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Motion Control Resources

Troubleshooting Tips: Lubrication - page 3

by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association

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Troubleshooting Tips: Lubrication - page 3

The most critical function performed by lubricants is to extend equipment service life. The important objectives accomplished by lubricants include: reduction of friction and wear, corrosion prevention, reduction of operating noise, improvement in heat transfer, and removal of foreign or wear particles from the critical contact areas of the gear tooth surfaces.

—I. D.

What can a poor choice of lubricant due to make a system vulnerable to failure (e.g. premature burnout, seizing, etc.)?  

At the fundamental level, the incorrect lubricant will not properly separate and protect metal surfaces, leading to metal-to-metal contact and accelerated wear. This will in turn lead to higher friction, higher temperatures, metal removal, loss of clearances, and ultimately shortened equipment life/failure.

— T. S.

The wrong choice of lubricant or means of introducing the lubricant will almost certainly result in premature failure. I feel that the use of the wrong viscosity or type of lubricant is secondary to not getting sufficient lubricant to where it is needed. Even a lot of the wrong lube will be better than not enough of the correct stuff. There are gravity effects, as well as aerodynamic effects, like air pressure in rotating machinery that should be considered. For example, in high speed gear drives, the oil is introduced on the exit side of the mesh instead of the more traditional closing mesh side. In this application, oil sprayed into the closing mesh would have to be done at high pressure to overcome the air pressure on the closing side of the meshing gears. On the exiting side of the mesh a vacuum is created that will actually suck the oil into the area. There is also needs to be consideration for draining the excess oil with gears operating at very high speed. There is also a practical limit to the pitch line velocity of gears dipping in oil baths for splash lube applications. Gears rotating at high speeds will churn oil into foam, which doesn’t lubricate very well.

—J. C.

A poorly selected lubricant can have a catastrophic effect on performance. For instance, selecting an oil with too low of a viscosity would lead to boundary friction (insufficient lubricating film) that would generate heat, excessive wear, and eventually failure. Even selecting a lubricant that is incompatible with sealing materials can lead to leakage and lubricant starvation (wear/failure). A grease that is incompatible with an existing grease may "de-gel" which reduces the ability of the mixed thickeners to retain the oil. This would result in excessive oil loss and could lead to immediate failure.

—S. M.

Gear lubricants are formulated and applied to prevent premature component failure, assure reliable operation, reduce operating cost, and increase service life.

—I. D.

Most new and rebuilt equipment is shipped without oil. A gearbox, for example, is not an approved container for shipment of lubricants. I have seen several examples of brand new and rebuilt equipment being put into service without being filled with oil prior to starting them. One of the worst was a scrap chopper rebuild in an aluminum mill that was in service about 8 hours without oil. Attached are some photos of the gears that melted from the excessive heat. This error did several thousand dollars’ worth of damage to the scrap chopper gearbox itself, as well as cost the owner several hours of unnecessary downtime.

—J. C.

What do you wish that your customers knew about lubricants that they typically don't? 

Just how important lubrication is to their equipment  and that all lubricants are not created equal . The phrase "lifeblood of the equipment" really does hold true. Proper lubrication means the proper lubricant in the proper place at the proper time and in the proper amount. If this task can be mastered, the longest life and most efficient operation of the equipment will occur.

— T. S.

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