Having become the industry standard for physical toughness in various components including o-rings, polyurethane sees active service in applications requiring resistance to abrasion, tear, and high tensile strength. Urethanes possess a unique molecular structure of tight bonds between soft polyol segments and hard isocyanate segments, creating a strong but flexible elastomeric backbone. Polyurethanes are also unique in that they have a number of serviceable forms, from low strength liquids to highly cross-linked thermoplastics. Premiere urethane product supplier Real Seal commonly handles the two most often used in the sealing industry; Thermosetting and Thermoplastic.Thermosetting polyurethanes possess bonds that are similar to standard elastomeric materials in that they are non thermally-reversible; that is to say that once they are formed, the bonds cannot be broken down and then reformed with the addition and subsequent subtraction of heat. Thermosetting polyurethanes are typically processed in the same manner as other thermosets, being mixed in standard rubber equipment such as rubber o-rings. Typically molded through compression, transfer, or hot platen injection molding methods, this class of urethanes also covers those formed through liquid casting, rotational molding, RIM, and autoclave.
Thermoplastic polyurethanes possess thermally reversible bonds that allow gasket seals, for instance, to liquefy with the addition of sufficient heat and resolidify upon cooling. Thermoplastic urethanes are typically formed using injection molding equipment, however, extrusion, thermoforming, vacuum molding, and hot-knife welding are also possible.
The chemical type of the polyol backbone used when compounding polyurethane material is one of the two major contributors to its physical properties and relative chemical resistances. There are three types normally utilized in the production of o-rings and specialty seals:
Polyester Based: The most commonly used, providing excellent mechanical properties with resistance to hydrocarbon oils and hydraulic oils. Most urethane seals are based on polyesters.
Polyether Based: Compounded for better hydrolytic stability and good low temperature properties while maintaining the other excellent properties that urethane possesses.
Polycaprilactone Based: A subgroup of polyesters, polycaprilactones impart some of the hydrolysis resistance and low temp properties of the polyethers to the outstanding oil resistance and mechanical properties of polyesters. For additional information on polyurethane o-rings and seals, please visit http://www.real-seal.com/ to learn more.
