with excellent load carrying capabilities and rust protection.
Boosting Productivity with Synthetics
One company to benefit from the use of advanced greases in a high temperature environment is an aluminum plant in Germany.
To protect wheel bearings, the plant had been using a grease with a base oil viscosity of 100cSt and had been experiencing routine bearing failures and significant mechanical wear and tear due to lubricant degradation as a result of excessive heat. In addition, the plant was also incurring high lubricant costs.
A team of ExxonMobil technical experts were asked by the plant’s maintenance team to help provide a comprehensive analysis of the plant’s operations and equipment maintenance practices to help address the issues. Following the audit, the ExxonMobil team made specific recommendations to convert the lubricant protecting the wheel bearings to Mobil SHC Polyrex 462, in addition to implementing a best practice programme to help increase re-greasing intervals.
The higher base oil viscosity offered by Mobil SHC Polyrex 462 provided the machinery with improved levels of protection, resulting in a noticeable reduction in component damage. The introduction of Mobil SHC Polyrex led to an overall improvement in performance and resulted in an annual saving of €39,000*.
With ongoing developments in machinery to increase output, and the high ambient temperatures of many industrial sectors, lubricants that can operate effectively in extreme conditions will enable companies to build a competitive advantage into their operations by reducing downtime and increasing productivity.
For more information about ExxonMobil’s range of Mobil-branded lubricants and services, please contact the ExxonMobil Lubricants Technical Help Desk on TechDeskEurope@exxonmobil.com or +420 221 456 426, or visit Mobil Industrial Lubricants' website.
*This Proof of Performance is based on the experience of a single customer. Actual results can vary depending upon the type of equipment used and its maintenance, operating conditions and environment, and any prior lubricant used.
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