Bonded magnet refers to a composite body formed by mixing the magnetic powder with certain permanent magnetic properties and a certain proportion of binder according to a certain molding process. If an orientation magnetic field is applied during the molding process, the easy magnetization direction of the magnetic powder is in the same direction in the magnet, which is an anisotropic bonded magnet, otherwise, it is an isotropic magnet. Bonded magnets are mainly used to make micro motors, stepping motors, magnetic sealing rings, various toys, etc.
Benefits of Bonded Magnets
Design Flexibility
Bonded magnets can be easily molded into complex shapes and customized designs that are difficult or impossible to achieve with sintered magnets. This allows for greater flexibility in product design.
Cost-Effective Production
The manufacturing process for bonded magnets, such as injection molding or compression bonding, is generally more cost-effective, especially for high-volume production runs. It is perfect for mass production since it rarely requires cutting the material it involves.
Low Magnetic Losses
Bonded magnets typically exhibit lower eddy current losses compared to sintered magnets, which makes them suitable for high-frequency applications such as motors and sensors.
Corrosion Resistance
Bonded magnets are often made with materials that are inherently resistant to corrosion, or they can be coated with protective layers, making them suitable for use in environments where moisture or chemicals are present.
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We specialize in Permanent Sintered Neodymium-Ferrum-Boron (NdFeB) magnets, Samarium-Cobalt (SmCo) magnets, Aluminum-Nickel-Cobalt (AlNiCo) magnets, and related assemblies, all ISO9001 and SGS certified.
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Our annual output includes 800 tons of NdFeB magnets and 6000 tons of ferrite magnets, along with Alnico, SmCo, and plastic rubber magnets.
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Types of Bonded Magnets
Bonded Ferrite Magnet
Bonded ferrite magnets, also known as ceramic magnets, are made from a combination of iron oxide and barium or strontium carbonate, blended with a polymer binder. These magnets are produced through a molding process that allows for complex shapes and sizes, offering a cost-effective and versatile solution for various industrial applications. They are known for their moderate magnetic strength, excellent corrosion resistance, and thermal stability.
Bonded NdFeB Magnet
Bonded NdFeB magnets are a class of rare earth magnets made by bonding NdFeB powder with a polymer binder, resulting in a composite material that combines the magnetic properties of NdFeB with the versatility of various shapes and sizes. These magnets offer a range of advantages, making them suitable for diverse applications across multiple industries.
Bonded SmCo Magnet
Bonded SmCo magnets are composed of finely powdered SmCo magnetic material mixed with a polymer binder, such as epoxy or nylon. The SmCo powder typically contains samarium, cobalt, and other elements like iron and copper to enhance the magnetic properties. This blend results in magnets that exhibit excellent thermal stability and resistance to demagnetization.
Surface Magnetism
Sintered magnets have a strong magnetic pull on their surface because they are dense and compact. This makes them ideal for high-performance uses like electric motors and MRI machines, where strong and stable magnets are needed. They are often designed to work best in specific directions, increasing their performance in those orientations.
Bonded magnets have a weaker surface magnetism because they include a polymer binder, which makes them less dense. However, they can be easily shaped and are cheaper to produce. They can have a uniform magnetic strength or a preferred direction, making them suitable for items like consumer electronics, small motors, and sensors, where flexibility in shape and moderate magnetic strength are important.
Material Composition and Properties
Sintered magnets are made from compacted and heated magnetic powders, resulting in a dense and robust structure. They are primarily composed of materials like NdFeB (Neodymium-Iron-Boron) and SmCo (Samarium-Cobalt), known for their high magnetic strength and thermal stability.
In contrast, bonded magnets are composed of magnetic powder mixed with a binder, such as a polymer or resin. This allows for flexibility in shape and size but results in lower density and magnetic strength compared to sintered magnets.
Manufacturing Processes
The manufacturing process for sintered magnets involves powder metallurgy, where the magnetic powder is compacted under high pressure and then sintered at high temperatures. This process results in a densely packed magnet with higher magnetic properties.
On the other hand, bonded magnets are produced by mixing the magnetic powder with a binder and molding the mixture using injection or compression molding techniques. This process is more straightforward and more cost-effective, allowing for the production of magnets with complex shapes without the need for additional treatments.
Physical Characteristics
Sintered magnets boast high strength due to their dense structure, making them ideal for applications where strong magnetic fields are required. However, they are brittle and can break easily if not handled carefully. They also need protective coatings to prevent corrosion.
Bonded magnets, in this case, are more flexible and durable due to the binder in their composition. This makes them easier to mold into precise shapes and sizes, with inherent corrosion resistance reducing the need for additional coatings.
The Composition of Bonded Magnets
To comprehend bonded magnets further, it is essential to look at their structure. These magnets are a marriage of two key components: magnetic powders and binding materials.
Magnetic Powders
The magnetic particles employed in making bonded magnets are critical to their operation. These powders can be made from various materials, each offering unique characteristics: These powders can be made from multiple materials, each offering unique characteristics:
Ferrite: Ferrite powders are also known as ceramic magnets, and they are comparatively cheaper while, at the same time, they have the advantage of not being easily demagnetized.
