Original equipment manufacturers and specialist truck body builders use a variety of methods for assessing a customer’s
requirements and for translating that information into a set of criteria for selecting the right dump body.
Body of Work
Selection of the right dump body for the job requires careful thinking,
both inside and outside the box
By Russell A. Carter, Managing Editor
However, once a haul truck is released into the wild—put to work in a production environment—its carefully coordinated components must cope with the challenges of daily operations, which can range from truck or loader operator error to changing weather, road surface and rock conditions and variable material density. Probably nothing on a hauler takes more overall punishment from these external factors than the truck’s dump body. Consequently, manufacturers put a lot of engineering, not to mention a lot of metal, into their standard body configurations to enable them to provide a reasonable balance of payload rating and service life over a wide variety of possible applications. Most also offer optional configurations that can handle site-specific needs such as high-volume bodies for coal or ultra-lightweight designs for deep pits, and specialist body suppliers provide even more alternatives to standard styles.
In pursuing the contradictory ultimate goals of achieving the lightest possible truck body with the highest possible payload rating and acceptable service life, OEMs and specialist suppliers alike employ an increasingly sophisticated set of tools, such as Finite Element Analysis (FEA), to design their body styles and have developed worksheets that help customers identify and select the best body for their business. But body design can’t be an isolated engineering exercise in the overall truck design process; even though each pound removed from empty-vehicle weight may potentially represent another pound of payload, under actual operating conditions the payload volume, fill factor and distribution within the body can impose unexpected and often damaging stresses on the truck’s frame and tires under everyday conditions. Added to the equation are the variables introduced by differing degrees of impact and wear protection (liner packages) necessitated by customer and site demands.
Liebherr’s introduction of the radical TI 274 hauler at Bauma 2007 provided a new design approach for handling the interplay of stresses between body and frame. The six-wheel, diesel-electric TI 274 has two side-by-side independent rear axles with all four rear wheels independently driven by individual motors. Engineered for greater stability, the truck’s rear suspension and dump body support points are spaced farther apart and integrated into the dump body of the truck. The hoist cylinders were also relocated to the front of the chassis, which allows the forces created by the payload to be directed straight to the ground for a more optimized chassis weight. They also provide continuous support of the dump body and payload, not just during the dump process, the company said.
Repositioning the dump body also reduces weight on the truck frame, and external support mechanisms in the hoist cylinders direct forces away from internal components and help to absorb load impacts. New guides added to the hoist cylinders limit lateral movement during operation. Castings were integrated to the high-stress areas of the dump body, and a specially designed transverse beam was incorporated to perform the functions of the rear cross member used in conventional frames.
The Phil MSB and rear-dump models from other specialist suppliers such as DTHi Load, Kador Engineering and Haul Supreme—all Australian firms—are conventional in appearance but can be engineered to fill either generic or specific haulage requirements. Kador, for example, recently delivered the first of seven 150-m3-capacity dump bodies it built for Komatsu Australia for installation on Komatsu 830E trucks that will be used to haul overburden at the new Clermont mine. Kador, which builds all of its bodies under license, has delivered more than 120 dump bodies for installation on haul trucks of all sizes.
DT-Hi Load Australia, or DTA, specializes in building lightweight truck bodies and claims sales of more than 700 of these units worldwide. Most of these bodies have been manufactured by DTA’s Chilean-based shareholder Desarrollos Technologicos S.A (DTSA). In October 2007, Australian drilling services company Brandrill acquired 70% of DTA for $3 million. DTSA retains 10% of the issued capital, and an individual investor holds the remaining 20%. In an ASX exchange announcement Brandrill noted that, while most of DTA’s body components have been cut and bent in Chile with kit assembly completed in Australia, it intends to eventually relocate all facets of manufacture to Australia. Brandrill also said it would maintain an ongoing component-supply agreement with DTSA until that relocation is completed. As of late 2007, DTA said it had orders in hand for 70 new haul truck bodies.
South African steel fabricator VR Steel reported earlier this year that it has developed an innovative rear-dump body with unique features that reportedly can reduce operating costs per ton. As a manufacturer of shovel dippers, hydraulic face shovel and backhoe buckets, VR Steel said it now can match loading tools with truck bodies for higher efficiency. Customers also can order custom-designed truck bodies to suit their particular operations.
According to the company, the new truck body offers an overall design that enables quicker and more reliable maintenance and repairs; a body/bowl that increases payload potential of the truck without sacrificing the overall life of the bowl, yet is more durable, lighter and empties faster; and a rounded design that reduces carryback of sticky materials.
Unique features include a ridge-back floor which provides improved load distribution on the chassis. The ridge continues into the canopy to protect against poorly distributed loads. The body shell features an integral wear package, an I-beam skeletal design improves overall durability and the top rail is designed to withstand heavy impact during loading. VR claims the body can be adapted to any make or model of truck. The first of these truck bodies are in use at the Sishen iron ore mine in Northern Cape, South Africa.
