Lifting Magnets Design

What do we study and calculate when designing a lifting magnet?

Designing lifting magnets means having to take into consideration many variables more than power of the magnet and lifting capacity of the crane. Airpes engineers put many other variables into the calculator for designing an effective lifting device that works through magnetisation. In this article we will try to describe some of these variables in a practical way and without going too deep into technical vocabulary.

Electricity interacts with magnetism? Yes it does

Hans Christian Ørsted was a Danish physicist and chemist who discovered that electric currents create magnetic fields, which was the first connection found between electricity and magnetism. In 1820 Øersted made an experiment: he placed a long cable in a horizontal and parallel position just above the magnetic needle of a compass, so that both the compass and the cable followed exactly the magnetic north-south direction of the Earth. When Øersted connected the ends of the cable to the terminals of a battery, the needle rotated until it adopted an east-west orientation, almost perpendicular to the cable. Ørsted verified that a resting current does not affect a magnet, but here was the proof that moving charges (an electric current) actually exert a force on a magnet.

Image above: Ørsted experiment with a compass (Wikipedia)

The two types of lifting magnets

After Ørsted experiment and proof that electricity affect magnets it is time for describing how can electricity be used together with magnets. And for this part it is important to get to know the two different types of magnets we have and how electricity affects them.

Image above: one of our lifting magnets design

Type #1: Lifting electromagnet

An electromagnet consists of a coil of wire wrapped around an iron core. A core of ferromagnetic material like iron serves to increase the magnetic field created. The strength of magnetic field generated is proportional to the amount of current through the winding and the number of windings.

Electricity in an electromagnet:

In an electromagnet we apply electricity to create a magnetic field and lift the load.

Factors to calculate the lifting capacity of an electromagnet

The magnetic field strength of an electromagnet depends on various variables like:

  • The core material
  • The number of solenoid windings
  • The intensity of the current

If the current is powerful enough, the electromagnet can develop a magnetic field much more intense than a permanent magnet.

Image above: lifting electromagnet

Type #2: Lifting electropermanent magnet

In the other hand permanent magnets provide magnetic flux which flows from their North pole to their South pole. So in an electropermanent magnet the energy from the permanent magnets keeps the load clamped for infinite period.

Electricity in an electropermanent magnet:

In a permanent magnet we apply electricity to cancel the magnetic field and release the load.

Image above: lifting electropermanent magnet

Factors that decrease lifting capacity of the magnet

Working environment of every company in the world is always changing and almost never “perfect”. There are many factors that can affect and decrease lifting values and that Airpes take into consideration too. Some of these factors are:

Air gap caused by dust, coatings in the material or worn magnet face

Vibration during transportation of the load that may need extra power

Extreme temperatures inside the working area or extreme difference of temperature of the material (materials lose magnetisation capacity when temperature rises)

Percentage of carbon of the material to be lifted (more carbon in the metal means less magnetisation for that piece of metal)

Image above: lifting magnet in the test bench

Complete study prior to design

Before Airpes processes any order of lifting magnets, we try to obtain all the information on customer’s lifting operations, factors in all conditions and provide recommendations with highest safety factor. In the vast majority of the cases our customers need to lift a wide range of steel materials so we study all the cases to design the best lifting magnet for that case.

Experts in lifting magnets design

The lifting magnet in the video below has been working in a high-service factor plant since 2012: