June 2003
Versatile, high-capacity portable plants help Romero Construction claim a place in the contract market.
By Bob Drake
A Nordberg 3055 portable jaw crusher provides Romero Construction with relatively rapid mobilization, high-volume production, and flexibility to take on large concrete and asphalt recycle or rock crushing jobs.
Contract crushing — particularly concrete and asphalt recycling — can be a brutal business. Many inexperienced companies have learned expensive lessons that attest to this. Profitability hinges on efficient processing, reliable equipment, rapid mobilization, and bidding and winning a continuing succession of suitable jobs. Flexibility is key. Jobs can vary from crushing rock in a quarry one week to recycling concrete and asphalt in an urban setting the next.
Romero Construction, Escondido, Calif., began contract crushing about three years ago, taking on both rock and recycle jobs. Its new venture, however, was built on a solid knowledge base. Don Lubanko, general manager of Romero’s materials division, brought to the company more than 30 years experience in crushing, including about 25 years in recycling. That experience allowed Romero to quickly claim a place in the Southern California market, taking on a number of large jobs and establishing recycle yards.
Romero operates two identical portable crushing/screening spreads with some additional screens and stackers available to adapt plants to specific jobs. “We can do just about anything,” says Lubanko. “We have four of our own recycle sites, taking in asphalt and concrete. We do contract crushing on the outside also, including quarry crushing.”
Each portable plant comprises a Nordberg 3055 jaw crusher, a Nordberg HP400 cone crusher, and an 8- x 20-ft. triple-deck JCI screen. Two 48- x 48-in. Trio belt magnets — one mounted over the jaw discharge belt and one over the cone discharge belt — remove rebar and reinforcing wire during concrete recycling operations.
Lubanko opted for jaw/cone plants partly because of his familiarity with the machines and partly for versatility. “I haven’t had that much experience with impactors, but I know contractors here that have, and they’ve tried them and gone back to the jaw/cone,” he says. “I’ve had pretty good success with the jaw/cone combination. Especially now, with the new equipment — the HP400 cones. I can out-produce an impactor.”
Versatility is critical to handle Romero’s diverse jobs. “Our jaw is a hardrock jaw crusher,” Lubanko says. “It’s not a lightweight. Same with our HP400 cone. I can go from a recycle job to a hardrock job. We can go into virtually any kind of quarry and make aggregates. We’re very diversified.”
That kind of versatility, however, comes with some tradeoffs, such as being less mobile than a single-chassis plant. Each of Romero’s plants requires about 10 loads to relocate, Lubanko says. And that, combined with the plant’s high production capability, can limit the size of jobs on which the company bids.
“I stay away from smaller contracts, usually anything under 20,000 to 25,000 tons, because it almost takes us less time to crush it than it does to set up,” Lubanko says. “You don’t get a lot of money for mobilization or set up, so the larger the quantity the better. From the time we move to the time we’re set up might be a day and a half.”
Nevertheless, considering the size and capacity of the plant, he describes it as “highly portable.” The jaw and cone use hydraulic leveling jacks for set up and during operation, eliminating the need for blocking the plant up. All electrical cables are labeled to simplify hookups.
Even with the larger, less-mobile plants, set up and tear down are often-repeated rituals. “We get such good production with these crushers, we move more frequently,” Lubanko says. “We can move into a 100,000-ton job and have the darn thing crushed in probably a month and a half.”
Of course in environmentally protective Southern California, achieving high production rates involves more than just cranking up the crushers. The Los Angeles South Coast Air Quality Management District, with jurisdiction over four counties, inspects plants and issues permits that set maximum production rates, depending on dust control measures being used.
Romero uses a NESCO DustPro spray system. High-pressure (200 psi) water is pumped through fog nozzles at strategic points throughout the plant to suppress dust. The company has nozzles on the primary hopper, at the intake and discharge on the cone, and at each dump point. The dust suppression system has been effective in meeting strict air quality requirements. “We are the first [portable plant] in Southern California permitted to do up to 1,000 tons per hour,” says Lubanko. “It’s not too often we do that much, but we run so clean that that’s what they’re allowing us to do.”
