Have you ever encountered this situation – the mechanically processed ferrous materials stick together, seriously affecting the efficiency of subsequent processes. Or the magnetism of the magnetic components is too strong to achieve the expected design effect. If you have been troubled by these problems, you have come to the right place. Now, I will tell you 5 ways to demagnetize magnets and 4 common demagnetization systems. Help people to the end, and also casually reveal some control and measurement methods that need to be paid attention to during the demagnetization process.
How to Demagnetize A Magnet?
Demagnetization is a process that reduces or eliminates residual magnetism. You may find it strange that everyone is always discussing how to prevent magnet demagnetization, so why would anyone deliberately demagnetize magnets? For example, the dimensional accuracy of a ferromagnetic part is 0.02mm. If this part is magnetic, it is very easy to attract dust, which will increase the difficulty of machining the workpiece. Therefore, demagnetization of ferromagnetic parts is becoming an increasingly necessary process during machining, drilling, laser processing or other operations.
What are the methods of demagnetization?
Once a permanent magnetic material is magnetized, the magnetization will theoretically continue indefinitely, but some methods can also be used to achieve the purpose of demagnetization.
Alternating current demagnetization method
This is one of the most common and effective demagnetization methods without destroying the magnet. The working principle is simple: Place the magnet in an alternating magnetic field coil, and the fluctuating magnetic field generated by the alternating current will constantly flip the direction of the magnetic domain of the magnet like a chaotic instruction, making it dizzy. Eventually, the magnetic domain will lose its orientation and achieve a complete demagnetization effect.
There are three key points to keep in mind when implementing this method:
- The initial magnetic field strength must be more than 3 times the coercive force of the magnet;
- The demagnetization time must be maintained for at least 30 seconds;
- The magnetic field must be slowly decayed (sudden power failure will cause residual magnetism);
High-temperature demagnetization method
When the ferromagnetic material is heated to above the Curie temperature (the temperature at which the magnetic domains inside the magnet lose their arrangement direction), the ferromagnetic material will be demagnetized. For example, when the common brand N48 neodymium magnet is heated to above 80℃, the magnetic domains inside the magnet will be like a group of ants dispersed by the heat wave, completely losing their neat queue, and eventually leading to the loss of magnetism.
This method is only suitable for those who want to completely eliminate the magnetism of large components or magnets, because the magnets treated at high temperature are like overcooked noodles, and they cannot recover their original strength even if they are magnetized again.
Physical shock method
In some cases, neither heating nor electricity can be used, such as the explosion-proof area of a chemical plant. At this time, applying physical shock or vibration to the magnet can help reduce its magnetism. The impact will destroy the internal structure of the magnet, causing its magnetic domains to shift or dislocate, thereby destroying the magnet’s magnetic structure. The wildest way I have seen is to use an ultrasonic cleaner – soak the magnet in kerosene and bombard it with 40kHz ultrasound for 2 hours, and the magnetic force is attenuated by 60%.
This method is suitable for smaller magnets. It is more of a stopgap measure than an industrial long-term solution. And the force of the knocking needs to consider the shape and type of the magnet. The hardness of samarium cobalt magnets is high, requiring an impact energy of more than 20J. Excessive force may cause the thin sheet magnet to break or crack.
Reverse demagnetization method
After measuring the current magnetic field direction of the magnet, apply direct current (DC) in the opposite direction that is more than 1.2 times higher than the coercive force of the target magnet. A strong reverse magnetic field can destroy the magnetic domain array in a short time (a few minutes). This method is often used for precision instruments that require directional demagnetization, but it has high requirements for equipment and personnel operability to avoid excessive interference.
Electromagnetic pulse
This is definitely the black technology in the demagnetization industry! We tried it during the development stage of customizing magnetic components for a research institute in Beijing: releasing 100,000 amperes of current in 2 milliseconds, and the resulting transient magnetic field strength is as high as 3 Tesla (60,000 times the earth’s magnetic field). Just like using lightning to split the dark clouds, the magnetic domain structure can be shattered in an instant. Their working principle is to generate an alternating magnetic field or a pulsed magnetic field to instantly change the magnetic domain structure. The two biggest highlights of this demagnetization technology are the ability to penetrate the metal shell to demagnetize the internal magnet and accurately control the residual magnetic flux.
