April 2003
Innovative conveyor engineering and applications are helping producers stack up the savings.
By Therese Dunphy
Cherenzia Excavation, Inc. is saving at least $3,000 per day, while eliminating the need for haul trucks to cross a busy road 120 times a day.
When it comes to improving production costs, incremental improvements can translate into big savings. To achieve those results, savings-savvy aggregate producers are leveraging newer conveyor technologies and engineering applications in various locations throughout their operations.
Before making a switch from hauling to conveying, however, producers should consider some of the following factors:
- Capital expenses including equipment procurement and depreciation;
- Operating costs such as fuel and maintenance;
- Personnel costs including salaries, insurance, and workers’ compensation; and
- Compliance costs for Part 46 training, berming requirements, and potential citations.
At the crusher
Sam Cherenzia, owner of Westerly, Rhode Island-based Cherenzia Excavation, Inc., analyzed those costs at his aggregate operation. After deciding to relocate his primary jaw crusher closer to the pit, he found that the increased truck traffic between the primary and secondary resulted in significantly higher operating costs. “I was seeing dust and smoke and dollar bills flying all over the place,” says Cherenzia.
He estimates that his operating costs for the two haul trucks, used to transport the material across the street and down the hill from the primary to the secondary, and a loader were approximately several thousand dollars per day.
After running the numbers, Cherenzia opted to build a culvert under the road running through the operation and to install a 1,300-ft., 30-in. Continental Red Line conveyor.
“Now, I’m saving at least $3,000 a day, and I don’t have trucks crossing the highway 120 times a day,” says Cherenzia.
In addition to the production benefits, the conveyor has also helped Cherenzia lower dust emissions, improve safety, and build better community relations at his operation.
“One way to look at it is, we’ve replaced three 300-horsepower diesel motors with a single 40-horsepower electric motor,” he explains. “Also, the roads are safer and the overall environment is improved. The local authorities — police department and town council — were happy to let us put a tunnel under the road. I mean there are school buses and such running on the road, and I consider safety to be a number one priority. Also, the environment around the site is a lot nicer with all the dust and exhaust (from the trucks) off the road. We have already started a greenery program; now we’re planting grass and flowers around where the trucks used to run. The (conveyor) is definitely a much more community-friendly solution.”
At the stockpile
Another potential area for savings is at the stockpiles. Superpave requirements and pavement warranties have driven aggregate producers to look for better ways to prevent stockpile segregation and ensure products that meet specifications.
According to Allan Cowan, crushing superintendent for Odessa, Texas-based Jones Bros. Dirt & Paving Contractors, Inc., an investment in conveyors has helped him in three key areas of his operation: lowering his cost per ton, eliminating segregation, and preventing the material degradation he experienced when using trucks.
He says that using a fully automated telescoping radial stacker has enabled his operations to keep products in spec by creating thin, 6- to 8-in. lifts at the stockpile. Cowan, who recently purchased his third TeleStacker Conveyor from Superior Industries, says that the system has helped him create stockpiles in layers, with each layer consisting of a series of windrows of material.
“By using an automated telescoping radial stacker that is stockpiling in very thin lifts and spreading material evenly across the entire length of the pile, material remains uniform even if the nature of the material changes,” says Cowan. “For example, if you hit a clay deposit, with trucks you could have six truck loads of clay in one spot of your stockpile.” With the use of the conveyor system, however, the material is spread throughout the stockpile.”
Windrow stockpiling can lead to higher quality materials, better performing pavements, and — importantly — protect the producer against the high costs of failing to meet specifications, he says.
“If you have segregation in your aggregate stockpile, you’re going to be in deduct on your belt sampling. Deducts can range from $1 to $3 per ton, and any three consecutive failing gradations means you will have to shut down your operation,” Cowan explains. “Also, needless to say, the cost of restoring previously in-spec material to a desegregated state is unimaginable, considering the additional labor expenses, fuel usage, and wear and tear on the loading equipment.”
In addition to preventing material segregation costs, Cowan says the stockpiling technique helps prevent compaction and speeds up loading at the stockpile.
“With a traditionally built stockpile, you hit the stockpile in second gear,” he explains. “You have to work the bucket, and you incur more costs because you’re spinning your tires. You have to spend five to 10 minutes to load one truck. I can load one now in about 30 seconds.”
