brass

[julian atkinsParticipant @julianatkins58923]

it is very simple.

on a miniature steam loco with copper silver soldered boiler all bushes silver soldered to the boiler should be made of bronze or copper. copper was an LBSC thing that isnt followed nowadays for bushes. for bronze avoid gunmetal as can be porous and isnt as tough for threading as good old fashioned hard drawn phos bronze, and avoid phos bronze with lead added.

brass is a NO for boiler bushes firstly because in the course of silver soldering up the boiler the brass can get over heated, plus as stated, is subject to dezincification. now if the fittings are brass and suffer dezincification they can be replaced. if the boiler bushes deteriorate then that usually results in a scrapped boiler.

whether you make boiler fittings out of brass or bronze is entirely up to the builder, and most commercial fittings are all brass. however boiler bushes silver soldered to the boiler are quite another matter as explained above.

i still have brass boiler fittings on many of my locos. they get checked regularly. no dezincification. some of these fittings are 30 years old. i have injectors the same age with no dezincification on the brass cones. i even have a Linden injector over 60 years old with no dezincification on the brass cones.

however ive replaced all the brass fittings on boilers of club locos where dezincification has occured, but probably not until after 20 years or so use and probably the boiler not being blown dowbn after each run/steam up.

cheers,

julian

[nigel jones 5Participant @nigeljones5]

thanks Julian…my doctrine entirely, no brass bushes but everything else ok, checked regularly.

[AjohnwParticipant @ajohnw51620]

I think Tim got the message more than maybe you did Julian. The changes basically may delay the inevitable but wont totally remove the problem. I also explained why the changes are encouraged and it seems may be legislated in Oz. The term bronze covers all sorts of things. Gun metal too. Brass very much the same/even more so. Did you follow the brass link I posted? This is probably why I have seen the term good brass is ok but not any old brass. Brass even comes in different hardnesses.

Over heating when these metals have melting points up around 1000C also sounds a little odd to me. It leaves me wondering how they can be cast. I do know the answer to that – carefully. The problem there is more likely to be poor silver soldering techniques – too much heat and also probably not realising that heat draws solders towards itself so even where the heat is applied can matter. This area has cropped up on here recently – flux burning off. Replacing it with borax really isn't a good idea from the over heating point of view. Silver solder fluxes are intended for silver soldering at temperatures that are suitable for the process. Borax isn't really. Capillary action comes into it as well for a strong joint – I have seen a suggestion from some one in Oz that bigger gaps might be better – just encourages the stuff to tun in without actually forming any sort of joint.

John

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[julian atkinsParticipant @julianatkins58923]

John,

when you've built as many miniature locos as i have over 32 years and run them regularly including IMLEC, and repaired and overhauled many locos and parts for friends and clubs i might heed your advice.

however there is no reason whatsoever not to have basic fittings made of brass below the water line or regulator bodies of brass inside the boiler above the water line. on my current construction project (a 5"g LBSCR Terrier) all the fittings are made of hard drawn phos bronze – because they are all rather special finescale fittings and not easily replaced. if i need to replace an old blowdown valve below the water valve on my other locos that isnt a problem and is a few minutes work. the above new loco complies with the now recommended advice for captive valves so are a bit more complicated.

in 2011 i took off the boiler fittings of a 5"g loco finished in 1963 and which had seen an awful lot of use. the blowdown valve and plugs above the foundation ring were ok but starting to show signs of dezincification. the bottom water gauge fitting showed no signs of dezincification at all. in 1985 i took off the boiler fittings on a 3.5"g loco run very rarely since the late 1960s where the blowdown valve was very badly dezinc'd (and also probably very badly made and looked after). i could give many other examples but brass should give at least 15 years service on blowdown valves. the Trade make them of brass anyway though i always make my own.

there is some merit in having replaceable boiler plugs just above the foundation ring in brass – a sort of version of Admiralty practice. there appears to be some evidence from my own experience that not blowing down boilers and emptying same after a steam up and very cheap brass aggravates the potential problem. most of my brass is ex clerkenwell stuff of superior grade.

cheers,

julian

[AjohnwParticipant @ajohnw51620]

Cheers Julian it sounds like we agree and maybe neither of us are what might be called politically correct in our view on the subject. If I do anything I suspect it will be in SAE660 bronze. It states not subject to dezincification not that I wholly believe this as the techniques used for this sort of thing seem to rely on the metals that are added blocking pores.

It's an interesting area from my point of view. If I want to make a steam engine I would also want to make a boiler with no real interest in buying any parts at all other than materials. If I make a boiler I would want it to be suitable for any engine I might make – all that really means to me is the possibility of higher pressures if needed. This area is why I have a Lady Stephanie kit knocking around with very little work done on it. Also the fact that scale wise the flywheel looks more suitable for a loco wheel. Plus until recently I have been tied up with other things – bits and bobs and odd things for microscopes in need of repair. I also need to make a couple of tools so am in the middle of a tidy up which seems to be going rather slowly.

The only difficult part to make on the usual boiler in my view is the water level gauges that include a glass tube. Sealing the taps fitted and the glass must be tricky at small sizes and so far I haven't found any information on self built ones at all. Some clues always help with problems like that.

John

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