Process for the production of filter elements for backwashable filter apparatuses

摘要

A filter element (10) designed for a backwashable filter apparatus is composed of a rigid supporting body (12) and a filter sock (18) arranged within the supporting body (12), furnished at its ends with locking rings (14, 16). The locking rings (14, 16) are detachably engaged at corresponding end locking surfaces (20, 22) of the supporting body (12), with the filter sock (18) being tightened. The production of the locking rings (14, 16) and their joining to the filter sock (18) is carried out in the injection moulding process. On cooling after the injection moulding process, the two locking rings (14, 16) shrink, while the fabric remains cold during the welding-on process and does not also shrink. Diameter differences result thereby which lead to a material surplus in the fabric area and thus to a bead. In order to eliminate this bead, the finished filter element (10) is pushed onto a hot mandrel and left there until the relatively thin fabric has been heated approximately to the mandrel temperature of 100 to 150 DEG C and the remaining parts remain cold because of their larger heat capacity and poor thermal conductivity. As a result it is achieved that the fabric, with conformity to the mandrel diameter, experiences a plastic deformation in the sense of a smoothing and calibration. <IMAGE>