EP0408591B1 - Process and device for the suspended conveyance of material in sheets or in webs over a conveying route, in particular a curved conveying route - Google Patents

Abstract

The material (1a, 1b, 1c) in sheets or in webs is conveyed, following the principle of the air cushion, over suspension nozzles arranged on one side. Suction shafts are arranged between individual suspension nozzles, so that the material is subjected alternately to overpressure and to underpressure forces while it is being conveyed. It is thus conveyed on the desired conveying surface without being crushed and without any flutter. Said invention is particularly suitable for conveying material over convex or concave curved conveying routes, as for example for tractionally conveying printed sheets between the output of a printer and its delivery point.

Description

The floating guiding of sheet-like or sheet-like material is still problematic in spite of the various devices for floating guiding that work according to the air cushion or wing principle, if thinner material with a touch-sensitive surface has to be conveyed over differently curved paths. In sheet-fed offset printing machines, transport speeds are currently used at which the sheets flutter. The transport time from the printing unit to storage is so short that the color oil, especially with double-sided 4-color printing on coated and smoothed paper, cannot strike away quickly enough to prevent smearing of the print when the sheet is touched as a result of fluttering. The guidance of the bends over ventilated guide surfaces is problematic because, due to the different curvatures of the conveying path, the centrifugal forces effective on the bend in their direction and size switch. By one-sided support of the sheets on air cushion nozzles, contact of the sheets with the guide surfaces cannot be reliably prevented. Contact with wing nozzles cannot be prevented either, because such nozzles blowing in the conveying direction push the sheets together and such nozzles blowing against the conveying direction intensify the fluttering of the bow end.

In a known device for floating guidance (DE-GM 69 39 363) the material web is alternately supported on an air cushion and exposed to negative pressure. The device consists of perforated nozzle bodies through which air is alternately blown out in the direction of conveyance to build up air cushions or is sucked in through the air. In this way, there is a strict separation in the conveying direction between areas in which the material web is only exposed to compressive forces and areas in which the material web is only exposed to spitting forces. This has the consequence that such a device can only transport material webs that are under web tension without contact. Free-running arches, on the other hand, would be drawn in with their front and rear ends in the areas in which only suction forces are effective, so that contact is unavoidable.

The object of the invention is to provide a method and a device for the floating guiding of sheet-like or sheet-like material, in which or with which the material is transported flutter-free and absolutely contact-free even with the most varied curvature of the conveying path.

The invention relates to a method for floating Execute sheet or sheet material over a conveyor line, in which the material is supported on one side on air cushions and a vacuum is applied between the air cushions. In this method, the object is achieved in that the adjacent air cushions are formed by free jets flowing past and crossing one another with a sufficient distance, and in that the negative pressure is built up on the side of the material facing away from the free jets and penetrates through the free jets.

The invention furthermore relates to a device for the suspended guiding of sheet-like or web-shaped material over a conveying path, which consists of blowing agent-fed floating nozzles arranged at a distance from one another, between which nozzle bodies and the material by the blowing agent an overpressure can be built up in the form of air cushions is and between their adjacent nozzle bodies means are arranged to build up a negative pressure effective on the material. In such a device, the object is achieved in that free jet nozzles are arranged in series in order to build up the air cushions in the nozzle bodies at a mutual distance and at a distance from the respectively opposite nozzle bodies, of which the free jet nozzles formed in one nozzle body are opposite those in the other Nozzle bodies designed free jet nozzles are offset by about half a pitch (distance between adjacent free jet nozzles) in the direction of the row in such a way that the free jets flow past one another and intersect and that as a means of building up the negative pressure effective on the material between the nozzle bodies, suction shafts for generating the negative pressure the side of the material facing away from the free jet nozzles are arranged.

In the invention is achieved by the overpressure superimposed, adjustable in its strength that the effective suction and pressure forces on the material over the entire conveying path are kept in such an equilibrium that the material is compressed and flutter-free in a desired level is promoted without the risk that the material comes into contact with nozzle bodies. The constant change between pressure and suction forces has a positive effect on the stable guidance because the material takes the form of a standing wave.

In the solution according to the invention, use is made of the means known per se for the floating guidance of material in the form of free jets flowing past one another (DE 36 07 370 C1) in order to allow the negative pressure on the material which penetrates the free jets to take effect in this area. The particular advantage here is that a comparatively small volume of blowing agent is used and defined flow conditions for the blowing agent flowing out of the air cushions are obtained.

