brass

Hi guys

I'm in the processof building a sweet pea and I was wondering with the bronze and gunmetal ...would brass be an alternative. And maybe Ali Nickel bronze ( I can get plenty of off cuts from work ) please forgive my ignorance this I s all new to me

Kind regards

Paul

very short answer is...if its a non load bearing, static part then pretty much yes.

The flips side of which is if it is a load bearing or moving part or part or exposed to high pressure steam (boiler fittings) then no.

Believe me, you do NOT want to start learning on Ali Bronze.

This stuff is hardaswitches tits and will break a tap as soon as look at it.

In the amounts you need for a model then bite the bullet and not risk more in time and materials than what others have already discovered.

Should not be a problem using it in contact with steam, its the hot water you don't want it to come into contact with so don't use on the boiler or fittings below water level.

hi guys

many thanks

will stick to the expensive stuff then p/bronze and gunmetal

cheers

paul

I'm surprised that no one mentioned the impossibility of silver soldering ali-bronze. It would be a shame to turn up a set of bushes only to find that the solder does not take.

Silver soldering aluminium bronze? Impossible?

If the aluminium content is less than 2% it is relatively straight forward.

Above that, capillary flow and alloy penetration into the gap does start to become a problem due to the amount of aluminium oxide present on the surface. The flux requires an increase in the amount of chloride ions to remove it.

Buy a proprietary aluminium bronze flux or simply add 25% by weight of table salt to your standard flux i.e.EF.

Mix to a paste and use as normal. The mix is good for upto 10% aluminium content.

Keith

What about SAE660 bronze ? Machining wise it's reckoned to be 70% compared with brass at 100% and gun metal 80. Bronze is way way down on that.

I also thought that there was a grade of brass that was ok but can't find any info.

John

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> I also thought that there was a grade of brass that was ok but can't find any info.

You may be thinking of admiralty brass which resists de-zincification.

Neil

I no longer use brass bushing on boilers but no fittings made of brass? I think pretty much every fitting I have is brass.

So no brass for the safety valve ..

Paul

mine are brass - everything availible to buy is brass....steel might rust! More PC nonsence??

"Should not be a problem using it in contact with steam, its the hot water you don't want it to come into contact with so don't use on the boiler or fittings below water level".

Can someone please explain the problem with using brass fittings ? Many model suppliers for boiler fittings are selling brass whistles, water gauges, etc. Are these OK ?

Paul.

Surely the important point here is that any thing that becomes a permanent part of the pressure vessel needs to resist de-zincification. Therefore all the threaded bushes that are silver soldered into the boiler shell need to be made of bronze. The screwed-in fittings are easily removed for inspection and can be replaced if necessary - although they are unlikely to be in contact with water at high temperature for sustained periods. These can be made of common zinc containing brass.

Just my twopennyworth,

Rod

Good morning all,

Re:

Surely the important point here is that any thing that becomes a permanent part of the pressure vessel needs to resist de-zincification. Therefore all the threaded bushes that are silver soldered into the boiler shell need to be made of bronze.

The foregoing is totally correct and for the amount of bronze and work involved, costs in both materials and time add very little to the overall boiler cost. Fittings however below the water line must be able to resist de-zincification whereas those above the water line could be made from brass, but it seems odd not to make all of the fittings from bronze.

There are areas of the country where de-zincification is quite a problem; sadly de-zincification of miniature fittings does give any indication of impending failure until it's too late. I have witnessed a couple of failures due to de-zincification, a bottom fitting on a gauge frame failing and a blowdown valve giving up when being opened at the end of a running session; on each occasion the owners have been relatively lucky to avoid serious scalds. Of more concern was the blowdown failure, the valve being located low down on the side of the firebox, what if a child had been unfortunate to have been in the way when the valve body finally gave up at say in the station area, the consequences could have been horrendous.

No sir, I will always advise the use drawn bronze for all fittings and boiler bushes, for that little extra cost and work I can rest assured any fitting on my locomotives will not give up due to de-zincification, the risk is just too great particularly in todays litigious society.

Regards,

Bob

It's down to the dissimilar metal problem. This chart illustrates the problem

Basically if 2 dissimilar metals are placed together they form a battery cell when damp if there is something in the water that allows it to behave as an electrolyte. There usually is. The metals sit a different voltages / potentials. The same applies when metals are separated in water. The effect is worse when the metals are carrying current which is why you might come across electrical parts described as passivated but as you can see from the chart the effect can't be totally ignored unless the metals are the same and not oxidised to varying degrees. This is why gold and other metal plated contacts in electronic items are often used.

Brass is supposed to be a solid solution of 2:1 copper to zinc. It may well be when the ratio is correct. I have seen comments that it's ok if it's "good brass", The general answer seems to be to add small amounts of tin or even aluminium to it - a bit like bronze but not bronze. This is what gun metal is but it seems brass with 1% tin can be used, sort of sub gun metal which in turn is sub bronze.

Steam should be ok in brass? LOL. It's reckoned to be pure water which can't form an electrolyte. LOL because that is a bit of a dubious statement. De ionised water can't for a very short period even when just exposed to air as it takes up carbon dioxide rapidly and form an acid. Distilled water is stable but not pure. One answer to using brass might be to only fill the boiler with distilled water which some do anyway. Ships use sacrificial anodes even with the correct alloys as salt water is a good electrolyte. Tap water varies across the country.

I have also seen "live steam" comments that brass is ok up to 2 bar and a problem above that. I suspect that is a dubious statement as well. Effects are likely to depend on temperature so all that will happen is that the rate will change. It would be interesting to see the rate of change with temperature but there are some extremely old working low pressure steam engines about that use lots of brass. I'd guess they use a tinned brass as I suspect domestic taps etc do. Pass really as it's an area where it's hard to find definitive information - only that such and such is better in some respect.

John

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Thanks John, I knew that bronze was preferable to brass but did not know the technical reason. (never too old to learn something).

Regards, Paul.

I've done a bit of work on a Lady Stephanie and might finish it one day so this area is of interest. I see the answer is to use SAE660 bronze. Looking around that is being sold as gun metal which seems to be disappearing. I'd guess that red brass is also a safe alternative.

I'm no metallurgist but the addition of tin to solve zinc problems seems a little odd to me. There doesn't seem to be any alloys made up of just these so it could just be a case that it improves resistance. Red brass I believe is red as it has an excess of copper so if brass is a solid solution ( sort of like a chemical compound ) it should mop all of the free zinc up - pass. Alloys are funny things.

A lot of what I see on boilers I feel is aimed at making something potentially dangerous safer but only after a fashion - not totally eradicating the risks. Doing this helps people to continue to be able to make them if they wish rather than the whole area being banned and people having to buy them.

John

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