PAPER TAIL NIP THREADER

Abstract: A paper tail nip threader for guiding a moving paper tail over and around a contoured surface. The apparatus is particu­ larly useful for automatically threading a paper tail through a calender roll stack. A guide surface is shaped to conform to a portion of the surface over which the paper is to be passed. An air stream is directed across the guide surface in the desired direction of movement of the paper. The air stream is thus forced to flow in a contoured path which corresponds to the surface over which the paper is to be passed. The moving air stream "catches" the paper tail and carries it between the guide surface and the surface over which the paper is to be passed.

Description: Field of the Invention This application pertains to a paper tail nip threader for directing a moving paper tail from point to point within an operating paper machine. More particularly, the application pertains to a paper tail nip threader for automatically threading a moving paper tail through a stack of rotating rolls by guiding the tail from an out-running nip of a pair of counter-rotating rolls, along a desired path (i.e. over and around a roll) and into an in-running nip of another pair of counter-rotating rolls. Background of the Invention At various stages of a typical paper making operation a moving, continuous sheet of paper is passed, at high speed, over a plurality of rolls which are rotated with respect to one another. For example, at one stage of the paper making operation the moving paper sheet is passed over a plurality of dryer rolls. Adjacent pairs of dryer rolls are rotated in opposite directions so that the paper is drawn from roll to roll. The roll surfaces are heated to evaporate moisture from the paper. The pressure applied to the moving paper sheet by pressing it against the roll faces also assists in moisture removal. At a subsequent stage of the paper making operation the moving paper sheet is typically passed between adjacent pairs of counter-rotating calender rolls (the "calender stack") which calender the paper by imparting the desired smooth finish thereto, after which the sheet is passed to a reel and onto a wind-up spool. Since it is difficult to thread a full width moving paper sheet between a pair of counter-rotating rolls, a narrow tail is typically cut to one side of the moving sheet before the paper encounters the counter-rotating rolls. The tail can be more easily threaded through the rolls and, once correctly threaded, is used to draw the full width of the paper sheet between the rolls. This method is used to transfer the paper from the last dryer roll through the calender stack, and is also used to transfer the paper from the calender stack to the reel and wind-up spool. In the prior art, the paper tail threading procedure is typically time consuming and labour intensive. Often, the operating speed of most of the paper making machinery must be reduced so that the paper can be manually handled and guided between adjacent pairs of counter-rotating rolls. Conventionally, workmen use air hoses to direct blasts of air at the paper tail in an effort to force it into the desired position between a pair of in-running rolls, until the tail is caught and pulled through; after which the air hose must be used to direct the paper tail to the next pair of rolls in the sequence. Sometimes, mechanical prods, or hand-held dual rolls are used to force the tail into the desired position between the rolls. Unfortunately, these techniques are not only cumbersome and time-consuming, but also expose the workmen to possible serious injuries if their hands or arms become trapped between the rapidly rotating rolls. The present invention provides a paper tail nip threader or "guide" for automatically guiding a moving paper tail from point to point within an operating paper machine; for example, over or around a contoured surface such as the surface of a roll. A plurality of such guides may be arranged to guide a moving paper tail at high speed over and between adjacent pairs of counter-rotating rolls, thereby vastly simplifying the tail handling and threading procedure and overcoming the foregoing difficulties by reducing labour costs, while operating the paper making machinery at its maximum speed and minimizing the potential for operator injuries. There are arrangements previously known, see e.g. DE-C-684 139 and DE-C-36 474, for threading by pneumatic means a moving paper sheet through a stack of rotating rolls in a paper processing machine. Here the full width of the paper sheet is forced to follow the surface of the rolls by jets of air being directed towards the sheet, pressing it against the roll. Should the moving paper web rupture, the end of the web is forced to remain on the surface of the roll and follow the same by this series of air jets blowing against the paper, thus forcing it to cling to the surface of the rolls. However, as indicated above, it is unpractical, in particular in high speed paper mashines, to thread moving paper sheet, full width, through a stack of rolls, so therefore the said narrow tail is cut to one side of the moving sheet, to be used in the threading operation. Now, pressing a paper tail towards the surface of rotating rolls by the prior art method has proved unpractical and in particular the paper does not flow smoothly under this method which, moreover, does not ensure safe and reliable threading throughout the paper stack of the machine. Instead, it is proposed according to the invention to have a moving air stream catching the paper tail and carrying it freely around a roll, instead of pressing it against the surface of the roll, see below. It has also been proposed, see GB-A-581 836, in cases where the end of the paper sheet or web is more or less in free flight and has to be caught and carried into the nip of a selected pair of rollers, to meet the end of the web with a blast of air and to direct it thereby towards the nip. The blast