12/21/2009, Düsseldorf / Germany


Henkel’s new acoustic damping material improves driving comfort all along the line


Terophon HDF minimizes noise in vehicle interiors

Weight-saving designs are essential in vehicle manufacturing in order to reduce resource consumption and costs. However, the new lightness of automotive being does have its price: noise in vehicle interiors is an undesirable consequence of this trend. With its new Terophon HDF, Henkel has developed a novel and highly efficient acoustic damping material specifically for the automotive and transport industries.

HDF: these three letters stand for high damping foam. These foams are capable of damping noise-producing vibrations extremely fast and well, thus “swallowing” the acoustic effects. The idea for developing this material was prompted by the continuing trend toward light weighting in the automotive industry. To save weight, car design engineers are using ever thinner sheet steel material and turning to alternatives such as aluminum and magnesium. However, these new material grades usually have poorer acoustic performance, which results in noticeably higher driving noise levels inside the car.

Stopping sound transmission
Noise is mainly caused by the banging of car doors, the engine, the gears, the axles and numerous smaller servo motors. The latter serve for the adjustment of seats and windows and as a motor for the heater blower. The acoustic vibrations generated by these sources are propagated throughout the car so that they become audible to the occupants. These sound transmissions are caused particularly by the cavity profiles that are essential to the safety of the chassis. Similar to a pipe organ that resonates, these profiles can turn into resonators and reinforce the noise that is produced.

Up to now, vehicle designers have tried to combat these effects by installing more and more sound-damping bulkheads. These are polymeric materials that start foaming when exposed to heat and that fill and seal cavities in order to prevent the acoustic noise to be transmitted. But designing and building these parts is both time-consuming and costly.

Damping the sound right at its source
The innovative material from Henkel tackles the problem at source instead of fighting the symptoms. This requires a highly efficient material that can eliminate vibrations quickly and completely. And at best, it does so within a single oscillatory period which only lasts a split second.

The mode of action can be exemplified by a simple experiment: A steel ball is dropped from a height of 50 cm onto a flat mat of Terophon HDF foam only a few millimeters thick. Instead of bouncing back off the mat, the ball stops dead upon impact. Trying the same experiment with conventional sound-damping foam demands a high degree of agility from the experimenter, who has to quickly catch the ball as it bounces up from the foam before it has a chance to rocket off the table onto the floor.

The new Terophon HDF can be installed in various parts of the vehicle, e.g. doors and roofs – their resonating cavities tend to behave like the membrane of a huge loud speaker. Furthermore, the new damping material can be applied on longitudinal front beams in the engine compartment and the motor frame with the objective of avoiding sound transmissions. Finally, the foam can be used for the cavity beam of the chassis.

Henkel’s acoustic foam offers many advantages for car manufacturers. In addition to improving the acoustic driving comfort, it can significantly reduce not only the weight of the car but also the consumption of conventional materials such as bitumen.

Advantages for lightweight construction
While the acoustic improvements are instantly revealed by the efficient damping of vibrations and transmissions, the advantages mentioned above require further explanations. The usage of the highly efficient and light damping foam Terophon HDF supports automotive manufacturers by excluding the undesirable acoustic side effects of lightweight construction. A practical example: In the case of a car door the standard acoustic damping mat weighing around 500 grams per door can be eliminated by replacing the anti-flutter adhesive with more or less the same weight of new Terophon HDF. In a four-door limousine, this results in an overall weight reduction of about two kilograms, savings achieved thanks to the reduction of the plate profile not even included. At the same time, the acoustic quality of the doors - meaning the sound that occurs when doors are being closed - increases noticeably.

Decreasing production costs
Also regarding its application, Terophon brings along significant advantages. The product is delivered as granules with a durability of six months. It is not applied manually but automated by means of direct extrusion. This also leads to further reductions of production costs. Upon application, Terophon passes different phases of the automotive manufacturing chain without interferences and eventually foams and cures in the electric paint curing oven at 180°C. This process leads to an irreversible bonding with the auto body with the result that the innovative damping material provides its acoustic performance even beyond the entire life cycle of the car.

“After having proved Terophon HDF on a “test market”, we now secured a global order from a nameable automotive manufacturer”, Bernd Schenzle, Business Manager Acoustic & Preformed Parts Europe, announces. “In addition, selected potential customers are putting the product to the test in order to verify its performance on the basis of tangible referential projects.” Generally, Terophon HDF offers a wide range of application options: Beside the automotive sector, the aviation industry and manufacturers of commercial vehicle and railway cars benefit from the innovative product. But Terophon may also be applicable in other industries: Wouldn’t it be nice to have a dish washer that one hears only upon the “beep” it releases which indicates it is done with the dishes?

Henkel AG & Co. KGaA