Abstract:
A paper machine for one of making and processing a fiber material web. A plurality of rolls carry the fiber material web. The plurality of rolls include a load roll and another roll defining a nip therebetween. The fiber material web travels through the nip and defines a gore with the load roll on an approach side of the nip. A movable cutoff knife includes a cutting edge positioned in the gore at a slight distance from the nip and adjacent to the fiber material web. At least one impulse exchanger is positioned in association with the cutoff knife. The impulse exchanger is configured to transfer impulse energy to the cutoff knife whereby the cutting edge cuts the fiber material web.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for the cutoff of a fiber material web, such as a web for paper or cardboard, in a paper machine such as a paper-making machine, rewinder, coater and/or rotary slitter. 
     2. Description of the Related Art 
     A cutoff apparatus as described above may be configured with a machinewide knife that extends transverse to the direction of paper travel (see, e.g., DE 38 15 277). The cutting edge of the knife according to DE 38 15 277 has a large distance from the impact point of the cutting edge to the splice on the splicing roll. As a result, an excessively long paper remnant, or paper tail, remains behind the splice after cutoff of the material web and gluing it to a new web. This leads to breaks, for example in a follow-on coater, notably with thin paper grades. Furthermore, the apparatus according to DE 38 15 227 has the further disadvantage that a serrated blade is used, as a result of which the web undesirably has a serrated cutoff edge. 
     DE-U-94 13 363 shows an apparatus for cutoff of a traveling material web. The apparatus is equipped with a cutoff knife heavily slanted opposite to the direction of web travel and avoids the latter of the aforementioned disadvantages. The angle occurring during the cutoff process between cutoff knife and material web is with the object according to DE-U-94 13 363 smaller than 45 degrees. At low web velocities, a cutoff edge which is extensively straight across the material web can be achieved with it, but, especially with high web velocities, &gt;1500 m/min, the measures according to DE-U-94 13 363 are no longer sufficient to achieve the desired reliability of operation. A factor in addition to the known problems with the above high web velocities is that the cutoff velocity of the cutoff knife is mostly insufficient to achieve a non-serrated cutoff. 
     What is needed in the art is a cutoff apparatus which overcomes the disadvantages that occur at high web velocities with the prior-art apparatuses. 
     SUMMARY OF THE INVENTION 
     According to a first embodiment, the cutting edge of the knife disposed underneath the material web is in the inoperative position located in the gore between the paper web and a load roll, spaced slightly from a nip formed by the load roll and a roll. This creates the advantage that the material web remnant which after web cutoff enters the nip, e.g., a splicing nip, is very short. 
     The invention provides for coordinating with the cutoff knife an actuator that comprises at least one impulse exchanger. Achieved with the use of such actuator, as compared to the actuators known heretofore, is the advantage of a non-serrated cutoff at very high web velocities. 
     According to the invention, the impulse exchange may take place mechanically or pneumatically. The impulse exchanger produces a collision, or impulse exchange, between two masses. As is evident from the following formula for a mechanical impulse generator, it is especially advantageous for the mass of the cutoff knife to be very slight,          V   2     =       2        m             1       ×     V   1           m   1     +     m   2                                
     where V 2 is the velocity of the cutoff knife with the mass m 2  after the collision, and V 1  is the velocity of the striking mass m 1 . With m 2  being much smaller than m 1 , all that can be achieved in the most favorable case is a cutoff knife velocity twice as high as the velocity of the striking mass. 
     As mentioned already above, a pneumatic impulse generator may also be employed; it uses a directional flow—for example compressed air—that is directed at the cutoff knife and accelerates it by exchange of the flow impulse. 
     Moreover, the acceleration of the cutoff knife can be aided when the actuator features in addition to the described impulse generators an energy store, for example a spring or store of compressed air. The energy stored in these systems is upon knife actuation released abruptly and converted to kinetic energy of the cutoff knife. 
     Of particular advantage is slanting the cutoff knife opposite to the direction of web travel. A preferred embodiment provides for the angle created in the cutoff process between the cutoff knife and the material web to be less than 45 degrees. The slanting of the cutoff knife shortens the cutoff times further still as compared to prior solutions, so that the material web cutoff proceeds very quickly. For example, an escape of the web and, thus, the tendency of wrinkling is nearly precluded. 
