Casting process(part 1)

Theory:

             Casting process is based on the property of a liquid to take up the shape of vessel containing it. Molten metal poured into a mould flows into the corners and fills all the voids. When metal solidifies it takes the shape of mould but not exactly the same because solid being demos there is reduction of volume. A foundry is a collection of the necessary materials or equipments to produce a casting. Practically all metals are initially cast. The casting process involves the following basic steps.

       1)     Pattern making

       2)     Mould making

       3)     Melting the metal

       4)     Pouring it into the cavity

       5)     Allowing the molten metal cold and solidify it the mould

       6)     Removing the solidified component, cleaning it and subjecting it for further treatment if necessary.

            One of the most attractive features of casting is its ability to form any shape in one operation. Casting is one of the most versatile forms of mechanical process for producing components; because there is no limit to the size, shape and intricacy of the articles that can be produced by casting. It offers one of the cheapest methods and gives high strength and rigidity even to intricate pasts, which are difficult to produce by other methods of manufacturing.

Types of Casting Methods:

   1)   Casting in metallic moulds

1.      Permanent mould casting

2.      Stush casting

3.      Press casting

4.      Die casting

   2)   Casting in non-metallic moulds

1.     Centrifugal casting

a)      True centrifugal

b)     Semi centrifugal

c)      Centrifugal

2.     Precision casting

a)      Lost wax method

b)     Plaster moulds

c)      Mercast process

d)     Shell molding

3.     Moulds of wood, rubber paper etc.

   3)   Continuous casting

1.      Reciprocating moulds

2.      Draw methods

3.      Stationary moulds

4.      Direct sheet casting

Tools required:

    1.      A pattern

    2.      Molding box

    3.      Metal

    4.      Furnace

    5.      File

A pattern:

             A pattern is a model made of suitable material and is used for making to cavity in molding sand or other suitable mould materials. A pattern is defined as a model of casting, constructed in such a way that it can be used for forcing as mould in damp sand. The first step in making a casting is to prepare a model, known as a pattern, which differs in a number of respects from the resulting casting. Most patterns are made of wood because of its cheapness, ease of availibity, lightness, ease of obtaining smooth surface and preserving surface by applying coating of shellac, ability to be worked on easily. It has been said that a poor casting may be produced from a good pattern but a good casting will be made a poor pattern.

     The Mould:

               A mould is the container that has the cavity or cavities of the shape to be cast. Good casting cannot be produced without good mould. Mould may be of two types.

    1)     Permanent type

    2)     Temporary type

According to the sand there are various types of mould

     a)      Green sand mould

     b)     Dry sand mould

     c)      Loam sand mould

     d)     Core sand mould 

     e)      Cemented bounded mould

     f)       Resin bounded sand mould

     g)      Skin dry sand mould etc.

            The mould must be strength enough to hold the weight of the metal and resist corrosive action of the rapidly flowing metal during pouring. The mould must generate a minimum amount of gas when filled with molten metal and must be constructed so that any gases formed can pass through the body of the mould itself. The necessary equipment that a mould being made are given below-

     a)      Molding board

     b)      Shovel

     c)      Riddle

     d)     Rammer

     e)      Bellows

     f)       Lifters

     g)      SW

     h)     Vent wire

     i)        Gate cutter