Paul Fears reveals how to solve tramp metal problems
Tramp metal exists in all mining operations, causing costly damage to processing equipment. It is defined as rogue metal not naturally present in the mined ore and includes digger teeth, pit props, blasting caps, nuts and bolts, and metal originating from process plant wear and tear.
Crushers and screens are particularly vulnerable to tramp metal damage, resulting in downtime and out-of-specification material. The nature of the ore, the process and the tramp metal dictate the optimum separation solution using magnetic separators and metal detectors.
Magnetic separators automatically separate iron and steel tramp metal with the most commonly used being overband (with a self-cleaning belt) and suspension magnets (manual-clean magnet block), both installed over conveyors. The enclosed casing of permanent magnets or an electromagnetic coil generates the magnetic field.
Many mining operations feature wide conveyors transporting large volumes and deep burdens of ore. Subsequently, this raises the overband magnet’s suspension height, as well as creating a more difficult separation environment. In such applications, the electromagnetic field’s shape and strength enables the best separation, especially of smaller tramp iron such as bolts and nuts.
Magnetic head pulleys separating tramp metal
A second option, the permanent or electromagnetic magnetic head pulley, replaces the head pulley of a conveyor and produces enhanced tramp ferrous metal separation. On a conveyor, tramp iron migrates to the bottom of the burden, closer to the surface of the magnetic head pulley, which attracts and holds metal onto the surface of the conveyor. As the returning conveyor leaves the under-surface of the pulley, separated metal falls away under gravity into a designated collection area.
The magnetic head pulley suits existing installations with limited space, restricting the installation of overband or suspension magnets over conveyors.
The drum magnet achieves the highest level of tramp metal separation, with a controlled feed of material flowing closer to the intense magnetic field of a stationary magnet element. Attracted metal is held to the surface of the rotating outer shell and deposited in a separate collection area under the drum. Larger diameter electro and permanent drum magnets, rotating at high speeds, handle larger volumes of ore. However, space restrictions in existing and even new ore processing plants restrict the use of drum magnets.
Working together for improved mining operations
Magnetic separators commonly work alongside metal detectors, which locate non-ferrous metals such as manganese steel. The metal detector features a coil mounted around a conveyor carrying ore. Detection of metal occurs through the disturbance of the metal detector coil’s magnetic field, with a signal sent to a remotely located control. On receiving the signal, the control either stops the conveyor and initiates an alarm or sets off a diverter gate to reject a batch of material.
In many large volume mining operations, where stopping the conveyor is not an option, a section of metal-contaminated ore diverts into a collection area, where the ore is either manually checked for metal or sent through a separate secondary system for tramp metal location and removal.
Correct installation of magnetic separators and metal detectors ensures the effective removal of tramp metal, protecting plant and saving time and money on downtime and repair.
Paul Fears is with Bunting-Redditch