Abstract:
A device is provided for stabilizing a paper web in an unwinding and splicing station. The splicing station includes a primary paper roll and a secondary paper roll. A suction trough extends across a width of the paper web and includes a suction zone adjacent the paper web. The paper web unwinds from the secondary paper roll and passes the suction trough. The suction zone extends substantially across the width of the paper web and is configured to effect a substantially uniform vacuum in its area, wherein the unwinding paper web runs evenly over the suction zone area.

Description:
This is a continuation of application Ser. No. 08/614,740, filed Mar. 13, 1996 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for stabilizing a paper web. 
     2. Description of the Related Art 
     Suction boxes are used, e.g., for web stabilization in unwinding stations of a coater. The paper webs are made endless in these unwinding stations, thus enabling a continuous processing operation. This action consists of splicing the one paper roll, before it is fully depleted, to the next full roll. The web remainder of the nearly depleted secondary paper roll is cut off by means of a serrated blade, and the new web leader of the large paper roll is passed through the coater instead. Taking place on the fly, this procedure is mostly called &#34;flying splice&#34; in the paper industry; refer to the Voith publication entitled &#34;Splice View-Electronic Components for Visualization, &#34; publication No. p. 2827. The aim in such unwinding stations is to perform the cut-off operation as safely as possible. Among others, it is necessary to safeguard keeping the paper web maximally plane. This is important in order for the serrated cut-off blade to penetrate the paper web simultaneously across its entire width and, thus, also sever it evenly. But with corrugations present in the paper web that extend in the direction of web travel, the &#34;higher areas&#34; of the paper web are severed only after the lower areas. The result is a curvilinear progression superimposed on the serrated cutting line. Such irregular cutting lines can result in uncontrolled web breaks and, thus, interruptions of the operation. 
     According to DE-OS 38 15 277, a web stabilizer is arranged behind the cut-off blade. This arrangement has the disadvantage of leaving a relatively long web remainder after the cut-off operation (at least the web length from the cutting point to the point of contact between splicing roll and new paper roll). As the paper web continues passing through the coater, a hazardous flapping of the web remainder occurs frequently on the web guide rolls, which may lead to a break of the entire paper web and, thus, standstill of the paper machine. 
     SUMMARY OF THE INVENTION 
     The present invention provides a maximally clean and safe cut-off operation, where the waviness created in the paper web is extensively eliminated. 
     The action of the inventional suction zone--in the presence of vacuum--is such that the paper web is sucked down uniformly across its entire width, thereby smoothing any waves that are present and extend in the direction of web travel. This makes a clean cut-off from the secondary paper roll possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic illustration of an unwinding and splicing station including an embodiment of a suction box of the present invention; 
     FIG. 2 illustrates an embodiment of a suction box of the present invention in an unwinding and splicing station of a coater analogous to FIG. 1, but with an additional, primary paper roll kept in reserve; 
     FIG. 3 is a basic illustration of corrugations formed in a prior art paper web; 
     FIG. 4 is an exemplary defective paper web cut-off; 
     FIGS. 5 and 6 are perspective views of alternate embodiments of a suction box according to the present invention; 
     FIGS. 7, 8, 9 and 10 illustrate embodiments of so-called spreaders on the suction box; 
     FIGS. 11, 12 and 13 are plan views of alternate embodiments of the inventional suction zone of the suction box; and 
     FIG. 14 is the inventional suction box according to FIG. 6 with a modified suction zone. 
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an embodiment of the structure of the inventional device and the splicing of the paper web 7. The same basic structure is also depicted in FIG. 2. 
     The web leader of the new paper roll on the so-called primary roll 1 is attached to the paper roll itself using a specific, not illustrated adhesive tape. At the same time, however, splicing points are skipped, which are then attached, later in the splicing operation, on the still unwinding paper web 7. Owing to the shape of the approach rounding 17 of suction box 4 and the boundary air layer created with paper webs traveling at high speed, the paper web passes across the suction box 4 without touching it, so that a suction box can be installed even above the common tangential plane of splicing roll 5 and paper guide roll 6. 
     To preclude damage to the paper web at the exit edge of the suction box, a defined rounding is provided there--the exit rounding 18 (FIGS. 5-7 and 9). Shortly before depletion of the secondary paper roll 2 (i.e., of the unwinding paper web), the primary roll 1 is accelerated rotationally until the peripheral speed of the primary paper roll 1 matches the speed of web travel. 
     Just a few seconds before the splicing operation, a defined vacuum is allowed to act on the suction box 4, causing the paper web 7 to no longer glide across the suction box, but to be pulled in the recess (suction zone 25) illustrated in FIGS. 1, 5 and 6. This results in a good smoothing effect on the web (i.e., corrugations extending previously in the longitudinal direction of the web are being smoothed out) between the splicing roll 5 and the preceding paper guide roll 6. Since the paper web 7 is being smoothed also before and after the suction box, the cut-off device or cut-off blades 10, 10&#39; (FIG. 1) can be arranged both between the suction box 4 and splicing roll 5 or between suction box 4 and the preceding paper guide roll 6. The first position (cut-off blade 10) has the advantage of producing a considerably shorter web remainder. 