On the move
Quick crushing and mobilization are important to the nomadic process of serving the company’s four recycle centers and some of its longer-term contracts. For example, Romero recently began a two-year contract at U.S. Marine Corps Base Camp Pendleton, recycling what Lubanko estimates is more than 500,000 tons of concrete and asphalt.
“We’ll go in and crush maybe 100,000 tons and then we’ll move out,” he says. “I don’t want to have a lot of inventory sitting on hand. We can move in and crush so quickly. If the need is there, we can move in and set up.”
Asphalt and concrete debris at Camp Pendleton was dumped over a period of years into two separate piles. Romero is blending the materials to make a recycled product called Crushed Miscellaneous Base (CMB). It also meets specifications for Caltrans Class 2 base.
“Fortunately, someone guided them right and they separated the piles (asphalt and concrete),” says Lubanko. “When you have that quantity, it’s best to have it separated so you can do your own blending.”
Some of the CMB is being used on the military base; but Romero also uses some of it on its own projects as a highway construction contractor and sells some to outside customers.
Other recent large contracts include crushing and placing about 1 million tons of base at the Pier 400 project at the Port of Los Angeles and site preparation for a large housing project. Pier 400 is a large dredging and landfill project creating docking, unloading, and truck and rail transfer facilities to accommodate the world’s largest ocean container ships.
The large housing project involved crushing and screening about 500,000 tons of dirt and minus-24-in. rock blasted from a hillside to produce a base material and a minus-3/4-in. fill. Romero used an extra screen to separate the dirt overburden.
Consistent crushing
Although Romero handles a variety of projects, there is a consistency to its operations that helps avoid major production problems and equipment failures that can quickly eat profits. For example, in recycling reinforced concrete, sizing and preparation of the feed material is a primary concern, Lubanko says.
“If we’re pretty consistent with nothing larger than 2 ft. x 2 ft. and the steel is cut off flush with the concrete, it breaks it loose,” he says. “Then we have a plate under the jaw that deflects the steel and it goes forward with the run of the belt. That way it doesn’t tear belts.”
The company handles equipment maintenance and most repairs in house. “If you’re maintaining right, then you can be pretty consistent,” says Lubanko about minimizing problems with equipment breakdowns and component wear. “We get about 400,000 tons through a set of cone liners and over 600,000 tons through a set of jaw dies. Probably the most frequent thing we have to do is change our screens.”
A Nordberg HP400 cone crusher operates in closed circuit for final sizing. Romero uses two Trio belt magnets over crusher discharge belts when recycling concrete.
Bob Drake is editor for Aggregates Manager.
Stockpile Tips for Recycled Asphalt
Stockpile management — height, gradation, moisture, and testing — key to maintaining quality standards.
By Sandy Lender
Aggregate producers and hot mix asphalt (HMA) plant operators can improve their chances for success in the recycling arena by maintaining quality standards when handling and using recycled asphalt pavement (RAP). Increased use of RAP in highway pavements makes this an even more critical issue for state and federal transporation departments.
Two recycled asphalt bills that New Jersey Governor McGreevey signed in 2002 mandate certain percentages of RAP in publicly funded projects, according to Joyce Watson, public relations director for Tilcon New York, Inc. “Each [agency] has its own requirements on how much they should accept and where it could be used appropriately,” she says.
The New Jersey Department of Transportation (NJDOT) allows 15 percent RAP in the surface course and 25 percent in the base and intermediate courses for “open-system” RAP coming from any source, according to Eileen Sheehy, state materials engineer. “We also have a provision in some of our projects for a closed system, which would allow up to 50 percent RAP in intermediate and base courses,” Sheehy says, “but it has to be material that is taken off of that project, then processed back into the hot mix asphalt for that project.”
Bob Buono, quality control operations manager for Tilcon, says the price and availability of aggregate and asphalt cement (AC) didn’t factor into New Jersey’s reasoning behind the use of RAP. But since the price of oil went up, Tilcon sees a monetary benefit to current RAP percentages. “We’ve always maximized the amount of RAP without jeapordizing the quality of the mixes,” says Buono.