has to be controlled and guided, and to this end a curved guide plate is provided along which a main stream of air passes to combine with secondary air flowing out from perforations in the guide plate. Regulator means are provided for controlling the combined air flow so as to direct the paper web end as desired, thus into the nip. The arrangement is cumbersome and power consuming and does not lend itself to the threading of rapidly moving paper webs. Again, the invention offers an improvement in proposing the threading of a narrow paper tail by means of a thin high speed air layer along a curved guide surface, as will be described. Summary of the Invention In accordance with the preferred embodiment the invention provides a paper tail guide for guiding a moving paper tail along a desired path; for example, over a contoured surface such as the surface of a rotating roll. The paper tail guide comprises a guide surface which is shaped to conform to a portion of the surface over which the paper is to be passed. An air directing means is provided for directing a low volume air stream across the guide surface at high speed in the desired direction of movement of the paper. The guide surface constrains the moving air stream to flow in a path which corresponds to the shape of the surface over which the paper is to be passed. The paper tail is caught by the moving air stream and carried through a narrow space between the guide surface and the surface over which tie paper is to be passed. The paper tail may be ejected from the guide surface at a point close to the in-feed nips of a pair of counter-rotating rolls so that the tail will be caught by the rolls and pulled between them. The air directing means may comprise an aperture in the guide surface and a deflector for deflecting air passed through the aperture across the guide surface in the desired direction of movement of the paper. Advantageously, a plurality of apertures may be spaced, in the desired direction of movement of the paper, over the guide surface and a deflector associated with each such aperture. Preferably, the deflectors each comprise a portion of the guide surface so as to avoid obstruction of the moving paper. The apertures extend across the guide surface in a direction generally perpendicular to the desired direction of movement of the paper. Brief Description of the Drawings Figure 1 is a side elevation view which illustrates how a plurality of paper tail nip threaders or "guides" of the preferred embodiment may be positioned relative to a stack of counter-rotating rolls. Figure 2 is a side view of one of the piper tail nip threaders of figure 1. Figures 3 and 4 are cross-sectional side views of the upper and central sections, respectively, of the paper tail nip threader of Figure 2. Detailed Description of the Preferred Embodiment Figure 1 illustrates two pairs of "calender stacks" 10, 12 each of which comprises a plurality of counter-rotating calender rolls 14. A moving, continuous sheet of paper 16 is passed, in the direction of arrows 17 and at high speed, over and between desired pairs of rolls 14 to "calender" the paper by imparting the desired smooth finish thereto. Adjustably positionable vacuum transfer units 18 of the type generally described in United States patent No. 4,022,366 assist in transfering the paper between dryers 20 and 22, calender stacks 10, 12, and ultimately onto wind-up reel 23. Since it would be extremely difficult to thread the full width of moving paper sheet 16 through either of calender stacks 10 or 12, a narrow tail is cut to one side of sheet 16 by tail slitter 25, as the sheet passes from dryer 20 to dryer 22. The tail is more easily handled and threaded through stacks 10 and 12 and is then used to draw the full width of sheet 16 through stacks 10 and 12. Rolls 14 comprising calender stack 10 counter-rotate, relative to one another, in the direction indicated by the arrows on each of rolls 14. It can thus be seen than when the paper tail is delivered, from the left, to the top of roll 14′, the tail is caught by the rotating roll and pulled over the roll to the right side of calender stack 10. If nothing further were done then when the paper tail passed over to the right side of roll 14′, it would tend to fly out to the right of calender stack 10, rather than be carried downward over the rotating surface of roller 14′ and between counter-rotating rolls 14′, 14″ as desired. The moving paper tail must then somehow be threaded downward over the rotating surface of roll 14′ and between the infeed nips to the right of roll pair 14′, 14″. This is accomplished by paper tail nip threaders or "guides" 24 which are closely spaced, relative to rolls 14, to guide the paper tail from point to joint over and around the rotating roll surfaces. As may be seen in figure 1, threaders 24 have contoured guide surfaces 26 which are shaped to conform to a portion of the surfaces of rolls 14 over which moving paper sheet 16 is to be passed. If it is desired to pass the paper tail along some reasonably short path other than a path conforming to the shape of a roll, then the shape of contoured surface 26 may be altered accordingly to conform to the shape of the desired path. In any case, surface 26 is made slightly wider than the width of the paper tail to be guided across surface 26. As may be seen in figure 2, paper tail nip threader 24 may comprise a plurality of sections such as upper section 40 (shown in greater detail in Figure 3), central section 42 (shown in greater detail in figure 4) and lower section 44. The sections are coupled together with brackets 27, which enable variable positioning of the sections relative to one another, yielding a relatively wide range of possible shapes for guide surface 26. As may be seen in figures 2, 3 and 4, an "air directing means", namely narrow (approximately 0.4 mm/0.015 inches measured in the direction of desired movement of the paper tail) slotted apertures 28, is provided in guide