What factors affect the adhesive force and strength of a magnet?
As an indication, we add the approximate adhesive force in grams or kilograms to the description of our magnets.
We measure the adhesive force of our magnets ourselves, and you can learn more about our method in our FAQ about adhesive force measurement.
The stated figure is always a theoretical maximum value, which can only be obtained under ideal conditions.
The actual adhesive force depends on the factors mentioned below.
Table of Contents
Distance between magnet and adhesive surface
Adhesion diagram of article S-10-05-N
If there is no direct contact between the magnet and the object, the adhesive force decreases quickly with increasing distance.
Even a small gap of half a millimetre can reduce the adhesive force by half.
A thin coat of paint on the object will also contribute to a decrease in adhesive force.
With our adhesive force tool, you can determine the adhesive force at various distances.
With our adhesive force tool, you can determine the adhesive force at various distances.
Direction of force
The theoretical value for the adhesive force is valid if the load applied to the magnet acts perpendicular to the contact surface. Due to the displacement force, also called shear force, a significantly higher adhesive force is required on the wall in order for the magnet to hold the same weight. That’s because, in the direction of displacement, the adhesive force is reduced to approx. 15–20 % of the theoretical adhesive force. So if you want to attach a load of 1 kg to a wall with a magnet, you need at least 6 kg of magnetic adhesive force. The surface condition of the two contact surfaces also plays a role, as it can further reduce the adhesive force. Even though adding rubber or caoutchouc to the magnet does increase the distance of the magnet to the contact surface, it also protects the magnet from slipping out of position on the wall. You can find additional information on this topic in our FAQs about shear force.By the way: If you would like to know the adhesive force in newton, multiply our specification in kg by 9,81. A mass of 1 kg equals a weight of 9,81 newton.
Counterpart material
The theoretical value for the adhesive force is valid if the magnet’s counterpart consists of pure soft iron. For S235 structural steel, you have to reduce this value by about 5 %, for E360 by approx. 30 %. Generally, all ferromagnetic materials can be used as an adhesion surface for magnets. In addition, two magnets can also be combined and will attract each other. Materials such as copper, zinc or aluminium are not ferromagnetic and therefore unsuitable as a surface for magnets. You can find additional information in our FAQs about ferromagnetic materials.Counterpart surface
The smoother the surface of the counterpart, the greater the adhesive force. If the surface is rough, you should anticipate a considerable reduction in adhesive force because pockets of air will form between the magnet and its counterpart. This, in turn, reduces the available contact area for the magnet to attach to the counterpart. Based on the counterpart’s material properties, roughness can occur in the form of a coat of paint on the counterpart, rust or dirt. For this reason, you will need to make sure that the surface of your magnet counterpart is clean.Counterpart thickness
The counterpart should not be too thin, or else it will reach magnetic saturation and part of the magnetic field will remain useless. Generally, you should never rely on our indications regarding the adhesive force for a specific application but conduct your own tests first. We measure the adhesive force of our products with a 2 cm thick steel sheet. The thinner the counterpart, the less adhesive force is achieved.Material quality and direction of magnetisation
Not only the size but also the strength of the magnet material plays an important role in the level of adhesive force a magnet achieves. You can learn more about this topic in our FAQ about magnet grades. Depending on the application, the direction of magnetisation is also important. It determines the path of the field lines in a magnetic field. You can find additional information in our FAQ about the magnetisation direction.Number of magnets used
You can, of course, increase the magnetic adhesive force by using several magnets. What one magnet cannot do on its own, maybe two magnets can do next to each other. Stacking flat disc magnets also multiplies the adhesive force until the stack reaches a height of half the diameter of a single disc magnet at a maximum. You can learn more about it in our FAQ about stacking magnets.Magnetic attraction vs repulsion
All magnets have a north and a south pole. Two magnets always attract each other at the opposite pole, respectively. Like poles can not be combined, as they will repel each other. The magnet will automatically want to turn the right way so that it is attracted to the opposite pole of the second magnet. You can find out more in our FAQ about attraction and repulsion. To determine both poles (north and south pole), we have developed a pole detector app for you.Temperature
Most of our magnets have a maximum working temperature of 80 °C. Higher operating temperatures can destroy the magnetic field.Tip: You can find the maximum working temperature of our products in the technical data below the product description.