How does steel thickness affect holding or clamping performance of a magnet?

Why is steel thickness important for magnetic lifting or gripping?

To effectively lift or clamp steel with an appropriate magnet the target load must have adequate thickness to accomodate or absorb sufficient flux from the magnet to enable rated duty. By way of illustration, a large 2 mm thick steel plate may have a mass of 100 Kgs, but will not be lifted with a magnet rated for a 100 Kg lift for two reasons: A) 2 mm does not provide enough 'meat' for the magnetic field to be effective and, B) a large 2 mm thick sheet will sag and peel from the magnet face. (In this case, multiples of shallow-field magnets will be required). The type is steel is important because not all steel types have the same magnetic properties: stainless steels are of varying magnetic susceptibilities as are special steels such as magnganes wear-resitant steel, among others. In addition, surface treatments or styles such as perforated plate, raised tread-plate or even galvanizing and temperature will affect magnet capacity and effectiveness.

Generally time is not a problem and Rare Earth magnets lose less than 1 or 2 percent strength over very long periods--scores of years. Elevated temperatures have the greatest effect on Rare Earth magnets. NdFeB (Neodymium/Iron/Boron) magnets are the strongest magnets available and at temperatures up to 150 degrees C, they are stronger than SmCo (Samarium Cobalt). At about +150 degrees C Neodymium magnets do not perform as strongly as SmCo. With elevation of temperature, recoverable losses occur up to about 230 Degrees C for NdFeB magnets and 300 to 350 degrees C for SmCo. If your application is high temperature let us know and we will provide SmCo pricing for you.

The short answer is no—unless… Let’s begin here: The task required of a magnet will determine what type of magnetic field is necessary. In general terms Permanent Magnet circuits can be designed with stronger surface gripping strength than most Electromagnets. Switchable Permanent Magnet devices are therefore ideal for many steel lifting or gripping applications, providing the steel has sufficient thickness. Permanent magnet devices are also used for various types of magnetic separation, for example Grate Magnets and Plate Magnets to recover damaging iron from food or powdered products. And, the ‘unless’? Superconducting electromagnets have been designed and are in use for specialised mineral separation and other applications. These have their coils cooled to operate at near absolute zero temperature, enabling the development of immensely strong magnetic fields.