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I recall there were cases of mechanisms of spacecraft that failed due to cold-welding, but are there any records of accidental cold-welding on EVA? of e.g. an ill-prepared tool cold-welding to a part of the spacecraft, or two parts astronauts worked on welding together accidentally, or similar mishaps?

SF.
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    If the contact area of cold weld is very small, a small force will break it. To get a cold weld resisting a large force, the contact area should be large. This would require clean, metallic, well aligned and polished surfaces with small roughness and the same shape. The probability of such surfaces getting contact should be small – Uwe Aug 30 '18 at 16:27
  • There have been a couple cases of parts being unexpectedly hard to remove but I don't remember it ever being attributed to cold-welding. – Organic Marble Aug 30 '18 at 16:28
  • @Uwe: or a hit sufficiently strong to make the surfaces aligned and contact area large. Providing they are clean. – SF. Aug 30 '18 at 16:28
  • This is one of the (many) reasons, for example, that all aluminum parts on orbit are either anodized or conversion-coated. – Tristan Aug 30 '18 at 17:48
  • Does cold welding work on those timescales? – Hobbes Aug 30 '18 at 19:44
  • @Hobbes: why wouldn't it? There are no chemical reactions, evaporation, diffusion or any of that slow stuff involved. Two atoms of metal come into contact and form a bond, that's it. The cases of 'slow cold welding' where some bearings or other mechanisms failed are slowed by time it takes whatever insulating substances were present originally to dissipate, evaporate, get worn off etc. – SF. Aug 31 '18 at 00:38
  • "a hit sufficiently strong to make the surfaces aligned and contact area large" would require surfaces of the same shape and with small roughness. A very strong hit is needed to reshape the surfaces over a large contact area for a good alignment. If the surfaces were treated with shot peening before, the effective contact area would be small. – Uwe Aug 31 '18 at 09:11
  • @Uwe: Roughness sufficiently small that is smoothed out by hammering. Shape similar enough that after the hit it becomes the same. Two smooth pipes (or round bars), one perpendicular to the other, would be quite likely to produce a fragment of such surface; what would otherwise result in a dent should result in a cold weld. Similarly, contact producing scratches, or operating near limits of material durability (screwing bolts in/out.) And while yes, protection is easy, there are so many metal parts it's possible some were overlooked and didn't pass the needed surface treatment. – SF. Aug 31 '18 at 09:39

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