Application nozzle, and method

Abstract

The invention relates to an application nozzle for applying a coating medium onto a running surface, in particular onto a running surface in a machine for producing or processing a fibre web, wherein: the application nozzle comprises a fluid head and a blowing head; the fluid head is designed to produce a film of coating medium and the blowing head is designed to produce a linear jet of gaseous medium; the jet of gaseous medium impinges on the film of coating medium at a line of impingement, forming a spray curtain; the fluid head and the blowing head are mechanically decoupled such that the fluid head and the blowing head can be independently longitudinally extended.

Description

[0001] Application nozzle and process.

[0002] The invention relates to an application nozzle for applying a liquid or pasty coating medium to a moving surface, in particular to a moving surface, especially in a machine for the production or processing of a fibrous web, and to a corresponding application method.

[0003] Numerous coating processes are known for applying coating media to paper or cardboard webs. Film presses are frequently used, particularly for applying starch. In this process, a film of the coating medium is applied to a transfer roller and then transferred to the fiber web in a transfer nip.

[0004] The coating medium is often applied in excess to the transfer roller and then metered to the desired application quantity using suitable doctor blade metering systems. Such doctor blade metering systems are described, for example, in German patent DE102004029565 A1.

[0005] A well-known alternative to these doctor blade metering systems is spray application. For example, EP3332955 B1 describes application systems in which the coating medium is sprayed onto the application rollers via a series of spray nozzles. The direct metering of the sprayed coating medium eliminates the need for contacting doctor blades. However, a disadvantage of the EP3332955 method is that it requires a large number of spray nozzles, which are also prone to becoming dirty during operation.

[0006] As an improvement, the applicant presented an alternative spray application method in patent specification DE 10 2022 105 518 B4, which eliminates the need for a multitude of individual nozzles. In this method, a spray mist or spray curtain is generated by a linear air jet spanning the width of the web, which strikes a film of coating medium. The object of the present invention is to further develop this machine-wide spray application. In particular, it is an object of the invention to ensure a consistently uniform spray application, even under varying conditions. Furthermore, it is an object of the invention to further improve the application of starch.

[0007] The problem is solved according to the invention by an embodiment according to the independent claims. Further advantageous embodiments of the present invention are found in the dependent claims.

[0008] A coating nozzle is proposed for applying a coating medium to a moving surface, in particular to a moving surface in a machine for producing or processing a fibrous web, wherein the coating nozzle comprises a fluid head and a blow head, wherein the fluid head is configured to produce a film of coating medium and the blow head is configured to produce a linear jet of gaseous medium, wherein the jet of gaseous medium impacts the film of coating medium at an impact line, forming a spray curtain.

[0009] According to the invention, the fluid head and the blow head are mechanically decoupled in such a way that independent longitudinal expansion of the fluid head and the blow head is possible.

[0010] In principle, a wide variety of gaseous media can be used. For certain reactive coating media, the use of inert gases can also be advantageous. However, in the most important application, namely starch application, the gaseous medium will be air. For ease of reading, the term "air jet" will therefore be used throughout this application when referring to a jet of gaseous medium. Other media are always included in this definition.

[0011] In modern coating systems, it is crucial that the coating medium is applied with high accuracy. This requires taking into account effects such as the thermal expansion of the application nozzle. This is particularly relevant for starch coating, as starch solutions are typically applied at high temperatures in the range of 50°C–60°C or higher.

[0012] It is known from the prior art – for example, DE102022121756 A1 or DE202020107431 U1 – to selectively temperature nozzles for starch application, for example by incorporating heating channels. However, this leads to more complex nozzles, is more expensive to operate, and the efficiency in compensating for thermal expansion is unclear.