Between the various savings, Cowan estimates that he saves up to 25 percent of his annual cost per ton since implementing the conveying system.
Use of a telescoping radial stacking conveyor can help eliminate segregation, prevent material degradation, and help lower the cost per ton.
At the loadout
Finally, aggregate producers are turning to unique conveyor configurations at the loadout in order to achieve savings.
“No matter how you use conveyors, you have to look at the bottom line,” says Mary Erholtz, marketing manager for Superior Industries. With an increasing trend in rail and water shipments, she says that products such as Superior’s new Extender series create an opportunity for producers to deal with flexible requirements without investing in multiple conveyors.
“For producers to sustain businesses and grow their businesses in times such as these, they have to be pretty conscious of where their costs are,” says Erholtz. “I look at conveyors as helping producers cut down on their cost per ton.”
Editor’s Note: Some information for this article was supplied by Superior Industries and Continental Conveyor & Equipment Co.
Therese Dunphy is editorial director for Aggregates Manager.
Changing Bushing-Change Routines
Cast polyurethane bushings can provide greater strength and longer life in suspension systems.
For many fleet maintenance crews, changing bushings has become a routine to which few give much thought. But, considering the advancements in cast polyurethane formulations, optimizing bushings for particular equipment and applications can result in considerable time and cost savings.
Today, cast urethanes are formulated to provide greater physical properties: tensile strength to 9,000 psi, Die C tear to 800 pli, elongation to 600 percent, hardness from 40A to 80D (Shore), rebounds of 5 to 65 percent, and even greater flex strengths.
By formulating and testing various chemistries, one can tailor a urethane for almost any application. Some companies have been able to formulate urethanes that isolate a particular resonant frequency.
For example, ATRO Engineered Systems formulated a cast urethane spring eye bushing that replaces the copper, brass, or steel pin and is completely greaseless. The company manufactures an axle and suspension bushing for the M-1000, which has 10 axles, eight of which steer. The original steering link bushings were steel taper bearings that failed.
The original metal bushings used in this application had 154 failures in field tests on the 16-bushing set. The urethane bushing design had no failures and no measurable wear. The same results were experienced with a new greaseless spring eye bushing and with other designed applications.
The first cast polyurethane bushings for heavy-duty suspension applications were produced in the 1980s. Urethane resins and curatives selection was limited, but a patented mechanical design, called free rotation, provided the first bushings guaranteed to last three years. Development and testing showed that urethane, a thermoset elastomer, plus the free rotation design, outlasted rubber by three to five times. Field results confirmed this.
The key was the free rotation bushing design, which bonds the urethane to one surface, leaving the other to rotate 360 degrees. The bonding feature is vital because elastomers under load will flow from the point of stress. Bonding, in effect, holds the urethane in place and allows it to display its maximum physical properties. Elastomeric materials that are not held in place by bonding will keep flowing, which will decrease the load bearing and cross-section area until failure occurs.
Cast urethane bushing designs had to be confined to the spring rate and geometry of rubber bushings they were to replace. Urethanes are chemically non-reactive and therefore resistant to environmental elements such as aromatic hydrocarbons, acids, and akalines. Also, modulus and elongation can be many times that of rubber.
Spring rates must match those of rubber to provide the same conical deflection versus load designed into the suspension. Figure 1 shows typical load-vs.-deflection curves for rubber and a urethane using an effective hardness calculation. Note that the curves meet at “no load” and “maximum load,” but the urethane displays a convex shape and the rubber is concave. A little less deflection at the same load in the operating range provides a more stable bushing for heavy-duty applications.
Advantages urethane displayed were enhanced many times by the patented free rotation design. The design eliminated shear and torsional stresses and put the bushing material only in compression. The feature increased the performance and life of the suspension because only centerline loading of the components and attaching parts occurred. As designed, the suspension absorbed shock rather than multiplying the force through moment arms. This left the affected parts and brackets free from loads that could bend or crack them.
In addition, the design allowed for easy installation of torque rods. To eliminate torsional stress in the bushing material (bushing wind-up), torque rods must be installed at vehicle ride height. Care and considerable adjustment are normally necessary for proper positioning in any vehicle, but are mandatory for air-ride suspension since the ride can be adversely affected by bushing wind-up.
