Injection molded magnets are highly suitable for manufacturing key magnetic components in elevator sensors due to their advantages of high shape design freedom, good dimensional accuracy, high mechanical strength, mass production capability, and controllable costs. Typical applications include: multi-pole magnetic rings in absolute encoders, magnetic gears in rotary encoders, magnetic scales in linear displacement sensors, position detection magnets in door operator systems, and car leveling induction magnets.

Their core manufacturing process can be summarized into the following key steps, with many enterprises having accumulated rich experience in this field. For instance, since its establishment in 2018, Ningbo Buji Magnetic-Electronic Technology Co., Ltd. has focused on the R&D and manufacturing of various magnets and components. In the area of injection molded magnets, it has established product lines including Neodymium Iron Boron (NdFeB) magnets, Ferrite magnets, as well as magnets using PPS and PA binders. Its core team possesses over twenty years of professional experience in the field of magnetic materials.

Core Processes for Applying Injection Molded Magnets in Elevator Sensors

1. Raw Material Preparation and Compounding

• Magnetic Powder: Primarily uses isotropic Neodymium Iron Boron (NdFeB) or Strontium Ferrite (Sr-Ferrite) powder. NdFeB offers stronger magnetic properties, suitable for applications requiring smaller size and higher performance; Ferrite has a cost advantage and offers good corrosion resistance.

• Binder: Typically uses high-performance engineering plastics such as Nylon (PA6, PA12), Polyphenylene Sulfide (PPS), or Polypropylene (PP). These must possess good flowability, thermal stability, and compatibility with the magnetic powder.

• Compounding and Pelletizing: Magnetic powder, binder, and additives like coupling agents and lubricants are uniformly mixed in a high-speed mixer according to a specific ratio. This mixture is then melt-compounded and extruded via a twin-screw extruder, followed by cooling and pelletizing to produce magnetic compound pellets. The homogeneity of this process significantly impacts the consistency of the final product's performance.

2. Precision Injection Molding

This stage places high demands on equipment and molds, requiring specialized magnetic injection molding machines.

• Mold Design: Molds are often made from cemented carbide to enhance wear resistance and require precise venting systems to avoid defects. Gate design is critical for controlling magnetic powder orientation and internal stress.

• Injection Molding Process:

  • Drying: Pellets are thoroughly dried before molding to prevent air bubbles.

  • Injection and Holding Pressure: The molten material is injected into the mold cavity under high pressure. Precise holding pressure control helps reduce shrinkage and ensure dimensional accuracy.

  • Cooling and Demolding: The product is cooled and solidified before ejection. Parameters like temperature and pressure must be precisely controlled.

3. Magnetization

The as-molded magnet is in a "green" state and requires magnetization to achieve the predetermined magnetic field.

• Magnetization Method: Accomplished using a magnetizer and custom fixtures. Multi-pole magnetic rings (e.g., 32-pole, 64-pole) require multi-pole magnetization technology.

• Magnetization Fixture: Pole pieces need precise arrangement to achieve orderly alignment of the magnetic domains within the magnet via a high-intensity pulsed magnetic field.

• Key Point: Magnetization is performed after injection molding. Its stability directly affects the accuracy of the sensor signal.

4. Magnetic Performance Testing and Sorting

• Performance Testing: Equipment like Gauss meters and flux meters are used for 100% inspection of parameters such as surface magnetic field strength, magnetic flux, and inter-pole angle error.

• Sorting: Products are graded based on test results to ensure performance consistency, meeting the reliability and safety requirements of elevator systems.

5. Post-Processing and Assembly (Optional)

• Machining: Processes like turning or milling can be performed to meet special installation requirements.

• Overmolding: Secondary injection molding can be used to enhance corrosion resistance and impact resistance.

• Assembly: The magnet is assembled with chips, housings, etc., to form a complete sensor module.

Core Process Requirements and Challenges

• High Precision and Consistency: Pole position accuracy errors typically need to be controlled within a tight range, and magnetic field strength fluctuation must also be strictly controlled to avoid signal distortion.

• High Strength and Durability: Products must possess good mechanical strength to withstand vibrations and shocks during elevator operation.

• Environmental Resistance: Performance stability must be maintained under varying temperatures, exposure to lubricants, and other environmental conditions.

• Multi-pole Magnetization Technology: Magnetization processes requiring high pole counts and high precision place significant demands on equipment and fixtures.

Summary

The manufacturing process for injection molded magnets used in elevator sensors encompasses material formulation, precision mold making, injection molding, multi-pole magnetization, and 100% inspection, constituting a technology-intensive process. This field imposes high requirements on product consistency, precision, and reliability. Currently, domestic companies such as Ningbo Buji Magnetic-Electronic Technology Co., Ltd., leveraging years of technical accumulation, can provide various products and solutions including injection molded magnets, bonded and sintered NdFeB magnets, and magnetic assemblies. This supports the elevator sensor industry in achieving more stable and efficient magnetic applications.