EP0723523A1

EP0723523A1 - Process and device for stabilising a travelling web

Info

Publication number: EP0723523A1
Application number: EP94928752A
Authority: EP
Inventors: Kurt F. Krieger
Original assignee: Krieger GmbH and Co KG
Current assignee: Krieger GmbH and Co KG
Priority date: 1993-10-11
Filing date: 1994-10-07
Publication date: 1996-07-31
Anticipated expiration: 2014-10-07
Also published as: DE4334468A1; FI961573A0; DE59404840D1; DE4334468C2; WO1995010474A1; EP0723523B1; FI961573A; ATE161240T1

Abstract

The invention relates to a process and a suitable device for implementing it to stabilise a travelling web (B) in a free-running stretch between two supports, in which air is blown on the web (B) on one side from a nozzle arrangement (16) which is surrounded by a substantially flat wall surface (9). The wall surface (9) is parallel to the web (B) and comprises an air duct (14) extending transversely to the direction of travel of the web (B) and having a V-shaped cross section, in which the nozzle arrangement is fitted. The nozzle arrangement consists of mutually staggered hole-like outlets (16, 16') machined in the opposite walls of the air duct. The underpressure region generated by the crossing air flows draws the web towards the flat wall surface (9) on going below a critical distance so that it assumes a position of equilibrium at a certain distance which is determined by the diameter of the outlets and hence the thickness of the air cushion generated by the crossing air flows.

Description

Process and device for stabilizing a moving web

The invention relates to a method of the type corresponding to the preamble of claim 1 and also includes a device suitable for the application of the method.

When gluing or coating a web made of a sensitive material such as paper or the like, it has proven advantageous to avoid damage to the web or its surface, the web for the duration of the drying process of their surface coating floating between to hold two support points. Since the trend in the coating of paper webs is towards ever higher working speeds of the devices of known design used for this purpose, the drying rate of a surface section of the web after coating has an upper limit, for example due to the maximum thermal load capacity of the web material and the coating, which leads to the surface piece having to be in a _floating state for a minimum period of time, the webs have to be guided in a floating manner over ever greater lengths. Naturally, the tendency of the free-running web sections between adjacent floating guides to flutter increases. whereby the uniformity of the drying process can be considerably impaired and which--due to the considerable mechanical stress on the web--may lead to the web tearing under certain circumstances.

In order to suppress this damaging fluttering movement, it is known to blow air on the web between two adjacent floating end guides on opposite sides, viewed in the running direction.

Although transverse deflections of the web can be reliably suppressed with this method, it cannot be used for webs which have a sensitive surface, e.g. after gluing or pigmentation, since a strong directed air flow would lead to a reduction in the coating quality or even to the destruction of the coating. Therefore, this method cannot be applied to webs coated in this way, and the only possibility is to counteract the fluttering by reducing the web speed and the resulting possibility of reducing the distance between two adjacent floating end guides.

For floating guidance, in particular of webs which have a sensitive surface coating, the use of a method is known in which air is blown onto the web only on one side from a nozzle arrangement which is at least partially surrounded by an essentially flat wall. In this method, the initially unexpected effect occurs that the web is not deflected in the direction of the air flowing against it, but rather is pulled towards the flat wall when it falls below a critical distance, taking up an equilibrium position at a certain distance from it .

Responsible for this effect is the fact that in a closed system, there is less pressure in areas where fluids flow faster than in those areas where they flow more slowly. more flow. This physical law is formulated in Daniel Bernoulli's equation, which states that the sum of the static pressure and the dynamic pressure of a moving fluid medium including the flow component corresponds precisely to the pressure that would prevail in the fluid medium at rest. In other words: the static pressure of a fluid medium moving in a system is always lower than that of the medium at rest. This connection, which strictly speaking only applies to the flow of ideal liquids, is responsible for the fact that there is a negative pressure in the air flowing along the flat wall, which pulls the path so far towards the flat wall that the blown out air can still flow out unhindered.

By utilizing this effect, a running web can be stabilized without the surfaces being subjected to any appreciable mechanical stress.

A device for using this method is known from DE 36 30 571 AI.

This device comprises a so-called blower box, which extends essentially over the width of the web and into which the blower air can be introduced. The upper side of the blower box facing the web is designed as a supporting surface onto which air jets are blown from the blower box, with the aid of which the non-contact support of the web is achieved with the aid of negative pressure. The air flows from two parallel slotted nozzles running transversely to the web, which are designed in such a way that the outflowing air flows along a convexly curved flow surface extending to the adjacent edge of the blower box.

The air streams blown out towards the edge generate between the slotted nozzles above a support level provided here, which is lower relative to the web plane than the flow paths running laterally to the slotted nozzles. surfaces, a negative pressure field that exerts a force on the web that is directed towards the supporting plane.

