Always Adapting - Since their early days, when they were made of rawhide, radial shaft seals, rotary shaft seals or lip seals - all different names for the same component - have played a key role in the automotive and chemical industries. Of course, as chemical and automotive engineering progress, making possible what was once thought to be impossible, these little but vital elements are called upon to keep pace.

No wonder PTFE is recognized as a high-tech plastic, as its outstanding physical attributes and superb processability have helped make it the material of choice for numerous sealing challenges throughout these industries. Yet, even PTFE must adapt to meet ever-changing technological and environmental demands.

Recognizing the seal market's need for innovative materials, Dyneon, part of the 3M Advanced Materials Division, strives to stay ahead of the advances by anticipating requirements before they become acute. Through its commitment to providing new materials for sealing applications, the company has succeeded in developing and manufacturing an exciting new high-performance PTFE compound for use in the manufacture of dynamic seals, such as radial shaft seals and rod packings.

The new material, named 3M Dyneon Compound NST 1111R, offers many significant advantages for every step in the automobile industry's value chain, as well as the chemical industry, consumers and the environment. The innovation constitutes a major breakthrough and promises to make possible a multitude of solutions that will be useful to meeting today's and, more importantly, tomorrow's sealing challenges.

Compounding Expertise Is Key

Until now, PTFE compound lip seals have usually contained fiberglass, which, although strengthening the seals, left much to be desired because of the fibers' irregular form and disorientated configuration within compounds. NST 1111R, the first advanced PTFE compound in Dyneon's New Sealing Technology (NST) portfolio, shows significantly improved features, such as a lower permeation and improved wear. It also complies with the requirements for sealing applications.

Dyneon NST 1111R is the product of compounding Dyneon's high-performance PTFE with 3M solid ceramic microsphere fillers, an effort that required a sizeable financial investment for the development, significant time and a great deal of technical knowhow. However, the outlay was worth every cent.

To unleash the enormous potential of this new material, though, 3M had to master several challenges first. For example, one of the biggest challenges encountered in trying to compound the micro-sized 3M Microspheres with PTFE was the spheres' inherent tendency to agglomerate.

Having overcome this hurdle, 3M contracted an independent testing institute (the University of Stuttgart's Institut für Maschinenelemente) to test the new material. Both these and other tests performed at Dyneon's facility in Kerkrade, Netherlands, confirm, among several other key improvements, the superiority of NST 1111R over the conventional PTFE-fiberglass-filled compounds. The reference materials used for the comparative tests were the standard Dyneon PTFE-fiberglass compounds used in the application today: 3M Dyneon PTFE Compound TF 4105, containing 25% fiberglass, and TF 6711, containing 5% glass fibers and 5% molybdenum disulfide.

Dynamic Seal Applications

The tests performed by the Institut für Maschinenelemente clearly demonstrated that with NST 1111R it is possible to reduce lip seals' thickness to 0.5 mm and 0.65 mm from today's commonly used 0.8 mm, thus lowering the radial load and consequently the friction torque. Even with these reduced lip-seal thicknesses the findings proved a significantly reduced leakage rate compared with the reference material (Dyneon TF 4105). All PTFE compound test specimens showed only minor wear after the 240-hour endurance tests.

"The new material clearly outperformed the conventional materials in our tests, displaying superior durability, lower friction torque, lower leakage rate while using less material," said Professor Werner Haas, director of the Institut für Maschinenelemente. For dynamic radial applications in the automotive and chemical industries, the test results are welcome news, confirming that NST 1111R has a bright future, whether as a seal for axles, or hydraulic or chemical pumps.

The list of Dyneon NST 1111R's advantages compared with Dyneon TF 4105 is long, including 17% lower friction coefficient for better economy, greater component durability and life-cycle time, as well as longer service intervals and 13% greater thermal conductivity - which leads to enhanced heat dissipation. Particularly useful to the chemical industry are the new material's significantly lower leakage rate, and a 98% improvement in permeation, based on tests using helium. The material shows improved tear resistance as a result of the ceramic microspheres' smooth and round geometry.

Static Seal Applications

In general NST technology's improved permeability is also very welcome in static seal applications, as is its excellent deformation-under-load performance. Therefore, in still another new product development, Dyneon will announce the launch of its second sphere-filled PTFE, this time with 3M Glass Bubbles, microscopic hollow glass spheres. This PTFE compound is engineered specifically for static applications in the chemical industry.

Processors Have a Lot to Gain

"3M's microspheres' uniform roundness permits significantly better processing of NST 1111R into and from billets or rods, providing smoother surfaces, which is an enormous benefit to processors" said Gerd Beul, Dyneon marketing manager for general industry. "Another clear-cut advantage for processors is improved material utilization."

NST 1111R's superior physical properties allow processors to reduce waste and the amount of raw material per manufactured unit, thus boosting the efficiency and environmental performance of their operations.

There's More To Follow

Like our world, technology that improves the quality of our lives - directly or indirectly - never stands still. For this reason, even materials like PTFE compounds require further innovative development to remain viable solutions to future sealing requirements. Dyneon's New Sealing Technology portfolio is being developed to meet exactly these needs. NST 1111R, a compound engineered for automotive and chemical industry applications, is the first of what promises to be many more high-performance PTFE compounds. The next product is already on its way, featuring 3M Glass Bubbles and holding great promise for static sealing uses. And especially interesting: All the PTFE compounds may be varied to meet specific sealing application and processing requirements.