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Rough-terrain forklifts have to deal with more than just rough terrain. Such terrain almost always means constant outdoor use, so they must perform equally well in hot, arid climates; frigid temperatures and other Arctic-like conditions; and everything in between. But these conditions do not minimize those of rough terrain, where steep grades produce wide swings in loads and uneven ground can transmit shock throughout a machine’s hydraulic system.
Kalmar Global manufactures a wide variety of off-highway equipment, including the RT022 rough-terrain telescopic forklift. Compact enough to drive right inside a container, it features two-wheel, four-wheel, and crab steering modes for excellent maneuverability on the most challenging surfaces. With side-shifting forks for container loading and unloading, and a tight turning radius of just 30 ft., the RT022 is well-suited for lifting operations in tight spaces.
With a lifting capacity of 5,000 lb., the RT022 is used to handle ISO containers, which primarily contain supplies and ammunition for expeditionary operations. The machines are small enough to drive directly into a container and can ford water up to 0.9 m (3 ft.) deep.
Randy Wingenroth, Vice President of Product Development at Kalmar, says that Eaton’s DuraForce hydrostatic drive train provides the best cost/performance ratio: “The performance of the RT022 has met the demanding needs of the application, and this success has been due, in part, to the DuraForce product and the support we’ve received from Eaton.”
DuraForce pumps and motors use an unconventional rotating kit that replaces the traditional bronze piston slipper with a steel version. In so doing, the DuraForce product strengthens a traditional weak link of piston product design. Other design features, such as the rigid housing and hydrostatic bearing, ensure high reliability under high duty cycles at peak operating pressures to 500 bar (7,250 psi).
Vince Duray, Product Manager at Eaton Hydraulics, says, “Eaton’s DuraForce products have been installed on more than 1,000 machines so far, with no issues in the field. Eaton’s DuraForce product line offered Kalmar both a solution that could meet the 15-year life criteria as well as a consistent and precise torque delivery to the wheels to meet their performance requirements. These characteristics were available in an out-of-the-box system solution that Kalmar could leverage for their drive train. The DuraForce solution saved Kalmar a lot of time and development cost that otherwise would have been required with an on-board controller and custom software development."
Regarding the 15-year life requirement, Duray added, "DuraForce is a high-pressure product with a peak pressure rating of 500 bar. The robust design begins with an innovative piston-shoe assembly that offers greater strength in the primary pumping mechanism of the product. The stronger design also offers increased flow from a similar package size so the DuraForce power density is increased over other axial product.
"The precise and repeatable torque delivery is achieved from the DuraForce pump and motor though the pump’s low-speed control and the high operating efficiency of both products. The pump’s displacement control, which determines the flow output, is an independent, dynamic and balanced hydrostatic circuit within the pump. This design feature creates a pump flow control behavior that is independent of external factors such as load on the machine, traveling speed, or ambient temperature. The pump and motor are also designed to be highly efficient through the operating range. The DuraForce motor offers very high starting torque efficiency that provides machine movement at very low engine speeds."
For more information on Eaton's Durforce pumps and motors, including a video and case histories, click here.