WO1998053142A1

WO1998053142A1 - Return trough in a coater

Info

Publication number: WO1998053142A1
Application number: PCT/FI1998/000390
Authority: WO
Inventors: Rauno Rantanen; Markku Lummila
Original assignee: Valmet Corporation
Priority date: 1997-05-20
Filing date: 1998-05-06
Publication date: 1998-11-26
Also published as: FI972138A; DE29808894U1; AU7337498A; DE19882412T1; DE19882412B4; FI110848B; FI972138A0

Abstract

The present invention relates to a return trough (16) particulary suited for collecting excess coat or size back to the return circulation of a transfer roll coater or a doctor blade coater. The coat/size return trough (16) is supportingly connected by means of a first pivotal joint (9) to an applicator unit (5) or a support beam (6) thereof and by a second pivotal joint (10) and a pivoting arm (11) to a stationary structure (2) or the applicator unit support beam (6). The loading arm (11) is adapted to guide the front wall upper edge of the return trough (16) so as to move the trough upper edge toward the coat/size applicator roll (1) when the applicator unit (5) is moved away from the roll (1). Thus, the position of the front wall upper edge of the return trough (16) follows a force-guided trajectory in a construction having the pivoting arm (11) connected to a stationary structure (2), or alternatively, the trough front wall upper edge can be positioned by means of an air or hydraulic cylinder if the pivoting arm (11) is implemented using such a cylinder.

Description

Return trough in a coater

The present invention relates to a return trough according to the preamble of claim 1 particularly suited for collecting excess coat or size back to the return circulation of a transfer roll coater or a doctor blade coater.

In transfer roll coaters, the coat is first applied by means of an applicator to the surface of a transfer roll, wherefrom it is subsequently transferred with the help of the roll as a thin film of coat to the web being coated. Transfer roll coaters can be used for surface sizing and coating of paper or board, wherein they have shown a very good runnability. Conventionally, a transfer roll coater has a construction similar to that of a short-dwell coater in which the coat is metered from an applicator chamber that has the roll rotation sealed on the roll outgoing side by a doctor blade or rod and on the roll ingoing side by a front wall, blade or rod. As the applicator chamber must be fed with the coating mix at a volumetric flow rate larger than that required for establishing the metered amount of coat on the surface of the coat film transfer roll, the excess coat must be collected to the return circulation.

Hence, a proper collecting technique for the excess coat flowing over the front wall edge of the applicator chamber must be devised. Conventionally, the excess coat is collected back to the return circulation by means of a return trough attached to the support beam of the applicator device. Adapting the return trough into the space remaining between the applicator device support beam and the coat film transfer roll is extremely difficult, and this design task is further complicated by the need for tilting the support beam outward during coater shutdown and web break situations. To permit the outward rotational movement of the applicator device off from the surface of the coat transfer roll, the center of rotation of the applicator support beam must be located under the applicator device. Obviously, the excess coat/size return trough must also be mounted under the applicator device, whereby the outward rotation of the applicator support beam will move the trough closer to the roll . As the trough must not be allowed to touch the roll, the operating position of the trough must be designed such that the edge of the return trough wall remains spaced sufficient - ly far apart from the roll thus assuring that, e.g., the web possibly winding up about the coat transfer roll during a web break will not stick between the upper edge of the return trough front wall and the coat transfer roll. In such web break situations, the opening movement of the applicator support beam assembly must be performed rapidly, which means that the motion of the return trough shall also occur in a rapid and controlled manner. An alternative technique is to mount the trough pivotally by its front wall upper edge so that it can tilt away from the roll in the direction of the applicator device.

A disadvantage of a trough mounted in a fixed manner or pivotally by its upper edge is that the front wall upper edge of the trough in its operating position remains too far from the roll, whereby the size or coat to be returned to recirculation splashes or drips past the trough and also directly to the web from the applicator device located above the web, thus causing unnecessary broke in the produced paper. The splashes also soil the paper machine and increase the need for cleaning and servicing the machine and make its operation inconvenient.

