I. Pre-screening Working Principle

The jaw crusher pre-screening system consists of a vibrating feeder (with a grizzly screen section) and a bypass conveyor (soil discharge belt). As raw material enters, coarse material larger than the screen aperture falls into the crushing chamber, while fine material, soil, and stone dust smaller than the aperture pass directly through the screen and are discharged via the bypass conveyor. This process occurs simultaneously with the feeding operation, without interrupting the main machine's operation.

II. Multiple Benefits of Pre-screening

Increased Throughput: When raw material contains 20%–30% of acceptable fines or soil, these materials occupy effective crushing space if allowed to enter the crushing chamber. Pre-screening separates fines beforehand, allowing the crushing chamber to focus entirely on coarse material, thereby increasing production capacity by 15%–30%.

Improved Product Quality: Crushing soil-laden raw material directly mixes soil into the final product, often resulting in excessive soil content. Pre-screening removes soil prior to crushing, ensuring a clean, well-graded product that meets high-quality aggregate standards.

Prevention of Blockages: During rainy seasons or when processing high-soil-content materials (such as weathered rock), wet mud tends to adhere to jaw plates and chamber walls, impeding flow or even causing shutdowns. Pre-screening removes soil in advance, significantly reducing the risk of blockages.

Reduced Equipment Wear: Fine powder and soil do not require crushing; allowing them into the chamber wastes energy and accelerates jaw plate wear while increasing the load on bearings and the eccentric shaft. Pre-screening can extend jaw plate service life by 20%–40%, resulting in substantial maintenance cost savings.

Dust Reduction: Repeated compression of fines within the chamber generates significant dust. By ensuring only coarse material enters the crusher, pre-screening reduces dust emissions by 30%–50%, improving the working environment.

III. Application Case Study

A granite crushing plant in Jiangxi processes open-pit mined material with a soil content of approximately 25% and a feed size of 0–600 mm.

Before Modification (No Pre-screening): Production rate was approx. 170 t/h; jaw plate service life was approx. 500 hours; product soil content was 8%–12% (partially exceeding limits); and chamber blockages occurred 2–3 times per week. Post-modification (pre-screening gap: 50mm): Throughput increased to 220 t/h (+29%), jaw plate lifespan extended to 700 hours (+40%), finished product clay content reduced to 2%–4%, clogging virtually eliminated, and dust emissions lowered by approximately 40%. Monthly savings on jaw plate replacement costs amount to ~20,000 RMB, with increased production and revenue adding ~50,000 RMB/month; the investment payback period is less than two months.

IV. Selection Recommendations

Pre-screening is strongly recommended for: feed material with >15% soil content, weathered rock or quarried stone, operations during the rainy season, construction waste recycling, and applications requiring high product cleanliness.

Pre-screening may be omitted for: feed material with <10% soil content, clean blasted stone, and short-term or budget-constrained projects.

V. Summary

The jaw crusher's pre-screening function (scalping section) delivers comprehensive benefits—increased output, improved quality, reduced consumption, and lower dust emissions—at a low cost, making it an essential feature for handling high-soil-content materials. Shuman’s entire mobile jaw crusher lineup comes standard with pre-screening capabilities; the grizzly bar spacing is adjustable to suit various operating conditions, ensuring optimal performance.