About magnetic lifting

Lifting principles

Lifting magnets serve to move and position ferromagnetic (often steel) work pieces with various shapes and lengths, quickly and without damage. With lifting magnets you save both valuable storage space and time.
Electromagnets have long been used for picking up ferromagnetic objects. The advantage of electromagnets is that they can lift heavy weights (up to 15 tonnes) and are switchable. A disadvantage is that a loss of power will result in release of the load. Therefore all electromagnetic lifting systems are equipped with a backup system that will continue to hold the load for an additional 20 minutes. Such a backup system is not only expensive but also requires annual inspections.
This is why Goudsmit also offers switchable permanent magnets. These retain their magnetic force indefinitely and therefore do not require a backup system.

We offer permanent lifting magnets based on three different working principles:

  1. Manually-switched permanent magnetic lifters
    Working principle: The system utilizes a powerful Neoflux® (neodymium) magnet that can be short-circuited by means of a handle or twist knob; in one direction it is ‘off’ and in the other the poles are reversed, switching it ‘on’ again.
    Maximum lifting capacity: approx. 30,000 N per magnet.
    For products see: Permanent magnetic lifters
  2. Pneumatically-switchable permanent lifters
    Working principle: This is a Neoflux® (neodymium) magnet in an aluminium housing. This magnet is moved up and down by means of compressed air.
    Maximum lifting capacity: approx. 435 N per magnet.

            Magnet 'ON'                                 Magnet 'OFF

    For products see: Magnetic gripper and Magvacu combi grippers

  3. Electrically-switchable permanent lifters
    Working principle: the hoisting of an object is realised by a permanent magnet, while releasing occurs by an electromagnet that neutralizes the permanent magnetic field.
    Maximum lifting capacity: approx. 500 N per magnet.
    For products see: Electro-permanent lifters

Important note: If you want to pick up steel objects, it is not sufficient to pick a magnet based purely on the weight of the object to be lifted. For safety's sake, we recommend that you first carefully consider the object and the surroundings

 

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 absorb all the magnetic energy. If the object does not meet these requirements, less holding force will be applied to the object.
The following factors have an impact on the lifting capacity:

  1. Surface conditions
    Magnetic lines of force pass easily through iron, but not air. Therefore anything that creates space or an air gap (e.g. dirt, paper, moisture, burrs, rust or paint) between the magnet and the lifted object 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 change the structure of the steel also reduce lifting capacity. The harder a type of steel is, the poorer the lifting capacity, and hardened steels often retain some ‘residual magnetism’:
    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 load is 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.
  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.
  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, yet this is often insufficient to prevent the problem entirely, so sheet separators are placed beside the sheets to ensure they are picked up one at a time.

All these factors contribute to a reduction of the lifting capacity. To calculate the total reduction of lifting capacity you must take the product of all the various factors.

 

Risk analysis

When objects are to be lifted, a risk analysis must always be performed.
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 retaining device that will catch and hold the falling load. Keep in mind that such a retaining device reduces the ease of use.

If heavy loads are to be lifted you must also consider that the load will swing. 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.

 

Guidelines for manual lifting

When considering loads that will be lifted by persons, you must keep in mind the applicable guidelines for lifting and dragging:

Persons Often lift and drag under average working conditions Occasionally lift under favourable working conditions 
Men 18 to 25 kg 40 to 50 kg
Women 8 to 10 kg 13 to 15 kg
Pregnant women 5 kg 10 kg