If the material is conveyed over conveyor lines with convex curvature and conveyor lines with concave curvature, the negative pressure on the conveyor lines with convex curvature increases with increasing conveyor speed and on conveyor lines with concave curvature with decreasing conveyor speed.

As is customary in sheet-fed offset printing machines, the material is preferably conveyed slowly by tensile forces acting on its front edge. Since in the method according to the invention the material is not in a flat position over a ventilated guide surface, but because of the alternating overpressure and underpressure is conveyed in a wave shape, the end of the sheet cannot flutter and / or its corners turn over. In the case of web-shaped material, the longitudinal folds caused by tension in the conventional method and which reduce the quality of the finished product cannot form.

The suction shafts are equipped with injectors to generate the negative pressure without connecting all suction channels to a fan. In the case of curved guidance, the injectors consist of a tube fed with blowing agent and provided with small nozzles in a narrow division, or are supplied within the suction channel by a common blowing agent supply of the floating nozzles when the guide is level.

As is known per se from devices for conveying the sheets printed in an offset printing machine to a tray, the invention provides that for the sluggish transport of the sheets extending across the conveying line, driven rods with grippers are provided with which the Leading edge of the sheet is detectable.

Since the material is conveyed via the nozzle bodies via a very large number of very small free jets blowing in and against the conveying direction, there is no resulting flow component of the blowing agent in or against the conveying direction. The air cushion effect includes the presence of the material above the nozzle body and the vacuum effect includes the presence of the material above the gap. The outermost end of the arch alternately and incompletely covers these areas, so that this end of the arch is less well guided and therefore tends to flutter. In order to avoid this, according to one embodiment of the invention it is provided that further rods circulate between the rods equipped with grippers and that all rods are provided with blades along their length, the flow shadow of which extends to the next blade. This flow shadow ensures that the differential speed between the material and the blowing agent remains so small that the buoyancy forces acting on the material can no longer cause flutter. This effect can be further improved if the conveyor line is shielded by a wall. Additionally or alternatively, it is possible to arrange nozzles-fed nozzles at a great distance above the conveyor section, the free jets of which blow flat onto the conveyor plane in the conveying direction and generate a blowing agent flow in the channel formed by the wall and the material at a lower speed than the conveying speed.

• Fig. 1 eine Vorrichtung zum schwebenden Fördern von bogenförmigem Material von einer Druckmaschine zu einer Ablage in schematischer Darstellung in Seitenansicht,
• Fig. 2 die Vorrichtung gemäß Fig. 1 in Seitenansicht in einem vergrößerten Ausschnitt unmittelbar vor der Ablage,
• Fig. 3 die Vorrichtung gemäß Fig. 1 in Aufsicht in einem vergrößerten Ausschnitt unmittelbar vor der Ablage,
• Fig. 4 ein Diagramm für die Tragkraft in Abhängigkeit vom Abstand des Materials von den Schwebedüsen der Vorrichtung gemäß Fig. 1,
• Fig. 5 die Vorrichtung gemäß Fig. 1 in Seitenansicht in einem vergrößerten Ausschnitt in einer zu Fig. 2 und 3 anderen Ausführung,
• Fig. 6 die Vorrichtung gemäß Fig. 5 in Aufsicht in einem Ausschnitt.

The invention is explained in more detail below with the aid of a drawing representing an exemplary embodiment. In detail show:

• 1 shows a device for the suspended conveying of sheet material from a printing press to a tray in a schematic representation in side view,
• 2 shows the device according to FIG. 1 in a side view in an enlarged detail immediately before the filing,
• 3 shows the device according to FIG. 1 in supervision in an enlarged detail immediately before the filing,
• 4 shows a diagram for the load capacity as a function of the distance of the material from the floating nozzles of the device according to FIG. 1,
• 5 shows the device according to FIG. 1 in a side view in an enlarged detail in a different embodiment from FIGS. 2 and 3,
• Fig. 6 shows the device of FIG. 5 in supervision in a detail.

