Centrifugal Casting- Parts, Working, Types, Advantages, Disadvantages and Applications.

Centrifugal casting is the process of casting in which centrifugal force is used for the casting process. It is also called roto casting.
Before knowing about centrifugal casting, you must know what is a centrifugal force:
Centrifugal force is the force that is felt by any object moving in a curved path and is directed radially outward.
Centrifugal Casting was invented by Alfred Krupp in the year 1852. He used it for manufacturing railway wheels.
High-quality products can be created using this casting technique by proper control of metallurgy and crystal structure.
This casting technique is mainly used to produce rotationally symmetric products.
The product obtained by this process is not the final product, it requires some machining for providing a good finishing.

This technique is a cost-effective technique for producing complex shapes. The use of the machining process is reduced in this technique. The manufacturing cost in this technique is much lower as compared to other processes like forging.

In this process, the outer diameter of the component is determined by the interior dimension of the mold and the inner diameter of the component is determined by the amount of metal poured inside the mold.

Vacuum Centrifugal Casting:
It is an advanced type of centrifugal casting. In this type of centrifugal casting, the casting of metal is done in a vacuum.
This type of centrifugal casting was introduced because some alloys like nickel-cobalt superalloys are reactive to oxygen, so these alloys should be cast in absence of oxygen, and hence vacuum centrifugal casting is used to cast these type of alloys.
The products produced by vacuum centrifugal casting are very reliable. This process is often used in aerospace and military applications.

Materials cast using Centrifugal Casting:
Centrifugal casting is mainly used for casting materials like glass, iron, steel, stainless, steel, and alloys aluminum, copper, and nickel.

Types of Centrifugal Casting:

There are mainly two types of Centrifugal Casting:
1) Vertical Centrifugal Casting.
2) Horizontal Centrifugal Casting.

1) Vertical Centrifugal Casting:
Vertical centrifugal casting is preferred for producing cylindrical shapes that have a diameter more than the length or height of the cylinder. example – rings and bearings production.

2) Horizontal Centrifugal Casting:
This process is especially used for long cylindrical parts where the casting length is much longer than the outside diameter.
When the height of the product to be cast is long then horizontal centrifugal casting is used so that the effect of gravity is evenly distributed.
It is a cost-effective method of producing high-quality tubular components.

Horizontal Centrifugal Casting is preferred for long cylinders and vertical centrifugal casting is preferred for rings and bearings production.

Parts Used In Centrifugal Casting:

i) Ladle:
The ladle is used to put the molten metal into the pouring basin.

ii) Pouring Basin:
The pouring basin is used to pour the molten metal into the mold. the molten metal is introduced to the pouring basin using a ladle.

iii) Rollers:
There are four rollers, two on the bottom and two on the top. The bottom rollers are connected to the motor and rotate with it while the two rollers on the top provide support to the mold while rotating.

iv) Motor:
The motor is used to provide rotatory motion to the two bottom rollers which in turn rotates the mold.

v) Mold:
The mold is used to contain the molten metal and rotate it at high speed. The mold rotates continuously about its axis at high speed. The molten metal is poured into the mold using a pouring basin.

Working Of Centrifugal Casting:

In this casting method, high speed rotation of permanent mold is done and molten metal is poured simultaneously.
When the molten metal s poured into the preheated rotating mold, the molten metal spreads inside the wall of the mold due to the centrifugal force created due to rotation. The pressure created by the centrifugal force is nearly 100 times the force of gravity.
The mold cavity rotates at a speed of nearly 300 to 3000 RPM about its axis.
As the mold starts filling, more dense metal move towards the wall of the spinning mold.
After some time the molten metal solidifies after cooling. The molten metal solidifies in a particular direction from the outer diameter towards the inner diameter. Due to directional solidification mid-wall shrink is avoided and hence resulting in a defect-free structure without cavities or gas pockets.
After the rotation, the mold is taken out of the rotating rollers. The mold is allowed to cool down evenly and gradually so that the metal does not get blistered and rendered.
In this process, the impurities present in the mold move inward towards the inner diameter and can be easily removed after casting by machining processes.
Due to controlled solidification and secondary refining, high quality components can be produced using this casting process.

