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| Wax master and latex skin mould used to produce a set of paraffin wax patterns for casting |
The master pattern for this piece was sculpted in modelling wax. This is a blend of various different waxes, which is hard enough for small models to be self supporting and take fine detail but still soft enough to sculpt easily. I made a latex skin mould from the master and used that to produce half a dozen pattens for the sand moulds which would be used to cast the iron.
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| Pattern coated with graphite release agent in with one half of a bonded sand mould |
The mould material is a fine silica sand which is set with a two part resin system. Because the mould is rigid careful attention needs to be paid to part lines and undercuts. The part lines are established using a bed of oil sand which is carefully compacted around one half of the pattern.
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| Bonded sand mould dusted with graphite, with keys in place and ready to have the second half of the mould rammed |
The mould is constructed in a wooden box, the resin sand need to be rammed quite hard over the pattern to ensure that is picks up all of the surface detail and is free from any voids. A layer of graphite powder between the various parts of the mould prevents them from sticking together. Once the first half of the mould is set it is turned over and the oil sand is carefully scraped and brushed out. The mould box reassembled and, with a dusting of graphite, it's ready from the second half to be rammed.
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| Mould opened up |
The two halves of the mould are carefully separated and the pattern removed, keys cut into the mould surface ensure that it can be put back together accurately.
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| Mould with gates and vents carved into the hardened resin sand |
With all of the parts of the mould made the gating system can be carved directly into the sand mould.
Gates (on the left in this picture) allow metal to flow into the mould and
vents allow gas to escape. Any gas trapped in the mould is likely to cause porosity, incomplete filling and other casting defects.
The final stages of preparation are to pain the internal surface of the mould with graphite powder suspended in alcohol. The alcohol is burnt off leaving a fine layer of graphite which helps to protect the fine surface detail of the mould from the intense heat of casting. The the mould is reassembled, clamped together with bolts and wooden yokes and finally has pour cups added.
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| Pouring a set of moulds |
Running and iron furnace is a complex process which requires close cooperation and teamwork.
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| An iron casting straight from the mould with sprue still attached |
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| The finished piece ground and polished on an oiled hardwood base |
