lengthwise movement can also be executed with high precision fig2 shows the forming tool 17 in the direction of its longitudinal axis this forming tool 17 comprises a lower part 27 and an upper part 28 and therefore can be opened very easily the forming chamber is coated with a material that has good sliding properties for example sheet bronze 29 the sliding properties can be further improved by introducing appropriate processing liquid the metal strip 11 is fed to the tool through a slit opening 30 rests against the inner wall and is accordingly flanged the possibility of opening the forming tool results in a substantially shorter set up time the metal strip which is shaped to a helical tube in the arrangement is usually of perforated metal sheet the disadvantage of perforated metal sheet is that a substantial amount of material is lost due to the perforation if on the other hand a rib mesh is used for the metal strip the material used will be utilized one hundred percent no scraps remain a helical tube made from rib mesh has the additional advantage that its helical tube only touches the filter element at certain points thus the effective filter surfaces are only minimally lessened by the supporting body fig3 shows a section of a helical tube made with rib mesh it has an outer lock seam 32 and an inner lock seam 33 which effect the joinder of the helical tube in addition the rib mesh has ridges 34 35 which are formed by stamping and stretching and on which the filter element not shown here is supported a further advantage of the rib mesh support body is that a lower flow resistance can be achieved with the same rigidity in addition the production.