Themes

Portsmouth Dockyard was different to the other Royal Dockyards because it had three foundries. There was the iron foundry, the steel foundry and the brass foundry. They produced any metal item needed on a ship from valves to ships badges. Founders made these by pouring molten metal into moulds. When the metal had cooled the item was ready. The images below document the last smelting in the iron foundry in 1982.

Patternmakers made the moulds using wooden patterns. The patterns were precision made and had to be larger than the desired end product. Molten metal shrinks when it cools and different metals have different shrinkage rates. Patternmakers had special rulers to help them work out the expansion rate of the metal. This allowed them to make the wooden patterns the right size to allow for this shrinkage.

Pattern makers made each pattern in two parts. Foundry workers prepared the moulds which consisted of a metal cylinder called a frame. They placed the bottom half of the pattern into the mould, filled it with sand, packed it down and pegged in the top half of the pattern. Finally they placed another frame on the top, filled it up with sand and tapped it down. They baked the mould dry because if they attempted to pour molten metal into wet sand it would explode. Two holes were cut into the mould, the first allowed the founders to pour the molten metal into the mould and the second allowed the molten metal to drain out. When the metal had hardened removing the frame and pattern revealed the finished piece.