Food Metal Detectors

Set metal detector sensitivity to the smallest test-piece size the machine can detect reliably at the center of the aperture with your actual product running, not the best number in the brochure. Sensitivity is always worst at the aperture's geometric center and degrades as aperture size grows: the MQ-MD-C detects Φ0.6 mm ferrous at a 100 mm aperture but Φ3.0 mm at 400 mm, so choose the smallest aperture your product physically passes through. Wet, salty, or chilled products create product effect that forces a coarser setting; the detector must first learn the product so its baseline signal is compensated. Over-tightening sensitivity beyond stable limits causes false rejects, which erode operator trust and waste good product, so validated, repeatable settings beat aggressive ones.

Use controlled and identifiable ferrous, non-ferrous and stainless-steel test pieces in or on a representative product. Challenge the least favourable validated position and confirm both detection and physical rejection. Achievable sizes depend on aperture, product effect, frequency, pack orientation and line conditions; stainless steel is commonly more difficult, but no universal ranking should replace a real-product test.

A facility hazard analysis determines whether metal detection is a CCP or another control measure. Validation establishes that the selected system and procedure can control the defined hazard under worst-case conditions. Routine verification then challenges the detector and reject system at intervals set by the plant quality plan, risk, customer requirements and applicable rules. There is no responsible one-size-fits-all testing interval.

A standard balanced-coil metal detector cannot reliably inspect foil-packed products, because the aluminum packaging itself reads as a large metal signal that masks real contaminants. There are two proven solutions. A ferrous-in-foil detector such as the MIQI MQ-AF-D uses a magnetic detection method that ignores the non-magnetic foil and finds magnetic contaminants from Φ0.6 mm, at 26 m/min for packs up to 5 kg. Alternatively, an X-ray inspection system detects all dense contaminants, including stainless steel, glass, and ceramic, regardless of packaging material. The right choice depends on the risk profile: if ferrous and magnetic stainless fragments are the dominant hazard, ferrous-in-foil detection is far more economical; if glass or non-magnetic stainless must also be caught, specify X-ray.

A metal detector checkweigher combo performs contaminant detection and 100% weight inspection in one frame, saving roughly a full machine's length of line space and one control point. The MIQI MQ-MCL4530L2 combines Fe 0.6-1.2 mm, NonFe 0.8-1.5 mm, and SUS 1.2-2.0 mm detection with 1-2000 g checkweighing at ±0.3-1 g, sharing one infeed, one reject zone with separate reject reasons, and one operator screen with 100 recipes. Compared with buying two machines, the combo cuts cost, floor space, and integration work, and both inspections are logged against the same pack. The trade-off is a shared belt speed, 5-28 m/min on this model, so very high-speed lines may still separate the two functions.