Making Castings
Sand casting
I have previously made loco weights by making single sided castings from lead. Plastic masters were set into plaster of Paris until set and then removed to leave a hollow. I then melted lead in an old aluminium pan on the gas stove and poured it into he mould before cleaning up with an old file and gluing into the loco.
The ICI bogie hopper wagons have an open chassis construction so any great slab of lead sheet would be visible. I needed something a bit more subtle, slim enough to be held on the central chassis spine but tapered to hide behind the side sheets. In order to get enough mass the weight would also have to span the width of the chassis but with a top cast to represent the central cross bearers on the prototype. This would require a double sided casting and therefore a two part mould. This would be do-able in plaster but I would have to construct a more elaborate mould and I thought the effort would be better directed into a long term solution....sand casting.
Black barn design supplied the basics, a two part cast Iron mould, Petrobond oil bound casting sand, Calcium carbonate release agent and some graphite stirring rods.
The masters were made from Plasticard, set into the bottom part of the mould and filled with compacted sand. Release agent was spread onto the mould and sand before the top part was placed on and again filled with compacted sand. Dowels were inserted to form the holes for pouring and channels were created in the moulds to direct the molten metal into the cavities.. The patterns were removed, the mould parts placed together and set aside waiting for the metal
My trusty Aluminium pan was set on the hob and some lead offcuts, bits of whitemetal and old wheel balance weights were added and heated up. After about 10 mins it had all melted and I used the graphite rods to stir it all together and bring the slag to the surface...this was scooped off and discarded. The metal was then carefully poured into the mould and after a couple of minutes the mould was opened to reveal two almost perfectly cast lead weights. These were broken out of the sand and cleaned up ready for use. the process was repeated to make the 8 weights required for the batch of wagons. The results improved with each cycle as I learned how to improve the technique.
