Adhesion: The bonding force to surfaces

The term adhesion comes from the Latin "adhaerere" (to adhere) and refers to the force that acts between two different materials or surfaces when they are in contact with each other. In the context of magnets, adhesion refers in particular to the adhesive force of a magnet on a metallic surface, which is generated by magnetic forces.

Adhesion in magnet technology

In magnet technology, adhesion describes the ability of a magnet to adhere firmly to a surface (usually made of iron or steel). This adhesive force is a combination of the magnetic properties of the magnet, the surface properties and the physical interaction between the two materials.

Factors that influence adhesion

1. Material of the magnet:

   • The strength of the adhesion depends on the magnet class:
     • Neodymium magnets: Highest adhesion force per volume.
     • Ferrite magnets: Lower adhesive force, but more corrosion-resistant.

2. Surface material:

   • Magnetically conductive materials (such as iron or steel) increase the adhesive force.
   • Non-magnetic materials (e.g. aluminium, wood) do not lead to adhesion.

4. Surface finish:

   • Smooth: Maximum contact surface and therefore strongest adhesion.
   • Rough: Reduces the contact surface, which reduces the adhesive force.

6. Distance:

   • The magnetic adhesive force decreases exponentially with distance. A distance of just a few millimetres through a coating or air gap significantly reduces adhesion.

8. Alignment of the magnet:

   • Axially magnetised magnets generally adhere better than diametrically magnetised magnets, as the adhesive force is concentrated along the axis.

Measuring adhesion

The adhesive force of a magnet is usually measured in Newtons (N). It indicates how much force is required to detach the magnet vertically from the surface.

Formula for calculating adhesion: F=B2⋅A/(2⋅μ0)F = B^2 cdot A / (2 cdot mu_0)F=B2⋅A/(2⋅μ0)

• FFF: Holding force (N)
• BBB: Magnetic flux density (Tesla)
• AAA: Contact area (m²)
• μ0mu_0μ0: Magnetic field constant (4π⋅10-74 pi cdot 10^-74π⋅10-7 H/m)

Applications of adhesion in magnet technology

1. Office magnets:

   • Magnets on whiteboards or refrigerators adhere to the metallic surface by adhesion.

2. Mounting systems:

   • Permanent magnets are used in mounting solutions such as tool holders or mounting magnets.

3. Mounting systems:

   • Magnets are used as an invisible fastening solution in the furniture industry or in trade fair construction.

4. Sensor technology:

   • Magnetic adhesion makes it easy to position sensors or measuring devices.

5. Automotive industry:

   • Magnets with high adhesive force are used in doors, bonnets and fasteners.

Technical properties of adhesion in magnets

1. Maximum adhesive force:

   • Neodymium magnets can support several kilograms of weight per square centimetre of contact surface.
   • A typical disc magnet with a diameter of 25 mm can achieve an adhesive force of up to 10 kg.

3. Reduced adhesive force due to distance:

   • A coating (e.g. paint, plastic) of just a few millimetres reduces the adhesive force considerably.
   • Example: An air gap of 0.5 mm can reduce the adhesive force by up to 50 %.

5. Temperature dependence:

   • The magnetic adhesive force can decrease at high temperatures. Neodymium magnets lose their adhesive force from 80 °C, while ferrite magnets remain more stable.

Adhesion and friction:

In addition to the magnetic adhesive force, the frictional force also plays a role, especially with lateral loads (e.g. pushing). e.g. pushing). The adhesive force then depends on:

• The material pairing (e.g. steel-magnet, magnet-rubber).
• The roughness of the surface.

Holding force ≠ holding force:

• The holding force is the maximum vertical pull-off force.
• The holding force also takes into account friction and other influences, e.g. lateral load.

Practical examples of adhesion

1. Magnetic knife holder:

   • Knives are securely attached to a steel holder by adhesion.

2. Magnetic building blocks:

   • Toy building blocks with magnets use adhesion to remain stable.

3. Mounting magnets:

   • In furniture assembly, strong magnets serve as invisible holding components.

Did you know?

• The adhesive force of a magnet is directly proportional to the size of the contact surface, but even small magnets can generate impressive adhesive forces due to high magnetic field strengths.
• In space, where there is no gravity, magnetic adhesion is used to attach tools to surfaces.

Conclusion

Adhesion is one of the most important properties of magnets and makes them indispensable for countless applications in industry and everyday life. The ability to adhere to surfaces through magnetic forces enables innovative solutions - from holding systems to precise sensors. The adhesive force depends not only on the strength of the magnet, but also on the material pairing and the ambient conditions.