Method of making a filter insert of nonwoven material in the form of a

Abstract

A filter insert of nonwoven material in the form of a pleated pack is self-supporting and consists of thermally weldable nonwoven (1). Each of the two outside ends (3) of the pleated pack (2) is hemmed by the nonwoven material (1) forming the pleats, which is folded over in the same direction and at the same time is fixed in tight contact to the corresponding folded of the adjacent pleat end. At the same time the nonwoven material projects beyond the near crease of the adjacent pleat end by 0.5 to 1.5 times the pleat spacing. For manufacture, the flat filter material (1) is first pleated and then a defined pleat spacing (7) is produced by drawing it apart to a limited extent. Then the two outside edges (8) of the pleated pack are gripped between comb-like tools (9) entering pincer-wise into the pleating at top and bottom, leaving the filter material projecting beyond the tools on each side by 1.5 to 2.5 times the pleat spacing (7). The projecting material (10) is folded over on both sides by means of a first pressers (11) acting thereon, until the projecting material (10) contacts the adjacent pleat end, so that the edges overlap one another. Energy permitting the thermal welding is delivered through these pressers (11). Additional pressers (12) that follow fix the welds during the cooling. Then the comb-like tools (9) are removed and the pleated pack is cut to length.