Aggregates screening well-specified
December 11, 2008 By: Carol Wasson Pit & QuarryVibrating screens must be properly selected and designed, or they can become the biggest bottleneck within an operation. Certainly, everyone wants more tons per hour across the screen. However, the key to optimum screening is maximizing capacity without losing efficiency, and that involves a number of key engineering and design parameters. So when Callanan Industries, a subsidiary of Oldcastle, erected a new plant at its Bridgeville Quarry, its management team wanted its screening operations customized according to a well-specified wish list.
Located along the Neversink River, a popular trout stream in the Catskill region of Southeastern New York, the Bridgeville Quarry is one of 17 Callanan asphalt, crushed stone, and sand and gravel operations. The operation’s general manager, Bryan Francett, is an industry veteran who has learned the quarry business from the ground up. Consequently, he has a wealth of hands-on experience, and a firsthand knowledge of the benefits of efficient screening — issues such as greater productivity, consistent in-spec material, maximum uptime, reduced wear and minimal maintenance.
“Because we put out the best in quality products, we need the best screening equipment and components, each piece being designed and engineered to our exact specifications,” said Francett, who worked closely with Deister Machine Co. and its New York-based representative Dibble Equipment to design its highly customized screening circuits.
The new plant, engineered by Grasan Equipment, is a stunning upgrade to an existing quarry where trucks had once been required to haul material (three miles round trip) to a circa-1920s gyratory crusher perched atop a steep hill.
Now the new plant is located within the quarry, and consists of a Deister 54-in. x 24-ft. grizzly feeder, a Lippmann 4248 jaw and a Deister double-deck, 6-ft. x 16-ft. scalping screen in the primary circuit. The secondary circuit includes an HP400 cone and a 7-ft. x 20-ft., double-deck Deister coarse material screen. An additional HP400 cone and two, triple-deck, 7-ft. x 20-ft. Deister finishing screens comprise the tertiary circuit.
The annual production goal at the Bridgeville plant is near the one-million-ton mark, and includes the processing of a wide variety of DOT-spec products, as well as the ability to custom manufacture to stringent customer specifications.
Customization counts
Although Francett says he has always chosen Deister screens for their reliability and heavy-duty construction, he stresses that the biggest plus is being given the opportunity to customize the units to fit specific needs. “When I first started in this industry, I was responsible for changing screen cloth, and many of us had some choice words for screen manufacturers as we all wondered how we were supposed to fit between the decks to change the media,” he said.
So when Francett asked for more space between the decks of his 7-ft. x 20-ft. finishing screens, Deister engineers added 6 in. of space (to allow at least 18 in.) between the top and second deck. “Although you can allow as much space as you wish between decks, you don’t want to have so much distance that material falls with an impact that causes premature wear,” Francett explained.
At the outset of the primary circuit, the grizzly is angled at 10 degrees to accelerate material flow into the jaw, and to minimize any bridging or plugging.
Next, the 6-ft. x 16-ft. scalping screen is also customized with the lowering of the top deck into the frame. “On scalping screens, we used to have trouble with larger-sized material hitting the synthetic rubber media and bouncing out. So we lowered the deck into the frame to create about 1.5-ft. of steel side plates. This prevents material from bouncing over the edges and possibly injuring workers on the catwalk. Safety is very important to our organization, so this has really worked well for us,” Francett said.
Additional customized features include placing rubber liners on the screen discharge lips and feed boxes to maintain longer wear life. And Grasan Equipment designed feed chutes to match up with the full width of the screen, thus utilizing maximum open area for greater efficiency.
Lastly, Callanan decided to add the Deister System Saver to its screening operations. When applied to the screen’s lubrication system, the System Saver allows the cost-effective use of premium grade synthetic oils, and extends oil change intervals by filtering the used oil while it is still in the machine. “Where typically we would have to change the oil every 500 hours, now we can extend it to 2,500 hours. It’s quite a savings in time and money,” Francett said.
As to overall screening performance, Francett added, “Once we got all the units installed, we really didn’t have to do any fine tuning to the speed or stroke.” This was accomplished by Dibble Equipment working in conjunction with Deister, while using Callanan’s feed gradations and tonnages to properly size each screen.
After the screens were completed at the factory, each unit ran on a test stand with Callanan’s screen media in place. This ensures that all screens run with the proper speed and stroke prior to delivery, thus ensuring optimum performance in the specific application.
Deister Machine Co., www.deistermachine.com
Carol Wasson is a veteran freelance writer for the aggregates and construction equipment industries.
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