In order to prevent the web from being pulled so far down by the vacuum field that it touches the support plane, an air pipe opens out into it, through which air from the environment is fed to the vacuum field. A throttle valve is provided in the air duct, by means of which the quantity of air supplied can be controlled and thus the force exerted on the web can be adjusted.

Although the floating end of a web is possible with this device in principle, without at least the surface of the web facing away from the device being exposed to any significant mechanical stress, the device is, however, due to the slotted nozzles and the air duct opening into the support plane, which is used to adjust the forces acting on the web requires an additional throttle flap, which is quite expensive to manufacture. The web-facing support surface of the blower box is also greatly weakened by the continuous slot nozzles, so that particularly in the case of blower boxes that are intended for guiding relatively wide webs of material, stiffening ribs that are technically complex to implement must be integrated into the blower box in order to ensure adequate maintain wing stability. Furthermore, the energy requirement to be expected with this device is relatively high, since on the one hand the large opening area of the slot nozzles means that the amount of air required to build up the air flow is quite large and on the other hand additional air has to be entrained through the air duct in order to prevent contact between the Train and the air box to avoid the.

The invention is therefore based on the object of further developing the method for stabilizing the running web, in which air is applied to it on only one side, in such a way that the energy requirement required for the application of the method is reduced. It is a further object of the invention to use the invention to develop a suitable device according to the method of the invention, which is optimized in terms of its production costs. Of course, the method and the device according to the invention should also be suitable for stabilizing uncoated webs.

These objects are achieved by the method specified in claim 1 and by the device specified in claim 4 .

Due to the fact that the air flow required for the method according to the invention is generated by a blower which is only supplied with electrical power when the web is actually fluttering, the method according to the invention can be used particularly economically. This is done by measuring its spatial position in situ while the web is running and air is only applied to the nozzle arrangement when a deflection of the web from its normal position is detected. The pressure is regulated by regulating the power supplied to the blower.

So that the web or its surface is not damaged by contact with the device provided for use of the method according to the invention when fluttering begins, it is advantageous according to claim 2 to move the nozzle arrangement at a distance from the web when it is running in its normal position To ver¬ store web surface, so that such contact is excluded.

If a web deflection is then measured, it is advantageous if air is first applied to the nozzle arrangement and then displaced in the direction of the web until the web interacts with the air stream emerging from the nozzle arrangement (claim 3).

A device suitable for use of the method according to the invention, in which the nozzle arrangement comprises a substantially flat wall facing the web, which is aligned approximately parallel to the web and at least partially surrounds the nozzle arrangement laterally, is the subject of claim 4. Optimal utilization of the As a rule, the Bernoulli effect is achieved when the nozzle arrangement is completely surrounded laterally by the wall.

In order to generate a relatively low-turbulence air flow, the nozzle arrangement is arranged in an air duct extending transversely to the running direction of the web. The air duct comprises two duct walls which are arranged on both sides of a transverse plane which is in its longitudinal direction and perpendicular to the web plane and which each form the same acute angle with the transverse plane. The nozzle arrangement consists of a series of outflow openings provided in the duct walls, which are arranged on opposite walls of the air duct in such a way that the air streams exiting from the outflow openings of one duct wall flow out of the outflow openings of the other duct wall cross. The Bernoulli effect of the outflowing air creates an area above the air duct in which--compared to the environment--there is a negative pressure through which the material web is drawn in the direction of the device after falling below a critical distance air currents crossing in the area of the air ducts close above the air duct an air cushion supporting the web so that contact between the web and the device is effectively avoided without the need for special measures.

In addition to this considerable advantage over previously known devices, tests have shown that the design of the nozzle arrangement as individual outflow openings increases the efficiency of the device - i.e. the ability to stabilize the web at the desired distance with the aid of the device.

Individual outflow openings can also be incorporated in the duct walls of the air duct in a simple manner--for example by stamping--and an air duct provided with such openings is mechanically only slightly weakened. Due to the special arrangement of the channel walls, the Air duct of the device according to the invention stabilizes on the surface facing away from the web, so that reinforcing ribs, which would considerably increase the production costs, can also be dispensed with in devices provided for wider webs of material.

In an advantageous embodiment of the device, the outflow openings are in the form of holes. This measure optimizes the efficiency of the device on the one hand, and on the other hand the thickness of the air cushion supporting the web and thus the distance between the web and the upper side of the device can be adapted to the respective requirements by selecting the diameter of the hole-shaped outlet openings ( claim 5).

According to claim 6, the diameter of the outflow openings is preferably 5 mm to 20 mm.

In a particularly streamlined configuration of the device, the outflow openings lying opposite one another are arranged laterally offset and are surrounded by concentric flow-guiding edges (claims 7 and 8). This configuration achieves a particularly low-turbulence air flow, which has a positive effect on the efficiency of the device.