     A mark on the periphery of the primary paper roll 1 allows the control electronics array to recognize where the prepared splicing point is located on the periphery of the primary paper roll 1. As a splicing operation is now initiated (manually or also automatically), the splicing roll 5 is in timed dependence on the revolution of the splicing point forced abruptly on a primary paper roll 1 while the cut-off blade 10 strikes the paper web 7. The already unwound web of the secondary paper roll 2 is then in known fashion kept away from the splicing location or nib N (FIG. 1) by means of (here not illustrated) blowing devices. 
     FIG. 3 serves to illustrate the amplification effect of the web waviness in the imaginary perpendicular plane 8 relative to the direction of web travel 22, by the interaction of the web travel and the motion of the cut-off blade 10 according to the prior art. 
     The amplified corrugation is illustrated by dash-dot line in the resulting sectional plane 9, in which the cut-off blade 10 engages obliquely the paper web 7. 
     FIG. 4 depicts various web cut-off defects occurring without suction box. Section 11 represents a correct cut, with only the serration effect showing on the paper web, due to the serrated cut-off blade. In section 12, a paper waviness superimposes on the serration line. Section 13, in contrast, could have produced a cut-off line resembling that of section 12. Due to the web having been partially severed already, however, an uncontrolled tear continued at this point in the paper web. In section 14, the waviness of the paper web is evident again. Nonetheless, the waviness was considerably reduced at this point, so that the serrated shape is not so much superimposed by a curvilinear shape. 
     Suction box 4 illustrated in FIG. 5 is a sheet metal structure attached to a suction system 15. Instead of numerous suction perforations 19 facing the paper web, as shown in FIG. 11 through 13, only a single suction perforation 19 may be provided as well, as shown in FIG. 5. Moreover, the suction box contains rounded rims 16 in the suction zone, approach rounding 17 and exit rounding 18, and endwise suction zone bounds 20. 
     Suction trough or box 4&#39; depicted in FIG. 6 is of a simple design, but fashioned from pipe stock. The area between facing pipes 27 and 28 must be nearly airtight--possible with the use of a connecting part. Pipes 27 and 28 are disposed side-by-side and connected to each other. The suction perforations 19 are provided either in at least one pipe 27 or 28. The suction system 15 may be arranged on the pipe ends or arbitrarily on the pipe shell. The suction zone 25 is endwise bounded by suction zone bounds 20&#39;. Due to the shape to be sealed at the pipe ends, suction zone bounds 20&#39; are wedged-shaped here. 
     FIG. 7 is a section through a suction box 4&#39; made of pipes, such as illustrated in FIG. 6. 
     FIG. 8 shows the pertaining view A in FIG. 7. The course of the paper web is shown in an unsuctioned state (straight dash-dot line) and suctioned state (concave dash-dot line). 
     The web is partly pulled into the suction zone 25, creating a wave which extends crosswise to the direction of travel 22 of web 7 (this is the concave line) whereby--as mentioned before--waves (longitudinal waves depicted in FIG. 3) extending in the longitudinal direction 22 are being smoothed, thereby accomplishing a clean cut-off of web 7 from the secondary paper roll 2. So-called spreaders are provided on the suction box 4 or 4&#39; to enhance the smoothing effect. The spreaders may be either spreader slots 23 (FIGS. 7 and 8) or spreader cams 24 (FIGS. 9 and 10). 
     The spreader slots 23 and spreader cams 24 are arranged preferably on each end section of the suction box 4 or 4&#39;. Viewed in the direction of web travel 22, the spreaders slant toward the nearest paper web edge 21. This slant increases from spreader to spreader, deviating up to about 30° from the direction of web travel. 
     In addition to FIGS. 8 and 10, spreader slots 30 and spreader cams 32 are also shown in FIG. 5. 
     Provided in addition to spreader slots 23, the suction perforations 19 are required for a good wrap of the rounded suction zone rims 16. 
     FIGS. 9 and 10 illustrate an option analogous to FIG. 7 and 8. Instead of a suction slot, however, an oblong spreader cam 24 is used here as spreader. Owing to the tight wrap around spreader cams 24, their edges exert a good spreading effect. 
     A so-called spreading effect with the spreader slots 23 and spreader cams 24 results in that the paper web 7 slides over the spreader slots 23 and spreader cams 24 as described before. This aids additionally in smoothing the web. 
     FIG. 14 shows another variant of the suction zone 25. While FIGS. 6 through 10 show a suction zone 25 that is open toward paper web 7, suction zone 25 in FIG. 14 is bounded by a plate 30, which prevents the web from being pulled into the &#34;recess.&#34; A plurality of suction perforations 19 are fashioned in the plate 30. The suction perforations 19 are arranged preferably in parallel succession, such as illustrated in FIGS. 11 through 13. In order to produce upon connection of the suction system 15 a uniform vacuum across the entire web width and thus pass the web free of waves and flat across the suction zone 25, the areas of suction perforations 19 increase gradually in size. The starting point of the gradual area enlargement of perforations 19 in the longitudinal direction of plate 30 is the application site of suction system 15. This means that the suction effect is the greatest where suction system 15 is effective. Suction perforations 19 may in this area be smaller than those arranged in an area farther removed from suction system 15. Instead of the illustrated and described plate 30, a screen type structure is also possible. 
     Plate 30 may include suction perforations 19 instead of the sole, oblong suction perforation 19&#39; illustrated in FIG. 5. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.