Boosting Throughput

DufferinButler 1-150


By Carol Wasson

Frequent plugging or pegging within a screening circuit is a costly maintenance downtime issue. Pegging is the result of near-sized material becoming wedged in the openings of the screen media – a situation which halts efficient aggregate processing and can often create a fines carry-over condition and consequent product contamination.DufferinButler 1-400

When an operation experiences a consistent pegging problem, it doesn’t take long for management and maintenance teams to put a full-court press on finding the right solution. That was certainly the case when industry veteran Brian Janssens recently took over as foreman of the Dufferin Aggregates Butler Pit, located in Cambridge, Ontario.

During the past season and into spring startup, the operation had been facing an ongoing pegging problem on the top and middle decks of its wash plant screening circuit.

“Our production numbers weren’t where we needed them to be and we could quickly see why,” said Janssens, who recalls that after his maintenance crew would dislodge material from the pegged screens, each screen would peg again the very next day. “When the panels would peg over, we would have to drop our production way down to try to get the plant to screen more efficiently. After the shift, it would take about three hours for two workers to clean out just one screen,” he said. “It was a tedious task done within a very confined space,” he added.

Choosing the Right Solution

DufferinButler 2-400After talking with several screen media manufacturers, Janssens decided to work with Polydeck Screen Corp. “We chose them because they did a complete analysis of our plant setup, and they also gave us a performance guarantee that the recommended screen decks would deliver the desired specifications and throughput,” said Janssens.

During the quotation stage, a complete screen performance analysis was conducted by Polydeck Ontario Regional Manager Alex Caruana and Product Support Specialist Mike Garrison, who collected extensive data on the current screen circuit, the application, machine performance parameters and the required specifications.

“There are many possible reasons for plugging or pegging,” said Caruana. He lists a number of causes including screen media material that is too hard or too stiff to allow product to pass through; an opening that is not designed with the correct relief angle to allow passage of the product; a high percentage of near-size material on the screen deck; or a vibrating screen with incorrect stroke and speed settings.

After careful analysis, Polydeck specified modular polyurethane panels in a VR (zig-zag) design, which is specifically engineered to reduce plugging, particularly in wet applications. The bridges in the VR design are connected only at key points, allowing the bridges to vibrate so that near-size particles will easily pass through or otherwise dislodge.

“The durometer or hardness of the polyurethane material is also very important. Not to be mistaken for a softer material, this specially-formulated polyurethane allows the panels to flex, while providing superior wear life over that of conventional screen media. The flexing action resists pegging and the less-rigid polyurethane material delivers the added benefit of noise reduction during operation,” said Caruana.

Ease of Installation

According to Janssens, the installation of the new screen media at the Butler pit was a fairly seamless process, and the Polydeck team was onsite to guide the project. “Unlike the ease of this installation, the other media manufacturers we talked with could not easily retrofit their panels to the sub-frames of our machine. There would have been far more work involved in adapting to our units,” he said.DufferinButler 3-400

Replacing a competitor’s existing synthetic media, the Polydeck modular polyurethane panels were installed on the top and middle decks of an 8- x 20-ft. triple-deck wash/sizing screen. “We changed out the top two decks as those were the decks that were giving us the pegging issues. The original panels are still in use on the bottom deck,” said Janssens.

Caruana said that the new top deck is comprised of slotted screen panels in the impact zone where the feed hits aggressively, followed by the panels with the VR zig-zag openings to combat the severe pegging that was previously experienced. Four rows of 2-in.-tall dams are integrated into the deck layout to aid with stratification in such a high bed depth application.

Three rows of dams are integrated into the middle deck configuration as well. “We manufacture our panels using an injection molding process that ensures that every modular panel has accurate opening sizes and shapes, and is thoroughly cured throughout. Injection molding also means that surface features, such as dams and skid bars, are not glued or bolted on, but are an ‘integrated’ part of the panel’s construction,” said Caruana.

Caruana said that the modular panels are installed on the Polydeck PipeTop I frame system, which easily attaches to the existing cross members of most screen machines. “A PipeTop II conversion is typically pre-jigged into two sections per deck and allows a simple remove-and-replace process during installation,” he said.

Fine-tuning for Optimum Performance

According to Caruana, fine-tuning begins when the media is first being specified. “After correctly matching the media to the vibrating screen parameters, we review all the potential product mixes so that potential gradation inconsistencies and plant bottlenecks can be identified and adjustments made upfront,” he said. Caruana goes on to explain that Polydeck combines “hands-on” plant experience with customized software tools to capture the critical processing statistics. “We run ‘what-if’ scenarios to optimize media specifications to the applications, while examining how changing variables within screening operations will affect overall efficiency,” he said.

“Beyond supplying the media itself, Polydeck worked with us to maximize performance by tweaking and adjusting a number of key parameters during the installation and startup process,” said Janssens. “The biggest adjustment affected the motion of the screen. Polydeck recommended adjustments to the speed and stroke of the machine, and we brought in the screen supplier to re-establish those parameters,” he added. “In consultation with Polydeck, we tweaked the material feed and discharge methods to maximize processing capacities. We also experimented with the location of certain panels, particularly those outfitted with dams, while making adjustments to water pressure,” said Janssens.

Meeting Production Goals

Following the startup phase, Janssens was able to evaluate the efficiency of the wash plant screening circuit. “With the new Polydeck screen media panels, we have eliminated any pegging issues. As a result, we are saving a ton of maintenance time and costs. Importantly, we’re getting a substantial increase on our production capacity at the wash plant,” he said.

The site normally processes up to six products at a time, with the addition of certain specialty products. “All products are meeting specifications,” said Janssens. “All our production goals for throughput, uptime and quality have been met,” he added.

Carol Wasson is a Fort-Wayne, Ind.-based freelancer.

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