The characteristics of centrifugal casting
Compared with other casting methods, centrifugal casting using rotation to generate centrifugal force has its unique advantages, mainly including the following parts:
(1) Hollow cylindrical and circular castings, as well as pipes of different diameters and lengths, can be cast without the need for sand cores, resulting in high production efficiency and low production costs.
(2) Some castings do not require any sprues, which improves the utilization rate of molten metal. Taking centrifugal ductile iron pipes in copper sleeves, copper worm gears, bearing shells, and cast iron pipes as an example, a 1 ton cast pipe only consumes 1040kg of molten iron, resulting in a yield rate exceeding 96% (including loss of scrap).
(3) Metal liquid solidifies under centrifugal force, resulting in a fine and dense structure. Lighter inclusions such as slag and oxides will float out of the metal liquid body under centrifugal force and remain on the inner surface, which can be removed by mechanical processing methods to ensure the high performance requirements of castings such as engine cylinder liners.
(4) Adjusting the cooling rate of the metal mold can achieve directional solidification of the microstructure from the outer wall to the inner wall within a determined range of casting wall thickness.
(5) It can pour bimetallic castings of different metals, such as rollers, flour mills, turbines (worm gears), bearings, etc., to make the parts hard on the outside and tough on the inside, and have better performance in use.
In addition to the above advantages, centrifugal casting also has limitations that cannot be overcome by the process itself, mainly including the following aspects:
(1) The true centrifugal casting process is only applicable to hollow axisymmetric castings, and there are not many varieties of such castings.
(2) Centrifugal casting requires the use of complex centrifugal casting machines, which are generally more expensive, so the investment in centrifugal casting workshops is greater than other casting methods.
(3) Due to the effect of centrifugal force, it is easy to cause density segregation in certain metal liquids during the solidification process. If centrifugal casting of ductile iron pipes is used during pouring
Excessive carbon equivalent can cause inward segregation of graphite.
(4) The inner surface formed by centrifugal force is relatively rough and often cannot be directly applied.
Application scope: From the advantages and limitations of centrifugal casting mentioned above, it can be seen that centrifugal casting is suitable for specific large-scale production castings.
At present, centrifugal casting has become a widely used casting method in China, especially in the production of some pipe and cylinder castings such as turbines (worm gears), bearings, copper bushings, cast iron pipes, copper sleeves, cylinder sleeves, bimetallic steel back copper sleeves, copper alloy products, etc. Centrifugal casting is a main method. In addition, centrifugal casting method is very effective in the production of heat-resistant steel rollers, some special seamless steel pipe blanks, and paper machine drying drums. Almost all casting alloys can be produced using centrifugal casting method. The minimum inner diameter of centrifugal castings is 8mm, the maximum outer diameter can reach 3m, the maximum length of castings can reach 8m, and the weight range of castings can range from a few thousand grams to more than ten tons.
Production conditions are relatively complex compared to gypsum molds, mainly manifested by the complex structure of centrifugal casting machines and the high cost of equipment compared to gypsum molds. Therefore, the initial investment required is higher than that of gypsum molds, and corresponding centrifugal casting metal molds are also required.