Preparation of Core

Explain the preparation of Core.

Preparation of Core

Core sand ingredients should be mixed carefully so that all the grains of sand may be covered by the binder. To fulfill this requirement core-sand mixing machines like roller mills are mostly used because mixing with hand does not give prompt results. Sand may be tempered with suitable amount of water.

Cores are made either by hands or by core jolting, squeezing and roll-over machines. Stock cylindrical cores of varying size are readily and economically made in core extrusion machine whose principle of working is similar to that of the meat-grinder. A core-blowing machine rapidly produces irregularly-shaped cores of small and medium sizes. Cores are dumped on steel plates for temporary storage. After that they are sent to the core baking ovens. Carbon dioxide method of core making is a recent development. In the core sand, a certain amount of sodium silicate is added. After ramming ‘the core in a core box, it is brought into the presence of carbon dioxide which acts to precipitate a. silica jell. This-results in the rigid bonding of sand particles. Gas is passed for about thirty- seconds and immediately after that tore - may be used for casting without any baking and danger of breakage in its holding. Another technique of core making involves, the principle of making shell molds. On the face of a core box which- has been heated to about 20°C, some parting agent is first applied. Later a mixture of resin sand is blown in the core box. After about thirty seconds, sand from core box is drawn out. Some of the sand found sticking with core box, is heated in an oven for about two minutes. This way a core with after they are baked at suitable temperature.