TLT: How did you get involved in tribology, and what attracted you to sealing technology?
Bock: I was about 18 years old when I decided to study mechanical engineering. After my bachelor’s degree, I took a class about sealing technology and found the topic both interesting and challenging. During my diploma thesis, I expanded the research I had already done on seals with Professor Heinz. K Müller to delve deeper into tribology. I continued to pursue the field of sealing systems and their tribology at the university until I completed my doctorate. Once I graduated, I started my career at Freudenberg Sealing Technologies and have been involved in the development of dynamic sealing systems and tribology ever since. 

Tribology and sealing technology encompass not only product development, experimental tests and proof of function, but also theoretical considerations, modeling and simulation. My teams have been working together on this for more than 25 years, expanding our understanding and development of new tribology applications that address friction, lubrication and wear in interacting surfaces that are in motion.

TLT: What recent tribology topics are you focusing on?
Bock: I’m currently interested in the fully coupled elastohydrodynamic lubrication (EHL) simulation model for the prediction of the leakage and performance in radial shaft seals (RSS). I worked with colleagues who presented a paper on this topic at the International Sealing Conference in Stuttgart, Germany, on Oct. 1-2, 2024. The summary tells the story: The pumping and leakage behavior of RSS has challenged researchers for more than half a century. While the main phenomena contributing to reverse pumping have been identified some decades ago, to this day there is no conclusive proof nor a comprehensive model for the exact sealing mechanisms, making it impossible to derive precise guidelines for radial shaft seal design. 

We, therefore, have developed our own simulation tool based on EHL to gain insight into the pumping mechanism and the sealing performance of RSS. This tool includes all the steps required to simulate the pumping rate, from finite element analysis to the EHL modeling of the sealing contact, including the circumferential deformation of the sealing lip roughness and the treatment of dry spots that may occur locally. Using this tool, we can accurately simulate the pump rate of RSS, and we can get new insights in the sealing mechanism (see Figure 1). 


Figure 1. These graphic representations show results of simulations of RSS that provide unique insights into the tribological mechanisms in the sealing gap. The left side shows the newly developed pressure seal design, and the right side shows the local contact pressure distribution considering real surface roughness.

This model offers deep insight and understanding about the fundamental tribological processes at work in the sealing contact. This software can be used to develop optimized RSS designs. One example is a pressure seal that has just recently been invented with the help of this tool.¹

TLT: How do you think the research and/or development will make a positive impact on society and the scientific community?
Bock: Controlling the tribology of machine elements like seals is the enabler to optimize performance, reduce friction and develop advanced technology solutions across industries. This helps, for example, reduce friction, wear and related emissions.

Driven by intensified regulations, the lubricant industry is facing challenges in terms of restrictions regarding the use of additives, as well as increasing demands for better lubricant performance. As a consequence, lubricant technologies are continuously changing and enhanced. In the tribological system of dynamic elastomer seals, changes in elastomer and lubricant technologies come together (see Figure 2). This leads to interactions between complex substances, such as physical interactions like swelling and shrinkage or chemical interactions like crosslinking and degradation. 


Figure 2. Interactions of elastomer and lubricant technologies. 

The aforementioned simulation methods help to understand the fundamentals of lubricant flow in the sealing contact. By precisely analyzing and controlling physicochemical interactions and how they occur under different conditions, the performance and lifetime of the sealing system can be optimized. Therefore, advanced characterization methods are essential.

TLT: Can you give an example of the latest innovations of these characterization methods?
Bock: When characterizing the interactions between elastomer and lubricant, the micro-mechanical elastomer properties in the contact zone of the sealing system are of the utmost importance because they are linked to the dynamic sealing mechanism.

For example, consider oil-elastomer interactions—the swelling of the elastomer by the diffusion of the oil, hardening created by additional tribologically-caused crosslinking or the formation of hard deposits. Until recently, the characterization of hardening or softening was done manually with a visual haptic approach. 

A new characterization method is based on micro-indentation and provides quantitative and reproducible data (see Figure 3). With this new method, small but important changes in the elastomer properties can be precisely determined and differentiated. 


Figure 3. A new characterization method is based on micro-indentation and provides more quantitative and reproducible data.

TLT: What are the biggest challenges you face in your research and/or development?
Bock: Today, a key challenge is the combination of application demands driven by enhanced performance requirements, increasing speeds, higher temperatures and so forth, while pursuing developments that meet new sustainability requirements. 

Regardless of whether new seal designs are developed to address increased performance conditions, or new materials and lubricants that are tested with environmental sustainability in focus, extensive development resources are a key success factor. 

For my team of engineers and technical specialists, all essential resources are available. We are focusing on understanding the complex tribology of RSS, developing analytical methods and collaborating with customers to provide application-specific optimizations of the tribological system. 

These resources and a focus on the fundamentals of RSS tribology enable us to find solutions to these challenging trends.

TLT: Please give any suggestions or advice to young researchers and engineers.
Bock: Tribology has an immense impact on CO₂ emissions in the lifecycle of products and thus on the potential to help address climate change due to global warming. Friction requires a lot of energy; the service life of products is shortened, and huge economic damage occurs. Reducing friction and extending longevity can be important industrial strategies for defossilization that will help save the environment. We need new minds to help develop tribological technologies that will guide these efforts forward with vigor and dedication. 

Studies revealed that today 20%-23% of total primary energy consumption is lost to friction with an estimated long-term savings potential of 30%-40%.

This potential must be leveraged and expanded upon going forward! In the end, tribology is about minimizing wasted energy and optimizing performance across industries. It enables more energy efficient machinery, reduces the environmental impact of friction and wear in mechanical components, thus extending their life and is critical to advancements in fields like alternate energy, renewable resources, transportation and medical devices, among others. 

Supporting these achievements will require a lot of research to generate further knowledge and leverage potential. I strongly recommend that tribology—in all its aspects—is considered a fundamental requirement and field of study for new professionals in the engineering and research and development communities. We must maintain a strong pipeline of experts who understand that if a product lives twice as long, this not only saves energy but other resources as well. This is more topical today than ever before. Tribology will always remain important in addressing sustainability in every respect. We must build this for the future!

REFERENCE
1. International Sealing Conference (Oct. 1-2, 2024), “Sealing technology – Challenges accepted!,” https://doi.org/10.61319/2oahh0dh.

You can reach Eberhard Bock at eberhard.bock@fst.com.