What to look for when you specify an electromagnet for a lifting application.

An electromagnet is a highly versatile and efficient means of handling large amounts of steel scrap, billet, slab, plate or bar. So if you want to specify a new magnet for your operation, what are the key features you need to look for? Here at Rotary Burnand we’ve been making and repairing our customer’s electromagnets since 1896, so we’ve got quite a lot of knowledge to assist you.

First of all, what is the shape or form of the steel you are handling?

General scrap – typically requires a circular electromagnet. We manufacture a range of circular electromagnets and the choice is greater than you might think.  Many scrap yards find that an electro magnet with a lightweight construction maximises the lifting capacity of the crane because the electromagnet uses up less of the available lifting capacity. Primary steel processing plants on the other hand, require really heavy duty electromagnets suitable for working in adverse conditions and robust enough to survive a harsh environment.

The electromagnetic field also requires some consideration as a greater electromagnetic field depth might increase the overall lifting capacity in certain applications.

Plates are best lifted with rectangular electromagnets as the electromagnetic flux is distributed in line with the load, reducing the potential to peel off. For large plate applications a number of electromagnets can be supplied on a large beam and the electromagnetic field depth of the electromagnet can be designed to pick up single sheets of plate from a stack.

Bars and profiles suit bi-pole electromagnets. These electromagnets are designed so that the electromagnetic field can be concentrated in a specific area to maximise the lift. As with plate lifting applications the bi-pole electromagnets can be designed to lift one-offs from a stack and can be mounted on a beam for long products such as railway tracks and rolled steel joists.

Billets and slabs can be handled with high powered rectangular electromagnets made to order to suit the exact application or with high powered circular magnets. With a safe working load of up to 40 tonnes and suitable for working in hot conditions these magnets are designed with an electromagnetic field depth to match your process and give you the assurance that you need for heavy handling applications.

So what else do you need to know?

Electromagnets require a DC electrical supply and it is most likely that your existing supply is AC.  So you will require an electromagnet control panel to convert your AC supply into a DC supply, this is done via a rectifier in the control panel. The magnet control panel will need to match the power requirements of your electromagnet so it is an important factor to consider in the specification process.

Another important consideration residual magnetism. When the power supply to an electromagnet is switched off the magnetism in the electromagnet dissipates and allows the electromagnet to release the load. Each time the electromagnet is turned on and off a small amount of magnetism will be retained in the electromagnet and without correction the electromagnet will eventually become permanently magnetic. The solution to this is contained in the electromagnet control panel. As the power supply is switched off to the electromagnet, the magnet control panel provides a momentary reverse pulse in the  polarity of the magnet. This process eliminates residual magnetism and maintains your electromagnet at optimum performance. The reverse polarity process also makes the release process faster and more efficient as the residual magnetism is reversed rather than left to dissipate.

All electromagnets need a suitable electromagnet control panel able to provide a DC supply to the magnet and to ensure there is no build-up of residual magnetism in your electromagnet. Complete with any electromagnet quotation from Rotary Burnand we give you a specification of the supply voltage and current required to power your electromagnet to the full potential. In addition we will specify and supply a suitable electromagnet control panel.

How do I connect up my electromagnet?

Connection of your electromagnet requires DC electrical plugs and sockets suitable for the voltage and current to the electromagnet. We supply plugs and sockets up to 90amps suitable for 220V DC.

Cable management is also a key issue to consider when installing your electromagnet. It is essential to ensure that the electricity supplied to your electromagnet is not cut by a severed cable. Rotary Burnand will assess your application and recommend suitable cable management systems to ensure the safety of supply to your electromagnet.

What if there is a power cut on the supply to my electromagnet?

In all electromagnetic lifting applications we recommend a battery back-up system. Typically we would advise a 20 minute battery back up to give you sufficient time to restore power or put your load safely in place. Battery back-up systems, like all failsafe devices should be tested on a regular basis as part of your general plant maintenance schedule or as part of a service provided by us.

Other considerations?

Duty Cycle

The duty cycle of an electromagnet relates to how long the magnet is turned on in proportion to the period of time it is turned off. Some electromagnets, such as those used in separation applications have a 100% duty cycle because they are permanently turned on. These electromagnets are specially designed not to overheat and damage the coil. For general lifting applications electromagnets generally have  a lower duty cycle, more like 50% which means that the electromagnet is on and off in equal proportions.  Assessing the duty cycle is critical in the design of any electromagnet and this is something that Rotary Burnand discusses with customers and an early stage with any electromagnet advice.

Electromagnets in hot applications.

Electromagnets are largely used in steel processing and this can include working in very hot conditions. Any electromagnet if left for a lengthy period of time at very high temperatures will eventually fail as the coil will overheat. However, with the right design and insulation inside the magnet we can protect the coil inside the electromagnet and deflect the heat to protect the electromagnet from damage. Our electromagnets are used in some of the largest steel plants in the UK and have been for many years.

Electromagnet is wet applications

As with all electrical equipment, electromagnets need to be protected from water ingress. In many applications the magnets may be used outdoors and it is important to ensure that the connections to the electromagnet have a reasonable degree of protection from water ingress. Waterproof electromagnets may be worth considering where there is a risk of water ingress. Waterproofed electromagnets can be made to order after a detailed specification has been produced for your specific application.

Are electromagnets only used for lifting applications?

Electromagnets are highly versatile and can be used for separation, solenoid activation, failsafe systems and pick and place systems. Our electromagnet design team have worked with universities and world class engineering companies to deliver bespoke electromagnetic solutions.

Whatever your electromagnet requirement the team at Rotary Burnand will find a solution.

Contact us to find out more.

www.rotary.co.uk

+44 114 2513134