Crushing costs of poor screening

Efficient crushing is a critical factor in a screening plant’s profitability. Crushers are a significant investment, both to own and to operate, and the entire process depends on the crusher working effectively. However, what often goes unnoticed —and frankly, undiagnosed—is the effect that poor screening can have on an operation’s profits. Inefficient screening silently runs up costs as material is needlessly recirculated through the crusher.

To truly maximize a processing plant’s efficiency, operators must minimize or eliminate unnecessary crushing. To do this, they must understand how recirculation could be hurting their profitability and what they can do to minimize it.

Material recirculation

If the screen box is not doing its job well, material that should have fallen through the screen media ends up circulating back through the crusher. Recirculation is hard to detect and even harder to measure, making it difficult for operators to evaluate its true cost. It can wreak havoc on an operation’s bottom line but sometimes never be identified as the problem.

Given the high costs to fix or replace a crusher—up to three times the cost of replacing a screen box—tracking wear and tear on the machine is an important consideration. Material recirculating through the crusher accelerates its retirement, bringing that replacement expense to bear more quickly than otherwise would have been the case.

In addition, one of the biggest consequences of recirculation for a processor is lost revenue. This pattern reduces the amount of near-size material, which is the most valuable product to an operation, being produced. The producer winds up taking a double hit—first, from the expense of crushing the material a second time and, second, from the loss in revenue and reputation from producing less near-size material.

Preventing the problem

Screen media choice is often the single biggest factor in improving screening efficiency. Where most media falls short is in delivering efficient stratification. Some producers use high-vibration wire screens, which are designed to promote material stratification and offer exceptional screening performance.

High-vibration screen media magnifies the screen box’s own vibration. Independently vibrating wires run along the full length of the screen media, increasing vibration frequency. A typical screen box vibrates between 600 and 1,200 strokes per minute (spm), with high-frequency machines reaching in excess of 4,000 spm. Because high-vibration screens vibrate independently of the screen box, the wires can reach frequencies ranging from 6,000 to 10,000 cycles per minute—up to 13 times greater than that of a standard vibrating screen with traditional media.

This high vibration accelerates material stratification, causing coarse material to rise to the top of the material bed faster. Fines and near-size material come in contact with the screen much faster, as well. This, combined with a wide material spread—thanks to the extreme vibration—puts fines and near-size material in contact with the screen for a much longer time, drastically improving the screen’s effectiveness and reducing the amount of material sent back to the crusher unnecessarily.

High-vibration screen media can be a game-changing solution for operations struggling with productivity. Recirculation is a frustrating drain on efficiency, racking up crushing costs and diminishing the quality of the final product. Reducing or eliminating recirculation with more efficient screening is a relatively low-investment solution for a potentially high-dollar problem.

Serge Raymond is a product specialist at Quebec-based Major Wire Industries Ltd., a Haver & Boecker company. For more information, visit www.majorflexmat.com/en.