The main difference between semi-centrifugal and centrifuging casting processes lies in the resulting shape of the cast part, specifically the presence or absence of a central void.
While both processes utilize centrifugal force during solidification to improve casting quality and produce parts with rotational symmetry, they differ in how the mold is filled and oriented.
Key Difference Highlighted
The most significant distinction, as supported by the provided reference, is the final form of the casting:
Parts cast using a semi-centrifugal process will retain rotational symmetry, but will not have the central, cylindrical void achieved by true centrifugal castings.
This means:
- True Centrifugal Casting: Produces hollow cylindrical or tubular parts. The centrifugal force pushes the molten metal outwards towards the mold walls, leaving a clean central bore.
- Semi-Centrifugal Casting: Produces solid or spoked parts that are rotationally symmetrical but do not have a through-and-through central hole formed by the centrifugal force itself. The center is typically filled with metal, although it might be a solid hub or core area rather than a void.
How the Difference Arises
The operational setup contributes to this difference:
-
Centrifugal Casting (True):
- The mold rotates around its own axis, which is usually horizontal.
- Molten metal is poured directly into the rotating mold.
- The centrifugal force distributes the metal evenly against the inner wall, forming a uniform hollow cylinder. The inner surface is the result of the free surface of the liquid metal under rotation.
-
Semi-Centrifugal Casting:
- The mold rotates, often around a central vertical axis.
- The mold typically has a central gate or sprue through which the metal is poured.
- Centrifugal force helps fill the mold cavities, push the metal outwards towards the periphery, and improve density, especially in areas away from the center. However, the central area is usually designed to be filled, often serving as a riser or hub. The mold cavity itself defines both the outer and inner shape (if any non-void inner features exist).
Comparing the Processes
Here's a simple comparison:
| Feature | Centrifugal Casting (True) | Semi-Centrifugal Casting |
|---|---|---|
| Resulting Shape | Hollow cylinder/tube with central void | Solid or spoked rotationally symmetric part without a central void |
| Primary Use | Pipes, tubes, rings, bushings | Wheels, gears, pulleys, flywheels |
| Mold Filling | Metal adheres to inner mold wall due to force | Centrifugal force aids filling and densification of mold cavity |
| Central Area | Forms a self-formed void | Is a filled part of the casting |
| Typical Axis | Horizontal (often) | Vertical (often) |
Practical Examples
- Centrifugal: Cast iron pipes for water systems, bronze bushings, composite rocket casings.
- Semi-Centrifugal: Car wheels, large gear blanks, industrial sheaves.
In essence, if you need a self-formed hollow cylindrical shape, true centrifugal casting is the process. If you need a solid or spoked round part with improved outer quality and density, semi-centrifugal casting is appropriate.
