November 2003
American Sand & Gravel mines a deep, underwater aggregate resource with a 16-cu.-yd. clamshell.
By Bob Drake
Using a 16-cu.-yd. clamshell bucket, American Sand & Gravel’s automated Rohr dredge extracts about 700 tons per hour from a depth of about 100 ft. The company added rubber “curtains” on the railing around the digging well to decrease mud and water splashing onto the deck as the large bucket enters and exits the water.
Men and mules were the mining machines used in the mid-1920s to extract sand and gravel from some glacial hills north of Massillon, Ohio. That’s as far back as American Sand & Gravel has been able to trace the history of the site of its Crystal Springs Plant #4. Today, the site’s gravel hills are mostly gone — now a part of rail beds, roads, highways, houses, parking lots, and buildings throughout Northeast Ohio — and the company has embarked on a new mining phase to more fully develop its rich aggregate resource.
The new phase involves excavating as much as 200 ft. below water using a 16-cu.-yd. Rohr clamshell dredge. “We mined about 10 years just in the upper cuts above the water table,” explains Christopher Scala, president of American Sand & Gravel. “But we always knew from our testing that this was a very deep deposit. I actually met with Rohr prior to building the plant. We had permitting in place in anticipation that we would be going after [the deep deposits].”
American Sand & Gravel, which has three sand and gravel operations in Northeast Ohio and a dock in Cleveland to ship in crushed stone from Great Lakes-based quarries, is part of family owned Kenmore Companies, a general contracting firm founded by Scala’s father in 1956. Kenmore also operates five asphalt plants and consumes about half of American’s aggregate production, Scala says.
American Sand & Gravel purchased the Massillon property in the late 1980s and began operations in 1990. The deposit had been mined sporadically through the years by a number of companies, including Greenville Sand & Gravel (predecessor to American Aggregates, now Martin Marietta) and Standard Slag (now Lafarge North America).
The site contains two distinct glacial deposits, Scala says. The upper layers, now partially depleted, comprise a brown sand and gravel common to Northeast Ohio that contains a greater proportion of large boulders and some softer particles such as sandstone and chert. The lower layers — extending more than 200 ft. below the water table — are a gray, dense sand and gravel with a greater proportion of hard granite particles with excellent soundness, according to Scala. An estimated 60-percent sand/40-percent gravel mix provides American the materials for its primary products: concrete and asphalt sand, washed 57s, 8s, 9s, and a minus-2-in. base material (Ohio 304).
Dredge Operator Mitch Patterson has an elevated view of the digging well, on-board crusher and dewatering screens, and on-shore stacking conveyor.
The deposit thickens from one side of American’s property to the other, possibly placing some of the deposit beyond the reach of the clamshell dredge as currently configured. The dredge, which Scala says is the largest of its kind in Ohio based on bucket size, is designed to dig to 200 ft.
“This is sized to fit our plant capacity,” he says. “It’s all a matter of cycle time.”
Working shallower sections of the expanding lake allows the dredge to quickly build a stockpile of material to feed the plant. Digging at a depth of about 100 ft., the dredge produces about 700 tons per hour. Production rates decrease as the dredge digs deeper and bucket cycle times increase.
Ideally, as the dredge digs, material flows into the hole created by the clamshell. “The key to these dredges is having a good flowable deposit — one that will move to you,” says Scala. “If you have a clayey deposit or high silt content, the material is going to stand up and you will have problems. Our [material] fortunately flows very well.”
A rake scrapes oversize gravel into the on-board Lippmann-Milwaukee 2436 jaw crusher. The company installed a jib crane to remove oversize and for maintenance.
Operators periodically use a tape measure around the edges of the dredge and in the center digging well to get a sense of the lake-bottom profile.. “You want to see a nice slope in the area,” Scala says. “If it starts to stand up, you move back over the hump and eat down through it to open it up.”
The dredge also features a bucket monitoring system that Plant Superintendent Darrell Hylton says indicates whether the bucket is open or closed and if it is tilted. The system also shows bucket depth, travel speed, and amperage draw to open and close it and monitors oil level and temperature.
Operated in the automatic mode, the dredge has three digging positions within the well. “You can set it to go down in three different spots, or one spot or two,” Hylton says.
