Freudenberg develops advanced sealing for ‘demanding’ cobot applications

Weinheim, Germany – Freudenberg Sealing Technologies (FST) has developed a urethane-based sealing system offering enhanced flexibility, wear-resistance and friction properties in cobot applications.

The design, according to the German-bsed company, can support robotic arms to be used in multiple applications – from working in a welding cell one day and a packaging line a week later.

In a release 14 Nov,  FST said it was approached by a customer who needed a sealing system to protect cobot joints from dust, spraying water and other contamination.

“Simple PTFE rings”, widely used for the application, were not able to "guarantee the required IP54 protection class”, said the statement.

The issue, it said, was linked to the high travel speeds and the forces generated in the robot arm, which created temperatures as high as 60°C.

As a first step, FST's team presented a U-ring made of polyurethane, but practical tests showed that frictional forces “to be too great” due to the ring’s relatively large surface.

The limit for those forces, the seals maker said, was 1 newton metre, an “extremely low value”, which made it necessary to significantly reduce the radial forces.

At the same time, FST worked on reducing contact stresses on the dynamic seal lip. The engineers then changed the overall geometry to a z-profile and integrated a second groove.

This, said the German manufacturer, “greatly reduced the contact pressure and met the requirement for a moment of friction of less than 1 newton metre”.

In the practical test, however, the level of wear was still far too high, due mainly to the cobots’ lightweight, largely aluminium construction.

The surface of the cobot material, FST explained, is “relatively rough” due to the methods used during its processing and its basic characteristics.

As a solution, the company engineers developed a three-component solid film lubricant coating, with high carbon content, to further reduce the amount of wear.

With a Shore hardness of 92, the material 92 AU 21101, was “very soft and flexible”, though its tensile strength, at 59MPa, was above the required minimum level of 50MPa.

In response FST said the seal geometry had to be completely reworked once again, FST selecting a Z-geometry with “further optimised” dynamic seal lip, while a static area with a groove was constructed externally.

Using finite element analysis calculations for the lip thickness and a later simulation, FST said it achieved “significant savings” by cutting unnecessary process steps.