There are multiple ways to seek out and recover both ferrous and non-ferrous metal contamination. Certainly, the most efficient and accepted method includes using industrial metal detectors in tandem with suspended magnets.
Tramp metal can enter a production stream in many ways. Any place where heavy machinery is involved is a potential source of tramp metal contamination. Examples of this include chain-driven equipment where pieces of the chain can break off, or shavings from drill bits that get embedded into the rock face.
Bucket teeth, stray bolts, nails and tools can easily find their way into the aggregate stream before entering chutes and crushers.
To combat this, it is recommended that suspended magnets and metal detectors be used together. In most mining and quarrying installations, a suspended magnet is positioned above the primary conveyor to remove any large pieces of tramp or other ferrous metal that may cause product contamination or increase the risk of damage in downstream equipment. Metal detectors are installed after the magnet to detect non-ferrous contamination, such as stainless steel.
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The ‘workhorse’ suspended magnets remove large amounts of ferrous materials and can be sized and designed to capture tramp in shallow or deep burden depths on almost any type of conveyor or chute. They are ideal for all types of applications – wet, dry, fine, or coarse – over a wide range of tonnages. Suspended magnets are best positioned right at or before a transfer belt, to maximise tramp recovery, which minimises damage to both the belt and downstream equipment.
A metal detector is placed at a point after the suspended magnet and before any cone crushers, screens or other processing equipment. Should any non-ferrous metal such as work-hardened stainless steel pass through the metal detector, an alarm is triggered and the conveyor is stopped so the contamination can be removed.
Metal detectors can also be installed as a ‘last line of defence’ before the product is hauled from site and delivered to customers.
Most metal detectors can be set for a high detection sensitivity, ensuring that even smaller problematic tramp metal can be detected, thus providing better protection for crushers, screens and conveyor belts.
The detectors can even be set up to properly identify contamination on steel-corded belts or locate tramp on high speed belts, which reduces downtime and saves operators time and money. Metal detectors can also be used effectively on highly conductive products such as gold and copper ore, giving operators far more flexibility and protection.
Source: Eriez Magnetics