EP0708203A2 - Device and method for humidifying a moving web material - Google Patents

Abstract

A moistening appts. for a running web of material has a chamber with a surface where steam exits treat the web facing it and a front facing against the web run at the end of the treatment surface. Here, a strip (15), placed before said surface (8), esp. at the chamber front (9) and projecting, at least partially over strip length, to the web over the surface, has an edge (17) facing the oncoming web (2). Also claimed is a process using the appts. where at least one steam jet is directed at the web and where, here, the air layer adhering to the web is at least partially stirred about or stripped off before steam application. Pref. the strip is arranged to have an adjustable spacing between the web and the chamber edge which also is adjustable in a curve across the web. The spacing width (A), following web curvature, is constant over the web breadth and is between 2 and 12 mm. The strip, formed from at least two layers placed together, has slits which travel from the edge opposite the steam-side edge (17), end in holes of dia. greater than slit widths, the slits of one layer being displaced from those of the other. One layer, being heated on the chamber, lies flat and is made from heat-conducting material at least equivalent to copper. The strip has elongated holes to take bolts inserted from the chamber front to attach the two layers at pre-set points where between any two is placed a slit from each layer. The air layer is stripped off just before the gap through which steam is blown. Alternatively the strip is bent at an angle facing against web run at angle, alpha, between 30 and 70 degrees .

Description

The invention relates to a device for moistening a passing material web with the help of steam with a housing which has a treatment side with steam outlet openings facing the material web and a front side at the inlet end of the treatment side and a method for moistening a passing material web with the help of steam, in which at least one steam jet is directed against the material web.

Devices and methods of this type are used, for example, in the paper industry to moisten the paper web, which here forms the material web, before the paper web is passed through a nip of a roller arrangement. By moistening you can influence some parameters of the paper web, such as gloss and smoothness.

DE 43 01 023 A1 shows such a device, which due to its wedge shape can be arranged relatively close to a nip of a roller arrangement, and a corresponding method. The treatment side of such a device does not have to be flat. Rather, depressions can also be provided in which the steam outlet openings are arranged. The front is the side of the device to which the material web runs. When used in connection with a roller arrangement, it is therefore the side that faces away from the roller arrangement.

The dampening of the material web with the help of steam has proven itself. A relatively uniform moistening is achieved here. It is problematic, however, that the steam must first penetrate the air layer adhering to the material web before it can moisten the material web. This is particularly important if you want to control the humidification in such a way that the steam first condenses on the material web, that is, it does not previously condense in the air and is then deposited on the material web in the form of droplets. Good results have been achieved by increasing the steam speed. The steam then has such a high energy that it can penetrate the adhering layer of air. The higher the desired steam speed, the higher the steam pressure must be selected, which increases the expenditure on equipment of the device and the energy expenditure during operation. In addition, there is a risk that the steam will then no longer be completely absorbed by the material web, but will be partially reflected and distributed in the environment.

The invention has for its object to improve the moistening of a passing web of material.

This object is achieved in a device of the type mentioned above in that, in the direction of travel of the material web in front of the treatment side, in particular in the region of the front, a bar projecting at least over part of its length in the direction of the material web over the treatment side with one facing the material web Edge is arranged.

In this way, one can first of all achieve that an evaporation space that is at least largely closed on one side is created between the device and the material web. The bar has only a very small extension in the running direction of the material web. In abstract terms, you can call it a kind of line. The bar can thus be arranged at a smaller distance from the material web than the device itself. Even if there is a small gap between the material web and the edge, the steam is blocked from entering the surroundings. The small remaining gap is fluidically acted upon by the passing material web so that any steam that gets there is immediately carried away from the front towards the treatment side. However, the edge may have another effect. Because of the possibility of arranging the edge relatively close to the material web, a kind of peeling effect probably results, so that the air layer adhering to the material web is disturbed or even lifted off. The steam can then easily reach the material web behind the edge and condense there. This significantly improves efficiency. You can either reduce the effort required for moistening with the same dampening result or you can increase the amount of moisture that can be transferred to the material web with the same effort. The latter case is particularly interesting when the speed of movement of the material web increases. The edge can also referred to as working, peeling, draining, tear-off or sealing edge.

