Dump truck
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A dump truck or production truck is a truck used for transporting loose material (such as sand, gravel, or dirt) for construction. A typical dump truck is equipped with a hydraulically operated open-box bed hinged at the rear, the front of which can be lifted up to allow the contents to be deposited on the ground behind the truck at the site of delivery. In the UK the term applies to off-road construction plant only, and the road vehicle is known as a tipper or tipper lorry.
[edit] Types of dump trucks
The dump truck was first conceived in Saint John, New Brunswick when Robert T. Mawhinney attached to a dump box to a flat bed truck in 1920. The lifting device was a winch attached to a cable that fed over sheave (pulley) mounted on a mast behind the cab. The cable was connected to the lower front end of the wooden dump box which was attached by a pivot at the back of the truck frame. The operator turned a crank to raise and lower the box.[1] [2]Today, virtually all dump trucks operate by hydraulics and they come in a variety of configurations each designed to accomplish a specific task in the construction material supply chain.
[edit] Standard dump truck
A standard dump truck is a full truck chassis with a dump body mounted to the frame. The dump body is raised by a hydraulic ram mounted forward of the front bulkhead, between the truck cab (traction unit) and the dump body (semi-trailer). The tailgate can be configured to swing on hinges or it can be configured in the "High Lift Tailgate" format wherein pneumatic rams lift the gate open and up above the dump body.
A standard dump truck has one front axle, and one or more rear axles which typically have dual wheels on each side. Common configurations for a standard dump truck include the six wheeler which has one rear axle, the ten wheeler with two rear axles, and the tri-axle with three rear axles. These are mainly found in inner cities and in the deep south. The largest of the standard dump trucks is commonly called a "centipede" and has seven axles. The rear two axles are powered and the front axle is the steeing axle. The intermediate axles are present to support the weigh over the length of the chassis and sometimes to provide additional braking power.
The short wheelbase of a standard dump truck makes it more maneuverable than the higher capacity semi-trailer dump trucks.
[edit] Articulated dump truck
An articulated dump truck has a hinge between the cab and the dump box, but is distinct from semi trailer trucks in that the cab is a permanent fixture, not a separable vehicle. Steering is accomplished via hydraulic rams that pivot the entire cab, rather than rack and pinion steering on the front axle. This vehicle is highly adaptable to rough terrain. In line with its use in rough terrain longer distances and overly flat surfaces tend to cause driveline troubles, and failures. Articulated trucks are often referred to as the modern scraper, in the sense that they carry a much higher maintenance burden than most trucks. See the first mass produced articulated dump truck (articulated hauler): [1]
[edit] Transfer dump truck
A transfer dump (colloquially referred to as a "Slam-Bang!" because of the noise made when transferring) is a standard dump truck which pulls a separate trailer which can also be loaded with aggregate (gravel, sand, asphalt, klinker, snow, wood chips, triple mix, etc.)
The second aggregate container, (B box) on the trailer which is powered by either an electric, pneumatic motor or hydraulic line from a PTO (power take off) mounted on the transmission of the tractor, rides on small wheels and rolls on rails off of the trailer frame and into the empty main dump (A) box. The key advantage of this configuration is to maximize payload capacity without sacrificing the maneuverability of the short and nimble standard dump truck. Transfer dumps are typically seen in the western United States because of the peculiar weight restrictions on western highways.
Another configuration seen is called a Triple Transfer Train, which consists of a B and C box. These are common on Nevada and Utah Highways but not in California. Depending on the axle arrangement, a Triple Transfer can haul up to 129,000 with a special permit in certain US states. The Triple Transfer usually costs a contactor about $105 an hour while a A/B config usually runs about $85 per hour (2007 stats).
[edit] Truck and pup
A truck and pup is very similar to a transfer dump. It consists of a standard dump truck pulling a dump trailer. The pup trailer, unlike the transfer, has its own hydraulic ram and is capable of self-unloading.
[edit] Superdump truck
A Superdump is a straight dump truck equipped with a trailing axle, a liftable, load-bearing axle rated as high as 13,000 pounds. Trailing 11 to 13 feet behind the rear tandem, the trailing axle stretches the outer "bridge" measurement—the distance between the first and last axles—to the maximum overall length allowed. This increases the gross weight allowed under the federal bridge formula, which sets standards for truck size and weight. Depending on the vehicle length and axle configuration, Superdumps can be rated as high as 80,000 pounds GVW and carry 26 tons of payload or more. When the truck is empty or ready to offload, the trailing axle toggles up off the road surface on two hydraulic arms to clear the rear of the vehicle. Truck owners call their trailing axle-equipped trucks Superdumps because they far exceed the payload, productivity, and return on investment of a conventional dump truck. The Superdump and trailing axle concept was developed by Strong Industries of Houston, Texas.
[edit] Semi trailer end dump truck
A semi end dump is a tractor-trailer combination wherein the trailer itself contains the hydraulic hoist. A typical semi end dump has a 3-axle tractor pulling a 2-axle semi-trailer. The key advantage of a semi end dump is rapid unloading. A key disadvantage is that they are very unstable when raised in the dumping position limiting their use in many applications where the dumping location is uneven or off level.
