EP0415882A2 - Pull roller unit for a rotary printing machine - Google Patents

Abstract

The pull roller unit has only one suction roller (20b, 21b) as the pull roller, in which a constantly acting suction effect is effective along the circumferential section which is wrapped in the paper web, while the remaining circumferential section is not subject to any suction effect. The suction roller has a solid, hollow roller core (65) and a roller jacket (61) made of carbon fibers impregnated with plastic and rotatable about this, with suction openings (62) distributed over its circumference. The roller core (65) is on one side with an axial socket (68b) for attachment to the machine frame and for connection to a vacuum source, on the other side with a bearing pin (66) and on its passage openings (70) with two radial circumferences , provided at a certain angular distance from each other partition walls (69) which enclose a suction chamber between them. The roller jacket is mounted on the bearing journal (66) with its conical connecting flange (61b), which is attached directly to the rotor shaft of the drive motor, and with its other end on the connecting piece (68b), the gap between the roller jacket and partition walls (69) are approximately airtight. Instead of a suction roller, it is also possible to provide a pull roller to which compressed air is applied on the outside along the circumferential section mentioned, or else suction air and compressed air effects are combined.

Description

The invention relates to a draw roller unit for transporting a paper web in a web printing machine.

Previously known pull roller units used in web-fed printing machines, which are used to transport the paper web, each consist of two rollers, namely a driven pull roller and a pressure roller pressing the paper web against this pull roller. Since the paper web is clamped on both sides between these two rollers, these tension roller units can only be used in a printing unit after the printing of the paper web if it is ensured that the fresh printing ink has already dried sufficiently when the paper web has finished printing Pull roller unit passes through.

While the printing ink used in offset printing can be dried with the help of rather short drying devices, so that a drawing roller unit pulling the paper web can be provided at a distance corresponding to this short drying path behind the printing nip, in the case of intaglio printing the drying path is due to the much slower drying intaglio printing ink, the relief-like color pattern forms so long that previously known draw roller units can only be installed at a very large distance behind the printing nip. Otherwise, not only would the roller of the draw roller unit coming into contact with the freshly printed side of the paper web be soiled, but the fresh color relief would also be leveled. Because of this long drying path, rotogravure printing machines in particular have so far not been able to be operated with a paper web transport in the pilgrim step, which pull roller units are as close as possible in front of and behind the printing gap required.

Furthermore, when installing previously known pull roller units, two rollers with their bearings, adjusted relative to each other, must be installed, which increases the material and work involved.

While in conventional web-fed printing machines with continuous paper web transport, in which generally no major accelerations or rapid changes in speed occur, the known draw roller units essentially entail the disadvantages mentioned above, web-fed web presses with paper web transport which can be controlled in the pilgrim step, apart from the mentioned problem with intaglio printing , still other problems associated with the very rapid changes in speed of the web transport. Such a web printing machine, which works with conventional draw roller units of the type described above, is known from DE-C 31 35 696 and is used to print on a paper web with changeable, adjoining formats. For this purpose, a first and a second drawing roller unit and in between a first paper web storage and in front of the printing nip a third and a fourth drawing roller unit and in between a second paper web storage are provided before the printing nip; the first and fourth draw roller units are continuously driven to move the paper web uniformly, while the second and third draw roll units for moving the paper web forward and backward are each controlled by a controlled electromotive drive. All draw roller units each consist of a draw roller and a pressure roller pressing the paper web against it.

In these web printing presses, which operate in the so-called pilgrim step or stop-and-go operation, the paper web is transported by the two cylinders forming the printing nip, that is, in the case of a perfecting machine which works in offset printing, the two blanket cylinders, as long as these sector-shaped cylinders during affect the printing on the paper web. The upstream and downstream draw roller units are controlled so that they generate a certain paper web tension. If, on the other hand, the cylinder pits of these two cylinders pass through the printing nip, the aforementioned second and third controlled drawing roller units transport the paper web in such a way that it decelerates to a standstill within fractions of a second, then moves it backwards by a predetermined distance, then brakes again to a standstill and is accelerated again in the forward direction until normal operating speed.

