Causes of demagnetisation in magnetic separators

The strength of a magnet, usually measured in gauss or pull, is one factor that determines the effectiveness of a magnetic separator. In the food industry, equipment is exposed to a variety of different temperatures, environments, products and other circumstances that can affect the magnet’s strength.

High-quality magnetic separators can retain adequate strength and effectiveness for many years; however, low-quality cheap systems can lose their strength rapidly — despite being 10,000 gauss or higher upon supply.

Loss of magnetic strength is referred to as ‘demagnetisation’.

Can magnets regain their strength?

One question that is frequently asked, is ‘can magnets regain their strength?’ The answer to this question can vary.

If magnets are heated, some magnetic strength loss will occur. This is temporary up to the maximum operating temperature of the magnetic material. Below this, the original magnetic strength is restored provided thermal shock is not experienced. If magnets are heated above their maximum operating temperature, permanent partial loss occurs — which requires re-magnetising to restore.

If a magnet is heated beyond its Curie point, the magnet is completely demagnetised.

Contributing factors of demagnetisation

It is inevitable that magnetic separators will lose their strength over time; however, not all systems will demagnetise at the same rate. Often, it is not one sole factor that is responsible for demagnetisation, but a combination. The rate of a magnet’s demagnetisation is determined by a variety of factors including the quality of the magnet and the environment which the magnet is exposed to.

There is no way of knowing when, or by how much, a magnet will decline in strength. Usually, high-quality magnet separators will retain within tolerance of 10,000 gauss strength for many years, but sometimes they can unexpectedly decline at a fast rate.

Contributing factors which may cause magnet strength loss include:

• Low-cost inferior rare earth magnet elements.
• Settling in strength loss. This is usually 5–7% in the first 6 months for high-grade magnets.
• Poor quality manufacturing procedures, including welding.
• Oxygen and moisture absorption, corrosion.
• Magnet damage resulting from mishandling, impact or excessive vibration.
• Magnet wear from abrasive product types and/or high-tonnage lines.
• Operating temperatures and thermal shock.

To explore these factors in further detail and learn how you can guard against magnet strength loss, download the Magnattack whitepaper ‘Contributing Factors to the Demagnetization of Food-Grade Magnet Separators’ at https://www.magnattackglobal.com/demagnetisation.

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