Wednesday, August 24, 2016

WHAT IS PERMANENT MOLD CASTING, WHAT ARE ITS TYPES

PERMANENT MOULD CASTING:-

  As the name is Permanent Mould Casting, in this method of casting the mould used for casting is permanent i.e. mould can be used repeatedly. In this method mould can be made of metals, ceramics etc.
             This process has the properties of both die casting and die casting. The difference is, in sand casting an expandable mould is used and for permanent mould casting an un-expandable mould is used, that can be used many times repeatedly.
There are some basic types of permanent mould casting given as follows-

  1. Gravity
  2. Slush
  3. Low pressure
  4. Vacuum

GRAVITY CASTING

  • In the gravity process the mould is preheated to 300-450°F. Preheating causes a better flow of material and it reduces the possibilities of casting defects.
  • Now the mould is required which has two part dies. For complex shapes cores can be used.
  • The mould will use a coating of a material to prevent the sticking of the casting for the achievement of required precision and surface finish.
  • Both expandable and un-expandable cores can be used in this process.
  • The cavity is filled with molten metal gradually i.e. slow rate of pouring is required. In the sprue of the mould, then the liquid metal will pass through the runner and then the cavity is poured with molten metal.
  • Cooling of the molten metal will occur for the solidification of metal.
  • Following the process given above the desired product is produced.


SLUSH CASTING

  • Slush casting is a type of permanent casting which is specially used to cast the hollow object.
  • In this the molten metal is poured in the cavity and allowed to solidify only at the walls of the mould and the rest of the material poured out of the mould.
  • In the mould cavity only a hollow shell will remain at the walls of the mould.
  • This method is generally used for production of toys, ornamental products etc. in which less material and light weight is required.

LOW PRESSURE CASTING

  • In this the material is forced with a low pressure gas. The pressure is applied at the top of the molten metal to force it to fill in the cavity.
  •  The low pressure causes the shrinkage in the material so there is no requirement of the riser in the setup of mould.

VACUUM CASTING

  •  In this process of permanent mould casting the vacuum pressure is used to pour the material. It is beneficial for the elimination of the gases present in the molten metal and purifies it.
  • It possesses almost all properties and benefits of low pressure permanent casting.
  • Thin casting can be produced with high precision and very fine surface finish.
  • Improved mechanical surface finish. Improved mechanical properties can be achieved by this method.

 Advantage of Permanent mould Casting

  • The main advantage of permanent mould casting is reusable mould.
  • It provides nice dimensional accuracy and surface finish.



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