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A plant that cannot reach its rated tonnage is more often limited by screening than by crushing. Bed depth
18 Jun 2024
Crushing stages are usually sized with headroom, and screening is usually not. That is the first reason a plant falls short: the crusher can make the tonnage, but the screen cannot pass it. A screen separates by giving particles repeated chances to meet an aperture, and the number of chances depends on how long the material stays on the deck and how thick the layer is. Load the deck too deeply and the lower particles never reach the surface, so they travel to the oversize end and go back to the crusher. The plant then produces circulating load instead of product, and consumption rises while output does not.
Stroke and angle set the material speed along the deck. Too fast and the bed is thin but the dwell time is short; too slow and the bed is deep and stratifies poorly. The right combination depends on the feed: a heavier, coarser feed needs more energy to be lifted and thrown; a fine, damp feed needs a gentler action and often a different deck type altogether. Moisture is the factor most often underestimated, because a small amount of surface water makes fine particles stick to each other and to the mesh, and no amount of stroke will separate a sticky bed.
The deck arrangement follows from the target splits. A double-deck screen is not two single-deck screens stacked for convenience; the top deck protects the bottom one by removing the coarse material, and the bottom deck works on a feed that is already narrower. Getting the deck sizes right is usually cheaper than buying a larger screen, and it is the first thing worth reviewing when a plant underperforms. Measure the actual bed depth and the actual circulating load before changing anything, then decide whether the problem is the screen, the feed it is given, or the split it is being asked to make.
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