This article is provided by The Association of Equipment Management Professionals (AEMP), formerly the Equipment Maintenance Council (EMC), an individual membership organization comprised of equipment maintenance and management professionals. AEMP offers a certification program for the industry, the Certified Equipment Manager (CEM). For more information, contact Stan Orr, CAE, AEMP executive director, at 970-384-0510, e-mail at ceo@equipment.org or visit AEMP’s website at www.equipment.org.
A New Bent on Hauling Efficiency
Latest generation of articulated haul trucks provide options for improved equipment utilization.
By Bob Drake
The current generation of articulated haul trucks (artics or ADTs) are larger, more robust, and smoother riding than their predecessors. Brakes, suspensions, serviceability, and engine power have been improved. In many applications, manufacturers claim they can outperform comparably sized rigid-frame haul trucks — move more tonnage at a lower cost. The machines have proven effective in many sand and gravel operations, as well as for stockpiling and stripping in quarries, but can artics competitively haul shotrock in a crushed stone production environment?
“Many ADT manufacturers are now in their third or fourth generation design and better understand the demanding hauling conditions an ADT can be subject to,” says Kevin Bellows, business analysis manager, ADTs, for John Deere Construction and Forestry Co. “Machine structures and components have been made more robust for extended longevity, such as sealed wet disc brakes, which are now standard on most 40-ton ADTs.”
Operating with poor haul road conditions, artics have a distinct advantage. “Because of the ‘go anywhere’ nature of the machine, it can be used in a wide variety of job applications, meaning that for the owner there may be more productive time from that unit,” says Jeffrey Strickson, marketing and scheduling supervisor (articulated trucks), Caterpillar Peterlee Ltd. “This is not the case with a rigid machine, [which requires] smoother, graded haul roads, which in turn require more maintenance.”
Operations using artics can concentrate on hauling, not on haul road maintenance, which requires support personnel and additional equipment, according to Bellows. “ADTs offer high transport speeds and the ability to go places a rigid truck would never consider, minimizing the need for production site development,” he says. “ADTs have shown better tire wear characteristics due to less spin out and less sensitivity to road conditions.”
Ian Marshall, ADT product consultant, John Deere Construction and Forestry Co., lists the following advantages of articulated haul trucks compared to rigid-frame trucks: significantly lower price; less fuel consumption; similar cycle times; lower tire costs; greater versatility (use for both stripping and mining); better gradeability and traction to negotiate steeper, shorter roads without wheel spin-out and subsequent driveline damage; and greater resale opportunities.
Under certain operating conditions, therefore, artics can be competitive production tools. But limited payload size can preclude their use as a production hauler in larger aggregate operations. Many medium to large operations use 50- to 80-ton or larger rigid-frame trucks to match the production capabilities of their loading tools and primary crushers. The largest artics available offer payloads of only 40 to 45 tons.
In addition, even the more robust artics may not long endure continual rock handling duties. “The artic is not designed to stand the shock from loading large pieces of rock,” says Fred Casten, director of sales (artics /scrapers) for Terex Construction Americas. “Bed liners would need to be installed to handle the wear and tear of the loads. This would be short lived though because the artic life is not near as long as the rigid frame companion. Rigids will normally have a life of 40,000 to 50,000 hours as compared to the artic at 10,000 to 12,000 hours.”
Artics may not be appropriate for the toughest hauling duties or for high-production operations, but recent design improvements and new features may make them the most cost-effective machines for aggregate operations seeking better equipment utilization and versatility. Following are the latest offerings of articulated haul trucks with payloads of 30 tons or more.
