Galling Tendencies and Particles Produced by Ultra Clean Screw Threads

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LIGO-T040111-x0
22 Jul 2010, 12:13

Abstract:: A test was conducted to evaluate the tendency to gall and to collect the particles generated by screw threads that were thoroughly cleaned for ultra high vacuum service. Bars of stainless steel and aluminum were tapped to size 1⁄4-20 using a wide variety of tap configurations, with 20 holes per bar. Screws of various materials and treatments were inserted, torqued and removed 10 times per hole, on 10 of those holes, to check for the effects of material and tap choices on galling tendencies. Particles from these were collected by means of a strip of transparent tape placed before insertions under the row of holes in each bar. After testing, each strip of tape was transferred to a report sheet, which was then scanned at 1600 dpi. The data were evaluated and recommendations are made to minimize particle generation and galling in future designs.

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Notes and Changes:: 1) v1 is equivalent to rev. 00
2) Please note - Silver plated screws should not be used in aluminum threaded holes as they are likely to cause galling (cold welding).
3) This guidance can also be found in section 3.9.1 of the "Generic Requirements and Standards for Detector Subsystems", https://dcc.ligo.org/LIGO-E010613-v2 as well as https://dcc.ligo.org/LIGO-T040111-v1 (this page), https://dcc.ligo.org/LIGO-G020394-v1 and a wiki page on Fasteners for LIGO https://awiki.ligo-wa.caltech.edu/aLIGO/Fasteners .

LIGO Document T040111-v1