Engineering Slips can they join together?

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Offline confusious says

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Engineering Slips can they join together?
« on: 17/05/2013 09:36:17 »
I was told years ago by a production engineering colleague that if two engineering slips (those used for measuring gaps) in imperial or metric increments, were left joined together for too long, would eventually join permanently by the electrons passing over from one slip to the other, is this true?


Online yor_on

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Re: Engineering Slips can they join together?
« Reply #1 on: 21/05/2013 15:03:24 »
Read about using two surfaces, very finely done, joining them in a vacuum (space?) finding them to join, exerting a 'force', as you tried to separate them, somewhere a long time ago? But I don't know where, and I'm not sure if it was a actual experiment either, or just an idea. Maybe it was the Casimir force involved?
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Offline evan_au

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Re: Engineering Slips can they join together?
« Reply #2 on: 22/05/2013 12:09:29 »
If just the electrons crossed over (like any electrical contact), the metal surfaces would not weld together. You would be able to separate the metal surfaces easily.

However, you may need to slide them apart, as very smooth surfaces can develop a fairly strong attraction due to Van Der Waals force when they are in close contact with no air between them. Also, trying to pull them directly apart means you are fighting air pressure.

If you apply a considerable electric current to two metal surfaces (as in spot-welding), the two surfaces do join together. This is mainly due to the very high currents and temperatures during the welding - the high temperatures cause the atoms to become liquid and merge together.

If surfaces are left in contact in a vacuum (so there are no surface oxides), thermal movement of atoms at temperatures found in direct sunlight can be enough to vacuum-weld the two surfaces together, over a long period of time. This does not require high currents, or temperatures high enough to melt the metals.