Types of Casting Processes used in Manufacturing

Types of Casting Processes used in Manufacturing

Following are the various type of castings:
(1) Centrifugal casting                                (4) Hollow casting
(2) Chilled casting                                      (5) Sand casting
(3) Die-casting                                            (6) Vertical sand casting

(1) Centrifugal casting: In this type of casting, the molten metal is poured into moulds which are kept rotating. The quantity of metals should be carefully determined and accurately controlled. The moulds are cylindrical and made of metal. The molten metal is spread uniformly by the centrifugal force and it is held till it becomes solid. This method is generally used to prepare pipes and it is found that these castings are stronger and compact than ordinary castings.

(2) Chilled casting: In this type o casting, the outer surface is made hard by sudden cooling or chilling and the inner surface remains comparatively soft. The mould is either made of metal or is lined with metal. The hot molten metal is suddenly cooled or chilled as it comes into contact with the metallic surface of the mould. the outer surface thus becomes suddenly hard and the inner surface becomes soft and tough due to pressure of contraction on the molten metal. This type of casting is adopted to pressure wearing surfaces as in the case of tyres and axle holes of railway carriage wheels, etc.

(3) Die-casting: In this type of casting, the molten metal is poured into metal moulds under pressure. These castings are cheap, smooth and compact. They required no finishing treatment except for the removal of surplus metal.

(4) Hollow casting: In this type of casting, the mould is made as usual and a solid core is suspended in the middle of the mould from the cavity. The thickness of casting is represented by the space between the core and mould. the metal is poured into the annular space and when it has cooled down, The mould is removed and the core is withdrawn. This casting is used for preparing hollow columns, pipes, piles, etc.

(5) Sand casting: This is the ordinary type of casting and its procedure is described above.

(6) Vertical sand casting: In this type of casting, the sand mould and solid core are held in a vertical position. This method of casting is used to prepare the cast-iron pipes for carrying water under pressure.

Qualities of good casting:
  1. Its edges and corners should be sharp, perfect and clean.
  2. Its fresh fracture should exhibit a fine-grained texture with bluish-grey colour.
  3. It should be free from air bubbles,  cracks, etc.
  4. It should soft enough for drilling or chiselling.
  5. It should be uniform in safe and it should be consistent with the requirement of the design.
  6. Its outer surface should be smooth.
  7. No sludge formation during casting.
  8. There should be no impurity in casting material.
  9. It should be free from porosity.
  10. It should be free from surface defects.

Defects in casting:

The sand castings are commonly adopted and if proper precautions are not taken during the process of sand casting, there is a chance for the development of the following defects:

  • Cold-short
  • Drawing
  • Holes
  • Honeycombing
  • Lifts and shifts
  • Scabbing
  • Swelling
  • sludge formation
  • porosity

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