It's hard to imagine a piece of equipment that works harder in tougher conditions than a pavement mill. These tireless machines grind away all day long under load, at times removing more than a foot of asphalt as they trudge ever forward. In the process, they're generating debilitating heat and abrasive silicon dust, all potential roadblocks to performance and productivity.
So how does one maintain a machine that cost anywhere from $300,000 or more for intermediate models to upwards of $500,000 and beyond for high-production models? How does a pavement contractor optimize its performance so a project stays on schedule? The answers lie within a rigorous preventive maintenance program and daily inspections.
"We recommend that contractors clean, lubricate, and inspect their machines at the end of every day," says John Hood, manager of product development and sales for Bomag Americas paving products located in Kewanee, IL. Bomag manufactures five pavement milling machines on 300- and 600-hp platforms. The 300-hp platform features models with 24-, 40-, and 48-inch drums.
Hood notes that by completing daily maintenance at day's end, most any repair issue discovered during inspection can be rectified prior to starting the project the next morning. The evening maintenance regimen, he adds, should begin with a thorough washing – with special attention given to the cutter drum and both the top and bottom conveyors. "The drum works like a garden tiller, except instead of cutting through soil it is cutting through asphalt," Hood says. "Maintenance personnel should check the cutting tools to make sure that none are broken and that they're wearing evenly and then inspect the spray bars to make sure the tips are not plugged. The spray bars both lubricate and cool the tools and if they're plugged, operators will likely burn up cutting tools."
After pressure washing the conveyors, he advises contractors to slowly turn the belts to inspect them for tears or other imperfections. "It takes anywhere from four to six hours to replace a belt," he adds. "Again, contractors would rather take the time to make the repairs at the end of the day rather than be forced to replace the belts when they should be milling."
Lubricating up to 30 grease points follows a complete wash-down and visual inspection of the machine and provides an opportunity to check all seals and bearings for leaks and possible failure. Tracks should also be inspected to ensure that pads are in place, and then adjusted once a week. This, of course, is above and beyond checking the oil and following the manufacturer's recommendation for cleaning and changing filters, Hood emphasizes.
"Pavement milling machines are very simple to run, but hard to maintain," he adds. "A pavement contractor can invest $350,000 for our 4-foot commercial mill and rental rates can vary from $3,500 a day to upwards of $5,000. These machines get tough jobs done in a hurry, but they need daily maintenance to ensure top performance."
The heart of the machine
"There's no question that the number one maintenance item on any size pavement milling machine is the cutter drum, says Jeff Wiley, vice president of sales and marketing for Wirtgen America Inc., Nashville. "Giving the cutter drum and its tools a spot check throughout the day and during the daily maintenance regimen is paramount to keeping the milling machine in top performance. Improperly maintained drums may also cause excessive vibration and machine wear."
Wirtgen manufactures 17 pavement mill models that range in drum size from 14 inches wide on the cut to 14.6 feet. Wiley explains that the company's 4-foot drum has 115 cutting tools that on average will last anywhere from one to three days depending on the application. The tools have a carbide tip and steel body that absorbs the shock, and are secured in a holder that allows them to rotate to wear evenly and retain their sharpness. "Tools should be checked at the end of the day, after the drum has been washed, and replaced if one breaks during the milling operation," he says. "If one breaks while milling, operators will notice a white line or high ridge in the pattern of the cut," adding that this is just one reason to be observant during the milling operation.