1. Case
Case Construction Equipment offers two models in its 300 Series articulated truck line — the 30-ton-capacity Case 330 and the smaller Case 325. The Case 330 features a six-cylinder Cummins 286-net hp engine linked through a ZF six-speed transmission to ZF limited-slip axles. The truck has an oscillating front suspension and torsion-reactive rear rocking-beam suspension. Rocking beams attached to the axles by steel castings allow the axles to float independently, preventing the rear of the truck from bouncing around over uneven terrain, Case says. InfoExpress 701
2. Caterpillar
Caterpillar offers four artics with capacities of 30 tons or greater, the 730, 735, 740, and 740 Ejector. Design features shared by the four models include center-mounted cabs; electronically controlled engines and transmissions; rear-mounted radiators that improve forward visibility and service access; a box-section front frame designed to decrease stress in the hitch area; a two-piece, articulating, oscillating hitch; and wet-clutch cross-axle and inter-axle differential lock systems. The inter-axle differential lock splits torque between the tractor and the trailer and the cross-axle differential lock provides full driveline locking. All differentials can be engaged and disengaged on the go, Cat says. The 740 Ejector has a hydraulic ejector mechanism to spread or dump loads without raising the body. InfoExpress 702
3. John Deere
John Deere’s lineup of ADTs includes the 30-ton 300D, the 35-ton 350D, and 40-ton 400D. The 300D is powered by a 285-net hp John Deere turbocharged, inline six-cylinder diesel. A Mercedes Benz turbocharged V-6 diesel provides 380 and 413 net hp to the 350D and 400D, respectively. Deere’s use of high-strength steel and composite materials results in ADTs with higher horsepower-to-weight ratios, the company says. Automatic planetary transmissions feature hydraulically actuated multiple-disc clutches and electronic control. “Adaptive Shift Logic” programming makes instant adjustments to gear-shift instructions to suit load and terrain, which produces smoother shifting, according to Deere. All four models have exhaust and engine valve brakes. InfoExpress 703
4. Komatsu America
Komatsu America says its three artics — HM-300-1 (30-ton), HM-350-1 (35-ton), and HM-400-1 (40-ton) — offer the lowest loading heights in their classes, 9 ft. 2 in., 9 ft 4 in., and 9 ft. 9 in., respectively. All three models feature six-wheel, oil-cooled multiple disc brakes; trailing-arm front suspensions and rear bogie suspensions with hydropneumatic cushions; switches to lock the front axle to the rear axles plus differential lockup on all axles; and K-ATOMICS six-speed, fully automatic transmissions with electronic controls that select the ideal gear based on vehicle speed, engine rpm, and the shift position chosen, Komatsu says. The HM-350-1 and HM-400-1 are equipped with continuously oil-cooled multiple disc retarders. InfoExpress 704
5. Moxy
Moxy Truck’s latest generation of trucks incorporate what the company calls the “Plus1 Concept.” In the 30- to 40-ton range, that includes its models MT31 and MT36. Among other features, Moxy says its Plus1 trucks have higher engine power ratings (340 hp and 400 hp, respectively), greater stability with a sloping rear frame for lower center of gravity, and larger capacity at 31 and 36 tons, respectively. Both trucks use Scania in-line six-cylinder engines and electronically controlled, automatic planetary transmissions with automatic lock-up in all gears. Moxy’s 40-ton MT40B Series II artic is equipped with a 448-hp Scania V-8 diesel and ZF six-speed automatic transmission. An exhaust brake and hydraulic retarder brake are standard. Service brakes on all wheels are air over hydraulic dry disc. InfoExpress 705
6. Terex
Terex is in the midst of upgrading its line of five artics ranging from 25- to 40-ton capacity. Generation 7 upgrades to the three smallest machines, including the 30-ton TA30, were unveiled late last year; 35- and 40-ton models (TA35 and TA40) are slated for upgrades this year, Terex says. Front and rear frames on the company’s artics are all-welded steel fabrications with rectangular box-section beams forming the main side and cross members. They have permanent all-wheel (6x6) drive with differential coupling between each axle and automatic limited-slip differentials in each axle. ZF fully automatic transmissions feature integral hydraulic retarders. The TA30 uses a new ZF rotational pressure compensated transmission that Terex says provides accurate clutch filling at all speed and load conditions, smooth gear changes, and fast and accurate reaction on load change demands. All three artic models have all-hydraulic brake systems — dry disc with double calibers on the TA30; dry disc with single calibers on the TA35; and sealed, oil-cooled multiple discs on the TA40. InfoExpress 706
7. Volvo
Volvo Construction Equipment’s larger D-series artics — the A30D, A35D, and A40D — are rated to haul 31 tons, 35.6 tons, and 41 tons, respectively. Common features include operator selectable 6x4 or 6x6 drive; one longitudinal and three transverse differential locks; rear axle terrain bogies; and Load and Dump Brake. Use of 6x4 drive on good haul roads reduces tire wear and fuel consumption, Volvo says. On-the-move, the operator can switch to 6x6 drive and lock differentials on one or all axles when greater traction is needed. The Load and Dump Brake allows the operator to press a button to automatically apply the trailer brakes and place the transmission in neutral. Moving the gearshift lever automatically turns the brake off. The A30D and A35D have fully hydraulic dry disc brakes on all wheels; the A40D has enclosed oil-cooled disc brakes on all wheels. InfoExpress 707
Bob Drake is editor for Aggregates Manager.
