Slow and Steady

Sudden, major technological breakthroughs are not necessary for improved productivity and performance for any technology. For a mature technology such as tippers and live floors, incremental improvements accumulated over time can have a major impact on the entire waste management industry. In this case, the technology in question is the mechanical means of efficiently offloading waste at the landfill working face by the use of tippers and live floors. In keeping with the theme of this article, these improvements have been “slow and steady” in the areas of hydraulics, leak prevention, safety improvements, and controls. Individually, by themselves, each advancement may be small but taken all together they add up to increased overall operation efficiency and the improved productivity of the equipment that utilizes both tipper and live floors—transfer trailers. These specialized trucks are the vehicles used to transport bulk quantities of waste economically from Point A (the transfer station) to Point B (the landfill).

Point A—Transfer Stations
Transfer stations allow for the economical long-distance hauling of waste. They do so by providing a focal point where multiple waste collection trucks can offload their daily waste loads into larger transfer trailers situated at the transfer stations. The transfer trailers are designed to carry large bulk loads of waste over long distances in an economical manner. And they achieve this through economy of scale. They do it so well, they justify the upfront capital costs of constructing the specialized transfer station buildings to accommodate them. Fewer and large trucks are economical if only for the labor costs, as they require fewer drivers to haul the same amount of waste. Fuel cost savings are also incurred as a single large truck with multiple axles can carry a heavier load for longer distances while consuming less fuel. Lastly, fewer vehicles to maintain and repair means lower upkeep and maintenance costs.

Transfer stations are the second step of a daisy chain of operations that collect, haul, and consolidate wastestreams. The first step is the curbside collection of household and commercial waste by waste collection trucks. The second step is the hauling of these individual waste loads to a centrally located transfer station. The third step is the offloading and transfer of this waste into transfer trailers parked at the transfer station. The fourth step is the long-distance transport of accumulated waste by transfer trailers to either a waste-to-energy plant, recycling facility, or landfill for final dis­position. Some transfer stations utilize river barges or rail cars to ­perform this fourth step. Each transfer station’s purposeand function is essentially the same, accounting forregional differences in population, hauling distances, waste generation rates, and roadway network (or other regional transportation infrastructure).

However, the size, layout, and internal operations of each transfer station can vary widely. Each is related to the size dependent on the amount of the incoming wastestream with the floorplan layout matching its operational requirements (a perfect example of “form follows function”). The wastestream inflow rate drives both the size of the tipping floor where the waste is deposited for transfer to the trailer trucks and the exterior property requirements necessary to accommodate anticipated truck queuing lengths.

Once the overall size requirements are determined, the detailed design of the transfer station can be worked out. The typical size would accommodate trucks with over 100 cubic yards of capacity. The large hauling truck mitigates the need for potentially expensive compaction and baling operations for reducing the volume of the outgoing waste. The simplest design has a series of recessed bays or pits large enough for a transfer truck to back itself into and park. Adjacent to these pits is an elevated tipping floor where the waste collection trucks stop to deposit their loads. Made of reinforced concrete and often including steel beams in its surface for reinforcement, the size and dimensions of a tipping floor are determined by the waste transport rates (both in and out of the transfer station) with its overall dimensions governed by the number and arrangement of the adjacent truck pits. Once deposited on the tipping floors, the waste is pushed into the top of transfer trucks parked in the adjacent pits, a task usually performed by either wheeled front-end loaders or dozers. Once filled, loads of uncompacted waste are then covered with a protective tarp and the truck exits the station to transport its load to its final destination.

However, there is usually a mismatch between waste deposit rates (measured in cubic yards per hour) and waste hauling rates. Waste often arrives faster than it can be loaded. The first is determined by the local waste collection and hauling schedule, while the second is a function of the number and size of available transfer trucks. So, during daily operations, deposited waste tends to accumulate on the tipping floor until waste hauling operations cease for the workday Truck loading and hauling continue afterward until the waste has been completely removed and hauled away.

This is why even basic transfer stations tend to utilize a substructure called a surge pit. This is not necessary to utilize any kind of compaction technology, just a recessed floor area lower than the tipping floor with enough airspace to safely and conveniently contain peak daily amounts of incoming waste. It serves as an intermediate step, with the dozers and front-end loaders first pushing the excess waste into the surge pit before it is then lifted and loaded into the transfer trailers. Once in the pit, compaction can be performed utilizing the station heavy equipment if its operating plan calls for it. This is accomplished by having the equipment run back and forth on the top of the accumulated waste (impacting it both the with dynamic loading of the equipment’s movement and its dead weight) or shoving up against the rigid side walls of the pit. This has the effect of increasing the waste’s density and reducing its volume prior to loading and makes for even more efficient hauling operations.