The bar for adjusting a distance between the material web and the edge on the housing is preferably arranged to be adjustable. This gives greater freedom in the assembly of the humidifier. In many cases it is quite difficult to place the housing so precisely that the desired close distance between the material web and the edge is set. If, however, the bar on the housing is adjustable, rough positioning of the housing is sufficient, while fine adjustment is achieved by moving the bar on the housing.

In a particularly preferred embodiment it is provided that the edge is curved transversely to the direction of travel of the material web and the curvature is adjustable. In many cases, a so-called spreader roll is arranged in front of the roll nip of the roll nip arrangement, for example a calender, which ensures that the material web receives its greatest possible transverse extent when it passes through the roll nip. Such an spreader roller has, at least at the point where the material web rests, a curved surface, which can be achieved, for example, by the spreader roller being somewhat bent. However, this means that the material web no longer lies exclusively in one plane, but is given a corresponding curvature. This changes the distance of the material web to the housing in the transverse direction. For example, it can be larger in the middle than at the edges. The distance to the edge would change accordingly. If the edge is now curved accordingly, the edge can track the material web in a direction transverse to the running direction of the material web, ie in the transverse direction.

The edge is preferably at a constant distance from the material web over the width of the material web. Because a constant distance to the material web can be maintained over the web width, a very uniform moistening is also achieved. The uniformity of the moistening is attributed on the one hand to the fact that the vapor pressure can be kept essentially the same over the width of the material web. The gap between the material web and the edge is so uniform that there are no major flow differences at any point which could cause the steam to form a certain preferred flow path to the outside. In addition, this measure also ensures that the disturbance of the air layer adhering to the material web is substantially uniform over the width of the material web, so that here too the corresponding uniformity of the moistening can be ensured with the aid of steam.

The distance is preferably in the range from 2 to 12 mm. With this size, there is on the one hand a sufficient distance between the material web and the edge to keep the risk of damage to the material web small. On the other hand, the edge is still close enough to the material web, on the one hand to prevent a large amount of steam from escaping and, on the other hand, to sufficiently disturb the air layer adhering to the material web.

The strip preferably has slots which start from the edge opposite the edge and optionally end in holes whose diameter is larger than the width of the slots. In this way it is possible to bend the bar, which is essentially designed as a flat structure due to its function as a boundary wall of the vapor deposition space, that the edge curves. When the strip is bent, the distance between the boundaries of the slits changes, ie the slits become wider or narrower at their end opposite the edge, depending on the direction in which the curvature of the edge is to take place. The slots can be relatively narrow. A width of about 5 to 8 mm is sufficient in most cases. The distance to the edge is preferably approximately in the range of 10 to 12 mm and the diameter of the holes can be approximately 15 mm. The holes have the advantage that the stress distribution in the material at the ends of the holes is improved, so that the risk of cracking is reduced.

For this purpose, the bar is preferably composed of at least two layers of material, each layer of material having slots and the slots being arranged offset from one another. In this way it is possible to produce a largely tight boundary wall of the vapor deposition space, which is nevertheless bendable so that the edge can be set with a predetermined curvature.

Preferably, one of the two layers of material is at least partially flat on the housing, which is heated at this point, and has good thermal conductivity, which in particular corresponds at least to that of copper. Due to the good thermal conductivity, the temperature of the housing is distributed quickly and evenly on the bar. This temperature is then also transferred to the other material layer. In this way, the bar is heated with relatively simple means. This can at least largely prevent the formation of condensate on the bar.