[0013] In contrast, with application nozzles as described in DE 10 2022 105 518 B4, a uniform application can be achieved very efficiently and cost-effectively, even with hot coating media. The inventors recognized that while the fluid head and the blow head must supply their respective media to the impact line in a defined manner, these two heads are relatively independent units up to this point. In particular, it is possible to mechanically decouple the fluid head and the blow head from each other. In this case, the fluid head and the blow head can expand independently in length (i.e., in the transverse direction of the machine). A greater expansion of the fluid head—caused, for example, by the hot starch—then has no effect on the blow head. In particular, this prevents any deformation of the blow head.Both the fluid film and the air jet meet at the point of impact in a defined manner, even under fluctuating temperatures. Thermal expansion results in only a slight elongation of each nozzle head, which has no effect on the other head's ability to generate the spray curtain. In advantageous embodiments, the fluid nozzle head and the air jet head can also be thermally decoupled, preventing heat transfer from the fluid nozzle head to the air jet head during operation.

[0014] With such a design, for example, it is possible to avoid cooling the starch solution through heat transfer from the fluid head to the blow head, or to reduce the energy required to maintain the starch temperature.

[0015] In advantageous embodiments, the application nozzle may also include a sealing element, particularly made of a polymer material, and both the fluid head and the blow head are in contact with the sealing element without directly touching each other. The sealing element does not create any mechanical coupling. The blow head and / or the fluid head can move relative to the sealing element during thermal expansion and, in effect, slide along it.

[0016] The fluid head and the blow head are typically made of metal. Heat transfer occurs when the two heads come into contact. This can be prevented by incorporating a polymer sealing element positioned at a suitable location between the two heads. The sealing element can also prevent the escape of air or coating medium.

[0017] Advantageously, the fluid head may have a first holding device for connection to a support body, and the blow head may have a second holding device for connection to a support body, wherein the first holding device and the second holding device are mechanically and / or thermally decoupled from each other.

[0018] The first and / or second holding device can be designed as retaining ribs or as a linear guide. These two designs of holding devices are also advantageous in the case described here because they allow for longitudinal expansion of the blow head or fluid head and prevent deformation of the respective head.

[0019] It may be provided that the blow head and the fluid head each have their own support body to which they are attached or can be attached by means of the appropriate holding device.

[0020] Alternatively, the fluid head and the blow head can be attached to, or be attachable to, a common support body. Mechanical and thermal decoupling of the blow head and fluid head can also be achieved with a common support body. Since retaining devices are provided between each head and the support element, and these retaining devices allow for the thermal expansion of the blow head and fluid head, independent thermal expansion of the fluid head and blow head is possible despite their attachment to a common support body. This means that the two elements are considered mechanically decoupled within the meaning of this application. Thermal decoupling can also be ensured.At the usual temperatures of the coating medium (~ 60770°C), even metallic holding devices cool down sufficiently quickly, so that these holding devices are usually cooled to ambient temperature by the time they are attached to the support device.

[0021] Furthermore, in another advantageous embodiment, the air intended for the blow head flows through the support body as it is introduced to the blow head. This is advantageous because the support body is cooled by the flowing air. Additionally, the air is heated simply and cost-effectively, thereby reducing the temperature difference between the coating medium and the air – and thus also the difference in the thermal expansion of the heads.

[0022] It can therefore be provided that the blow head and / or the fluid head is connected to the support body by means of the holding device, and that a guide is also provided through which air can flow to the blow head via the support body. In particular, it can be advantageous if one or more connecting lines are provided between the guide and the blow head to direct the air from the guide to the blow head. This air is then used to generate the jet of gaseous medium. While in principle one connecting line is sufficient, several connecting lines can be advantageous to ensure a uniform air jet.

[0023] If the second holding device is designed, for example, in the form of retaining ribs, these connecting lines can conveniently be guided along some or all of these ribs.

[0024] Furthermore, a method for applying a coating medium to a moving surface, in particular to a moving surface in a machine for the production or processing of a fibrous web, is proposed, using an application nozzle according to one of the preceding claims.

[0025] The use of starch solution as a coating medium is particularly advantageous. The starch application can be done online, i.e., directly in the paper machine during web production. Alternatively, external starch application can also be used.

