“Airspace” is the name of the game in landfills. Because the US sends 258 million tons of municipal solid waste to 3,000 active landfills that are quickly reaching their capacity, according to a report by the Solid Waste Environmental Excellence Protocol, making the most of the available space is crucial.
In order to make the most of the limited landfill space remaining, compaction must be maximized and airspace eliminated. “A higher compaction rate means less airspace,” summarizes Austin Phares, regional sales manager for Humdinger.
That is achieved by unique wheel and tip configurations designed for different waste characteristics to provide better traction and stability for the landfill compactors, enhancing their performance to reach maximum density. “Traction and stability are key performance criterion for landfill compactors operating in landfill applications, due in part to the unconventional underfoot conditions these machines operate on,” elaborates Marck Welch, global waste industry specialist, Landfill Equipment & Application, Caterpillar Inc.
The wheel and tip should be designed to complement the landfill compactor to assist in attaining the expected compaction. The tip layout pattern on landfill compactor wheels is critical for machine efficiency, which translates into compaction (density) improvements. “These expensive landfill compactors are highly researched and engineered machines designed to maximize airspace in a landfill,” says Welch. “If the wheels and/or tips are not designed to complement the machine correctly, then this expensive machine might not perform as expected or not save the airspace originally planned for.”
The wheels are located on the rotating planetary, which requires extensive research and design to optimize machine performance and life of the components. The balance of the wheel is critical for the life of gears, bearings, and other components of the drivetrain, Welch explains. The wheel should absorb the loads and distribute them evenly over the planetary.
Too heavy of a steel wheel will shorten the life of rotating components and slow down a machine at full speed or require additional energy to keep intended speed. Too light of a wheel will cause excessive wear and decrease the life of wheels. “There is a fine balance of life versus performance/speed.”
Compaction of waste occurs when the material is compressed to remove the void spaces or air from the waste. Therefore, the more a wheel sinks into the waste, the more void space is eliminated. Because the characteristics of the material varies dramatically, a compactor needs to make multiple passes of the layer of waste to eliminate as much rebounding of material as economically possible. Too few machine passes results in more rebounding, which means less compaction. Over an operating day of 8 hours, a 0.25 mile-per-hour change equals 2.0 miles of distance a machine loses or gains.
“There also is a possibility of too fast,” notes Welch. In that situation, the weight of the machine or wheel pressure doesn’t affect the material. This is referred to as dwell time. “This is all part of the research required to maximize airspace.”
The most important considerations when choosing wheels are the size of the landfill and the type of material it contains, believes David Sonnentag, owner of Terra Wheels. C&D (versus MSW), residential trash, sludge/sticky, and industrial waste all require a different type of cleat pattern.
There’s an “endless number of cleat patterns,” continues Sonnentag. The right pattern can provide stability while doing slope work. Some work better in sludge. But it’s largely a matter of operator preference, he believes.
An inverted chevron is the most common pattern: the standard, with cleats close together. That means it clogs in certain conditions. The chevron has more space between the cleats to shed material better. “You need to know the type of material to spec the cleat pattern,” insists Sonnentag. Other necessary information includes the tip, the weight of the wheels, and the weight of the machine.
While the characteristics of the material and operating techniques are most important, weather and environment also factor into the choice. Hot, dry climates contribute to more abrasive cover material that might require life overweight. A cold, humid climate might require traction over life and seasonal weather might require a mix of both styles, Sonnentag advises.
The working conditions can also affect the requirements. “Does the compactor work alone and perform the pushing as well as compacting application?” asks Sonnentag. “Where this occurs, a lighter tip configuration might be preferred, as there is more work to do and speed is important. If a landfill operation is working on a slope and pushing material uphill, then traction is more important than speed and the slippage or spinning of wheels will create more wear, and life is important. Working the waste downhill might allow for a combination of tips to equally balance the characteristics of tips.” Tip and wheel design should keep the compactor moving across the face without slippage. This is critical to obtain the desired level of compaction.
The cell size could affect the speed requirements as well. More distance to travel is important for getting the number of passes required for targeted density. Less distance allows for more passes or heavier components.
Keep It Clean
Caron offers self-cleaning wheels with patented Pin-On teeth that minimize wheel plugging. Instead of blades or tampers, Caron compactor wheels feature two types of specifically designed teeth that clean themselves automatically as they compact, providing better compaction in few passes, according to the president of Caron, Jim Caron. “Teeth and wheels remain free to chop, grind, and compact a wider range of refuse without fluffing lightweight materials.” Full penetration allows greater compaction density in less time. Firmly packed surfaces can reduce cover materials by as much as 30%. The Pin-On teeth have abrasion-resistant caps for long wear and can be replaced onsite.