Higher degrees of compaction can be achieved with specialized equipment. These include balers and hydraulic rams. Balers compress the waste into large high-density “bricks,” often securing with steel wire. Once compacted, the waste can be managed with forklifts. This allows for the use of simpler, less expensive trucks, such as a flatbed truck, for hauling. However, the baling equipment itself can be very expensive and tends to be utilized at large-scale transfer stations. Stationary hydraulic rams, on the other hand, actually compact the waste while it is being loaded onto the truck. By shoving it into the rear of the truck until it reaches the front end of the truck bed, high densities can be achieved but high pressures are also created that affect the truck body. As a result, the truck body frame has to be reinforced, adding to its cost and weight in exchange for more efficient high-density waste hauling.

Point B—Offloading Transfer Trailers at The Landfill
Transfer trailers are not generic; they each come with different designs and unique features. Since the whole idea of using transfer trailers is to reduce cost, rugged reliability is a primary concern of transfer trailer design and construction. And these trucks take a lot of abuse. Waste gets dropped into their beds from a significant height (impacting the floor) or gets rammed into place (impacting the side walls). Waste itself, especially when compacted, has a significant density and contains large, often sharp and abrasive, objects. The moisture content inherent in the collected waste can also lead to long-term corrosion and rust issues, especially of surfaces that have had their protective surface coatings worn away. So, the initial construction of the truck’s suspensions, engine specifications, brakes, tires, drive train, framework, and body surfaces have to be done with an eye to long-term survivability under harsh operating conditions. These improved features also add to the vehicle’s inherent safety—the primary concern of all waste hauling operations. All of the above changes make for a different kind of truck design than most over-the-road trucks. This includes the mechanism used to offload the trucks once they reach their destination.

The simplest method of offloading a waste hauling truck is to self-unload, using hydraulic jacks to tip the bed of the truck into near vertical conditions causing the waste to empty out the rear. This method utilizes hydraulic lift jacks installed between the bottom of the truck bed and the underlying truck frame. As the hydraulic pressure within the piston increases, the jacks extend in length, raising up the bed. Once offloaded, the pressure in the jacks is released, causing the arms to shorten to their original length and the bed to fall back into its flat position. The use of hydraulic jacks creates potential safety issues, especially at sites where there is limited vertical clearance. Raising the truck bed without support can also lead to instability when performed on a sloped or unstable landfill working face. There are also limits as to the force that can be exerted by the hydraulic jacks, which limits the weight of the allowable load or requires more expensive hydraulic systems.

The next method of offloading a transfer trailer is the live floor. This is a very efficient method of offloading large loads and consist of a series of parallel steel planks arranged horizontally along the entire length of the bed from front to rear. One to three planks at a time rise up and fall in a sequence that creates a wave motion from the front of the bed to the open rear. This wave motion created by a repeating and reciprocating sequence of planks rising and falling lifts and moves the waste backward to the offloading direction. Further efficiency is achieved when this movement is augmented by a hydraulically operated pusher blade.

Not having to raise the truck bed to offload provides considerable operational flexibility and improved safety. Existing trucks can be retrofitted with a walking floor system (along with the additional hydraulics and a reservoir kit required to operate the live floor), which is relatively easy to install, affording a cheap upgrade for existing vehicles. And while this represents an additional cost, it is comparable to the cost of a hydraulic jack system and allows for offloading even heavy loads of waste. And not having to utilize a site-specific mechanism for offloading the truck frees the transfer trailers to go to different and remote locations no matter what site equipment is available.

The last method of offloading the transfer trailer does not rely on the truck at all. Instead, pre-sited tipper facilities are installed at a fixed location at the landfill. This method involves the truck driver backing his trailer into position with the help and guidance of a spotter to a position over the tipping mechanism. Once in position, the truck bed is detached from the truck’s supporting framework and left in place on the tipper. The rest of the truck is driven back out of position to a safe location outside the tipper’s operational area. The tipper than raises the front end of the truck bed to a vertical 90 degrees, allowing the waste to fall out of its rear. Shortly after the waste has been removed, the truck can be backed into position once again and the truck bed reattached to the frame. Having completed its offloading, the truck can drive offsite, allowing the next truck in the queue to perform its offloading. Though the procedure may sound complicated with its multiple steps, the entire process can take half the time that a self-offloading truck does. This increased productivity makes a tipper suitable for large-volume waste management operations, which further justifies their initial upfront capital costs.

