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Eriez Trunnion Magnet System

Permanent magnetic separation system for the automatic and continuous removal of grinding ball fragments from the ball mill discharge.


Trunnion Magnet System



Eriez has pioneered magnetic separation techniques to improve grinding circuit efficiency in mineral processing plants. The Trunnion Magnet System bolts directly to the ball mill discharge flange to provide continuous magnetic collection of the grinding ball fragments. A permanent magnetic circuit collects the grinding ball fragments and discharges them to a collection hopper.

Grinding ball fragments discharging from ball mills cause extreme wear to downstream processing equipment. These ball fragments, circulating in a milling circuit, will cause excessive wear to sumps, pumps, hydrocyclones and interconnecting piping. Grinding ball fragments contribute very little to the grinding process while consuming power.


  • Permanent magnetic circuit designed to provide maximum performance
  • No energy consumption
  • Rugged construction ensures long service life
  • Minimum maintenance
  • Continuous “Operator Free” process

Principle of Operation

The system consists of the blind trommel, magnet sector, support structure and the discharge hopper. The blind trommel is a short extension that bolts directly to the discharge flange of the ball mill. The function of the blind trommel is to transport the mill discharge material through the magnetic field. The blind trommel is fabricated from stainless steel and has an abrasion resistant wear liner. The magnet sector is comprised of permanent magnets and has an approximate 200-degree arc. This magnetic arc is mounted on a steel support pedestal and is positioned around the blind trommel. The permanent magnets are enclosed in stainless steel canisters and incorporate a steel backbar for support and projection of the magnetic field. The discharge hopper and support structure is positioned just inside the blind trommel to collect the grinding ball fragments. The hopper collects the grinding ball fragments as they rotate past the end of the magnetic sector at the top of the blind trommel.

Trunnion Variations

Several variations and modifications of the Trunnion Magnet system are available for any specific application.

  • The size of the blind trommel and magnetic circuit can be varied to retrofit an existing ball mill and available space at the discharge.
  • The magnetic circuit is designed to provide maximum strength for high slurry throughputs and up to 4 inch diameter grinding balls.
  • The trunnion magnet can be configuration for reversing or bi-directional mills.

Magnetic Separation Techniques to Improve Grinding Circuit Efficiency

Grinding ball fragments can damage crushers and cause premature wear to pumps, sumps, piping and hydrocyclones. Read this white paper to learn why an Eriez Trunnion Magnet System offers a significant return on investment with tremendous cost savings.

Document Download: White Paper- Eriez Trunnion Magnet Technology Delivers Quick Payback

Featured Article: North America Mining Products - Trunnion Magnet Technologly Delivers Quick Payback 


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Headquarters | 2200 Asbury Road | Erie, PA 16506
814.835.6000 | 800.345.4946