The known pulling roller units are unfavorable for carrying out these rapid decelerations and accelerations, because on the one hand the masses of two rollers are braked and accelerated quickly and on the other hand both rollers have to be pressed against one another with very strong force in order to avoid slippage of the paper web. However, it has been shown that with rapid changes in the speed of the controlled pull roller, the non-driven, freely rotatable pressure roller, which has to be carried along by the paper web itself, is unable to follow strong decelerations and accelerations and therefore results in slippage of the paper web, which is what of course, the perfect printing and correct register accuracy impaired.

The present invention has for its object to provide a pressure roller unit working without a pressure roller, which strikes only one side of the paper web, ensures a slip-free transport of the paper web and in particular allows the paper web to be given rapidly defined speed changes with high accelerations, as shown in Web presses with paper web transport controllable in the pilgrim step are desirable.

This object is achieved according to the invention by the features specified in the characterizing part of claim 1.

The pull roller is preferably a hollow suction roller provided on its periphery with suction openings and connected to a suitable vacuum source. However, it is also possible to use a pulling roller which is pressurized with compressed air from the outside along the circumferential section wrapped by the paper web, such that the paper web is pressed against the periphery of the pulling roller by this compressed air. Advantageously, the pull roller is also provided on its circumference with openings which open into an inner cavity which is connected to the outside air. In this way, the inside of the paper web covering the openings is subject to normal atmospheric pressure, while the outside of the paper web is under excess pressure. Furthermore, the pull roller according to the invention can be designed in such a way that the contact pressure acting on the paper web is generated by a combination of the negative pressure prevailing inside the roller and the external positive pressure.

So far, suction rolls have only been known for transporting individual pieces, such as, in particular, notes of value, as is described, for example, in EP-B-029268. Here, a suction roller is used to separate out marked notes of value from a series of consecutive notes of value that are continuously transported along a conveyor track and are conveyed on the conveyor track by a chain with push fingers. If a bill is to be discarded, the suction roll is connected to a vacuum source and therefore lifts this bill from the conveyor track, which is transported on the circumference of the suction roll, transported by it to another suction roll and finally fed to a magazine. When sorting out and transporting notes of value through suction rollers, there are practically only forces acting radially to the roller, which only have to be sufficient to bring a note of note, which is only very light, to the circumference of the roller. Tractive forces acting in the tangential direction, such as occur to a considerable extent when transporting an endless paper web, play no role in the transport of notes. For this reason, simple suction rolls were previously not considered as pull rolls for paper web transport, for which a sufficiently strong jamming of the web between two rolls was considered necessary.

Since the pulling roller unit according to the invention has only one pulling roller and the pressure roller that was previously required is omitted, construction and assembly are simplified. In addition, the lack of the pressure roller makes it possible to print the paper web on one side in a intaglio printing unit in pilgrim step operation, since immediately after the printing nip, a pull roller wrapped around by the unprinted paper web side after Invention can be installed. With previously known traction and pressure rollers, intaglio printing could not be carried out in pilgrim step mode because drying of the freshly printed paper web is not possible in front of the traction roller unit because of the length of the drying path required for intaglio printing ink.

Preferably, the traction roller according to the invention has a rotating roller jacket made of a light plastic, in particular made of carbon fibers impregnated with synthetic resin, so that the moving masses are particularly small and have only a small moment of inertia, which is extremely rapid changes in speed in fractions of a time when paper web transport is controlled in pilgrim step mode Allowed to achieve seconds.

The strong adhesion of the paper web to the circumference of the pulling roller, which is necessary for slip-free transport, is probably favored in the case of a roller jacket provided with openings in that the paper web bulges a little into the openings of the pulling roller under the suction or compressed air effect, which makes possible Displacement of the paper web relative to the pull roller is prevented with great certainty even under strong accelerations. The air pressure differences required for reliable adhesion of the paper web between the outside of the paper web and its inside, which covers the openings in the roll shell, are 0.1 to 0.8 bar, depending on the type of paper.

Appropriate embodiments of the invention result from the dependent claims.