[edit] Semi trailer bottom dump truck
A semi bottom dump (or "belly dump") is a 3-axle tractor pulling a 2-axle trailer with a clam shell type dump gate in the belly of the trailer. The key advantage of a semi bottom dump is its ability to lay material in a wind row (a linear heap). In addition, a semi bottom dump is maneuverable in reverse, unlike the double and triple trailer configurations described below. These trailers may be found either of the windrow type shown in the photo, or may be of the 'cross spread' type with the gates opening front to rear instead of left and right. The cross spread gates will actually spread gravel fairly evenly the width of the trailer. by comparison, the windrow gates leave a pile in the middle. The cross spreads jam and do not work well with larger materials. Likewise they are not suitable for use where spreading is not desired such as when hot asphalt paving material is being dumped in front of a paving machine.
[edit] Double and triple trailer bottom dump truck
Double and triple bottom dumps consist of a 2-axle tractor pulling one single-axle semi-trailer and an additional full trailer (or two full trailers in the case of triples). These dump trucks allow the driver to lay material in wind rows without ever leaving the cab or even stopping the truck. The main disadvantage is the difficulty in backing double and triple units in reverse.
The specific type of dump truck used in any specific country is likely to be closely keyed to the weight and axle limitations of that jurisdiction. Rock, dirt and other types of materials commonly hauled in trucks of this type are quite heavy, and almost any style of truck can be easily overloaded. Because of this, this type of truck is frequently configured to take advantage of local weight limitations so as to maximize the allowed weight. For example, within the United States, a maximum weight limit of 40 tons is mandated throughout the country except for specific bridges that may not be safe with that weight, however, individual states in some instances are allowed to authorize trucks up to 52.5 tons, however, most states that do so, require that the trucks be very long so as to spread the weight out over more distance. It is in this context that you see the double and triple bottoms within the United States.
[edit] Side dump truck
A side dump truck consists of a 3-axle tractor pulling a 2-axle semi-trailer. It has hydraulic rams which tilt the dump body onto its side, spilling the material to either the left or right side of the trailer. The key advantages of the side dump are that it allows rapid unloading and can carry more weight in western United States. In addition, it is almost immune to upset (tipping over) while dumping unlike the semi end dumps which are very prone to tipping over. It is, however, highly likely that a side dump trailer will tip over if dumping is stopped prematurely. Also, when dumping lose materials or cobble sized stone, the side dump can become stuck if the pile becomes wide enough to cover too much of the trailer's wheels. Trailers that dump at the appropriate angle (50° for example) avoid the problem ove the dumped load fouling the path of the trailer wheels by dumping their loads further to the side of the truck, in some cases leaving sufficient clearance to walk between the dumped load and the trailer.
[edit] Off-road dump truck
Off-road dump trucks more closely resemble heavy construction equipment or engineering vehicles than they do highway dump trucks. They are used strictly off-road for mining and heavy dirt hauling jobs.
The term ‘Dump’ Truck is not generally used by the mining industry, or by the manufacturers that build these machines. The more appropriate US term for this strictly off road vehicle is, ‘Haul’ truck. The classification bottom and side for example, describes how the loaded material is discharged once loaded. In the case of the Haul truck illustrated, a Liebherr T 282B the load is discharged to the rear, designating this particular vehicle as an end dump. Bottom dump normally describes a trailer that discharges its load by opening two clam shell doors under the load space, in some examples several trailers (road train) are pulled by one truck mainly these are on road machines. The only remaining example of what is described as a unitized bottom dump coal hauler is manufactured by Kress Corporation. This large capacity truck is used for the transportation of coal from a loading device (shovel) directly to a power station or bulk storage area.
One of the largest dump trucks currently available is the Caterpillar 797B, which has a payload of 400 tons and can travel at 42 mph. It is powered by a 24-cylinder diesel engine that is rated at 3,300 hp (2,461 kW). Caterpillar 797-series dump trucks are extensively used in oil sands in Alberta, Canada.
[edit] Winter service vehicles
Many winter service vehicle units are based on dump trucks, to allow the placement of ballast to weigh the truck down or to hold sodium or calcium chloride salts for spreading on snow and ice covered surfaces.
[edit] Dangers
Potentially flying goods must be covered (i.e. using a tarpaulin, straps, or rope) to prevent loose material from flying outside the bed while the truck is moving, potentially damaging other vehicles. Also, heavier items loaded over the edge of the truck must be secured to prevent them from dropping off the truck in turns, on bad roads, or when braking the vehicle.
Dump trucks are normally built for some amount of off-road or construction site driving; as the driver is protected by the chassis and height of the driver's seat, bumpers are either placed high or omitted for added ground clearance. The disadvantage is that in a collision with a standard car, the entire motor section or luggage compartment goes under the truck. Thus, passengers in the car could be more severely injured than would be common in a collision with another car. Several countries have made rules that new trucks should have bumpers approximately 40 cm (20 in) above ground in order to protect other drivers better. There are also rules about how long the load or construction of the truck can go beyond the rear bumper to prevent cars that rear-end the truck from going under it.
Another safety consideration is the leveling of the truck before unloading. If the truck is not parked on a relatively horizontal ground, the sudden change of weight and balance due to lifting of the skip and dumping of the material can cause the truck to slide, or even - in some light dump trucks - to turn over.
[edit] Education
The National Association of Heavy Equipment Training Schools (NAHETS), established 2002, uses dumptruck training and schools curriculum as a method to test and train users in the ability of dump truck use.
[edit] See also
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[edit] Vehicle types[edit] Other |
[edit] References
- ^ Mario Theriault, Great Maritme Inventions 1833-1950, Goose Lane Editions, 2001, p. 71
- ^ Sketch of the first dump truck
