Method and apparatus for transferring a web

An apparatus transfers a moving web of a flexible material from a web guide surface. The web guide surface outputs the moving web, and the moving web has at least one web edge. The apparatus includes at least one edge nozzle, each edge nozzle being positioned so as to be proximate one at least one web edge. Each edge nozzle is configured for separating the moving web from the web guide surface and is further configured to function as a severing device. Each edge nozzle is thereby configured for transversely severing the moving web and forming a new start portion thereof. Each edge nozzle briefly ejects therefrom a high-energy air jet, each high-energy air jet being ejected between the web guide surface and the moving web.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and an apparatus for transferring a web made of a flexible material, especially a paper web, from a web guide surface that outputs the web to a web conveying apparatus.

2. Description of the Related Art

Normally, web transfer concerns the transfer of a threading tail, which is part (for example, an edge strip) of the aforementioned paper web. The transfer takes place, for example, from a first machine section to a following second machine section. Such machine sections can be, in particular, parts of a machine for producing or converting a paper web. For example, it concerns the transfer of the tail within or at the end of the press section of a paper making machine; within or to a winder; and/or from the end region of the drying section of the paper making machine to a following calender. This “tail transfer” is used to make threading the paper web into the machine easier.

It is the intention of the present invention to improve the methods and apparatuses which are described in U.S. Pat. Nos. 3,355,349 and 4,501,643, and also in the brochure “Double Tail Elimination” from the FIBRON Machine Corporation, New Westminster B.C., Canada. Reference is also made to German patent application DE 199 62 731.2.

U.S. Pat. No. 3,355,349 describes a vacuum belt conveyor for conveying a threading strip or tail of a paper web from the drying section of a paper making machine to the first nip of the calender thereof. The belt conveyor includes an elongated body and an air-permeable endless belt, which is mounted such that it can be moved on the body with the aid of two rollers. The endless belt has a conveying run (for example, its upper run). The conveying run travels from the region of the last drying cylinder to the region of the first nip of the calender. The belt is arranged in such a way that it picks up the threading strip from the last drying cylinder. The elongated body of the conveyor is designed as a vacuum box having a perforated upper part. The length of the vacuum box extends underneath the conveying run of the belt. Measures are provided to produce a vacuum in the box, in order to hold the threading strip on the moving belt.

At the infeed end of the known belt conveyor, a severing device or tail cutter is fixed. The severing device or tail cutter is a toothed knife which extends in the transverse direction, i.e., parallel to the roller axis. Before the belt conveyor begins to transport the tail of a web, the complete web, including the tail, runs downward from the last drying cylinder “outputting the web”, past the inlet region of the belt conveyor, the web finally reaching a broke container or a broke pulper. A narrow “tail doctor” is provided on the last drying cylinder, in order to separate the tail from the outer of the drying cylinder and to transfer the tail to the belt conveyor. When the latter comes into action, the tail cutter severs the tail and, in this way, forms a new start of the tail, which is then transported to the calender. If no tail cutter were to be present, the belt conveyor would pull a piece of the tail upwards again out of the broke container and therefore transport a “double tail”. Transporting a “double tail” would cause problems during the threading operation (as addressed in the abovementioned brochure “Double Tail Elimination”).

The belt conveyor design which is disclosed by US '349 and by the referenced brochure has been tried and tested in operation. However, improvements are desirable with the aim that the belt conveyor be able to operate still more reliably and/or at an even higher working speed. In addition, a tail doctor should be avoided, since such an element causes impermissible wear of the outer surface of the drying cylinder.

According to US '643, an apparatus for the transverse severing and guidance of a tail is designed in such a way that it avoids moving parts and a cutting blade or knife. The tail is separated from the last drying cylinder with the aid of two edge blowing nozzles and is severed transversely with the aid of two pneumatic guide plates, which pull the tail in two different directions. The onward transport of the tail is then carried out exclusively by one of the pneumatic guide plates. It is doubtful whether this known design operates satisfactorily, at least when a paper web is to be transferred at a relatively high speed and/or when a very high operating speed is to be used.

