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Get current to improve ferrous separation

The eddy current separator (ECS) is a crucial tool in maximising the efficiency of an MRF and its bottom line through effectively removing high-value non-ferrous metals, such as aluminium, from the waste stream.

ECS technology was first developed commercially in the 1980s and has become the machinery of choice to separate non-ferrous metals from 1mm in size (fines) and above to larger shredded scrap metal.

The technology behind ECS is simple but effective. The head drum of an ECS conveyor contains a high-speed rotating magnet system which spins rapidly with alternating polarity.

This alternating magnetic field generates eddy currents of electrical energy in non-ferrous metals, causing movement within them and repelling them away from other materials. This allows their separation and recovery from other materials, which simply fall off the belt due to gravity.

Most magnetic separators which remove ferrous metal are unlikely to be 100% effective. This leads to missed ferrous metals reaching the ECS conveyor where they are attracted to the rotor by its magnetic force.

Eddy currents generate heat very rapidly within ferrous metal and this can subsequently cause significant damage to the belt. Smaller pieces of ferrous metal are most likely to be missed by the magnetic separator because they can be more easily obscured by other material. These small pieces, such as metal shards and nails, cause the most damage.

Even a small piece of ferrous metal reaching an ECS unit through the belt can result in considerable rotor cover damage which, if left, can lead to the rotor being destroyed completely.

Dire consequences

The consequences of this damage or destruction are far-reaching. First, it can be dangerous from a health and safety perspective because the high-speed rotating shaft can be exposed, risking injury to operators.

An ECS unit not working to its maximum effectiveness due to damage will also result in a loss of income from the non-ferrous metal stream, as well as downgrading any material it does recover which this will now be contaminated with metals.

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As an example, if an ECS is processing one tonne of aluminium per hour in a 40-hour week, even a 1% variation in performance can equal 400kg per week or 20 tonnes per year of missed fractions. This could equate to up to £14,000 in cash terms.

ECS units are most often installed within the processing line, so any failure can cause the complete plant to shut down while repairs and/or replacement works are carried out. This will have a severe impact on a plant’s operations and revenue, as well as its reputation as a reliable MRF.

There are two main ways in which MRF operators can minimise the risk of ECS damage. The first measure is to install a unit with an eccentric ECS rotor, which will always provide a more reliable rotor solution because it is less prone to damage from ferrous metal.

This is because eccentric rotors release ferrous metal due to their magnetic field being focused in the separating area. This field then reduces as the belt moves around the rotor, allowing the ferrous metal to drop off.

The second solution is to install a ferrous protection magnet on the processing line before the ECS to remove any potentially harmful pieces of ferrous metal. These magnets tend to be top-fed, such as a magnetic head pulley in the preceding conveyor or a top-fed drum magnet before the ECS.

This solution is relatively cheap, and is likely to cost less than the price of a repair to a significantly damaged rotor, cover and belt. As the ferrous material is presented to the high-intensity surface of the magnet, it is more likely to be extracted than with an overband separator.

Protecting ECS units is a shrewd move to prolong the effectiveness and lifespan of these vital pieces of equipment. Magnapower is regularly tasked with repairing ECS rotors from all manufacturers which have problems that are most often due to ferrous metal having caused damage.

The beauty of making additional ferrous protection is that it can often be retrofitted, reducing the risk of ferrous damage quickly and efficiently, and at less cost and inconvenience than having to stop MRF operations to repair or replace ruined equipment.

Rob Jones is managing director of Magnapower   

www.magnapower.co.uk

Get current to improve ferrous separation

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