The strip preferably has elongated holes through which bolts fastened to the front of the housing are guided. You can now loosen the bolts or nuts screwed onto the bolts, adjust the strip and the curvature of the edge accordingly and fasten the bolts or nuts again. In this way, simple adjustment is possible, which is particularly advantageous because the adjustment can take place with the material web in place. You can use it to check the distance between the edge and the material web immediately after the setting or to adjust the position of the edge to the position or location of the material web.

The material layers are preferably connected to one another at predetermined connection points, with at least one slot of each material layer being arranged in the transverse direction between two connection points. The bar can be handled as a single, coherent part by the connection. This makes handling easier, especially when adjusting the curvature. Nevertheless, the bendability of the bar is ensured.

The bar is preferably bent in the region of the edge in the direction of the running material web. The edge of the material web presents itself as a curve. This drastically reduces the risk of damage to the material web. Smaller touches of the edge through the material web can now also be accepted, although these are also not desired. Because the strip is bent in the direction of the running material web, a somewhat longer throttle section is additionally created, which makes it difficult for the steam to escape from the vaporization space at this point.

In an alternative embodiment, the strip in the area of the edge can be angled in the direction of the incoming material web by an angle in the range from 30 ° to 70 °. With such a configuration, the peeling effect of the edge is even stronger. The air adhering to the material web is lifted off in the manner of a plane, in particular when the edge of the material web is relatively closely adjacent. It is advisable to round off the edge. Nevertheless, a certain minimum distance to the material web must be maintained in order to rule out accidental contact as reliably as possible. The remaining gap can then be largely sealed off by the vapor pressure on the other side of the material web.

In a particularly preferred embodiment, a second ledge projecting in the direction of the material web over the treatment side is arranged on the rear side of the housing, the edge of which facing the material web is adjustable with its curvature. This bar corresponds essentially to the bar arranged on the front. Such a second strip is always useful when the device for moistening the web between a spreader roll and the nip is used and the distance to the nip is still so great that the web still has a non-negligible bulge when it is steamed. The steaming chamber is closed off to the rear, that is to say the roll gap, by the second bar, so that the evenness of the steaming does not suffer because the steam can escape more easily in the middle of the material web.

The housing advantageously has an at least partially bevelled back, on which a sealing strip is arranged. Training with a beveled sealing strip is known from DE 43 01 023 A1. Through the additional measure of the sealing strip can now also close the vaporization space between the housing and the material web on the back. This prevents or hinders the escape of steam at this point, so that the environment is less exposed to steam. In addition, this sealing strip also complicates the introduction of air into the vaporization chamber with the cooling caused thereby, so that less energy is required to maintain the desired temperature in the vaporization chamber.

The sealing strip is preferably formed from a little abrasion-resistant plastic. The abrasion resistance refers here to the relationship between the roller which is to be arranged adjacent to the sealing strip and the sealing strip itself. If the roller rubs against the sealing strip, the ratio of the abrasion resistance is chosen so that practically no changes can be observed on the roller are, while the sealing strip is ground very quickly. This has the advantage that the housing provided with the sealing strip can be moved into the desired position in front of the nip. The sealing strip is somewhat oversized. The roller will then grind in the sealing strip so that a very narrow gap is created between the sealing strip and the roller without further adjustment work being necessary. Once the roller has ground the sealing strip accordingly, the sealing strip is no longer stressed. For this reason, the sealing strip can be dimensioned relatively weak.

It is particularly preferred that the sealing strip is connected to the housing via a quick-change connection. Since the sealing strip is designed as a wearing part, so to speak, it should be replaced with little effort. The quick change connection can be formed, for example, by a rail on which the sealing strip is pushed. In many cases, however, a plug connection or the like will also suffice.

The object is achieved in a method of the type mentioned at the outset in that the air layer adhering to the material web is at least partially swirled or peeled off before the steam is applied.

As explained above in connection with the device, this disturbance of the air layer adhering to the material web means that the steam has to overcome a lower resistance. It also reaches the material web when it is running at a lower speed.

