Mechanical properties of cast parts refer to the physical and mechanical characteristics of the materials used in the casting process. These properties determine the strength, durability, and performance of the cast parts. Different casting methods have varying effects on the mechanical properties of the cast parts. Among the given options, centrifugal casting is known to provide superior mechanical properties compared to the other casting methods.

1. Shell-Mould Casting:
- Shell-mould casting is a precision casting process that uses a shell made of a resin-bonded sand mixture to produce complex and accurate castings.
- The process involves creating a hollow shell by curing the sand mixture coated on a pattern, which is then removed to leave a cavity.
- Molten metal is poured into the shell, and after solidification, the shell is broken to retrieve the casting.
- While shell-mould casting allows for high dimensional accuracy and good surface finish, the mechanical properties of the cast parts may not be as superior as in centrifugal casting.

2. Investment Casting:
- Investment casting, also known as lost-wax casting, is a process that uses wax patterns to create molds for casting.
- The wax patterns are coated with a ceramic shell, which is then heated to remove the wax and harden the ceramic.
- Molten metal is poured into the ceramic shell, and after solidification, the shell is broken to retrieve the casting.
- Investment casting offers excellent dimensional accuracy and surface finish but may not provide the same level of mechanical properties as centrifugal casting.

3. Permanent Mould Casting:
- Permanent mould casting, also known as gravity die casting, is a process that uses a reusable metal mold to produce castings.
- Molten metal is poured into the metal mold, and after solidification, the mold is opened to retrieve the casting.
- Permanent mould casting can provide good dimensional accuracy and surface finish, but the mechanical properties may not be as superior as in centrifugal casting.

4. Centrifugal Casting:
- Centrifugal casting is a process that utilizes centrifugal force to distribute molten metal in a mold.
- The mold is rotated at high speed, causing the molten metal to be forced against the mold walls.
- This process ensures a dense and uniform structure, resulting in superior mechanical properties.
- The centrifugal force helps to eliminate gas and impurities, leading to improved strength and integrity of the cast parts.
- Centrifugal casting is particularly suitable for producing cylindrical and symmetrical parts, such as pipes, cylinders, and rings.

In conclusion, centrifugal casting is known to provide superior mechanical properties compared to shell-mould casting, investment casting, and permanent mould casting. The centrifugal force and uniform distribution of molten metal in the mold result in dense and strong cast parts with excellent strength, durability, and performance.