Por: Rodney Garrett (Seen in Aggregates Manager, 10/2004)


A new tertiary crushing system helps a Pennsylvania producer take a bite out of the profitable market for white sand.


With demand strong and supply scarce, many aggregates producers with access to white-rock reserves are fishing for ways to increase production and profits. One strong market can be found in the thousands of golf courses throughout the United States that prefer pristine white sand for their bunkers. With only a few quarries producing such sand, they are willing to trade shipping costs for material quality. Of course, golf courses are not a quarry’s only outlet for white sand. Other major markets include decorative landscape applications, special masonry sand, and special concrete block sand.


With high profit margins, some quarries already successfully mining and processing white rock are looking for ways to increase production. As they do so, they learn the challenges involved in plant upgrades. A number of potential obstacles must be overcome such as determining a way to process economically, to generate a high percentage of sand from coarse feeds, and to minimize maintenance costs and unscheduled downtime.


Valley Forge Stone Quarry of Honey Brook, Pennsylvania, has successfully dealt with these potential problems. At the heart of its sand manufacturing plant is a SandMax VSI crusher manufactured by Livermore, California-based REMco (Rock Engineered Machinery Company, Inc.).


Martin Limestone, Inc. owns Valley Forge Stone as well as a number of limestone quarries. Valley Forge Stone produces both stone and sand aggregates, as well as other aggregate products. The white sand is produced for many applications including golf course bunker sand and pool-liner sand. To supply its 10 different markets, it produces eight different sand products to accommodate market requirements.


Expanding production capabilities
Valley Forge Stone is a modest size quarry atop the imposing Welsh Mountains ridge that divides the valley towns of Honey Brook and Morgantown. Martin Limestone bought the quarry from the Lloyd Zimmerman family in 1998, at which time the annual aggregates production was 250,000 tons. Today, under themanagement of Lloyd Zimmerman’s son, Mike, annual production is near 500,000 tons.


In addition to the sand products, there are nine crushed stone products and low permeability clay to round out the company’s offerings. For many years, crushed stone had been the main fare, but sand products are now of equal importance.


Both crushed stone and sand production lines start at the primary crusher. A new 36- by 48-inch jaw crusher was recently installed to increase the crusher’s production from 275 to 350 tons per hour. The rock-size reduction is minus 24-inch to minus 7 inch.

After the jaw crusher, the rock is conveyed to a triple-deck screen. All minus 3/8-inch rock is directed to a wash plant as a final product. Intermittently, 3- by 1-inch rock is stockpiled for sale as temporary haul road base.


The remainder of the primary crushed rock is fed to the secondary plant’s 48-inch cone crusher to produce minus 2-inch crushed rock. A second triple-deck screen separates 2b stone for French-type drain-field construction. No. 67 aggregate and minus 3/8-inch aggregate are also separated for concrete block production. All screened-out 2 1/2- by 1-inch rock is then conveyed to the tertiary plant for further reduction by a second cone crusher.


Prior to the addition of the VSI crusher, the cone crusher was operated in a closed circuit for making different stone and sand aggregates. A triple-deck screen was used for screening out a modest quantity of No. 1 and No. 3 sand products sold for manufacturing concrete block. Three sizes of stone were also produced (and still are); No. 57 aggregates for ready-mix concrete production, No. 10 rice (5/16-inch) for concrete block, and a special anti-skid sand that is used for spreading on ice and snow covered roads. With this configuration, the throughput of the tertiary cone crusher was 280 tons per hour with a closed side setting of 1/2-inch; but it yielded only 50 to 60 tons per hour of crushed sand with a poor geometric shape.


The anemic 60 tons per hour sand production was unacceptable for Valley Forge Stone. There was simply more demand for the company’s white sand than could be produced. “Not only do we have a demanding market for more block sand than we could produce, but there is a need for [golf course] bunker sand as well,” Zimmerman explains. “We certainly had to do something to increase our production.”


Netting larger sand production

A special Martin Limestone equipment evaluation team, including Zimmerman, did rectify the low sand production condition. They talked to other sand producers to find out what they were doing to increase sand production. These discussions led them to REMco.
In discussing the issue with the manufacturer and its local distributor, Kemper Equipment, the team became interested in the SandMax, a VSI crusher specifically designed to produce a high percentage of sand relative to the total rock crushed.


