The majority of Stuart Models castings are made using the shell moulding process. The advantage of shell moulding is that it produces a casting that is very dimensionally accurate with a beautifully smooth surface.
There is generally a complete absence of blow holes in the casting process and in addition, no sand can be incorporated in the casting itself, which occasionally occurs with other processes.
A casting together with its shell
The Shell Moulding Process
A brief outline of the shell moulding process is as follows. Sand mixed with Bakelite is placed in a “dump box”, an open topped box on trunnions. The pattern is pre-heated in an oven to around 400 degrees fahrenheit, coated with a parting solution and placed face down on the dump box and clamped in position.
The latter is inverted so that all the sand mixture drops onto the pattern. The hot sand-bakelite is “cooked” by the hot pattern for at least 15 seconds, the longer it is left the thicker the shell of sand. The dump box is then turned back and all the loose sand falls off. The pattern with the sand shell on it is then returned to the oven for a few minutes to harden the shell, and is then removed from the pattern.
The other side of the shell is moulded similarly and then the two halves are then attached either using metal clips or a special adhesive, the shell is then ready to pour.