Volvo Construction Equipment partnered with Terra Compactor Wheel Corp., a leading manufacturer of landfill compaction wheels, cleats, rolling wire guards, and machine parts, on the development of a new product introduced in the second quarter: the LC450H landfill compactor, the company’s first purpose-built landfill compactor for the North American market.
The LC450H comes standard with Terra wheels, with the option of two-cleat patterns or three-cleat configurations. The cleats are 8.5 inches tall with “hard facing” on the tips for longer wear life. “We put a wheel with a tip and guarding on the LC450H that has been in the industry a long time and has proven capabilities and results,” says Sonnentag. “If it’s proven to work, stick by it. Don’t reinvent the wheel.”
To further maximize both uptime and wheel performance in the presence of difficult landfill conditions, the wheels are equipped with:
Weld-on rolling wire guard—an attachment Sonnentag calls “anti-wire wrap protection” to prevent wires from wrapping around the axles and damaging the seals. This standard feature is “welded on the inside of the drum in the wheel axle housing, one inch lower than cleat height to prevent downtime.”
1.25-inch-thick wheel wrapper with horizontal and vertical hard facing on the edges provides for long life.
The 26.5-inch ground clearance is higher than many competitor compactors.
Two striker bars covering both the front and rear wheels keep material away.
The striker bar, or cleaner bar, protects the machine, Sonnentag explains. “It knocks off the clay and other material from the drums.” Weld-on cleaner fingers are an optional attachment to clean the wheel. In addition, the LC450H can be fitted with a Terra semi-u blade or a straight blade, giving operators the option to pick the blade that best fits their needs.
Mark DeBrosse, product manager at Volvo Construction Equipment, adds, “Landfill conditions are typically rugged and demanding on machines. We designed the LC450H to withstand the rigors of this type of work, fitting it with durable wear parts, heavy-duty guarding, and an efficient powertrain.” The 90,000-pound LC450H is powered by a 416-horsepower Volvo D13J Tier 4 Final engine. Working in cooperation with the engine and the axle is an HTL310 transmission with lock-up converter, delivering high torque output and excellent fuel efficiency.
The number of teeth and the types of teeth, whether traction or contour, provide the ability to achieve penetrations into the refuse per day. Caron’s wheels have two teeth designs: wedge-shaped for extra traction and compaction, and contour-shaped to minimize side slippage and wheel spin and increase demolition capabilities on slopes and grades.
“We have developed teeth specific to machine size, weight, and horsepower,” explains Jim Caron, who adds that both teeth and wheels are designed to meet site-specific requirements. “Our wheels are made with different size teeth and incorporate patterns to adapt to the job conditions, including weather, the composition of the waste—i.e., the percentage of municipal solid waste, sludge, construction and demolition materials, and soil conditions from rock, sand, and loam to cohesive clays.” He says that the height of each tooth, as compared with O.E.M. designs, which are shorter and smaller, and the metallurgy to achieve higher wear life, are additional factors that are important.
“It’s not about the tooth,” counters Humdinger’s Phares. “It’s about how the tooth is set up along the drum.” By fitting teeth on the ridge in a single line with no pattern, he says their system realizes 8-inch tooth compaction with no blowout. “They push the weight down.”
The purpose of teeth is to break up the trash, of course, but, Phares contends, “they’re only good when they’re clean. If the trash gets between the teeth, there’s no compaction.” Cleaner bars between each row assist with this, and because the cleaner bars are inside the machine, they are somewhat protected.
Maximizing the cleanliness of the drum helps achieve higher ground pressure. Tana has 28 to 40 internal scraper bars that keep the drums clean and 8 wire cutters eliminate debris wrapping around the drum. The higher number of teeth also help to increase compaction results. With a combination of our high amount of teeth combined with our smaller diameter drum we achieve the highest teeth strikes per foot which is a major factor in our ability to provide the highest compaction results.
But you won’t compact anything if you can’t get to it. The Humdinger’s TANA Series E compactors have 35 inches of ground clearance, which Phares says is higher than the competition’s. Improved traction contributes to greater uniform compaction force, creating a smooth, level surface in which high spots get maximum force applied without the blade digging in. According to Phares, maximum compaction per hour is achieved in 30–40% less time with two full-width passes, saving fuel and labor.
