The carbon fiber winding process for the permanent magnet rotor is a core manufacturing technology for high-speed permanent magnet motor rotors. It mainly involves winding carbon fiber tows onto the rotor according to a specific pattern and combining this with resin curing to form a high-strength carbon fiber sleeve, which offsets the centrifugal force at high speeds and protects the permanent magnets.
The Role of the Carbon Fiber Winding Process
| Counteracting centrifugal force: When a high-speed motor rotates, it generates enormous centrifugal force. The carbon fiber winding sleeve provides pre-tension (pre-compression) to the rotor through high-tension winding, keeping the rotor in a compressed state during high-speed rotation and preventing the permanent magnets from being flung out or the iron core from deforming.
| Weight reduction and loss reduction: Carbon fiber features low density and high specific strength. Replacing traditional metal sleeves with carbon fiber can significantly reduce rotor weight. Moreover, since carbon fiber is non-magnetic, it effectively reduces eddy current losses during high-speed rotation.
Classification of the Carbon Fiber Winding Process
| Wet winding: Carbon fiber tows are impregnated with liquid resin in a dipping bath and then wound directly onto the rotor core under tension control, followed by heating to cure. The advantages of this method are the wide selection of fibers and resins, good adjustability, and relatively low cost; however, the resin content (glue content) is not easy to control precisely, and problems such as uneven resin distribution, uneven surfaces, and a relatively poor on-site environment can occur.
| Dry winding: Pre-fabricated carbon fiber prepreg is used, softened by heating, wound onto the rotor core, and then the whole assembly is heated to cure. This method is characterized by precise resin content control, neatly arranged fibers, stable product quality, and a clean on-site environment; however, prepreg costs are higher, the available materials are relatively limited, and high demands are placed on the heating equipment.
| Semi-dry winding: After the fiber tows are impregnated with resin, some of the solvent is removed through drying, and they are then wound onto the core and cured. This method combines some of the advantages of both wet and dry winding, allowing better control of glue content and improving the environment; however, it requires additional drying equipment and is used relatively less often.
Precautions for the Carbon Fiber Winding Process
| Carbon fiber matching: The appropriate specification of carbon fiber must be selected based on the rotor size and strength requirements. In addition, the carbon fiber should be dried before use to remove surface moisture, preventing moisture from affecting resin impregnation and causing micro-cracks.
| Temperature control: A reasonable heating, holding, and cooling curve should be established based on the resin system to ensure the resin is fully cross-linked, and to avoid cracks or excessive residual stress inside the material caused by too-rapid cooling.
| Winding tension control: Tension directly affects the pre-tension force and interlayer bonding strength, so the tension must be strictly controlled. If the tension is too low, the layers become loose with high porosity; if too high, the inner layers can be crushed or fibers in the dome section can slip.
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