SUMMARY OF THE INVENTION

The invention is based on further developing methods and apparatuses with the effect that as many as possible of the requirements specified below are satisfied:

1. It should be possible to carry out the transferring of the web or the threading tail more reliably than hitherto possible and to do so in the production as many different paper grades as possible, even at the extremely high operating speeds of a modem paper making or converting machine (for example, at 2000 m/min or above);

2. On the web guiding surface that outputs the web (for example, roll or cylinder outer surface), a tail doctor that has previously frequently been required should be made superfluous;

3. Likewise, a mechanical severing device (knife) for the transverse severing of the web or the tail is to be avoided;

4. During the transverse severing of the web or the tail, damage to the web or tail edges is to be avoided as much as possible in the region of the new start of the web or the tail, in order that the web or the tail does not tear in its further course, even at an extremely high running speed. For the same reason, the most stable run possible of the web or the tail from the web guide surface that outputs the web to the following web conveying apparatus, possibly to the vacuum belt conveyor, is desired to be achieved; and

5. It is to be possible to arrange the following web conveying apparatus (in particular, if present, the vacuum belt conveyor) as close as possible to the normal web running path, for example close to the web running path which runs through a scanner, as it is known.

An important finding which has led to the invention is that the edge nozzles already known previously (see, for example, U.S. Pat. No. 1,688,267, FIG. 4, numbers 80 and 82) can be used not only to separate the paper web, in particular the tail, from the web guide surface that outputs the web, but, in addition, can also be used for the transverse severing of the web or the tail. This severing succeeds under the precondition that the edge nozzles eject a high-energy air jet, whose flow velocity is as high as possible yet only briefly so (ideally, if possible, only for a fraction of a second).

According to additional concepts relating to the advantageous refinement of the apparatus according to the invention, in the inlet region, e.g., of a vacuum belt conveyor or a rope conveyor (e.g., a rope guidance system), a transfer subassembly is provided which is used specifically for the safe transfer of the web or the tail from the web guide surface that outputs the web. This subassembly includes a pneumatic guide plate with devices for producing an air flow running on the guide plate in the web running direction. In addition, the subassembly for the transverse severing of the web or the tail includes a separating and severing device, which is designed as at least one edge nozzle. The air supply to the at least one edge nozzle is designed in such a way that a high-energy air jet is ejected briefly, specifically being done so between the web guide surface that outputs the web and the web or the tail, so that the web or the tail is severed transversely immediately as it is separated from the web guide surface.

An important idea which furthers the invention is making the aforementioned transfer subassembly (i.e., including guide plate and severing device) movable (for example, relative to the vacuum belt conveyor) such that the distance between the web guide surface that outputs the web and the aforementioned subassembly can be varied. In this way, during the threading operation, the subassembly can be positioned temporarily at a very short distance from the web guide surface that outputs the web. It is therefore possible for the gap between the web guide surface that outputs the web and the web conveying apparatus to be reduced, so that the size of the web or of the tail during the threading operation is reduced to the greatest possible extent. Before the threading operation (and possibly between successive threading attempts), the aforementioned subassembly can be positioned at a certain distance from the roll or cylinder that outputs the web. As a result, the web or the tail can run downwardly without hindrance (for example, into a broke pulper), so that blockages and/or damage to the web conveying apparatus are avoided.

Because, according to the invention, both the separating of the web or the tail from the web guide surface that outputs the web and the transverse severing are carried out pneumatically with the aid of the edge nozzles, both an additional tail doctor, often required earlier, and a mechanical severing device are dispensed with.

The transfer subassembly including a guide plate and severing device can be further configured to better promote the most secure transfer possible of the new start of the web or the tail. It is possible to provide additional blower openings immediately at the infeed end of the guide plate in order to produce an air flow that supports the transport of the web or the tail. These additional blower openings should preferably briefly eject high-energy air jets or a corresponding air curtain, preferably at the same time as the edge blower nozzles. As an alternative or an addition to such blower openings, the guide plate should have at its infeed end a so-called Coanda nozzle, such a nozzle having a rounded edge which, by using the Coanda effect, deflects an air flow (of the highest possible speed) in the direction of the guide plate. By this device, a vacuum zone is produced at the rounded edge and ensures secure guidance of the tail. This produced Coanda effect avoids the situation where the edge blower nozzles, in spite of only brief effect, compress the new start of the tail laterally after the transverse severing thereof. If the guide plate has a plurality of further blowing devices arranged one after another in the manner of a cascade, at least one of these further blowing devices can also be designed as a Coanda nozzle.

According to a further, supplementary embodiment of the invention, at its end on the outlet side (i.e., close to the conveying run of the belt conveyor), the guide plate has an air guide channel, which is curved in such a way that it leads away from the running path of the web or the tail. This air guide channel has two effects. First, it ensures deflection of the air boundary layer carried along by the belt and therefore renders the latter undamaging (i.e., it is ensured that at most part of this air boundary layer passes to the point where the tail is gripped by the vacuum belt conveyor). In addition, the air flow led along on the guide plate is led on the shortest route into the suction zone of the vacuum belt conveyor, and the major part of such air flow is extracted there. As a result, the web or the tail is gripped securely by the vacuum belt conveyor and conveyed onwards as intended. The air guide channel acts in a similar way when the tail is transferred into the rope pinch of a rope guidance system.

