A Balanced Three Wheeled Roller Shown at World of Asphalt 2006
Sakai's R2H, a balanced three-wheel roller will be shown for the first time at World of Asphalt 2006 in Orlando, Florida.
Although vibration has been king on a majority of asphalt compaction jobs for the past thirty years, static can still be put to good use on any number of chores such as thin lift overlays or city streets built over fragile infrastructure. For these tasks and others, static compaction is still the norm. But to meet today's "I want it faster, smoother, more dense and cheaper" attitudes, the old static rollers just don't cut it.
This new, 83-inch-wide machine, on the other hand, blends the key benefits of the old three-wheel and tandem rollers into a new concept in static compaction the balanced three-wheeler. Sakai engineers combined the force and traction characteristics of the tandem roller with a few new wrinkles gleaned from their high-tech vibratory line, rolling a whole bunch of compaction talent into one.
In order to grasp what is good about the new concept, let's see what was bad about the old: First, the guide roll on the older models was for just that: steering. It had no traction purpose and the compaction effect pli of that roll was about 30% of the two larger diameter wheels. This meant to get equal coverage, you had to basically compact with these two bigger wheels, resulting in a nightmare of a rolling pattern.
Looking from the asphalt's point-of-view, we would like our density, and thus the compaction effort providing that density, to be even across the mat. If not, it is penalty time by today's tough standards. If the operator is not real good and real careful, densities could become very helter-skelter across the mat. Sakai's new three-wheeler incorporates three equal diameter drums which means equal force per linear inch across the compaction width. The R2H develops 365 pounds of force per linear inch across its 83-inch rolling width. All else being equal, this means equal density across the rolling width of the machine. Other big plusses include the ability to add water ballast to vary the output force (pli) across each drum enabling the machine to work on thicker lifts or even soil compaction jobs.
The smaller guide roll of the old three-wheeler was not for traction. Thus it was not driven. Non-driven rolls or drums tend to shove the mix forward, creating a bow wave out front which can lead to transverse cracking. The smaller diameter of the older models also meant a sharper approach angle to the material which amplified shoving of the mix.
Sakai's R2H not only improves traction and gradability, but that torque helps pull the mix under all three drums for blemish-free compaction. The flatter approach angle of the larger diameter drum decreases rolling resistance so that the drum can roll over the mix rather than push it. This lesser angle also means more drum surface contact with the mix, extremely important to the compaction of unstable mixes.
And like the drums of Sakai's vibratory asphalt rollers, the balanced three-wheeler's drums are machined for perfect concentricity leading to a perfectly smooth finish. Drum edges are rounded so as not to mark the mat.
Steering plays a very important role in compaction. Center-point articulated steering techniques first employed in double drum vibratory rollers and now in the newer balanced three-wheeler, ensure tracking.
That is, the single center drum follows the outer drums wherever they go. This precise tracking, combined with a built-in drum overlap, means even coverage and compaction effort no matter where the machine goes. This is a big plus when changing lanes in the pattern and compacting around curves or cul-de-sacs.
And it knows how to pinch a longitudinal joint. With the two leading outer drums straddling the joint and in essence providing two compacted edges, material movement under the following center drum will be in a downward direction for an extremely impermeable joint.
It also does a nice job on vibration-sensitive areas like bridge decks and city streets. For large parking areas that do not have to meet high mainline paving densities, the balanced three-wheeler can work by itself.
With all this versatility and field-proven cost-effectivity one would think this new concept destined for today's hot rental market, too. "It's coming," claims Dave Brown, vice president of sales and marketing for Sakai. "We're seeing the leading edge of that now. Once these rental houses see that this is an easy-to-use, maintenance-free profit maker, we expect they'll be adding it to their fleets."
Sakai engineers have breathed life into a tried and true concept with balanced three-wheeler designs that get a lot of different jobs done, cost-effectively, for busy asphalt paving contractors.
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