Centrifugal casting, as an efficient casting method, is widely used in modern industrial fields.
It involves injecting liquid metal into a high-speed rotating mold, using centrifugal force to ensure the molten metal fully fills the mold and forms the casting. This technique not only creates free surfaces but also allows for the creation of cylindrical internal holes without the need for cores, while also helping to remove gases and inclusions from the metal. By influencing the crystallization process of the metal, centrifugal casting can significantly improve the mechanical and physical properties of the casting.
Common types of centrifugal casting include horizontal centrifugal casting, vertical centrifugal casting, and inclined-axis centrifugal casting. Horizontal centrifugal casting refers to centrifugal casting where the mold’s axis of rotation is horizontal or at a very small angle to the horizontal; while vertical centrifugal casting is a casting method where the mold’s axis is vertical. Although inclined-axis centrifugal casting is relatively less common in practice, it is also a type of centrifugal casting.
Applications and Development of Centrifugal Casting
Centrifugal casting, this efficient casting technology, has demonstrated its unique advantages in various industrial fields since its inception. Initially, it was mainly used for the production of cast pipes, but with continuous technological advancements, its application range has expanded to metallurgy, mining, transportation, irrigation machinery, aerospace, national defense, and automotive industries. In these fields, centrifugal casting is widely used in the manufacture of steel, iron, and non-ferrous alloy castings, especially in the production of centrifugal cast iron pipes, internal combustion engine cylinder liners, and bushings. Furthermore, for some forming tools and gear castings requiring high precision and high mechanical properties, centrifugal casting technology also demonstrates its excellent effectiveness. By using centrifugal force to pour molten metal into the mold shell, not only can the accuracy of the casting be improved, but its mechanical properties can also be significantly enhanced.
1) During the centrifugal casting process, because the molten metal is thrown out under high-speed rotation, there is almost no metal consumption in the gating system and riser system, thus improving the process yield. 2) The production of hollow castings does not require the use of cores, which significantly simplifies the production process of long tubular castings, improves metal filling capabilities, and reduces the ratio of casting wall thickness to length or diameter.
3) Centrifugal casting produces castings with high density, reducing defects such as pores and inclusions, thereby improving mechanical properties.
4) This technology is also suitable for manufacturing cylindrical and sleeve-shaped composite metal castings, such as steel-backed copper bushings and bimetallic rolls. During casting, centrifugal force can further improve the metal’s filling capacity, making the production of thin-walled castings possible.
However, centrifugal casting also has some drawbacks:
Centrifugal casting has certain limitations in producing irregularly shaped castings.
The inner diameter of the casting may be inaccurate, and the inner surface is relatively rough and of poor quality, requiring a larger machining allowance.
Because the casting is prone to density segregation, this process is not suitable for alloys that are prone to density segregation, especially for alloys where the density of impurities is greater than that of the molten metal.
Several key steps need attention during the centrifugal casting process:
First, metal filtration is essential. Some molten alloys may contain difficult-to-remove slag, so a filter screen, such as a ceramic foam or glass fiber filter, should be installed in the gating system to remove the slag.
Secondly, controlling the pouring temperature is also crucial. Since centrifugal castings are mostly tubular, sleeve-shaped, or ring-shaped, the resistance encountered by the molten metal during filling is relatively small, and the centrifugal pressure or force enhances the metal’s filling capacity. Therefore, the pouring temperature during centrifugal casting can be appropriately lower than that of gravity casting, by about 5-10°C.
In addition, the selection of the mold rotation speed is critical. Different castings and casting processes require different rotation speeds. Too low a speed may lead to poor metal filling, while too high a speed may cause defects such as cracks and segregation in the casting. Therefore, when selecting the mold rotation speed, the smallest value should be chosen while ensuring the quality of the casting.
Furthermore, utilizing slag is also an effective process improvement measure. For thick-walled centrifugal castings, bidirectional solidification can cause subcutaneous shrinkage defects. By adding a slag-forming agent to the molten metal during pouring, the slag can cover the inner surface of the casting, preventing heat dissipation and thus creating a sequential solidification condition from the outside in, eliminating subcutaneous shrinkage. At the same time, the slag-forming agent also refines the molten metal.
Finally, the use of coatings is also an important aspect to consider. The coatings used for centrifugal metal molds are similar to those used in gravity metal mold casting. However, when casting long, slender centrifugal castings, because it is difficult to remove residual coating from the working surface of the mold, the residual strength of the binder in the coating after high-temperature operation should be as low as possible to facilitate subsequent cleaning.
Casting demolding is a crucial step in the centrifugal casting process. To improve production efficiency and ensure quality, we should demold the casting at the appropriate time. In some cases, to prevent cracking, the demolded casting is immediately placed in a holding furnace or buried in a sand pile for cooling. For castings that are difficult to demold and require slow cooling to prevent cracking, we can immediately remove the mold with the casting from the centrifugal casting machine after the mold stops rotating and bury it in a sand pile for slow cooling. The demolding operation is then performed when the casting has cooled to room temperature.
In the centrifugal casting process, the gating system plays a vital role. It mainly includes the pouring cup that receives the metal and the pouring channel connected to it, and sometimes also includes the sprue within the mold. These components together form a smooth path for the molten metal from the pouring cup to the mold.
In addition, pouring quantity is also a critical aspect of the centrifugal casting process. Since the inner diameter of centrifugal castings is usually determined by the amount of molten metal poured, it is essential to precisely control the amount of molten metal poured into the mold during centrifugal casting to ensure the accuracy of the casting’s inner diameter.
Centrifugal casting, at its core, involves pouring liquid metal into a rotating mold, using centrifugal force to fully fill the mold and solidify the metal. To achieve this process, the use of a centrifugal casting machine is crucial, as it provides the necessary conditions for mold rotation. Based on the difference in the position of the mold’s rotation axis in space, centrifugal casting machines can be divided into two main types: vertical and horizontal.
The entire process includes several steps, such as mold assembly, preheating, coating application, quantitative pouring of the alloy, water cooling, demolding, and mold cleaning.
Centrifugal casting is a well-established and mature metal casting process. If you have a large-volume custom order for centrifugal castings, you can choose to cooperate with Mulan Manufacturing Group. Mulan Manufacturing Group has 13 years of experience in metal casting, helping customers in more than 30 countries worldwide complete the production and processing of various castings, and has received consistent recognition. We look forward to your cooperation inquiry.
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