“Each of us was challenged with providing different types of spray configurations, and each machine came equipped with a variety of spray configurations,” Richmond says. “At Mill Fest we determined the best practices for spray systems and the best use of spray systems.”
While additional components continue to gain importance in milling equipment, it remained crucial to establish best practices information for the water spray systems. Regardless of milling machine modifications, water spray systems will remain essential to the milling process because it’s an important element in cooling the cutter drums and cutter bits.
Terex made changes to include a piston-type pump that can develop higher pressures.
“It is a positive displacement pump, and every rotation of the pump produces a certain amount of volume allowing us to optimize the nozzle placement of water and the penetration,” says Musil. “If you run it at a higher pressure the water can get to where it needs to be quicker, and you are also using less water by having it go directly to the hot tip.”
Musil also discovered that by utilizing the better piston pump design and nozzles that they were able to reduce the volume of water used while accomplishing the same cooling effect. In some cases, by using the higher-pressure piston style they were able to dramatically extend the life of the cutter teeth.
Implementing extraction systems
For years the only means of dust suppression was through the water system. However, this was only a side benefit to a system whose primary design is to cool cutting teeth. “In some cases, the water hitting the hot cutter teeth turns into steam, which expands the volume to create a positive pressure inside the cutting chamber, which results in the dust escaping the chamber,” says Musil.
The consensus was made by the Silica/Milling Machine Partnership that an alternative method was needed to work in conjunction with the water system controls in order to efficiently reduce silica dust. As a result, the team turned to mechanical evacuation systems to be used in conjunction with the water spray systems.
“Construction equipment manufacturers were already using vacuum system controls on asphalt pavers resulting from a similar successful partnership effort in the late 1990s,” Lyons says. “It became evident that vacuum-based controls could provide another level of reduction in airborne dust.”
With the focus turned to mechanical evacuation systems, Musil believed that the only successful option was to place the milling chamber under a negative pressure so that clean air from the outside would be sucked into the milling chamber while no particulate dust would be released.
“A fan was used to create the negative pressure,” Musil says. “The covered and side-sealed conveyors already on the machine were used as duct work, and the rubber flaps placed on the conveyors became section seals. I collected the dust in the air stream and it’s discharged into the truck where the RAP millings from the milling machine are already going. Terex (CMI) had used a similar vacuum evacuation system on its milling machine in the 1980s.”
According to Richmond, from a design point, the changes aren’t too radical. “We’re looking at the changes as an addition to our existing machinery, and it will be an add-on extraction system/fan system,” Richmond says. “We have currently engineered the addition into all of our Tier 4-powered products and will make this a standard feature at a point in time when NIOSH goes forward with its decision about regulation and compliance.”
While the water spray systems are generally efficient, Richmond believes the fan system will take dust suppression to the next level. Roadtec’s system has an independent hydraulic fan with a series of duct work designed to draw the dust out of the transition between the cutter housing and the primary conveyor as preliminary testing has verified that this is the best capture point for the airborne dust.
Wirtgen developed its VCS (Vacuum Cutter System) overseas to reduce dust collection in and around the mechanical systems onboard the machines.