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Maintaining open gear drives

Production equipment using open gear drive units in the mining and aggregate industries, as well as in many large manufacturing and processing plants are generally the most difficult to service, maintain and properly lubricate.


June 30, 2011
Kathy Smith

Production equipment using open gear drive units in the mining and aggregate industries, as well as in many large manufacturing and processing plants are generally the most difficult to service, maintain and properly lubricate.

Kevin Ray, sales manager for grease and specialty products for Fuchs Lubricants Canada Ltd. in Cambridge, Ont., addressed open gear issues in a recent presentation to the Hamilton Section of the Society of Tribologists and Lubrication Engineers (STLE).

He said lubricants for open gear drives must exhibit a low wear rate, good sprayability and pumpability, low dust attraction, corrosion protection, suitable flushing behaviour, good adhesion to metal surfaces, extreme load carrying capability, good dry running properties and shock absorbing capability: all of that, plus they should have a minimal environmental impact and a high-viscosity range.

To satisfy these many requirements, use grease, oil or graphite. Greases are contained in thickener systems, light-coloured oil is an option, and graphite is a solid lubricant with a certain crystal structure. Your choice depends on the application and on whether the open gear unit is indoors or outdoors.

Grease is preferred in many cases, but it may build up in gear housings. Light-coloured oil lubes have lower disposal costs, but fluids cannot be filtered again. However, existing spray systems can use sprayable fluids, saving some money.

When selecting an open gear lubricant, consider tooth flank temperature and gear condition, such as pre-damaged gear flanks. Specific loads and circumferential acceleration also play a decisive role. Misalignment can cause a temperature variance of up to 10 degrees C across gear tooth faces.

The amount of lubricant used is important. Of all open gear problems, 18% can be directly attributed to incorrect or insufficient lubrication. And the need to adjust lubricant amounts is directly related to gear wear. Wear begins early and moderate wear occurs all the time. Appropriate quantity and frequency of lubrication must be scheduled to slow down normal gear wear and compensate for it.

Examples of gear damage that can be mitigated by proper lubrication are micropitting, progressive or destructive pitting, severe scoring, and plastic deformation caused by high temperatures.

Smoothing out pitting and grinding rectifies damage. To detect gear damage, monitor vibrations and tooth flank temperatures, and take digital photographs of running conditions.