Important parameters that determine the demagnetization process:
- Frequency: The rate of change of polarity reversal.
- Field strength: The strength of the alternating magnetic field.
- Material magnetic susceptibility: Soft magnetic materials (such as iron) tend to lose alignment under weak reverse magnetic fields. Hard magnetic materials (such as neodymium) are more resistant to demagnetization.
- Amplitude attenuation: The amount of attenuation is a measure of the reduction in the amplitude of the alternating magnetic field.
- Field symmetry: The symmetry of the alternating field relative to the zero field.
- Field uniformity: measures the uniformity of the field within the effective area.
- Flux direction: The direction of the alternating magnetic field relative to the object being demagnetized
Choosing the appropriate degaussing method depends on the size of the magnet, its purpose, and the tools you have available. Demagnetization is not a joke! Last month, a customer used a strong magnet to do reverse demagnetization himself. As a result, the two magnets “snapped” together and the fragments scratched his arm. Remember three “never”s:
- Never use daily tools (such as magnets knocking against each other) to demagnetize
- Never operate strong magnetic equipment with bare hands
- Never use high temperature methods in flammable environments
Need professional guidance? Contact us now!
What Types of Demagnetization Systems are There?
Now that we’ve discussed how to demagnetize magnets, you may be wondering, “What systems are available to help?” Whether you run a factory, work in an industrial setting, or simply demagnetize magnetic tools, choosing the right demagnetization system can make a big difference. There are many types of demagnetization systems on the market, and each works best in different situations.
Cyclical Tunnel Coil Demagnetization System
The Cyclical Tunnel Coil Demagnetization System is widely used in industries that handle large quantities of magnets or parts that need to be demagnetized quickly and efficiently.
The Cyclical Tunnel Coil system generates a symmetrical, uniform alternating magnetic field based on a 50/60 Hz power supply. The area outside the coil is called the discharge zone. Usually the discharge zone is about three to six times the width of the coil, and the size of the alternating magnetic field is changed by adjusting the coil opening distance according to the geometry of the demagnetized component. This thing is like a “car wash tunnel” for magnets, especially suitable for batch processing of small parts. Throw a bunch of screws and bearings onto a conveyor belt and through that humming tunnel of coils. The alternating magnetic field slowly reduces the magnetism of the component by rearranging its internal magnetic domains. When they come out, they all become “non-magnetic state”.
Plate Demagnetization System
The plate demagnetization system has a built-in coil (including an iron core or a yoke) under the plate. The magnetic current is guided to the pole plate through the yoke and gathered in the air gap between the two pole plates. Therefore, a very high magnetic field strength can be obtained within a narrow air gap range (does it look familiar? Magnetic chucks are developed based on similar principles) to disrupt the arrangement of magnetic domains inside the component. However, the effective depth is very limited, only a few millimeters, so this process is only used to process flat components.
Magnetic Yoke Demagnetization System
The structure of the Yoke demagnetizer is that it has one less pole plate than the Plate Demagnetization System. Because its magnetic flux is not concentrated, the range of magnetic flux influence is large, but the magnetic intensity is low. This demagnetization system is often used in handheld demagnetizers.
Dual Magnetic Yoke Demagnetization System
The dual yoke demagnetization system is an upgraded version of the conventional yoke, with independent yoks configured in two opposite directions. Each yoke generates its own magnetic field, and the magnetic fields interact with each other to provide a stronger and more uniform demagnetization field in a larger area.