After lifting above the water surface and draining for a set time period, the clamshell empties into a hopper with grizzly bars on top to retain oversize gravel and boulders. Sand and smaller gravel is fed to two onboard, 8- x 24-ft. dewatering screens. Slurry underflow from these screens is pumped through a cyclone to a 5- x 12-ft. fine sand dewatering screen.
As needed, the dredge operator activates a rake to scrape oversize rock off the grizzly into a 2436 Lippmann-Milwaukee jaw crusher or the opposite direction to a chute back into the lake. Dewatered sand and gravel and crushed gravel combine on a single conveyor leading off the dredge to a series of floating conveyors that feed an on-shore field conveyor and radial stacker to build a primary surge pile.
The dredge operator also manages the stacker. A sonic sensor at the end of the stacker monitors stockpile height and initiates automatic movement of the stacker as needed.
American Sand & Gravel typically operates the dredge two shifts per day, varying shift length with customer demand. If demand requires only one shift, dredge operations move to the night shift to take advantage of lower electric power rates.
“Basically it’s a one-man operation,” says Scala. “When we do have two shifts, the shifts overlap a half hour to an hour so they have time for some greasing and clean up.”
Changing from a dry mining to a dredging operation did not require any changes to the main processing plant, Scala says. The plant is fed from the primary surge pile with a Cat 992 wheel loader.
“We considered a tunnel feed system, but the loader gives us versatility,” Scala says. “We figured with the tunnel feeder we weren’t going to cut a man off the plant. With the extra tunnels and conveyors, we would end up keeping the same number of men.”
Dewatered sand and gravel and crushed gravel combine on a single conveyor leading off the dredge to a series of floating conveyors to an on-shore field conveyor.
Custom touches
Before buying the dredge, Scala and Hylton spent considerable time observing other dredging operations. The research convinced them to customize a few items on their dredge to better suit their operation. “After driving around the country, Darrell and I had seen a lot of other dredges,” says Scala. “We made a lot of modifications that made this dredge unique.
“You have to go beyond just [making it] functional. It may be built right and it may work fine, but how do you go about servicing it? Those things all have to go into the design stage.”
Among the modifications to American Sand & Gravel’s dredge is the addition of a jib crane over the jaw crusher. This can be used to remove oversized rock from the crusher and to change jaw dies. The company added a catwalk to one side to allow workers to walk completely around the dredge without having to backtrack to reach any area.
To enhance safety and productivity during night operations, American added 1,500-W lights on swivel mounts on all four upper corners of the dredge and additional lighting on feeders and screens. Each upper corner light has its own breaker to allow the dredge operator to turn on only the lights needed. “We light the banks or the shore where we’re working,” explains Scala. “When you’re out here at night, it’s like daytime.”
The operator’s cabin is larger than normal, providing ample room for a desk and chair, a filing cabinet, and a microwave oven.
American Sand & Gravel named its unique dredge “The Boss” in memory of the company’s founder, William Scala. “My dad was an old sailor,” Scala relates. “He would have loved this project out on the water.”
 The clean, paved, and landscaped entrance to American Sand & Gravel’s Crystal Springs plant is the first indication of the company’s efforts to be a good neighbor. Community Caring |
Bob Drake is editor for Aggregates Manager. Contact: bob@aggman.com
Layered Stockpiles Stop Segregation
Automated telescoping stacker eliminates need for product reblending or extra material handling.
A cross section of one of Riverstone Quarry’s stockpiles shows its construction in multiple thin layers built by an automated, telescoping radial stacker.
Riverstone Quarry’s telescoping radial stacker builds desegregated stockpiles in thin layers by constantly adjusting the length, height, and radial position of the conveyor discharge point. Extension and retraction limits of the stinger can be programmed to automatically change for each layer to prevent overrun on subsequent layers.
Lean production is about doing more with less — less time, labor, and money. It reduces waste, production costs, and labor while accruing subsequent increases in capacity, quality, flexibility, and profitability. Lean production isn’t about wholesale cutbacks, spending freezes, massive layoffs, and merely making do. But rather, it’s about continually improving production processes through innovative solutions and well-targeted investments in human and technological resources.