• Figur 1 ein schematisch dargestelltes Rollen­druckwerk, welches mit zwei Zugwalzeneinheiten nach der Erfindung zum Papierbahntransport im Pilgerschrittbe­trieb ausgerüstet ist,
• Figur 2 einen Axialschnitt durch eine erste Ausführungsform einer als Saugwalze ausgebildeten Zugwalze, gemäss der Linie II-II nach Figur 4,
• Figur 3 eine teilweise geschnittene Teilansicht in Richtung des Pfeils III nach Figur 2,
• Figur 4 einen Radialschnitt der Saugwalze gemäss der Linie IV-IV nach Figur 2, in vergrössertem Massstab,
• Figur 5 einen Schnitt durch den Saugwalzen­mantel,
• Figur 6 einen Teil der in einer Ebene abge­wickelten Oberfläche des Saugwalzenmantels mit der Ver­teilung der Saugöffnungen,
• Figur 7 einen vergrösserten Schnitt durch den Saugwalzenmantel an der Stelle VII nach Figur 5 zur Veranschaulichung der Form einer Saugöffnung,
• Figur 8 schematisch eine zweite Ausführungsform einer Zugwalze,
• Figur 9 einen Axialschnitt desselben,
• Figur 10 schematisch eine dritte Ausführungs­form einer Zugwalze und
• Figur 11 einen Axialschnitt derselben.

The invention is described in more detail with the aid of three exemplary embodiments. Show it :

• FIG. 1 shows a schematically illustrated web printing unit, which is equipped with two draw roller units according to the invention for paper web transport in pilgrim step operation,
• FIG. 2 shows an axial section through a first embodiment of a drawing roller designed as a suction roller, according to line II-II according to FIG. 4,
• FIG. 3 shows a partially sectioned partial view in the direction of arrow III according to FIG. 2,
• FIG. 4 shows a radial section of the suction roll according to line IV-IV according to FIG. 2, on an enlarged scale,
• FIG. 5 shows a section through the suction roll jacket,
• FIG. 6 shows part of the surface of the suction roll shell developed in one plane with the distribution of the suction openings,
• FIG. 7 shows an enlarged section through the suction roll jacket at point VII according to FIG. 5 to illustrate the shape of a suction opening,
• FIG. 8 schematically shows a second embodiment of a pull roller,
• FIG. 9 shows an axial section of the same,
• Figure 10 schematically shows a third embodiment of a pull roller and
• Figure 11 is an axial section of the same.

First, the general structure of a web printing machine and the transport device for the paper web working in the pilgrim step and then examples of draw rollers are described with reference to FIG. 1.

The web printing machine shown in FIG. 1, which is traversed by the web P to be printed in the direction of the arrows, is in the example under consideration a multicolor offset printing unit working in perfecting. This printing unit has two interacting rubber cylinders 2 and 3, which are mounted next to one another in a frame 1 and rotate in the direction of the curved arrows, each with three sectors, on each of which a rubber blanket 2a or 3a is stretched. The sectors are separated by cylinder pits 2b and 3b, in which the means for tensioning the rubber blankets are subordinate. This offset printing unit is thus designed similarly to an arc printing machine.

Each blanket cylinder 2 and 3 works with four plate cylinders 4 and 5, which are mounted in the frame 1 and which carry offset printing plates and are colored in different colors by corresponding inking units 6 and 7, respectively. In the example considered, the top inking unit has a single ink fountain on each side, while the remaining three inking units are equipped with a double ink fountain on each side. As the dampening units assigned to each inking unit indicated in FIG. 1 show, the example considered is a wet offset printing press, which can alternatively also be operated as an indirect printing press or in a combination of both processes. All inking units 6 on one side are arranged in a removable inking unit frame 8 and all inking units 7 on the other side in a removable inking unit frame 9. In addition, automatic blanket washers 10 and 11 are installed on the circumference of the blanket cylinders 2 and 3, which are moved away from the blanket cylinders during the printing operation of the machine. Is above the rubber cylinders 2 and 3 a drying device 12, 13 installed, which works with UV radiation and through which the freshly printed web runs.

The transport device which is accommodated together with the printing unit in a common main frame 14 is described below.

The web P is unwound from a storage drum, not shown, and passes via a web feed device 15 and a turning bar 16 into a first draw roller arrangement 17, consisting of a draw roller 17a, which is wrapped by the web, and a pressure roller 17b, which presses the web against the draw roller presses. This tension roller arrangement 17 and the tension roller arrangement 23 mentioned later are driven uniformly. The web P then, guided by deflection rollers 24, arrives via a device 18 for laterally aligning the web into a first paper web storage 19, which in the example under consideration works with a vacuum chamber. Such a paper web store is known and is controlled in such a way that the paper web P between the draw roller arrangement 17 and the entrance of the paper web store 19 is tensioned tightly with a predetermined force and the tension of this section of the web is kept constant at a predeterminable value.