| Demagnetization System | Advantages | Disadvantages | Best Application/Use Case |
|---|---|---|---|
| Cyclical Tunnel Coil System | – High throughput, suitable for high-volume operations. – Easy to automate. – economical and robust. | – Limited precision for delicate parts. – May be less effective for parts with complex shapes. – Requires a longer discharge section; – High reactive power and low efficiency; | – Large-scale industrial production with multiple parts requiring quick demagnetization. – Continuous production lines where speed and efficiency are prioritized. |
| Plate Demagnetization System | – Precise and controlled demagnetization. – A strong magnetic field can be generated near the plates. | – Slower process for high volumes. – The magnetic field is unevenly distributed; – Not very suitable for sensitive or polished parts; | – Demagnetizing smaller parts or delicate components requiring high precision. – Small batches where quality and control are more important than speed. |
| Magnetic Yoke System | – Simple structural design; – Suitable for high continuous throughput; – Quick and easy to use in small operations. – Cost-effective for occasional use. | – Limited demagnetizing power for larger or heavily magnetized parts. – The magnetic field has a limited depth of influence, usually <15 to 20 mm. | – On-site maintenance or field service where mobility is important. – Ideal for repair shops and small-scale operations requiring localized demagnetization. |
| Dual Magnetic Yoke System | – Stronger magnetic field for more efficient demagnetization. – Effective for difficult-to-demagnetize items. | – Heavier and less portable compared to single yoke systems. – Only suitable for flat, stepless design. – Higher initial cost due to more advanced setup. | – Large or highly magnetized parts that need thorough and uniform demagnetization. – Best for large industrial components or parts with complex shapes. |
Each of these systems has its own advantages, and choosing the right demagnetization system should be determined by your specific needs. Based on the above four demagnetization systems, people can design and develop a variety of demagnetizers based on specific needs, operating environment and work efficiency. The three most common ones are: handheld demagnetizer, desktop demagnetizer and tunnel demagnetizer. They are like fruit knives, kitchen knives and food processors in the kitchen, each with its own use.
Handheld Demagnetizer
Handheld demagnetizer, as the name suggests, is a portable, user-friendly device designed for small tasks. Just touch the demagnetizer to the object to be demagnetized, press the button, and then sweep the entire body of the part evenly and comprehensively like giving a dog a bath. If you need to frequently remove the residual magnetism of tools or equipment during maintenance and on-site operations, a handheld demagnetizer is the best demagnetization tool.
- Advantages: Small, easy to carry, simple to operate, very suitable for small-scale quick processing.
- Limitations: Only suitable for small and scattered objects, not suitable for large-scale demagnetization.
Benchtop Demagnetizer
Benchtop demagnetizers are usually installed on a workbench or under/above a conveyor belt. The efficient demagnetization coil inside the demagnetizes the workpieces passing through during the workpiece conveyance process. The benchtop demagnetizer is efficient and stable, can handle larger objects, and is suitable for regular batch demagnetization. Therefore, it is favored in industrial applications with medium-scale processing.
Tunnel Demagnetizer
Tunnel Demagnetizer is the most advanced demagnetization equipment in industrial applications. It uses a tunnel design, and the alternating magnetic field (AC) can be adjusted by adjusting the size of the tunnel. It is suitable for workpieces of various sizes and shapes. With automated equipment, objects can automatically pass through this degaussing area to achieve rapid and continuous mass degaussing operations.
However, this type of demagnetization equipment is expensive, and installation also requires a certain amount of space and supporting equipment. It is mainly aimed at large companies with high production volumes. Last year, when I was chatting with a friend (a hardware factory opened by a friend), I calculated an account: using tunnel demagnetization instead of manual demagnetization, the cost can be recovered in 8 months. But later they found a hidden benefit-the oxidation of the surface of the parts after demagnetization was significantly reduced. It turned out that the alternating magnetic field also cleaned the static electricity on the metal surface.
As you can see, choosing the right demagnetizer depends on your actual needs. In short:
- Temporary emergency or outdoor work → Handheld
- Precision control or small batch processing → Desktop
- 24-hour continuous production → Tunnel
Choosing the right equipment can help you improve your work efficiency and ensure your production process goes smoothly.
So, my experience is this: demagnetization does not happen randomly – it happens for reasons that we can understand, measure and manage. Whatever the method, to accurately control demagnetization, you must adjust the demagnetization behavior based on the material’s demagnetization curve. Successful demagnetization is the goal, but measuring and controlling the process is the key to ensuring results. We know that every detail is important, so if you need custom magnets, batch demagnetization parts, or help designing magnets that can resist unnecessary strength loss, please feel free to contact us. Osencmag helps our customers solve real magnetic challenges with precision and meticulous service.
FAQs
Why does heat demagnetize magnets?
Heat above the Curie temperature of a magnetic material can damage domain walls, making the normally aligned magnetic domains prone to rotation and misalignment. When the atoms of the magnet material are heated, they become unreliable and move around. When the atoms are no longer aligned, they cancel each other out, causing the magnetic field to weaken and be lost.
