shell-molded-casting-essen-aluminium

Shell Moulded Casting

The shell molding process employing synthetic thermosetting resin mixed with high grade silica sand and is a method of producing sand castings to very much closer tolerances. It is, of course, a machine molding process. The pattern plates used for this process must be of metal and capable of withstanding temperatures of 250-300°C. The amount of “draw” required for these patterns can be greatly reduced and rapping the pattern is not used for ejecting the mould from the pattern plate.

The shell molding process employing synthetic thermosetting resin mixed with high grade silica sand and is a method of producing sand castings to very much closer tolerances. It is, of course, a machine molding process. The pattern plates used for this process must be of metal and capable of withstanding temperatures of 250-300°C. The amount of “draw” required for these patterns can be greatly reduced and rapping the pattern is not used for ejecting the mould from the pattern plate.

The main advantages of this process may be claimed in improved surface finish of the casting, and the improved definition obtainable; castings of complicated section and shape may be easily mass-produced without the use of skilled labor, and very much closer tolerances can be achieved.

In the last connection it is recommended that the contracting foundry should be consulted in regard to what tolerances can be held on shell molded castings, because whilst on certain dimensions it is possible to hold tolerances of the order of 0.003 in. (≈0.1 mm), this is not possible on all dimensions of shell molded castings, particularly where these dimensions are across the joint line of the mould.

The pattern plates for shell molding are, for reasons of accuracy, generally rather more costly to produce than the conventional pattern plates for plate molding. The cost of the resin and high grade sand has also to be absorbed in shell molded casting costs, and as a rule, shell molded castings cost more per kilograms than conventional sand castings.

However, for many applications, machining operations can be eliminated if shell molded castings are employed, and machining allowances can be greatly reduced in almost all cases. The resultant lower weight of metal of the casting shows substantial advantages in many cases over other methods of production.

Shell molding also has the advantage of a greater degree of consistency, dimensionally, with regard to surface finish, and in regard to soundness, than sand castings, once the correct running and feeding techniques have been achieved.

In regard to mechanical properties, shell molded castings exhibit similar characteristics to sand castings, and all copper base alloys, with the exception of the particular die-cast specifications, are suitable for shell molding.

Shell Moulded Casting

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