Originally Posted by FBinNY

Sorry, but no.

Earlier, specifically to avoid endless argument, I linked an authoritive article explaining galling. I gather you didn't bother, and I get that because it's longish.

But here's the opening paragraph....

An important aspect of any part’s design and maintenance is the component’s resistance to wear. Adhesive wear is the product of two metal surfaces being rubbed together. Under a sufficient load, this will penetrate the oxide film on the surface of metals like aluminum and stainless steel. When the force exceeds the metal’s strength, adhesion or cold welding occurs.

It goes on and into greater depth. But the takeaway is that galling results from a metal's affinity for itself, not heat.

So, while we can all speculate, I'm a fan of Occam's Razor....

We have a material prone to galling, we have the right conditions for galling, we have an end result that looks like it might galling, so I'm going to guess that it's probably galling.

FWIW, it's a mistake to think only about rubber brake shoes. The shoes pick up all kinds of grit capable of abrasively machining rims, resulting in aluminum bits embedding in the shoe, giving the aluminum on aluminum friction that galling is about.

I've seen countless examples over the years, and it's most pronounced in certain alloys, so I see it on low end rims, and less so on better rims.

Originally Posted by Duragrouch

Trying to grind a piece of aluminum on a bench grinder, aluminum will immediately embed into the grinding wheel, requiring hours of flicking out each piece, or dressing the wheel to remove both the aluminum and some abrasive. (Thus signs at machine shop grinders, "NO ALUMINUM".) Steel?

Originally Posted by awac

Another reason for those signs.

https://en.m.wikipedia.org/wiki/Thermite

“The thermite reaction can take place accidentally in industrial locations where workers use abrasive grinding and cutting wheels with ferrous metals. Using aluminium in this situation produces a mixture of oxides that can explode violently”.

Originally Posted by Kontact

The "cold welding" described in the article is an explanation of what happens that causes metal to tear away, not be permanently deposited. It is a description of how surface friction can briefly exceed the shear strength of the metal. Galling is common in fasteners and applications where closely fit parts rub together at high speeds.

Cold welding is not a description of two materials being permanently bonded.


As I already explained, the pores galling leaves can allow chunks to get wedged into the in a process that is more like riveting. But a very large chunk requires an equally large hole, not just some light surface roughness.

Originally Posted by Duragrouch

I think if A=B, B=A; That if cold welding due to galling can lift away metal, it can also be redeposited. From wiki:

Originally Posted by Duragrouch

Good point! I knew of thermite from other things, but never made the connection on grinders. Thanks. I recall stationary disc/belt sanders used for chamfering edges and other stuff on materials of all kinds, wood, steel, aluminum, never recall seeing a warning sign, but sounds like there should have been, or at least daily cleaning of the swarf from them.

Originally Posted by Duragrouch

I saw a blurb about Dahon's "safety disc", clicked on Dahon's euro web article, it redirected me to the USA site in a second (with no info), I hate that! I wish I knew a way around that, tried a different more incognito browser, no help.

Originally Posted by grumpus

The easy solution to that is a VPN that lets you select endpoints in different countries.