Driven by increasingly stringent requirements for energy conservation and environmental protection, high-efficiency, low-energy-consumption Brushless DC (BLDC) motors are progressively becoming the core power source choice in the pump industry. Injection molded magnets, as key components of BLDC motor rotors, are seeing increasingly widespread application in this field due to their unique comprehensive advantages.

Core Advantages of Injection Molded Magnets in Pump Rotors:

• High Design Freedom and Lightweighting: Enables one-step molding of complex shapes (such as multi-pole or embedded magnetic circuit structures), facilitating optimal rotor magnetic circuit design while effectively reducing rotor weight.

• Excellent Dynamic Balance: The high consistency and low deviation inherent in the injection molding process ensure the rotor possesses good initial dynamic balance, reducing vibration and noise during motor operation. This is particularly crucial for pump applications where quiet operation is prioritized.

• High Mechanical Strength and Reliability: Utilizing engineering plastics as the binder grants the magnet good toughness, enabling it to withstand the centrifugal forces generated by high-speed rotation and resist fracturing.

• Good Corrosion Resistance: By selecting corrosion-resistant binders (like PPS) or applying surface treatments, the rotor can effectively resist corrosive media encountered during pump operation, such as moisture and chemicals, thereby extending product lifespan.

• Mass Production Capability and Cost-Effectiveness: The high degree of automation in the injection molding process results in high production efficiency and controllable costs, making it suitable for large-scale manufacturing.

Core Manufacturing Process Flow:

The manufacturing of injection molded magnet rotors is an integrated process combining materials science, precision machining, and magnetic technology. The primary steps are as follows:

1. Raw Material Preparation and Compounding

• Magnetic Powder: Neodymium Iron Boron (NdFeB) magnetic powder is primarily used to meet motor requirements for high magnetic energy product and high coercivity, ensuring high motor efficiency and strong power output. In applications with slightly lower performance demands, Strontium Ferrite (Sr-Ferrite) may also be used to optimize costs.

• Binder: Commonly used binders include Polyphenylene Sulfide (PPS) and Nylon (PA66, PA12). PPS is often the preferred choice for many high-performance pump motors due to its higher heat deflection temperature, excellent dimensional stability, and outstanding chemical resistance.

• Compounding and Pelletizing: Magnetic powder, the binder, and various additives (e.g., coupling agents, lubricants) are thoroughly mixed according to a precise formula in a high-speed mixer. This mixture is then melt-compounded, extruded, cooled, and pelletized via a twin-screw extruder to produce homogeneous injection molding compound pellets. The uniformity achieved in this stage directly impacts the consistency of the magnetic properties in the final product.

2. Rotor Insert Preparation and Injection Molding

This is the core stage of the process, requiring advanced technical expertise.

• Rotor Core (Insert) Preparation: The rotor core is typically made from laminated silicon steel sheets or is a solid steel shaft. Pre-treatment such as cleaning and preheating is necessary before molding to enhance the bond between the plastic and metal and reduce internal stress.

• Precision Injection Molding: Using specialized injection molding machines, the magnetic pellets are heated until molten and injected under high pressure into the mold cavity containing the prepared rotor core. Mold design (including gate location and cooling channel layout) critically influences magnetic powder orientation, filling effectiveness, and product dimensional accuracy. Parameters such as melt temperature, injection speed, holding pressure, and cooling time must be precisely controlled to ensure a fully formed product, free of defects, and with minimal internal stress.

3. Magnetization

The injection-molded rotor must be magnetized to acquire magnetic properties.

• Multi-pole Magnetization: Pump motor rotors are typically multi-pole (e.g., 4-pole, 6-pole, 8-pole). They are magnetized at once using a high-voltage pulsed magnetic field within a specially designed magnetization fixture to create multiple accurately distributed magnetic poles.

• Magnetization Accuracy: The accuracy of the magnetization pattern and the uniformity of the magnetic field strength directly determine the smoothness of the motor's torque output and its operational efficiency.

4. Performance Testing and Post-Processing

• Dynamic Balance Testing: This is a critical inspection step for pump rotors. Testing and correction are performed on a dynamic balancing machine. Unbalance is corrected by material removal (deweighting) or adding balance weights to maintain the rotor's unbalance within strict standard limits (such as G6.3 or G2.5 grades), ensuring smooth operation.

• Magnetic Performance Testing: Instruments like Gauss meters and flux meters are used to check the surface magnetic field strength and distribution, ensuring they conform to design requirements.

• Surface Treatment (Optional): For harsh application environments, the rotor may undergo surface treatments like plating (e.g., nickel plating) or coating (e.g., epoxy resin) to provide additional protection.

Process Challenges and Core Requirements:

• Flowability under High Magnetic Powder Loading: High magnetic powder loading ratios affect melt flowability, posing challenges for mold design and injection molding process control.

• Strong Bond Strength: Extremely strong adhesion must be ensured between the injection molded magnet and the metal insert to prevent separation under high-speed operation.

• Stringent Dynamic Balance Requirements: Unbalance must be controlled within international standard grades, imposing high demands on material uniformity, molding precision, and subsequent correction processes.

• Long-term Environmental Resistance: The product must maintain stable performance under conditions involving high temperature, high humidity, and exposure to various chemical media.

Summary

The injection molded magnet process provides an efficient, reliable, and economical solution for manufacturing high-performance rotors for pump BLDC motors. Mastering this technology requires support from profound knowledge in materials science, precision mold design and manufacturing capabilities, stable injection molding process control, and specialized magnetization and testing expertise.

Currently, some specialized magnet suppliers in China, such as Ningbo Buji Magnetic-Electronic Technology Co., Ltd., leveraging their core team's two decades of technical accumulation in magnetic materials, have developed the capability to provide one-stop solutions ranging from injection molded magnets (including both NdFeB and Ferrite materials, with PPS and PA binders) to magnetic assemblies. Their products are applied in motor fields like pumps and fans, demonstrating a commitment to offering the market cost-effective magnetic application choices.