Being a large separate mechanism, a fixed tipper can exert much greater force from a more powerful immobile hydraulic system. Portable tippers with less hydraulic power are also available. The tippers themselves can be hauled around the site as needed during the course of landfill disposal operations. Rather than spend the cost of outfitting every truck in the hauling fleet with its own hydraulic offloading system, a single point tipping operation represents a significant cost saving. Furthermore, not having to install an offloading system reduces vehicle weight and with it, the cost of fuel per mile—or conversely, the truck can carry a heavier load of waste. Additionally, not having to maintain a complicated hydraulic system results in less money spent on vehicle upkeep and repair. However, if the operational efficiency and productivity of the tipper are insufficient, it can also become a bottleneck with a long queue of trucks waiting to be serviced. Also, by definition, the use of a tipper limits the location(s) where waste can be offloading, leading to a loss in operational flexibility at the working face. Waste ends up being deposited in a relatively small area which is good for limiting and controlling the area of the landfill working face, but potentially bad if there is not enough elbow room to choreograph the landfill’s equipment spreading and compacting the waste in place.

So which system works best? The answer of course is: “that depends.” Certain situations have to occur to justify to purchase of specialized transfer truck offloading equipment. ­Tippers have high productivity rates and are therefore most useful at large landfills with high daily waste disposal rates. But if waste receipts are greater during peak operating hours, a large truck queue can form waiting to use the tipper and causing reduced overall production efficiency. Individually they represent a large upfront capital acquisition cost, but they save on having to install hydraulic offloading mechanisms in each waste hauling truck. They limit the area of a waste dropoff which allows for better control of waste placement operations but can constrict the movements of the equipment performing this placement if the area is too small. Live floors allow for safer and more efficient disposal than standard hydraulic jack systems and can handle heavier payloads while allowing operation flexibility in load placement at the landfill working face with multiple trucks offloading simultaneously instead of waiting in a queue. Live floors are ideal where vertical space is limited at the disposal point, a situation typically found at materials recovery facilities (MRFs). But in any case, live floors represent an additional capital cost and maintenance demand that has to be justified by the projected increase in offloading efficiency.

Overall, victory will go to the most innovative system, which brings us to the leading innovators in the field of live floor and tipper technology.

Industry Innovators
East Manufacturing Corp is a leader in refuse trailer technology designed to reduce weight and guard against corrosion. According to Charlie Benton, Product Manager, Refuse Trailer at East, they continuously design trailers with the latest technological advances in equipment. The results are waste trailers equipped with components that reduce weight yet maintain the ideal balance of weight and strength. In addition to reducing weight, East incorporates components and procedures to guard against corrosion to increase life and residual value.

To accommodate additional payload, East strives to reduce the tare weight of its refuse trailers. They utilize technological advances in new alloys and extrusion design to reach these goals. Light weight is not the only goal. East achieves a high strength-to-weight ratio. One of these advances is embodied in the new Truck-Lite 99 Series wiring harness which will soon be standard on all new East Tipper and Unloader trailers. The Truck-Lite 99 Series is designed as a closed system by integrating a molded plug with two sealing surfaces, rather than just one. This two-seal plug keeps moisture and debris out of the plug, guarding against corrosion. Truck-Lite is the first harness manufacturer to design a trapezoid-shaped connection, which makes installation quick and easy, and it allows the operator to be confident that he has a proper pin alignment and a positive lock.

East finds weight savings in the truck’s wheels as well as its frame. East uses Alcoa Ultra ONE 22.5 x 8.25 wheel as standard on all of its trailers specified with 22.5 dual-tire setups. At just 40 pounds, the Ultra ONE Wheel is the lightest wheel in its class. The Ultra ONE wheel delivers high strength for unprecedented weight savings. Its one-piece forged aluminum strength is five times stronger than steel wheels with a 7,400-pound load rating and 130 psi inflation rating.

The JOST International AX150 Alumilight Series of landing gear is an option on all Tipper and Unloader refuse trailers. With no external gearbox that can be damaged and affect performance, the JOST Alumilight series aluminum landing gear is up to 50 pounds lighter per set than competitive landing gear for added payload and corrosion resistance. Its 6061-T6 extruded aluminum upper leg combined with a Polyester-coated HSLA steel lower leg provides durability to stand up to the harshest conditions. The gearing mechanism is integrated into the sturdy leg column, so it protects the gearing and significantly minimizes water intrusion. A silicone-sealed steel cover keeps moisture out to further protect the landing gear from water and road chemical damage and freezing. East also reverse mounts the landing gear legs on the wing brackets for more stability when the trailer is loaded.

East finds weight reductions even in the hydraulic systems. East recently made aluminum air tanks standard on its refuse trailers. Weighing 10.7 pounds less, the aluminum air tanks are made with a less corrosive and lighter material than steel air tanks. Air tanks on trailers provide air pressure volume to operate the pneumatic system, including brake actuation and suspension performance (including lift axles, steer axles), tire inflation and more. Since each East trailer (tandem axle) has a minimum of two tanks, a tandem-axle trailer has 21.4 pounds less weight. The more axles that are added to a trailer, the more tanks are required. For instance, each lift axle and each steerable axle requires an additional tank. In addition to the lighter weight, the aluminum is less corrosive.

