Cleaning of Castings

Cleaning of Castings

Castings need cleaning and trimming operations to be done on them after they have been removed from their molds. Removing of adhering sand, gates, risers, cores or fins is termed Cleaning or fettling. Various methods are in use to accomplish these operations. The casting may be cleaned for two purposes.

(1) Removing of gates, risers, cores or finns

(2) Cleaning of casting surfaces

(1) Removing of gates, risers etc.

For removing gates and risers etc. the various processes used include chipping, filling, shearing, sawing, grinding and flame cutting. Chipping may be done by hand or by a pneumatically-driven chipping hammer which employs the use of a chisel. This method is used for castings made from copper-base alloys of steel. For brittle castings, gates etc. may be removed simply by striking a hammer on them (the process known us “flogging). Castings made from soft steel, brass, bronze and aluminum sometimes employ the use of shearing machines. The use of a hand saw is a good technique employed for cutting the excess metal from a casting. Jobs of large varieties can be handled. It is extensively used for non-ferrous castings and gives a faster rate of working. Flame cutting process is used when the size of a gate or a mister is too large to be cut by chipping, shearing or by a hand saw. This process is not readily adaptable for copper-base castings because flame cutting cannot be easily achieved as copper does not oxidize enough to facilitate flame cutting and moreover its thermal conductivity is too high. Similarly aluminum castings are economically treated by sawing rather than flame cutting. The gates and risers of gray iron casting are usually broken by flogging flame cutting is not employed for them. When the casting is too hard to be cut by chipping, sawing and flame cutting is not possible, grinders are used to do the job. The process is comparatively costlier. Electrically operated portable grinders are quite often used for removing the surplus metal from a casting.

(iii) Cleaning of Casting Surfaces

Surface cleaning can be done by rapping the casting with hammer, wire brushing, tumbling in barrels, pickling and shot blasting.

The process of surface cleaning involves the removal of clinging and embedded sand pahicles and little amount of extra metal connected with a casting. Casting surfaces are usually cleaned by impact and grinding. The choice of various processes of cleaning depends upon the size and the intricacy of the casting.