Because of the housing market and the downturn in commercial construction, sales of mid-sized, tandem rollers have taken a tumble—by as much as two-thirds in 2010—according to one leading manufacturer. So it’s no surprise that there hasn’t been a whole lot of activity in this particular size class, except for upgrading engines to meet Tier 4-I emissions standards coming down the pike in the next couple of years. Some manufacturers have already made that move; others have yet to make the transition.
“There’s some activity in governmental, through cities and street departments or county road departments, but there’s just not the commercial activity with these smaller rollers as we’ve seen in years past,” says Bob Marcum, Volvo Construction Equipment product specialist-road machinery. Highway-class rollers, however, have seen sales boosted by stimulus money and highway projects, he says.
No doubt, much of the asphalt-roller “smart” technology has been focused on highway-class machines—10 metric tons and larger—because of the associated costs. Intelligent-compaction systems for any brand can list for about $35,000 to $40,000, which would be cost prohibitive on smaller units. Plus, that highway size class has the highest-selling volume in the world.
But the second highest-selling class is the 2.5- to 3-metric-ton class, which typically features 47-inch drums. Overall sales make up more than one-third of all the double-drum categories. Applications for that size typically would be shoulder/median work restricted to less than 5-foot working area between curb lines and shoulder surface mat areas.
“You would take a roller such as this—for an owner/operator—put it on a trailer behind your dump truck and go out and do the base work, and then the subbase work, and then maybe the binder, and the finish work,” says Chris Connolly, sales manager for Bomag. “You’d do everything on the job with one roller and go home—for a smaller owner/operator—which of course there are more of than there are larger contractors. It delivers energy like the larger rollers do, but it can work in smaller areas, plus you can transport it.”
Bomag offers three mid-size, double-drum rollers: BW120, BW135 and BW138. At 5,732 pounds, the BW120 is the largest-selling-size compactor in this size class. Models BW135 and BW138 are basically the same machine, but with 51- and 54-inch drums, respectively. According to Connolly, the BW120AD-4 boasts an industry-high centrifugal force of 10,125 pounds and a high and low frequency of 4,200 and 3,300 vpm. He also says model BW120 is manufactured to the same design parameters as the company’s larger machines. The drums feature two scrapers so that material doesn’t come up over the top of the drum. Another special feature on these models is that the center joint is bolted in, as opposed to being welded together.
“The front portion of it is like a hitch—the machine articulates—so if it bends in the middle, it’s going to be like a knuckle there so it can turn,” Connolly says. “What we do is bolt the two parts of that knuckle—one to the front and one to the back—so you can take it apart and service it easier, and it moves better.”
Another industry-high performance number comes from one of Volvo’s six-model lineup in the mid-sized class. At 4,020 vpm, the company says DD24 has the highest frequency in its class. As with Bomag’s BW120, the Volvo DD24 falls into the best-selling size category, after the 10-metric-ton units. The DD24 offers automatic or manual vibration and can operate in three modes: statically, front drum vibration only, or both drums vibrating.
“On the DD29, DD31HF and DD38HF,” Marcum says, “we’ve taken a common platform; we’ve made a couple of different drum widths underneath for different coverage, and we’ve made some changes in frequency. So there’s a performance difference, but the basic platform on which the machine is built and the engine is common.
“On the DD70 and DD70HF, this is also a case where we use the same platform and we make two different models out of it. You have a common engine, but you have two different figures on some of the drum specifications. The DD70HF has a higher frequency, that’s what the HF stands for, and it also has higher centrifugal forces. As you’ll notice, they’re going on the high side from 17,000 up to 21,000, so it hits harder; and with higher frequency, it hits more often. It has the potential to require fewer passes, and it has the potential for higher paving speed and more productivity.”
In addition, the DD70 and DD70HF have eight amplitudes on the machine (amplitude, of course, is how far the drum moves up and down when it vibrates). The operator can select from those, which gives him or her a range of eight centrifugal forces. So an operator has the ability to adjust and adapt the machine to specific job requirements. That feature is not on the DD38 and down, though, as it’s not really necessary on the smaller jobs.
On the high end of the Case four-model, mid-sized range is the DV207, which was recently introduced at Conexpo (along with the DV210 and DV213 larger models). Those models expand Case’s offering to handle highway-class jobs. With an operating weight of 16,226 pounds, the DV207 features a 57-inch drum width and is powered by an 80-horsepower Cummins diesel.
Case DV Series models include hydrostatic drive to both drums, infinitely variable speeds, manual or automatic vibration modes, and choice of front or both drum vibration. They are designed to handle many paving applications, from coarse bases to hot-mix asphalt surfaces. Recessed hydrostatic drum drives provide high curb clearance for excellent maneuverability. The DV Series also provides easy access to external engine components and routine maintenance points for lower maintenance costs.
Aside from the Case introduction, most mid-sized models haven’t seen recent developments aside from engine upgrades. Manufacturers (and contractors) are waiting for commercial construction to pick up its pace. Once that happens and sales start to pick up, more technological advances will likely follow.
