Cleaning of Castings

 Cleaning operations are the operations required in sand casting after the casting is removed from the mould. After the solidification of the casting, the mould is knocked out and solidified casting is taken out of the moulding sand. At this stage, the cast product is attached with risers and gates. Many times, the moulding sand also gets adhered to the casting as some of the sand gets fused with the molten metal. The cleaning of castings refers to the removal of gates, risers and sand. Also, cleaning may involve machining or abrasive finishing of the cast product. The cleaning operations usually performed on a casting are given below:

(a) Removal of gates, in-gates, riser, feeder etc.

(b) Surface cleaning

(c) Trimming

(d) Finishing

(a) Removal of gates, in-gates, riser and feeder:

There are various methods of removal of unwanted metallic parts from the solidified cast product. In case of brittle material, the gates, risers and feeder can be removed by impact force. It is usually done by shakeout or knock out devices. Other processes that may be used to cut off the metallic parts include band saws, grinding machine, shearing machine, cutting torches, etc.

(b) Surface cleaning:

As the temperature of molten metal is usually high, sand particles near the surface of the casting gets fused and adheres to the surface of the casting. Therefore, it is necessary to clean the surfaces both interior and exterior. There are several methods to remove the adhered sand from the castings. Some of the most common methods of removal of sand are tumbling and sand or metallic shot blasting.

Tumbling is done in a barrel like machine called tumbling mill which helps to remove the sand by rubbing action of the cast parts with each other. In shot blasting, abrasive particles are thrown on the surface of the casting in a carrying medium. Air is the most common medium used in this process. Sometimes, metallic abrasive powders are thrown on the surface of the castings along with air to remove the unwanted material. Blasting processes include air blasting, centrifugal blasting, hydro-blasting etc. Other methods to clean the cast surface include wire brushing and buffing.

(c) Trimming:

Trimming operations involves the removal of fins, gates and risers appendages, metallic chaplets, etc. These unwanted materials are removed by using hammer and chisel called chipping process, or by pneumatic chipping hammers or by the use of grinders.

(d) Finishing:

The finishing at this stage refers to the final cleaning. The castings after the removal of gates, risers, fins, chaplets, adhered sand are washed. Then depending upon the requirements of the end product final finish is provided by machining, polishing, buffing, chemical treatment etc.