Minimizing recirculation through better screening can help increase profitability and efficiency for C&D processors.

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.

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.

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. 

Given the diverse nature of construction and demolition (C&D) material, size inconsistencies are one of the biggest challenges for facility operators, especially when it comes to increasing their efficiency and protecting equipment.

With incoming material ranging from large chunks of concrete to gypsum drywall, it is important to modify a system to fit the size, shape and consistency of material the facility accepts. Bob Huffer, eastern regional sales manager for General Kinematics (GK) of Crystal Lake, Illinois, says a C&D recycler can employ several methods and design layouts to ease stress on equipment down the line.

In terms of crushing and screening, Huffer says GK’s philosophy typically is to keep material as large as possible to facilitate the manual sorting process.

“When we look at a process or a system that somebody is looking to either put together or modify, one of the things we have to look at and understand is [whether] the equipment downstream can handle it,” he says. “So, [for] a lot of the processes GK gets involved with, our philosophy is to keep the C&D material and debris as big as we can keep it without getting too big [that] manual sorters can’t manage it properly.”

With many C&D processors relying on manual sorting, larger pieces of material can be more easily sorted on a pick line than smaller pieces if the material previously was run through a crusher or shredder on the front end of the line. However, for some facilities, Huffer says shredding and crushing upfront can help reduce manual labor needed on the line.

“Everything is kind of a caveat in the right situation,” he says. “For some processors, where they do shred upfront, they shred down to say 6- or 8-inch minus material. Now, a lot of that material can be run through destoners and additional secondary screens to make finer cuts and remove some of the heavy aggregate materials. In that case, you can limit the amount of manual labor you have because now the equipment will do most of the processing for you.

“There are two different philosophies here, but for the most part, I would say the higher tonnage running systems—like 500-600 tons per day … all the way up to 1,200 tons a day—aren’t going to shred 1,000 tons a day of material, so they keep it big and they put it right on the primary screens and do some of that separation that way.”