American Quarries Install TN77 Metal Detectors

By Paul Fears | 15 May 2019

TN77 Metal Detectors are proving popular with quarry operators in the USA.  The industrial Metal Detectors identify tramp metal in conveyed aggregate and prevent damage to screens and crushers.

American Quarries Install TN77 Metal Detectors
TN77 Metal Detector

The TN77 metal detector is a tunnel-type Metal Detector used widely in the quarrying, mining and recycling industries where the conveyed material is non-metallic or non-conductive.  The TN77 detects tramp iron and manganese steel such as digger teeth, drill rods, crusher plates, bars, chains, nuts and bolts.  Such tramp metal causes significant damage to other processing equipment such as crushers, shredders, screens and conveyors.

TN77 Metal Detector in Operation

In operation, the coil of the Metal Detector (surrounding the conveyor) continuously emits a magnetic field.  Any tramp metal passing through the metal detector changes the magnetic field, which is registered by a control.  When a change in magnetic field is registered, the control processes the signal from the search coil and then sends a second signal to other circuits which stop the conveyor, operate an audible and/or visual alarm, or initiates a rejection mechanism.  One useful optional extra is a marker, whereby either a flag or spray of ink is deposited when tramp metal is detected.  This makes it easier to locate and remove the tramp metal.  Each TN77 Metal Detector installed in the USA has a control unit housed in an IP52 wall fixing cabinet.  This is positioned locally or remotely from the search coil of the Metal Detector.

TN77 Metal Detector Control
TN77 Metal Detector Control

Designed to Suit

The search coils of the TN77 Metal Detectors used in the USA vary considerably, with several designed to suit a customer’s specific requirements.  The flat-pack design of the Metal Detector keeps shipping costs low and installation simple.  There is no need to cut the conveyor belt during installation.

“We are seeing a significant increase in sales of Metal Detectors into the USA,” explained Adrian Coleman, the General Manager of Bunting-Redditch.  “We have designed the TN77 with export markets in mind.  The flat-pack design keeps shipping costs to a minimum whilst also making installation simple.  This design is being used in quarries and mines in many remote locations such as in Australia and Africa.  We anticipate a continued growth in our sales to the USA and other export markets.”

For additional information on detecting and removing metal from conveyed materials, please contact us on:

Email: Gordon Kerr at

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Telephone:  +44 (0) 1527 65858

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