Metal detectors aren’t just for small children to use to excitedly find bottle caps buried underground. They actually have a very useful place in various industries that require their products to be checked for impurities. Examples include the chemical and pharmaceutical industries, removing contaminants from tablets and materials prior to packaging, as well as in the minerals processing, coal, ceramics, glass, and plastics industries. In all of these, the idea is to produce as pure a product as possible by detecting and filtering out foreign metallic objects as efficiently as possible.
Of course, metal detectors are particularly useful in the food industry, where it’s really important to ensure that your product is not contaminated. Nobody likes biting into a pre-packed sandwich and breaking a tooth on a metal shard from a piece of machinery, after all. It’s crucial to ensure that the food you are sending out to customers doesn’t contain anything it shouldn’t.
There are many examples of food industries in which metal detectors are used:
• Bakery or Baked Goods • Dairy, Milk, Yoghurt • Fruit and Vegetables • Ready Meals • Fish, Seafood and Sushi • Candy, Sweets, Confectionery, Snacks, and Biscuits • Meat and Poultry • Cereals and Grains • Beverages, Drinks, Juice or Water
How Metal Detectors Work
Metal detectors are actually very simple devices, and unlike other scanning techniques like X-rays, they don’t produce any damaging ionizing radiation. They consist of a simple coil of wire known as the transmitter coil, through which an electric current is passed, creating a magnetic field around the coil. Magnetic fields can penetrate most materials, so if the field moves through a piece of metal buried inside some non-metallic material, an electric current is induced in the metal. This electric current creates its own magnetic field, which is what the detector picks up using a second coil, the receiver coil: as the coil moves through the field, an electric current is induced in it (much in the same way that the transmitter coil induces a field in the metal piece) and the detector is triggered. Bingo: you’ve found some metal.
Detectors and Contaminants
There are several types of metal detectors in the food industry, which can be broken down into four main categories:
• Conveyor system detectors: these are aligned along the conveyor belt that food travels down, and can automatically reject contaminants using reject devices like air blast, kickers and retractable belts.
• Free-fall system detectors: ideal for free-flow dry products in manufacturing lines, they can instantly and automatically divert contaminants from the production line and through a rejection gate.
• Pipeline system detectors: suitable for any pumped product, these scan products as they pass through the system, with contaminants sent through a separate rejection valve.
• Bulk product/high performance detectors can effectively scan 50–100 Lbs of product at once.
Industrial metal detectors can usually pick up three types of contaminant:
• Ferrous: magnetic and conductive, so easily detected
• Non-ferrous: not magnetic, but conductive so can be detected relatively easily
• Stainless steel: not magnetic and a poor conductor, so difficult to detect – and harder when the product is wet or has a high salt content
Metal detectors cannot pick up glass, calcified bone, ceramics, or stone contaminants.
Where should Detectors be Placed?
Because metal can be introduced at all stages of food processing, it’s important to carefully place the detectors to ensure the most efficient rejection of product. Inspecting raw materials means that metal particles are separated out before they break up into smaller bits during processing, which may be more difficult to detect.
However, consumer protection is the goal, so food grade metal detectors may be required at several stages of the manufacturing process, from initial processing (because bits of metal from broken tools can get into the product during harvest) to final packaging (because the processing apparatus itself might introduce contaminants).
Installations at critical control points throughout processing are vital to catch machinery failures, such as broken blades, before they become a larger problem. For the most optimal product protection, raw materials, critical control points and the final product should all be inspected.
Are Detectors Essential?
Metal contamination in your food product is definitely something you want to avoid, and qualifies as a food safety issue – potentially leading to recalls, governmental regulatory fines, and customer dissatisfaction. While steps can be taken vis preventive maintenance to ensure to the best of your ability that your machinery won’t break down and that no metal is in your product initially, this might not be a chance that you want to take.
In summary, metal detectors are a safe, easy way to detect metal contaminants in the food industry. It’s almost definitely worth using them rather than not, and they can operate in a wide variety of settings and with different food types. For the most comprehensive protection, they should be placed at several points through the process to ensure that consumers don’t find anything they didn’t order in their meal.
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