Innovations in Compaction

"Vibration isolation is a big thing," Wenzel says, adding that with increased forces and frequency variations comes the need for vibration dampening. "Dampening handles isolate the operator from the energy of the machine.," he says. "Contractors know the difference between units with and without improved vibration isolation, but not all contractors insist on these improvements. There's always a segment of the market looking strictly on price."

Wenzel expects that in the near future the improvements in vibration dampening will become a standard part of every plate - not an option.

Schulenberg says that improvements in steel, iron, and casting technology have improved the equipment, which translates into on-the-job improvements. He says Wacker Neuson's WP1550 plate has a ductile iron base plate, replacing the fabricated steel plates the company used to use. Those plates were composed of several steel plates welded together - and welds don't react well to vibration.

"The ability to cast in different shapes has also made an impact on the job and the jobsite," he says. "The design of the shape of the plate is a balance between good compaction performance and maneuverability of the plate.

"If the plate is designed with large rounded edges it's easy to maneuver while maintaining a good finish, but then you only provide compaction over a small area. However, if the edges of the plates are not shaped properly - if they're not rounded and smooth - the plates will leave marks or cuts in the mat."

Plastics. Schulenberg highlights the general acceptance and development of plastics and polymer technologies as playing a broad role in compaction innovation. "There's a lot more plastic on our new machines today than there was 25 years ago," he says. "Not only was it not available 25 years ago but it's much more accepted today."

He says use of plastics and polymers enabled manufacturers to make a number of important innovations, including improving their watering systems. "If you don't have a good watering system you won't have a quality finish to your job. Old water tanks used to be made of steel, and if you let any water sit in them over the winter they would rust. Then the next season the rust would flake off and clog your lines and suddenly there you were in the middle of a job with no water for your roller. New tanks are plastic so they don't have that problem at all.

"Plastic also allows us to design unique shapes and geometries we couldn't effectively do with steel because we can mold plastics into any shape we need. That means water tanks can be larger so you can carry a larger quantity of water on your roller so you don't have to stop and fill as often. It's a productivity issue."

Compactive Effort

Changes throughout the industry have led to increased compaction production, and manufacturers say that's a result of higher amplitude in the drums and increased vibration frequencies.

"The ability of machines to have higher amplitudes in the drum allows more energy to be put into the material, which means contractors can construct deeper lifts," Marcum says. "Higher amplitudes allow us to more efficiently compact the material with fewer passes of the machine."

He credits improvements in both the bearings in the drums and the lubricants for much of this gain. "If you go back 25 to 30 years the rating of machines in centrifugal force was around 25,000 lbs. Today they're in the 70,000 to 80,000-lb. range. Better material of bearings and better lubrication of bearings have supported that."

Hood adds that higher frequencies add to the impact of greater amplitude. Vibrations per minute (VPM) indicate how many times a minute the drum hits the material, and higher frequency allows faster rolling speeds, which results in more production. "In some cases we are seeing 4,000 VPM on highway class rollers, and that's a very high jump we were able to make because of the increased power that delivers very efficient compaction performance for the contractors," Hood says.

Wenzel says that high frequency vibrations have made an impact on the compaction operation and adds that the ability to change vibration speed - offered primarily on larger highway rollers - is another innovation that results in better compaction. "This allows the user to adjust the unit to the materials and conditions, which will result in a better finish," he says.