What is Demagnetization and How is it Done?

In some cases, residual magnetism on a material’s surface may be a desirable property, but in most industrial applications, this is problematic and its removal can be quite challenging. For instance, magnetising the tip of a screwdriver can help it hold screws more easily. However, when two steel moulds used in the plastic or metal industry become magnetised, it leads to undesirable outcomes.

The demagnetisation device produced by our company effectively eliminates the accumulated magnetic field on thick materials.

Magnetisation and demagnetisation are two opposing yet interconnected processes. Magnetisation refers to the process by which a metal gains magnetic properties when exposed to an external magnetic field. This process involves aligning the magnetic domains within the metal, making the metal behave like a magnet. In other words, it is the process of a material acquiring magnetic characteristics. Demagnetisation, on the other hand, is the opposite process.

Demagnetisation involves the weakening or removal of the magnetic field from a metal, causing it to lose its magnetic properties. This article explains in detail how these two processes, often referred to as the “two sides of the same coin”, are connected, and outlines how the magnetisation and demagnetisation of ferromagnetic metals like iron and steel occur. The information presented here is crucial not only for industrial applications but also for the design of magnetic materials.

The importance of this information becomes evident when deciding on the right demagnetisation device or machine. Ensuring that there is no loss in production or product quality requires a solid understanding of these processes. The only way to guarantee that workpieces have been completely free from magnetism or permanent magnetisation is through the appropriate techniques and equipment. Therefore, it is essential to remember that moving forward with any further work depends on successfully fulfilling this requirement.

In Which Cases Is Demagnetization Necessary?

We manufacture state-of-the-art demagnetisation machines. In the Turkish market, we provide the necessary devices for demagnetising thick materials.

Materials that come into direct contact with magnets share the magnetic energy present on their surfaces. For instance, steel mould materials being ground on a grinding machine, when in contact with a magnetic holder, will transfer the magnetisation property to the mould materials. Once these moulds are connected to a press, each product pressed will transfer the magnetic property to the sheet material. This can cause issues in subsequent processes such as painting, coating, or precision measurement. This magnetic field must be eliminated by passing it through a demagnetisation device.

Demagnetizer Machine

 

 

 

 

 

We manufacture demagnetisers (demagnetising machines) in custom sizes according to customer requirements, using our local engineering infrastructure. During the production process, the magnetic field that forms on the surface of the parts can lead to errors in processes such as painting, cleaning, or 3D measurements. To prevent this, the magnetic field on the surface of the parts must be removed, i.e., the parts must be demagnetised. Demagnetisation is not as simple as it may seem and requires a thorough approach to the entire process.

Why is Demagnetization Done Degauss ?

Magnetic metal materials, such as steel products and equipment, can easily become magnetised when used in the same environment as a magnetic field. For example, products become magnetised after passing through a magnetic mould clamping table or a magnetic conveyor. Other causes of magnetic field transfer include processes such as welding, bending, twisting, CNC machining, deep drawing, and mechanical vibrations.

Reasons for Demagnetization of Material

Unwanted residual magnetic field causes the following problems,

• • In mass production, the product sticks to the molds;

• • Rough surface after galvanizing;

• • Difficulty while welding;

• • The source is only on one side and does not pass to the other side;

• • Increased bearing wear

In order for dust particles not to remain on the surface, there should be no gauss value on the surface of the metal up to a certain range. The minimum gauss value varies between sectors.

What is Demagnetization?

Demagnetisation is the process of eliminating the magnetic field that occurs during the production of metal materials or when exposed to a magnetic field. Depending on the demagnetisation technique used, it is normal for the magnetic field on the product to remain within the range of 0-5 Gauss. Magnetisation, which is the process of a material acquiring magnetic properties, and demagnetisation, which is the process of eliminating magnetism, are two opposing processes. However, these two processes are interconnected. Magnetisation refers to the process in which a metal gains magnetic properties when exposed to a magnetic field. This process involves the alignment of the magnetic domains within the metal, causing the metal to behave like a magnet.