In operation, the operations mentioned above proceed at the full operating speed of the paper making or converting machine, for example at around 2000 m/min, and occur within a fraction of a second. Therefore, the features according to the invention form the basis for improved, successful threading operations, in particular in modem high-speed paper machines.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1reveals a vacuum belt conveyor8which is used to transport a moving web, preferably a threading tail9, specifically from last drying cylinder6of a paper making machine, for example, to a multi-roll calender7. As is known, threading tail9is part of a moving web (for example, a paper or board web). It is used to thread the web into the paper making or paper converting machine. Before the threading operation, severed web9aruns downward as indicated (FIGS.1and2), being guided by a machine-width doctor18from cylinder6into a broke chest (not illustrated).

Vacuum belt conveyor8includes an air-permeable, endless conveyor belt10, which runs over two rollers11,12and a suction box or vacuum box15. Rollers11,12are arranged such that they can rotate in holders (not illustrated) which are fixed to suction box15. One of rollers11,12is provided with a drive, not illustrated. Indicated schematically is a vacuum source17for producing vacuum in suction box15.

The conveying run of conveyor belt10, which runs in the web running direction, is the upper run in the present case; a converse arrangement is likewise possible. A suction box15has a top plate16, in which slots (or similar openings) are provided. The conveying run of air-permeable conveyor belt10slides on plate16. As a result, threading tail9is sucked onto conveyor belt10and transported thereby. For the further guidance of tail9into calender7, a nose shoe50, as it is known, and a pivotable guide plate63(which are known from EP 1 076 130) are provided at the outlet end of conveyor8. Following a successful threading procedure, tail9is widened in a known manner; and the complete web, designated by9′ inFIGS. 1 and 2, then runs from cylinder6over paper guide rolls13and14onto uppermost roll7′ of calender7. Suction box15is formed as an elongated body. Other designs which, for example, have an internal apparatus for producing a vacuum on the conveying run of belt10, can likewise be used.

Provided in the inlet region of belt conveyor8is a transfer subassembly20. Transfer subassembly20is a tail transfer apparatus according to the invention. Transfer subassembly20includes a pneumatic guide plate22; a low-pressure chamber24, which is connected via a line25to a compressed-air source26; and a tail severing device21in the form of two edge nozzles. In operation, each edge nozzle21is arranged in one of the edge regions of tail9(see FIG.2A). Each edge nozzle21is suitable for ejecting a high-energy air jet onto outer surface6aof cylinder6that outputs the web. This jet achieves the situation where tail9running downwards is separated from cylinder outer surface6aand, at the same time, tail9is severed transversely. From this point on, tail9runs with a new tail start over guide plate22to conveyor belt10and, with the latter, in the direction of calender7.

As can be seen fromFIG. 2A, width b (order of magnitude 0.2 m) of tail9is only a fraction of the usual width of paper web9′ produced or to be converted. It goes without saying that the working width of entire web conveying apparatus20is matched to tail width b. However, it is also conceivable to design transfer apparatus20according to the invention to be as wide as the machine in a relatively narrow paper converting machine.

FIG. 2reveals that transfer subassembly20is supported on a rail30that is connected to suction box15and specifically so by a support31which can be displaced on rail30and by a pivoting lever32. As a result, transfer subassembly20can optionally assume an operating position, illustrated by solid lines, or a rest position, which is illustrated by dash-dotted lines in FIG.2. In the operating position, distance a (seeFIG. 3) between edge nozzles21and cylinder outer surface6ais only a few millimeters. In addition, guide plate22is inclined with respect to belt conveyor8. By using this configuration, two outcomes are facilitated:

1. The conveying run of conveyor belt10runs rather close along the normal running path of paper web9′ between guide rolls13and14. This running path often rises upwards, as illustrated inFIG. 1, but in other cases may be approximately horizontal; and

2. At the same time, it is advantageous for the point at which edge nozzles21separate tail9from cylinder outer surface6ato be located rather far above the inlet region of belt conveyor8(i.e., in the region between cylinder6and paper guide roll13). The tail separation position is determined, inter alia, by the desired position of dryer-fabric guide roll5following cylinder6(FIG.1).

