# How to design a magnet to handle a known force?

There is a metallical structure. I can estimate how much steel are in it. I would like to know how tall/strong a magnet should be to maintain a certain object to the metallical structure.

The object is not that heavy, but it is submitted to multiple forces, like air flood, so it need to be sufficiently strong.

Knowing the force to handle, how could I know the size and optimal disposition of the magnet?

• What is the weight of the object? Oct 13, 2021 at 15:28
• the weight is 50 kilograms Oct 21, 2021 at 19:04
• Magnet strength is also related to thickness of the workpiece being held. Thinner pieces aren't held as strongly as thicker pieces. It's related to the flux being able to extend deeply enough into the material rather than straying out. That's why on magnetic cranes the magnet has different load capacities for different thicknesses of steel. Mar 7, 2023 at 22:46

This will be very difficult to calculate analytically. Your best bet will be to simply experiment, or use the rule of thumb specs that the magnet manufacturer provides. Usually this comes in the form of holding force on a standard iron plate of some kind.

• Thank you for the answer. So if I understand well the maufacturer wil gives the force of the magnet, but how can I convert this force into the force to handle? Especially if my magnet is hung up to an iron plate, but the other fore (other than magnetic) is applied parallel to the iron plate and orthogonal to the force of the magnet? Aug 31, 2019 at 18:20
• @totalMongot Magnet design generally is done with finite element analysis. You aren’t going to get an easy answer. Certainly not by being vague about the implementation. Feb 15, 2021 at 13:02

Well theoretically you will need the force that the magnet applies to the object you will like to hang. If i understand you correctly the object will be "sheared" off the magnet due to gravity. The closet thing you can do, is to calculate it via Friction. FR= µ*Fn.

Where µ is the friction coefficient, and FN is the Force that the supplier gives you. If FR is higher than the Force of Gravity your Object should stay.

BR

Experiment is your best bet. Start with the least-expensive magnet material (barium ferrite) in a variety of sizes, using data from the magnet manufacturer. Increase the size of the magnet if it is not strong enough to yield the desired clamping force.

Here is another trick: the attractive force between a magnet and a chunk of iron scales with 1/(distance^3). This means that if your clamping force is too great, you can significantly reduce it by inserting a thin piece of adhesive tape between the magnet and the iron. Add tape until you obtain the desired force.