Leveling the Playing Field
Although the System I jaw crusher is designed to be used in rugged applications, greater-than-normal rock fragmentation generated more oversize than typically seen in such sites. Improving rock fragmentation wasn’t a viable alternative due to the site’s urban location and the DEP’s tight blast-design parameters. Although Will Mains, TechniVate’s quarry manager, and Alistair Parker, Extec’s dealer technical services manager, both said they thought the jaw could handle the oversize material, a bigger machine seemed to a good option. Under such blasting limitations, they reasoned that a larger capacity jaw crusher would help to minimize the occurrence of oversize rock jamming. “It reduces the occurrences of jamming to only a day,” Mains says. “Before, there were two to three jams taking place each day.”
With the bigger jaw crusher’s higher price tag, the company decided to rent it rather than buy it. However, TechniVate bought all of the Extec equipment outright, and it will remain in the fleet as the company builds its recently launched recycling venture. Future quarrying beyond the present site is dependent on the availability of other sites. “If we find another quarry like this one, all the equipment — including the big jaw crusher — will be used there,” says Donald Taylor, vice president for TechniVate. “Nevertheless, we are starting the asphalt paving and concrete recycling business, and we certainly need our Extec jaw crusher for doing onsite recycling.”
Despite its smaller size, the C12 jaw crusher is capable of crushing typical quarry-size rock, asphalt paving, and concrete pieces. According to Taylor, the difference in throughput between the two crushers is not exceptional. He says that while the big jaw is very good in processing oversize rock, it is too time-consuming and expensive to move it from recycling jobsite to jobsite. Simply put, it is not as versatile as the Extec jaw crusher is, he says.
Versatility is an issue because Taylor is considering setting up a crushing and screening yard where contractors can dump their concrete and asphalt paving. However, he realizes that many times the contractors will want the portable plants brought to their sites for crushing. The current trend is for onsite crushing and with good reason — fuel prices are high and continue to increase so the contractors do not want the expense of hauling the blasted rock to a crushing/screening yard and then hauling crushed stone back to the construction site.
Mains agrees with Taylor’s assessment as to what equipment is best assigned to the combined quarry and recycling activities. “In my opinion, the big jaw is very good if it is kept in a quarry. Otherwise, it costs too much to move it from one site to another,” he says. “Many recycling projects have small quantities to crush, and we could not justify the mobilization costs. For instance, the C12 plant just returned from crushing only 2,500 tons of concrete, which is a small project. Nevertheless, our price was competitive.”
According to Mains, the smaller jaw crusher requires only 1.5 man hours of preparation before transport, as well as the use of one road tractor. A lowboy is not needed because the plant has its own bogie. At the site, the same crew member can have the plant production-ready in less than 1.5 hours. Mains says by comparison, it takes three men a day to prep the big jaw crusher to make it transport-ready. The time to haul it to the site must be accounted for, and finally, three men and another day are needed to make it production-ready.
That is not all that is involved, however. It requires the use of either a crane or a large hydraulic excavator to help reduce the plant into three major transportable components and three tractors with lowboy trailers to transport the three components. Once delivered to the site, a crane or large hydraulic excavator is again needed to help reassemble the plant.
Central to both crushing and screening systems at the quarry are the portable screens. The double-box design provides high-throughput capacities despite each screen’s compact size and each plant’s small footprint. Each box screen can be independently adjusted to a specified slope. The vibration rate, amplitude, and speed also are adjustable. This enables the operator to control the rate of undersize material that is removed upon its first impact on the screen, so the near size goes to the secondary screen box that is set at a gentler slope. The gentler slope efficiently screens out the remaining undersize material.
Plant optimization options
An efficient production layout is used for the crushing-screening systems. The jaw is fed the blasted rock, which in turn sends the crushed rock to the screen where the undersize (sand) is stacked with the side-delivery conveyor. The main conveyor stacks the desired aggregate size while the oversize is sent to the closed-circuit cone crusher for re-crushing. Lastly, the cone’s crushed material is sent back to the screen.
The big jaw crusher (at System II only) is fed rock sizes 36-inch minus and the smaller jaw crusher (at System I or System II) is fed 30-inch minus. Occasionally, the smaller jaw crusher replaces the bigger jaw at System II. Despite the big jaw crusher’s superior capacity, the Extec jaw crusher’s throughput is only 50 tons per hour less. The smaller jaw crusher substitutes at System II when the big jaw crusher must be serviced. “We use the jaw crushers interchangeably with the S-6 screen and X44 SBS cone crusher because it is more important to keep the higher producing System II running,” Mains says.
With the S-6 screen’s bigger capacity, System II’s production is said to be outstanding using either jaw crusher heading the system. The screen can more than handle what it is being fed. To illustrate, the bigger jaw crusher’s throughput rate is 450 to 550 tons per hour and the smaller jaw crusher’s throughput rate is 450 to 500 tons per hour. The crushing rates fluctuate depending on what ratio of rock to sand is fed the jaw crusher. Crushed rock fed into the Extec X44 SBS cone crusher from the screen is 2 to 6 inches, which is in turn reduced to 2-inch minus. The throughput for that cone crusher is 200 to 250 tons per hour, and the screened-products throughput delivers 450 to 550 tons per hour, which include a 2-inch minus aggregate and 1/4-inch sand.
The System I throughput is not as high because the cone crusher production is only 100 to 140 tons per hour, even though the crushed rock fed it is 5-inch minus instead of the 6-inch minus fed the cone crusher in System II. “The reason we feed a smaller size rock to the [System I] cone is that the throughput rate was too low when feeding it 6-inch minus,” Mains says.
Despite, the bottleneck of the smaller cone in System I, it has a finished-products throughput ranging from 250 to 300 tons per hour. The Extec S-5 screen throughput of 375 to 475 tons per hour is fed from the jaw crusher crushed rock and the recirculated crushed rock fed from the cone crusher.
According to Taylor, the portable crushing and screening equipment used at the quarry has been quite satisfactory, although he says he prefers the quality service he receives from the Extec dealer, Extec Eastern of Trainer, Pa. “All the equipment has been performing well, but the services we receive from Extec Eastern have been outstanding. We will continue our business relationship with Extec Eastern because of the services experienced and their products,” he says. “We lose practically no production downtime using Extec equipment because the dealer responds immediately to any plant issues. The high-quality services offered by this company are as important to us as the quality product it is selling.”
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