Vacuum / Cold welding

[TaO!]

Originally Posted by evil-mooo

Speaking of things joining when you touch them together, I thought this was pretty schmick.

I call BS. I'd like to see some actual documented cases from a reputable source such as NASA or a peer reviewed metalurgical journal where metalic objects spontaneously weld themselves together unless under specific controlled conditions.

From Wiki

Mechanical problems in early satellites were sometimes attributed to cold welding. However, there are no documented cases of it actually occurring in orbit, except in experiments deliberately designed to provoke it (with susceptible materials, great care to avoid contamination, and deliberate mechanical removal of oxide layers etc). While cold welding is real, an unqualified claim that "in space metals stick" should be treated as an urban legend.

[noboundaries-au]

It wont happen in space as anything they take with them will have an oxidised layer completely covering its surface... as the wiki suggests only objects with that removed will cold weld

[TaO!]

The question was "will it happen at all in orbit?" I was after some credible sources.

[GriMo33]

no it wont happen in orbit under normal conditions. Things in orbit come from earth, things on earth already have a layer of oxidisation around then. so unless u remove that layer it wont happen.

i think


edit: yes im aware not all things in orbits come from earth, but for the prupose of this experiment im assuming they did. try finding a piece of steel floating around in space to test the theory.

[swamp rat]

The OP is wrong in calling the link BS.
It states that 2 uncoated metal surfaces brought into contact will undergo cold welding. This coating can be oxidation or a special coating. It doesnt happen under ordinary circumstances because everything we put up into space originated in our oxygen rich atmosphere

[TaO!]

Originally Posted by swamp rat

The OP is wrong in calling the link BS.

I've yet to see anyone produce documented cases of this phenomena from anything like a reputable source. I think it's reasonable to ask for documented cases for anything that isn't really common knowledge (which is often wrong but anyhoo).

I looked up one journal article:

DLC films for prevention of cold welding in space environments.
Advanced Coatings & Surface Technology 19.11 (Nov 2006): p12(1).

Undesirable welding that occurs between clean metallic surfaces due to severe environment conditions of contact force and/or ultrahigh vacuum can be prevented by employing DLC films.

Like what conditions? Where's their references? What's their idea of severe contact force? They mention nothing about what happened in their control group or anything in general about the phenomena.

[TaO!]

Originally Posted by pawnhead

Where's the BS?

Here, in the link the claim is made:

In space, if unprotected pieces of metal touch each other, they stick together permanently.

Which sounds like

"in space metals stick"

As they make it out, this much is an urban legend. It's simply not the same claim as

...could lead, under high loading conditions, to cold welding--so astronauts may require more torque than necessary.

Which should probably read "usually necessary" but anyway...

I'm not disputing the phenomena of cold welding. I'm saying their claim that unprotected metals that touch, and become permanently stuck together, is misleading or at best disingenuous.

[TaO!]

There's also this one.

The relays installed in flight avionics failed to transfer when energized with a 50ms pulse. Verification testing of relays fielded hardware and in-house inventory was conducted. These tests and subsequent failure analysis indicate that the failure is a result of mechanical "cold welding" between the silver plated armature and a copper alloy stop, which prevents the armature from transferring when the relay coil is pulse-energized.

Although I don't know in what vehicle, or under what conditions that occured.

[aXis]

Even on Earth, Stainless Steel is well known for cold-welding itself. It's most common with bolts/nuts welding themselves together.

eg - http://www.waga.georgfischer.com/ind...77&o_lang_id=2

[brokenback]

Originally Posted by aXis

Even on Earth, Stainless Steel is well known for cold-welding itself. It's most common with bolts/nuts welding themselves together.

eg - http://www.waga.georgfischer.com/ind...77&o_lang_id=2

That link calls galling cold welding. Galling requires some other force to make it happen. For example, heat generated by nut and bolt under high tension/torque forces. In general terms unless there is some major external force such as heat/pressure friction this will not happen.

I've seen galling on high tensile bolts, usually some sort of graphite grease or copper type grease is used to prevent it. I cannot remember it exactly but i believe the copper grease had micro particles that squashed into the high spots of the nut/bolt preventing galling.

[aXis]

I got the impression that either heat or mechanical removal (due to friction) of the oxide layer could allow the galling to occur. I've seen non machine-tightened stainless components weld themselves together.