In order to prevent the particularly endangered longitudinal ends of the device - seen in web direction - from being touched by the running web, it is advantageous according to claim 9 to provide support nozzles which are spaced apart from the nozzle arrangement and are pressurized with compressed air. The support nozzles can be designed in a simple manner in that, viewed in the direction of travel of the web, rows of holes arranged transversely to the web and acted upon by compressed air are worked into the wall at the beginning and at the end of the wall (claim 10).

The economical use of the device according to the invention is possible when it is not in constant operation but is only used when required, ie when the web is actually fluttering. In addition it is advantageous, according to claim 11, to connect a device for measuring the deflection of the web from its normal position upstream of the nozzle arrangement. Advantageously, this device is connected to an arrangement for controlling the pressure under which air is applied to the nozzle arrangement (claim 12), so that compressed air is only applied to the nozzle arrangement when required and energy consumption accordingly only takes place when required.

In order to prevent the web from touching the not yet activated device according to the invention when fluttering begins, an arrangement for displacing the nozzle arrangement in the direction perpendicular to the web surface is provided according to claim 13, which device for measuring the deflection of the track is controlled. The control is advantageously carried out in such a way that when a fluttering of the web is detected, the nozzle arrangement is first acted upon by air, in order then to be displaced in the direction of the web just far enough for the web to interact with the air flow exiting from the device in the desired manner kicks.

Depending on the properties of the web such as composition or width, it may be sufficient to stabilize the web if the extension of the housing transverse to the web is only extended over a part of the web width lying in the edge regions of the web. Such a configuration allows the energy requirement of the device according to the invention to be reduced considerably.

In the drawing, an embodiment of a device according to the invention is illustrated schematically. Show it:

1 is a side view of the embodiment;

FIG. 2 shows the pressure chamber of the same embodiment in a front view (view A in FIG. 1);

3 shows a section through an air duct along the line III-III in FIG. 2 in a perspective representation, and 4 shows a schematic representation of a gluing press known per se, but equipped with a device according to the invention for stabilizing the web, for gluing a paper web on one side.

Whenever "above" or "below" is mentioned in the following, the upright operating position of the device shown in FIG. 1 is meant. Specifications such as "front", "back", "left" and "right" relate to a view of the side of the device facing the web, corresponding to view A in FIG.

The device, designated as a whole by 100 in the drawing, comprises a holder 1, which rests at its lower end in a receptacle 2 fixed, for example, on the floor. The receptacle 2 is designed in such a way that a displacement of the holder 1 in the direction of the normal to the web B, as indicated by the arrow V in FIG. 1, is possible.

At its upper end, the holder 1 carries a housing 3 which is closed all round and whose inner volume forms a pressure chamber 4 . The approximately cuboid housing 3, which extends with one long side over a substantial part of the width of the web B, comprises a rear side 5 facing away from the web arranged connecting piece 6, which the connection of a - not shown in the drawing - acted upon with compressed air hose serves. The upper side 7 and the lower side 8 of the housing 3 are provided near the surface 9 facing the web with two step-like housing shoulders 10, 10' which are parallel to one another and to the surface 9 and point inwards. Extending from the housing shoulders 10, 10' towards the track is a housing extension 11 which widens in the shape of a funnel in the direction of the track, the end of which forms the surface 9 facing the track.

As can be seen from FIG. 2, the surface 9 of the housing 3 facing the web includes two flat walls 12, 12' which run transversely to the web and parallel to one another and which—seen in the running direction of the web—at the beginning and at the end transverse rows of holes 13,13' which communicate with the pressure chamber 4 and form support nozzles for the web B.

Between the two walls 12, 12' there is an air duct 14 which runs transversely to the web and is open to it and which is let into the housing 3. The air duct comprises duct walls 15, 15' on both sides of a transverse plane Q which is in its longitudinal direction and perpendicular to the web plane E and which each form the same acute angle β with the transverse plane Q (cf. FIG. 3). Outflow openings 16, 16' are worked into the duct walls 15, 15' in a regular row arrangement and serve to allow air to escape from the pressure chamber 4. The outflow openings 16, 16' are surrounded by flow guide edges 17, 17' curved into the air duct 14, which serve to reduce the formation of eddies when the air flows out. In the exemplary embodiment shown in the drawing, the outflow openings 16, 16' lying opposite one another are arranged laterally offset, as a result of which the outflowing air streams do not meet directly on the other, which also makes it possible to achieve reduced eddy formation.