[0026] It is often provided that the starch solution has a temperature of more than 40°C, in particular 50°C or more, and that the gaseous medium has a temperature of less than 35°C, in particular 30°C or less.

[0027] The invention is explained below with reference to the figures. The invention is not limited to the embodiments shown here. The figures illustrate in detail:

[0028] Figure 1: Application nozzle according to one aspect of the invention

[0029] Figure 2: Application nozzle according to a further aspect of the invention

[0030] Figure 3a Application nozzle according to a further aspect of the invention Figure 3b Application nozzle according to a further aspect of the invention

[0031] Figure 1 shows an application nozzle 1 for applying a coating medium to a moving surface 4, which here is provided by the surface 4 of a transfer roller. The coating medium can, in particular, be a starch solution.

[0032] The application nozzle 1 comprises a fluid head 2 and a blow head 3. The fluid head 2 is configured to generate a film of coating medium 15, while the blow head 3 is configured to generate a linear jet of gaseous medium 6. This jet of gaseous medium, typically an air jet, impacts the film of coating medium 15 at an impact line 8, forming a spray curtain 5.

[0033] The fluid head 2 and the blow head 3 are mechanically decoupled in such a way that independent linear expansion of fluid head 2 and blow head 3 is possible.

[0034] The application nozzle 1, shown in cross-section here, typically extends across the entire width of the moving surface, such as the entire width of a paper machine. This can be 10 meters or more. Over this nozzle length, even small percentage thermal expansions add up to a noticeable overall expansion. Since the coating medium in the fluid head 2 is usually significantly hotter than the air jet 6, this nozzle will generally expand more than the blow head 3. There is a risk that the application nozzle 1 will warp, causing, for example, the impact line 8 to no longer form a precise line 8, resulting in an uneven spray curtain 5. Because the blow head 3 and fluid head 2 are mechanically decoupled from each other, both heads can expand independently, and the impact line 8 still remains a precise 8.

[0035] Figure 2 shows an application nozzle 1, which is essentially the same as the application nozzle 1 from Figure 1. The only difference is the inclusion of a sealing element 9 made of a polymer material. This sealing element 9 is positioned between the blow head 3 and the fluid head such that both the fluid head 2 and the blow head 3 are in contact with the sealing element 9 without directly touching each other. This is highlighted in the enlarged view of Figure 2. The sealing element 9 does not create any mechanical coupling. The blow head 3 and / or the fluid head 3 can move relative to the sealing element 9 as they expand and slide along it. The blow head 3 or the fluid head 2 may be provided with a holder to accommodate the sealing element 9.

[0036] Figures 3a and 3b show an application nozzle 1 according to one aspect of the invention, which is attached to a common support body 20. Figure 3a shows a section, and Figure 3b a rear view. The fluid head 2 is connected to the support body 20 by a first holding device 22, and the blowing head 3 is connected to the support body by a separate, second holding device 23. The first holding device 22 and the second holding device 23 are both mechanically and thermally decoupled from each other.

[0037] The first holding device 22 and the second holding device 23 are designed in the form of retaining ribs. As can be clearly seen in Figure 3b, the holding devices 22, 23 each comprise a number of retaining ribs, which are distributed along the length of the application nozzle 1 at suitable intervals from one another. These retaining ribs are advantageously relatively thin in the longitudinal direction L. This allows the retaining ribs to bend within certain limits in the longitudinal direction L, in order to accommodate the longitudinal expansion of the blow head 3 or fluid head 2. As indicated in Figure 3a, the ribs can be significantly thicker in a direction perpendicular to the longitudinal direction L than in the longitudinal direction L. This ensures that the longitudinal expansion of the fluid 2 and blow head 3 is not impeded. In this embodiment, the ribs of the two holding devices 22, 23 are in contact only with the respective head 2, 3, and the common support body 20.

