Compression joints

[Ian Stirling]

That a moth does not need much water, even a rare example that has reached

50 years.

[usenet]

Yes, OK, but not in quite the same way that a compression joint works.

They're "not difficult" in that the tools etc. have been specially developed to make it easy.

[usenet]

Not really, I think wire wrapped connections are cold welded but I doubt that crimps are usually.

[David]

You're beginning to sound like IMM, with statements of fact and nothing to back them or your cold weld theories up.

[David]

You may note that there was not an outright dismissal, but there has still been nothing to back any of your theories up, so you've not really given anything decent to dismiss. You have been making the definitive statements without anything to support them other than your experience of a process that carried out with specialist equipment under a controlled environment.

OK going down the x-ray route is out of the question so lets look at things to an order on magnitude sort of degree

cold weld --pull the wire and apply a direct force to a small area, any cleaning and surface prep before making the joint?

compression -- olive is deformed under compression, force is applied via torque of wrench turning the nut which applies the compression the force is not applied directly to eth copper/copper interface, but rather transferred as the olive is compressed.

Again for the case of a cold weld the wire is pulled, I would imagine that this plays a significant part of the process, it would affect the surface state of the material, and help to remove/break any oxide layer

I would reckon that there is an order of mag. difference in the direct stress applied to the olive, the surface area of the cold weld joint and olive are also radically different, and the surface conditions must also be considered.

Cold weld strength. I do not have your experience of this but I should imagine that it should be pretty good. This would not tie in with others experience where the olive can be removed after making the joint... experience/opinion on this may be mixed depending on how far up the nut is tightened.

While you see some very broad similarities you do not appear to be looking closer for any of the flaws in your theory, everyone likes to defend their own theory but you also have to be subjective, you are the one with some expertise and knowledge of cold welds, but it would appear that this makes you regard it as a simple process .

How about some finer details on cold welds in terms of force required, surface conditions, strength of finished connection, etc... I just don't see all these factors adding up to something comparable to a compression joint, which is perhaps why I may sound dismissive, but I've not seen any sort of ballpark analysis coming from your direction to support the theory, which is relatively radical after all

A direct electrical crimp connection would appear to be closer to a cold weld scenario, but I wouldn't rate that in comparison either.

cheers

David

[Capitol]

Compression joints are unlikely to achieve the conditions required for cold welding. Cold welds are normally achieved with freshly cut/abraded surfaces of preferably the same material, which are pushed together with sufficient force to produce cold flow and significant local deformation. Olives are always oxidised to some extent and will deform to fill voids, but not weld. Cold welding can take place, I understand on wire wrapped connections where the wire is pulled around a square pin, causing abrasion and very local deformation. I have never seen a crimp connection on single or multi stranded wire up to 8mm which achieved cold welding. As I was informed, the objective of the crimp was primarily to exclude air from the joint. Crimp welding does not seem likely to me. To achieve a cold weld, my experience is that very clean/freshly abraded surfaces or rotation is necessary. I've never tried vibration to achieve this, but it works on some plastics. Just a contribution.

Regards Capitol

Regards Capitol

[G&M]

This should not be possible if the joint is well made on a copper olive. Brass is different of course.

Give me a couple of days and I'll see if I can think of a proof one way or the other.

I'm not convinced a crimp is a cold weld - too many other elements involved.

[David]

it can be done with copper, on the other hand is you ramp up a brass olive hard enough that will be very difficult to move, simply from a mechanical point of view.

make a sound copper copper connection, cut in half and do a visual inspection, stick an approptiate piece of dowelk down the pipe when cutting to avoid deformation of the pipe. Repeat.

Yes, exactly a crimp is cetianly not a cold weld, but the analogy is that there are also too many other elements in a compresion joint as wel, if you care to examine them, primarily how the force is applied and the surface state of the material.

regards

David