Mobile material handling machines rely heavily on hydraulic technologies which pair well with the robust, sometimes challenging environments these machines work in.
By Josh Cosford • Contributing Editor
Material handling machines are some of the most widespread hydraulic applications developed. Where you must move product or material, a hydraulic machine is available to help. Industrial material handling often involves lifting, rotating, flipping, or moving products. The movement may lie within a process, such as a bin tipper that fills a hopper or the straightforward relocation of finished material.
Mobile material handling offers users a more diverse selection of machinery. The possible applications are focused on moving materials such as stone, lumber, scrap metal, recycling, freight, and produce, just to name a few. Although by all means no industry standard, a common material handling platform looks much like an excavator. With tracks or wheels and a large boom attached to a slew-driven body, it’s easy to confuse these versatile machines with their cousins. Literally called “material handling machines,” these versatile hydraulic vehicles offer a solution to many material handling challenges.
Elevated, adjustable cab allows easy reaching
The elevating cab is common to mobile material handling machines, which provides a field of view high above the ground to provide a bird’s-eye view of the work area. The adjustable-height workstation rests low like an excavator, yet using hydraulic cylinders will lift the boom many feet higher. The elevated perspective gives the operator a better view of the scrap piles, dump truck bodies, compactor hoppers, or lumber piles.
The adjustable cab height allows easy work in locations difficult for other machinery to reach, such as over a fence where arborists have felled and sawed a tree. High-lift machines offer an additional 6 ft or so for more extreme height requirements by elevating the entire slewed portion of the machine (Figure 1).
Every actuator on material handling machines is hydraulically powered; the arm, boom, slew, drive, and grapple. Using the same horsepower-limiting, load-sensing hydraulic piston pumps as excavators, these systems provide powerful, efficient hydraulics offering the highest possible combination of power and speed for any given power output. The horsepower limiting pump uses an extra internal valve that caps the power output of the pump regardless of demand. Essentially, this pump always offers maximum flow until load pressure rises above the power setting, which is a product of pressure and flow. Pressure always trumps flow, and when the operator demands high speed and force, the pump will reduce flow (and therefore speed) to maintain maximum load capacity.
Horsepower limiting pumps have been around for some time, initially an upgrade to improve productivity. Engineers understood their size, power and weight limitations for any given machine and that only so much real estate could be hijacked by the prime mover and pump (not to mention cooling). Getting more speed or power at the sacrifice of the other has offered machinery the best of both worlds while automatically delivering maximum power output. High force tasks are delivered at slow velocity while low force tasks are accelerated.
Modern material handling machines benefit from horsepower limiting operation in more than just productivity. Sure, they benefit in applications such as scrap handling, with the power to move giant piles of scrap steel while slewing or traversing in a highly productive fashion. But in today’s world of environmentally relevant design, horsepower limiting technology offers the top solution for low horsepower Tier IV Final machines offering surprising power and speed from small power units. Further developments in horsepower limiting technology employ electro-proportional pump and machine control, but that concept is deep enough for its own missive.
High-pressure grapple loaders
“Material handling machine” may have inherited the namesake, but plenty of other machinery are up to the task. Employing grapples not unlike the prior, the grapple loader body installed on trucks makes the perfect log transportation vehicle. In forested areas, the vehicle arrives at a logging location to collect and transport lumbar to the local mill.
Truck grapple loaders offer a wide range of payload capacities, from single-axle, light truck-mounted versions to those on semi-trailers. As for this discussion, the payload matters less than how it works — namely, hydraulically. Like many mobile machines, these operate at relatively high-pressure. Hydraulic energy comes from a PTO-mounted gear or piston pump, of which the latter is growing in popularity because of its efficiency. Often the grapple assembly is sold without the pump, filter and reservoir, leaving it up to the installer to coordinate.
A grapple loader assembly includes everything required to do the job — cab, boom, arm, grapple, control valves, hoses, and actuators. In addition, end users may option their machines with accessories such as oil-to-air coolers or wireless remote controllers. A wireless remote control provides flexibility to the operator, who may work high up from the command center or closer to the ground or hopper that the logs come from or are going into. With flexibility in the work location, the operator may more precisely place logs, ensuring the maximum payload possible without gaps or spaces.
You can expect a grapple loader to handle up to 15,000 lb per load, although that number depends on many factors. The boom angle and length factor in load capacity, and as you would expect, when the boom is straight out at full length, it cannot support the same mass. Some more advanced machines automatically control and limit the working range to prevent a frightening topple. Still, care should be taken on lesser machines that require only the operator’s experience.
Variations in log handling technology avoid the truck-mounted, slewed systems altogether. One version (Figure 2) looks more like a telehandler than a traditional grapple loader, with a long telescopic boom mounted to the extended chassis. These machines are perfect for high-volume lumber yards, where they enjoy load capacity sometimes four times the boom-operated grapple loader. The same limits to geometry apply; the log handler quickly loads, transports and unloads dozens of logs simultaneously.
The hydrostatic drive of the log handler offers much the same advantage to other mobile machineries, such as front-end loaders or dozers. The hydrostatic pump and motor combination provides powerful and efficient fore/aft movement control to enable rapid cycle times in a productive sawmill.
Rugged for indoor and outdoor use
Sophisticated machines employ four-wheel drive using individual wheel motors and, when combined with accumulators, may offer hydraulic hybrid drive. Imagine, instead of using brakes to slow the vehicle, the wheel-motor’s swash plates swing over-center and pump into accumulators to store energy. Then, once again, during acceleration, the process reverses to power the wheels from the accumulators. A laden machine may weigh over a hundred tons, so the extreme burst of hydraulic energy not only offers acceleration impossible with direct drive but also saves fuel and reduces C02 emissions.
Material handling applications are so diverse that it’s hard to cover every example. Industrial material handling often moves skids or boxes with forklifts, order pickers, or conveyor systems. Sometimes those applications require outdoor use, and mobile material handling machines won’t let you down just because it’s raining or snowing. For example, the self-powered mobile dock (Figure 3) offers a safe and effective method to access heavy products high upon truck beds when no forklift is available. Often, hand-bombing material is not an option, especially for skidded or heavy items.
Using a compact gas engine, much like a logsplitter, the hydraulic pump powers two hydraulic cylinders to lift the platform to gate height and automatically raise and lower the ramp plates. These ramp plates work double duty as protective cages to help keep operators safe. Valving is simple, requiring only the most elementary items — relief valve, directional valve and counterbalance valves. Also known as motion control valves, counterbalance valves prevent unintentional lowering of the platform, keeping operators safe.
What’s cool about mobile material handling applications is the nearly-exclusive use of hydraulics. Mobile machinery is still saturated with the convenient and reliable choice of internal combustion prime movers, which pairs perfectly with high-powered hydraulics. So if you need to move an object from point A to point B, there are countless mobile material handling machines at your disposal.