Posted by Gordon on Thursday, April 22, 2004 at 10:26AM :
In Reply to: I have already welded posted by John Foster on Thursday, April 22, 2004 at 10:16AM :
... that the housing isn't cast steel or ordinary cast iron.
the are some materials called 'spheroidal graphitic' or SG cast irons that have an additive to make the carbon content form little spheres, instead of the flakes it would form naturally.
The properties of this stuff are a decent halway between ordinary cast iron and steel. It's (relatively) cheap and easy to cast and machine, but much stronger and more impact resistant than ordinary cast iron, which is why here in the UK you'll find road grating and carriageway covers made out of it. I think the third member castings might be that stuff.
Gordon