     Another embodiment provides for optimally adjusting to one another, with respect to a non-serrated cutoff, the factors that influence the cutoff edge, such as the angle forming during the cutoff process between the cutoff knife and the material web, the velocity of the material web and the approach velocity of the cutoff knife. 
     With the present invention, the cutoff knife is by impulse exchange accelerated such that the traveling material web is being cut off at a high cutoff knife velocity. 
    
    
     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 one embodiment of a cutoff apparatus of the present invention in a gore between the fiber material web and a load roll, a slight distance from a nip formed by the load roll and another roll; 
     FIG. 2 is a more detailed illustration of the cutoff apparatus shown in FIG.  1 : 
     FIG. 3 illustrates another embodiment of a cutoff apparatus of the present invention including a cutoff knife and a mechanical impulse generator as an actuator; 
     FIG. 4 illustrates yet another embodiment of a cutoff apparatus of the present invention including a cutoff knife and a non-mechanical impulse generator as an actuator; and 
     FIG. 5 illustrates still another embodiment of a cutoff apparatus of the present invention including a cutoff knife, an impulse generator and an energy store. 
     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 shows an embodiment of the cutoff apparatus  10  of the present invention including a cutoff knife  12  in a splicer intended for use in coaters. The splicer includes a new paper roll  1  and an old paper roll  2  from which is unwinding a depleting fiber material web in the form of a paper web  3 . In splicing the end of web  3  to the leader of new paper roll  1 , the splicer is moved toward roll  1 . A nip or splicing point  5  is created between the load roll  4  and the new paper roll  1 , where the end of the old web  3  is glued to the leader of the new web from new paper roll  1 . Disposed on the approach side and directly before load roll  4  is a cutoff apparatus  10 , which in the present case is equipped with a cutoff knife  12  and an impulse exchanger  11 . The cutoff knife  12  has a cutting edge  13  that is slanted opposite to the direction of web travel. This arrangement of the cutoff apparatus  10  in the gore between roll  1  and load roll  4 , spaced slightly relative to the splicing point  5 , achieves that the old paper web remnant entering the nip upon cutoff of the paper web  3  is only short. 
     Owing to the illustrated design of the cutoff apparatus, moreover, the cutoff operation does not cause a liftoff of the web, thereby avoiding with the present invention the web stabilizers, such as suction boxes arranged in prior-art designs before the splice. 
     FIG. 2 shows the inventional apparatus relative to FIG. 1 in more detail. Similar to the arrangement according to FIG. 1, the cutoff apparatus  10  is disposed in the gore underneath the paper web  3  near the load roll  4 . Cutoff knife  12  includes a cutting edge  13  which is slanted opposite to the direction of web travel and mounted in a clamp  14 . The part of cutoff knife  12  that is not clamped in place is movable in vertical direction under the effect of bending forces. Clamp  14  is secured to a support arm  15  of cutoff apparatus  10 . Below clamp  14 , a mechanical impulse generator  17  is mounted pivotably on the support arm  15  in a bearing  16 . The mechanical impulse generator  17  mounted pivotably, or rotatably, in the bearing  16  is retained elastically, by clamping effect, between the underside of clamp  14  and a prop  18 , by means of two deformable elements, for example, elastic compressed-air hoses  19  and  20 . When now inflating the lower compressed-air hose  19  and deflating the upper compressed-air hose  20 , the mechanical impulse generator  17  pivots about the axis of bearing  16  and makes contact with the bottom edge of the cutoff knife  12 . In the process, an impulse exchange takes place from the mechanical impulse generator to the cutoff knife. The mounted cutoff knife  12  accelerates toward the paper web and cuts it off. The knife  12  being clamped in the clamp  14 , it retracts to the illustrated starting position under the recoil force that results from the clamping of the blade. A stop  52  prevents the knife from overshooting in the direction of the mechanical impulse generator  17 . In splicing the old web to the new one, the splicing or load roll  4  is located in the deployed splicing position  4 ′ depicted. 
