Sealing technology manual for the process industry - POM, PA, PU, PEEK

POM – Polyoxymethylene Polyoxymethylene (POM, also called polyacetal) is a semi- crystalline thermoplastic. POM has been on the market since 1956 and is used especially for precision parts because of its high rigidity, low friction coefficients and excellent di- mensional stability. POM is characterized by high stability, hardness and rigidity over a wide temperature range. It re- tains its high strength even at low temperatures down to –40 °C (–40 °F). Its natural color is opaque white due to high crystallinity, but the material can also be dyed in all muted colors. POM has a density of ρ = 1.41 to 1.42 kg /m3 . The water absorbtion factor is so low that it is of no importance for its use: at standard climatic conditions about 0.2%, and at full saturation with water at +23 °C (+73 °F) only about 0.8%. The physical characteristics of the molded parts thus vary only slightly. The good chemical resistance and low water absorption predestine POM for use in contact with food. Many types are FDA-compliant. Due to its high crystallinity, POM is more rigid and firmer than other thermoplastics, especially in the temperature range of +50 °C to +120 °C (+122 °F to +248 °F). POM has a clearly defined tensile yield point at about 8% elongation at room temperature. Below this yield point, it demonstrates good resilience even under repeated stress and is therefore particularly well-suited for elastic el- ements. The high creep rupture strength and low tendency to creep round off the benefits of POM. Suitable areas of application The mechanical properties of POM in conjunction with good friction and wear performance make this material pre- destined for a wide range of engineering applications. Products • Molded parts • Backup rings • Guide rings PA – Polyamide Most commercially important polyamides are partially crys- talline, thermoplastic polymers. They are characterized by high strength, stiffness and toughness, and have good chemical resistance and workability. The properties of the polyamides are largely dominated by the amide groups, which interact with each other via hydrogen bonds. Polyam- ides have a high wear resistance and good sliding properties. The mechanical properties can be further improved by means of fiber composites with glass or carbon fibers so that, for example, strength and impact resistance can be ad- justed to suit the application. Suitable areas of application PA is distinguished by its high strength values as an ideal material for use in mechanical elements such as gears, fric- tion bearings or guide rails. In the sealing area, PA rings are often used as backup rings for a wide variety of sealing ele- ments. PA is characterized in particular by: • High wear resistance • Good damping power • Good dry running characteristics • Low tendency to creep and • Low water absorption PA6: 2.5% – 3.5% • PA12: 0.2% – 0.5% Products • Backup rings • Guide rings POM, PA, PU, PEEK Engineering plastics 52

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