The S-shaped conveyor section for printed sheets 1a, 1b, 1c shown in FIG. 1 is arranged between a take-over roller 4 of an offset printing machine and a sheet deposit 6. For the sluggish transport of the sheets 1a, 1b, 1c, a pair of revolving chains 5 are provided which are guided over guide elements (not shown) and which carry bars 2 arranged transversely to the conveying direction and which are equipped with gripper elements 2a for detecting the start of a sheet. The takeover roller 4 and the bars 2 equipped with grippers 2a are matched to one another in terms of their speed so that the bars 2 meet with a recess 4a in the takeover roller 4 in order to be able to detect the beginning of the arc here without collision. Shovels 8a are attached to the bars 2. In addition, blades 8b are provided between the rods 2 on further rods, not shown.

Along the S-shaped conveyor line is on arranged on the printed underside of the sheets 1a, 1b, 1c are a plurality of floating nozzles fed with blowing agent, with nozzle boxes 3 and suction shafts 7 arranged between them. As FIGS. 2 and 3 show, each nozzle body 3 is designed as a hollow box and has on its side facing the conveying path a convexly curved back 11, on the edges of which there are circular transitions 12 and on the back a bottom 13 with inlets 13a, via which Blowing agent gets into the nozzle body 3. In the circular transitions 12, rows of holes 15 are arranged as nozzles, from which free jets 15a emerge. The holes 15 of adjacent nozzle bodies 3 are offset by half a division, so that the free jets 15a pointing in the opposite directions flow past one another at a distance and strike the opposite curved back 11. The structure and the aerodynamic function of such floating nozzles is known from DE 36 07 370.

Only half of the last nozzle body 3a in the conveying direction is executed. Its short, convexly curved back 11a extends close to a suction roller 20 which is directly upstream of the sheet stack 6 and which rotates synchronously with the grippers 2a.

The spaces between the nozzle bodies 3, 3a form suction shafts 21. On the back of the nozzle bodies 3, 3a, these suction shafts 23 are delimited by walls 16, which also delimit blowing agent feeds 14, from which the blowing agent is fed to the nozzle boxes 3 via the inlets 13a. In order to generate a negative pressure, blow pipes 17 are arranged between the walls widening at the top, the blow agent supply of which can be individually adjusted, and blow agent jets 18 a emerge from their nozzle holes 18 according to the injector principle and blow into the suction shafts 23. Due to the distances between the free jets 15a this negative pressure can penetrate the free jets 15a and take effect on the bends 1, 1a, 1b, 1c.

The sluggishly conveyed sheet 1a, 1b, 1c is exposed to an overpressure in the area of the back 11 and to an underpressure in the area of the suction channels 23 due to the free jets 15a directed towards one another, so that the sheet is conveyed over the conveying path in the form of a standing wave. Due to the blades 8a, 8b conveyed with the arc, a flow shadow which is dashed in FIG. 1 and which promotes flutter-free guidance is formed on the side of the arc 1a, 1b, 1c facing away from the nozzle bodies 3. The quiet conveyance is further favored by the fact that a channel 9a is formed by a partition 9 arranged in the convex region of the conveying path. In contrast, free-jet nozzles 10 are arranged in the concave region of the conveying section, which ensure that a blowing agent flow that runs along with the arc is established, which also favors the running flow in channel 9a.

The exemplary embodiment of FIGS. 5 and 6 differs from that of FIGS. 2 and 3 only in that the negative pressure in the suction channels is not generated by the blow jets from special blow pipes, but by blow jets 21 which emerge from the nozzle bodies 3. So that these blowing jets 21 from adjacent nozzle bodies do not interfere with one another with regard to their injector action, they are offset from one another and shielded from one another by separating plates 22. In this case, the suction force can be adjusted by throttling the nozzle holes for the injector jets 21 to a greater or lesser extent.

The diagram of FIG. 4 shows the load-bearing behavior of the floating nozzles in a dimensionless representation. The abscissa represents the distance of the Material 1 from the back 11 of the floating nozzles. The ordinate represents the load-bearing capacity of the floating nozzle. The dimensionless distance is the ratio of the distance to the length of the back 11 of the floating nozzles in the conveying direction. The dimensionless load capacity is the ratio of the absolute load capacity in the area of the back 11 to the product of the sum of the hydraulic hole cross sections of the nozzles 15 and the pressure of the blowing jets 15a acting on the material.

