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Hamm roller-compactors put their faith in the GFT 8000 gearbox

Hamm roller-compactors put their faith in the GFT 8000 gearbox
Marginal Column

July 2015


Rexroth components keep things rolling in the compactors built by the Hamm AG.

The forward section is home to a massive roller or drum while the rear section carries the driver’s cab, engine and huge tires. The two are connected with a three-joint, self-leveling, center pivot assembly. In a design like this, a heavy roller can apply as much as 50 tons of compaction power to the ground. Whether building a reservoir in the valley of Chile’s Rio Blanco or a dam in the eternal ice of the Tiefenbachferner glacier in Austria, rollers designed to compact the soil hardly shy away from extremes. Dirt, dust, vibrations and ambient temperatures between -40 and +50 degrees Celsius make the greatest conceivable demands on all the machinery components used in Hamm’s H Series.

Looking back to the year 2010, there was a flurry of activity on the part of all construction machinery manufacturers. Both the EU and the USA announced that, in 2014, they would be implementing the Stage IV/Tier 4 Final limitations on emissions. That represented a true challenge, since many machine concepts simply did not have the space for the components that were needed. Hamm decided to redesign not only the engine, the particulate filter and the nitrogen after-treatment, but to develop a complete new generation of soil compactors, as well. The objectives were ambitious. The prototype was to be presented in Munich in 2013, at the bauma, one of the world’s most important trade shows for building machinery.

Staying with the tried and true

Advancing from sketches to the finished pre-production machine in barely three years is certainly an impressive goal. It’s no surprise that product development engineers gave preference to time-tested partners. Since the year 2000 Bosch Rexroth has supplied components and has been a system partner for the Hamm road rollers in the 3000 series. Rexroth introduced the new series of HYDROTRAC GFT 8000 gearboxes just in time for use in the new H Series. The decisive plus for this integrated planetary gear and hydraulic motor: pressure can be developed up to a maximum of 500 bar. This made this the first choice for driving the vibratory drum in the new Hamm machines.

“The key components in a soil compactor are the drive train and the vibratory drum,” explains Reiner Bartsch, product manager at Hamm AG. “Those of our customers who are engaged in earthwork expect not only the highest reliability and compacting power, but also an abundance of torque in every operating situation.” Performance counts because road rollers must join the best compacting power with high climbing capacities and cross-country mobility. Thomas Bletcher, project manager responsible for the H Series at Hamm, adds: “In landfills, for example, slopes of up to 60 percent have to be negotiated. That needs lots of power.” The hydrostatic drive makes a decisive contribution to satisfying all these requirements.

Planetary gearbox for mobile uses

Hamm has taken account of the tough conditions under which roller-compactors are used and thus has adopted rugged engineering for a long service life. In addition, a compact design, a wide selection of gear ratios and drive torques, as well as simple configurability are important criteria for the hydrostatic drive. In the GFT 8000 Series, and depending on the design, a two- or three-stage mechanical planetary gear converts the torque. When building lighter rollers, Hamm draws on the GFT 8130 with a two-stage planetary gearbox, while in heavy-duty machines it uses the GFT 8140 with its three stages. The GFT 8000 Series offers for the first time the option of integrating Rexroth A6VE hydraulic motors from Series 71 in order to further boost the power density of the entire drive unit. This increase is made possible by the greater displacement of the A6VE/71. The result is about ten percent more torque than the previous series and a corresponding increase in power – and that improves driving performance noticeably.

Roller-compactors with rated weights of between eleven and sixteen tons make use of Rexroth components for the axle drives and the drum drives. The oscillating weight for the vibratory effect is also moved hydrostatically, using an A2FM bent-axis motor. The hydraulic pressure is supplied by a Rexroth A4VG variable-displacement pump. It, in turn, is driven by an eco-friendly, four-cylinder diesel engine with the most modern of combustion technology, exhaust gas after-treatment, and a particulate filter. Owing to intelligent air routing, the diesel engine satisfies EU Stage IIIB/Tier 4 Interim specifications even when operating at ambient temperatures as high as 50 degrees Celsius.

Transmission unit GFT Series 8000

Transmission units in GFT Series 8000 are suited for wheeled and tracked vehicles such as pavers, crop sprayers and heavy-duty transporters.


Maximum traction without slip

Special requirements are posed by the vibration drum which, in addition to the roller’s own weight, introduces additional energy into the soil by the rotation of a circular oscillator. Since the gearbox and the motor are built right into the drum, the components are exposed directly to the vibration. Hamm, supported by Rexroth, has thus engineered the supports and mounts to be especially sturdy. The plug-in, variable-displacement motor, model A6VE with its bent-axis design, can be adjusted electrically and, thanks to its wide regulation range, satisfies the demand for higher speed and high torque. It is regulated by the Hammtronic machinery management system – which also offers fully automatic traction and slip control. The drive powering the rotation of the oscillating weight can be set, at push-button control, in the range of between 20 and 40 hertz. Two differing indexing unbalance amplitudes are programmed as standard. Thus the operator can choose the right setting for every substrate.

On the road to success

A good two years after the launch of this series, product manager Reiner Bartsch attested to the superb quality of the H Series and its components. “Machines clocking 4,000 to 5,000 hours in operation, even in the demanding rental trade, run absolutely with no trouble.” The word has gotten around. This has made the H Series a very successful model produced by the mechanical engineers located in the Bavarian town of Tirschenreuth.