Eine mechanische Dichtung mit einem elastomeren Rotationselement: Theorie der Entwicklung. Experimentelle Ergebnisse
von A. Kholodenko u. M. Rivkin
This paper presents the results of fundamental research on flexible faced mechanical shaft seals. The effect of stretch and preload on the contact stress were investigated using a nonlinear finite element modeling package. The characteristics of the rubber materials including the stress-strain curves to elongation at break were required to complete the analysis. Pressure forces resulting from the static pressure in the pump stuffing box as well as the friction effects on all contacting surfaces were considered in the model. Stress distribution across the contact surface established the basis for the formation of multiple distinct lips: at least one on the outside or fluid side of the seal and the other on the inside or air side of the seal. This phenomenon is explained by the step change in magnitude of axial stress while traversing the contact in the radial direction allowing the formation of exterior lips and the development of an annular region trapping debris products and process fluid Photomicrographic images of the wear track taken with a Scanning Probe Microscope show distinct wear tracks and the topology of each. Although the chemical composition of the debris fragments of the monomers in the elastomeric rotary or migration of Teflon fillers. Axial variations in the stretched rotary dimensions (waviness) affects seal performance. Statistics for a typical batch of rotary elements are presented and a method of factoring these variations into the seal design is presented. The formation of axial waves on the contact vertex affects the seal performance and is considered in the final design of the seal pair configuration. The results of this work were incorporated into a suite of mechanical face seals covering shaft sizes from 1.125 to 5.000 inches using seven pairs of seals, each pair consisting of a stretched rotary sliding against an unlapped silicon carbide annular ring. Each of these seal pairs were tested on an experimental test device to determine te heat generation and friction coefficients for a wide? range of temperature, pressure, speed, and sealing fluid. Results of these experimental work are reported in a companion paper. An innovative flexible faced mechanical shaft seal using common elastomeric materials was designed and tested to determine it's friction coefficient at a wide range of temperatures and speeds, it's rate of heat generation, and it's feasibility for use in the process industry. The new seal was constructed using an elastomeric rotating element stretched over the sleeve to at last 20 percent of it's original length and an unlapped silicon carbide stationary annular ring. It was found that the main advantage of the elastomeric seal is it's ability to maintain stable lubrication with a fluid film considerably thinner than of traditional hard face seals, and consequently achieve negligible nek leakage. This part is particulary significant with respect to control of volatile organic carbon emissions. An experimental device was designed for precise measurement of the friction coefficient as well as the long term friction behavior of seal pairs in a wide range of liquid pressure and temperature. The original data were obtained for friction coefficient of EPDM, HNBR, HNBR, and TFE /P type elastomers in contact with silicon carbide in the temperature range 15-110°C, linear speeds 0-12ms, water pressure 0.15-0.40 Mpa, and effective contact pressure 0.8-1.2 Mpa. Experiments showed that the friction coefficient constantly grows, typically from 0.05 to 0.15 at sliding speeds of 2-12m/s, with temperature increases from 15 to 70°C. The temperature behavior of the friction coefficient above 70°C greatly depends on the elastomer. For high temperature elastomers, such as FKM, the friction coefficient may decrease slightly at 70°C; whereas, for EPDM, it continues to increase as temperature increase?