The operation of the device will be explained below. To stabilize the web B, compressed air is fed via the flange 6 to the housing 3 acting as a pressure chamber 4 according to the double arrow S in FIG. 1, for example by means of a blower not shown in the drawing. On the side of the housing 3 facing the web, part of the supplied air flows through the rows of holes 13,13' acting as support nozzles, which reliably prevents the web B from hitting the edges of the walls 12,12' during a transient process touched. The remaining part of the supplied air flows through the outflow openings 16, 16' into the air duct 14 and, caused by the so-called Coanda effect, essentially follows the duct walls 15, 15' and, further to the outside, the walls 12. 12', as indicated by the double arrows S in Fig. 3 clarified. As already explained, due to the increased flow velocity of the air, there is a lower pressure in comparison to the air in the environment at rest according to Bernoulli's equation, as a result of which the path is aligned essentially along the surface 9 .

4 shows a schematic of a glue press known per se for one-sided application of glue, which is equipped with a device according to the invention. In such a size press, the web is guided around a drying cylinder 20 and passes a downstream guide roller 21 before it is fed to the size press rollers 22, 22' arranged on both sides of the web. A glue application device 23 is provided on one side of the web in front of the size press rollers 22, 22', viewed in the running direction of the web B. The layer of glue applied to the web B is evened out by the size press roller 22', excess glue being taken up by a glue collecting pan 24 surrounding the size press roller 22'. A device 100 according to the invention for stabilizing the web is provided behind the size press rollers 22, 22', seen in the running direction of the web B, which acts on the uncoated side of the web B and, if necessary, prevents the web from fluttering. The web is then guided through a spreader device 25, which prevents the formation of folds in the web B, which would lead to the web parts sticking together and thus to their destruction. The web B is finally fed via a downstream guide roller 26 to a drying cylinder 27, on which the drying process of the coated side of the web takes place.

Claims

P atentClaims

1. Method for stabilizing a running web (B), preferably a moist paper web, in a free-running web area between two supporting points, in which the web (B) is sprayed with air on one side from a nozzle arrangement surrounded at least partially by a substantially flat wall surface 9 is blown on, the nozzle arrangement being acted upon by air by a blower, and with which, with the running web (B), its deflection from its normal position is measured in situ, characterized in that the pressure under which the nozzle arrangement is acted upon with air is controlled as a function of the deflection of the web from its normal position by regulating the power supplied to the blower in such a way that no power is supplied to the blower when the web (B) is running in the normal position.

2. The method according to claim 1, characterized in that with a web (B) running in its normal position, the nozzle arrangement is displaced at a distance from the web surface, that the web (B) has the nozzle arrangement and this Surrounding components are not touched, even in the case of the maximum anticipated deflection of the web.

3. The method according to claim 2, characterized in that after measuring a web deflection, the nozzle arrangement (16,16 ') is first acted upon by air and then so far in the direction of the web (B) is displaced until the web (B) with the from the air flow entering the nozzle arrangement.

4. Device for applying the method according to one of claims 1 to 3, with a compressed air source designed as an electric blower, with a nozzle arrangement acted upon by the compressed air, which extends in an air duct ( 14) is provided and comprises a substantially flat wall surface (9) facing the web, which is aligned approximately parallel to the web (B) and at least partially surrounds the nozzle arrangement, characterized in that the air duct (14) has two longitudinal ¬ direction of the air duct and perpendicular to the web plane (E) ste¬ existing transverse plane (Q) comprises duct walls (15) which each form the same acute angle (ß) with the transverse plane (Q) and that the nozzle arrangement consists of a row of in outflow openings (16,16') provided in the channel walls (15,15').

5. Device according to claim 4, characterized in that the outflow openings (16, 16') are designed in the form of holes.

6. Device according to claim 5, characterized in that the diameter of the perforated outflow openings (16, 16') is between 5 mm and 20 mm.

7. Device according to one of claims 4 to 6, characterized in that flow guiding edges (17) are provided which surround the outflow openings (16,16') concentrically.

8. Device according to one of Claims 4 to 7, characterized in that the outflow openings (16, 16') lying opposite one another are arranged laterally offset.

9. Device according to one of Claims 4 to 8, characterized in that support nozzles (13, 13') which are subjected to compressed air and are spaced apart from the nozzle arrangement in the running direction of the web are provided.

10. Device according to claim 9, characterized in that the supporting nozzles are rows of holes (13,13') arranged transversely to the web (B) at the beginning and at the end of the walls (12,12') viewed in the running direction of the web.

11. Device according to one of claims 4 to 10, characterized in that a device for measuring the deflection of the web (B) from its normal position is connected upstream of the housing (3) containing the air channel (14).

12. Device according to claim 11, characterized in that the device for measuring the deflection of the web is connected to an arrangement for controlling the electrical output of the blower, with which air can be applied to the outflow openings (16, 16').

13. The apparatus of claim 11 or 12, characterized ge indicates that an arrangement (2) for moving the fan (3) is provided in the direction perpendicular to the web surface, which is controlled by the device for measuring the deflection of the web.

14. Device according to one of claims 4 to 13, characterized in that the extension of the housing (3) transversely to the web (B) is only part of the web width and the housing (3) faces the edge region of the web (B).