At the exit of the paper web storage 19, the web passes through a drawing roller unit 20 which is individually and intermittently controlled for moving the web forward and backward. This pull roller unit 20 has only a single roller designed as a suction roller and functioning as a pull roller 20b, the construction of which will be described later and which is controlled by an individually regulated drive 20a in the form of an electronically controlled motor. The web emerging from the paper web store 19 wraps around it Pull roller 20b from below by approximately 180 ° and then, guided by a deflection roller, runs through the pressure gap formed by the two rubber cylinders 2 and 3, then through the drying device 12, 13 and then loops around a pull roller 21b belonging to a second pull roller unit 21 again about 180 °. This pulling roller unit 21 installed in a frame part 14a above the main frame 14 is constructed like the pulling roller unit 20, can be controlled intermittently for moving the web forwards and backwards and is in turn moved by an individually controlled drive 21a in the form of an electronically controlled motor. After the draw roller unit 21, the web passes through a second paper web store 22, which is constructed and controllable in the same way as the paper web store 19, and is then guided over a plurality of deflection rolls 24 and a further draw roll arrangement 23, which is constructed in the same way as the draw roll arrangement 17 and a uniformly controlled draw roll 23a and a pressure roller 23b pressing the web against it. At the exit 25, the web leaves the printing unit and is fed to further processing stations, for example another printing unit and then the cutting stations.

The transport device described is thus designed such that the paper web is continuously moved from its supply drum to the first paper web store 19 and behind the second paper web store 22, while the section of the web passing through the printing nip of the printing unit between the paper web stores in the so-called pilgrim step operation in a controlled manner. and is moved. He is briefly explained:

As long as the rubber blankets 2a and 3a of the rubber cylinders 2 and 3 act on the web P and pinch them during printing, the web is transported by the two rotating rubber cylinders 2 and 3 and the pulling roller units 20 and 21 at the nip speed. However, each time two cylinder pits 2b and 3b lie opposite one another and release the web for a correspondingly short period of time, the pull roller units 20 and 21 then take over the further transport of the web alone. During this short phase, the paper web between the two blanket cylinders 2 and 3 is decelerated in a split second from the normal printing nip speed to a standstill, then accelerated in the reverse direction, then decelerated again to a standstill and finally accelerated in the forward direction to the printing nip speed, whereupon the further transport again through the two rubber cylinders 2 and 3 when the rubber blankets of the two rubber cylinders following the cylinder pits mentioned again clamp the web for the following printing on both sides. This pilgrim step operation is controlled in such a way that the printed images successively transferred to the paper web follow one another in order to save paper, and allows the printing format to be changed in a known manner, for example between the repeat lengths measured in the transport direction 605 mm and 685 mm, without to have to replace the cylinders. It is sufficient to adjust the lengths by which the web is moved back and forth relative to the circumference of the moving rubber cylinders 2 and 3 during the pilgrim step operation, and to program the control of the drives 20a and 21a accordingly.

The pull roller units 20, 21 are used simultaneously for register correction by regulating them as a function of read register marks or print marks, and for printing length correction by adjusting and maintaining a corresponding paper web stretch between the pull rollers 20b and 21b by regulating the web tension which regulates the print length certainly.

FIGS. 2 to 7 show a preferred embodiment of the drawing roller 20b, 21b of a drawing roller unit 20, 21, which is designed as a suction roller. According to FIG. 2, the rotating part of this suction roller consists of a roller shell 61, which is made of a light carbon fiber reinforced plastic (CFRP), namely with Plastic impregnated carbon fibers, is manufactured and therefore has a relatively low rotational inertia. Since the suction roll must be repeatedly braked and accelerated strongly in a fraction of a second during pilgrim step operation, the lowest possible moment of inertia of the rotating part is desirable. In Figure 5, the roll shell 61 is shown as a single part, it typically has an overall axial length of about 100 cm and a diameter of about 15 cm. The representations according to FIGS. 2 and 5 show how the interruptions indicate that the suction roll is shortened axially.

An outer ring flange 61a is integrally formed on the roll shell 61 at one end, and the other end is tapered to form a connecting flange 61b. On its circumference, the roller shell 61 is provided with a plurality of suction openings 62, the distribution of which will be explained later. A flange part 63, preferably made of light metal, is fastened to the ring flange 61a by means of screws 64.

