Roads & Paving
Milling Making Better Roads
By Treena Hein
New milling machine technology enhances the entire road resurfacing process.
By Treena Hein
Not too long ago, the milling process was seen as a necessary evil, says
Jeff Wiley. Contractors were forced into using it to correct a curb
line or scarify a bridge deck.
Not too long ago, the milling process was seen as a necessary evil, says Jeff Wiley. Contractors were forced into using it to correct a curb line or scarify a bridge deck. “Today, milling is a vital part of the whole paving process,” says Wirtgen America’s senior vice-president. “There are all kinds of applications the milling machine can undertake, from mill-and-fill to full-depth excavation of a roadway and base trimming.”
|BOMAG’s cold milling machines are designed for selective milling of lane and ground linings, and are especially suited for agricultural roads and inner-city work.|
This versatility, in Wiley’s view, also relieves the stresses of the entire resurfacing job. “If the milled surface can be smoother than it was before, the paving process is enhanced and smoothness bonuses come in reach,” he says. “Today, the technology of milling machines is just as advanced as that of asphalt pavers.” Jon Sjoblad, worldwide head of sales and marketing at Caterpillar Paving Products, agrees that milling has evolved to keep up with all paving job site requirements – requirements that “have increased in terms of smoothness, level of precision and accuracy.”
The past five years in particular have seen many improvements according to John Hood, director of heavy equipment sales at BOMAG. “The depth of the cut is more precisely and more efficiently achieved,” he says. Grade control systems are much more accurate, Wiley explains, with cutting patterns customized to particular jobs, such as micro-milling (fine milling) with a fine-tooth drum. Also, fewer teeth are used today, Wiley adds, because they have three to four times the lifetime of those available long ago.
Hood also notes the tremendous advancement in mill electronic packages, and Wiley echoes that opinion. “Today you can read out dual-grade, grade-and-slope, stringline-sensing, averaging, laser-reference and GPS co-ordinates,” Wiley says. “Onboard computers boost productivity and performance, while optimizing fuel consumption and preventing overload of vital components.” Only one ground man is now needed to easily control grade from either side of the machine.
New designs also require less cutter maintenance. “Reliable bolt-on and pressed-in holder systems – which are critical to continued productivity when retooling a drum, or in tool replacement after hitting buried iron – are far superior to the weld-on holders of the past,” Wiley notes. He adds, “Today you can buy a machine on which a contractor can quickly change cutter patterns. You can also fit smaller cutter widths into the same unit…instead of having to acquire or rent a machine to do that width.”
On the market today
In 2010, Wirtgen America introduced a new lineup that Wiley says has revolutionized cold milling. These mills feature Parallel-to-Surface technology that automatically keeps the machine level, accelerating production and improving accuracy. In addition, he notes that “their Intelligent Speed Control system incorporates an electronic flow divider that makes the four tracks work in harmony when turning a radius, making for a smoother cut. Three selectable drum speeds will allow the operator to apply the maximum productive effort and reduce tooth consumption at the same time up to 20 per cent.” Extra-wide drum widths are available.
|The Cat PM200 cold planer includes Cat Grade and Slope Control.|
Wiley calls the Dual Motor Concept of the Wirtgen W 210i and W 250 mills “the ultimate” in efficiency. “The operator can select between one motor and two motors, depending on the type and hardness of the material cut, and only run one motor when not milling during transport, or walking the machine in or out of the cut,” he explains. “This can give up to 18 to 20 per cent savings in annual fuel consumption.” The optional Vacuum Cutting System extracts fine material particles at the cutter drum, allowing better air quality and visibility in the working environment, while reducing wear and tear on the machine.
Because an extremely high level of smoothness can be achieved, interest in micro-milling is also growing fast, says Wiley. A fine-milling drum in a cold mill can be used to shape up roads and remove rutting, he explains, allowing cash-strapped municipalities to avoid complete milling and repaving. “Approaches to bridges and slightly faulted concrete pavements also can be repaired in this manner,” Wiley says, “[and] fine milling is especially useful in advance of thin overlays.” To support these choices, Wirtgen offers its Flexible Cutter System which allows a contractor to change the cutter drum and get back to work in less than two hours.
BOMAG’s lineup of 300-horsepower cold milling machines (the BM 1000/30-2, BM 1200/30-2 and BM 1300/30-2) are designed for selective milling of lane and ground linings. “These mills are especially suited for agricultural roads and inner-city work,” says Hood. “The central rotor location and four fully steerable tracks make these units extremely manoeuvrable, and the tracks are designed for super-quiet running even at maximum working speed.” Accumulated material is cut through using pressure on the hydraulic side plates, which provides very accurate depth sensing. These mills also feature a water tank larger by 25 per cent for less downtime.
