As one of the inventors of Friction Inserts and an application engineer at Freudenberg Performance Materials, Tobias Speth tells the story of innovative friction enhancement technology. Where did the idea come from? How did it come to reality? Which important benefits will it bring to customers in various industries?
My father has been studying friction-enhancing technologies since 2001. Since 2010, I myself have been working with technologies and products used for this application. Together, we participated in project GECKO (Design and identification of characteristic data of friction contact optimized surfaces) of the FVV (Forschungsvereinigung Verbrennungsmotoren - Research Association for Combustion Engines). One important insight we gained from this research project was that a reproducible and efficient solution for increasing the friction coefficient must necessarily be based on hard particle technologies. Friction Inserts are the result of this development.
We were also motivated by the fact that increasing the friction coefficient represents a key technology for enabling lightweight manufacturing concepts, as well as satisfying future performance requirements in the automotive industry. Whether in hybrid, electric, or hydrogen vehicles, our technology has a critical influence on the efficient, reliable and sustainable design of these vehicle systems.
Initially, we were not thinking of a nonwoven carrier at all. It was critical for our development that the hard particles increase the static friction coefficient in the system without any additional tolerances occurring on the parts. In addition, efficiency and sustainability at the industrial scale had to be key requirements of the product, which made the selected materials and the manufacturing processes important factors as well.
In the first development phase, many of the tested materials significantly impeded the effect of the particles or failed to satisfy our requirements for other reasons. Interestingly, the nonwoven that was used, not only satisfied all requirements, but it also had the advantage of dimensional stability. As a result, the hard particles can be easily transported in a defined grain size and quantity allowing for a precise position in the friction joint between the two parts. The structure of the carrier material also ensures that no additional tolerances need to be taken into account.
Thanks to the physical application process for coating the hard particles onto the nonwoven surface, we can control the deposition rate of the particles within a very narrow tolerance window. The achievable static friction coefficient in the final customer application is therefore subject to only marginal fluctuations. In other words, the necessary prerequisites for utilizing our Friction Inserts as design elements were achieved already during the development phase. In comparison, typical hard particle technologies are still generally used today as repair solutions or with very high safety margins.
Our portfolio is unique with regards to the grain sizes of the hard particles applied. While previously available grain sizes were limited to 35 µm, we offer grain sizes up to 115 µm. With this increase in size of the hard particles, we can achieve a maximal increase in the static friction coefficient for instance even on e-coated parts, without negatively impacting the corrosion behavior of the joint. Another advantage of our Friction Inserts is that they consist entirely of inert materials, therefore no additional metal material is added onto the friction joint which could negatively influence the corrosion behavior of the components.
Because the entire diameter of the hard particle is available for increasing the friction coefficient, we can achieve coefficients of up to µ=0.95. A micro interlock is created in the friction joint of the connection during the bolting or press fitting of the components. The magnitude of the achievable static friction coefficient is based on the mechanism of material displacement at the friction joint. For the respective applications, this means that the harder a material pairing is, the higher the maximum achievable static friction coefficient can be achieved. For hard-soft combinations, the softer joining component is therefore the limiting factor for the performance. However, the friction coefficient is a system parameter and thus depends on many different factors. The materials of the joining components are only one factor that we take into consideration for selecting the correct grain size and particle distribution.
Initially, we ask customers to fill out our Application Information Sheet (AIS) and to provide a drawing of the application surface. Based on this information, we can search our database for similar material combinations and contact pressures to recommend a Friction Insert specification for the initial testing in order to achieve the customer desired performance. Based on the drawing provided, we then determine the geometry of the nonwoven cutting that will be applied to the part. Thanks to the properties of our product, it is possible to apply Friction Inserts locally in specific areas where load peaks arise, therefore optimizing costs.
We offer our customers the option of ordering initial prototypes for application tests in diverse configurations for a prototyping fee. After the test runs, we provide an assessment on the surfaces of the tested components. Based on the surface effects, we can identify which modifications to our product configuration are required to optimize the results.
When all test runs have been completed successfully and the customer has verified the performance of our Friction Inserts, we also support the customer in implementing a suitable application process. This process can be performed manually or fully automated as an inline or batch application.
Friction Inserts are currently used primarily in the automotive industry. Areas of application include engines, chassis, and the powertrain. One example where we have already successfully implemented our Friction iInserts is in a torsional vibration damper. With our broad portfolio, other new applications are also possible, particularly in the chassis for suspension arms, wheel carriers, as well as for bearing components of vehicle systems in general. Our Friction Inserts have also contributed to increasing the range of electric vehicles thanks to significant weight reductions.
In addition to the automotive industry, we have customers in other industry sectors, such as the wind turbine industry.
Here, the primary goal of our customers is to improve the efficiency of the systems by using longer rotor blades. However, this improvement is to be achieved without design alterations to the flange connections. Due to the significantly high torque requirements that must be transmitted by the flange connection, the bolts can deform under certain circumstances, causing service work to be more difficult. Increasing the friction coefficient with our Friction Inserts supports the connection’s ability to transmit the arising torques, and thereby preventing deformation of the connection elements.