The roller shell 61 is rotatable about a solid, hollow roller core 65, preferably made of metal. At the end facing the connecting flange 61b of the roll shell 61, a metallic bearing journal 66 is fastened to the roll core 65, the base of which tightly closes the inside of the roll core 65. On the circumference of the roller core 65, at a certain angular distance from one another, in the example considered at an angular distance of 180 °, two radial, preferably metal partition walls 69 are attached, which enclose a suction chamber 72 between them, as shown in particular in FIG. On both axial sides of the partition walls 69, ring walls 67 and 68 are attached to the circumference of the roller core 65, which preferably also consist of metal and which close the suction chamber 72 on their axial sides. The ring wall 68 at the end of the roller core 65 facing the flange part 63 is axially extended by an outstanding connecting piece 68b, which is used to fasten the stationary part of the suction roller to the machine frame and to connect to a vacuum source. The peripheral wall of the roller core 65 is provided with relatively large passage openings 70 within the suction chamber 72. All parts 66, 67, 68, 69 fastened to the roller core 65 are welded in the example considered.

As shown in Figure 2, the roller shell 61 is at one end with its flange 63 by means of a bearing 71 'in the example considered as a bearing 71' on the socket 68b and at its other end with its connecting flange 61b by means of a bearing 71 also designed as a ball bearing mounted rotatably on the journal 66 of the roller core 65. The arrangement is such that the gaps between the inner circumference of the roller shell 61 and the radially outer ends of the partition walls 69 and the outer circumference of the ring walls 67 and 68 are at least approximately sealed against air passage. In the example under consideration, this takes place by means of a suitable sealing material 73, which is inserted in recesses 69a, which run parallel to the axis, of the radially outer ends of the partition walls 69 and in annular recesses 67a and 68a (FIG. 3) on the circumference of the ring walls 67 and 68. This sealing material 73 can in particular be a self-adhesive brush, for example. However, the arrangement can also be such that only a very small gap is provided between the inner circumference of the roller shell 61 and the partition walls 69 and the ring walls 67 and 68, without the insertion of any special sealing material. Such narrow gaps offer such a high resistance to air passage that these gaps are sufficiently tight to maintain the required negative pressure within the suction chamber 72.

In the assembled state, the connecting piece 68b is continuously connected to a vacuum source, so that a sufficiently strong vacuum is maintained in the interior of the roller core 65, by means of the openings 70, in the suction chamber 72 and consequently at the suction openings 62 opening into this suction chamber 72 which the paper web, which wraps around the suction roller in the area of the suction chamber 72 by 180 °, is pressed against the outer circumference of the roller shell 61, that is to say is held by strong suction. Depending on the type of paper, the pressure inside the roller should be between 0.9 and 0.2 bar. A suitable surface treatment of the roll shell 61, the surface of which is preferably plasma-coated, for example with nickel or another metal, makes this surface impact-resistant and abrasion-resistant and with a certain roughness Mistake; This ensures that even with the high accelerations of the suction roll occurring in pilgrim step operation, there is no slippage between the latter and the paper web, which therefore follows all movements of the suction roll.

In order to achieve an easy and flawless detachment of the paper web from the suction roll at the end of the wrapping, that is to say at the end of the suction chamber 72, the suction openings 62 are distributed in a certain manner, as shown in FIG. In the illustration according to FIG. 6, which shows part of the roll shell 61 developed in one plane, the suction openings 62 are arranged in zigzag lines lying parallel to one another, that is to say on the roll shell 61 in each case along helical line sections which run in a zigzag shape. In this way, adjacent suction openings 62 are each arranged angularly and offset from one another parallel to the axis direction, the angular displacement being 6 ° in each case in the example considered. Viewed in the circumferential direction, successive suction openings are at an angle of 30 ° apart, and the distance between adjacent suction openings along a surface line, that is to say parallel to the axis, is approximately 5 cm in the example considered. As a result, the vacuum is gradually switched off at the end of the wrapping, so that the web is easily detached from the suction roll, and on the other hand, good web adhesion is guaranteed in the entire wrapping area. The shape of the suction openings 62 is shown in the enlarged illustration according to FIG. 7, according to which the inner region of this suction opening consists of a cylindrical bore and the outer region consists of a conical widening.

