Metal Separation from Recycled Wood
Ferrous and non-ferrous metals commonly contaminate wood waste, limiting the use of the recycled material, and also causing shredder damage and plant fires.
Bunting is one of the world’s leading designers and manufacturers of magnetic separators for the recycling and waste industries.
Figure 1 - Metal Separation Module (Feeder, Drum Magnet and Eddy Current Separator) for a wood recycling project
Problematic metal contamination occurs as nails, screws, and fixings. Removal of the majority of metal happens after at least one stage of shredding, where the contamination is liberated and free for separation. After the primary shredder, a permanent or electro Overband Magnet, suspended over the conveyed wood, lifts and automatically removes liberated ferrous metals such as nails and screws.
A tri-polar design Overband Magnet prevents nails and screws rising to the magnet point first and then becoming stuck in the Overband cleaning belt. A tri-polar design lifts the ferrous metals up onto the belt in a flat orientation, preventing belt piercing. In addition, a tri-polar magnetic field has limited leakage of magnetic field, when compared with standard single pole models, preventing the magnetic holding of ferrous metal on the Overband’s steel frame.
Figure 2 - Permanent Overband Magnet removing ferrous metal from shredded wood
After the first stage of magnetic separation, reclaimed wood is commonly screened into two different size fractions, with oversized material returning to the primary shredder feed. Tightening the particle size distribution enables fine-tuning of the separation equipment and enhances further metal separation.
At this stage, the focus turns to the removal of smaller ferrous metals and non-ferrous metals with a Metal Separation Module, consisting of a Rare Earth Drum Magnet and Eddy Current Separator. The shredded wood feeds onto a heavy-duty Vibratory Feeder, which spreads and regulates the flow of wood onto the surface of the Drum Magnet.
The high-powered magnetic field of the stationary element arc inside the Rare Earth Drum Magnet attracts and separates smaller and entrapped ferrous metal. To prevent excessive wear, the Drum Magnet has a single stainless-steel replaceable skin (up to 8mm thick).
The remaining wood flows down onto the feed belt of an Eddy Current Separator, which separates non-ferrous metals such as aluminium fixings and handles. The Eddy Current Separator has a high-strength magnetic rotor spinning at high speeds within a non-metallic shell, which ejects non-ferrous metal out of the surrounding wood. A strategically placed splitter separates the ejected metal from the cleansed wood.
In operation, a 2-metre wide Eddy Current Separator achieves excellent levels of non-ferrous metal separation from 50 tonnes-per-hour of shredded wood (5-20 mm particle size range).
A second stage of shredding is susceptible to costly damage from tramp metal. An industrial Metal Detector on the shredder feed conveyor checks the wood for any remaining metal contamination. This could be buried deep inside a piece of wood, which negated separation on previous equipment. Shredded wood passes through the Metal Detector, mounted around the feed conveyor, which identifies any remaining metal.
These four stages of separation and detection ensure that the final shredded wood product is free from both ferrous and non-ferrous metals. As many plants are unique, Bunting’s application engineers commonly visit site to discuss each project and determine the optimum metal separation solution.