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Unveiling the Advantages of Carbon Fiber Sleeved Rotors: Boosting High-Speed Motor Efficiency and Power

Advantages of High-Speed Permanent Magnet Motors

High-speed permanent magnet motors present several advantages, including high power density and efficiency. Nevertheless, when non-laminated steel is utilized for the rotor, significant losses can occur, potentially leading to irreversible demagnetization of the permanent magnets. Research indicates that substituting the high-conductivity non-laminated steel sleeve with low-conductivity carbon fiber composite materials can effectively mitigate rotor losses.

comparison of carbon fiber sleeve and inconel sleeve
comparison of carbon fiber sleeve and inconel sleeve
performance comparison of typical materials
performance comparison of typical materials

Carbon Fiber Composite Materials: “King of New Materials”

Carbon fiber is a fiber material with a carbon content exceeding 95%, bestowing it with remarkable mechanical, chemical, and electrical properties, hence earning the moniker “King of New Materials.” This strategically vital substance finds applications in both military and civilian sectors and is often colloquially referred to as “black gold” due to its high value.

Production Process of Carbon Fiber from Polyacrylonitrile (PAN) Fiber

Currently, the primary source of carbon fiber is polyacrylonitrile (PAN) fiber. The transformation of PAN fiber into carbon fiber involves three main steps:

  1. Pre-oxidation of polyacrylonitrile at temperatures below 300℃, inducing cerium molecular dehydrogenation, cyclization, and the creation of a heat-resistant structure in preparation for carbonization.
  2. Carbonization takes place in an inert gas environment at temperatures ranging from 1000℃ to 1500℃. During this process, unstable components and non-carbon atoms within the structure are eliminated, yielding a disordered graphite-like structure with a carbon content exceeding 92%.
  3. To attain even higher modulus fibers, a subsequent graphitization process is conducted at temperatures ranging from 2000℃ to 3000℃, building upon the foundation of 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.

carbon fiber

 

Matrix Materials and Curing Agents in Structural Composite Materials

Structural composite materials commonly employ matrix materials made of resins such as epoxy, phenolic, polyimide, and others. To achieve proper curing and meet processing requirements, curing agents and certain additives are often incorporated. Curing agents have a working temperature typically below 130°C, but some can withstand temperatures up to 185°C.

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

Press Fitting Method for Rotor Manufacturing

A specific interference fit is employed between the permanent magnet and the sleeve. Upon assembly, the elastic deformation of the materials leads to the generation of a compressive stress between the contact surfaces of the interference fit components, thereby ensuring the safety of the permanent magnet, provided the selected interference fit size is appropriate. In engineering applications, the assembly methods for interference fit components mainly consist of press-fitting, cold assembly, and hot-fit methods.

However, due to the low coefficients of thermal expansion for both carbon fiber composite materials and permanent magnets, cold assembly and hot-fit methods are unsuitable. As a result, the press-fitting method becomes the sole viable option. The process flowchart for manufacturing the rotor using the press-fitting method is as follows:

  1. Wind the fiber bundles layer by layer on the surface of the mold to ensure the inner diameter accuracy of the sleeve.
  2. Once the winding layer reaches a certain thickness, cure it, and then demold to obtain the carbon fiber sleeve.
  3. Subsequently, the permanent magnet is pressed into the sleeve using a hydraulic press.
carbon fiber sleeved rotor - press fitting method
press fitting method

Tension-Tension Winding Method for Rotor Manufacturing

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.

carbon fiber sleeved rotor - tension winding method
tension winding method

Ensuring Precise Alignment with Fixtures

To ensure precise alignment between the permanent magnet and the sleeve, the use of fixtures is a common practice to guarantee accuracy. Various rotors may necessitate different structural designs for these fixtures. We possess independent fixture design capabilities to accommodate diverse customer requirements, thereby ensuring the alignment accuracy between the permanent magnet and the sleeve. Below is a functional diagram of one of our autonomously designed fixtures.

press fit

 

Importance of Runout and Form Tolerance Checks

After the press-fitting process, it is essential to conduct runout and form tolerance checks, which encompass assessments for outer diameter tolerances and positional tolerances. For this purpose, specific inspection equipment is employed, as depicted in the pictures below.

Comprehensive Inspection Equipment and Collaboration with Customers

We take pride in having a comprehensive array of inspection equipment and a proficient technical team to conduct thorough testing on finished products. Our collaboration with customers begins from the early-stage development and extends to final product testing, ensuring that the products precisely align with customer requirements.

testing equipment

carbon fiber sleeved permanent magnet rotor

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Jonah Jin

Jonah Jin
Managing Director

Every customer deserves to be treated professionally and responsively.