A growing lean-production trend in the aggregates industry involves the use of fully automated, telescoping radial stacking conveyors for high-capacity, multi-product, segregation-free stockpiling. Riverstone Quarry, a 170-acre limestone operation near St. Louis, recently replaced a fixed-length radial stacker (circa 1979) with a fully automated, 150-ft. TeleStacker conveyor manufactured by Superior Industries, an Astec company.
“We wanted to prevent any segregation problems,” says Steve Rust, vice president of Riverstone Quarry, Inc. “The TeleStacker conveyor was installed to improve product quality and reduce loader-mixing time. It has not only reduced loader-mixing time, it has eliminated it completely. There is no need to reblend the material before we load into the trucks.”
Automated telescoping radial stacking conveyors cost-efficiently build desegregated stockpiles in layers, with each layer consisting of a series of windrows of material. Customized stockpiles can be created in any size, shape, or configuration.
The system consists of a stinger conveyor mounted inside an outer conveyor of similar length. Moving linearly along the length of the outer conveyor, the stinger conveyor varies the location of the discharge pulley. The discharge pulley height and the radial position of the conveyor are also variable. This three-axis variation of the discharge pulley is integral in building the layered pile that overcomes segregation.
Riverstone Quarry’s TeleStacker is outfitted with Superior’s Genius Automatic Control System, which uses a programmable logic controller (PLC). Extension and retract limits of the stinger can be programmed to automatically change for each layer. Making each subsequent layer narrower can eliminate overrun.
“It’s very simple to change the programming,” says Rust. “We’ve got dual consoles — one in the operator’s station and one mounted on the conveyor. We can go to either one and in just a matter of a few keystrokes, it’s reprogrammed.” Riverstone programs it to stockpile four products — 4-in. minus, 2-in. minus, 1-in. minus, and Type-5 road base.
Riverstone worked with Superior Industries to custom engineer a way to add moisture to products as they are stockpiled. “Our DOT Type-5 base rock has to have a certain percentage of moisture in it for compaction,” says Rust, “and the most economical way to add moisture is to introduce the water onto the rock as it’s being discharged from the conveyor. Obviously there has to be a way to get the water up to the end of the conveyor. On the fixed radial stacker that wasn’t difficult, but the TeleStacker changes in length, so Superior custom-designed an extending and retracting water line for us.”
Electric and hydraulic lines are housed in an ‘E-Chain’ that runs along one side of the main truss and the stinger conveyor. Superior put the same type of system on the other side to house the water line. Water is pumped from a deep well, up through the line, and out the discharge end of the conveyor at 75 gallons per minute. This was the first time that a water system had been combined with a TeleStacker conveyor. It is programmed to operate only when Type-5 road base is being stockpiled.
For many producers, the use of telescoping radial stacking technology over traditional haul truck/loader methods has delivered cost-per-ton savings of up to 25 percent, according to Superior Industries. In addition to eliminating the cost of haul truck/loader operations, lean-production stockpiling can provide the following benefits:
- Eliminates cost of additional material handling. Handling material twice adds significantly to costs per ton, and the cost of restoring previously in-spec material to a desegregated state is prohibitive.
- Eliminates stockpile maintenance. With haul truck/loader stockpiling methods, MSHA requires that the stockpile must be bermed at the upper perimeter to the height of the axle.
- Ensures stockpile uniformity. Because stockpiling can be done in 6- to 8-in. lifts, material is spread evenly across the entire length of the pile and remains uniform.
- Prevents compaction. Scrapers and trucks continually compact a stockpile with every lift. A soft, uniform stockpile can be loaded out quicker and more efficiently, with a smaller loader, and with far less wear and tear on equipment.
- Prevents costly penalties. A segregated stockpile can mean deducts on belt sampling. Penalties can range from $1 to $3 per ton.
Any conveyor system choice should be based upon the specific application, material type, desired capacity, and future production needs. “We chose the Superior TeleStacker due to its construction and its automation package,” Rust says. “It has a much heavier framework and structure than the other models and its automation package is more sophisticated. We can do virtually anything with the programming. Also, the other models were only available up to a 140-ft. length. We needed a 150-ft. model.”