These purpose-built waste compactors also feature full-width twin-drum construction on a rigid frame with crushing teeth that compact 15–25% more waste per cubic yard, according to Humdinger claims. “On average, Tana compactors cover 30% more area per pass. Other machines [deliver] partly compacted [surfaces]: less area, [fewer] teeth…Waste extrudes in the middle and sides,” adds Phares.
The importance of the wheel/drum design relates to the area coverage per pass. The blade remains level for an even spread of waste. On other models, the oscillation causes one wheel to drop into voids while waste on both sides is pushed out and up, creating mounds of uncompacted waste. The blade also gouges out additional voids, thus compounding the problem. The E series reduces waste blow-out created by wheeled compactors.
There are five sizes, featuring 160 to 220 cleats per compactor to maximize crushing force and provide even load spreading for maximum compaction. “The 520 has more weight in the drum than the 450,” says Phares, “and the 380 has the back of a big machine and the front of a small machine.”
Traction and stability are critical for efficiency and safety on the working face. The tips on Cat’s wheels provide the traction and stability needed to keep the landfill compactor moving in the direction it is steered as efficiently as possible, Welch says. “The tips provide the needed traction and machine performance to move across the material as efficiently as possible and provide some shredding and pulverizing of materials.”
While the tips need to puncture garbage bags as well as shred and pulverize material, in order to efficiently compact the waste, they also need to stay somewhat exposed in order for the machine to perform in an efficient manner. If too much waste material gets packed onto the wheel, eventually causing the tips to be completely covered, then the compactor will slow down due to its inability to get proper traction. That also increases the weight of the machine from excessive material on the rotating component. All these conditions negatively affect compaction as well as maneuverability and expected life-of-equipment.
Too small of a tip and traction is compromised, whereas too large of a tip adds excessive weight to the machine, in addition to resistance to penetration into the surface. If the tips are slowing down the penetration, the wheel sinkage is limited and thus loses compaction.
Similarly, too few tips equal a loss of traction, whereas too many tips add too much weight and tend to pack mud, clay, or other material between them. A balance is needed to complement the machine’s performance.
The most recent market introductions are extended life tips where there is no mid-life wear-out or replacement necessary. These add weight but increase life. “Other than lifetime changes, the market really hasn’t offered many shape or dimensional changes,” says Welch. As the wastestream characteristics change, then the shape and size of tips might need to change.
But when it comes to choosing the right tips, the first question is, “What is the material?” says Sonnentag. “If it’s mixed, we still go with the majority ratio.” The material, face, and size determine the equipment size, not the wheels and teeth.
The most popular tip by Terra Wheels is the Terra Twist Torque. “It is the cleat of choice,” confirms Sonnentag. It features a twisted base with two puncture points that are “more blunt,” he says, in a straight-forward horizontal pattern. The larger puncture point pulverizes C&D material. The cleat base creates a lateral torque that no other tooth can accomplish, using the machine weight to force out trapped air. It exerts extreme ground pressure to reduce the size of the material. Although the Twist Torque punctures plywood, DeBrosse observes that material can stick to the cleat, but a cleaner bar system helps keep the cleat debris-free.
Terra also offers a High-Density Traction wedge for tough landfill conditions, such as inclines and slopes. The wedged cleat penetrates landfill debris and greatly reduces the size of the material. They also offer multiple cleat patterns, including chevron and inverted chevron, available in different sizes, such as 7.5- and 8.5-inch-tall cleats.
There are some additional attachments that help with cleaning and preventing material from wrapping around components. Welch mentions Debris Dams, which are welded onto the inner row of tips to prevent material from falling between the wheels and frames and wrapping around planetaries and/or axles. “These work exceptionally well with carpeting, rope, wire, and other types of materials that could wrap around wheels and components.”
There are also cleaner fingers that actually peel off mud, clay, sludge, and other sticky materials that would pack between rows of tips and cause excessive weight and loss of traction.
Caron offers its patented Double Semi-U to funnel trash under the compaction wheels when spreading refuse in order to reduce the amount of loose material under the center of the machine. The unique center splitter helps break up piles of refuse left by compactor tracks and allows smaller compactors to strike loads head-on rather than from the side.
Whether adding attachments or choosing cleat configurations, landfill operators know the key to success is compaction—reducing airspace to make room for the unending intake of trash that must be accommodated.