Two Are Better Than One

In order to prevent sealing elements from entering the extrusion gap (detail image on the left), Freudenberg Sealing Technologies develops two-component seals with the required strength.

But in a sealing system made of two elements, there is the danger that the slide ring might be carried along with the shaft. The two sealing elements would then move in relation to one another and could thus be exposed to increased wear. The higher the stresses from the pressure and the temperatures in the hydraulic system, the greater the danger. Freudenberg wants to solve this problem with the new firmly joined two-component seals made of polyurethanes and high-performance plastics. Since the individual material components of the rotational seals no longer rub against one another, the seals can be used with an expanded power spectrum and thus in a broader range of applications.

In the development of its new rotating seals, Freudenberg Sealing Technologies benefits from the experience that the company has had with two-component rod seals for hydraulic cylinders. The requirements on the sealing system are similar, but in those cases, the seals must withstand linear movement, not rotation, because the rod in the hydraulic cylinder moves back and forth. In the production of the two-component seals, the polyurethanes with different degrees of hardness are bonded to one another in an injection molding process. The bond benefits from the fact that the individual components come from the same material family. One challenge that the developers of the new rotating seals are facing is transferring the process to two-component seals that combine substances from different material families.

For the manufacturers of hydraulic cylinders, the main advantage of the current two-component rod seals is that they allow greater tolerances in the design of pistons and rods. The seals exhibit greater strength with regard to the extrusion gap. As a result, it can be made larger than it would be in conventional sealing systems. The sealing ring can be mounted more easily because the material combination can be optimized to this end. Freudenberg Sealing Technologies now wants to develop this design flexibility for the manufacturers of applications that are equipped with rotary feedthroughs.