Grid Geometry and Downstream Sorting Efficiency: A Field-Tuning Case from an ELV Shredding Line
Grid aperture and discharge angle set both fragment size and how well the downstream sorters perform. A field adjustment on a 45–50 t/h ELV line raised non-ferrous purity from 82% to 94% and cut eddy current rejection from 18% to 6%, with throughput loss under 5%.
In ELV shredding, grids sit between the shredder rotor and the discharge conveyor, performing two jobs at once: controlling fragment size and feeding the sorting circuit. When aperture size or discharge angle drifts away from what the feed material actually requires, the downstream eddy current and sensor sorters start rejecting good material — and the operator absorbs the loss in both recovery rate and throughput.
Why Aperture Size and Discharge Angle Matter Together
Grid aperture determines which fraction of shredded material passes through to the sorting line and which fraction stays in the chamber for another pass. Too small an aperture, and the shredder over-grinds: fines generation rises, and fines confuse density-based sorters. Too large an aperture, and partially liberated fragments — still carrying copper plugs, rubber residue or glass — reach the sorting stage, where sensor sorters read them as contaminants and eject them along with the non-ferrous concentrate.
Discharge angle controls how long material stays in the active shredding zone before leaving the machine. A steeper angle shortens residence time, increases throughput, but reduces the chance that each fragment gets fully liberated. A shallower angle extends residence time, improves liberation, but lowers throughput and increases wear exposure per tonne processed.
The two parameters interact. Changing one without adjusting the other shifts the balance between liberation quality and circuit capacity — and the effect shows up most clearly in sorting recovery, not in the shredder itself.
A Field Case: Adjusting Grids on a Running ELV Line
We worked with an operator running a heavy-duty ELV shredder processing car body fragments at approximately 45–50 tonnes per hour. The existing grid setup used 80 mm round holes at a 35° discharge angle. Downstream, the non-ferrous concentrate carried a high contamination rate: eddy current separators were rejecting up to 18% of the non-ferrous stream because partially liberated pieces still contained embedded steel and dense plastics.
The first step was reducing aperture size to 70 mm oblong openings and shallowing the discharge angle to 25°. Liberation improved — more fragments broke free of embedded contaminants — but throughput dropped by roughly 12%, and the hammers saw higher impact frequency per tonne.
The effective adjustment was a two-zone grid layout: 75 mm round holes in the primary zone for initial sizing, transitioning to 65 mm oblong holes in the secondary zone for final sizing, combined with a 28° discharge angle. This configuration kept throughput loss under 5% while raising non-ferrous purity from 82% to 94%. Eddy current rejection fell from 18% to 6%.
What the Numbers Show
The improvement came from matching grid geometry to the actual liberation behaviour of the feed material, rather than treating aperture and angle as fixed machine settings. On this line, a 10 mm aperture reduction and a 7° angle change — applied together as a coordinated adjustment — delivered a measurable gain in sorting recovery without sacrificing throughput.
Grid geometry is a tunable process variable. When it is set against real feed conditions rather than default specifications, the sorting circuit downstream runs closer to its design recovery rate.
If your line is seeing sorting losses that trace back to the shredder discharge, we can review your current grid setup and feed material to propose an adjusted configuration. Send us your shredder model and operating conditions — we will confirm geometry, grade and lead time before production starts.