What Is a Bonded Magnet?
A bonded magnet is a generic term for magnets that are created by mixing fine-grained magnets into rubber or plastic, then processing and molding them.
Regular ferrite magnets are used as door seals for refrigerators and showcases, or they are turned into boards and coated with plastic to create whiteboards.
Rare earth magnets with high magnetic force, such as neodymium magnets, are molded into various shapes and used in industrial applications, including small motors, electronic components, and train drive motors.
Uses of Bonded Magnets
Bonded magnets offer the flexibility of design, manufacturing, processing, and molding after production.
Ferrite magnets are commonly used in daily life for applications such as magnetic tape and magnetic sheets. They are also used in refrigerator doors and whiteboards.
Highly magnetic magnets like neodymium magnets and samarium iron nitride magnets are incorporated into small motors, used in hard disks, and play a role in drive motors for automobiles, trains, and elevators.
Principles of Bonded Magnets
Permanent magnets used in industries are categorized as cast, sintered, or bonded magnets.
Bonded magnets, also known as polymer bonded magnets, are produced by mixing and dispersing a high concentration of fine magnetic powder (magnetic powder) from ferrite magnets or rare earth magnets into a binder like polymer resin or rubber.
After production, they can be processed and molded into complex structures with high precision. They not only exhibit excellent mechanical properties, such as resistance to cracking and chipping, but they can also be easily integrated with thin, long, and wide metals, which is impossible with cast or sintered magnets.
Bonded magnets can be mass-produced and offer many advantages as industrial materials.
In particular, the use of highly magnetic rare earth magnets is essential for small motors and electronic components widely used today. Improving the performance of bonded magnets themselves can achieve further miniaturization and efficiency.
Rare earth-bonded magnets also contribute to making generators smaller and more powerful, with potential for expanding their use in the field of energy generation.
Differences Between Bonded Magnets and Sintered Magnets
Bonded magnets are created by solidifying magnetic powder with resin, while sintered magnets are made by compressing magnetic powder and baking it at high temperatures.
In terms of magnetic properties and heat resistance, sintered magnets outperform bonded magnets made with resin, as the resin in bonded magnets is non-magnetic.
However, when it comes to dimensional accuracy, bonded magnets excel due to their ability to undergo more complex processing. Sintered magnets are subject to more significant sintering shrinkage during manufacturing.
Bonded Magnets and the Advancement of Motors
As environmental concerns grow, the motor market is undergoing significant changes. Motors are widely used in various applications, including automobiles and household appliances, and they account for a large portion of total power consumption. Energy conservation in motors is crucial for achieving a low-carbon society.
In this context, the demand for permanent magnet (PM) motors is rising.
PM motors, which utilize permanent magnets in the rotor, are more energy-efficient and effective than non-permanent magnet motors (e.g., induction motors) because they do not generate losses in the rotor. PM motors do not have secondary current flow in the rotor, making them more efficient.
PM motors come in two types based on rotor structure: Surface Permanent Magnet (SPM) motors and Interior Permanent Magnet (IPM) motors. IPM motors, with embedded magnets, can achieve higher speeds and enhanced mechanical safety.
Strong rare earth magnets play a vital role in the technology of these PM motors. However, the procurement of rare earth magnets has posed challenges due to soaring prices and unstable supply caused by export restrictions in China and other factors.
In recent years, new technologies have emerged, including the use of bonded magnets made from samarium, which are not rare earth magnets, in IPM motors. Bonded magnets are supporting the evolution of motors.