[0038] Alternatively, one or both holding devices 22, 23 could also be designed as linear guides or similar. These two designs of the holding devices 22, 23 are also advantageous here because they allow for the longitudinal expansion of the blowing head 3 or the fluid head 2, respectively, and prevent deformation of the respective head 2, 3. Figure 3a also shows, by way of example, a guide 25 through which the air for the blowing head 3 flows through the support body 20. At suitable points—not shown in the figure—the air from the guide 25 is then directed to the blowing head 3. This is advantageous because the support body 20 is cooled by the flowing air. Furthermore, the air is heated simply and cost-effectively, thereby reducing the temperature difference between the coating medium and the air—and thus also the difference in the longitudinal expansion of the heads.Furthermore, this is also cost-effective, since instead of a separate line, the existing support structure 20 can be used - possibly with minor modifications.

[0039] Reference symbol list

[0040] 1 application nozzle

[0041] 2 Fluid head

[0042] 3 Blowhead

[0043] 4 Running surface

[0044] 5 Spray curtain

[0045] 6. Jet of gaseous medium / air jet

[0046] 8 impact line

[0047] 9 Sealing element

[0048] 15 Film made of coating medium

[0049] 20 supporting structures

[0050] 22 First holding device

[0051] 23 Second holding device

[0052] 25 Airflow

[0053] L Longitudinal direction of the application nozzle (corresponds to machine transverse direction)

Claims

Patent claims 1. Application nozzle (1) for applying a coating medium to a moving surface (4), in particular to a moving surface (4) in a machine for producing or processing a fibrous web, wherein the application nozzle (1) comprises a fluid head (2) and a blow head (3), wherein the fluid head (2) is configured to produce a film of coating medium (15) and the blow head (3) is configured to produce a linear jet of gaseous medium (6), wherein the jet of gaseous medium (6) impacts the film (15) of coating medium at an impact line (8) forming a spray curtain (5), characterized in that the fluid head (2) and the blow head (3) are mechanically decoupled in such a way that independent linear expansion of the fluid head (2) and the blow head (3) is possible.

2. Application nozzle (1 ) according to claim 1 , characterized in that the fluid head (2) and the blow head (3) are thermally decoupled, so that in particular no heat transfer from the fluid head (2) to the blow head (3) takes place during operation of the application nozzle (1 ).

3. Application nozzle (1 ) according to one of the preceding claims, characterized in that the application nozzle (1 ) further comprises a sealing element (9) in particular made of a polymer material, and both the fluid head (2) and the blow head (3) are in contact with the sealing element (9) without directly touching each other.

4. Application nozzle (1) according to one of the preceding claims, characterized in that the fluid head (2) has a first holding device (22) for connection with a support body (20), and the blowing head (3) has a second holding device (23) for connection with a support body (20), wherein the first holding device (22) and the second Holding device (23) are in particular mechanically and / or thermally decoupled from each other.

5. Application nozzle (1 ) according to claim 4, characterized in that the first holding device (22) and / or the second holding device (23) is / are designed in the form of holding ribs or as a linear guide.

6. Application nozzle (1 ) according to one of the preceding claims, characterized in that the blowing head (3) and / or the fluid head (2) is connected to the support body (20) by means of the holding device (23, 22), and that a guide (25) is also provided through which air for the blowing head (3) can flow through the support body (20).

7. Application nozzle (1 ) according to claim 6, characterized in that connecting lines are provided between the feeder (25) and the blower head (3) to direct the air from the feeder (25) to the blower head (3).

8. Method for applying a coating medium to a moving surface (4), in particular to a moving surface (4) in a machine for producing or processing a fibrous web, using an application nozzle (1 ) according to one of the preceding claims.

9. The method of claim 8, wherein the coating medium is a starch solution.

10. Method according to one of claims 8 or 9, characterized in that the starch solution has a temperature of more than 40°C, in particular 50°C or more, and wherein the gaseous medium has a temperature of less than 35°C, in particular 30°C or less.

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