Technology: Reducing friction in seals

Weinheim, Germany – Freudenberg Sealing Technologies (FST) and Freudenberg Technology Innovation (FTI) have developed a new coating for rotary shaft seals to improve the wettability of the sealing lip.

The new 75 FKM 585 plus coating, said FST in a release, forms a flexible bond with the elastomer of the seal and significantly improves wetting with synthetic lubricants, particularly for poorly wetting lubricants based on polyglycol.

The wettability is an important factor in the optimum function of rotary shaft seals, as it reduces wear and prevents damages to the shaft caused by contact. 

The new coating, according to FTS achieves optimum lubrication in gears and pumps with synthetic lubricants. 

"We have succeeded in coating the sealing lip in such a way that polar oils distribute much better," explains Matthias Adler from FST's global materials development department in the Simmerring Industry division.

"The mechanics of the layer have been modified so that it forms a flexible bond with the elastic material of the elastomer over a long service life – even under dynamic load. In addition, the coating is applied where no wear occurs.” 

The product was specially designed for customers who already use the standard Simmerring 75 FKM 585 seals in drives for which the use of polyglycol oils is recommended by the manufacturers. 

The elastomer is coated using plasma-assisted chemical vapor deposition (PE-CVD). 

In this process, the elements in the process gas form a chemical bond with the surface of the base body. The decisive criterion for the optimisation of the wetting behavior is the targeted modification of the interaction between the coating and the synthetic lubricant. 

The measurements show that by using special components in the new surface coating such as carbon, oxygen and silicon in a certain molar ratio, optimal wetting can be achieved compared to the standard material 75 FKM 585. 

The layer thickness of 75 FKM 585 plus is a few hundred nanometers and its properties meet the standards of the manufacturers of industrial gear units with regard to oil/elastomer requirements, according to FST. 

Although designed for particularly low wear at high revolutions, the coating has reduced the coefficient of friction to significantly lower than that of the standard material, even at low speeds such as in the breakaway forces and mixed friction ranges. 

The newly developed technology is not limited to applications with FKM, according to Adler, "but can also be transferred to other materials. Initial tests on NBR and EPDM have also shown positive results in optimising the interaction between coating and poorly wetting oils.”