The coat/size return trough may also be the designed into a large, fixed pan having its front wall upper edge adapted close to the applicator roll . Such a fixed pan is adapted to extend under the support beam of the applicator device and the rotation of the beam is pivoted above the trough. Though a fixed return trough permits effective collection of the excess coat or size to the return circulation, it is handicapped by a long retention time of the collected excess coat or size in the open trough. During the long retention time, the collected excess coat or size may undergo a partial drying or thickening, which causes complications in its return circulation. Due to the drying of the collected coat or size, a large-volume fixed return trough is rarely a favoured construction in spite of its high coat/size collecting efficiency. Such a large-volume trough is very costly to make, because it must be made from a corrosion-resistant material. Also the available installation space is very limited to accommodate a separate return trough mounted in a fixed manner to the coater framework, particularly in coater constructions based on small-diameter coat transfer rolls and a deflected path of the web through the coater nip.

It is an object of the present invention to provide a return trough for the recirculation of coat/size in a transfer roll coater or similar apparatus, said trough serving to provide an improved technique of collecting the excess coat or size and preventing splashing of coat or size to the surroundings and the web in the coater.

The goal of the invention is achieved by mounting the return trough by means of a first pivotal joint to the applicator apparatus, or alternatively, to the support beam of the applicator and by a second pivotal joint and an articulated link to a fixed structure or the support beam of the applicator apparatus. The loading arm of the coater is arranged to guide the upper edge of the return trough front wall so that the trough upper edge is moved toward the coat transfer roll when the applicator unit is simultaneously moved away from the transfer roll. Thus, the position of the return trough upper edge will move along a forced trajectory when the articulated arm is connected to a stationary structure or the position may be controlled by an air or hydraulic cylinder if the articulated arm comprises an actuator cylinder. Alternatively the forced movement of the trough may be imple- mented with the help of a peg-and-slot guide mechanism.

Most advantageously, the articulated arm of the second joint is connected to the stationary framework structure of the transfer roll, within an area delineated by perim- eter of the transfer roll end, whereby a forced control structure is obtained capable of bringing the upper edge of the return trough closest to the coat transfer roll in both extreme positions of the support beam movement.

More specifically, the method according to the invention is characterized by what is stated in the characterizing part of claim 1.

The invention offers significant benefits

By virtue of the invention, the coat return trough can be brought in its normal operating position close to the coat transfer roll. Thence, the trough will effectively collect the splashes of the excess coat/size return flow and the return flow is prevented from dripping onto the web or soiling the machine surroundings. The structure of the trough becomes simple, requires a small footprint and permits a compact size of the trough. The material costs of such a compact trough are smaller and the retention time in the return circulation becomes short. The collected coat or size is exposed to the ambient atmosphere for the shortest possible time, thus keeping its quality higher and preventing excessive drying of the coat or size . In the following, the invention will be examined in greater detail by making reference to the appended drawings in which

Figure 1 shows a first embodiment of an applicator device equipped with a coat return trough according to the invention driven into its operating position;

Figure 2 shows the applicator device of Fig. 1 driven into its servicing position;

Figure 3 shows a second embodiment of an applicator device equipped with a coat return trough according to the invention driven into its operating position;

Figure 4 shows the applicator device of Fig. 3 driven into its servicing position;

Figure 5 shows a third embodiment of an applicator device equipped with a coat return trough according to the invention driven into its operating position;

Figure 6 shows the applicator device of Fig. 5 driven into its servicing position;

Figure 7 shows a fourth embodiment of an applicator device equipped with a coat return trough according to the invention driven into its operating position; and

Figure 8 shows the applicator device of Fig. 7 driven into its servicing position.