Portable Primary Supports Mine Plan
A skid-mounted roll impactor and pan conveyor hikes production capacity and increases plant flexibility.
Haul trucks dump directly on the pan conveyor of a DBT Roll Impactor primary crusher. Impact bars on the overhead-mounted rotor crush any size low-silica limestone that fits through the 6-ft. opening.
Crushing a low-silica, low-abrasion limestone at its Winchester, Va., quarry, Global Stone’s jaw dies and cone crusher mantles seemingly lasted forever. While that was desirable from a maintenance perspective, when mining plans required a different arrangement of the primary circuit, the company opted to try a less expensive and more productive crusher.
Global Stone replaced a 30-year-old, in-pit 3642 jaw crusher with a roll impactor, from DBT Mineral Processing, Plymouth, Pa., located adjacent to the secondary plant. “With our mining plan through the next seven or eight years, it’s more convenient to have the primary on the surface because it’s in the area we’re developing,” explains Mark Georgianna, Winchester plant manager. “We chose the [DBT] because of the high throughput and considerable less capital investment than a jaw of the same capacity, and the fact that it was portable.”
Portability plays a role in the company’s plan to increase aggregate production capacity and product mix. The primary roll impactor directly feeds the 500-ton-per-hour secondary circuit, which includes a Hazemag horizontal-shaft impactor. The primary currently is used at only half its rated 1,000-ton-per-hour capacity. However, the company plans to pull the primary crusher back about 300 yards and install a screen tower and conveyors in front of the secondary plant to produce a couple more products and to fully utilize the primary’s capacity.
“The DBT is portable — no concrete piers or big rock box like a typical jaw,” says Georgianna. “You just drag it back, put the screening plant in the middle and keep on going.”
Ground-level crushing
The skid-mounted DBT Roll Impactor uses what the manufacturer calls “horizontal flow crushing.” The unit is designed to be fed at grade using a pan conveyor with chains and flight bars to move material in a straight line through the crushing chamber. The rotor, containing eight impact bits, is mounted above the pan conveyor. Clearance between the rotor and the pan is adjustable to change the maximum size of the crusher output.
Georgianna describes the crusher as “basically a feeder-breaker for a coal mine — a big coal mine.” Haul trucks dump directly onto the ground-level pan conveyor. It does not require ramps or a hopper. The material forms a natural rock hopper as the pan conveyor withdraws material from the bottom of the dumped load.
Global Stone uses Euclid 35-ton and Caterpillar 45-ton trucks to feed the primary. Currently, two or three trucks are used, depending on from which area of the quarry they haul.
The roll impactor has a feed opening of about 72 x 72 in. that eliminates the need for a hydraulic hammer or other secondary breaker, according to Georgianna. “If it goes through that opening, it will crush it,” he says. Typical feed size at the Winchester plant is about 24-in. square x 0. The crusher is set at about 8 in. clearance between the impact bits and the pan conveyor.
The impact bits, or bars, arranged in two rows of four bits, are mounted perpendicular to the rotor axis rather than parallel to the axis like traditional horizontal-shaft impactors. As the 26-in.-long bits wear, they can be extended out from the rotor with an adjusting rod.
Georgianna says that in the Winchester plant, the inner bits on each row wear slightly faster than the outer bits, allowing them to swap positions to maximize utilization. “A typical set will be installed, adjusted once, swapped once, then replaced,” he says. It takes about one work shift to replace all eight bits, according to Georgianna. Global Stone has crushed on average about 350,000 tons with each set of impact bits.
The DBT Roll Impactor during installation shows the skid mount and the pan conveyor that provides straight-through feeding.
The Bottom Line
Taking advantage of the low-abrasive nature of its limestone deposit, Global Stone installed a DBT Roll Impactor that accepts larger feed and doubles the primary plant’s production capacity. The crusher’s portability provides flexibility to accommodate future plant expansion.
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: 330-966-2454or email at bob@aggman.com