Dual consoles in the plant operator’s station and on the conveyor allow convenient program changes to accommodate stockpiling requirements for different products. Riverstone programs it to stockpile four products.
The Bottom Line
Riverstone Quarry installed an automated, telescoping radial stacker that builds stockpiles in multiple thin layers, reducing product segregation. This allowed the company to reduce material handling time by eliminating loader mixing prior to truck loading.
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
A Straight Path to Competitive Drilling
As a contractor, Yankee Drilling finds that stronger steel can lead to higher profits in hard rock conditions.
Tom Donovan of Capitol Construction (center), Gary Davidson (right) of Yankee Drilling and the rig operator, testing straightness by lowering a flash-light into the hole..
As a specialist drilling contractor in New England, Yankee Drilling found that a simple retooling process improved its major drilling criteria — straightness — and its ability to compete for business.
Gary Davidson started Yankee Drilling in 1984 in partnership with his wife Paula. “Almost none of the quarries in this area do their own drilling,” says Davidson. “Generally, they’ll make a contract with a blasting company, who will then put out a tender for the drilling operations as a subcontract.”
As a specialty drilling contractor, Davidson says that his company uses quite a bit of used equipment. The key to cost-effective operations for him is a good maintenance program. The company does much of its maintenance during the winter. Work is performed in-house with support from its dealer, Capitol Construction Equipment & Supply Inc.
A maintenance issue caused by tough operating conditions in a quarry led Davidson to look at Sandvik60, a 60-mm drill steel. “I generally believe that the bigger the steel the better, but at the time we were working in a quarry with particularly hard rock, so I was particularly interested in trying a heavier steel.”
In fact, the rock was so hard that Yankee Drilling had to lower the percussive pressure normally used. “We had been customarily running the CHA 1100 rigs equipped with T51 steel at 150 bar. When drilling a 5-in. hole, this gives us a production of around 100 ft. an hour,” says Davidson. “In this rock, however, which was both hard and seamy, we were getting pitting of the steel, unacceptably high hole wander, and actual steel failures.”
After measuring the temperature of the steel couplings, he learned that it was higher than 350° F, well over the normal 200° F threshold. As a result, the contractor lowered the percussive pressure to 115 bar. That took care of the temperature problem, but cut the production rate to only 60 ft. an hour. Since Yankee Drilling’s contracts are calculated on a per-foot-drilled basis, this was a serious problem.
“Given this situation, I was willing to try the new steel,” Davidson says. “With the Sandvik60s mounted, we returned to drilling at 150 bar. Production went back to 100 ft. per hour, but this time without the problems. Performance of the drill steel is crucial for us. In many ways, I believe it’s the weak link in the equipment chain.”
Steel options
Davidson has two criteria for selecting drill steel: straight holes and minimal downtime. “Hole deviation can cause enormous problems both for us and for the quarries,” he says, also noting the importance of the relationship between the cost of the steel and its service life. “Service-life issues come in two forms; one is simple durability. I generally expect to get 20,000 ft. out of a single T51 steel and 10,000 ft. out of a T51 shank. I’ve now got a Sandvik60 shank that’s already gone beyond 10,000 ft. and still looks very good.”
The other service life problem is random steel failures. “This is a special problem for us because we’re not operating on our own sites, and we operate over large areas,” Davidson says. “If we have an unexpectedly large number of steel failures at a particular site, that can mean transporting replacement steel over long distances, which is expensive in itself, but also means prolonging our downtime from production.”
Another benefit to the new steel is an increase in flexibility that allows Yankee Drilling to be more competitive. “In order to increase production, there’s a general trend for quarries to want to drill the largest holes they can get away with from the blasting security point of view,” says Davidson. “The average hole size is still around 3.5 in., but more and more sites want 5-in. holes. Conventionally, holes this big will often be drilled by down-the-hole rigs, which have tended to produce straighter holes, but, on the other hand, are slower and consume more energy.
“Now that we’re using Sandvik60, we can compete on drilling 5-in. holes. This solution has the added advantage for everybody that we can also drill smaller holes, e.g. 3.5-in. development holes, on the same site with the same rig — we just switch back to the lighter drill steel.”
