Back in November, we saw the pattern for the Joffre cylinder coming together in the hands of a Very Clever Man - take a bow, Alan Frodsham. The pattern has finally been tested in its true environment - the foundry. Foundry work is no place for gifted amateurs - your author was once told that you only became an engineer once you had poured molten metal. In this case, the pattern was entrusted to experts -
J T &E Castings, Haigh Foundry, Wigan. For those unfamiliar with one of the oldest technologies on the planet, the casting process is basically a three step process. One - you make a wooden model of thing you want to be ultimately made out of metal. The model has to be somewhat larger than the final article, to allow for the metal to contract when cooling. Secondly, a sand mould is made from the pattern.Oh, but hang on - what about all the holes - eg the cylinder bore itself? We don't want those filled up with iron? These are deal with by means of Core Boxes. The pattern and the core boxes all fit together like a jigsaw. The sand mould is effectively a negative of the final object - there is space for metal to flow where one wishes metal to solidify. The mould is shown in the first picture - note the passageways - solid sand, and hence the iron flows around them. There are two complications (actually, there are a LOT of complications, but we'll focus on two). Firstly, the metal is a liquid, and subject to fluid dynamics - so one must think about how the molten metal will fill the mould. Secondly, it must be possible to extract the pattern and the core boxes from the finished mould to provide space for the metal to run into. Sounds simple, and isn't - especially when dealing with complex 3d shapes with internal passageways, such a locomotive cylinder. The third element of the process is pouring liquid iron into the mould. The iron is around 1100 deg C at that point. Any splashes on exposed skin mean a long stay in hospital (if you're lucky). After pouring the metal, one waits around for a while whilst it all cools, and then the slightly nervy bit of knocking off the sand mould and thus exposing a master piece. And in this case, it really is a master piece. Take a bow, lads!! As ever, get in touch with us here.
