Centrifugal casting: frequently asked questions
What are the advantages and disadvantages of the centrifugal casting process? How does the process work? And which components can be produced with it? We answer the most important questions about “centrifugal casting”. Continue reading
- How does the centrifugal casting process work?
- What is a mould?
- How fast does the mould rotate during the casting process?
- Does a new mould have to be made for each component?
- What does a centrifugal casting machine look like?
- Why are there horizontal and vertical casting machines?
- What is the main advantage of the centrifugal casting process?
- Are components manufactured by centrifugal casting comparable with forging quality?
- What are the disadvantages of the centrifugal casting process?
- Which components can be produced in the centrifugal casting process?
- What dimensions are possible in the centrifugal casting process?
- Which quantities can be cast by centrifugal casting?
- Is a composite casting made of different materials possible in the centrifugal casting process?
- For which fields of application is centrifugal casting not suitable?
- In which industries are components from the centrifugal casting process used?
How does the centrifugal casting process work?
In centrifugal casting, liquid steel or liquid iron with a temperature in the range of 1,300 to 1,600 degrees Celsius is filled into a rapidly rotating mould. Due to the centrifugal force, the material is pressed to the outside and thus onto the inner wall of the mould. There it slowly solidifies while the material cools down and thus takes on the inner shape of the mould. The mould can rotate lying (horizontal casting) or standing (vertical casting). After solidification, the cast part is removed from the mould and further processed as required in heat treatment and / or stock removal.
What is a mould?
A mould is a recyclable casting mould, also called a permanent mould. The mould is usually made of forged steel and is coated on the inside with a ceramic protective layer, the so-called dressing. In the centrifugal casting process, the mould rotates about its central axis.
How fast does the mould rotate during the casting process?
The speed of rotation depends on various factors. Due to the speed of rotation, the melt is exposed to the centripetal forces – similar to a carousel, only much stronger. In horizontal casting, these are in the range of 60 to 120 g (1 g = gravitational force on Earth). Depending on the diameter, horizontal gravity moulds therefore rotate in the order of a few hundred rpm to over two thousand rpm.
In vertical casting, the rotational speed is critical for the formation of the inner contour. Here, depending on the rotational speed, a cone is formed (similar to a water glass, which is quickly swivelled). Therefore, the rotational speeds in vertical casting are significantly lower.
Does a new mould have to be made for each component?
This varies. Moulds are often recyclable and the customer-specific dimensions and shapes are then created by machining the casting blank during stock removal. In order for this blank to be as close as possible to the final shape, centrifugal foundries usually have a stock of different moulds, so that it is not always necessary to create a new mould. However, there are also components in which the mould is designed individually for the corresponding outer contour.
What does a centrifugal casting machine look like?
A distinction is made between horizontal and vertical machines. The core of the machine is always the mould which is attached to a rotating central axis and is sealed with lids. In horizontal casting, the melt is poured into a “lying” gravity mould, in vertical casting into a “standing” one.
Why are there horizontal and vertical casting machines?
Originally, vertical casting machines were mainly used for the centrifugal casting of conical components or spherical shapes. In addition, vertical casting is superior to horizontal casting when it comes to the production of large, heavy-weight components.
What is the main advantage of the centrifugal casting process?
Due to the directional, centripetal solidification, centrifugal casting has distinctly isotropic material properties, which distinguishes it in particular from drawn or forged tubes. The quality of the cast structure is far superior to static casting, and centrifugally cast components are often almost the same in their properties as forged components, but offer significant advantages in the flexibility of the materials that can be produced and allow a close-contour design of the cast part, which in principle can be more efficient, environmentally friendly and cost-effective. Due to the special manufacturing process, it is possible to cast independently of the dimensions, i.e. in particular the wall thickness can be influenced in such a way that the necessary post-processing is reduced to a minimum.
Are components manufactured by centrifugal casting comparable with forging quality?
Yes. Due to the high centrifugal forces with which the liquid steel is pressed against the inner wall of the mould and the slow solidification during the centrifugal process, the components have considerably fewer pores and inclusions. Centrifugal casting is very pure and homogeneous in its properties. Therefore, the components are very resilient. In addition, materials and material modifications can also be manufactured efficiently and quickly for individual components.
What are the disadvantages of the centrifugal casting process?
The shaping is restricted by the necessary rotation. The process is therefore only suitable for ring-shaped and tubular components or, simply put, “everything that is round and has a hole in the middle”. In terms of materials, there are no significant disadvantages compared to static casting or forge products.
Which components can be produced in the centrifugal casting process?
In principle, all tubular and ring-shaped components can be produced by centrifugal casting. Classic components are: pipes, hollow shafts, shaft protection sleeves, rings, wheels, joint and liner bushings, seals, gear balls, tie rods, drums, rollers, cylinder liners, drum shells and screw bodies.
What dimensions are possible in the centrifugal casting process?
The dimensions depend on the available casting machines and compatible moulds and are therefore individual in each foundry.
Which quantities can be cast by centrifugal casting?
In principle, one-off productions as well as series productions are possible in the centrifugal casting process. The suitability of the process must therefore be determined individually, depending on the requirements of the corresponding component.
Is a composite casting made of different materials possible in the centrifugal casting process?
Yes. In the centrifugal casting process, it is possible to combine different materials. The layers are poured over one another, usually while the solidification has not yet been completed. In this way, different properties of steels can be combined and, for example, components can be cast that have a highly corrosion or wear-resistant outer layer of several centimetres and have a ductile core.
For which fields of application is centrifugal casting not suitable?
Each component produced by centrifugal casting has a central hole (at least a small one) due to the production in rotation. This means that flat components such as sheets, pans, etc. as well as complex, closed shapes cannot be cast by centrifugal casting.
In which industries are components from the centrifugal casting process used?
Components are used almost throughout the entire industry, usually as part of larger installations or motors and generators. Classic branches of industry are the construction of large engines, the chemical and pharmaceutical industry, disposal such as sewage sludge and paint sludge treatment or plastics recycling, pump construction, metallurgical technology, paper production or the food industry.