PDA

View Full Version : More Bearing Talk - Impressive Applications



Fasttrack
10-07-2009, 03:32 PM
Well this is pseudo-off topic, but I thought some of you might be interested. I ran across this information when I was searching for some information on a wobble-drive rotary-motion vacuum feedthrough that wasn't working properly.

So... here is the engineering challenge: Need a ball bearing that can run at 60,000 rpm in ultra-high vacuum to handle "moderate" loads. (beats me what "moderate" means)

The trouble of course being lubrication. At UHV most compounds gas off very quickly. Even materials that don't gas off can be mechanically flung off and contaminate the vacuum. The NASA-Goddard Space Flight Center developed the following procedure for dealing with this issue:

"Purchase high quality stainless-steel ball bearings with side shields and phenolic ball retainers, such as the New Hampshire PPT series or Barden SST3 series. Remove the sheilds and leach clean the phenolic by boiling the bearings in chloroform-acetone, and then vacuum dry at 100*C. The bearings are then lubricated by impregnating the phenolic with DuPont Krytox 143AZ, a fluorinated hydrocarbon. Impregnation is accomplished by immersing the bearing in the lubricant and heating to 100*C at a pressure of 1 torr or less until air stops bubbling out of the phenolic. After this process the bearing must be wiped almost dry of lubricant. The Texwipe Company makes ultraclean foam cubes for this process. The amount of lubricant in the bearing is determined by weighing before and after impregnation. About 25 mg of Krytox is required for an R4 bearing and about 50 mg is needed for an R8 bearing. This lubrication process should be carried out in a very clean environment and the bearing should be inspected under a microscope for cleanliness before the side shields are replaced. "

From Building Scientific Apparatus, Third Edition, by Moore, Davis and Coplan.

kevindsingleton
10-07-2009, 04:09 PM
Cool. No problem. I'll get the spaghetti pot heating on the stove! :D

philbur
10-07-2009, 04:10 PM
What's the point of replacing the shields.

Phil:)


Well this is pseudo-off topic, but I thought some of you might be interested. I ran across this information when I was searching for some information on a wobble-drive rotary-motion vacuum feedthrough that wasn't working properly.

So... here is the engineering challenge: Need a ball bearing that can run at 60,000 rpm in ultra-high vacuum to handle "moderate" loads. (beats me what "moderate" means)

The trouble of course being lubrication. At UHV most compounds gas off very quickly. Even materials that don't gas off can be mechanically flung off and contaminate the vacuum. The NASA-Goddard Space Flight Center developed the following procedure for dealing with this issue:

"Purchase high quality stainless-steel ball bearings with side shields and phenolic ball retainers, such as the New Hampshire PPT series or Barden SST3 series. Remove the sheilds and leach clean the phenolic by boiling the bearings in chloroform-acetone, and then vacuum dry at 100*C. The bearings are then lubricated by impregnating the phenolic with DuPont Krytox 143AZ, a fluorinated hydrocarbon. Impregnation is accomplished by immersing the bearing in the lubricant and heating to 100*C at a pressure of 1 torr or less until air stops bubbling out of the phenolic. After this process the bearing must be wiped almost dry of lubricant. The Texwipe Company makes ultraclean foam cubes for this process. The amount of lubricant in the bearing is determined by weighing before and after impregnation. About 25 mg of Krytox is required for an R4 bearing and about 50 mg is needed for an R8 bearing. This lubrication process should be carried out in a very clean environment and the bearing should be inspected under a microscope for cleanliness before the side shields are replaced. "

From Building Scientific Apparatus, Third Edition, by Moore, Davis and Coplan.

beanbag
10-07-2009, 05:57 PM
Manufacturers of turbo pumps do stuff like this all the time.

wierdscience
10-07-2009, 06:08 PM
Heard of a similar process,but the oil used was high temp turbine oil.

Fasttrack
10-07-2009, 06:30 PM
What's the point of replacing the shields.

Phil:)

You don't replace them. Just remove them so it can be cleaned and then impregnated.


[QUOTE=beanbag]
Manufacturers of turbo pumps do stuff like this all the time.
[QUOTE]

Do they still use bearings? Most of the turbo pumps I've seen are all magnetic bearings - no lubrication needed.

J Tiers
10-07-2009, 11:35 PM
You don't replace them. Just remove them so it can be cleaned and then impregnated.


read it again.... last line:


This lubrication process should be carried out in a very clean environment and the bearing should be inspected under a microscope for cleanliness before the side shields are replaced. "

J. R. Williams
10-07-2009, 11:57 PM
Use Ceramic bearings as used in a typical turbo pump.

JRW