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Issues to Consider when Operating a Motor in a Vacuum

07 Dec 2015
Hurley Gill

Vacuum ChamberQuestion: I need to operate a servo motor in a vacuum, what are some considerations?

Answer: In a word? Outgassing. You might think that proper motor sizing* is a big issue, it always is, however if you can't conform to the other process requirements, there is no point to attempting to size the motor.

The biggest issue for any given motor selection to be run in a given vacuum for a specific process is the outgassing requirement, or rather, the avoidance of materials that would affect the process being performed and/or the life of the motor.

Understanding the process requirements is the main key: level-of-vacuum, outgassing specifications and limitations, as well as expectations for the application (process and motor life.)

Outgassing example: Teflon lead-wire insulation has low outgassing properties but if used in a radiation environment will not survive as well as some other materials. In such case, Tefzel insulation may be a better material for the application. (It may not be better, you'll need to review its material information and compare it to other products.)

Or you may have bearing grease that has a low outgassing property that is good in a radiation environment, but it is not compatible for a typical semi-conductor manufacturing process.

Utilizing NASA class A requirements is a very good base-line from which to communicate between the OEM, customer, and motor's manufacturer. This standard can set the stage for 'same as except' changes for the individual application.

NASA's standard is: { < 1.0% TML (total mass loss), < 0.1% CVCM (collected volatile condensable materials)}

You will also have to consider all of the other materials and their potential effect on the application in the environment, whether of an organic source or not: varnishes, adhesives, coatings, resins, and solvents.

…..And don't forget the glue holding the nameplate on!

* Oh, and a quick word on motor sizing: In regard to proper motor sizing, calculated RMS torque requirements of the application for normal motor operation in standard atmosphere (like in a manufacturing plant) have been found to require a motor with a capability of 2.6-3 times that calculated RMS torque value when operating in a vacuum. One could compare this with the difference of current carrying capability of copper in normal atmosphere versus the current carrying capability of copper within the application vacuum.

About the Author

Hurley Gill

Hurley Gill
Hurley Gill is a 1978 Engineering Graduate of Virginia Tech who has been engaged in the motion control industry since 1980. Hurley is often called upon to deal with the toughest of applications for Kollmorgen. He can be reached at hurley.gill@kollmorgen.com. You can also connect with this author at Google+

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