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Lifting Magnet FAQs
What is an Electromagnetic Lifter?
An Electromagnet involves the supply of a constant (direct) current to a coil surrounding a pole. This current x number of turns around the coil will generate a magneto motive force through the pole. The more current and or more turns on the coil, the more magnetic force, and so electromagnets can be very strong.
They also have very good air-gap capability – scrap yard magnets, for example, are best served by electromagnets.
The biggest weakness of an electromagnet is its dependence on uninterrupted electrical power. The moment power is lost, the magnetic force is removed.
What is a Permanent Magnetic Lifter?
A permanent magnetic lifter utilizes permanently magnetized magnets that through the action of a lever make the product fully switchable between OFF and ON.
Permanent Magnetic Lifters seldom achieve safe working loads greater than 5000 LB (2300 KG). The greater the force, the greater the friction making it difficult to manually operate.
Permanent Lifting Magnets are very portable and with proper care, can last a long time.
What is a Permanent-Electro (Electro-Permanent) Lifting Magnet?
This technology combines the advantages of both permanent and electromagnetic lifters.
The safety of one and the power of the other.
Permanent-Electro Magnetic Lifters require a short (electrical pulse to turn ON and OFF but do not require electricity to maintain the magnetic force.
With no moving parts and the absence of heat, they tend to be more reliable.
What happens if I lose electrical power?
- Nothing changes with a permanent magnet.
- With a Permanent-Electro Magnet, the load will stay attached, but the magnet cannot be deactivated until the electrical power is restored.
- Unless a battery back-up is incorporated, an electromagnet will let go of the load the moment the current is removed from the internal coils.
How much force can a Magnet Lifter generate on a piece of steel?
The attractive force generated by a Lifting Magnet is dependent upon the permeability of the whole circuit. Like an electrical circuit, the ease in which the current can flow is dependent upon the whole resistance of the circuit. In a magnetic circuit, the resistance is known as “reluctance” and is determined by:
- All circuit Air gaps
- Length of the parts within the circuit
- Permeability of all circuit materials (particularly the load) as determined by composition.
- Volume of all materials to conduct the delivered quantity of magnetic flux
It is theoretically possible to generate a maximum force on permeable steels (low carbon, mild), suitably flat and with adequate volumetric dimensions of 16kg/cm2 (225 LB/sq.in) over the pole areas.
Is the force from a Lifting Magnet calculable?
Yes, the key is to know the flux density at the pole face in contact with the load. Any qualified magnet designer can make that calculation based on the parameters referred previously. Magnetic forces can then be compared with application forces and with the allowance of a suitable safety factor, feasibility can be established.
Can Lifting Magnets affect people with pacemakers?
At all times, personnel with pacemakers should keep away from any high magnetic field. With most Permanent and Permanent-Electro Magnetic Lifters, the magnetic field is not deep and most if not all, is absorbed by the load. Also, a correctly designed magnet has the field emanating from the pole/underside surface only. But as a precaution, it is always prudent to post warnings.
Some Electromagnets, scrap Lifters, for example have very high magnetic fields but these are seldom used in close proximity to personnel.
How much electrical power do I need to run a permanent-electro Lifting Magnet?
It depends on the size and type of magnet. Permanent-Electro Lifting Magnets can be powered from a 24 Volt battery or popular mains supplies (110-480V), but there is a limitation on the size of magnet that can be actuated and the maximum current that the manufacturer’s controller is designed to work at – large systems can be accommodated by sequentially firing zones. Consult with the manufacturer and they should be able to furnish the information given the size and style of magnet required. Actual current can be high, but since it is only for a very short time, fusing and cabling requirements are reasonable.
What makes a good magnetic lifting application?
The primary advantages of a Lifting Magnet are:
- Better accessibility to the load
- Greater Safety
- Speed of handling
- Economy of space
- Low maintenance
Awkward shapes are often best undertaken with a specially adapted Magnetic Lifter.
Is there a safety standard for magnetic lifters?
Yes, ASME B30.20-2010 refers to the safe use of “close proximity magnetic lifters”
What is the standard safety factor for magnetic lifters?
The ASME standard B30.20-2010 requires a minimum 2:1 safety ratio between safe working load (SWL) and test load. manufacturer’s have different standards that tend to be higher, most permanent magnetic lifter producers work to 3:1
Do I need to have my magnetic lifter inspected?
The ASME standard B30.20-2010 requires that periodic testing is performed on all magnetic lifters. Each manufacturer’s manual should detail the level and regularity of inspections required.
What if my load is scaly or has a painted surface?
Magnetic Lifters are designed for use with rough or scaly parts – to a point. Check the lifter manual for recommended use. Never lift a load that is questionable.
Will the load retain magnetism?
The amount of magnetism retained by a ferromagnetic material is dependent on the characteristics of the material itself. Generally, harder steels tend to retain magnetism more than softer materials. Some Lifting Magnet designs provide for a partial demagnetizing facility to reduce residual magnetism.
What if my load is smaller than the lifter poles?
Most Lifting magnets have a lifting capacity that is proportional to the polar contact surface. A load making contact with half the area of the poles should have a lifting capacity of around half the stated SWL. Check the lifter manual for recommended use. Never lift a load that is questionable.
How do I hold irregular shapes?
Some manufacturers offer a custom pole design service and will undertake proper testing of the load based on samples supplied. These “add-on” shoes make it possible to lift irregular shapes.
What is the minimum load thickness that can be lifted?
This is determined by the pole width. Check the lifter label and or manufacturer’s manual for specific lifting limitations. Be wary of manufacturers that provide down-rating formulas for lifting thinner parts – there are a number of other “dynamic” factors that are sometimes not taken into account. Never lift a load that is questionable.
Does my Lifting Magnet require a battery back-up?
For permanent and permanent-electro magnetic technologies, no battery back-up is required. If an electromagnet is used in close proximity to personnel, from a safety standpoint, it is recommended that a battery back-up be incorporated. The ASME standard does not insist upon it.