Demagnetisation, on the other hand, is the opposite process. It involves the weakening or complete removal of the magnetic field from a metal, resulting in the loss of its magnetic properties. This article explains in detail how these two processes, often referred to as the “two sides of the same coin”, are connected, as well as how the magnetisation and demagnetisation of ferromagnetic metals, particularly iron and steel, is carried out.

How Do Magnetization and Demagnetization of Magnetic Materials Occur?

The magnetisation of ferromagnetic materials occurs when these materials are exposed to an external magnetic field. Materials such as iron, steel, nickel, and cobalt, along with their alloys, become ferromagnetic when they gain magnetic properties. During magnetisation, magnetic moments of the atoms that exhibit magnetic behaviour are formed inside the ferromagnetic material.

Each magnetic domain, which is a small region with magnetic properties, behaves like a small magnet and represents the overall magnetic alignment of the atoms in that region. In an unmagnetised state, these domains have random orientations, and thus the material’s overall magnetic moment is zero. However, an external magnetic field applied to a ferromagnetic material exerts a torque on the magnetic moments of the atoms. This torque causes the magnetic domains to align with the external magnetic field.

In other words, the external magnetic field, known as the H field, is responsible for aligning the intrinsic magnets within the material. This is because in ferromagnetic materials, the intrinsic magnets are not freely arranged within the material. Instead, they are grouped into domains, known as Weiss domains, separated by domain walls. In unmagnetised materials, the size of these domains is typically below 100 µm, and the thickness of the domain walls is a few hundred atoms.

The domain walls move as the external magnetic field increases. This movement generates a magnetic flux known as the B field. However, the induced magnetic flux does not increase uniformly but rather in small and discontinuous jumps, known as Barkhausen jumps. As the magnetic field grows, larger domains are formed and the intrinsic magnets align in a more regular manner. The ideal scenario for magnetic saturation is the formation of a large single domain, where the intrinsic magnets align with one another.

After magnetisation, permanent magnetism, or remanence, occurs. This is the phenomenon in which ferromagnetic materials retain magnetic properties. Demagnetisation is the process of removing this permanent magnetism. Demagnetisation is achieved by transferring the aligned intrinsic magnets into a homogeneous disorder, using an alternating magnetic field. The demagnetisation power is defined by the magnetic field strength, which depends on the current, coil gap, coil length, and the number of coils.

Proper design of the demagnetisation pulse ensures the success of the process. The design involves reversing the polarity of all intrinsic magnets after reaching the maximum field strength in one direction. The polarity of the intrinsic magnets within the material is also taken into account. First, the intrinsic magnets are homogenised, and then the field strength is reduced. During this process, the magnetic structure inside the component is turned into a fine domain structure through the effect of frequency oscillation.

The magnetic properties inside the component are gradually eliminated by reversing the polarity of the intrinsic magnets at the outermost field and the surface. This process continues until the applied magnetic field completely disrupts the magnetic structure. Compared to fully magnetised materials, lightly magnetised components, which show moving domain walls but where the intrinsic magnets are not yet fixed, can be processed with a smaller demagnetising field.

Methods Available for Demagnetization

A magnetic material can be demagnetized by using some methods such as heating the product above the Curie temperature. The magnetization of a ferromagnetic material theoretically remains indefinitely. Another method is strong vibrations that can cause a slight decrease in magnetization due to their own magnetic field. Other methods are:

• • Demagnetization using an external, alternating decreasing magnetic field

• • Moving the magnetic field by applying a magnetic field of opposite polarity and then stopping the field source

• • The magnetism in the component jumps to almost zero with the field setting precisely measured, known as overturning demagnetization

What Are So-Called Non-Magnetic Stainless Steels?

Manyetik olmayan veya

There are some types of steel that are considered non-magnetic. However, this situation can be confusing because it is always said that it is not the case. Especially in stainless steel, due to the magnetic or non-magnetic nature of the band width within the material class, the material definition alone is not sufficient to determine the magnetic properties. The austenitic, ferritic and martensitic structure within the steel determines the magnetic properties and the distinction is made between these structures.

It can be easily determined whether a steel is magnetic or not. The magnet test can be used for this. The indicator of whether the steel is ferritic or martensitic is the adhesion of a magnet to the steel. Generally, the non-magnetic steel is austenitic stainless steel, whose structure can change as it is shaped. Austenitic steel can become martensitic because its structure can change as it is shaped. If the component allows this, the martensitic structure can be converted back to the austenitic structure by annealing.