Even if the company only puts 1 percent recycled AC in a mix, that’s 1 percent for which they didn’t have to pay current AC prices, which Buono laments were at $188 per ton at press time. “Let’s say we have a finished product going in the truck with 5 percent oil in it,” offers Buono. “If we’re pulling 1 percent out of the recycle, then we would only put in 4 percent virgin oil.”
The success of his example relies on good process control and proper testing to reveal exactly what a particular batch of recycled material contains. Both start with good stockpile management practices.
Controlled stockpiles
“The one thing you have to do is keep your stockpile under control,” says Buono, referring to both what you put in the pile and keeping the size of the pile manageable. “If you try to create a huge stockpile, you’re not going to know what’s in it and you’re going to get erratic results.”
For NJDOT projects, Sheehy says RAP stockpiles cannot exceed 15 ft. in height, unless the supplier intends to make some extra work for himself. “They are allowed to go over those heights if they then choose to reprocess it before they put it in the plant,” says Sheehy. “If they choose to have a pile more than 15 ft. tall, the material must be crushed and screened prior to being used in the hot mix. If you don’t have some kind of limits, then the pressure of the stockpile makes big chunks of asphalt that then clog up the screens.”
When providing material for Port Authority of New York and New Jersey projects, Tilcon must adhere to stricter guidelines because it is aviation paving. The Port Authority allows material suppliers to build 2,000-ton RAP stockpiles that are no more than 12 ft. tall. The supplier must take samples from five different areas of the stockpile and run an Abson recovery, a bitumen content, a moisture, and a washed gradation on each sample. “From the five tests, we obtain an average, then cannot add to that pile again,” says Buono. “That way the properties won’t change.”
The stockpile restrictions and testing for Port Authority jobs are standard, no matter how large the project. “If we want to run a big job, say 100,000 tons, which isn’t out of the ordinary for the Port Authority,” explains Buono, “to put 10 or 20 percent RAP in the mix, we’d have to have four or five 2,000-ton stockpiles, all tested the same way.”
No matter for what type of project a supplier prepares and tests a RAP stockpile, Buono recommends the next step be protecting the pile. “Once you have that tested, you have to tarp it and cover it so the moisture in it isn’t affected.”
Some plant experts caution against tarps due to moisture or condensation situations, but Buono has had good experiences with tarping. “Even though it is kind of humid under the tarp, your absorbed moisture will not change,” he says. “The key part of that is it doesn’t lose any of the moisture it originally contained.”
Buono recommends at least tarping the RAP stockpile if it will be used for state or public projects. “If it’s for commercial use, typically, there is no protection for it.”
Another aspect of good stockpile management is separating sizes. Tilcon’s recycling operation builds two piles: one with plus-1/2-in. and one with minus-1/2-in. material. Once the material is sized, Buono advises taking a sample of it to the lab and running the sample through a series of tests. He recommends starting with the National Center for Asphalt Technology (NCAT) ignition oven test to burn off the AC, leaving the stone.
“Then do a gradation on the stone to make sure the gradation complies with the parameters that are provided in the design of the material,” says Buono. “We have to make sure the constituent material going in has the same characteristics as the constituent material we used when we designed the product.”
He explains that by assessing exactly what is in the RAP stockpile, you can adjust the percent of RAP contributing to the individual stone sizes (counting the recycle as an individual stone size), and come up with a blend that meets the mix design’s gradation spec.
Tilcon also tests RAP viscosity. According to Buono, suppliers can have a pretty good idea what’s coming into the RAP stockpile based on the product going out of the quarry or plant on a regular basis. “Some of the RAP that’s in the pile doesn’t come right off the road,” he says. “Some of it is startup and shutdown, which means it’s not aged asphalt at all. The viscosity is different.”
