Capital Equipment News May 2017

COMPACTION

HAMM’S OSCILLATION COMPACTION PROWESS

Over 30 years ago, HAMM became the first roller manufacturer to offer an oscillation drum for tandem rollers, and they have become an integral part of its product offering. In the past five years alone, the compaction technology specialist has delivered more than 3 000 machines with this innovative technology. T oday, one in four of the tandem rollers made by HAMM is equipped with an oscillation drum. With more than 30

models to choose from, HAMM claims to have the widest offering of oscillation rollers in the world. The company is said to be the only OEM that builds oscillation tandem rollers in the compact class, as well as soil compactors with oscillation compaction capability. The HAMM portfolio encompasses tandem rollers for asphalt paving ranging from 2,5 to 15 t. When it comes to the pivot- steered rollers in the DV+ series, a popular choice for demanding road building projects, the share of oscillation rollers is particularly high: in 2016, around 40% of all DV+ series rollers were delivered with oscillation drums. Why oscillation rollers? Oscillation rollers make for fast, cost- effective and high-quality dynamic compaction. In particular, tandem rollers with one oscillation drum and one vibrating drum achieve at least the same degree of compaction as double vibrating drum rollers, but with fewer passes. Another benefit is the very low vibration provided by oscillation, making dynamic compaction on bridge overlays, of thin layers, and in sensitive areas, such as near hospitals, city centres, rail tracks, or industrial plants, possible for the first time. The scope of applications is enormous. Another bonus is that oscillation rollers can start dynamic compaction directly behind the paver (breakdown phase). They can then also deal with the main compaction (intermediate phase). And even with lower asphalt temperatures at the end of compaction (finish phase), oscillation ensures an increase in compaction without crushing the aggregate. Overall, when using oscillation rollers, the time available for compaction is significantly greater than with vibratory rollers. How it works But what exactly happens in an oscillation drum, and how does oscillation differ from vibration? With vibration, a single

A HAMM HD+ 120i OV tandem roller compacting the surface course of a busy highway.

unbalanced shaft generates the upward and downward movement of the drum, causing it to strike the ground at a rapid rate. In oscillation drums, on the other hand, two unbalanced shafts rotate synchronously, driven by a toothed belt. The unbalances are offset by 180° relative to one another. As a result, the drum performs a rapidly alternating forward/ backward rotary movement. Due to this movement, the drum directs the compaction force into the substrate tangentially to the front and rear in the form of shear forces. Here, unlike with vibrating drums, the compaction force acts continuously on the substrate because the drum is in contact with the ground at all times. This is why oscillation rollers compact dynamically as well as statically with their intrinsic weight the whole time. Benefits of oscillation Oscillation offers a wide range of benefits, enhancing efficiency, quality, productivity and profitability. Here are the most important ones: Benefit 1: High compaction power – great efficiency. Oscillation rollers compact very quickly. Or to put it differently: their compaction

power is very high. The reason for this is the superimposition of dynamic shear forces with the permanent load from the roller’s own weight. As a result, considerably fewer passes are needed, especially on large areas. Benefit 2: Easy operation. HAMM uses the laws of physics to generate vibrations in such a way that the oscillation roller is extremely easy to operate. Simply switch the machine on, and there’s nothing more for the operator to do. The appropriate amplitude is set automatically according to the rigidity of the material to be compacted. This happens so quickly that compaction is always adjusted perfectly, even with varying substrates. In this way, HAMM has eliminated the risk of operating errors due to incorrect settings. Benefit 3: Smooth, skid-resistant surfaces. Oscillation rollers produce surfaces with excellent longitudinal evenness, resulting from the drum remaining in contact with the ground at all times. Surface rippling, on the other hand, does not occur, not even at high working speeds. Asphalt compaction with oscillation also provides good initial skid resistance, because the oscillating movement of the drum rubs off asphalt from the top surface of the pavement. b

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