The new raised undercarriage supports on the BOMAG mills allow the undercarriage to be extended away from the milling track at full cutting depth, adds Hood. “This allows the unit to be levelled on uneven ground or when milling trenches, for example, and results in greater stability and safety on site,” he explains. “There is also extra sealing between the conveyors that prevents planed material from escaping. This reduces cleaning work and cuts dust emissions.” Options include a hydraulically foldable canopy, windscreens, hydraulic water pump, high-pressure cleaner, levelling with electromechanical sensor or ultrasound sensor, electrical diesel pump for fuel refilling and compressed air system.
Roadtec offers four milling machine models, with the largest three available in either three- or four-track configurations. All feature 60-degree front load-out conveyor swing and bolt-on track pads. All Roadtec mills also have two independent spray bars, one for dust suppression and one to cool the drum.
The 950 hp RX-900e/ex is the most productive cold planer available on the market for half-lane or full-lane milling, says Kyle Hammon, Roadtec’s technical marketing co-ordinator. It cuts up to 14" deep at widths up to 13' and additional custom width can be supplied. The 755 hp RX-700e/ex also cuts up to 14" deep, with an optional VCS Variable Cutter System for cutting widths up to 48". “The RX-600e/ex is a 620 hp versatile machine that allows a contractor to cut up to 13" deep and up to 7'2",” says Hammon. “It’s light and manoeuvrable for urban situations.” Lastly, the compact Roadtec RX-400e/ex utility-class mill features a unique cutter housing design that gives efficient material evacuation at any cut depth. Hammon says a hydraulically raisable, segmented rear moldboard allows the cutter housing to easily adapt to any of the three available widths.
|Pictured here is the SX-8e (755 hp), the largest in Roadtec’s new line of reclaimers.|
Caterpillar Paving Products now offers more rotor selections to perform a wider range of applications, from standard high production milling to micro-milling, says Sjoblad. “Our mills offer multiple cutting widths from 1 to 2.2 metres,” he adds. Cat has also introduced Grade and Slope controls that are more accurate and easier to use. “These systems are plug-and-play, featuring robust sensors and scalable design to complete a wide range of 2D and 3D milling tasks,” Sjoblad explains. “And a range of optional equipment to provide efficiency and jobsite versatility is available.”
Because Cat cold planers feature Cat engines, the power curve is optimized for milling work, something that other manufacturers are unable to do, says Sjoblad, because they buy their engines from other manufacturers. “This custom-tailored approach allows Caterpillar to use an engine with lower horsepower than other manufacturers without sacrificing production,” he notes. “The engine runs at lower rpm, which lowers fuel consumption and decreases engine wear. Customers enjoy high output with lower operating costs. And, emissions are reduced.” Caterpillar also offers highly efficient Master Grade cutting bits, which Sjoblad says stay sharper longer. Having to change bits less often lowers operating costs, as there is less downtime and fewer bits are consumed.
The newest milling machines from Volvo Construction Equipment – the Volvo MT2000 and the Volvo MW500 – offer features that increase productivity, serviceability and overall safety, notes Rob Hannan, Volvo Construction Equipment district sales manager. The Volvo MT2000 is a four-track, front-load, half-lane milling machine with intuitive dual-operating stations. “We have achieved an industry first with its ability to offer three distinct engine and drum cutting speeds selectable from the operator’s panel,” Hannan says. Low-speed provides higher torque to power through tough material or deep-cuts, high-speed is used for shallow cutting and standard speed is used for normal depths. Its four-track system features independently controlled gathering and discharge conveyors with variable speed adjustment to meet cutting drum capacity.
For small and tight jobs, Volvo offers the MW500, a four-wheel, rear-loading utility mill. “The right-rear support leg and wheel can be swiveled inboard for flush cutting,” Hannan notes. This mill is all-wheel-drive with anti-slip control (ASC) as a standard feature. In conjunction with ASC, Volvo’s patented line manager system allows the operator to maintain a constant speed of operation and direction of travel without being adversely affected by the rotation of the milling drum. “Options include a conveyor package with quick-disconnect conveyor and hydraulically raised rear moldboard,” Hannan notes, “And an adjustable steering wheel column and innovative control panel with automatic precision depth-control and advanced diagnostic capabilities.”