Can Stainless Steel Be Demagnetized?

Demagnetization does not change the physical properties of stainless steel. The remaining martensitic structure cannot be remagnetized, nor can non-magnetic austenitic stainless steel be obtained by demagnetizing the steel. This is because demagnetization removes the magnetization already present in the material.

How is Demagnetization Done Practically?

Demagnetization with a demagnetization device is done as follows:

• • The component to be demagnetized is pulled through the demagnetization device at a moderate, uniform speed, usually through a demagnetization tunnel..

• • The distance between the component and the magnetic field source increases during this process. As the distance increases, the alternating magnetic field gradually weakens.

• • The demagnetization power is created by the field strength created here. The alternating magnetic field frequency determines the penetration depth.

• • The speed at which the component moves away from the alternating field also depends on frequency. It is important that the component still experiences sufficient vibration as the alternating field decreases.

Demagnetization by the demagnetization pulse method is static demagnetization. During this process, a control unit uses current without moving the component to control the alternating magnetic field. First, the alternating magnetic field is increased to the maximum field strength. Then it is reduced monotonically to zero field. Demagnetization by demagnetization pulse provides many benefits.

Benefits of Demagnetization Pulse

It is necessary to say that the demagnetization pulse is considered the most advanced technology. First of all, the observation of the most important physical properties allows to understand the benefits of demagnetization by applying pulses. This observation is made using an air coil. Cyclic demagnetization is another positive factor in favor of pulsed demagnetization.

What are the Physical Properties of Each Coil?

The copper or aluminium coil is usually operated with a mains voltage of 110 V–480 V and a corresponding mains frequency of 50/60 Hz. The heat balance of the coil is adjusted to about 80°C by the inductance and resistance of the coil. Limiting the current prevents overheating. The extremely limited magnetic field strength is due to physical reasons. The maximum current is maintained for a very small fraction of a second during the demagnetization pulse and decreases within a few seconds.

Benefits of Pulsed Demagnetization Compared to Cyclic Demagnetization

Low field strength can prevent all the basic magnets in a component from aligning at maximum field strength due to heat. As a result, the basic magnets cannot be aligned. This causes the magnetization to increase. The factor that optimizes the penetration depth is the reduction of frequency. Optimizing the penetration depth is done by using frequency converters. Frequency converters are used to change the frequency of the grid connection.

In pulsed demagnetization, the field strength can be increased several times due to the short turn-on time. Overheating of the coil is prevented by the controlled cycle time and the maximum current duration of a few hundredths of a second. This results in much higher magnetic field strengths. If configured correctly, complete and reliable demagnetization is guaranteed even in the material.

Maurer Degaussing® Technology

Maurer Degaussing® technology uses a pulsed signal method to effectively neutralise magnetic fields in large structures. This process not only saves time but also preserves critical setups. For example, there is no need to disassemble cutting dies before demagnetisation. Even baskets fully loaded with cast parts can be demagnetised within seconds using high-performance systems.

This technology offers high-efficiency magnetic field elimination. Since the demagnetisation pulse is fully controllable, the process is highly reliable and can be carried out with zero defects. As long as the position of the components remains unchanged, optimal results can be expected. Compared to conventional methods, Maurer’s pulsed demagnetisation offers the following key advantages:

• High field strength

• Precisely decreasing alternating field

• Excellent field symmetry during discharge

• Ideal frequency for magnetic field removal

To effectively eliminate the magnetic field, the most crucial process parameter is the strength of the magnetic field. It is sufficient to generate a peak field for at least one full sine wave for a short duration. Although the alternating current flowing through the copper coil is physically limited by inductive and ohmic resistance, Maurer Degaussing® systems operate with multiples of the mains voltage to ensure the highest possible effective current.

In pulsed demagnetisation, once peak field strength is reached, the current must decrease smoothly and consistently. This precision in reduction directly affects the randomness and uniformity of the magnetic structure within the component. Even the slightest asymmetry between the north and south poles of the applied field can result in residual magnetism at the final stage of the pulse.