The Bottom Line
Outfitting its drilling rigs with heavier steel allows Yankee Drilling to work in hard rock conditions at optimal speeds. It also provides greater flexibility to drill both development and production blast holes with the same rig.
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
Depending on Conveyors
Engineered conveyor systems enhance efficiency of an increasingly critical aggregate plant component.
By Bob Drake
Homemade belt conveyors are a common sight at aggregate operations across the country. In-house welders piece together a truss frame and bolt on some pulleys, idlers, and a motor. Depending on the builder’s skill and the conveyor’s application, it may function adequately. But as automated plant-feed, stockpiling, and load-out systems and in-pit crushing place increased dependence on a growing number of conveyors, money saved — if any — building conveyors in-house can be quickly lost through decreased efficiency and increased maintenance.
From belts to bearings, reliable and efficient conveyors comprise carefully engineered systems. Improved performance from high-quality idlers, belts, and pulleys can decrease maintenance costs and extend component life. Well-designed belt cleaners, skirts, enclosures, and impact beds can reduce dust, spillage, and conveyor damage at loading and transfer points. Less spillage results in less clean up and maintenance and enhanced safety.
Following are examples of the latest designs and technology in belt conveyors and components. This review does not include belt scales and automated belt-sampling systems. Belt scales will be included in next month’s Tech Trends section focusing on scales. Belt sampling devices were last reviewed in the March 2002 issue of Aggregates Manager (page 28; available at www.aggman.com under the Archives link).
Additional information from each of the following manufacturers is available using the appropriate InfoDirect number and the link on Aggregates Manager’s web site.
1. Arch Environmental
Arch Environmental Equipment’s Dust Shark cleaning system has a two-stage belt washing action that flushes up to 98 percent of fine dust into a self-cleaning drain pan, according to the company. Dust Shark cleans the load side of the belt with a dual spray system that is squeegeed by two Gordon belt scrapers. The return side is then sprayed and squeegeed with a rubber-bladed Gordon V-plow. The system operates automatically when the conveyor is operating. InfoDirect 701
2. Assinck
Assinck offers the Stacker Plus series of portable, telescoping radial stackers in three standard sizes: 30 in. x 100 ft.; 36 in. x 140 ft.; and 42 in. x 130 ft. The company says, however, that it can custom build wider and longer stackers. Stacker Plus features include a PLC with pre-programmed variable stacking patterns, safety brake to restrain the stinger conveyor in case of a cable break, an outboard festoon cable, and a floating axle design that Assinck says allows independent wheel travel and maximizes ground traction. InfoDirect 702
3. Continental Conveyor
Red Line pre-engineered field conveyors from Continental Conveyor are available in belt widths from 24 to 54 in. and from 25 to 250 hp. Red Line standard components include A-frame-type discharge drive section, hydraulic take-up section, idlers and support structure, and impact bed loading section. Options include alternate boom drive section, gravity take-up section, impact idler loading section, electrical controls, soft-start technology, hold backs or brakes, and loading hoppers. InfoDirect 703
4. Douglas Manufacturing
Douglas Manufacturing introduces two pulley designs — Quarry Duty Class and Integra Series. Quarry Duty pullys have minimum 1/2-in.-thick rims on drum pulleys and minimum 1-in. full round contact bars on wing pulleys. Integra Series drum and wing pulleys feature integral piloted flange bearings that allow 33 percent higher load ratings than conventional pulley designs, Douglas says. This is achieved by integrating the bearing into the pulley, which reduces bearing centers. They can be used in most non-drive pulley applications. InfoDirect 704
5. Emerson
Emerson Power Transmission Manufacturing’s electric MXP motorized pulleys, available in several sizes, eliminate overhung gearboxes or motors and, because there are no rotating shafts, guarding requirements are minimized, the company says. The pulleys use NEMA inverter-duty motors mounted within the pulley drum, synthetic lubricant, a magnetic particulate trap in the drum, radial lip seals, and bolt-on endplates. An internal mechanical backstop clutch or electromagnetic “power off” brake are optional for incline conveyors. InfoDirect 705
6. Falk
