Machinery Lubrication

Machinery Lubrication September-October 2021

Machinery Lubrication magazine published by Noria Corporation

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30 | September - October 2021 | www . machinerylubrication.com Best Practices to Control Varnish in High-Volume Oil-Circulating Systems Kristine Mikulan | Schroeder Industries/HYDAC VARNISH In the context of lubricating and hydraulic systems, the term "varnish" is used to refer to gel- or resin-like or solid varnish-like deposits that form in fluid systems. Varnish causes: • Elevated turbine bearing tempera- ture due to increased friction in the bearing • Functional problems with the control valve due to increasing deposits in the gap between the piston and the housing • Cooling problems due to the varnish impeding heat transfer • Short filter lifetimes The cause of these lacquer- like varnish deposits is oil aging and becoming damaged at the molecular level. In most cases, however, the above malfunctions are not correctly attributed to the real cause. is results in ineffective (and often very expen- sive) repair work. Causes of the Increase in Varnish Formation Today, system operators are confronted with the fact that the base oils used are changing or have already been changed. While in the past, an oil was produced exclusively in crude oil distillation (Group I oils), modern processes are used to reduce the content of substances hazardous to health (e.g., aromatics). e change in the oil production process has resulted in base oils with a lower content of unsat- urated/polar hydrocarbons (Groups II, II+, and III). With Group 1 base oils being polar, polar substances were more easily dissolved. e changes in oil production have led to an oil with less polarity; therefore, a reduction of the amount of polar substances that can be dissolved in the oil is now being seen in hydraulic oil systems. Varnish is an incredibly polar substance that is no longer easily dissolved in the newer base stocks. Polar substances tend to dissolve more readily in polar substances. If the proportion of polar hydrocarbons in the oil is reduced, oil aging prod- ucts (more commonly referred to as "Varnish is an incredibly polar substance that is no longer easily dissolved in the newer base stocks."

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