     Further embodiments of a mechanical impulse generator (refer to FIG. 3) and of a pneumatic impulse generator are illustrated schematically in FIGS. 4 and 5. According to FIG. 3, the cutoff knife  12  is mounted rotatably in a massive bearing block  21 . Massive bearing block  21  includes a round bearing bore  22  that receives the bearing  16  of the cutoff knife  12 . Bordering on the bearing bore  22  is a V-shaped recess  23  formed in bearing block  21 . In its inoperative position, knife  12  rests on the bottom edge  24  of V-shaped recess  23 . Mounted on the massive bearing block  21 , by means of a holder  25 , is a mechanical impulse generator  26 . Mechanical impulse generator  26  includes, e.g., a cylinder assembly  27 , which can be operated by compressed air or hydraulics and includes a plunger  28  of a mass m 1 , attached to a plunger rod  29  fitted in cylinder assembly  27 . When actuating cutoff knife  12 , cylinder assembly  27  is actuated out of its illustrated inoperative position, and the mass m 1  of plunger  28  accelerates to the velocity V 1 , at which it impinges at point  30  on the inoperative, rotatably mounted cutoff knife. 
     The preferably dead jolt transfers the impulse of mass m 1  virtually entirely to the movable mass of cutoff knife  12  having a mass m 2  which is accelerated to a velocity V 2  and moves about the bearing axis to the dashed position, cutting the paper web  3  off in the process. The rotary motion of cutoff knife  12  is limited by the top edge  31  of V-shaped recess  23 . With the paper web  3  cut off, the cutoff knife  12  proceeds by reset forces, e,g., by gravity, to its starting position, in which the cutoff knife rests on the bottom edge  24  of V-shaped recess  23 , and the plunger  28  retracts to its indicated starting, or inoperative position. 
     FIG. 4 shows another exemplary embodiment of an inventional cutoff knife with a pneumatic impulse generator. As in the case of FIG. 3, the cutoff knife  12  is mounted rotatably in a bearing  22  in a massive bearing block  21 . The same as in FIG. 3, bearing block  21  has a V-shaped recess  23 . Several orifices  40  of a nozzle assembly are arranged successively in the underside  24  the V-shaped recess  23  in the bearing block  21 . Orifices  40  connect via ducts  41  to a pressure chamber  43  provided in the bearing block  21 , in which chamber rests a compressed-air hose  42 . In its inoperative position, cutoff knife  12  bears on bottom edge  24  of V-shaped recess  23 . In actuating the knife, compressed air released from compressed-air hose  42  flows from the compressed-air chamber  43  through duct  41  to the orifices  40 . The impulse carried along by the flow actuates the cutoff knife  12  and accelerates it to a velocity V 2 , thereby cutting the paper web  3  off. The rotary motion of knife  12  is limited by the top edge  31  of the V-shaped recess  23 , the same as in FIG.  3 . 
     Instead of using a compressed-air hose  42 , valves (not illustrated in FIG. 4) may initiate the flow out of the compressed-air chamber  43 . To that end, the valves are suitably integrated in the ducts  41 . 
     In accordance with the embodiment illustrated in FIG. 5, it is optionally also possible to combine an energy storage apparatus, or energy storage system, with an impulse exchanger according to, e.g., FIG. 3 or FIG.  4 . According to FIG. 5, a spring  50  serves as an energy store. Conceivable would be also other energy stores, such as inflated elastic compressed-air hoses. Spring  50  is in a compressed state when the cutoff knife, as illustrated, assumes its inoperative position. In order for cutoff knife  12  not to be actuated unintendedly by the energy stored in the spring, cutoff knife  12  is fixed in the illustrated position by a holddown  51 . Upon release of holddown  51 , cutoff knife  12  is in synchronism acted upon by a flow impulse while the holddown  51  pivots to the position shown by a dashed line, thereby abruptly releasing the energy stored in spring  50  and accelerating cutoff knife  12  in addition to the impulse exchange from orifices  40 . 
     The present invention thus makes it for the first time possible to achieve also in the case of material webs traveling at high speed a flawless cutoff the of the paper web, thereby preventing difficulties in subsequent processing, for example, in a splicer or coater.