The parts produced using centrifugal casting have a fine-grain microstructure that can easily resist atmospheric corrosion.

Steps Of Centrifugal Casting:

1) Mold Preparation:
At first, the mold is prepared before pouring the molten metal. The walls of the cylindrical mold are coated with refractory ceramic coating which involves steps like application, rotation, drying, and baking of refractory ceramic coating.

2) Pouring:
After the mold preparation, the molten metal is poured directly into the rotating mold without the use of a runner or gating system.
High speed rotation of permanent mold is done and molten metal is poured simultaneously.
When the molten metal is poured into the preheated rotating mold, the molten metal spreads inside the wall of the mold due to the centrifugal force created due to rotation. The pressure created by the centrifugal force is nearly 100 times the force of gravity.
The mold cavity rotates at a speed of nearly 300 to 3000 RPM about its axis.
As the mold starts filling, more dense metal move towards the wall of the spinning mold.
As the mold starts filling, more dense metal move towards the wall of the spinning mold.
Less dense metal and impurities present in the mold move inward towards the inner diameter. Hence, the impurities can be easily removed after casting by machining processes.

3) Cooling:
While the mold rotates, the molten metal cools slowly. The mold is allowed to cool down evenly and gradually so that the metal does not get blistered and rendered.
Cooling is directed from the mold walls towards the inner diameter of the molten metal. It means molten metal near the mold wall cools quickly.
Due to directional solidification mid-wall shrink is avoided and hence resulting in a defect-free structure without cavities or gas pockets.
Due to controlled solidification and secondary refining, high-quality components can be produced using this casting process.

4) Casting removal:
After the molten metal cools down and fully solidifies, the mold is removed from the roller, and rotation is stopped. Now the casting is removed from the mold.

5) Finishing:
When the metal cast is obtained after centrifugal casting, the product is then machined to provide the finishing. Finishing is done by machining, grinding or sand-blasting of the inner diameter of the product to remove impurities and make the inner and outer surface smooth.

Conditions in which centrifugal casting is used:

i) When a uniform grain structure is required.
ii) When dimensional integrity is required.
iii) When rotational symmetric parts are to be produced.
iv) When centerline shrink issue occurs in other casting processes.

Advantages Of Centrifugal Casting:

i) Thin-walled cylinders can be easily cast using this technique which is otherwise very difficult to cast by other techniques or processes.
ii) It can be used to produce products in which grain, flow, and balance is important for the durability of the finished products.
iii) This process can produce components with intricate geometries at a lower cost.
iv) The parts produced using centrifugal casting have a fine-grain microstructure that can easily resist atmospheric corrosion.
v) The parts produced using centrifugal casting have a fine-grain microstructure that can easily resist atmospheric corrosion.
vi) This casting technique ensure the purity of the final product as the all the impurities move towards the inner diameter and can be easily removed by casting.

Disadvantages Of Centrifugal Casting:

i) When producing products with small internal diameters, this technique becomes ineffective because it becomes hard to remove the impurities at the internal diameter.
ii) The centrifugal casting is good only for creating cylindrical shapes. For shapes other than cylindrical shapes, there is a loss in structural and purity benefits. More machining is required to produce shapes other than cylindrical shapes and chance making the process more costly.
iii) The size that can be produced using this technique is limited because of the following reasons:
During centrifugal casting parabola is created at the bottom which increases the machining time. To avoid the parabola at the bottom, the ratio of height to diameter is kept at 2:1. This limits the size that can be produced using centrifugal casting.

Applications Of Centrifugal Casting:

i) It used to cast hollow cylindrical metal pipes.
ii) It is also used to create flywheels, cylinder liners.
iii) It is used to create parts that are axisymmetric in shape.
iv) It is also used to cast sleeve valves of piston engines.
v) It is used to manufacture railway carriage wheels.