Suppliers can have a good idea of what’s in the pile, and what various tests will reveal. “Let’s say we have 85 percent surface courses and 15 percent base courses going out the door,” says Buono. “We have roughly that percentage coming back in because it’s replacing what’s out there, for the most part. Because of the specs that are in place, everybody that makes asphalt in this area would have to adhere to the same spec. Everybody’s material is very similar in composition, so we can make some assumptions about what’s coming in.”
But reasonable assumptions are no substitute for proper testing, especially if just starting out in the recycling arena. “So far, over the last 15 years or so, we haven’t found any variation in viscosity beyond the parameters we expect to see,” says Buono.
Involvement
One of the first steps toward creating a successful recycle operation is getting involved. George Thompson, president of Tilcon New Jersey, currently is president of the New Jersey Asphalt Pavement Association (NJAPA). The association’s legislative committee chairman is Robert Maragni, Tilcon’s vice president of public and political affairs. Richard Forman, NJAPA’s executive director, says Tilcon members sit on all the association’s committees and participate in association activities.
“Tilcon New York is committed to recycling,” says Tilcon’s Watson. “It makes sense for the company economically and environmentally. The two New Jersey recycled asphalt bills allow for the use of recycled asphalt on public highways maintained by the state’s three toll-road agencies and local governments.”
She explains the success of the bills depended on the efforts of NJAPA and producer companies such as Tilcon. The bills became law in late 2002. “This is a significant win for our industry,” says Watson, “and it is absolutely in the public’s interest to use recycled asphalt pavement.”
There’s no denying the trend toward inclusion of RAP in mix design. States are accepting and, in some instances, mandating its use. The quality standards suggested here offer producers a chance to incorporate some best recycling practices as those mandates hit closer to home.
The Recycle Pile
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Sandy Lender is editor-at-large for Aggregates Manager.
The Screen Debate: Flat vs. Inclined
Does the efficiency of a horizontal screen offset the capacity and lower capital cost of an inclined unit?
By Bob Drake
Ask several aggregate producers or full-line screen manufacturers whether a flat (horizontal) or an inclined screen is better for a certain application, and you’re likely to get several different answers. Even with high-tech design methods and extensive testing, in many cases there may not be a clear cut answer. Part of the uncertainty stems from a debate over screen efficiency vs. screen capacity.
“We often get into a great discussion as to which is more important, the capacity of the inclined or the efficiency of the horizontal,” says Mark Krause, vice president of Terex Cedarapids.
Material moves slower down the deck of a horizontal screen, Krause says, resulting in longer retention time, more efficient separation, and cleaner output. However, the slower rate of travel — 50 to 80 ft. per minute (fpm) for an oval-stroke flat screen compared to 100 to 110 fpm for an inclined screen — gives the capacity edge to inclined machines.
“All things being equal, inclined screens produce a higher travel speed and a thinner bed depth than a flat screen,” says Paul Smith, product manager for Johnson Crushers International (JCI). “This will enable high volumes of feed and reduce the potential for material to spill over the rear and sides.”
Not being able to use gravity to assist with material movement is a major drawback of a traditional horizontal screen, according to Ron Kuehl, product manager, vibrating equipment for Metso Minerals. “Without gravity, we are forced to increase speed and/or stroke to achieve higher accelerations. Although increasing the acceleration compensates for not having the benefit of gravity, horizontal screens will typically cost more to manufacture than incline screens. The structural design of individual screen components must be more robust in horizontal screens.”
The debate over whether flat screens are more efficient than inclined screens centers on how material “sees” the screen openings relative to gravity, says Jim Schreiner, marketing manager for Telsmith. Smith notes that on flat screens, “the trajectory to the screening media is at a true right angle, where incline screens essentially reduce the amount of open area. Some incline screen operators install cloth with larger openings to compensate for screening efficiency and production.”
Inclined screens also cause material to accelerate as it travels down the deck, Smith says. Horizontal screens can provide a more consistent and slower material travel speed. Some operators run inclined screens backward to slow material travel in order to improve efficiency or cleanliness of the product. In these cases, a horizontal screen may be a better alternative, according to Cedarapids’ Krause.
