Features of Bonded NdFeB Magnet
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What is Bonded Magnet
With the advancement in technology, many rare-earth magnet manufacturers are adopting technologies that can improve magnet performance.
So far, most bonded magnets are neodymium.
Bonded NdFeB Magnets
Bonded magnets are quite different from the normal magnet manufacturing processes such as casting or sintering.
First, to manufacture these magnets, you can adopt either:
- Injection molding
- Compression bonding
You can choose any of the two processes for your bonded NdFeB magnets manufacturing process. Let’s compare the two processes:
| Variable to Compare | Injection Molded Magnets | Compression Bonded Magnets |
| Mechanical Strength | Very good | Good |
| Magnetic strength | Lower | Higher |
| Particle density | Low | High |
| Manufacturing flexibility | Unlimited geometries | Limited geometries |
| Temperature range (°C) | -40 to 180 | -40 to 180 |
| Binder | PPS, Polyamide or Nylon | Epoxy |
Simply put – bonded magnets are magnets manufactured either through injection molding or compression bonding. More importantly, their composition includes:
- Magnetic material
- Adhesive or binder
- Other additives
Other processes you can use to manufacture bonded magnets are:
- Calendering Process
- Extrusion Process
Advantages of Bonded Neodymium Magnets
Economical Use of Magnetic Material
The cost of rare-earth magnetic material is quite high. Therefore, by optimal material utilization, you can still get high-performance neodymium magnets with less material.
Flexibility in Design
With bonded magnet technology, you can make permanent magnets with complex geometries. Besides, the size and dimensional accuracy is also high.
Bonded NdFeB Magnets Exhibit Consist Performance
Although they have low magnet performance, consistency is guaranteed. Additionally, they have high resistivity.
Also, these magnets have good mechanical and machinability properties.
Sintered NdFeB Magnets vs. Bonded NdFeB Magnets
Each magnet manufacturing process has unique benefits and limitations.
Therefore, whichever option you go for, will depend on specific magnet design requirements.
| Sintered Neodymium Magnets | Bonded Neodymium Magnets |
| · High-density magnet | · Low-density magnets |
| · Production involves sintering magnetic materials – heating magnetic material causing them to fuse | · Permanent magnet manufacturing is either through compression bonding or injection molding |
| · Higher permanent magnet performance | · Lower permanent magnet performance |
| · High production cost – produces blanks that require further processing | · Low production cost – produces magnets with better dimensional accuracy |
| · Low resistivity | · High resistivity |
| · Not suitable for complex-shaped permanent magnets | · Suitable for complex-shaped permanent magnets |
| · Have a crystal structure | · Have non-crystal structure |
Bonded NdFeB Manufacturing Process
When manufacturing bonded rare earth permanent magnets, you need the following:
- Magnetic material – in this case, neodymium or NdFeB
- Binder – you can choose epoxy, Polyamide, etc.
- Additive depending on the bonded magnet grade
Once you have the necessary material, you will:
Manufacturing NdFeB Magnets
Step 1: Prepare Material
Prepare the Nd-Fe-B material then mix it with an epoxy binder. Usually, the mixture proportion is such that:
- Magnetic material (neodymium) – 97%
- Epoxy material – 3%
Step 2: Compression and Curing
Once the material is ready, use a press to compress the mixture. The compressed part is always very accurate.
Place the compressed part in an oven and allow it to cure.
Note: The process includes injection, or extrusion depending on the specific manufacturing process.
Depending on where you intend to use these permanent magnets you will grind and clean the magnets. Ultrasonic cleaning is one of the most effective ways to clean a magnet.
Next, you should coat the magnets and magnetize them. The magnetization will align the magnetic poles.
By the end of the process, you will have an isotropic bonded neodymium permanent. That is, you can magnetize it in any direction depending on application requirements.
Even if you want a multi-polar arrangement, the bonded neodymium-iron-boron offers the perfect solution.
The best part, you can machine the magnet since it is not brittle. However, you must not thread these permanent magnets.
Magnetic orientation
Temperature Characteristics of Bonded Neo Magnets
When it comes to analyzing the rare earth magnet Curie temperature, it is important to note:
- 0% cobalt the Curie temperature is 310 °C
- 5% cobalt increases the Curie temperature to 370 °C
With Neo magnets, a temperature increase may reduce the magnetic output. Therefore, it will perform optimally at low temperatures.
Remember for most neodymium magnets, at a temperature above 80 °C, the losses may be irreversible.
Moreover, these neodymium magnets are not corrosion-resistant. Therefore, coating or plating the magnet is important for certain applications.
Applications of Bonded Neodymium Iron Boron Magnets
When it comes to flexibility, bonded rare earth magnets offer the perfect alternative in many applications such as:
- Oil pumps
- Sensors
- Window lifting motors
- Fan motors
- Fuel gauge
- Tachometer
- Instrumentation drive
In short, these permanent magnets are suitable for applications that require:
- Permanent and strong magnets
- Require magnets with special geometries
- Low to medium temperature