Casting Concepts Engineering Workshop MECHANICAL THEORY

Sand Casting Process – Definition,Steps,Diagram,Aspiration Effect,Elements of Sprue etc.

Sand Casting Process Definition: Casting is a process in which the liquid molten metal is poured into the casting cavity whose shape is same as that of the shape of the casting to be produced, allowing to solidify and after solidification, the casting will be taken out by breaking the mould called as Casting Process.

Steps in the Sand Casting Process:

  1. Pattern making
  2. Mould and Core making
  3. Pouring and Solidification
  4. Fetling
  5. Inspection

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Sand Casting Process Diagram:

 

 

Sand Casting Process - Definition,Steps,Diagram,Aspiration Effect,Elements of Sprue etc.
Sand Casting Process -Definition, Steps, Diagram, Aspiration Effect, Elements of Sprue etc.

 

Sand Casting Process/Procedure:

The diagram of sand casting was presented below. It consists of

1.Pouring Basin

2.Sprue

3.Runner

4.Ingate

5.Casting Cavity

6.Riser

The detailed explanation of above sand casting terms is presented below.

1.Pouring Basin:

  • The molten metal is to be poured into the Pouring basin so that it can enter into the mould cavity.
  • The pouring basin  separates the impurities[lighter and heavier impurities present in the molten material]
  • A thin plate at the end of pouring basin will absorb the excess heat available in the molten metal and the total plate will get melted at a time so that molten metal produced by plate and molten metal collected over the plate will try to flows through the gating system simultaneously which includes the full flow of molten metal through the gating system.
  • The size and shape of the pouring basin will not have much effect on the flow rate or pouring time of molten metal in the gating system.

2.Sprue:

It is connecting the passage between pouring basin and Runner. It is always vertical with a straight tapered circular cross section.

Characteristics of Sprue:

Basically, Velocity of molten metal in the gating system is represented by

          V = Sqrt.2gh

                      Where ‘h’ is the height of the sprue.

The height of the sprue is mainly responsible for producing the velocity of molten metal in a gating system. The height of the sprue is selected such that the velocity of molten metal in the gating system must always ensure laminar flow.

Straight tapered sprue is selected to avoid the aspiration effect in the gating system.

Aspiration Effect/Inhalation Effect/Breathing Effect:

During filling of molten metal into the casting cavity using gating system somewhere along the gating system due to some reason, if the pressure falls below atmospheric pressure, the pressure difference is existing between the inside and outside of gating system. Due to this pressure difference, the air starts flowing from outside to the inside of gating system through Porosity property of moulding sand called as aspiration effect.

Other Elements in Sprue:

1.Strainer:

  • Always kept in sprue only.
  • It is used for separating/filtering the impurities present in the molten metal.
  • It is made by using a Ceramic material with high porosity.

2.Splash Core:

  • Used for avoiding sand erosion from the bottom of Sprue.
  • Also made by using a Ceramic material with low porosity.

3.Skim Bob:

  • It is a Semi circular cut given in Runner.
  • It is used for separating Impurities present in molten metal.

By these additional elements in Sprue, all possible impurities are separated from the molten metal.

Runner:

It is a connecting passage between the bottom of the Sprue and ingate. It is always horizontal with uniform Trapezoidal Cross section.

It is mainly used for minimizing the sand erosion in the casting process.

        Qactual = Cd*Qtheoretical

A trapezoidal cross section has the highest value of the coefficient of discharge(Cd) and for that reason, it is selected for the design of a runner.

Ingate:

It is the last section of the gating system from where the molten metal is entering into the casting cavity. It is also horizontal and uniform trapezoidal in cross-section.

Casting Cavity:

It is the cavity in which the molten metal is filled and solidified in order to get the desired product.

Riser:

The riser is acting as a Reservoir for supplying the molten metal to the casting gravity for compensating the liquid Shrinkages taking place during solidification.

Parting Line:

It is the line that divides the Cope and Drag.

Vents:

It is a small opening in the mould to escape the gases during solidification.

Chaplets:

Chaplets are used to support the cores inside the mould cavity to take care of its own weight.

Cope and Drag:

The Top Flask is called as Cope and the bottom Flask is called as Drag.

This is the complete explanation of Sand Casting Process in a detailed way.

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