Pre-screening (also known as prescreening or scalping) is the first processing stage in a crushing and screening plant. It separates fine-grained material that already meets the desired grain size before the actual crushing process. This reduces the load on the crusher, increases throughput, and lowers energy consumption.
Typical pre-screening machines include grizzly feeders (bar vibrating grates at the crusher inlet), vibrating double-deck screens (two screening decks for two separation cuts), and drum screens (rotating screen drum). The separation cut is typically 40–80 mm — everything below this bypasses the crusher and goes directly to the stockpile or secondary screen.
Mobile screening plants from Kleemann, Finlay (Terex), and McCloskey can also operate as standalone pre-screening units ahead of a crusher. The savings: Up to 30% less throughput in the crusher, reduced wear on crusher plates and jaws, and fine material is not unnecessarily reduced further (avoiding oversized material).