An oscillating roller only exerts horizontal forces on the asphalt layer, together with the static load from the machine itself. The roller is always in contact with the surface and the horizontal movement ‘massages’ the surface.
This leads to efficient compacting with very little vibration transmitted to the surrounding environment. This more gentle compacting allows the roller to be used in vibration-sensitive areas.
Oscillation is beneficial when joining existing and newly laid asphalt layers. Road safety is improved since the top layer of bitumen is removed from the aggregate due to the oscillating movement, exposing the aggregate’s surface which creates higher friction.The lack of vertical movement with oscillation reduces the risk of over-compacting and damage to the aggregate. Oscillating compaction is also more quiet and more comfortable for the driver.
“In this project we have worked very closely with SSAB‘s wear and manufacturing experts. We used their knowledge to establish the best way to bend and weld the drums. This cooperation has been very valuable when developing our new oscillating rollers,” says Andreas Lager, manager for structural analysis and design at Dynapac.
When the production techniques were in place, a couple of full scale prototypes were constructed and put into action in regular field tests.
"Our prototype rollers were monitored for up to 1000 hours of tough operation and the oscillating drums showed hardly any wear at all. It was really satisfying to see that the grooves from the turning of the drums were still clearly visible on the drum surface,” says Andreas.
Oscillating compacting of asphalt is usually performed with rollers featuring twin drums, one with vibration and one with oscillation. The drums can be activated individually, and the oscillating drum is commonly placed at the rear.
In the oscillating drum, two rotating eccentric weights are placed away from the drum center to generate the horizontal back-and-forth motion of the drum as it moves across the surface. This means that, as opposed to the vibration system, the drum does not move its axis of rotation, but rather oscillates around it.
The trend towards thinner asphalt layers and harder aggregates favors the use of oscillating rollers. Oscillating avoids the drawbacks of vibration which is often too severe for the thinner layers that are becoming more common.
The horizontal oscillating movement although creates a grinding effect on the drum’s surface. The active life of a roller is often more than 10,000 hours. To avoid the need for a drum replacement because of excessive wear during this time, the usual solution is to use a thick drum made of mild steel such as S355. However, equipment manufacturer Dynapac decided to take their design in a different direction.
Dynapac wanted to use a relatively thin steel to make the drum light. There is no advantage of having a thick and heavy drum, quite the opposite. With a lighter drum, it’s possible to reduce the size of the mechanical components that rotate the drum and create the oscillations. This in turn reduces the fuel consumption of the roller, to the benefit of the operator.
When Dynapac’s design and production team looked for a working solution, they targeted a 16 mm (6.630 in.) thickness for the drum. To ensure the service life was long enough, they also needed a hard steel that was able to cope with the particular wear challenge seen on an oscillating drum. Plus, they needed to be sure it could be bent into a perfectly round shape without having to invest in new rolling equipment. Finally, as if that wasn’t a hard-enough specification, it had to be as easily weldable as a common steel.
The abrasion-resistant steel Hardox® from SSAB promised to deliver on all accounts. After consulting with material and production specialists at SSAB’s Knowledge Service Center and testing different grades of Hardox® wear plate, Dynapac concluded that Hardox® 450 had the optimum mix of hardness for wear resistance and ductility for workshop performance.
A large number of Dynapac’s oscillating rollers in the CO series are now in full operation around the world. Some of the machines have been involved in a prestigious project in Asia, ensuring a perfect surface on the new Formula 1 race track in Hanoi, which will be ready for racing in 2020.
Dynapac is an international company with a heritage that goes back to 1934, when the company was started in Sweden. Its main business is high-tech asphalt and soil compacting rollers between 1 and 21 tons, pavers and light equipment. Dynapac is now headquartered in Wardenburg, Germany, and has production facilities in Europe, South America, and Asia. Dynapac is part of the FAYAT Group.
Since 2017, Dynapac has been a member of Hardox® In My Body, SSAB’s quality program for companies that use Hardox® wear plate in products that are designed and manufactured according to the strictest quality requirements