Magnet pull force, or magnet holding force, refers to the weight of the material that a permanent magnet can lift or attract. This is a crucial parameter when using magnets, especially in applications like magnetic filter bars, where the magnet pull force is a key parameter.
Factors Affecting Magnet Pull Force
To help readers understand, let’s use an example of a magnet attracting an iron plate.
Attraction Area
Smaller than Magnet’s Area | When the iron plate’s area is smaller than the magnet’s area, the magnet pull force between the magnet and the iron plate increases as the attraction area grows.
Larger than Magnet’s Area | Once the iron plate’s area exceeds the magnet’s area, the increase in the magnet’s pull force slows down. When the iron plate is sufficiently large, further increasing its size does not significantly enhance the magnetic force.
Thickness of The Iron Plate
Thin Iron Plate | If the attraction area is fixed and the iron plate is thin, increasing its thickness can enhance the magnet pull force, provided the space allows for it.
Thickening Iron Plate | As the iron plate continues to thicken, the rate at which the magnetic force increases will gradually level off until it no longer rises.
Optimizing Magnetic Circuit Design
Optimizing the magnetic circuit design is another way to enhance magnet holding force when the attraction area S is fixed. Multi-pole magnetization provides significantly greater magnet pull force compared to single-pole magnetization. This is because multi-pole magnetization substantially increases the magnetic flux density B through the attracted object, effectively reducing magnetic leakage and thus enhancing magnet holding force.
As shown in the figure below, when the magnet is changed to bipolar magnetization, magnetic leakage is significantly reduced. A large portion of the magnetic field lines form closed loops within the attracted iron plate. If the number of magnetized poles is further increased, magnetic leakage will be further reduced, and magnetic force will continue to improve.
This optimized approach is particularly important in applications where maximizing magnetic force is critical, and space constraints limit changes to the magnet’s size.
Metal Sheet with High Magnetic Permeability
Adding a sheet made of low-carbon steel with high magnetic permeability, such as Q235, to one side of the magnet can effectively enhance its magnetic attraction. The German designer utilized this principle to create the famous “pot magnet.” Here are the key considerations:
Sufficient Thickness | The sheet must have enough thickness to avoid magnetic saturation. If the sheet is too thin, the magnet holding force won’t significantly improve as it will become magnetically saturated quickly.
Smooth Surface | The surface of the sheet should be smooth to prevent the formation of air gaps due to surface roughness. Air gaps can reduce magnet pull force by increasing the distance between the magnet and the attracted object.
Air Gap
An air gap is the distance between a strong magnet and the attracted object. The smaller the air gap, the greater the magnetic attraction; conversely, the larger the air gap, the weaker the magnetic attraction. Data analysis shows that the magnetic force of a permanent magnet decreases as the air gap increases, even a very small air gap can significantly impact the attraction force.
Magnet Grade
The higher the grade of the magnet, the greater its magnetic force. For instance, a neodymium magnet of grade N52 will have significantly stronger magnetic properties than one of grade N38.
Applications of Magnet Pull Force
Principle | Increasing the number of magnetized poles to enhance magnetic flux density and reduce magnetic leakage.
Application | Flexible magnets utilize multi-pole magnetization, which can be either double-sided or single-sided. This approach is adopted because the magnetic performance of the materials used in flexible magnets is relatively low. However, through multi-pole magnetic circuit design, the magnetic field is densely distributed on the surface of flexible magnets, resulting in minimal magnetic leakage when attracting objects, thereby achieving a better attraction effect.
Principle | Using materials with high magnetic permeability ensures that more magnetic field penetrates the attracted object, forming closed magnetic circuits.
Application | Doorstop magnets use a metal sheet with high magnetic permeability to guide the magnetic field, ensuring that nearly all magnetic circuits form loops within the attracted object. This greatly improves the utilization of the magnetic field and enhances the magnetic attraction.
This article aims to provide an understanding of magnet pull force. For more in-depth knowledge about magnets, please leave your contact information, and a Tengye magnet expert will promptly communicate with you
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* Image source for this article: Kjmagnetics & Rokhardware & Hvrmagnet & Web
