Wellendichtringe für höhere Betriebsanforderungen

FKM 1995 Issue No. 203 Project No. 165

Final report
Abstract:

Shaft sealing rings with PTFE sealing lips (PTFE sleeve sealing rings) are becoming increasingly important due to their high chemical and thermal resistance. In this study, both commercially available sealing rings and sealing lips manufactured at the institute were investigated experimentally. The investigations focused on radial force, frictional behavior, conveying behavior and tightness, preferably under unpressurized conditions. The influence of the shape of the sealing lip was investigated using the self-manufactured sealing lips and experiments were carried out with return structures for changing directions of shaft rotation. The sealing lip is pressed against the shaft only by expanding the sealing lip during assembly on the shaft, without the spiral spring that is usual with elastomer radial shaft seals (elastomer RWDR). When new, the sealing rings have a high radial force at room temperature, which decreases irreversibly due to creep and reversibly at high temperatures. The radial force is mainly determined by the thickness of the sealing lip; the material and overlap have little influence. Contrary to popular belief, the frictional torque of PTFE sleeve seals is not lower than that of elastomer RWDR. In dry running and with low lubrication, the frictional torque is determined by the high radial force; with good lubrication and therefore fluid friction, the large contact surface is the determining factor. The course of the frictional torque over the speed shows that liquid friction occurs in the sealing gap even at low sliding speeds. At high speeds, the friction values determined were between 0.2 and 0.7, which is much higher than the values often stated in the literature. When pressure is applied, the frictional torque increases approximately linearly with the pressure. With PTFE sealing lips, there is no natural recovery mechanism as with elastomer RWDR. Reliable tightness is only guaranteed for sealing rings with a spiral groove; high leakage must be expected without a spiral groove. Abrasive particles in the oil are not the cause of leakage, but lead to high wear on the sealing ring and shaft and thus to reduced tightness. With appropriately designed recirculation structures, recirculation in both directions of rotation is possible in principle. Among other things, the number, size, depth and position of the structures as well as the thickness and expansion of the sealing lip influence the recovery. If PTFE sealing lips are operated in dry running, the PTFE compound of the sealing lip is decisive for the service life of the sealing lip and the wear on the shaft. A long service life of the sealing lip and at the same time low shaft wear is possible.

Scope of report:
1175. ,101 Fig., 40Ut.
Start of work:
01.04.1992
End of work:
30.11.1994
Funding body:
BMWi I AIF-No. 8911
Research unit:
Institute for Machine Elements at the University of Stuttgart
Head:
Prof. Dr.-lng. G. Lechner Project manager: Prof. Dr.-lng. H. K. Müller
Editor and author:
Dipl. -lng. Ch. Hoffmann
Chairman of the working group:
Dipl. -lng. 5. Merzianis, Mercedes Benz AG Dr. -lng. D. Frey, Zahnradfabrik Friedrichshafen
Chairman of the advisory board:
Prof. Dr. -lng. H. Kipphan Heidelberger Druckmaschinen AG, Heidelberg