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Silver Plated Screws and fasteners for high vacuum cleanliness, and anti-galling
Q. I have an application where I need to attach a large stainless steel structure together with high strength bolts (typically large grade 8 Alloy fasteners about 1.5" dia.). In the past, I have taken alloy fasteners, nuts and washers and had them nickel plated, then used a 'clean' lubricant like Braycote 601EF to keep the Ni plated fasteners from galling.
For once, I have to go to high vacuum (10^-7 torr) and the volatile count is already too high to allow for use of a thread lube. My questions:
How high is the risk of galling Ni plated Bolts/Nuts?
What would be the best way to proceed? Ni plated bolts with Silver Plated Nuts? or Ni plated Alloy bolts with a stainless steel nut? Or other?
Thanks,
- California
2005
A. Why not use graphite as lubricant? I understand it has very good properties.
Guillermo MarrufoMonterrey, NL, Mexico
2005
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A. Hi Mike. I can't say what is "best", and have never conducted 'stick-slip' tests or other tests for galling in this situation, but I can confirm that manufacturers of vacuum systems routinely use silver plated fasteners for this application.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005
Q. Guillermo - Graphite thread lubes still outgas when going to high vacuum levels. The TML for most graphite lubes varies between .3 and 1.0 TML (total mass lost). For this application I need to be an order of magnitude better than that (like .01 TML) which is a tough thing to do with a lubricant.
Ted -- Are there any industry referenced specs for silver plating? Mil-std or such?
Thanks!
- California
2005
A. Hi again. Many Mil standards have been cancelled or superseded, but AMS2410 might be a good one because it covers nickel striking (necessary for pre-treating stainless) followed by silver plating. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 13, 2012
There are a couple of possible solutions. First, most of the vacuum products companies offer a lubricating grease specifically designed for very high vacuum applications. However, they are temperature challenged, so if temperature is a problem you can look at boron nitride. You can get it as a paste or a spray. Either way it must be dry before you put it into the chamber. Boron nitride is extremely lubricious, and has virtually zero vapor pressure even at very high temperatures. I've also used a graphite paste that we got from Russia that worked well, but I've never tried other versions.
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California
2005
June 9, 2008
Q. My company uses hardware, screws and nuts, (typically 00-90 to #10 hardware made from brass and aluminum) that is silver plated and fastened into silver plated copper, brass or aluminum "bodies". Typical plating thickness is .0002" to .0004" thick on both the hardware and the "bodies". The hardware serves as a tuning element and also has a "jam nut" that is tightened against the "body" to hold the screw from moving.
Problem my company has is that the smaller hardware after a couple of uses often seizes in the threaded hole of the body and will break off if you try to take the screw out.
Silver plating is needed since good conductivity is needed at RF and Microwave frequencies.
Question is, is there a way to have a small piece of hardware that is plated not bind up in the threaded body?
RFQ: Are there any specialists out there who make and can silver plate custom hardware that may be 1" in diameter? My company makes filters for the communication industry for broadcast, high power radio, etc.
Carl F [last name deleted for privacy by Editor]buyer & product designer - East Syracuse, New York
A. We use S.S. bolts WITH silver plating, nuts with NO plating, no washers, and NO lubrication. We bake chambers to 250 °C and get 1x10-10 torr.
Tobey Moore- Ithaca, New York
April 14, 2009
A. UC Components makes silver plated screws in all varieties for the UHV industry. Expensive but they work. Only use them in SST-SST joints.
David Swift- Livermore, California
May 6, 2009
Q. Will 3 mm silver plated screws hold up as Panel Screws?
A lot of our panel screws on our Clean Room equipment are 2.5 to 3 millimeter stainless screwed into stainless panel. They constantly get galled up.
- Richardson, Texas, US
July 29, 2013
A. Hi Donald. As reported, other companies do it.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2013
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