Helically wound filter made from roving - wound on under tension and radial pressure without crushing

摘要

A method of making a filter, esp. for a filter cartridge, consists of pretreating a fibrous roving with a hardening agent, then winding the roving helically onto a core and gluing it. Pref., the roving is made sufficiently stiff by the hardening agent to prevent if from being crushed while it is wound on. The hardening agent may be heated to harden it and then dried at a lower temperature; in particular the agent is an epoxy resin which is completely chemically hardened in the final treatment. It may contain a solvent which is evaporated. The hardening may be continued during the winding operation. Before winding on, the roving may be tensioned to stretch it, esp. by passing it during impregnation through a funnel shaped die. A radial pressure may be applied by rollers during winding. During the gluing stage, an axial load is applied to the resultant filter. A stable filter, permitting the passage of particles smaller than the designated size, is obtained.