Lifting capacity influencing factors

The maximum breakaway force is the force to pull the magnet from the product. The values on this site - in the specifications on the product pages - are indications. These are measured on a clean, flat steel sheet of a specific thickness: thick enough to absorb the full magnetic force. In practice, the maximum breakaway force is therefore not always feasible.

Lifting capacity factors

All the factors mentioned below collectively reduce the lifting capacity. To calculate the final reduction in lifting capacity, you have to multiply the various factors.

Surface conditions/air gap

Lines of magnetic force pass through steel very easily and through air with difficulty. Anything that creates a space or air gap between a magnet and a load to be lifted reduces the lifting capacity of a magnet. This can be, for example, dirt, paper, moisture, burrs, rust or paint.

Material

Steel with a low carbon content, such as St37, is nearly as good a conductor as iron. Alloys, however, contain non-magnetic materials, which impair magnetic conduction. AISI304, for instance, is a material that conducts magnetic field lines almost as poorly as air.

Heat treatments that affect the structure of the steel can also reduce the lifting capacity. The harder steel is, the poorer the lifting capacity. Hardened steel also often retains residual magnetism.
See below the lifting force for different materials:

St37 (0.1-0.3% C): 100%
Non-alloyed Steel (0.4-0.5% C): 90%
Cast steel: 90%
Alloy steel F-522: 80-90%
AISI430 (magnetic stainless steel): 50%
Cast iron: 45-60%
F-522 tempered (60 HRC): 40-50%
AISI304 (stainless steel/nickel): 0-10%
Brass, aluminium, copper, etc.: 0%

Load thickness

The greater the number of field lines that can ‘flow’ from the magnet through the load, the higher the efficiency of the magnet. If the load is too thin, the material becomes saturated with field lines and not all field lines from the magnet can flow through the material. This reduces the lifting force. Only if the load is sufficiently thick is it possible to utilise the magnet’s full capacity. Once this point is reached, a greater material thickness will not result in any additional lifting capacity.

Magnet contact surface on lifted load

If not the entire magnet surface makes contact with the load during lifting, the lifting capacity will be reduced in direct proportion.

Bending of the lifted load

If a thin sheet is lifted with a single magnet, or if the load is much wider or longer than the contact surface of the magnet, the load will bend and 'peel off' of the magnet. This peeling effect greatly reduces the lifting capacity.
Therefore, lift thin plates with several magnets, evenly distributed over the entire surface. Make sure that the magnet contact surface is always in line with the load to be lifted and not transverse to the load length.

Temperature of the load to be lifted

The higher the temperature, the faster the molecules in the steel move. Rapidly moving molecules are more resistant to an applied magnetic field and therefore result in a lower lifting capacity. The magnets used may be loaded up to a maximum of 80°C, otherwise they will become permanently demagnetized.
Magnets for use in higher temperatures are available on request.

Stacking of the lifted load

A magnet is designed for a certain lifting capacity; this is for a single load to be lifted. A lifting capacity calculated for a single sheet 10 mm thick is not the same as for two sheets that are each 5 mm thick. If you want to lift more than one sheet/profile at a time, you must state this clearly when placing your order. The specialists at Goudsmit will determine how this can be done safely for you.

It is often undesirable that two or three sheets are picked up together when taking them from a stack. The last sheet can come loose during transport. For that reason, there are magnets with a shallow field for picking up thin sheets. If this is not enough, place sheet separators next to the stack of sheets so that they are always picked up one at a time.