surface 26. Apertures 28 extend transversely to the desired direction of movement of the paper tail from side to side across guide surface 26 and are spaced from top 30 to bottom 32 of guide surface 26 as shown in figure 2 (i.e., the apertures are spaced in the desired direction of paper movement). Preferably, each of narrow slotted apertures 28 comprises a series of longitudinally aligned apertures each measuring about 0.4 mm/0.015 inches (in the direction of desired movement of the paper tail) by about 9.05 mm/0.375 inches (in the direction transverse to the direction of desired movement of the paper tail), with gaps of about 38 mm/1.5 inches between adjacent apertures of each series. This lends rigidity to nip threader 24 in the region of apertures 28. A deflector 34 is associated with each of apertures 28. Deflectors 34 each comprise a portion of guide surface 26, so as to minimize interference with the passage of the paper tail over guide surface 26. Compressed air is injected, at relatively low volume and pressure, into the hollow spaces 29 within the various sections comprising paper tail nip threader 24 and is forced, at high speed, through each of narrow apertures 28. The moving air streams which emerge from apertures 28 are deflected by deflectors 34 and thus constrained to pass across guide surface 26 in the desired direction of movement of the paper tail (i.e. from top 30 to bottom 32 of nip threader 24 as viewed in figure 2). With reference to figure 1, it will thus be understood that, for example, when the paper tail emerges from between rolls 14′, 14″ to the left of calender stack 10 it passes into the upper region of the space between roller 14″ and paper tail nip threader 24″. The paper tail is urged toward guide surface 26 of nip threader 24″ by the negative pressure created by the moving air stream which is deflected across surface 26 by an aperture 28 and associated deflector 34 positioned across the top of nip threader 24″. The moving air stream carries the paper tail across guide surface 26 and through the narrow contoured gap between surface 26 and roller 14″. Additional (optional) apertures 28 and deflectors 34 may be spaced over guide surface 26, as described above, to maintain a continuous low volume, high velocity air stream across guide surface 26 in the desired direction of movement of the paper tail. The moving paper tail is thus carried to the bottom of paper tail nip threader 24″ and emerges at the infeed nips between and to the left of counter-rotating rolls 14″, 14″′. The paper tail is caught by counter-rotating rolls 14″ and 14″′, pulled between those rolls and emerges to their right. Paper tail nip threader 24″′ then guides the moving paper tail over the surface of roller 14″′ and delivers it to the infeed nips of the next counter-rotating roll pair. The outer edges of nip threader sections 40, 42 and 44 parallel to the desired direction of movement of the paper tail are made flush with guide surfaces 26 of each section. Thus the moving air stream passing between the paper tail and surface 26 may escape over the edges, thereby preventing build-up of air between the paper tail and surface 26 which could interfere with smooth passage of the paper tail over surface 26. It will thus be understood that by positioning paper tail nip threaders 24 as shown in figure 1 relative to counter-rotating rolls 14 the moving paper tail may be automatically threaded through any desired combination of counter-rotating calender rolls 14.

Claims: 1. A paper tail threader for a paper processing machine, comprising guide means (24) for guiding the movement of a paper tail and causing it to follow a curved path over a roll (14) in said machine, said guide means comprising a box-like unit having an incurved external guide surface (26), characterized in that said incurved guide surface extends close to and substantially parallel to the periphery of said roll (14), air directing means being provided for directing an air stream closely along and parallel to said curved guide surface (26) in the direction of travel of the paper to form a moving air layer or bed which supports and carries said paper tail around the roll (14) and leaves it to proceed in free flight at the end of said guide surface (26) to enter, for example, into the nip between rolls in the machine, said air directing means comprising deflector portions (34) of said curved guide surface (26) which are raised slightly above the surface to form tangential nozzle means (28) therein which directs air along the surface to form said moving air layer. 2. A paper tail threader as defined in claim 1, characterized in that said deflector portions (34) with associated nozzle means (28) are spaced across the guide surface (26) in a direction generally perpendicular to the direction of travel of the paper. 3. A paper tail threader as defined in claim 1 or 2 further characterized in that said deflector portions (34) with associated nozzle means (28) are spaced along the guide surface (26) in the direction of travel of the paper. 4. A paper tail threader as defined in any of the preceding claims, characterized in that said raised deflector portions (34) of the guide surface overlap said surface downstream of said portions, said nozzle means thus being constituted by a gap (28) between each deflector portion and the guide surface beneath. 5. A paper tail threader as defined in any of the preceding claims, characterized in that said guide means is composed by a plurality of sections (40, 42, 44) each with its curved guide surface (26) and air directing means (28, 34), said sections being coupled together by adjustable coupling means (27) for variable positioning of the sections with respect to one another to change the curve of their combined incurved guide surfaces (26) and thus to provide a conformal guide path.

Inventors: MOHRSEN, LEIF
Applicants: FIBRON MACHINE CORPORATION
Application year: 1986
Main classification: D21G9
IPC codes: D21G9, B65H20