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Posted on May 3, 2008
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Learn the basics techniques and processes of Metal Casting.
Learn about Sand Casting and Spin Casting.
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.
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.
About the author
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Tags: accuracy, additives, casting sand, castings, composition, dry sand, green sand, indefinite period, metal casting, mixture, moist clay, mold, molten metal, novel, rough texture, sand casting, sand molding, sand molds, silica, solidification
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