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Sealing technology manual for the process industry - Friction optimization

The friction of elastic materials on hard surfaces differs significantly from friction processes between two metals. The known states describe the conditions during the fric- tion of sealing materials only insufficiently: • Fluid friction (the two gliding partners are completely separated from each other by a lubricant film) • Mixed friction (the gliding partners touch each other only on the roughness peaks) • Dry friction (no lubricant available) Due to the elasticity of the sealing material, the elastomer adapts to the roughness of the mating surface, which in- creases the friction force significantly. The softer the elas- tomer and the higher the force with which it is pressed against the mating surface, the more this effect is evident. The conditions are therefore significantly different from those of classical friction between two solid bodies. Reasons for a necessary friction reduction in elastomer products: • Reduction of the adhesion of seals to each other or to the container walls. This is particularly necessary in case of automatic assembly. O-rings, for example, should not “stick” to each other, but glide easily • Reduction of friction during installation of seals. For ex- ample, if O-rings must be pushed over shafts or shoul- ders, they can easily become twisted in case of excessive friction and therefore also lie twisted in the groove. This increases the risk of leakage • Reduction of friction in dynamic applications with the aim to increase the service life of the seal Dusting with talc (magnesium silicate hydrate) Treatment with talc prevents the seals sticking to each other and to container walls. It simplifies installation, but is not suit- able as a durable friction reduction for dynamic applications. Automatic assembly equipment can be contaminated by talc. Immersion in emulsions The same effect as in talc coating occurs by wetting the sur- face with emulsions. The coat application here does not rest loosely and in powder form (and thus dusty) on the surface, but is liquid and adheres to the surface. Therefore, the con- tamination tendency is lower than for talc dusting. FRICTION OPTIMIZATION APPENDIX PRODUCT PORTFOLIO MATERIALS RESISTANCE & PURITY ENGINEERING PLASTICS ELASTOMERIC MATERIALS TECHNICAL FUNDAMENTALS INTRODUCTION 29

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