Monitoring for varnish buildup in your gearbox is important for the life of your unit. Varnish is a thin, hard/ sticky, oil insoluble contaminant found in the oil that can deposit or “plate out” on the internal components. This can result in loss of operating clearance for moving parts with tight tolerances and may lead to sticking, seizing or other malfunctions. Varnish is often caused by heat related stress on the oil. Varnish is a cyclical in a sense that the more varnish that forms, the more thermal stress caused, the more varnish produced.

Root Causes of Varnish

The root causes of varnish include:

• Mechanical: shearing of oil molecules between two surfaces
• Chemical: Oxidation may lead to the formation of decomposition products that include varnish precursors
• Thermal: oxidation, nitration, and varnish formation rates all increase with thermal stress

A huge negative effect of varnish is that it reduces your clearances and effectiveness of your hydrodynamic lubrication. This is obviously a big issue for things like hydraulics with very tight clearances, but in gear boxes this can pose a problem as well.

How varnish Forms

Your gearbox is an essential component in your mechanical system. To ensure that your gearbox runs as smooth as possible, oil plays an even more crucial part in the system. This reduces friction, dissipates heat, and prevents abnormal wear from occurring. Due to high temperatures, oil degradation, and contaminants, varnish can occur within your gearbox.

1. High temperatures: thermal stress contributes to the formation of varnish. With higher temperatures, the oxidation rate increases and increases your varnish rate. It is important to not only monitor the varnish potential of your system, but also tests like oxidation. You can also use other temperature monitoring techniques such as sensors or infrared to make sure your system is running at an ideal temperature.
2. Oil degradation: the products of oil degradation overtime due to oxidation, nitration, and mechanical stress create by-products that contribute to the formation of varnish.
3. Contaminants: particles such as dirt, soot and water can act as catalysts for the formation of varnish.

negative effects of varnish

Your gearbox can experience negative effects from the buildup of varnish.

1. Reduced lubrication: varnish deposits hinder your lubricant’s ability to create the proper hydrodynamic film on your gears, which increases friction and wear.
2. Poor heat dissipation: varnish can act as an insulator for heat, causing oil degradation to increase.
3. Increased noise and vibration: Varnish deposits can cause irregular operation in the meshing of the gears resulting increased noise and vibration. Listen to your machines!
4. Sticking and seizing: if your components seem sluggish, stick or seize, you need to rule out varnish being the cause.

preventing varnish formation

1. Put a routine visual inspection and oil analysis program in place. Our PLANT4 test package is built to monitor for varnish and include the Varnish Potential test.
2. Adjusting or optimizing your oil change intervals.
3. Modifying your maintenance schedule to reduce the chance of varnish formation based on the run time of the specific component.
4. Use a side-stream filtration system for components that use the same oil for long periods of time. (e.g. large hydraulic systems and turbines).
5. Monitor operating temperature to reduce thermal stress and oxidization.

Check out our Podcast

Varnish is something that you can and should be monitoring. As industry is producing equipment that runs at hotter temperatures and higher pressures, varnish is becoming more prevalent than ever before. Performing routine oil analysis tests (such as ICP, FITR for oxidation, TAN and MPC) can give you the insights you need to investigate the potential for varnish in your system.
 
Contact us today to learn more about the tests available to monitor varnish. You can also learn more about varnish in lube oil by listening to our Fluid Life Unfiltered podcast.