Application and Selection of Gravity-Fall Metal Detector Separators in the Powder Industry

A gravity-fall metal detector separator is usually installed in a vertical powder pipeline. Material falls freely through the detection coil under gravity, and when metal contamination is detected, a pneumatic flap or reject valve acts within milliseconds to divert the contaminated material to a waste outlet while good powder continues downward. Compared with conveyor-based units, it needs no extra conveying power and has a compact structure, making it suitable for flour, starch, milk powder, chemical powders and plastic pellets, often placed before the packing machine or after the vibrating screen as a final check.

When selecting a unit, first clarify the material properties: bulk density, flowability, moisture content and temperature all affect falling speed and detection stability. The pipeline diameter should match line capacity; an oversized diameter reduces the ability to detect small metal particles. Sensitivity should be evaluated together with product effect, and figures for ferrous, stainless steel and non-ferrous metals should be stated for the specific diameter and material condition. For the reject mechanism, pay attention to flap response time, sealing and residual material to avoid frequent false rejects and product waste, and confirm the unit offers self-test and fault alarm functions.

Installation and acceptance are equally important. Keep the unit away from vibration sources and large motors, ground and damp the pipeline connections, and keep the falling section vertical and long enough to reduce splashing and buildup. During acceptance, test with standard test pieces in both empty and loaded conditions, record detection and reject results, and recheck sensitivity with test pieces regularly. Routine maintenance mainly involves cleaning the detection channel and checking the air circuit and flap action; keeping inspection records helps the unit perform reliably on powder lines over time.