What is Plaster Mold Casting Process? (All you need to know)

plaster mold casting process
Cast component of section thickness 1 mm made by plaster mold casting process

What is Plaster Mold Casting?
Plaster Mold Casting (also known as plaster casting) is a metal casting process which is similar to the sand casting process, except the molding material is Plaster of Paris instead of sand.
Plaster mold casting process is generally used for casting non-ferrous metals.

Few important things about the plaster mold casting process.

  • By using a plaster casting process, small castings of around 30 grams as well as large castings of around 45 kg can also be manufactured.
  • The components like gears, fittings, toolings, lock components, valves, and ornaments can be manufactured using a plaster casting process.
  • Plaster Casting is used to manufacture the castings from aluminum, magnesium and copper based alloys.

Plaster Mold Casting Process (Steps)

The steps involved in plaster mold casting process are mentioned below.

  • First of all, the powdered form of Plaster of Paris (POP) is mixed with water in order to form the plaster.
  • In the next step, the POP and water mixture is mixed with additives like talc and silica floor.
  • These additives are added during the plaster molding process which increases the setting time and improves the strength of the mold.
  • In this mixture, the gypsum is around 70 to 80%, while  the additives are around 20 to 30%.
  • The slurry is kept for around 20 to 25 minutes so that it sets properly before removing the pattern.
  • The pattern used for the plaster molding process is either made up of plastic or metal.
  • Wood patterns are not preferred as wood shows a tendency to warp when it remains in contact with the moist plaster for a longer time.
  • After this, the mould is separated from the pattern and it is baked at temperature between 120 °C to 260 °C. The baking is done for several hours which removes the moisture content from the mold and it also gives strength to the mold.
  • Two halves of the mold are assembled with each other and finally the molten metal is poured in the mold cavity.
  • The molten metal is allowed to solidify and after this, the final casting becomes ready.

You can see the final casting component that is manufactured by using a plaster mold casting process. (See below image).

plaster mold casting process

The components having thickness ranging from 0.25 mm to 1 mm can also be manufactured by this process.

Having said that, let’s discuss the advantages and disadvantages of the plaster mold casting process.

Advantages of Plaster Mold Casting

Advantages of Plaster mold casting are mentioned below.

  1. By using plaster mold casting, the components having thickness upto 0.6 mm can be manufactured.
  2. Manufacturing of complex shapes is possible at less cost, because this process produces minimum scrap material.
  3. Good geometric accuracy can be obtained by using a plaster casting process.
  4. Smooth surface finish can be obtained.

Disadvantages of Plaster Mold Casting

Disadvantages of Plaster mold casting are mentioned below.

  1. The plaster mold can not handle temperatures higher than 1200 °C.
  2. The materials having higher melting point cannot be casted using the plaster molding process.
  3. The manufacturing of each component takes more time as the mold preparation and setting of plaster consumes more time.
  4. If the moisture content is more in the mold, then it will cause casting defects. And if the moisture content is less, then it will possess less strength.
  5. Cooling of molten metal takes more time, because the plaster mold has less thermal conductivity as compared to sand molds.
  6. Because of the longer time for solidification, the production rate is slow.
  7. The stability of plaster is less as compared to the stability of sand. So, there should be enough monitoring of factors like plaster composition, pouring procedure, etc, otherwise mold can damage, shrink upon drying, may have poor surface finish, it may develop cracks or it may fail completely.
  8. This process is used only for casting non-ferrous metals like aluminum, copper, zinc, and magnesium.
  9. Plaster mold can not be reused.

Applications of Plaster Mold Casting

Applications of Plaster mold casting are mentioned below.

  1. Plaster mold casting is used in manufacturing industries for casting non-ferrous metals like zinc, magnesium, aluminum and copper based alloys.
  2. Parts like valves, gears, tooling, lock components, etc. can be manufactured by using a plaster mold casting process.
  3. Lighter components having weight 30 grams to the heavier components weighing 45 kg can be manufactured using a plaster casting process.

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