Falk offers a range of pre-engineered, shaft-mounted, right-angle drive systems. Drive One drives are supplied completely assembled on a modular swing base and are mounted to the driven equipment shaft with a single tapered bushing assembly and torque arm. The system reduces field assembly and alignment time, lowers foundation fabrication costs, and reduces drive maintenance expenses, according to Falk. Options include NEMA or IEC motors, flexible or fluid couplings, cooling devices, backstops, and inching drives. InfoDirect 706
7. Fisher Industries
Fisher Industries’ portable Overland Telescoping Conveyor uses tapered-head truss sections mounted on a Budd braked axle. The 36-in.-wide conveyor extends to its full 225-ft. length using a wheel loader. It has dual 25-hp. electric motors, a 14-in. self-cleaning tail pulley, 21-in. lagged drive pulley, 12-in. lagged bend pulleys, 5-in. troughing idlers, rubber disc return rollers, adjustable gravity take-up at the head end, and screw take-up at the tail end. It can handle 1,000 tph at 450 fpm, according to Fisher. InfoDirect 707
8. Flexco
Flexible Steel Lacing Co. (Flexco) offers a new family of economically priced, do-it-yourself belt conveyor accessories called Rockline. EZP1, a belt head pulley precleaner, is the initial Rockline product. It features a visual indicator for tension control and a one-piece, slide-in urethane blade. Rockline’s Belt Width Minus 8 in. blade sizing alternative prolongs EZP1’s concentration of cleaning action on the central load-carrying portion of the belt, Flexco says. A single-spring tensioning system provides specific spring-length dimensions to guide adjustment. Tension is monitored by observing gaps between spring coils. InfoDirect 708
9. Georgia Duck
Georgia Duck’s Quarry King line of economical conveyor belts is designed for general purpose applications where material size is 4 in. or less, material drop is 3 ft. or less, and the idler troughing angle is 35° or less. The 220- and 330-PIW rated belts stretch less than 2 percent at full working tension, the company says. Quarry King has full between-ply rubber gauges and exhibits fastener retention safety factors of 5 to 1, according to Georgia Duck. InfoDirect 709
10. Goodman Conveyor
Goodman Conveyor offers belt conveyor idlers and components in load ranges from CEMA B through E and says it is the only supplier with idler rolls available with any one of the leading bearing technologies — tapered roller bearings, ball bearings, and deep-groove ball bearings. The company’s high-performance, tapered roller bearing idlers feature Jeffrey Permaseal III, a multi-pass, multi-directional, grease-filled labyrinth seal combined with multiple exterior shields. InfoDirect 710
11. Grasan
Grasan transfer and feed conveyors are available in road-portable, pit-portable, and stationary designs from 18 to 60 in. wide, up to 1,000 ft. long, and in capacities up to 1,500 tph, the company says. The conveyors are available with engineered drives and options including walkways, covers, and support legs. Standard truss main frames are 36 in. deep and all jig welded. Truss sections are through-bolted. Portable models are available with hydraulic fold. InfoDirect 711
12. Goodyear
Goodyear Engineered Products’ Conquest is a heavy-duty 600- to 800-PIW belt incorporating the company’s Triple-Warp fabric reinforcement. The three-ply construction increases belt resistance to punctures, tears, rips, and fastener pullout, Goodyear says. Goodyear Survivor is an abrasion-resistant cover compound designed to extend belt life on systems with intense top-cover wear. InfoDirect 712
13. Hewitt-Robins
Hewitt-Robins manufactures a full range of CEMA B, C, D, and E idlers in regreasable and sealed-for-life versions. Products include troughing, impact, return, and transition idlers. The company says its seal design is effective in extending lubrication cycles, and its one-shot lubrication system can relubricate all six bearings from one accessible grease fitting. Additionally, quick-change rolls require less than two minutes to change all three rolls, according to Hewitt-Robins. InfoDirect 713
14. Marco
Marco tubular truss frame conveyors, a product of E.F. Marsh Engineering Co., have interchangeable truss sections with chord flanges that connect with four bolts, making the sections easier to align, assemble, replace, or rearrange, the company says. The tubular frames resist debris buildup and have a two-component urethane finish, including a rust-inhibiting pigment. Marco idlers are angled 2 degrees in the direction of travel to facilitate training and idler rolls have a double thickness at the roll edge to extend component life, the company says. InfoDirect 714
15. Martin Engineering
