Well-Oiled Machines

Lubrication problems are often described in terms of not enough grease or oil. And sometimes that is the case, as lubrication leaches out or is squeezed out of linear bearings, leaving them susceptible to metal-on-metal wear. There is a flip side to the lubrication issue. Maintenance workers, with grease guns in hand, often over-lubricate linear bearings, potentially blowing out seals and introducing oil into the environment. And lubrication also qualifies as a contaminant. So over-lubed bearings can also worsen the contamination problem or force machine builders to opt for bellows or physical covers.

Getting just the right amount of lube into a linear bearing at the right interval can be tricky because it depends on app lication-specific factors such as the type of bearing and the duty cycle. The application’s sensitivity to oil contamination comes into play, too, with sensitive industries demanding lighter lubrication schedules.

There are ways to make sure linear bearings stay properly lubricated through out with little intervention on the part of maintenance workers. On the expensive end are automatic greasing sys tems. These systems are a legacy of the linear way systems used in the machine tool industry. The auto-greaser was crucial for maintaining the film of oil that separates a linear way’s bearing surfaces.

Some of these expensive auto-lubrication systems have made their way into applications that employ more modern linear guides, and they can be a valid way to get the lube levels right while reducing the maintenance burden. But aside from their cost, auto-greasing systems can introduce unacceptable levels of contaminants into the factory environment, which, again, will create problems in cleanroom and other sensitive manufacturing operations.

A lower-cost, cleaner alternative to automated lubrication exists in the form of self-lubricating wipers that integrate into the linear bearing’s carriage. These provide lubrication for two million cycles before they need to be refreshed, and they cost a fraction of what PLCcontroll ed auto-greasing systems cost.

The very idea that automatic lubrication is the only way to achieve optimal lubrication is somewhat outdated. Some linear guides, such as those based on recirculating balls, do require regular lubrication in all applications. But bearings based on sealed rolling elements may not need much, or any, external lubrication in many applications.

This article was contributed by Rollon Corporation, Hackettstown, NJ. For more information, visit http://info.hotims.com/40436-322.

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