“The increased efficiency or cleanliness of the output of the horizontal allows us to use one size smaller screen than an incline for the same job,” says Krause. “We can accomplish with a 6 x 20 horizontal what an 8 x 20 inclined can do.”
Horizontal screens provide better wet processing, either dewatering or washing material with spray bars, according to Krause and Metso’s Kuehl. “In wet screening applications the horizontal screen is always the preferred choice,” Krause says. “Water can actually double the efficiency of a horizontal screen.”
Nevertheless, skeptics remain. “Test studies indicate there is no significant advantage to either inclined or flat screens with regard to sizing efficiency,” says Schreiner. “Still, opinions run strong on both side of the debate among producers across the country.”
There is little debate, however, about the height advantage provided by horizontal screens, particularly for low-profile and portable applications. Flat screens have lower travel heights and require less time to set up. “With a lower feed height, the feed conveyor is relatively short, saving on the cost of the conveyor and reducing the footprint of the plant,” says Schreiner. In stationary applications, lower supporting structures and shorter stairways, chutes, and electrical and water lines can be used.
Gerry Mangrich, sales manager for Universal Engineering Corp., adds that shorter feed conveyors run on less horsepower and that horizontal screens “allow for lower overall elevation above grade that in some cases may make for easier and safer maintenance tasks.”
Horizontal screens typically fall into two classes based on shaft design — twin overhead eccentric shafts or through-the-body triple shafts. Twin shafts produce a straight-line stroke at a fixed angle of about 45 degrees. Stroke length may be adjustable by adding external counterweights. Triple shafts produce an oval stroke, usually with adjustable stroke length, angle, and speed.
There are benefits to each design, according to JCI’s Smith. On overhead-eccentric twin-shaft screens, the shafts do not interrupt the basket, so the shafts and bearings are not as likely to be contaminated by dust and water. Twin-shaft screens have fewer parts and generally cost less to manufacture and purchase. Triple-shaft through-the-body screens use smaller bearings with a higher B10 life and can be operated faster, Smith says. Shafts located at the true center of gravity reduce basket stress and provide a lower profile. The greater G forces produced by the oval stroke better resist screen plugging and with adjustable stroke length and angle, the screens can be “tuned” to the application. This is a significant benefit for portable plants that process a range of materials from different mines.
“With adjustable strokes, the customer is able to optimize the performance of a machine when they change products or materials,” says Metso’s Kuehl. “Having an oval stroke on a horizontal screen is preferred to straight-line motion because of the tumbling effect that it can provide.”
The greater G forces produced by horizontal screens, however, have structural-design and cost implications that may be unfavorable when compared to inclined screens. “Horizontal screens do not have the advantage of using gravity to assist in moving the material,” explains Al Van Mullem, engineering manager for vibrating equipment at Telsmith. “As a consequence, the horizontal screen must vibrate with more force. The G force in a horizontal will run in the 4.5- to 7-G range while an inclined screen may operate at about 3.5 Gs. This increase in force means that the horizontal screen will normally be built heavier than a comparable size inclined screen.”
Side plates on horizontal screens should be reinforced or made thicker in the center of the basket where stresses are the greatest, according to Smith. “Supporting structures for flat screens must also be designed to withstand more forces than what incline screens produce,” he says. “It is critical that structural upright supports for flat screens be located directly under the springs to isolate vibration.”
Universal’s Mangrich says that as with any screen, it is important to keep the screen balanced when adding extended discharge lips or feed boxes and to plan for the use of modular polyurethane media. “The screen deck frame must be designed to withstand the added weight,” he says, “and it should be noted that the added weight may alter the stroke characteristics.”
Following are brief descriptions of horizontal screens — twin- and triple-shaft units — available from a number of manufacturers. Additional information is available on-line using the appropriate InfoExpress number and the link on Aggregates Manager’s web site (www.aggman.com).