A perfect balancing of the roller shell 61 is expediently achieved by making appropriately arranged and dimensioned bores 74 in the conical wall of the connecting flange 61b (FIGS. 2 and 5) and optionally in the ring flange 61a between the openings for the passage of the screws 64. If such bores are not sufficient, small pins can also be glued in on the opposite side to achieve perfect balancing.

The roller jacket 61 is pressed directly onto the shaft of the drive motor with its integrally formed connecting flange 61b.

FIGS. 8 and 9 schematically show a pull roller 30 which is pressurized with compressed air along the circumferential section wrapped by the paper web P. The pull roller 30 has a rotating roller shell 31, on the circumference of which openings 32 are provided and which is designed and constructed similarly to the roller shell 61 in the first exemplary embodiment. On one side, the roller jacket 31 forms a conical flange 33, with which it is fixed in a rotationally fixed manner on the shaft 34 of the drive motor in question, which belongs to one of the regulated drives 20a or 21a (FIG. 1). At the other end of the roller shell 31, which in turn is preferably made of a light plastic, a flange part 35 is fastened, which is rotatably seated on a hollow connecting piece 36, which serves to fasten the arrangement to the machine frame and connects the inside of the roller shell 31 to the outside air. The roller core of the pull roller described in the first embodiment can be omitted in this case.

The pull roller 30 dips with a segment, which is determined by the circumferential section wrapped by the paper web P, in the example under consideration with its upper half, into the open side of an otherwise closed box 37, which via an inlet connection 38 is indicated by an arrow Compressed air source 39 is connected. The gaps between the edges delimiting the box opening and the circumference of the roller jacket 31 are only dimensioned so large that the paper web P can pass this box 37 unhindered, but the overpressure prevailing inside the box only escapes insignificantly through this column. The arrangement described creates an overpressure on the outside of the paper web P in the region of the box 37, which should be between 1.1 and 1.8 bar, depending on the type and quality of the paper, while normal atmospheric pressure prevails in the interior of the draw roller 30. This difference in air pressure is sufficient to keep the paper web non-slip on the pull roller even when the accelerator is strongly accelerated.

FIGS. 10 and 11 schematically show a third exemplary embodiment of a pull roller according to the invention, in which suction effect and external overpressure are combined for pressing the paper web against the pull roller. In the example under consideration, this pulling roller 30 'is designed as a suction roller and is constructed in exactly the same way as in the first exemplary embodiment according to FIGS. 2 to 7. The roller shell 61' provided with openings 62 'is thus seated in a rotationally fixed manner with its conically tapering connecting flange 61b provided at one end the shaft 34 of the relevant drive motor of the drive 20a or 21a and is at the other end with its flange part 63 'rotatably mounted on the hollow axial connector 68b', which in turn for fastening and serves at the same time for connection to a suction air source 40 indicated by an arrow. Inside the pull roller 30 ', as in the first embodiment according to Figure 4, a suction chamber 72' is formed, which is connected to the hollow nozzle 68b '. In addition, as in the second exemplary embodiment according to FIGS. 8 and 9, an outer box 37 is provided, via which the circumferential section of the roller shell 61 ', which is subject to the internal suction effect, is acted upon from the outside with compressed air. The combined suction and compressed air effect achieved in this way ensures particularly good adhesion of the paper web to the draw roller.

The invention is not limited to the exemplary embodiments described, but rather allows for numerous variants with regard to the design of the pull roller. For example, in the second exemplary embodiment according to FIGS. 8 and 9, the holes in the roll shell can be dispensed with. The draw roller can of course also be used in other printing units with continuous paper web transport or with paper web transport in pilgrim step operation, especially in intaglio printing units. The circumferential section of the draw roller wrapped around by the paper web can generally be between 90 ° and approximately 180 °.