Neodymium-Iron-Boron (NdFeB): Some rare earth magnets have a magnetic solid force and are ideal for high-power uses.
Samarium-Cobalt (SmCo): There are more options for rare earth materials, and SmCo powders have temperature stability and corrosion resistance features.
Alnico: Alnico (aluminum-nickel-cobalt) powders are used in specific applications where high temperature is the common characteristic.
Binding Materials
The binder is the medium for connecting magnetic particles, enabling bonded magnets to possess their characteristics. Common binding materials include:
Thermoplastics: Some materials include nylon, polyamide, and polyphenylene sulfide (PPS), which provide better moldability besides the mechanical strengths.
Thermosets: Epoxy resins have good thermal stability and a degree of shrinkage or swelling, and this property makes them suitable for making automotive electrical connectors.
Elastomers: Materials with characteristics of rubber, like Nitrile Rubber, are used and are flexible with impact strength.
What are the 4 Production Processes for Bonded Magnets?
Compression Molding
Compression molding is widely used to manufacture bonded magnets and is one of the most straightforward processes. Here's how it works: The magnetic powder is added and incorporated into a thermoset binder, usually epoxy resin. The molding of the two articles is done by placing the mixture in a mold cavity. This results in curing and solidifying the binder and applying heat and pressure at this stage. The end product is thus a high compound magnet with good dimensional stability.
Injection Molding
Injection molding is preferred for high-volume production of bonded magnets: Injection molding is preferred for high-volume production of bonded magnets: Magnetic powder is incorporated with a thermoplastic base material. The mixture's components are melted and heated until they attain a fluid-like consistency. The molten material is then forced into a mold cavity through tremendous pressure. After that, the mold is cooled down; this process also firms up the magnet.
Extrusion
Extrusion is used to create long, continuous shapes: Extrusion is used to create long, continuous shapes: The magnetic powder and thermoplastic binder are combined where they are heated together. The prepared mixture is squeezed through a die with the required cross-sectional area on the part produced. The extruded material is cooled and then cut to the required length.
Calendering
Calendering is used to produce thin, flexible magnetic sheets: Magnetic powder and an elastomeric binder are compounded. It is then rolled between rollers to get a thin layer of the mixture to make chips. The sheet must be taken and made to have a magnetic property before being cut to the required size.
Application of Bonded Magnets
Transportation Industry
In the transportation industry, an optimally designed motor with isotropic bonded magnets helps lower the motor weight and volume by 50% to 60%. Therefore, increase in adoption of bonded magnets in the automotive industry, owing to their lightweight property, is expected to drive the global bonded magnets market during the forecast period.
Electrical Devices
Bonded magnet plays an important role in various electrical devices essential for everyday life. These are utilized in various electronic items such as hard disks, scanners, DVD and CD drivers, and mobiles. Bonded magnets are also used in audio equipment such as speakers, headphones, and microphones.
Medical Devices
Bonded magnets are essential in medical devices like MRI machines, hearing aids, and small precision motors used in diagnostic equipment. Their stability and ability to be customized for specific applications make them valuable in the medical field.
Aerospace Industry
In aerospace applications, bonded magnets are used in gyroscopes, actuators, and sensors. Their high strength-to-weight ratio and resistance to temperature fluctuations make them suitable for use in harsh environments.
How to Properly Store Bonded Magnets
Humidity and Temperature
Bonded magnets should be stored in a dry environment with low humidity to prevent corrosion. Ideally, they should be kept at room temperature, as extreme temperatures can affect their magnetic properties. High temperatures, in particular, can cause demagnetization.
Corrosion Prevention
Although many bonded magnets are coated with protective layers (such as nickel, zinc, or epoxy), they are still susceptible to rust if exposed to moisture. Using silica gel packets in storage containers can help control humidity levels and protect the bonded magnets from corrosion.
Storage Methods
Use non-magnetic containers to store bonded magnets. Plastic or wooden boxes are ideal as they do not interfere with the magnetic fields. For smaller bonded magnets, individual compartments within the container can prevent them from attracting each other.
Use of Spacers and Keepers
Spacers are materials placed between magnets to keep them apart, reducing the risk of accidental collisions. Keepers, often made of soft iron, are used to bridge the poles of bonded magnets, reducing the external magnetic field and making the bonded magnets safer to handle.
Organizational Tips
Labeling storage containers with the bonded magnet size, shape, and strength can help in organizing and quickly locating the required magnets. Additionally, keeping an inventory log can assist in tracking the usage and storage of your bonded magnet collection.
Safety Tips
Do not store bonded magnets near electrical devices. Magnets generate a far-reaching strong magnetic field that can damage your computer, laptop, speakers and other data storage devices (e.g. HDD).
The magnetic field also damages the magnetic strip of credit and EC cards, rendering it unreadable. Therefore, make sure that the bonded magnets are stored away from sensitive bank cards.
Store bonded magnets so that people with pacemakers cannot get too close. Magnets can interfere with the function of these devices.
When choosing a storage place, consider the temperature resistance of your bonded magnets. Most bonded magnets will permanently lose part of their adhesive force at temperatures above 80 °C.
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