A forming assembly comprises two presser members (22,24) each having a corrugated surface for receiving a workpiece made up of generally diamond-shaped pockets (10). Each presser member is made up of sections (22a,22b; 24a, 24b) mounted on slide rods (38) for movement between a spaced-apart position, in which a workpiece can be located therebetween, and a closed position, movement into which, while the workpiece is held between the presser members, is effective to compress the workpiece laterally. For holding the pockets in their diamond shape formers (20) are inserted therein. A flange (18) is formed at one end of the workpiece and integral therewith by pressing outwardly folded material against a lateral end face of the presser members (22,24) using a presser plate (52). This forming method is especially suitable for forming self-supporting filter units.

An apparatus (10) for manufacturing a filter element includes a first mould element (12) having a plurality of spaced parallel rib (14) defined thereon. A second mould element (18) is arranged in spaced alignment relative to the first mould element (12), the second mould element (18) carrying a plurality of spaced parallel ribs (22) displaceably thereon. A displacement means (24) which includes a cam arrangement (28) is mounted on the second mould element (18) for displacing the ribs (22) of the second mould element (18) sequentially towards the first mould element (12) such that, in use, when the ribs (22) of the second mould element (18) are displaced into meshing engagement with the ribs (14) of the first mould element (12), pleats or folds are formed in a sequential fashion in a batt of filter material arranged between the mould elements (12,18). The cam arrangement (28) comprises a plurality of cam members (32), a cam member (32) being associated with each rib (22) of the second mould element (18) and the cam members (32) having consecutively greater dwell angles to facilitate the sequential formation of the pleats or folds in the batt.

Das Verfahren ist für die Herstellung einer plissierten Filtereinlage (4) aus einem Thermoplast vorgesehen. Die Faltenwände (7, 8, 9, 10, 11, 12, 13, 14) sind in den zur Abströmseite (6) der Filtereinlage (4) hin offenen Filterfalten durch aus dem Filtermaterial selber geformte, längliche Ausbuchtungen (15) beabstandet. Im ersten Verfahrensschritt wird das bandförmige Filtermaterial gerafft. Die länglichen Ausbuchtungen (15) werden durch eine spannungsfreie, bleibende Formung des gerafften, auf eine unter der Schrumpftemparatur und über der Verformungstemperatur des Filtermaterials liegende Temperatur erwärmten Filtermaterials zwischen den Bakken einer Formungseinrichtung hergestellt. Die für die Bildung von Faltkanten bestimmten Bereiche (19) des Filtermaterials werden durch mindestens einen Heizbacken auf eine zwischen der Verformungstemperatur und der Schmelztemperatur des Filtermaterials liegende Temperatur erwärmt, bis sich die Unebenheiten des Filtermaterials im Zwischenbereich (19) ausgeglichen haben. Die zur Distanzhaltung in den Filterfalten mit länglichen Ausbuchtungen (15) versehene Filtereinlage (4) behält dabei an den Faltenwänden (7, 8, 9, 10, 11, 12, 13, 14) die ursprünglichen Filtereigenschaften des Filtermaterials, erhält an den Faltkanten eine glatte Oberfläche und weist eine ausreichende Stabilität auf.

A ring-shaped corrugated filter element blank (10) having radially alternate peak and valley folds (12, 14) is placed on a first mold (16) having as many first concentric projections as the number of the peak folds of the ring-shaped blank and as many first concentric grooves as the number of the valley folds of the ring-shaped blank, with the peak folds fitted respectively over the first projections (18) and the valley folds fitted respectively in the first grooves (20). Then, the ring-shaped blank is pressed between the first mold and a second mold (28), the second mold having second projections lying along concentric lines fitting respectively in the first grooves with the valley folds received therein, and second concentric grooves receiving respectively the first projections with the peak folds fitted thereover. The ring-shaped blank is heated while it is being pressed between the first and second molds, thereby forming a ring-shaped filter element. Thereafter, the ring-shaped filter element (10A) is cooled.

A filter manufacturing machine includes a forming device (3) for forming filter tow (5) into a hollow rod-shaped continuous filter body, a forming tube (12) included in the forming device (3) and having a tubular forming path (2) through which the filter tow (5) is passed while being brought together, a mandrel (13) arranged in the forming tube (12) and forming the tubular forming path (2) in cooperation with the forming tube (12), and a heat treating section (17) included in the forming tube (12) and configured to heat the filter tow (5) while the filter tow passes through the tubular forming path (2). The mandrel (13) has a small-diameter portion (13a) located at the inlet of the forming tube (12), a large-diameter portion (13b) located at the outlet of the forming tube (12), and a diameter expansion portion (6) located between the small-and large-diameter portions (13a, 13b). The diameter expansion portion (6) is located downstream of the heat treating section (17) as viewed in the moving direction of the filter tow (5).

In the process according to the invention, an orthogonal filter is manufactured by a knife folding machine. An orthogonal filter comprises a succession of corrugated and non-corrugated sheets which are assembled so as to form a pack or roll. The corrugations form a plurality of channels arranged side by side and having alternately open and closed ends, so as to force the fluid, which is to be filtered, to cross the channel walls. According to the invention, the knife folding machine comprises a folding channel (113) and two folding knives (111A, 111B) which carry out a translation, or combined rotation and translation, movement and push the sheet (103) to be corrugated into the folding channel (113). The invention also relates to an apparatus for manufacturing orthogonal filters.