Claims (13)

1. pull roller unit for transporting a paper web (P) in a web printing machine, characterized in that the pull roller unit (20, 21) has a single pull roller (20b, 21b; 30; 30 ') which of the paper web (P) along a certain one Circumferential section is wrapped, and that means for producing an air pressure effect along this circumferential section are provided such that the paper web (P) on this circumferential section is pressed against the surface of the draw roller, while the remaining circumference of this draw roller is not subject to such an effect. 2. pull roller unit according to claim 1, characterized in that said peripheral portion of the pull roller (20b, 21b; 30; 30 ') extends over an angular range between 90 ° and approximately 180 °, preferably about 180 °. 3. traction roller unit according to claim 1 or 2, characterized in that the traction roller (20b, 21b; 30 ') is a suction roller with openings (62, 62') distributed over its circumference and that an inner sector delimited by the mentioned circumferential section is fixed Suction chamber (72) is formed, which can be connected to a vacuum source. 4. pull roller unit according to one of claims 1 or 2, characterized in that said peripheral portion of the pull roller (30) is acted upon from the outside with compressed air. 5. pulling roller unit according to claim 4, characterized in that the pulling roller (30) with a segment delimited by the said peripheral portion dips into an otherwise closed box (37), the interior of which is connected to a compressed air source, and that the gap between which the box opening limit the edges and the circumference of the pull roller only are just so large that the paper web wrapping around the draw roller can pass this box unhindered. 6. pull roller unit according to claim 3, characterized in that the suction roller consists of a solid, hollow roller core (65) and a rotatable roller shell (61) made of light material with openings (62) distributed over its circumference, that the roller core (65 ) on one side with an axial socket (68b) for attachment to the machine frame and for connection to a vacuum source, on the other side with a bearing journal (66) and on its circumference with two radial partition walls (69) arranged at a certain angular distance from each other is provided, which include the suction chamber (72) between them, that the peripheral wall of the roller core (65) has openings (70) within the suction chamber, and that the roller shell (61) by means of bearings (71, 71 ') at one end the bearing journal (66) and at the other end on the connecting piece (68b) is rotatably mounted, the gap between the inner circumference of the roller shell (61) and the radially outer end n of the partitions (69) are at least approximately airtight. 7. pull roller unit according to claim 6, characterized in that on the two ends of the roller core (65) ring walls (67,68) are attached, which close the suction chamber (72) at both axial ends, that the gap between the inner circumference of the roll shell (61) and the outer circumference of the ring walls are at least approximately airtight, the ring wall (68) arranged on the socket side preferably forming a part with the socket (68b) on which a flange part (63) fastened to the roller shell (61) by means of one of the bearings ( 71 ') is mounted, and that the nozzle (68b) facing away from the end of Roll shell (61), which preferably tapers conically, is designed as a connecting flange (61b) for attachment to the rotor shaft of the drive motor and is mounted on the mentioned journal (66) by means of the other bearing (71). 8. draw roller unit according to claim 6 or 7, characterized in that in the mentioned gaps sealing material (73), in particular self-adhesive brushes, is arranged or that the gaps mentioned are so small that they without one sealing material to maintain the desired negative pressure in the suction chamber (72) form sufficient air resistance. 9. pull roller unit according to one of claims 1 to 8, characterized in that the pull roller (61 ') is provided on its circumference with openings (62'), to a vacuum source (40) connectable suction roller and also along the mentioned circumferential section from the outside compressed air from a compressed air source (39) is applied. 10. Pull roller unit according to claim 4 or 5, characterized in that the pull roller (30) has a roller shell (31) with openings (32) distributed over its circumference, which open into an interior of the pull roller which is connected to the outside air, so that there is a difference in air pressure between the outside of the paper web wrapped around the draw roller and the inside of the opening covering the openings (32). 11. pull roller unit according to one of claims 1 to 10, characterized in that the roller shell (31, 61, 61 '), the pull roller consists of plastic impregnated carbon fibers, preferably the surface of the roller shell (31, 61, 61') plasma-coated with nickel, for example. 12. pull roller unit according to one of claims 3 or 6 to 11, characterized in that adjacent openings (32, 62, 62 ') in the roller shell (31, 61, 61') are each offset angularly such that these openings run along helical sections that are zigzag. 13. pulling roller unit according to one of claims 1 to 12, characterized in that the pulling roller (20b, 21b; 30; 30 ') is part of a web printing machine with paper web transport controllable in pilgrim step operation, wherein for forward and backward movement of the paper web (P) before Pressure nip a paper web storage (19) and a downstream drawing roller unit (20) and behind the printing nip a drawing roller unit (21) with a downstream paper web storage (22) are installed and both drawing roller units can be controlled by a controlled drive (20a, 21a).

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