In this case, the material web is preferably guided as a boundary of a gap located in front of the steam jet, the thickness of which can be adjusted. The gap thus serves to swirl or peel the air layer. Because the material web forms a moving boundary of this gap, no further measures are required to cause this disturbance of the adhering air layer. With the adjustability of the thickness of the gap, it is now possible to influence the disturbance of the air layer relatively precisely. Additional parameters can be taken into account here, for example the speed of the material web or the pressure of the steam of the steam jet.

The thickness of the gap is preferably adjustable in the range from 2 to 12 mm. As already stated above, this thickness has proven to be advantageous.

It is particularly advantageous to set the gap so that it follows the curvature of the material web. Problems have so far been encountered in particular when using an expander roller before moistening because the moistening over the width of the material web could only be adjusted uniformly with the aid of additional measures. In the middle, in particular, where the distance between the moistening device and the material web was greatest, the steam has been able to escape many times before it had acted on the material web. This is now at least largely prevented by the curvature of the gap.

The gap is preferably set to a constant thickness transverse to the running direction of the material web. No constancy in the mathematical sense is required. It is only necessary that the gap has no pronounced differences across the width of the web, so that on the one hand the steam finds the same flow conditions everywhere, on the other hand the disturbance of the air layer on the material web takes place essentially uniformly everywhere.

It is preferred that the swirling or peeling of the air layer takes place at the beginning or immediately in front of the gap which is acted upon by a vapor pressure against the direction of travel of the material web. In most cases, the gap is necessary to prevent damage to the material web or even tearing off. This risk exists if the material web hits the treatment device as it passes. A small gap can, however, be easily sealed by a corresponding steam pressure, which is created in the treatment room when steam is applied to the material web.

Fig. 1

eine Bedampfungsvorrichtung vor einem Walzenspalt,

Fig. 2

eine Einzelheit X aus Fig. 1,

Fig. 3

eine schematische Ansicht aus Richtung III nach Fig. 1,

Fig. 4

eine Leiste,

Fig. 5

die Leiste in gekrümmten Zustand und

Fig. 6

eine alternative Ausgestaltung der Leiste.

The invention is described below with reference to a preferred embodiment in conjunction with the drawing. Show here:

Fig. 1

an evaporation device in front of a nip,

Fig. 2

a detail X from Fig. 1,

Fig. 3

2 shows a schematic view from the direction III according to FIG. 1,

Fig. 4

a bar,

Fig. 5

the bar in curved condition and

Fig. 6

an alternative embodiment of the bar.

A device 1 for moistening a material web 2 passing by is shown in FIG. 1 in a typical working environment, namely between a nip 5 formed by two rollers 3, 4 and an spreader roller 6. The spreader roller is, as can be seen from FIG. 3, bent. The material web 2, for example a paper web, is accordingly curved. As a result, as shown in broken lines, it is raised further in the middle of its transverse dimension than at its edges. This curvature decreases in the direction of the nip 5. There the material web 2 is completely flat again.

The device 1 has a housing 7 which has a treatment side 8, a front side 9 and a rear side 10. With a running in the direction of an arrow 11 from the spreader roller 6 to the nip 5 Material web 2 faces the front 9 of the incoming material web.

Steam outlet openings 12 are provided on the treatment side 8 and are shown schematically in FIG. 1. The treatment side 8 does not have to be formed by a flat wall. Rather, the steam outlet openings 12 can also be arranged in a recess 13, as is known from DE 43 01 023 A1. An evaporation chamber 14 is thus formed between the treatment side 8 and the material web 2.

On the front 9 of the housing, a bar 15 is arranged displaceably in the direction of a double arrow 16. The strip 15 has an edge 17 which can be brought closer to the material web 2 or moved further away from it by the displacement of the double arrow 16. The edge is bent towards the treatment side, i.e. in the direction of movement 11 of the material web 2. The strip 15 is fastened to the front 9 of the housing 7 with the aid of bolts 18 and nuts 19 which are guided through elongated holes 20 (FIGS. 4 and 5). After loosening a nut 19, the bar 15 can be moved in the direction of the double arrow 16. A gap of thickness A is formed between the edge 17 and the material web 2.

