Foreign Material Control
What the exam tests
Prevention and detection of foreign material, test-piece verification, and response to breakage.
Core rules
- Prevention first: covered lights, brittle-material register, no glass over exposed product, controlled maintenance, sieve and filter checks.
- Metal detection finds ferrous, non-ferrous, and stainless; performance depends on aperture, product effect, orientation, and test-piece size.
- X-ray detects metal, glass, stone, bone, and high-density plastic; it does not detect low-density foreign material.
- Magnets remove ferrous material from dry streams; sieves and filters catch larger pieces.
- Verify detectors at start-up, during production, and after adjustment with test pieces; record rejects and challenge tests.
Worked example
A 2.5 mm stainless test piece is rejected on top of the belt but missed when embedded in a wet cheese block. The product effect and orientation mask the signal. Corrective action: reduce aperture, change frequency, or add X-ray; revalidate with the test piece in the product matrix, not on the belt.
Traps
Testing only ferrous; placing test pieces on the belt surface; assuming metal detection works for foil-packed products; releasing product after a detector alarm without investigation.