A New Fine-Tuned Washing and Screening Circuit Boosts Throughput and Product Quality.
By Carol Wasson
Washing and screening circuits must be properly selected, designed and applied – and must be operated under the correct parameters to avoid any costly bottlenecks. For optimum screening, the goal is maximizing capacity without losing quality and efficiency.
Recently, a major Tennessee-based concrete producer achieved the latter with the installation of a new fine-tuned washing and screening circuit. The result is a significant increase in production capacities and overall efficiencies; and continual improvement in the quality and consistency of the company’s products.
The family-owned Sequatchie Concrete Service Inc. is a leading supplier of ready-mixed concrete, commercial and residential block, structural precast products, and more. Serving east Tennessee, north Alabama and north Georgia, the company maintains 15 locations.
Fitting its mission of efficiency and quality performance, Sequatchie Concrete recently eliminated a washing and screening bottleneck at its Sand Switch Plant, an aggregate-processing facility in Sewanee, Tenn.
The challenge was efficiency loss with material and water overriding the deck of an older wash screen, creating flooding issues with the belts and crusher. The plant also faced costly maintenance downtime with the frequent changeouts of worn screen media panels and chute liners.
Their solution was the installation of a heavy-duty, triple-deck vibrating wash screen manufactured by Deister Machine Co. The new wash screen is outfitted with modular synthetic rubber and polyurethane screen media manufactured by Polydeck Screen Corp.
“We gave Deister and Polydeck the specs, gradations and tons per hour that we needed to meet; and they gave us the right screen and media for our production requirements,” said Malcolm Bennett, plant manager for Sequatchie Concrete’s Sand Switch Plant.
Bennett said that after the installation of the new washing and screening circuit, they have increased throughput at the wash screen by at least 20 tph; and have increased overall production through the plant by more than 10 tph. “Our products are cleaner, our gradations are better, and as far as maintenance and downtime, we have cut that by more than half,” said Bennett.
The new washing and screening circuit was initiated by Robert Kelly, the territory manager for Alpharetta, Ga.-based 1st Quality Equipment, a regional aggregate equipment dealer who represents both Deister and Polydeck. Kelly examined the existing circuit and made several recommendations, followed by onsite consultations with Joe Schlabach, Deister vice president of marketing and sales; and Tommy Daniel, Polydeck Southeast regional manager.
The Vibrating Wash Screen
A new heavy-duty 6- x 16-ft. Deister triple-deck wash screen was installed in August 2017.
“We weren’t shedding water very well on our previous screen and it had such a rough vibration. The new screen has such a smooth and quick vibration. In fact, it’s so smooth that you can hardly tell that it’s running,” said Bennett. “Deister set the machine up according to our tonnage-per-hour requirements. Once we hooked the electric motor up to it, and turned it on, it was ready to roll. We’re putting about 170 tph through it, while our previous screen could barely make 150 tph,” he said.
Schlabach explained that optimum screening efficiency results from proper adjustments in speed, rotation (or throw) direction, and angle of inclination. Each of these parameters affect proper depth of bed and greater throughput. As to the unit’s vibrating mechanism, he said that it’s located between the decks. On this model, Schlabach adds, its “Type O” vibrating mechanism produces a uniform circular movement of the vibrating frame and screening surface.
“The spray equipment on the wash screen is also key to throughput. Deister wash screens are provided with a pre-assembled manifold and spray system from the factory that is attached to the machine and is ready to be hooked up,” said Schlabach.
He explained that the nozzles fan out water jets into sheets, which provide broad bands across the screen, giving complete coverage under each header. The nozzles are staggered to provide two solid sheets of water per header.
“The spray should hit the screening surface at 30- to 45-degrees. Depending upon the desired washing/rinsing efficiency and material properties, the nozzles can be positioned to spray against or with the flow of material; and for most applications, a pressure of approximately 40 psi is desired at the nozzles,” said Schlabach.
Synthetic Screen Media
Polydeck Regional Manager Tommy Daniel said that 38-mm Rubberdex modular rubber screen panels are installed on the top deck of the wash screen and 16-mm Polydex modular polyurethane screen panels on the middle deck.
“We’ve placed polyurethane panels with 5-mm slotted openings on the bottom deck, and also utilize panels with integrated dams to slow the material and increase washing efficiency,” Daniel said.
One of the reasons why the screen is so quiet during operation, said Daniel, is the fact that rubber and polyurethane media (versus wire cloth) can reduce noise levels by as much as 9 decibels, which is a 50-percent reduction as perceived by the human ear. “That means that plant personnel can work nearby for longer periods of time without damaging their hearing,” he said.
Maximum open area is built into the screen with the use of the Polydeck PipeTop II stringer frame system.
“This framework system features unique half-inch-wide attachment rails versus the mounting styles on conventional frame systems that result in up to 3-in. of dead space per rail where fines build up. Furthermore, in-house tooling capabilities allow us to provide many more options in these frame systems – from varying fastening options, material options, and stringer styles and types,” said Daniel. “We’ve combined this framework system with our Maxi-Style modular screen panels. This allows more product pass-through over that of conventional modular media, resulting in more efficient screening, and more saleable product on the ground.”
Daniel said that in certain spots they have utilized VR panels with zig-zag-shaped openings for additional open area to help relieve the deck of the water. “Also, the zig-zag shape of the openings creates a vibrating action that greatly reduces or eliminates plugging,” he said.
“We’ve been running the wash screen for 50 hours per week since its installation and we’ve had no maintenance issues whatsoever,” said Bennett. “I have not replaced any of the Rubberdex screen panels on the top deck – and that is where you get the most beating and abrasion. After almost four months, I replaced just a few of the panels on the bottom deck,” he said, adding that his previous polyurethane media wore far more quickly.
“Also, with our previous frame and fastening system, it was hard to get the screen panels in and out. It took three times more maintenance time to changeout the previous screen panels over that of the new Polydeck panels,” he said.
Rubber Chute Liners
|Malcolm Bennett (left) and Tommy Daniel.|
Even before Sequatchie Concrete considered upgrading its washing circuit, Kelly had presented the operation with the solution of using Polydeck Rubberdex chute liners on their splitter box, which follows the screen.
Since this solution worked so well, the Sequatchie Concrete management team was quite open to what Polydeck and Deister could do to improve overall washing and screening efficiencies. Bennett said that they previously used 4- x 6-ft. polyurethane sheets as liners in the splitter box.
“They were extremely heavy and hard to bolt in, especially when you’re 30 ft. in the air. They would wear quickly, and changing out just one of the three sheets would take more than three hours,” said Bennett. Now, they use Polydeck’s 1- x 2-ft. modular rubber chute liner panels. “We can change out just the panel that is worn in a matter of minutes, rather than changing out an entire polyurethane sheet. It’s made a world of difference in reducing material waste and maintenance downtime,” he said.
A properly-designed washing and screening circuit boosts product quality and throughput, while reducing costly maintenance downtime and lowering costs-per-ton. “We’ve never seen our plant run as efficiently as it does now,” said Bennett.
Carol Wasson is a Fort Wayne, Ind.-based freelancer.