HAMM – More than 35 years of oscillation:
Tried and tested solutions for asphalt construction and earthwork
Over 35 years ago, HAMM became the first roller manufacturer to offer an oscillation drum for tandem rollers. These rollers have now become an integral part of the product programme. In the past five years alone, the specialists for compaction technology delivered more than 3,000 machines with this particular technology. Today, one in four of the tandem rollers leaving the Tirschenreuth factory is equipped with an oscillation drum. One reason for this is the large variety of models, because with more than 35 models, HAMM has by far the widest offering of oscillation rollers in the world. Moreover, only HAMM builds oscillation tandem rollers in the compact class as well as compactors for earthwork with oscillation compaction capability. And last but not least, the HAMM programme includes oscillation rollers for every market. To reflect this diversity, at Road Technology Days 2018 HAMM is displaying rollers with oscillation from all product segments.
In the 1980s, HAMM undertook pioneering work in the development of oscillation compaction and was long the only supplier in the market. Customers were quick to appreciate the benefits of this technology. In the meantime, oscillation has proved itself and become successfully established in the market; as a result, most roller manufacturers have recently begun to offer this type of roller as well.
Fast, cost-effective and high-quality
The reason for this success is simple: 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 a double vibrating drum, but with fewer passes. Added to this is the low vibration emission. This has made dynamic compaction on bridges, of thin layers and in sensitive areas (such as city centres, rail tracks, industrial plants) possible for the first time. In short, the scope of applications is enormous.
Compaction at every construction phase
A further bonus is that oscillation rollers can start dynamic compaction directly behind the paver. They can then also deal with the main compaction. And even with lower asphalt temperatures at the end of compaction, 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.
When building oscillation drums, HAMM – unlike its competitors, which have all entered the market with this technology in recent years only – can draw on decades of experience. And it is precisely this experience that makes the difference, as Head of Marketing Gottfried Beer explains: “You can copy technical solutions, but you can’t copy experience.”
Thanks to its wealth of experience, HAMM possesses extensive know-how in application technology. This knowledge is not confined to a few specialists in the factory, but extends to the subsidiaries all around the world. Due to the large number of oscillation rollers on the market, spare parts availability is also very high. In addition, the service engineers all over the world are thoroughly familiar with the technology and trained with regard to oscillation.
Comprehensive portfolio for asphalt construction and earthwork
The HAMM portfolio encompasses tandem rollers for asphalt construction ranging from 2.5 to 15 t. Especially when it comes to the pivot-steered rollers in the DV+ series, a popular choice for demanding road construction projects, the share of oscillation rollers is high: in 2016, around 40% of all DV+ series rollers were delivered with oscillation drums.
The oscillation rollers for the compact class from 2.5 to 4.5 t also enjoy great market demand. Hardly surprising, because HAMM is the world’s only manufacturer in this market segment. This also applies to earthwork. Customers worldwide seeking a solution for compactors with the facility to choose between oscillation and vibration find that only HAMM has the answer in the form of its VIO drums.
The oscillation principle
But what exactly happens in an oscillation drum, and how does oscillation differ from vibration? With vibration, a single unbalance shaft generates the upward and downward movement of the drum on the ground. In oscillation drums, on the other hand, two unbalance 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. 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, throughout, oscillation rollers compact dynamically as well as statically with their intrinsic weight.
Split drums with oscillation
Starting from Road Technology Days 2018, HAMM is expanding its portfolio to include split drums with oscillation. They prevent crack formation in the asphalt surface when compacting in tight curves and making pronounced steering movements. In the patented HAMM solution, two complete, separately powered oscillation units operate in each drum. The two drives are synchronised so that they vibrate in phase.
This makes HAMM’s split oscillation markedly different from other solutions: HAMM’s split oscillation vibrates with a comparatively high amplitude, thus delivering the same high compaction power as an undivided oscillation drum. Accordingly, HAMM’s split oscillation drum combines all the advantages of efficient oscillation compaction with the optimised driving and steering characteristics of a split drum.
Maximum wear resistance
HAMM’s experience of more than 35 years is also reflected in the way in which the technology is incorporated in the design. An example of this is the drum shell. With oscillation drums, it is inevitably subject to greater stresses than with vibrating drums, due to the constant ground contact. Thanks to ongoing product and material development, the operating life of HAMM oscillation drums is today nearly the same as that of vibrating drums. This is made possible by using highly wear-resistant fine grain steel for the drum shell. Its material thickness is significantly greater than that of comparable competitors’ machines. In addition, an integral reinforcing ring ensures that the drum is extremely hard-wearing. Furthermore HAMM oscillation drums are completely maintenance free.
