True centrifugal casting
This is normally China CNC machining used for the making of hollow pipes, tubes, hollow bushes, etc., which are axisymmetric with a concentric hole. Since the metal is always pushed outward because of the centrifugal force, no core needs to be used for making the concentric hole. The axis of rotation can be either horizontal, vertical or any angle in between. Very long pipes are normally cast with horizontal axis, whereas short pieces are more conveniently cast with a vertical axis.
A normal centrifugal casting machine used for making cast iron pipes in sand mould is shown in Fig. 11.12. First, the moulding flask is properly rammed with sand to confirm to the outer contour of the pipe to be made. Any end details, such as spigot ends, or flanged ends are obtained with the help of dry sand cores located in the ends. Then the flask is dynamically balanced so as to reduce the occurrence of undesirable vibrations during the casting process. The finished flask in mounted in between the rollers and the mould is rotated slowly. Now the molten metal poured determines the thickness of the pipe to be cast. China CNC machiningAfter the pouring is complete, the mould is rotated at its operational speed till it solidifies, to form the requisite bubing. Then the mould is replaced by a new mould machine and the process continued.
Metal mould can also be used in the true centrifugal casting process for large quantity production. A water jacket is provided around the mould for cooling it. The casting machine is mounted on wheels with the pouring ladle, which has a long spout extending till the other end of the pipe to be made. To start, the mould is rotated with the metal being delivered at the extreme end of the pipe. The casting machine is slowly moved down the track allowing the metal to be deposited all along the length of the pipe.
The machine is China CNC machining continuously rotated till the pipe is completely solidified. Afterwards, the pipe is extracted from the mould and the cycle repeated.