2017-05-15 14:56:31

Metal Casting Processes

There are various casting processes being implemented now days. The oldest amongst them is sand casting. Spin casting is also widely used. They can be described as follows:

Sand Casting: Sand casting involves formation of mold from a mixture of sand and to pour a casting liquid, most probably, a molten metal into mold. The metal is then allowed to solidify and the removal of mold, takes place. Sand molding consists of two types: green sand method and air set method. The first one consists of mixture of clay, moisture, silica, and many other additives. The second one consists of mixture of dry sand and other materials, not moist clay. They are mixed with the help of a quick curing adhesive. The collective use of these materials is called 'air set'.

At times, there is temporary plug placed to pour the fluid which is to be molded. Air-set molds usually form molds consisting of two parts-the bottom and the top. The mixture of sand gets tamped down after its addition. It does not generate any by-product. After the solidification and cooling of metal, the mold gets usually destroyed. This is because its removal involves a lot of breaking and cracking. The casting accuracy depends a great deal on the sand and the process of molding used. Castings composed of green sand result into formation of rough texture on casting surface, and this characteristic makes them easily recognizable. Air-set molds produce smoother castings.
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Many a times, the casting process results in losing of components of sand mixture. It is possible to reuse green sand by the way of adjusting the composition to get the lost additives and moisture replenished. The entire pattern itself is eligible to be reused for producing novel sand molds. The method of reuse can be continued for an indefinite period. In 1950, casting process got automated partially. They have been in great demand for developing production lines since then.

Spin Casting: Spin Casting is better known as Centrifugal Rubber Mold Casting (CRMC). It implies utilization of centrifugal force for producing castings out of rubber mold. As a customary practice, a mold having shape of a disc gets spun through its 'central axis' at a pre-decided speed. The material used for casting is usually thermoset plastic in the liquid form or a molten metal. It gets poured into the mold through the opening at its centre. Corresponding to the solidification of metal, or the setting of thermoset plastic, the spinning of the filled mold takes place.

Normally, organic rubber or vulcanized silicone is used as a mold-making substrate in spin casting. Vulcanization takes place in the middle of process of mold-making. After the successful completion of vulcanization process, venting and gating must be undergone by the mold. This implies carving of channels for ensuring proper material flow and air during the course of casting. A scalpel or knife is used to carry out the above two processes. The mold complexity is directly proportional to the time required in implementation of venting and gating.

 

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