Quality thanks to chamfered drums
To ensure that the drums leave no impressions in the still soft asphalt, especially in curves, HAMM gives all drum edges a slight chamfer. Such impressions have to be re-rolled afterwards, wasting time. Otherwise, they remain visible in the asphalt and compromise quality. Both issues are avoided from the outset thanks to HAMM’s design solution. By the way: this chamfer can also be found on all of HAMM’s vibrating drums. A small yet effective detail that ensures top quality.
A glance at the exciter system drive inside the oscillation drum also shows that it is based on a great deal of experience. HAMM has continuously optimised the position of the unbalance weights in the oscillation drum to enable the resulting forces to be utilised as effectively as possible.
At the same time, HAMM’s oscillation drums are designed to require a minimum of maintenance. The toothed belt, the core element of the drive, has been perfectly attuned to the overall system: its operating life corresponds to that of the entire drum. Checking the belt tension after 2,000 operating hours is all that is recommended.
Use for all layers
Oscillation rollers can be used to compact all earthwork and road construction layers. They come into their own in earthwork, where re-loosening of the upper layers has to be effectively prevented, such as in garden and landscaping work. Another important application is the compaction of soils in vibration-sensitive areas, for example above gas, water and other pipework.
In asphalt construction, base courses, binder courses and surface courses can be reliably compacted with oscillation rollers. They perform especially well in the compaction of generally hard-to-compact asphalts such as SMA or in the case of polymer-modified material mixes. This is because, in contrast to vibration compaction, the effective direction of the vibrations during oscillation promotes the desired redistribution of long-chain binding agents.
Other applications include work on thin layers (surface courses, thin overlays), in vibration-sensitive areas (bridges, confined urban spaces, buildings or parking decks) and wherever the mix cools quickly (thin layers, windy or cold environments). Of particular importance is joint compaction where the hot asphalt is to be compacted without damaging the adjoining cold asphalt.
Benefits of oscillation
Oscillation offers a wide range of benefits. They influence efficiency, quality and profitability. Here are the most important benefits:
Benefit 1: High compaction power – great efficiency
Oscillation rollers compact very quickly. In other words, 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 makes use of the laws of physics to generate vibrations in such a way that the oscillation roller is extremely easy to operate. Simply switch it on – 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. It results 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 the bitumen from the top surface of the carriageway.
Benefit 4: Low vibration emissions
Oscillation drums do not lift off the ground while compacting. In comparison to vibrating drums, with oscillation drums only around 15% of the vibration is directed into the substrate around the roller. This means that oscillation rollers can also be used without problems for dynamic compaction near vibration-sensitive buildings or installations. Because the rollers are also much quieter, they help to protect the environment. Another benefit provided by low-vibration compaction is that it reduces component wear and is also perceptibly less tiring for the roller drivers.
Benefit 5: Material-friendly compaction
With vibration compaction, once a certain level of rigidity has been achieved, there is a risk of destroying the material structure or crushing the aggregate. This is not the case with oscillation: it ensures that the aggregate particles are redistributed undamaged. Oscillation thus avoids detrimental aggregate crushing and over-compaction. Moreover, oscillation compaction produces watertight, long-lasting joints without damaging the cold asphalt.
Benefit 6: Wider temperature window
Oscillation widens the temperature window in which compaction is possible because even at lower temperatures, it can be used to compact without damage. For this reason, oscillation is particularly suited to the compaction of thin layers or on fast-cooling surfaces such as on bridges. Moreover, this characteristic increases flexibility during the construction process.
Customers worldwide are moving to oscillation
As the examples show, dynamic compaction with oscillation has many intrinsic benefits and increases road construction quality. This is common knowledge among building authorities and private customers alike. It is hardly surprising, therefore, that they increasingly specify the use of oscillation rollers for compaction when quality and longevity are paramount. Very recent examples include the construction of the Formula 1 motor racing circuit in Baku, where medium and heavyweight tandem rollers were used, and refurbishment work in the city of Vienna, for which the use of compact rollers with oscillation was specified.
Last but not least, oscillation has also proved its worth in large projects. Here, the rapid increase in compaction ensures an optimised process that can be carried out with fewer rollers.