Metal Detectors and X-Ray Foreign Body Inspection

Do You Have to Have a Metal Detector?

The regulations don't say "every food factory must buy a metal detector," but they do say what must be achieved:

• Point 7 of Annex 3 of the Regulations on Good Hygiene Practice for Food (食品良好衛生規範準則) requires processes to have "measures to prevent metal or other foreign matter from entering products and to prevent cross-contamination."
• Article 9 of the Standards for Food Factory Construction and Equipment (食品工廠建築及設備設廠標準) lists "metal or other foreign-matter detection equipment" as production equipment frozen food factories may provide as needed; Article 7 requires machinery and equipment to be constructed so as to prevent lubricating oil, metal fragments, wastewater, and the like from entering products.

In other words, a metal detector is the most common tool for "preventing metal contamination," but not the only method. Machine maintenance, parts inspection, blade and screen management, and glass and hard plastic controls are all part of preventing foreign matter. Many large retailers and export customers also include metal detection among their requirements when auditing factories.

Where Does the Metal Come From?

• Chipped meat grinder blades or grinding plates.
• Loose machine screws or washers.
• Steel brush bristles or scouring pad fragments from cleaning.
• Metal fasteners at conveyor belt joints.
• Carried in with raw materials, such as needle fragments in meat or wire in vegetables.
• Tools or parts left behind after repairs.

What Metals Can It Catch?

A metal detector uses coils to generate a magnetic field; when metal passes through, it disturbs the field and triggers rejection. Testing generally covers three categories:

• Ferrous (Fe): easiest to detect.
• Non-ferrous (Non-Fe): copper, aluminum, etc., with intermediate sensitivity.
• Stainless steel (SUS): hardest to detect, especially non-magnetic stainless steel, and food machinery happens to use a great deal of stainless steel.

How small a particle it can catch depends on the aperture size, product characteristics (moist or salty products generate a signal themselves, called the product effect), conveyor speed, and settings, and must be confirmed with the actual product and standard test pieces. In addition, aluminum foil packaging is itself metal, so standard metal detectors can't inspect sealed foil bags; inspect before packaging or use X-ray instead.

How X-Ray Machines Differ

X-ray foreign body inspection machines look at density differences, and besides metal can also detect:

• Bone fragments, glass, stone, and dense plastic or rubber.
• Foreign matter in products inside aluminum foil packaging.
• Some models can also check for missing pieces, short counts, and misshapen products at the same time.

The trade-off is a higher equipment price, and low-density foreign matter (such as wood chips, hair, or thin plastic film) is still hard to detect. Most producers start with a metal detector and consider X-ray when the product carries a bone risk or uses metallic packaging. X-ray equipment is ionizing radiation equipment, so relevant radiation protection regulations must be followed before use.

How HACCP Views Metal Detection

The Hazard Analysis and Critical Control Point (HACCP) approach lists physical hazards in the hazard analysis and then decides at which step to control them. Article 5 of Taiwan's Regulations on Hazard Analysis and Critical Control Point System (食品安全管制系統準則) requires the control team to list all possible biological, chemical, and physical hazards; Article 6 covers determining critical control points; Articles 7 and 8 cover setting critical limits and monitoring plans.

Metal detection is often designated as a critical control point (CCP), with controls including:

1. Critical limits: for example, the specifications of ferrous, non-ferrous, and stainless steel test pieces.
2. Monitoring: At start-up, at fixed intervals, and when changing products, pass test pieces through the detector to confirm correct rejection, and record the results.
3. Corrective action: When a test fails, re-inspect all product made since the last passed test.
4. Handling rejects: Collect rejected product in a locked container and trace the source of the metal.

Whether HACCP is mandatory depends on the business categories and scales announced by the TFDA; even if you're not within the announced scope, this approach is a good tool for managing foreign matter. Internationally, HACCP principles are set out in the Codex General Principles of Food Hygiene (CXC 1-1969).

FAQ

Q: Must a small factory buy a metal detector?
A: The regulations require measures to prevent metal contamination, and a metal detector is the most common approach; retailers and export customers often require one.

Q: Can metal detectors catch stainless steel?
A: Yes, but stainless steel is the hardest category to detect, and sensitivity is usually lower than for ferrous metals; confirm with stainless steel test pieces.

Q: Can products in sealed aluminum foil bags go through a metal detector?
A: Not with a standard metal detector; inspect before packaging or use an X-ray machine instead.

Q: How often should test pieces be run?
A: According to your own monitoring plan; common practice is to test at start-up, at fixed intervals, when changing products, and at shutdown, keeping records.