Tramp metal is an unavoidable challenge in mining and quarrying operations. The extraction process, which involves large machinery and heavy equipment, inevitably introduces unwanted metal contaminants into the mined material. These contaminants can cause significant damage to processing equipment such as crushers, screens, and conveyors. Additionally, mining operations often have strict limits on metal contamination, particularly in industries like coal supply for power stations. Identifying and removing tramp metal is crucial to maintaining efficient operations and preventing costly damage.

Tramp metal refers to any unwanted metallic objects that are not naturally present in the extracted material. Common examples include digger teeth, pit props, blasting caps, nuts and bolts, and worn parts from processing equipment. These contaminants pose a serious risk, especially during size reduction (crushing and milling) and material segregation (screening), where they can damage expensive machinery.

The optimal solution for dealing with tramp metal depends on the specific mining process, the type of material being processed, and the nature of the contaminants. The most effective technologies used in mining and quarrying operations to prevent equipment damage are Magnetic Separators and Metal Detectors.

Magnetic Separators

Magnetic separators remove magnetically susceptible metals like iron and steel, automatically extracting them from the conveyed material. The two most common types are Overband Magnets and Suspension Magnets.

  • Overband Magnets: Installed above conveyor belts, these magnets attract and remove tramp iron. The self-cleaning design continuously removes separated metal, making it ideal for operations with high contamination levels.
  • Suspension Magnets: Similar to Overband Magnets but require manual removal of collected metal. These are more suited to operations with occasional contamination.

Permanent Overband Magnets are commonly used on mobile crushers and screens, especially in quarries and recycling sites. However, in high-volume mining operations with deep material layers, Electro Overband Magnets are preferred due to their stronger magnetic fields. These electromagnets require efficient cooling systems, either oil or air-cooled, to maintain optimal performance.

Another effective magnetic separation method is the Magnetic Head Pulley, which replaces the head pulley of a conveyor. It captures tramp iron as the material reaches the end of the belt, directing contaminants to a collection area.

For the most effective separation, Drum Magnets are used. These feature a stationary magnetic core with a rotating shell, ensuring maximum tramp metal removal. They are especially useful for processing large volumes of rock, as the metal particles are exposed to a strong magnetic field.

Metal Detectors

Unlike magnetic separators, metal detectors identify all types of metal contamination, including non-magnetic metals like aluminium.

Metal detectors can be installed either before or after magnetic separators, depending on the setup. If positioned before a separator, they can activate electromagnets only when metal is detected, reducing energy consumption. When placed after a separator, they ensure the detection of any remaining non-magnetic contaminants.

Real-World Applications

In a gold mine in Northern Finland, a 13-tonne Electro Overband Magnet removes tramp metal from 2.7 million tonnes of ore annually, protecting critical processing equipment.

Similarly, in a Swedish iron ore mine, 1.2-meter-diameter Magnetic Head Pulleys remove large tramp metal from iron ore before crushing and screening.

Customised Solutions

Large mining projects often require customized solutions to handle unique challenges such as deep burden depths and wide conveyors. Bunting’s engineering team collaborates with contractors and designers to develop tailored magnetic separation and metal detection solutions.

With over 40 years of experience in designing and manufacturing this technology, Bunting ensures efficient tramp metal removal, protecting both equipment and operational efficiency.

Conclusion

Tramp metal contamination is a major issue in mining and quarrying. By integrating Magnetic Separators and Metal Detectors, operators can effectively remove unwanted metal, prevent costly equipment damage, and maintain compliance with industry regulations. As mining technology advances, customized metal removal solutions continue to play a vital role in ensuring efficient and safe operations.

Electro Overband Magnet installed in a gold mine

Typical tramp metal separated by a magnetic separator

TN77 Metal Detector operating in an aggregate quarry