CHAPTER 10 - Manufacture of Seals and `O' Rings

Abstract

This chapter provides an outline of the processes used in the manufacture of rubber seals and ‘O’ rings. Some base formulations of rubber compounds, along with their use and physical property data are also included for reference. In the case of manufacturing of “O” rings, the specified rubber compound is mixed and calendered and plied up to the desired thickness, then sheeted out on a two-roll rubber mill, or extruded. These unvulcanized rubber blanks are then prepared in for subsequent molding operations. Vulcanization is done in case hardened mild steel or Nitralloy molds. Large and small ‘O’ rings can be molded concentrically in the same mold. The flash at the parting line is either stripped off by hand or by trimming in a tumbling barrel using solid carbon dioxide. The manufacturing process for rubber seals consists essentially of at least five operations: forming; either calendering, remilling, extrusion or press curing; cutting to produce blanks of the required size from the calendered sheet or extruded profile, or from the remilled sheet for filling the molds; hand building of blanks and fabric inserts; molding and curing; and trimming to remove molding flash. Millions of seals and ‘O’ rings, manufactured from many kinds of rubbers and with varieties of compounding ingredients are produced in order to conform to the varying requirements of the industries that use them. The main constraints faced by the molding shop are the differences in mold output versus press output.