Since January 2012 the British Retail Consortium (BRC) requires that magnets (magnetic separators), that are used for metal contamination removal in the food industry, are tested and documented:
Greenwood Magnetics offers magnet testing services to both new and existing customers. We provide full documentation which can be used together with existing HACCP procedures. We use a certified gauss meter to test the gauss strength of the magnets. The gauss meter is calibrated on an annual basis, and we can supply a copy of the calibration certificate. The report identifies the strength of the magnets required in a particular location, the type of magnet, the actual reading, and whether the magnets have passed or failed. The report also assesses the general state of the magnets and the housing and identifies where remedial action is required. We also supply accompanying photographs which are emailed to you for ease of identification
Magnets do not lose their strength if they are left in their natural state. However if they are exposed to excessive heat, vibration or shock, then they will lose some strength. For example, does the product flowing over the magnets sometimes exceed 80 degrees? Are the magnets are in a vibrating sieve or chute? Do the operatives bang the magnets when they clean them to remove excess product?
There is no specific frequency for magnet testing. It depends on the customer, what other protection is in the process (eg metal detectors) the level of contamination that may be present, and the production environment. As a general rule, most customers have their magnets checked annually.
Ferrite (also known as ceramic) magnetic assemblies typically have a gauss rating of 1500-2000 gauss, and are generally used in the primary stages of production to remove larger tramp metal. However, as technology has progressed more powerful rare earth magnets are being used increasingly in the food industry. Rare Earth magnets can achieve strengths of up to 12000 gauss, and therefore give a far superior performance. They are generally used in the secondary and final stages of production where smaller metal particles need to be removed. As well as location, thought must also be given to type of product. It is sometimes important that the magnets are not too powerful. Flour for example has iron additives, and if the magnets are too strong these additives will be extracted. In such circumstances, we recommend that the magnet strength does not exceed 7000 gauss. We charge our magnet test services on a half day or full day basis, which depends on the number of magnets that need testing, and the distance to location.