Identifying brass from bronze

[Adrian Parker 1Participant @adrianparker1]

Please can anyone advise me how to tell Phospher bronze hexagonal bar from brass hexagonal bar?

I have a number of pieces but am unsure if it is brass or bronze.

regards

Adrian

[Adrian Parker 1Participant @adrianparker1]

[Rik ShawParticipant @rikshaw]

Machine a tiny piece of the end of each using the same tool. The swarf of phos bronze is likely to come of in "waxy" strands where the brass comes of in smaller bits or even dust.

Not fool proof by any means but quick and easy to do.

Rik

[Deltic007Participant @deltic007]

Just look at the colour,Yellow is brass n Bronze has a more copper tinge to it.

Jack

[jacques maurelParticipant @jacquesmaurel42310]

Find the density (weight devided by volume), brass has the lower density because brass contains about 30 to 40% zinc and bronze about 10% tin, zinc and tin having almost the same density.

J Maurel

[Norman LortonParticipant @normanlorton75928]

Oh this is a can of worms! The short answer to Adrian is that it is hard to tell. If you cut a fresh face, from my experience, the brass will leave a yellow face and stays yellow for a week. Phosphor bronze will cut yellow but turn orangey in a week. Brass will typically 'powder' as it cuts while bronzes can produce larger chips. Old sticks of phosphor bronze are more orange on the outside than old sticks of brass.

However, the only true phosphor bronzes are PB1, PB102 and (perhaps) Colphos 90, and each of these contain phosphorous. Gunmetal, SAE660, and Colphos 90 also contain lead and zinc (which is why Colphos 90 in my view should not be regarded as a phosphor bronze). The leaded bronzes do cut easier than the pure phosphor versions. Commercial SAE660 and Colphos 90 sticks seem to have spiral silver and dark patterns on the outside skin.

I have spent time looking at this realising that the correct material for locomotive boiler bushes is PB102 (copper, tin and phosphorous only). Some people seem to use the leaded bearing bronzes for this purpose and there is a thought that this material may not be suitable.

Unfortunately, I am not sure that all metal suppliers are always clear about what they are supplying.

Norm.

[Adrian Parker 1Participant @adrianparker1]

Thanks to all for the replies. I have to agree with Norm. I have just spent an afternoon cutting small shaves off bits of metal. I think that the conclusion is, if in doubt its brass!

Round bar especially the PB102 seems to have the distinctive spiral marks on the outside. Somebody told me that bronze larger than 12mm is likely to be PB102 not SAE660. The hexagonal bar is more difficult but maybe most of what I have is brass.

The colour of PB102 is fairly obvious but the leaded stuff appears quite yellow to me. I will see if I can get a piece of Colphos 90 next week and try and compare the colour. I might try the density calculation but I doubt if SWMBO's kitchen scales are accurate enough.

Adrian

[Norman LortonParticipant @normanlorton75928]

Sound like you are having fun making dust! Yes, the leaded bronze seems to keep its yellow – and it machines better.

I have found that it is SAE660 and Colphos 90 in diameters 1" and more that have the silver or grey metallic sheen, often spiralled.

PB102 in sticks under 3/4" seems uniformly orange/brown on the outside. I do have some PB102 in larger sizes up to 3" and then the surface shows extrusion marks that indicate a weak spiral, but it is more orangey than silver.

Regarding sizes and identity I have seen the reverse of what somebody said to you: there is one metal retailer who supplies PB102 if it is 7/16" and under and SAE660 if it is over that size.

Norm

[Adrian Parker 1Participant @adrianparker1]

Actually, I think that I got it the wrong way around and the bigger sizes are usually leaded these days; confusion reigns supreme.

I came across this when making my inner dome and was nervous about silver soldering leaded bronze. In the end I cheated and machined the thing out of a solid lump of bronze bar. (Expensive solution.)

Adrian

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