Since the invention of the pneumatic tyre in 1888, there has, in principle, been no change to the combination of a stiff, load-bearing rim surrounded by an elastic rubber tyre filled with pressurised air. From bicycles to lorries, they all depend on this same connecting element between the vehicle and the ground. This is not without good reason: with its suspension and shock absorption properties, the rim wheel system contributes considerably to the driveability and comfort of a vehicle. In spite of further development over the last 127 years, one drawback still remains: if air escapes from the tyres, unrestricted mobility is no longer a possibility.

Michelin tackled this problem and the result is an airless concept which combines the tyres and rim in one component, hence the name Tweel® – created by combining the words tyre and wheel. Combined, a hub made from metal, flexible elastomer spokes, and a tread made from conventional tyre rubber create a maintenance-free and almost failsafe wheel concept, whose suspension and shock absorption properties do not just match up to its air-filled counterpart, but in fact even surpass it in several requirement areas. In addition, the wheel-tyre combination is designed so that the tread ensures low and even distribution of contact pressure. The Tweel® is therefore perfectly suited for terrain that is heavy or damaging to tyres as well as for uses in which the ground surface should be protected, as is the case with lawn surfaces, for example.

It is not for nothing that Michelin North America are currently concentrating the Tweel® production spectrum on land cultivation, gardening and earth moving machines. At the end of 2014, the company opened a new production site for Tweel® manufacture in Peidmont in the US state of South Carolina. Serial production of the new wheel tyres as an original equipment option for professional riding mowers also started at this site.

During production, the metal hub for the lawn mower's wheel is laid into a mould for the spokes and this is filled with cast elastomer. Here Michelin focused its attention on achieving extremely high metering accuracy, reproducibility of the specific formulation, homogeneous component mixing as well as bubble-free filling. After casting, the spokes cure in the oven, forming an almost inseparable bond with the hub. In the last production step, the rubber tread is attached.

With the production of Tweel® the tyre specialist trusts in Hennecke's decades of expertise in the area of low-pressure processing of cast elastomers. The company uses ELASTOLINE F low-pressure metering machines from Hennecke in the production of the elastomer spokes. The machines are suitable for processing up to four principal and four auxiliary components and provide the user with the option of structuring the metering lines in a modular construction. The consistent use of high-quality materials and reliable machine components ensures the best possible production results over the long term. For example, through the use of highly precise gear pumps, which guarantee reliable metering even with extreme mixing ratios.

In addition, product containers with tempered circulating air and stirrers, which are installed in insulated individual cabins, ensure homogeneous and precise temperature conditioning of the raw materials. The mixhead technology of the ELASTOLINE type series is already equipped ex works with a hydraulic control: a special feature which guarantees the processor a superior metering quality. The mixhead nozzles' hydraulic control is responsible for the extremely short and synchronised switching cycles, without which precise metering of this quality would not be possible. The sophisticated mixing chamber and stirrer geometry was developed in elaborate flow simulation procedures, and was further improved through lengthy test series in Hennecke's technical centre. This ensures the best possible mixing quality even with hard to mix raw materials. For particularly high durability and precision, Hennecke produces the mixhead and stirrer in a special alloy.

The metering machine's and mixhead's extremely high-end technology, perfected right down to the smallest detail, reflects Hennecke's decades of experience. Spanning different disciplines, the machine manufacturer's specialists work to create the best possible technology for their customers.

Michelin also aims to further develop the Tweel® concept and make an entirely new connection to the road possible for other vehicles in the future. Tests are already being carried out for conventional vehicles. Perhaps the next revolution is already rolling up to us for equipping passenger cars with the innovative wheel-tyre combination.