Lifting magnets

About magnetic lifting

Lifting magnets serve to move and position ferromagnetic (often steel) work pieces with various shapes and lengths, quickly and without damage. With magnetic lifters you save both valuable storage space and time. They are often a safe alternative to slings, chains or clamps.

Note: If you want to pick up steel objects, you cannot simply choose a magnet based on the weight of the objects. From the safety standpoint we recommend that you also carefully consider the object to be lifted and the safety of the work environment.

Factors influencing lifting capacity

The lifting capacities specified on this website assume you will be lifting a clean, flat, steel plate that is thick enough to interact with the full magnetic flux. For an object that does not meet these requirements, the lifting capacity will be lower.

The following factors have an impact on the lifting capacity:

1. Surface conditions/air gap

   Magnetic lines of force pass easily through iron, but not air. Therefore anything that creates space or an air gap between the magnet and the lifted object (e.g. dirt, paper, moisture, burrs, rust or paint) will have a negative impact on the lifting capacity of the magnet.

2. Material to be lifted

   Steel with a high carbon content, such as St37, is nearly as good a conductor as iron. Alloys, however, contain non-magnetic materials that have a negative impact on the magnetic conductance. AISI304, for instance, is nearly as poor a conductor of lines of force as air.
   Heat treatments that affect the structure of the steel can also reduce the lifting capacity. The harder a type of steel is, the poorer the lifting capacity. Hardened steel also often retains some residual magnetism.

   The table below shows the lifting power of various materials:

   Material	Lifting Force [%]
   St37 (0,1-0,3% C)	100
   Non-alloy 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

3. Thickness of load to be lifted

   The greater the number of lines of force that can ‘flow’ from the magnet through the load, the more effective the magnet field will be. If the thickness of the material to be lifted is too thin, the material will become ‘saturated’ with lines of force, preventing some of the lines of force produced by the magnet from ‘flowing’ through the material. Only if the load is sufficiently thick is it possible to utilize the magnet's full capacity. Once this point is reached, a greater material thickness will not result in any additional lifting capacity.
   In the case of a thin steel sheet, for instance, only a portion of the magnetic force will hold it in place because the sheet becomes saturated, effectively reducing the holding power of the magnet.

4. Magnet contact surface on lifted load

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

5. 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. The ‘peeling effect’ results in a certain reduction of the lifting capacity. Therefore thin sheets should be lifted with multiple magnets evenly distributed over the entire surface, and the magnet contact surface should always be in line with the lifted load, not perpendicular to its length.

6. Temperature of the lifted load

   The higher the temperature, the faster the molecules in the steel vibrate. Rapidly moving molecules are more resistant to an applied magnetic field and therefore result in a lower lifting capacity. The magnets that are used must not be exposed to temperatures above 80 °C. Otherwise they may become permanently demagnetized.
   Magnets for use in higher temperatures are available on request.

7. Stacking of the lifted load

   A magnet is designed for a particular lifting capacity; this capacity applies to a single lifted load. A lift capacity calculated for a single plate 10 mm thick is not the same as for two plates that are each 5 mm thick! If you want to lift more than one plate/profile at a time, you must state this clearly when placing your order. The specialists at Goudsmit will determine whether and, if so, how this can be done safely.
   It is often undesirable for two or three sheets to be picked up together when taking them from a stack. This can be dangerous, because the lowest plate can detach during transport. To avoid this, shallow field magnets are used for picking up thin sheets. If this is not enough, you can place sheet separators next to the stack of sheets so they will always be picked up one at a time.

All the factors mentioned above collectively reduce the lifting capacity. To calculate the total reduction of lifting capacity you must take the product of all the various factors.

Risk analysis

When lifting objects, it is important to conduct a risk analysis beforehand.
In areas where a falling load (or portion thereof) could pose a danger to persons, you must take measures to limit the distance to 1.5 metres.
This restriction does not apply, however, if you install a retention device (fall protection) that will catch and hold the falling load. Keep in mind that such a retaining device reduces the ease of use.

When lifting heavy loads, you should also pay attention to the swaying of the load. In this situation the weights are so high that they cannot be easily corrected by hand. A good lifting system is a combination of the magnet, the suspension and the control system.

For lifting of smaller and/or light objects: see our handling-magnets.