The source of magnetism is not limited to process precision. External magnetic fields, such as the Earth’s natural magnetic field, can also cause asymmetry. This is particularly true for long stretched components and cast parts. To address this, shielding components from the Earth’s magnetic field during the process can significantly improve results, especially with long or bulk materials.

Maurer’s patented technology maintains deep, application-specific frequencies. These typical frequencies include:

• 50–200 Hz for strip materials and wires

• 16–50 Hz for baskets with bulk material or small components

• 8–16 Hz for medium-sized parts

• 4–8 Hz for large components

• 1–4 Hz for very large and bulky parts

Lower frequencies enable better magnetic penetration by overcoming material inertia and preventing eddy current blockages. For fine magnetic structures, higher frequencies are also useful. To achieve the best outcome, the frequency must be selected based on the volume of the component, often requiring a compromise or a combination of multiple frequencies.

In cases of magnetic saturation, internal resistance within the material can only be overcome by applying high magnetic field strengths. Maurer systems achieve this, ensuring even weak magnetisation is eliminated. This approach also significantly improves cost-efficiency. The ideal parameters for demagnetisation are determined during preliminary testing.

Thanks to the Maurer Degaussing procedure, high field strengths can be applied even at high frequencies, such as 15–50 Hz. These high frequencies are especially advantageous for fast, reliable, and effective demagnetisation.

Demagnetization Frequency Adjustment

The demagnetization frequency is set in the factory for the component and the required cycle time. Very large and bulky parts are demagnetized using a specially developed universal pulse operating over a very wide frequency band.

Pure Active Power

Maurer Degaussing® is a special demagnetization procedure to solve the problem of reactive power in coils operating with AC voltage. This procedure eliminates unwanted reactive current and reactive power caused by inductivity, reducing unnecessary load on the grid and reducing costs.

This technology provides energy efficiency because it completely compensates for reactive power while consuming active power. Thus, it allows a more effective use of electrical energy and contributes to energy saving.

Comparison Between Demagnetization Types

During the demagnetisation process, a component is ideally surrounded by a magnetic field that is as homogeneous as possible. To achieve this, demagnetisation coils are commonly used. In the context of electromagnetism, a demagnetising field refers to the magnetic force that opposes the magnetisation of a material. When a ferromagnetic or ferrimagnetic material becomes magnetised, it generates its own internal magnetic field.

However, in real-world conditions, such materials are rarely isolated and often interact with their surrounding environment. These interactions can lead to complex magnetic responses.

The demagnetising field arises as a reaction to this interaction, applying an opposing force to counteract the material’s magnetisation. Understanding and effectively managing this field is crucial for a wide range of applications, particularly in magnetic data storage, transformers, and electromagnetic shielding.

Demagnetisation coils help eliminate unwanted residual magnetism by creating a uniformly distributed magnetic field around the component. This process also helps reduce the impact of external magnetic influences. As a result, it plays a vital role in achieving stable and controlled magnetic conditions in industrial applications.

1. Demagnetization Using a Circular Tunnel Coil

The tunnel or air coil is a simple demagnetizing device, usually operated directly from the mains at a frequency of 50/60 Hertz. This coil is used to obtain an alternating field that decreases with increasing distance. It is important that the component is moved evenly across the coil. The discharge area is the area beyond the coil, called the discharge area, which is usually three to six times the width of the coil, depending on the geometry of the component and the coil aperture.

 

2. Demagnetization Using Plate Type Demagnetizer

Plate type demagnetizers operate with an internal coil with an iron core or yoke, and the magnetic flux is directed through the yoke to the pole plates. High field strengths are achieved in a narrow air gap by coupling in the air gap between the two pole plates. However, the effective depth of this device is limited to only a few millimeters, so it is generally suitable for thin components.

 

• • Typically suitable for flat components

• • Typical detail depth < 10 to 15 mm

• • Lack of 100% opening time in some cases

• • If operated manually, the field exposure is usually above the permissible limit value.

• • Sensitive or polished components may be scratched

• • In conclusion, plate-type demagnetizers can be effective in certain applications but have advantages and disadvantages that are specific to the use case.