1. Cedarapids
Cedarapids offers 16 models of its ElJay triple-shaft flat screens in sizes from 4 x 12 ft. to 8 x 20 ft. Adjustable angle of throw, stroke amplitude, and speed accommodate coarse- to fine-material screening applications, the company says. Deck frames are huck-bolted to the side sheets and 7- and 8-ft.-wide models have herringbone bracing on the decks for increased strength to allow heavier loads and installation of heavier modular media. Clamp bar strips protect sidesheets from damage by clamp bar hardware, Cedarapids says. InfoExpress 701
2. Deister Machine
Deister Machine offers complete lines of twin-shaft and triple-shaft horizontal screens featuring its Slingermist lubricating system that the company says allows the screens to operate at higher speeds and lower temperatures. Twin-shaft units, ranging from 3- x 12-ft. single-deck to 8- x 20-ft. triple-deck units, are available with overhead or underslung vibrating mechanisms. Deister’s triple-shaft screens range from 5- x 14-ft. double-deck to 8- x 20-ft. triple deck, including a triple-deck 6- x 24-ft. Stroke amplitude is adjustable from 3/8 in. to more than 11/16 in.; stroke shape adjusts from near linear to near circular, the company says. InfoExpress 702
3. Gator Machinery
Gator Machinery Co.’s RMSH series horizontal screens currently are available in 6- x 16-ft. two-deck, 6- x 16-ft. three-deck, and 6- x 20-ft. three deck models. Additional sizes are in production for delivery later this year, the company says. The triple-shaft screens feature huck-bolted assembly and interchangeable decks. Rubber spring mounts reduce basket stress, according to Gator. Maximum stroke amplitude ranges from 1/2 to 3/4 in. in a recommended speed range of 675 to 875 rpm. InfoExpress 703
4. JCI
Johnson Crushers International’s double- and triple-deck, triple-shaft horizontal screens range in size from 5 x 14 ft. to 8 x 20 ft. The ability to quickly change the speed, length, and angle of the vibrating action allows the screens to be configured for scalping, sizing, or fine screening applications, JCI says. The screens have reinforced side plates and huck-bolted deck and basket construction. Shafts located at the true center of gravity provide more even screening action in all areas of the decks, according to the company. InfoExpress 704
5. Metso Minerals
Metso Minerals’ range of horizontal screens include its new Flat Series (FS), the HR-Eliptex Horizontal (HREH), and the SC-Horizontal (SCFS). Triple-shaft FS screens are designed for a wide range of conditions, the company says. Most components, such as cloth support bars and cross members, are completely bolted, which simplifies parts replacement. The screen operates at high G forces. HREH screens feature an overhead vibrating mechanism that Metso says produces three-way motion — horizontal, vertical, and elliptical. The SCFS uses an overhead, heavy-duty vibrator shaft assembly that also is used on Metso’s grizzly feeders. InfoExpress 705
6. Simplicity
Simplicity offers horizontal screens with eccentric drives mounted above, below, or through the screen body. Twin- or triple-shaft units are available in sizes from 4 x 8 ft. to 8 x 20 ft. with one, two, or three decks. Simplicity says its horizontal screens also are suited for dewatering applications. InfoExpress 706
7. Tabor Machine Company
Tabor Machine Company’s horizontal screens with overhead vibrating mechanisms are built using 3/8-in.-thick, A-36 steel side plates with horizontal and vertical stiffeners. Stiffeners between the side plates reduce body flexing, the company says. The deck support frame also uses steel tubing. Tabor offers a choice of suspension systems — steel coil, air, or rubber springs. InfoExpress 707
8. Telsmith
Telsmith’s horizontal screen is a three-shaft, six-bearing unit with rated capacities of 500 to 650 tons per hour. The screens are available in 5-, 6-, and 7-ft. widths and 16- and 20-ft. lengths. Options include v-belt drive, heavy-duty top tray, finger gates on one deck, extended discharge chute, and Quiklok tension plate fasteners. InfoExpress 708
9. Universal Engineering
Universal Engineering reintroduces the horizontal ScreenMaster with air spring/phasing arm suspension system that helps isolate framing and support structures from damaging vibration. The tubular steel phasing arms provide a flexible connection between the screen basket and the frame. A visual gauge shows when the screen requires adjustment of the air springs. Each screen deck is 4 in. wider than most competitive models, according to Universal, to provide 10 to 20 percent more useable screen area. Two counterweighted, overhead shafts are timed through positive timing and drive gears. InfoExpress 709
Bob Drake is editor for Aggregates Manager.
