1. Overview of Rubber Magnet Products
Definition and Basic Structure
Definition of Rubber Magnets
Rubber magnets are composite materials made by combining magnetic powders (such as ferrite or rare – earth magnetic powders) with polymer rubber matrices (like NBR or EPDM) through processes like mixing and calendering. They possess both permanent magnetic properties and the elasticity and processability of rubber, and are widely used in advertising stickers and motor accessories.
Role of Magnetic Powder
Magnetic powder, accounting for 60% – 80% of the material, is the core source of magnetic properties. Common types include strontium ferrite (low – cost and stable) and neodymium – iron – boron (high magnetic energy product). It directly determines key magnetic parameters such as residual magnetic flux density (Br) and coercivity (Hc).
Function of Rubber Matrix
The rubber matrix, with a proportion of 15% – 30%, usually uses materials like nitrile rubber (NBR, oil – resistant) and ethylene – propylene – diene monomer (EPDM, weather – resistant). It wraps the magnetic powder through molecular chains to form a continuous phase, endowing the material with flexibility and moldability.
Effect of Additives
Additives, less than 5% of the total, include plasticizers (e.g., DOP for better flexibility), anti – aging agents (e.g., RD for anti – aging), and coupling agents (e.g., silane to enhance the bonding between magnetic powder and rubber). They improve processing or usage performance in a targeted way.
Product Classification and Common Forms
Classification by Magnetic Powder Type
Ferrite rubber magnets (based on strontium ferrite) are the mainstream in the market, with low cost (about $15 – 30 per kg) and good temperature resistance (- 40°C – 120°C). Rare – earth rubber magnets (based on neodymium – iron – boron) have high magnetic performance (magnetic energy product up to 12 – 20 MGOe) but higher cost (about $50 – 80 per kg).
Classification by Shape
Sheet materials (thickness 0.5 – 5 mm, size 300×500 mm) are suitable for flat attachment; coil materials (width 50 – 1000 mm, length 5 – 50 m) facilitate continuous processing; special – shaped parts (such as rings and arcs) are formed by molding to meet specific installation requirements. For example, multi – pole magnetization (magnetic pole interval ≤2 mm) can achieve high – precision positioning, commonly used in encoder magnetic rings.
aication by Magnetization Direction
Single – sided magnetization (magnetism concentrated on one side) is suitable for adsorption scenarios; double – sided magnetization (magnetism on both sides) is used for double – sided fixation; multi – pole magnetization can meet more complex application needs, such as in some high – precision sensors.
2 .Core Performance and Technical Parameters
Residual Magnetism (Br)
Residual magnetism (Br) refers to the magnetic induction intensity retained by the rubber magnet after the external magnetic field is removed after saturation magnetization. For low – grade products, Br is about 0.2 – 0.3T, suitable for ordinary refrigerator magnets. Medium – and high – grade products can reach 0.35 – 0.5T, meeting the requirements of industrial sensors and precision adsorption scenarios, directly determining the initial adsorption capacity of the product.
Analysis of Key Magnetic Performance Indicators
Coercivity (Hc) is the reverse magnetic field strength required to completely demagnetize the rubber magnet. The coercivity of conventional products is in the range of 200 – 350 kA/m. High – coercivity models (350 – 450 kA/m) can resist environmental interference such as high temperature and vibration, and are suitable for long – term stable scenarios such as automotive dashboards and outdoor electronic devices.
Maximum Energy Product (BHmax)
The maximum energy product (BHmax) is the maximum value of the product of the magnetic field strength and magnetic induction intensity inside the magnet. Low – performance products have a BHmax of about 10 – 20 kJ/m³, mostly used in toys. High – performance products can reach 30 – 40 kJ/m³, suitable for fields such as motors and magnetic levitation devices that require efficient energy conversion.
Hardness (Shore A)
The hardness of rubber magnets is usually Shore A 50 – 80. Soft – grade products with 50 – 60A can fit curved surfaces (such as curved advertising boards), while hard – grade products with 70 – 80A are suitable for industrial fixtures that require structural support, balancing flexibility and deformation resistance.
