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Motion Control Resources

Troubleshooting Tips: Lubrication - page 4

Motion Control & Motor Association

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Troubleshooting Tips: Lubrication - page 4

Keeping the lubricant clean is one of the most important things that any equipment owner/operator can do to assure that the machine runs a long time. Without filtration or regular oil changes, contamination and metal particles are recirculated. These metal and dirt particles act as abrasives when caught between moving metal parts, creating fine scratches that accelerate wear. Often times these particles are larger than the film thickness of the oil, so they make contact with both metal surfaces even if the oil is sufficient to do the job.

—J. C.

The amount of lubrication is often an overlooked aspect by customers; however, it is very critical. Customers tend to think more lubrication is better, however (often times especially with grease based lubricants) too much can actually result in leakage. Conversely, not enough lubrication means increased heat and wear on the gear teeth.

—M. P.

All greases are not created equal. The characteristics that you see and feel are not likely to be the most important characteristics for an application. For instance, some customers specify a certain color, a certain consistency, or a certain thickener type. While sometimes there are valid reasons for a specific consistency of thickener type, they are not usually the most important decision factors. Base oil viscosity, shear stability, corrosion protection, thermal stability, and additives could be much more important for a particular application.

—S. M.

Gear speed is a key factor in the selection of proper oil viscosity. The pitch line velocity determines the contact time between gear teeth. High velocities are generally associated with light loads and very short contact times. For these applications, low-viscosity oils are usually adequate. In contrast, low speeds are associated with high loads and long contact times. These conditions require higher-viscosity oils.

—I. D.

The difference between oil and grease is that grease doesn’t dissipate heat as well as oil does so you end up with a slightly lower operating temperature and thus a slightly lower viscosity. In some gears that doesn’t matter but in other gears it does. If you’ve got a gearbox with an input speed of 60 RPM and an output speed of 40 RPM that does not generate any heat, use grease. If you’ve got a gearbox with a 10,000 RPM input speed, use oil.

—R.B.

What are the most common errors machine builders make when choosing a lubricant or lubricating parts?

I think that one of the most common mistakes that engineers make is not to give the lubricant enough attention at the design stage. Oftentimes they use the same lubricant that they have always used. Meanwhile, the machine may have changed or been designed for a slightly different application, but there is no consideration given to the lubricant in that application.

—J. C.

One of the more common errors is to underestimate the conditions under which the equipment could operate. Lubrication is much easier to accomplish under ideal or typical conditions, but once the equipment is experiencing temperature extremes, run under higher than expected loads, operated at different speeds, or subjected to contamination, the challenge becomes much greater.

— T. S.

The most common mistake is to only consider the lubricant at the end of the design cycle...almost as an afterthought. Subtle changes in the actual design could simplify the lubricant selection and optimize the system for the end user. Some examples are:  adding relubrication ports (in and out) which allow easy access and effective relubrication to the lube point, considering seal compatibility to allow the ideal base oil viscosity and type for the lube point, using shielded bearings where there is a high potential for grease migration,  shielding/locating the lube point away from a high heat source, and many more.

—S. M.

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