3. Yoke Demagnetization

Demagnetization using a yoke is essentially similar to plate demagnetization, except that pole plates are not used. The magnetic flux is more dispersed, resulting in more stray current, and therefore lower field strength. However, it has the advantage of simple design and high field strength of about 40 to >100 kA/m. Compared to plate demagnetization, it provides more comprehensive demagnetization and achieves consistently high efficiency.

 

Advantages

• • It has a lower amount of field strength with the use of a yoke.

• • Provides a wider range of demagnetization compared to plate demagnetization.

• • Delivers consistently high efficiency.

Dezavantajları

• • Field strength is often insufficient.

• • The demagnetization effect depends on the movement of the component.

• • Typically better suited to flat components.

• • Having a typical penetration depth of <15 to 20 mm.

• • Lack of normal 100% opening time.

• • When operated manually, field exposure is generally above the permissible limit value.

• • Delicate or polished components may be scratched.

• • In addition, the stray field provides a better containment than low power plate demagnetization.

4. Double Yoke Demagnetization

In double yoke demagnetization, one yoke is placed below the component and the other above. This method, which is usually used for larger components or parts on product carriers, offers the option of height adjustment. It has the significant advantages of high field strength of about 40 to >100 kA/m near the pole plates and high continuous efficiency. However, a homogeneous field is only produced for flat plates and components of the same height.

 

In addition to this disadvantage, there are other disadvantages such as the need for height adjustment close to the workpiece, the field stopping after leaving the effective range, the demagnetization effect being dependent on the movement of the component, the typical lack of a 100% turn-on time, the field strength being generally insufficient, and it being suitable only for flat, stepless designs. Consequently, double-yoke demagnetization is a suitable option for large components. However, it does have certain limitations and disadvantages.

Do Magnets Demagnetize?

AlNiCo and Ferrite Materials vs Rare-Earth Magnets in Demagnetisation

AlNiCo and ferrite materials can be effectively demagnetised using alternating magnetic fields. However, this method is not fully effective for rare-earth magnets. These permanent magnets have significantly higher coercive field strength compared to materials like iron or steel, requiring much stronger magnetic fields for successful demagnetisation.

Magnets are typically magnetised using field strengths of up to 5 Tesla. This process is applied after the magnets are manufactured and processed, using powerful magnetic fields appropriate to the type of magnetic material. In the case of rare-earth magnets, conventional industrial demagnetisation systems may not generate a strong enough field to return the material to its original unmagnetised state.

The main reasons for this are the strong magnetic retention properties of rare-earth materials and the lack of sufficient nucleation for reverse magnetisation.

• • Hard Ferrite:
    Hard ferrite magnets are most effectively demagnetised at temperatures above 450 °C. Alternatively, strong demagnetising systems and appropriate flux concentrations can also be used. Field strengths exceeding 800 kA/m are typically required for this process. This results in a return to near-original magnetic states, aside from minimal residual magnetism.

• • AlNiCo:
    AlNiCo magnets are among the easiest magnetic materials to demagnetise. Field strengths starting from around 350 kA/m can remove their magnetism entirely without damaging the magnetic structure. However, remaining magnetic cores may require higher field strengths during remagnetisation.

• • Plasto-Ferrite:
    Plasto-ferrites lack sufficient heat-resistant plastic or binding agents to withstand thermal demagnetisation. Therefore, the only effective method is via strong demagnetising fields. No damage to magnetic properties is expected during this process.

• • Neodymium:
    Neodymium magnets are highly resistant to demagnetisation using magnetic fields alone. Heat-assisted demagnetisation is more effective but can weaken the magnet. After remagnetisation, a power loss of a few percent typically occurs, and surface coatings (usually galvanic) may become damaged. In addition to heating, the tumble method can also be used.

• • Samarium Cobalt:
    Samarium Cobalt magnets behave similarly to Neodymium types and are extremely brittle, though corrosion-resistant and do not require coating. Field strengths above 4,000 kA/m are necessary for alternating field demagnetisation. The preferred method is thermal demagnetisation, although even this does not ensure complete core reversal. As a result, a slight loss of magnetic strength (typically a few percent) may still occur due to heat exposure.