Departing significantly from conventional design is the Suspended Dump Body System built by the Duratray subsidiary of Chilean equipment manufacturer Conymet Ltda. According to Conymet-Duratray, the unique suspended body offers significantly extended wear life—typically 20,000 to 30,000 hours—when hauling hard, abrasive material as well as virtual elimination of carryback material in the truck beds. The design also is claimed to significantly reduce shock and vibration on the equipment and operator.
The Duratray unit replaces a truck body’s conventional steel floor and wear plates with a rubber mat that is suspended like a hammock above a steel framework by elastomeric transverse ropes. The suspended rubber floor never rests upon the steel frame, creating the suspension effect that Duratray claims contributes to longer body life and less frame stress. Because the flexing of the rubber mat prevents material from sticking to the tray, load sticking is significantly reduced if not eliminated, according to the company, which also claims the rubber mat provides a wear life two to three times that of a lined steel body, with up to a 20% weight savings and payload increase.
Beneath the wear mat, a rubber support acts to locate the load-bearing ropes and protect them from accidental damage when tipping. The suspension ropes have a core of polyester fibers designed to suit the required load. In order to provide the desired elasticity, the fibers are oriented to allow the ropes to stretch under load but return to original length when the body is emptied. The ropes are sheathed with heavy-duty rubber to protect the polyester fibers from dust, dirt and water. The company said each rope is individually adjustable, enabling the customer to maintain nominal clearance between the support mat and the frame of the dump body; and that intervals of 1,000 hours are normal between rope adjustments.
The welded, steel body frame, said the company, is designed to accept twisting and flexing forces associated with the suspended body. The steel front plate and side walls can be protected with wear-resistant steel or rubber liners in abrasive conditions. Rock ejectors and canopy guards are standard.
Where to Look
Considering the large number of body
styles and options offered by OEMs and
aftermarket suppliers, what’s the best way
to go about selecting the proper model for
the job? Two equipment experts from
Caterpillar suggest customers begin by
looking at their mine or project, not at sales
brochures.
At Caterpillar’s 2007 Global Mining Forum, Keith Underwood and Rod Bull provided a detailed summary of the factors that play major roles in body selection, ranging from rock properties to operational issues (loading equipment and dumping practices, for example). One way to get a good general idea of the type of body needed, they noted, is to look at the age of the mine at which the equipment will be used. Is it a mature mine with excellent, timetested blasting and loading techniques and a solid maintenance program? If so, a lightweight body could be the best choice. If it’s a greenfield project or will involve contractor mining—situations often involving new operators and/or new practices and an untested maintenance program—the best choice may be a body style that reduces potential maintenance problems, such as a standard body with a hefty liner package.
Once a general body style is determined, body sizing becomes important. According to the Cat experts, bodies are sized to handle the lightest material on site; if there are areas of the mine that contain heavier materials, haulage from that area might require payload management. Fill factor is another consideration: No material provides a perfectly consistent, homogenous load; there are always cavities, or voids, in a truckload—with some types of material creating more than others. Rock or overburden is generally considered to have an 87% fill factor, while coal is around 90%–95%. In addition to the range of body sizes available to meet targeted payloads, sideboards and tailgates are options that can be used to gain additional load flexibility when dealing with certain kinds of materials or conditions.
For determining impact and wear protection packages, Underwood and Bull recommend using FACLT—a Caterpillar acronym for a process that evaluates blast Fragmentation, material Abrasion and Cohesion, and Loading Tool characteristics to make a liner selection. Although the complete details of the process are beyond the scope of this article, here are a few guidelines:
Fragmentation—Bodies that aren’t lined to provide adequate protection against the impact force of the rock fragments that will be loaded will quickly show deterioration and cracking in the understructure. Understructure damage is expensive to fix and significantly shortens body life. Fragment size, along with the type of loading tool used, will play a major role in determining the location, liner type and liner thickness required.
Abrasion—Look for abrasion wear indicators elsewhere first; loader bucket tip wear, for example. Minimally abrasive material would allow a tip life of 20,000 hours or more; severely abrasive material can cut tip life to less than 500 hours. If previous body liner packages wore out in less than 10,000 hours, abrasion is considered severe; if the package lasted more than 20,000 hours, abrasion is minimal. For truck bodies, the areas that require wearspecific focus are the rear one-third of the bed, the middle section and the transition between the floor and sidewall.
Cohesion—Sticky material that results in carryback can degrade the accuracy of payload monitoring systems, resulting in possible overloading if the monitoring system simply ignores the carryback weight. Smooth plate liner material is recommended for the rear third of the bed. Another solution can involve installation of octagonal or “stop sign”-shaped plates in the bottom front corners of the bed; when combined with exhaust heating, this measure often can be useful in stopping carryback from building up in the front of the bed and then accumulating down the sides.
Loading Tool—The type of loading tool is important in determining liner placement and thickness. Some types loading equipment may impose specific kinds of impact on the body that others don’t and viceversa— large wheel loaders vs. front shovels or backhoes, for instance— and liner packages should take into account the characteristics of the loading tool. However, at mines where different loading tools will be used with the same truck, the body must be lined to meet the requirements of the most “severe” loading tool. In any case, proper loading technique is extremely important for minimizing body maintenance and maximizing service life.
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