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Carbon Fiber Rotor

Carbon Fiber Rotor

August 15,2023

What is Carbon Fiber?

Carbon fiber is a fiber material with a carbon content of over 95%. It possesses excellent mechanical, chemical, and electrical properties, making it known as the "King of New Materials." It is a strategically important material for both military and civilian applications, and due to its high price, it is often referred to as "black gold. "Currently, most of the carbon fiber used is produced from polyacrylonitrile (PAN) fiber.

The process of converting PAN fiber into carbon fiber involves three main steps:

1. Pre-oxidation of polyacrylonitrile at temperatures below 300, leading to cerium molecular dehydrogenation, cyclization, and the formation of a heat-resistant structure in preparation for carbonization.

2. Carbonization in an inert gas at temperatures between 1000 and 1500, during which the unstable components and non-carbon atoms in the structure are removed, resulting in a disordered graphite-like structure with a carbon content of over 92%.

3. To achieve even higher modulus fibers, a further graphitization process is performed at temperatures between 2000 and 3000 based on the carbonized fibers.

Note: The process description may involve some technical terms and may not be an exhaustive account of all carbon fiber production methods.

Why fiber sleeve becomes more and more popular? Here are some reasons:

1. High forming efficiency & Small forming damage

The preparation method with high efficiency and low damage has difficulty realizing the application of sleeve engineering. The two-step prestressing manufacturing method of winding first and then press-fitting has the disadvantages of a complicated preparation process and easy damage to the rotor. The one-step prestressing manufacturing technology of large tension winding with low damage and high preloading effect has obvious advantages.

2. Easy realization of stress design

In recent years, researchers have adopted the high-tension winding method to prepare the carbon fiber sleeve for the rotor of a permanent magnet motor, and the one-step method is used to form the sleeve pre-tightening, which provides pre-tightening force for the permanent magnet while preparing the carbon fiber sleeve and can make the stress distribution of the sleeve uniform by designing the tension of the winding layer.

3. High preloading effect

High-speed permanent magnet motors offer advantages such as high-power density and efficiency. However, when using non-laminated steel for the rotor, there can be severe losses that may lead to irreversible demagnetization of the permanent magnets. Research has shown that replacing the high-conductivity non-laminated steel sleeve with low-conductivity carbon fiber composite materials can effectively reduce rotor losses.

The conventional manufacturing methods for carbon fiber rotors include the press-fitting method and the tension-tension winding method.

1. Press-fitting method

In engineering applications, the assembly methods for interference fit components mainly include press-fitting, cold assembly, and hot-fit methods.

The process flowchart for manufacturing the rotor using the press-fitting method is as left picture: first, wind the fiber bundles layer by layer on the surface of the mold that ensures the inner diameter accuracy of the sleeve. When the winding layer reaches a certain thickness, cure it and then demold to obtain the carbon fiber sleeve. Subsequently, the permanent magnet is pressed into the sleeve using a hydraulic press.

2. Tension-tension winding method

The tension-tension winding method for manufacturing the rotor does not require a mold. Instead, the fiber is directly wound around the surface of the permanent magnet. During the winding process, a sufficient initial tension is applied to the fiber bundle. This results in the carbon fiber sleeve already having a certain pre-compressive stress on the permanent magnet after curing, thereby protecting the safety of the permanent magnet.