Lubrication starvation will create elevated heating, accelerated wear, and increased buildup of contaminants.
A constant and sufficient level of lubrication is required to prevent lubrication starvation. When lubrication starvation occurs the fluid film is no longer able to ensure full separation of moving surfaces, which leads to excessive heat and friction, wear, noise, vibration and subsequently seizing of moving mechanical parts.
Adequate thickness of the hydrodynamic film between bearing surfaces is required for elastohydrodynamic boundary lubrication under pressure to occur. The primary effect of starvation is that it inhibits the generation of this fluid pressure. Fluid film thickness is primarily created in the inlet region. A starved inlet region inhibits the pressure buildup and reduces the central film thickness. Variables that can affect the lubricant flow in the inlet region are related to speed, viscosity, and design. Therefore the minimum required film thickness is relevant to the inlet region.
Soap breakdown in grease lubricated bearings will result in oil bleed out, thus reducing the available lubrication in inlet regions. The degree of starvation increases with increasing rolling speed, base oil viscosity and thickener in grease lubricated applications. When temperatures begin to rise increased temperatures accelerates grease dry-out.
Some high speed gear designs can also operate under elastohydrodynamic boundary lubrication. Without a minimum film surface excessive wear and seizing of gear components will also occur.
A constant and adequate flow are critical factors, along with proper viscosity and additive formulation, to ensure a proper fluid film.
Lubrication starvation can be attributed to factors other than inlet flow design. These can be restricted oil supply or pathways, dry starts, low oil level in sumps, oil foaming, wrong viscosity, worn or improperly operating circulating pumps.
Since lubrication starvation can occur in systems that experience circulating lubricants going back and forth from low pressure areas to high pressure areas, cavitation can be a symptom of lubrication starvation occurring in the system.
Monitoring with ultrasound instrumentation and temperature sensors are tools that can monitor and detect the occurrence of lubrication starvation in mechanical components. This can complement testing of the lubricant for assessment of lubricant degradation, as well as wear and increased contaminants.
ALS can work with your asset reliability team and lubricant supplier to ensure a testing program that will optimize early detection and sign of problems such as lubrication starvation.
For more information please contact ALS Tribology laboratory or any of our regional testing labs to meet your oil, coolant or fuel testing needs.
David Doyle, CLS, OMA I, OMA II
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