And East is a leader in corrosion resistance technology. East uses 20-mil high-density polyethylene (or HDPE) plastic in conjunction with ECK Corrosion Prevention Coating during the assembly process for every trailer. The HDPE is die-cut to match areas covered and then both sides are coated with ECK. ECK is the only coating product proven to prevent dissimilar metal corrosion, preventing electrolytic reactions between aluminum and steel as well as other dissimilar materials. ECK prevents this corrosion in three ways. It seals out moisture and the road de-ice chemicals, providing a barrier between dissimilar metals, and its Zinc powder and Zinc dust absorb the natural corrosive energy. East also offers an aftermarket Anti-Corrosion Hanger Kit, which includes an HDPE sheet and the ECK coating. Custom templates are available.

The lighter weight is not purchased at the expense of durability and reliability. The East Elite Wheel-End assembly recently increased its warranty from 5-Year 350,000 Miles to 5-Year Unlimited Miles. The industry-leading parts used include Walther EMC’s Dura-Light Hub (lightweight austempered ductile iron [ADI] hub), General Hyatt HM Bearing Cones, SKF Scot Seal Plus XL Seal and Retainer, Dual Dynamics Aluminum Hub Caps, Axiloc Unitized Wheel Bearing Nut System.

There are numerous differences between a tipper and a moving floor (East Unloader) refuse trailer. The tipper refuse trailer is typically used for high-volume operations, where the load is unloaded using a landfill tipper. Because small landfills do not have the tonnage to justify an expensive tipping platform and busy landfills often lead to long wait times, the moving floor refuse trailer with its flexibility to unload at any landfill is preferable, since a moving floor trailer can also be easily tipped and used in the landfills with tipping platforms.

Together with the emerging technologies from suppliers and development of new alloys, East has equipped its refuse trailers with components that reduce weight while maintaining the ideal balance of weight and strength and that also guard against corrosion to increase life and residual value.

East manufactures aluminum flatbed, drop deck, dump, and refuse trailers as well as aluminum truck bodies for the commercial vehicle industry. East aluminum trailers are designed to maximize payload, delivering strength and durability to meet the needs of a wide variety of trailer applications. By incorporating the lightest-weight and longest-lasting components into every trailer, East trailers have earned the reputation of having higher resale value.

Mac Trailer Manufacturing is a leader in the manufacturing of tipper and moving floor transfer trailers. They build trailers designed to withstand the demanding conditions of waste hauling operations: abrasive operations, corrosion, and the loading and unloading of mass volume and heavy bulk materials from waste, to wood, to agricultural, to recyclables, to scrap. Their moving floors utilize the design-construction of either the original fully welded aluminum sheet and post with side skins to a gauge of 0.250, or the smooth sided “MVP” (MAC Vertical Panel) MACLOCK configuration that incorporates 2 1/4-inch hollow core aluminum extruded panels. Slats and decking components range from the aluminum smooth surface traditionally used for movement of agricultural-wood materials, the high-impact designs for solid waste, or the steel slat for abrasive loads of scrap, white goods, crushed cars, or sand. Similarly, the MAC Tipper maximizes volume while minimizing tare weight. Designed for the long haul, it comes in tapered designs with lengths to 53 feet and can provide volumes up to 148 cubic yards. The design can consist of fully welded sheet and post or the greater capacity “MVP” MACLOCK extruded aluminum panel construction.

Since the 1980s, Western Trailers has been engineering strong, lightweight refuse trailers for the North American market. Western Trailers manufactures trailers for all types of refuse hauling including C & D, MSW, dewatered sludge, urban wood, and both green and food waste. Trailer lengths range from 28 to 56 feet with payload capacities and axle configurations designed to maximize loads in your area. All Western refuse trailers use a high tensile steel mainframe that is treated to a level 4 paint system. The level 4 paint process includes steel grit blast on all steel parts, acid etches, catalyzed urethane primer, catalyzed acrylic top coat, and infrared bake. When the paint process is complete, our weight-saving impact and corrosion-resistant upper structure is installed. All Western tipper trailers are standard with Hard Ox floors giving Western the durable flooring. All Express Floor Refuse trailers are available with floors from either Hallco or Keith Manufacturing. All Western Refuse trailers are standard with top hinge rear doors with options available for side swing and double swing rear doors. Rear corners and bumpers are reinforced and suitable for all types of tippers. Compactor rear bumpers are availabl