Caption: Wear and friction data from application testing on two grades of PEEK.

In today’s manufacturing environment, and especially in the automotive industry, the benefits of High Performance Plastics (HPPs) are driving an ongoing increase in their use. Use of these materials in design and engineering applications provide flexibility, a high strength-to-weight ratio, improved tribological performance and unique chemical formulas that meet a variety of performance requirements. Usage is further being driven by pressure on OEMs to reduce vehicle weights, cut CO₂ emissions, reduce system friction and heat, increase long-term material compatibility and control costs.

While the advantages of HPPs in manufacturing are clear and real, traditional standardized methods for testing the tribological performance of plastics as a measure of part performance in the end application are often less than reliable. Additionally, traditional test methodologies are slow – taking up to five days to yield results – and generally accommodate only four tests per month. This time limitation significantly slows the production development cycle for OEMs.

A challenge

Consider the recent challenge faced by an automotive OEM that needed to reduce production time and costs in the manufacturing of its transmissions. To avoid regrinding the transmission shafts after outsourced heat treatment, the OEM chose to move to a softer metal for its shafts that didn’t require these steps. The softer material also required a change to HPPs sealing elements with the correct tribological performance to prevent surface compatibility issues between the seals and the shaft. Using standard test methods to find the right plastic could have taken months. The OEM needed an accurate but faster solution.

A better way

In developing a new methodology, it was essential to increase the intensity of testing without altering failure mode – the accurate measure of the wear of the plastic. Many existing methods currently in use confuse wear failure with the creep, or melting, of plastic.

Freudenberg Sealing Technologies began work in 2016 on the development of new test methods for HPPs. The company’s customers – in the automotive, aerospace, marine, rail, commercial truck and bus, construction and agricultural industries, among others – were all exploring the use of HPPs in powertrain and hydraulic systems to solve a variety of environmental and performance challenges. Scientists worked closely with material engineers to study the test methods being used in the U.S., Germany and Japan. By extracting and combining critical processes from these methods, Freudenberg developed a new approach to test Plastic Materials.

The methodology delivers reliable, accurate, real-world results in a fraction of the time normally required for traditional HPPs testing. When the automotive OEM working on transmissions approached the company about HPPs compatibility with softer metal shafts, the company was able to identify an optimal solution within days, not weeks, of the request.  

Why it’s better

While faster is important – reducing testing time from five days to four hours, allowing for two tests per day – so is test accuracy. The HPPs test methodology that was developed generates extremely accurate component performance data under real application conditions.

Wear and friction characterization of HPPs is complicated because they are dependent upon a number of system parameters including loads, speeds, temperatures, roughness/hardness, material geometry and others, which can change significantly based on application. Accurate evaluation of tribological performance of HPPs needs to account for these variables, as recommended in this innovative methodology, enabling it to be predictive of part performance.

Environmental advantages

This improved test methodology facilitates real environmental advantages as well. A recent study published by Holmberg and Erdemir (Ref. 2) on the effect of friction and wear on energy consumption, economic expenditure, and CO₂ emissions, concluded that 23 percent of the world’s total energy consumption in the transportation, manufacturing, power generation and residential sectors results from tribological contacts.

Through the appropriate application of tribological technologies, CO₂ emissions and the related economic costs could be significantly reduced – with those improvements underpinned by more accurate testing and reliable results. As shown in the application example in the figure below, changing material essentially reduced friction by a factor of 2.2 or approximately 55 percent. This means that the Co₂ emissions are proportionally reduced by about 55 percent at that specific component in the transmission. Note, however, that this does not mean that the CO₂ footprint of the entire transmission is reduced by 55 percent, as there are several components with frictional losses in the transmission.

Existing and commonly used tribological testing methodologies often fall short of the needs of OEMs and their customers. This innovative approach in testing saves manufacturers time through accelerated product development cycles, improved industry performance and numerous environmental improvements. It’s good for manufacturers, good for the industry and good for the world.

References
1. Sundararaman, S., “Improved Test Method for Tribological Evaluation of High-Performance Plastics,” SAE Technical Paper 2019-01-0183, 2019, doi:10.4271/2019-01-0183.

2. Holmberg, K., and Erdemir, A., “Influence of Tribology on Global Energy Consumption, Costs and Emissions,” Friction, Vol. 5, No. 3, pp. 263 – 284, 2017.

For more information:

Freudenberg Sealing Technologies
Phone: (734) 354-5505
www.freudenberg.com

About the Author:  Dr. Sai Sundararaman is senior scientist at Freudenberg-NOK Sealing Technologies. In this role, he leads research and development projects in the area of polymer tribology for Freudenberg’s Fluid Power Division. Dr. Sundararaman also oversees implementation of product technology collaboration with global partners, leads project planning and management, provides technical capabilities and support across the organization and contributes as a team member to growth and business developments within Freudenberg’s Fluid Power Automotive Lead Center in Findlay, Ohio.