Wash Plant Balances Primary Overload
A new wet secondary circuit increases plant efficiency and extends proven reserves for Pennsylvania producer.
An aggregate conditioner (top) discharges minus 1-3/4-in. stone to a triple-deck wash screen. Sand and slurry from the screen flow to a 10- x 32-ft. classifier, which feeds two dewatering screws.
Glenn O. Hawbaker’s corporate mission says in part, “We will meet the challenge to grow . . .” For more than 50 years, the family owned and operated company based in State College, Pa., has overcome that challenge, expanding from small-scale excavating and grading into full-service heavy construction, including site development, road construction, asphalt paving, and aggregate production. Its annual sales exceed $100 million.
But Hawbaker is a relative newcomer to the aggregates industry, opening its first operation in Pleasant Gap, Pa., in 1983. In the 20 years since then, the company’s aggregate enterprise has grown to eight facilities in north-central Pennsylvania and one in southern New York, producing a total of about 4 million tons per year of crushed limestone, sandstone, and gravel.
About three years ago, Hawbaker upgraded the primary circuit at its Pleasant Gap quarry, increasing its capacity in the process. The next step — increasing the secondary circuit’s capacity to balance the plant — met one of those challenges to growth: a lack of space. In order to maintain the stockpile area by the existing secondary plant, Hawbaker opted to expand capacity on some adjacent property at a different elevation. That option also provided an opportunity to build some flexibility into the new secondary circuit in the form of an aggregate conditioner, wash screen, sand classifier, sand screws, thickener, recycle water tank, and settling ponds.
The existing secondary plant operates dry, using a Buell air classifier to produce asphalt sand. “We didn’t want to install [another] dry system because of the expense, the need for additional dust collectors,” says Mike Long, a mining engineer with Glenn O. Hawbaker. “We also had an excess of water that we were pumping out of our pit, so we chose to go with a washed secondary.”
The new secondary wash plant provides Hawbaker the ability to process stone reserves previously considered marginal, according to Long. “We can pull off that material prior to putting it to the dry plant,” he says. “It makes our primary screen more efficient by not sending the additional tonnage to it.”
Discharge from the primary crusher is split, with part going to a surge pile for the existing dry secondary plant and part going to the new wash plant. Oversize passes through a 40-in. FrogSwitch cagemill to maintain a minus 1-3/4-in. feed to the 44-in. x 20-ft., twin-shaft McLanahan aggregate conditioner. The conditioner provides an extra level of processing to improve product cleanliness. It discharges to an 8- x 20-ft. triple-deck Simplicity wash screen that pulls off 37.5-mm stone, AASHTO #8s and #57s. Wash water, sand, and fines flow to the 10- x 32-ft. McLanahan Sand Manager classifier. A McLanahan 44-in. x 33-ft. screw and Eagle Iron Works 30-in. x 25-ft. screw dewater asphalt sand and anti-skid material from the classifier underflow.
An 82-ft. diameter Denver thickener receives overflow slurry from the classifier and the two screws. Thickener underflow currently is sent to a settling pond. Hawbaker plans to either blend its recovered pond fines with other material for future sales or use them for site reclamation backfill. Another 82-ft. diameter tank adjacent to the thickener holds recycled clear water for use in the wash plant.
The Bottom Line
To take full advantage of a primary circuit upgrade, Glenn O. Hawbaker added a secondary wash plant at its Pleasant Gap, Pa., facility. The new secondary increases total plant production by about 400 tph and provides the ability to process stone reserves previously considered marginal while using excess pit water.
To submit a suggestion for a Success in the Field or for more information about any of these stories, contact Aggregates Manager at 330-966-2454, Fax: 330-966-2454 or email at bob@aggman.com