For an assessment of which model would be best suited for the application, Zimmerman shipped a barrel of the quarry rock to REMco. Its application engineers could then determine the appropriate model, requisite motor drive power, and total crusher configuration would be the most productive and cost efficient for the operation’s needs.

“We test a quarry’s rock with one of our SandMax VSI crushers at our testing laboratory to ensure the optimum size VSI and the best internal component configuration of the crusher to fit the customer’s requirements,” explains Kevin Cadwalader, sales manager. “Essentially, each crusher’s internal components can be custom-configured by our mechanical design team and that configuration is based on the crushing characteristics of the rock, its input size, the required tonnage rate, and the final sizes of the sand products wanted.”


Balancing costs and benefits
While seriously considering other makes, the team selected the SandMax VSI crusher because of its reputation for producing sand at a lower overall cost. “We [Valley Forge Stone] do not endorse any equipment brand,” Zimmerman says. “When I recommend a certain product to my people, it is based on what I think is the best product for my company to buy and (the) one that has the lowest cost.


“By cost, I do not mean the purchase price of the crusher. In the case of selecting a VSI, we were interested in the crusher cost per ton of sand produced,” he continues. “Besides the purchase price, we considered the dependability of the crusher, the cost to replace wear parts, the percentage of sand produced from rock fed to the VSI, and the throughput rate.” The manufacturer’s guarantee of a maximum wear part replacement cost — calculated on a per-ton of finished sand product basis — clinched the deal.

The recommended crusher was the SandMax model 8000 VSI with a 300-hp electric motor. Following the tertiary plant, the VSI crusher is set up in a closed-circuit system.

Despite a relatively hard/abrasive quartz rock, the crusher is showing outstanding cost-effective sand production results. Silica content in this quartz rock ranges between 96 and 98 percent. LA tests show the rock abrasion characteristics range from 40 to 55, depending on where the rock was mined in the quarry. All sand products are made from the LA 53-55 rock. The lower numbers-value rock is crushed into the various aggregate products.


Since the VSI crusher was installed, a number of major changes have been made at the tertiary plant. The tertiary cone crusher is now in an open-circuit mode, which reduces its operating and general maintenance costs. The rock fed to the cone crusher is still 2- by 1-inch. With a wider closed side setting of 3/4 inches, the rock is reduced to minus 1-inch. From there it is screened using a triple-deck screen for making the same three-size aggregate products as before. Feed to the VSI is a 1-1/4 by 1/2-inch rock that is reduced to minus 3/4-inch with 75 percent of it passing through a 1/2-inch screen and 50 percent passing through a No. 8 mesh for producing a minus 7/32-inch sand.


The production results experienced from these changes show the tertiary cone crusher throughput increased from 280 to 300 tons per hour. Not a significant increase, but that was not what Zimmerman was looking for. First, the oversize was not being recycled through the crusher as before. Second, the 280 tons per hour produced only 60 tons per hour of sand. With the VSI crusher in operation, it produces 150 tons per hour of sand from a 300-tons-per-hour total plant feed rate. That is 50 percent of the total compared to only 21 percent before the VSI was part of the sand production system. To ensure an optimum feed rate and top crusher performance, a surge bin with a vibratory feeder controls the power level and discharge grading from the VSI.


According to Zimmerman, OEM crushing replacement parts costs are in line with those guaranteed by REMco. The same holds true with labor costs for parts replacement. For example, Zimmerman says the distributor plates are replaced every 80 to 90 hours of crushing time, and take only 30 minutes labor. Every 150 hours of crushing time, the top and bottom plates are replaced, taking two to three hours. “I am surprised at how well these parts stand up under such abrasive rock abuse. It was our greatest concern when we recommended the crusher to our company managers, but the REMco people were right on target in projecting the usable life to expect with these parts,” he says.


Since the VSI crusher installation, four years ago, the SandMax VSI has operated eight hours per day producing about 1,000 tons per day of sand. This compares very favorably with the 400 tons produced by the cone crusher. During the summer months, the VSI crusher’s production is 20,000 tons per month compared to only 8,000 tons per month that was produced by the cone crusher.


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