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Yep but copper does lose ductility when deformed. When put under enough stress to deform it, it "work hardens." This is why thick copper wires break if bent bac
by bityard 5y ago
Yep but copper does lose ductility when deformed. When put under enough stress to deform it, it "work hardens." This is why thick copper wires break if bent back and forth too much (and hence why we have multi-stranded wires for applications with movement and vibration), and why crush-sealing washers can't be reused. This work hardening can be undone by heating the copper until it gets red hot, but this isn't practical in many applications.
- MisterTea 5y agoI was under the impression crush seals are used once not because of work hardening but from deformation. You can only crush them into place once. e.g. on conflat vacuum flanges the harder stainless steel knife edge on the flanges sandwich the copper gasket biting into it creating a tight metal-to-metal seal. That biting plastically deforms the copper forcing it into the tiny surface imperfections in the stainless to form an extremely tight seal. Once you break that formed copper seal it is permanently damaged. It cannot be reused as the mating area has has been deformed and the majority of its material squeezed away from the mating area. You have to start over with a fresh flat seal that will deform into the cracks and crevices.
- bityard 5y agoYou're totally right, it depends on the application. I was thinking of oil drain plug washers, which can be reheated and reused many times, basically until they are too thin to do the job.
- pengaru 5y agoI usually just sand the washer surfaces flat on some high (600-800) grit wet-dry paper, never had a problem. Works on banjo bolt washers too.