The strip 15 consists of two layers of material, namely a copper sheet 21 and a VA sheet 22, ie a sheet made of stainless steel. The copper sheet 21 lies flat against the housing 7. The housing 7 is heated at least at this point. This allows heat to be transferred to the copper sheet 21. The copper sheet 21 transfers the heat to the stainless steel sheet 22, so that the bar 15 is at an elevated temperature. This reliably prevents condensation on the bar 15.

4 shows a top view of the bar 15. The stainless steel sheet 22 is shown here with solid lines, the copper sheet 21 with dashed lines. As can be seen, both the stainless steel sheet 22 and the copper sheet 21 have slots 23, 24 which extend from a longitudinal edge 25 of the strip 15 opposite the edge 17. The slots 23 of the stainless steel sheet 22 and the slots 24 of the copper sheet 21 are arranged such that the stainless steel sheet 22 covers the slots 24 in the copper sheet 21, while the copper sheet 21 covers the slots 23 in the stainless steel sheet 22. The slots 23, 24 have a width in the range of 5 to 10 mm. They penetrate the respective sheets 21, 22 almost completely. In the region of the edge 17 there remains a web with a height of approximately 10 to 15 mm. The slots 23, 24 end in a bore 26, 27 with an enlarged diameter, which can be approximately 15 mm. This configuration makes it possible to bend the bar 15 in its plane in such a way that a curved edge 17 is formed, which is enlarged in FIG. 5 and shown with a greatly exaggerated curvature.

As can be seen from FIG. 3, the curvature of the strip, more precisely the curvature of the edge 17, can then be adjusted so that it corresponds to the curvature of the material web 2 caused by the spreader roller 6.

The copper sheet 21 and the stainless steel sheet 22 are connected to one another by welding spots 28. The welding points 28 only serve to ensure that the two sheets 21, 22 can be handled together. The main fixation of the two sheets 21, 22 to one another, however, takes place by means of the nuts 19 on the bolt 18. Accordingly, the welding spots 28 are also provided only at larger intervals. The distances are so big that at least one pair of slots is provided between two adjacent welding spots in the transverse direction. In the illustrated embodiment, even four pairs of slots are provided. Despite the connection of the two sheets 21, 22 to one another, the edge 17 can thus be set with the desired curvature.

A second bar 31 is arranged on the rear 10 of the housing and also protrudes beyond the treatment side 8. The structure of the bar 31 corresponds to that of bar 15, i.e. the edge adjacent to the material web 2 is curved, the curvature being adjustable so that it follows the curvature of the material web caused by the spreader roller.

A sealing strip 29 is alternatively or additionally provided on the rear side 10 of the housing 7, which is at least partially inclined. This sealing strip 29 is pushed onto a rail 30 on the housing 7. Accordingly, it can be replaced relatively quickly and easily. The sealing strip 29 is adjacent to the roller 4 adjacent to the housing 7 during operation. It consists of a little abrasion-resistant plastic, so it is designed as a wearing part. The sealing strip 29 is used with a slight oversize. Then when the device 1 is brought into the working position, the roller 4 grinds the sealing strip 29 into the desired shape without being damaged itself. As a result, the vaporization chamber 14 is also largely sealed on its rear side.

Fig. 6 shows an alternative embodiment of a bar 15 ', in which parts which correspond to those of Figs. 1 to 5 are provided with the same reference numerals. Modified parts are provided with crossed reference numerals. The only change compared to the embodiment of FIGS. 1 to 5 is that the bar 15 'is now no longer bent in the direction of the running material web, as can be seen from FIG. 2, but that it is angled against the running direction of the material web 2, namely by an angle α, which is in the range from 30 ° to 70 ° can move. The choice of the exact angle depends, among other things, on the desired web speed. With such a configuration, an improved peeling effect can be achieved. The air layer adhering to the material web is literally lifted off by the wedge formed by the edge 17 '. Since, as a rule, a certain minimum distance A in the range of 3 to 10 mm must be maintained, this lifting is supported by a vapor pressure which is formed on the rear side of the bar 15 '.