The maximum load capacity at point A is around 20. It must not be reached, otherwise contact will occur. The maximum distance at point B is 0.2. It is not reached because no material is without weight. The load capacity O-C at point C corresponds to the weight G of the material on a level, horizontal route. On a concave path, the load capacity at point D corresponds to the weight O-C of the material plus the centrifugal force C-D acting on it according to the ordinate yB. In order to maintain the point D as a working point on the straight part of the conveyor line, where no centrifugal force is effective, a vacuum of the size of the load capacity 5 must be superimposed, which is the same size as the centrifugal force C-D at point D. The load capacity curve remains unchanged, but the abscissa is then at level E and ordinate yE is valid. In the convex part, the centrifugal force must also be compensated, which corresponds to the load capacity 5 if the same curvature is assumed as in the concave part. The abscissa with level F and the ordinate yF apply to the convex part.

If working point D is now also desired when the machine is started, the vacuum remains on the straight line obtained unchanged according to yE, it is built up by the amount K on the concave route and reduced by the amount K on the convex route, ie at the start all negative pressures are 5 and the abscissa is E. for all areas

Claims (10)

1. Process for the suspended guidance of material in sheet or web form over a conveying section, in which the material is supported on one side on air cushions and is subjected to negative pressure between the air cushions, characterised in that the neighbouring air cushions are formed by free jets which flow past one another at a sufficiently great distance and cross one another, and in that the negative pressure is built up on the side of the material facing away with respect to the free jets and is effective through the free jets.
2. Process according to Claim 1, characterised in that the material is conveyed over conveying sections with convex curvature and conveying sections with concave curvature, the negative pressure increasing with increasing conveying speed over the conveying sections with convex curvature and decreasing with decreasing conveying speed over conveying sections with concave curvature.
3. Apparatus for the suspended guidance of material in sheet or web form (1a, 1b, 1c) over a conveying section, which comprises suspension nozzles which are arranged with mutual spacing from one another, are fed with blowing medium and between the nozzle bodies (3) of which and the material (1a, 1b, 1c) a positive pressure in the form of air cushions can be built up by the blowing medium, and between the neighbouring nozzle bodies (3) of which means (16, 17) are arranged for building up a negative pressure acting on the material (1a, 1b, 1c), characterised in that, for building up the air cushions in the nozzle bodies (3), there are formed free-jet nozzles (15) which are arranged in series with mutual spacing and at a distance from the respectively opposite nozzle bodies (3) and of which the free-jet nozzles (15) formed in the one nozzle body (3) are offset with respect to the free-jet nozzles (15) formed in the other nozzle body (3) by approximately half an interval (spacing of neighbouring free-jet nozzles 15) in the direction of the series in such a way that the free jets (15a) flow past one another and cross one another, and in that, as means for building up the negative pressure acting on the material (1a, 1b, 1c), suction shafts (23) are arranged between the nozzle bodies (3) for generating the negative pressure on the side of the material (1a, 1b, 1c) facing away with respect to the free-jet nozzles (15).
4. Apparatus according to Claim 3, characterized in that the negative pressure of the suction shafts (23) can be set.
5. Apparatus according to Claim 3 or 4, characterized in that the suction shafts (23) are fitted with injectors (18) arranged distributed over their length.
6. Apparatus according to Claim 5, characterised in that, in the case of a uniform guide section, the injectors have a common blowing medium feed (14).
7. Apparatus according to Claim 5 or 6, characterized in that, in the case of an only rectilinear guide section, the injectors and the suspension nozzles have a common blowing medium supply.
8. Apparatus according to one of Claims 3 to 7, characterized in that, in the case of dragging transport of the material in sheet form (1a, 1b, 1c) by means of driven rods (2) extending tranzversely over the conveying section and having grippers (2a) with which the leading edge of the material in sheet form (1a, 1b, 1c) can be seized, between the rods (2) fitted with grippers (2a) further rods run around and all the rods are provided over their length with paddles (8a, 8b), the aerodynamic shadow of which reaches up to the next paddle (8a, 8b).
9. Apparatus according to Claim 8, characterized in that the conveying section is screened off on the side facing away from the nozzle bodies (3) by a wall (9).
10. Apparatus according to Claim 9, characterized in that there are arranged at a great distance above the conveying section nozzles (10) which are fed with blowing medium and the free jets of which blow flatly onto the conveying plane in the conveying direction and generate in the channel (9a) formed by the wall (9) and the material (1a, 1b, 1c) a stream of blowing medium of lower speed than the conveying speed.

Images