Gunmetal castings

[David Clark 13Participant @davidclark13]

Gunmetal castings

[David Clark 13Participant @davidclark13]

what should the spec be for gunmetal locomotive cylinders, horns and axle boxes be? Should it be leaded or not?

[JasonBModerator @jasonb]

I'd go with Leaded LG2 on the horns and boxes for the better bearing qualities and the cylinders could go either way as they only see steam the lead won't be an issue.

J

[Nigel BennettParticipant @nigelbennett69913]

BS 1400 of fond memory shows that you can have 1.5% lead in G1 gunmetal; the leaded LG1 & LG2 have 4% – 6% lead. It is quite likely that the casting supplier will only do LG2 in any case. You may get LG4, which has has less lead – 2.5% to 3.5%.

LG2 is a "useful all-round alloy, used in pressure-tight castings"
LG4 is "used widely in the valve industry" for sand & chill castings.

Strength: LG1/LG2: 180MN/mm^2
G1: 270MN/mm^2
LG4: 250MN/mm^2.

I have often silver-soldered leaded gunmetal with very good results. The lead will promote machining (as well as improving its bearing performance, as Jason has already said).

Hope that either helps or clouds the issue further!

[Norman BarberParticipant @normanbarber28134]

Nigel says that he has often silver soldered leaded gunmetal with good results. In their publication "Joining of Copper and Copper Alloys" the Copper Development Association do not recommend brazing of copper alloys containing more than 1.5% lead. They state that there is a danger of parent metal cracking and the solution of lead into the brazing material resulting in the formation of a brittle joint. Obviously this is irrelevant as far as castings for cylinders, etc are concerned but is a consideration to be born in mind when making boiler fittings.

[norm nortonParticipant @normnorton75434]

The lead embrittlement is interesting to note. LG2 also contains around 5% zinc, whereas the phosphor bronzes PB1 and PB102 do not have any zinc present. Would anyone give their view, or refer to study, on whether the zinc content is beneficial or detrimental when it comes to steam engine parts?

[JasonBModerator @jasonb]

Depends where they are used, as I said above the cylinders will only come into contact with steam which won't do any harm, its the hot water that has the impurities which affect the metal.

Also LG2 is said not to suffer embrittlement, see here

[JasonBModerator @jasonb]

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