Unbendable casting!

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Unbendable casting!

This topic has 7 replies, 6 voices, and was last updated 1 December 2018 at 14:15 by Nigel Bennett.

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30 November 2018 at 21:22 #29872
AJW
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@ajw
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30 November 2018 at 21:22 #383115
AJW
Participant
@ajw
Cracking on with my Centaur build I have now got to the cast gunmetal head casting.
I noticed one of the rocker lugs was out of line and would not be recovered in machining.
So I had a bright idea of heating the affected area with my propane/oxygen torch so I could ‘bend it straight’
It just cracked and broke off! Well happy.
I take it cast gunmetal is quite hard and in annealable?
You live and learn.

Alan
30 November 2018 at 21:54 #383123
Michael Gilligan
Participant
@michaelgilligan61133
Condolences, Alan

My guess is that you de-zincified it by using the torch.

MichaelG.

.

https://en.m.wikipedia.org/wiki/Gunmetal

http://www.airproducts.com/Industries/Metals/ask-the-experts-metals/heat-treating/dezincificatiion-apply-thermal-processing-brass.aspx

Edited By Michael Gilligan on 30/11/2018 21:56:07

Edited By Michael Gilligan on 30/11/2018 21:59:16
1 December 2018 at 07:04 #383137
JasonB
Moderator
@jasonb
I find GM castings are very soft and easily bent if you are careless with your clamping or have a major tool dig in. Probably would have been better to tweak it cold. Only last week I had some GM bearing s that had cupped a bit and just gave then a good squeeze in teh vice to flatten them out before starting to machine, these were 1" x 1/2" section.

On the bright side it is easier to silver solder the offending part back on than it would be with an iron casting.
1 December 2018 at 09:12 #383149
MichaelR
Participant
@michaelr
Sorry to hear that, I had the same problem on my Centaur cylinder head I got it back inline by bending cold, as Jason says you should be able to silver solder the arm back on.
1 December 2018 at 11:08 #383161
AJW
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@ajw
In hindsight I should have checked it over better upon receipt when I would have spotted it and had a word with the supplier or sent it back!
I get the feeling that the bend was caused as it came out of the mould, dropped?
I’m not sure about silver soldering it back, there is a crack further down the arm meaning I would have to remove it first, meaning 2 breaks in the same section. On top of this the arm, which is webbed, still has a bend in it!

Alan
1 December 2018 at 11:16 #383164
Former Member
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@formermember19781
[This posting has been removed]
1 December 2018 at 14:15 #383193
Nigel Bennett
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@nigelbennett69913
Many copper alloys are known as "hot short". This means that they don't take kindly to being battered when hot. I found this out myself once when trying to form a head on a piece of bronze bar. It simply turned to mush under my hammer! Hence forming copper alloys is generally best when they're cold.
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