The 56-inch by 68-inch solid steel rotor lies at the heart of the three-stage crushing action, and the impactor is capable of producing between 400 to 600 TPH, in which Stavola Contracting currently averages 500 TPH. With the industry's heaviest rotor, the impactor provides optimum penetration and energy to deliver efficient initial reduction, up to a 24:1 ratio, without sacrificing the impact forces necessary for secondary reduction.
Even when crushing RAP to the smallest, 1/2-inch minus spec size, Stavola estimates achieving at least 75 percent passing the 9/16-inch bottom deck screen on the first pass. This is critical when processing RAP, since every pass through the crusher increases the chance of the asphalt binder being broken away from the aggregate.
Two Cat 980 loaders with 7.5-cubic-yard buckets strain to keep the impactor's 19-cubic-yard feed hopper filled with material. "The UM69 keeps our loader operators moving to keep up with it," says Stavola. The all-electric circuit is powered by a 300 hp motor. Once crushed, the recycled material outlets onto a 48-inch by 40-foot discharge conveyor.
Crushed material is sorted by an Eagle Crusher 6- by 20-foot, triple-deck screening plant. Stavola Contracting uses a variety of screen sizes on each deck, depending on the final size of the material being processed. The entire circuit, including the BTI breaker mounted to the hopper to prevent material bridging, is operated by a single person in the control tower.
Through a collaborative effort between Stavola Contracting and Capitol Equipment, the circuit's design was laid out for efficiency and to lower costs. According to Bob Mrozinski, territory manager for Capitol Equipment, "We raised all of the circuit's major components two feet by using Sona-Tube bases to better keep the crushing area clean."
Since installing the new UM69 impact crusher and circuit, which began operation in June 2004, Stavola's plan has been realized. Significant overtime hours are now history with the new crusher's increased production. According to Stavola, "We now run the crusher approximately 4.5 days a week and only 8 hours per day, eliminating the need for overtime."
Stavola Contracting opted for no grizzly on the feeder to improve the circuit's production. Stavola explains, "In order for a grizzly to be efficient, you need about a three- to four-inch separation between the bars. With our final product, we would have too much recirculating load, which defeats the purpose of a grizzly." He adds that the recirculated material would dump into one side of the crusher, resulting in uneven bar wear and increased wear costs.
The impactor's durability and ability to handle massive slabs of RAP and heavily reinforced concrete has also impressed Stavola Contracting. According to Mrozinski, "We loaded a complete 6-foot-long, 2,500-pound Jersey barrier into the crusher, and the UM69 ate it up in a matter of seconds." With the combination of recycled asphalt and concrete material crushed by Stavola Contracting, the UM69's proprietary N1 alloy steel blow bars from Eagle Crusher are delivering approximately 32,000 tons of finished product per set.
Switching from crushing concrete to a 1 1/2-inch recycled asphalt final product could not be any easier. It takes just a matter of minutes to clear the circuit and move the 100-foot radial stacker a couple hundred feet to begin stockpiling the different final product.
When crushing to smaller RAP sizes, the crew switches out the middle and bottom deck screen cloths to size openings that will deliver the desired gradations. More recently, Stavola has added a second, 5-foot by 12-foot screen to the circuit in an effort to reduce the number screen cloth changes and improve screening efficiency.
The UM69 runs surprisingly quiet when devouring feed material, leading the way to a very quiet overall crushing circuit, one that is well within the state guidelines for noise regulations. The NJ State regulations require that continuous airborne sound levels to be less than 65 decibels (dBA) at adjoining properties.
Sound measurements taken next to the impactor indicate that it runs quieter than the average lawnmower. At a 50-foot distance, sound levels generated by the impactor are comparable to that of the dreaded morning alarm clock, and at 100 feet are approximately the same as conversational noise levels. "This is one of the quietest impactors and crushing operations that I have been around. Even in the control room, which is right beside the hopper and impactor, the noise levels register only 74 dBA," says Mrozinski.