SURFACE CLEANING OF THE CASTING

Wire Brushing: Wire brush of hardened steel wires, embedded in a wooden block, is extensively used for cleaning the casting surface.

Tumbling: In this method, the castings to be cleaned are placed together with a number of small cast iron pieces called stars inside a large steel barrel. Both ends of the barrel are closed and the same rotated along a horizontal or inclined axis for about half an hour. The casting, during this period of rotation, rub against each other and the sand particles, scale, etc. are separated out from the surface of the casting.

Sand Blasting: In this method a stream of high velocity air carrying large grain size of sand particles is thrown on to the surface of the casting. The abrasive sand removes the dirt, sand, and scale from the surface of the casting.

Shot Blasting: This method is similar to sand blasting, but here metallic abrasives are fed into the air blast instead of sand grains.

Hydro Blasting: In this method, a high velocity stream of water and sand is thrown on the casting surface with a speed of about 100 m/s, which removes the dirt, sand, and scale from the casting surface.

Pickling: In this process, an acid is used for cleaning the sand from casting surface. For brass castings nitric acid and for iron castings hydrofluoric acids are commonly used. In order to neutralize the acid remaining on the surface it is necessary that the acid pickled casting should be dipped in an alkaline solution, followed by dipping in water.