Question about Grades of Phosphor Bronze.

[ron]

Hi Everybody again
More questions from Ron;
I've two grade of phosphor bronze, an easy to machine one almost like gunmetal for boiler bushes and a tough hard one for bearings anyone know what I should ask for if I want to buy more of either?
Ron

[the_viffer]

Cast PB is the stuff that turns well and drawn PB is a complete Australian. I think the cast stuff is PB102 but here in my cell they don't let me loose on my books to check. Anyway with the straitjacket it is hard to turn the pages.

[chris vine]

Hi,

The tough pinky coloured stuff, solid drawn is PB102. (I don't know any other grade names.)

It machines easily with a sharp carbide tool and lots of coolant and really high speed.

Chris.

[baggo]

I think the 'nice' stuff is leaded bronze SAE 660

John

[Deleted]

I've used Colphos 90 from Colombia Metals www.columbiametals.co.uk/ for many years. Probably the nicest metal I have ever had to machine, silver solders fine, takes threads beautifully and err no; I don't have shares in the company.

[chris vine]

Hi Usra,

I half remember an article in ME years ago about a type of phospor bronze that was, apparently, not suitable for boiler bushes etc. Colphos 90 seems to ring a bell but it is possible I have it totally out of context. It might have been a type of silver solder that I am thinking of, with a trade name, perhaps it contained phosphorus.

I know I am rambling but does anyone know what I am talking about???!!!!

Chris.

[baggo]

Chris,

there is a letter in Postbag in issue 4175 (2002) from M L Breeze stating that none of the bronzes containing lead should be used in boiler work. He doesn't say why though! He also condemns gunmetal (LG2) as unsuitable because it contains a small percentage of lead. The letter refers back to a note by Neville Evans in his Jones 'Big Goods' series in which Neville warns readers to beware of using leaded bronzes. Apparently the lead can leach out on soldering and inhibit adhesion of the silver solder.

Colphos 90 also contains lead to give the free machining properties ( although less than SAE 660), so would fall into this category.

Perhaps it would be best to stick to plain PB102 for bushes even though it can be a pig to machine!

John

[Shawki Shlemon]

Hi all
we are building models and I think there must be a limit for how much technical details we need to get into.I only use two types of bronze ,gunmetal and phosphor bronze for bearings. That is enough for me . ;D

[abby]

I think that is a good point Shawki , we are doing this thing for fun and surmounting problems is an integral part of the hobby. The skills needed are something that we learn by experience and doing the job , and if the job turns out to our satisfaction, how is important only to us.
However I suspect that, like myself , most model engineers obtain their materials from sources other than ones with ISO ratings , in the skip at work and local scrapyard or boot sale seem to be prime suppliers for many of us so a little knowledge is helpful , not all yellow metal is brass , as I discovered after buying a large bar of ally bronze LOL!
Likewise the little tips can be useful even though most of us think we know it all.
Abby.

[chris vine]

Yes, I think there can be too much sucking of teeth and "....oooh you don't want to be using that stuff"

The thing to watch out for though is material for boiler bushes, dome rings etc. Partly because they have more danger but they will probably just leak if they become porous. Much worse though is that they might render and expensive boiler unserviceable.

I once made a fitting in the smokebox from some bronze which turned out to be leaded. It was totally porous after I had silver soldered it. The more I tried to patch it up, the worse it got.....

Chris.

[ron]

Shawki
The thing with the two grades of PB I have is they're like chalk and cheese to work with, even though they look more or less the same, the hard one would make superior bearings whereas the soft one was specifically supplied for boiler bushes. It would be handy to know for future reference if I was buying more. Unfortunately I bought the hard stuff on Ebay a long while ago so I've no idea what grade it is, but I'd like more!
Ron

[baggo]

Ron,

As mentioned above the 'hard' stuff will be the pure phosphor bronze i.e. PB102 which most ME suppliers sell. The next common one is the SAE 660 which they sell as 'free cutting' bronze.
Actually the leaded bronzes are supposed to be superior for bearings as the lead content tends to give them a degree of self lubrication and reduces friction. I have seen advice not to use hard bronze bushes for silver steel axles/crank pins as the bronze can pick up' on the silver steel and cause scoring if the lubrication is not all it should be.

I agree that it is easy to get carried away with the technical side of things and some-one will always come up with a reason not to do such and such. But, as Chris says, when it comes to boilers you have to be careful, if only to avoid an expensive 'scrapper' !

John

[Deleted]

Hi Chris,
Yes Colphos 90 does contain lead, however locos I built 20 years ago using boiler bushes made from the stuff are still running without any corrosion problems I am aware of. One of the great advantages of Colphos 90 is that it machines fine without any form of coolant or cutting oil, which for many model engineers is a real boon.
The material one should never use for boiler bushes is brass which will more likely have become like a sponge after that length time.
As some folks have said it's very easy to get bogged down in technicalities over materials, but it's good to talk about it!