Martin Engineering introduces the Bull Dawg belt cleaner, designed for installation at the “five o’clock position” of the head pulley. It can be used as a stand-alone cleaner or installed as a pre-cleaner or secondary cleaner as part of a complete multiple-cleaner system, the company says. Bull Dawg uses multiple tungsten carbide blades on arms that mount to an elastomer pillow. Positioned inside the cleaner’s mainframe, these pillows cushion each arm and blade separately, allowing splice passage and momentary conveyor reversal without damage, Martin says. InfoDirect 715
16. Metso Minerals
Metso Minerals supplies a full range of conveyor accessories through their Trellex product line, including impact beds, belt guiding systems, sealing systems, conveyor hoods and covers, pulley lagging, and conveyor belt cleaners. Its ABC — Absolute Belt Cleaning — belt cleaners are designed to constantly maintain proper contact angle, contact area, and contact pressure throughout the cleaner’s blade life, the company says. Trellex ABC 70 Pre-cleaner blades feature a dual durometer polyurethane technology. They have an outward facing side made of a softer, 70° Shore A polyurethane for wear resistance and an inward facing side made from a harder, 65° Shore D polyurethane for rigidity. These dual-durometer blades provide as much as three times the blade life as standard 85 to 90 durmeter blades, according to Metso. InfoDirect 716
17. Parramatta Group
Parramatta Group’s Controlled Flow Material Transfer System has three major components: 1) an inlet hood collects and concentrates material from the discharge belt; 2) a ceramic-lined transition channel helps establish a fluid-like flow for the material; and 3) a discharge spoon softly and uniformly lays material onto the receiving belt at low impact angles. According to Parramatta, the system provides controlled, uniform, non-turbulent, centered belt loading, which helps prevent tracking problems; eliminates the need for skirt rubber and impact beds; and reduces or eliminates requirements for dust suppression and containment systems. InfoDirect 717
18. Richwood
Richwood Industries’ Combi-Pact impact saddles feature slide-on segments with ultra-high molecular weight polyethylene wear surfaces and rubber, shock-absorbing pads to dissipate impact loads. The impact saddle is directly interchangeable with any standard CEMA idler and can be installed with the belt in place, the company says. Individual wear segments can be replaced by sliding off and inserting a replacement. The smooth, curved trough formed by the saddle eliminates pinch-point damage to the belt, Richwood says. InfoDirect 718
19. Rockwell Automation
Rockwell Automation offers the Dodge Torque-Arm II shaft-mounted speed reducer in 12 case sizes through 400 hp. Torque-Arm II has increased torque ratings resulting from extended gear centers, wider gear faces, and increased gear tooth contact, the company says. The sealing system uses a standard double-lip, spring-loaded, rubber-coated oil seal protected by a metal excluder seal with rubbing lip. A new steel motor mount adjusts to multiple center distances and mounts in shaft mount and screw conveyor positions. InfoDirect 719
20. Superior Industries
Superior Industries developed the Land-Link conveyor system for quick assembly of field conveyors of any length. Head and tail sections ship fully assembled and intermediate sections can range in length from 20 to 60 ft. Truss frame sections assemble with a pin and wedge bolt design and the channel frame has bolt together sections. The Land-Link system can use several types of conveyor take-ups, including vertical gravity and scissors take-ups, tower take-ups, and hydraulic take-ups. InfoDirect 720
21. Thor
Thor Global Enterprises’ ThorStack2 portable, telescopic radial stacker is available in 120-, 130-, 135-, 140-, and 150-ft. lengths with belt widths of 30, 36, or 42 in. A standard Allen Bradley PLC and ThorTouch operator input system provides several pre-programmed, automated stacking options. Ultrasonic sensors maintain the drop distance from the head pulley to the stockpile and stop the radial movement if no material is detected on the conveyor belt. A Load Equalizing System distributes the constantly changing load of the stinger conveyor as it extends and retracts, resulting in longer truss life, according to Thor. InfoDirect 721
22. Van der Graaf
Van der Graaf drum motors are available in nine sizes from 3.9 in. to 19.7 in. in diameter and rated up to 40 hp. The self-contained drive mounts with two brackets and is hermetically sealed in a steel shell that protects the motor from harsh environmental conditions, the company says. The only required maintenance is an oil change every 50,000 hours. Options include metal tread lagging, dual motors, two-speed motors, variable-speed motors, and a manual release backstop for incline conveyors. InfoDirect 722
Bob Drake is editor for Aggregates Manager.