In the rest position of transfer subassembly20, guide plate22lies approximately parallel to belt conveyor8. Here, the distance between cylinder outer surface6aand edge nozzles21is many times greater than in the operating position. If required, transfer subassembly20can also be placed temporarily in a central, intermediate position provided between the rest and operating positions. In addition, a pivoting device, not illustrated, can be provided in order to pivot the entire apparatus (belt conveyor8with transfer subassembly20) out of the region of the machine.

As illustrated, edge nozzles21are preferably fixed immovably in transfer subassembly20. However, it is also conceivable for edge nozzles21to be movable relative to guide plate22.

In order that edge nozzles21are capable of ejecting the required brief high-energy air jets, the following, by way of example, is provided: transfer subassembly20includes a high-pressure chamber34, to which both edge nozzles21are connected (FIGS.2and3). High-pressure chamber34can be connected via a high-pressure line36to a high-pressure source35, producing compressed air having a pressure of about 5 to 15 bar (preferably about 7 to 10 bar). Provided in line36is a control valve23which, by of a timer signal carried by line38, can be opened briefly (for example, for 0.05 to 0.5 seconds). It is important that edge nozzles21eject the high-energy air jet only briefly, in order that the new start of tail9runs onward as far as possible without damage. In order to shorten the ejection time still further, each edge nozzle21can be assigned its own control valve23(FIG.2A). As an alternative toFIGS. 2 and 3, edge nozzles21can form with each other a C-shaped tubular piece40or41into which high-pressure line36opens, as shown inFIGS. 4,5. If a particularly high air outlet velocity (for example, ultrasonic velocity) is needed at edge nozzles21, it is possible to design edge nozzles21as Laval nozzles21A, as shown in FIG.6.

According toFIG. 3, transfer subassembly20includes high-pressure chamber34, formed so as to have a rectangular hollow profile, and guide plate22which, at42and possibly at42a, has at least one step, and which at43is fixed in a stepped manner to high-pressure chamber34. Guide plate22and high-pressure chamber34, together with other walls45,46, bound low-pressure chamber24, already mentioned. On step42(and possibly on step42a) there is a row of blower openings44, which extend transversely over plate22and through which the air flows out of chamber24. At step43, additional blower openings44are provided on high-pressure chamber34and are configured to eject high-energy air jets briefly at the same time as edge nozzles21. All blower openings44produce air streams which guide tail9along guide plates22in the direction of belt conveyor8. The number of steps42,42aand43can be greater than or less than shown in the drawing.

Wall45, running approximately parallel to outer surface6a, can have an extension which extends downwards, in order to guide severed part9aof tail9downwards. Here, too, if necessary, a step48with blower openings44can be provided.

A further special feature is that guide plate22has an air guide channel49at its end on the outlet side thereof, close to the conveying run of belt10. Air guide channel49is curved in the direction opposite to the running direction of the conveying run. The effect of such curvature has already been described further above. In further refinement (illustrated by dash-dotted lines), a resilient seal60slightly touching belt10can be provided.

According toFIG. 4, high-pressure chamber34ais configured in such a way, including C-shaped tubular piece40(which forms edge nozzles21), that blower openings44which are active at the same time as edge nozzles21are positioned at a shortest possible distance a from cylinder outer surface6a.

FIG. 5shows a very advantageous further development: at the infeed end of transfer subassembly20′ there is a Coanda nozzle50,51with the following features: by use of a rounded edge of nose shoe50and thereby using the Coanda effect, an air stream led upwards from blower openings51is deflected in the direction of guide plate22. As a result, in the region of rounded edge50, a negative pressure zone is produced, which increases the security of the start of the transfer of tail9still further. In addition, within guide plate22, air can be supplied by at least one Coanda nozzle52, in order to produce a negative pressure zone. By such at least one Coanda nozzle52, tail9is supplied to belt10in a flat state, without any risk of fluttering.

FIG. 7shows that a tail transfer apparatus20″ according to the invention, including edge nozzles21and a pneumatic guide plate22, can also be used to transfer a tail9separated from a cylinder outer surface6ato another transport apparatus, e.g., to a rope guidance system70, instead of to a belt conveyor8. Illustrated schematically are two ropes71and72which run towards a roll75(in each case, over a rope pulley73,74) and there form a rope pinch, thereat gripping incoming tail9in order to transport tail9onwards together.

Here, too, provision is made for edge nozzles21to eject a brief high-energy air jet, in order to separate tail9from cylinder outer6aand, at the same time, to sever tail9transversely, so that a new tail start is supplied to rope guidance system70without forming a double tail. Double arrow69indicates that transfer apparatus20″ can be displaced to and fro between an operating and a rest position, in a manner similar to that described above with respect to FIG.2.