Draw-roller unit for a web-printing machine

A draw-roller unit for the transport of a paper web (P) in a web-fed printing machine comprising:

• a draw-roller unit (20,21) having only one single suction roller (20b, 21b;
• 30') formed by a draw roller, round which the paper web (P) is looped along a specific circumferential portion;
• means for generating an air-suction effect along said specific circumferential portion, in such a way that on said specific circumferential portion on the paper web (P) is pressed against the surface of the suction roller, whereas the remaining circumferences of this suction roller experiences no such effect;
• said suction roller consisting of a fixed hollow roller core (65) and a roller casing (61;
• 61') rotatable about said core and made of light material, consisting of plastic impregnated with carbon fibers, and provided with suction portions (62) distributed over its circumference, said suction ports being arranged in successive zig-zag patterns, each pattern consisting of line segments alternating at one of a first and a second angle with respect to the direction of movement of said web, each line segment being defined by at least three suction ports with the spacing between the suction ports of a pattern being smaller than the spacing between the patterns;
• a drive motor having a rotor shaft, wherein the roller core (65) is equipped on its one side with an axial hollow connection piece (68b) for fastening to a machine stand and for connection to a vacuum source, on its other side with a bearing journal (66) and on its circumference with two radial partition walls (69) arranged at a specific angular distance from one another and enclosing a suction chamber (72) between them, wherein the circumferential wall of the roller core (65) within the suction chamber has passage orifices (70), and wherein an end of the roller casing (61) facing away from the connection piece (68b) tapers to form a connecting flange (61b) which is intended for fastening to said rotor shaft of said drive motor and which is mounted rotatably on the bearing journal (66) by means of a bearing (71), whilst another end of the roller casing (61) is mounted by means of another bearing (71') on said hollow piece (68b);
• and
• wherein gaps are provided between an inner circumference of the roller casing (61) and radially outer ends of the partition walls (69) which are approximately airtight.