Maintenance Manpower Planning
Part 1: Tracking categories of maintenance activities is a first step toward maximizing asset reliability
By Andy Page
Manpower planning has historically been an activity that takes place during budgeting and is rarely brought up again unless marketplace conditions change drastically during the planned business cycle. However, manpower planning — especially maintenance manpower planning — can be a source of dramatic improvements in downtime reduction and in productivity, costs, and profits.
The first part of this two-part series focuses on maintenance manpower resource measurements and how they change as the maintenance effort matures.
All maintenance activities fall into one of three main categories: reactive, preventive, or planned. Reactive maintenance is commonly referred to as emergency maintenance. Any mechanical or electrical failure that interrupts or delays the regular scheduled production is an example of reactive maintenance. Repairing a locked tail pulley bearing on a conveyor after it caused an interruption in production is an example of emergency maintenance.
Preventive maintenance (PM) is any interval-based maintenance activity. A 250-hour service on a haul truck is a common example of a PM. Changing the screen cloth on a screen after a given number of tons have run across it is another.
Planned maintenance is any activity that is the result of an inspection, where parts and manpower are assembled ahead of time and the maintenance activity is performed in concert with the production schedule. The replacement of cone crusher liners based on their measured wear is an example of planned maintenance.
Maximizing asset reliability is accomplished by maintaining the proper levels of all three types of maintenance activities. Figure 1 shows the typical progression of these measures as the maintenance effort of an organization matures.
Figure 1: Progression of the relative amount of effort required for reactive, preventive, and planned maintenance as an organization matures..
Notice that the only time the sum of the three measures equals 100 percent is at the beginning and end of the graph. It equals 100 percent at the beginning of the graph because maintenance manpower resources are estimated based on a host of assumptions and calculated guesses. As the amount of PM starts to climb toward the correct levels, numerous planned maintenance activities are required to correct previously undiscovered or uncorrected deficiencies. Temporarily, this requires more maintenance resources than previously estimated. As these two trends continue, the amount of reactive maintenance starts to slowly decrease. There comes a point where the deficiencies are corrected and the amount of planned maintenance begins to taper off to a much more easily managed level. As the maintenance effort reaches full maturity, the amount of PM flattens out at about 60 percent, the amount of planned maintenance flattens out at about 30 percent, and the required level of reactive maintenance quickly drops to about 10 percent. And now the maintenance manpower resources are stabilized at a level that provides the highest level of asset reliability.
Of course the trick to this system is knowing where your maintenance effort is on the maturity curves. To be able to accurately determine where an organization is on the curves, the amounts of each type of maintenance activity must be known. This requires some type of manpower tracking scheme.
The types of manpower tracking systems are as varied as the number of operations trying to track them. Some operations use a paper system whereby maintenance activities are simply documented daily by operators. This is typically not a good system for determining the amount of maintenance in each of the three categories because manual tabulation of all of the maintenance manpower and which category it appropriately falls into becomes almost a full-time task for management.
More sophisticated operations use some type of computerized maintenance management system (CMMS) to track their maintenance activities. This is a much easier, efficient, and more cost effective method to determine where manpower resources are utilized on a daily, weekly, monthly, or even yearly basis. Most systems have pre-programmed reports, charts and graphs that display these measures at the click of a mouse.
The ability to measure where the maintenance resources are going is paramount to finding an operation’s position on the curves and determining the appropriate course of action to take the maintenance effort to a level that maximizes asset reliability.
Next month’s article will discuss how each of these three measures can be used in conjunction with an operating schedule to accurately determine the amount of maintenance manpower to maintain and even improve the levels of asset reliability.
Andy Page is the managing partner of Page Industries, Ltd. (www.pageindustriesltd.com), an Ohio-based consulting firm specializing in maintenance engineering for the mining and construction aggregates industries. Contact: andy@pageindustriesltd.com or 513-252-7243.