Claims (22)

Device for moistening a passing material web with the help of steam with a housing which has a treatment side with steam outlet openings facing the material web and a front side at the inlet end of the treatment side, characterized in that in the direction of travel of the material web (2) in front of the treatment side (8), in particular in the region of the front side (9), a bar (15) projecting at least over part of its length in the direction of the material web (2) over the treatment side (8) with an edge (17) facing the material web (2). Apparatus according to claim 1, characterized in that the bar (15) for adjusting a distance (a) between the material web and the edge on the housing (7) is adjustably arranged. Device according to claim 1 or 2, characterized in that the edge (17) is curved transversely to the running direction of the material web (2) and the curvature is adjustable. Device according to one of claims 1 to 3, characterized in that the edge (17) is at a constant distance (A) from the material web (2) over the width of the material web (2). Device according to Claim 4, characterized in that the distance (A) is in the range from 2 to 12 mm. Device according to one of claims 1 to 5, characterized in that the strip (15) has slots (23, 24) which start from the edge (25) opposite the edge (17) and optionally end in holes (26, 27) whose diameter is larger than the width of the slots (23, 24). Apparatus according to claim 6, characterized in that the strip (15) is composed of at least two layers of material (21, 22), each layer of material (21, 22) having slots (23, 24) and displacing the slots (23, 24) are arranged to each other. Apparatus according to claim 7, characterized in that one of the two layers of material (21) on the housing (7), which is heated at this point, is at least partially flat and has good thermal conductivity, which in particular corresponds at least to that of copper. Device according to one of claims 6 to 8, characterized in that the strip (15) has elongated holes (20) through which bolts (18) attached to the front (9) of the housing (7) are guided. Device according to one of claims 7 to 9, characterized in that the material layers (21, 22) are connected to one another at predetermined connection points (28), with at least one slot (23, 24) of each material layer (2) in the transverse direction between two connection points (28). 21, 22) is arranged. Device according to one of claims 1 to 10, characterized in that the strip (15) is bent in the region of the edge (17) in the direction of the running material web (2). Device according to one of claims 1 to 10, characterized in that the bar (15 ') in the area of the edge (17') is angled in the direction of the incoming material web by an angle (α) in the range of 30 ° to 70 °. Device according to one of claims 1 to 12, characterized in that a second strip (31) projecting in the direction of the material web (2) over the treatment side (8) is arranged on the rear side (10) of the housing, the material web (2 ) facing edge is adjustable with its curvature. Device according to one of claims 1 to 13, characterized in that the housing (7) has an at least partially bevelled back (10) on which a sealing strip (29) is arranged. Apparatus according to claim 14, characterized in that the sealing strip (29) is formed from a little abrasion-resistant plastic. Device according to claim 14 or 15, characterized in that the sealing strip (29) is connected to the housing (7) via a quick-change connection (30). Process for moistening a passing material web with the aid of steam, in which at least one steam jet is directed against the material web, characterized in that before the steam is applied, the air layer adhering to the material web is at least partially swirled or peeled off. A method according to claim 17, characterized in that the material web is guided as a boundary of a gap in front of the steam jet, the thickness of which is adjustable. A method according to claim 18, characterized in that the thickness of the gap is adjustable in the range from 2 to 12 mm. A method according to claim 18 or 19, characterized in that the gap is adjusted so that it follows the curvature of the material web. Method according to one of claims 18 to 20, characterized in that the gap is adjusted to a constant thickness transverse to the direction of travel of the material web. Method according to one of claims 17 to 21, characterized in that the swirling or peeling of the air layer takes place at the beginning or immediately before the gap, which is acted upon by a vapor pressure against the direction of travel of the material web.

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