Safety and reliability are what count when it comes to the use of the high-performance rubber Therban® in ship couplings, sometimes of massive proportions. The task of the HNBR rubber in this application is to protect the ship’s diesel engine and drive shaft from damage and so to maintain operational reliability over long distances. That is no mean feat. On cost grounds, the diesel engines of these ocean-going giants – tankers, container ships or floating hotels, which can easily be as tall as a house – run on particularly heavy diesel fractions such as gas oil or heavy oil.

However, since this fuel does not burn anywhere near as uniformly as the light diesel used by modern car engines, the irregular forces acting on the drive shaft, which transfers the engine torque – ranging from 2,400 Nm in yachts to 800,000 Nm in container ships – to the propeller, cause it to vibrate. If left unchecked, these vibrations can lead to damage or even failure of the drive.

In order to absorb these vibrations, a coupling is installed between the diesel engine and drive shaft, the elastomeric insert in which absorbs the shock. Owing to its good dynamic properties, natural rubber is often preferred. The disadvantage, however, is that it ages prematurely in the hot environment laden with oil vapor and ozone. That is why the coupling manufacturer Vulkan Kupplungs- und Getriebebau GmbH & Co. KG, based in the German town of Herne in North-Rhine Westphalia, has also opted for the use of the hydrogenated HNBR rubber Therban®. Resistant to heat, oil, lubricants and ozone, this rubber plays an important part in extending the maintenance interval, thereby minimizing costly dock time.

In order to deliver the performance profile demanded by Vulkan, rubber chemists at LANXESS adapted the properties of Therban® to the requirements of these particular couplings. The results of this collaborative project were unveiled at the “K 2007” plastics fair in Düsseldorf. The coupling presented there by LANXESS transfers the torque via eight cylindrical rubber elements, each weighing 350 g, positioned vertically to the direction of rotation in correspondingly shaped cavities between two metal coupling discs. Rather like press rollers, these cylinders have to resist substantial pressures and dynamic loads without developing any significant internal frictional heat.