Referring to Figs. 1 and 2, therein is shown an applicator unit of a transfer roll coater having the actual applicator unit 5 mounted on a tiltable beam 6. In the context of the present invention, the term tiltable beam refers to a support structure in which the beam 6 is con- nected to the applicator unit body 3 by means of a pivotal joint 7, which is offset from the center of the beam. Opposite to the applicator unit 5 is adapted a coat transfer roll 1 mounted on the coater framework 13 by means of a bearing block 2. The pivotal joint 7 of the applicator unit is adapted to the lower edge of the beam 6, and between the beam 6 and the applicator unit body 3 is connected a hydraulic cylinder 4 serving to rotate the applicator unit. The return trough 16 is adapted into the space remaining between the coat transfer roll 1 and the body 3 of the applicator unit. The return trough 16 comprises a guide lip 15 and a trough 8. The upper edge of the guide lip 15 is connected by means of a pivotal joint 9 to the support beam 6 of the appli- cator unit 5, close to the front edge 14 of the coating mix chamber of the applicator unit. To the upper edge of the trough 8 is connected by means of a pivotal joint 10 a loading arm 11, whose other end is connected to the bearing block 2 of the coat transfer roll 1. The coat return flow can be guided to the guide lip 15 of the return trough 16 by means of a guide plate 17 or a similar element, and when desired, the fixed guide lip 15 of the return trough may be replaced by a separate guide element. The return trough 16 has a length extending over the entire cross-machine width of the applicator unit 5 and the coat transfer roll 1.

Fig. 2 shows the apparatus of Fig. 1 in an exploded view. Herein, the applicator unit 5, 6 is shown rotated outward from the coat transfer roll 1. During the outward rotation of the applicator unit beam 6, the upper edge of the trough 16, which is connected to the beam 6, will be moved along with the beam outward from the transfer roll 1. In this forced-type arrangement of trough move- ment control, the upper edge of the return trough front wall that is connected to the loading arm 11 will then move under the guidance of said loading arm 11. Since the loading arm 11 is connected close to the rotational bearing point of the roll 1, it is force-guided to move close to the surface of the transfer roll 1 so that the upper edge of the return trough 16 in both extreme posi- tions of the support beam 6 of the applicator unit 5 is located closest to the coat transfer roll 1. Through this arrangement, the loading arm 11 and the pivotal joint connection of the guide lip of the trough 16 will bring the trough 16 in the vicinity of the transfer roll 1 when the applicator unit 5, 6 is actuated into its operating position. In this position, the return trough covers the space between the transfer roll and the applicator unit almost gaplessly and can effectively collect the entire return flow of excess coating and coat splashes emitted by the applicator unit and the transfer roll.

In Figs. 3 and 4, the return trough is shown adapted to operate in conjunction with a rotatable support beam. The construction of the rotatable beam of the applicator unit 5 differs from that of a tiltable beam therein that the beam 5 is pivotally mounted on bearings at its center of rotation 18. The structure of the return trough 16 is similar to that used in the above-described embodiment, and also in this case, the loading arm 11 is connected to the bearing block 2 of the transfer roll 1. As the diameter of the transfer roll 1 herein is smaller, also the length of the loading arm 11 is correspondingly shorter. In the illustrated embodiment, the loading arm 11 is comprised of a hydraulic or air cylinder. By means of the cylinder, the return trough can be brought very close to the roll 1 in the operating position of the applicator unit, and in the case of a web break with the web winding about the coat transfer roll, the return trough can be rapidly outdistanced from the roll 1. The loading arm is advantageously implemented using an air cylinder that offers a faster method for trough withdrawal movement than a hydraulic cylinder. The opening of the applicator unit 5, 6 takes place in a similar manner as in the above-described embodiment and also the trajectory of the return trough is essentially similar.

In the embodiments shown in Figs. 5 and 6, the loading arm 11 is connected to the support beam 6 of the applicator unit. Advantageously, the loading arm is an air or hydraulic cylinder adapted to guide the upper edge of the return trough 11 so that the trough upper edge can be brought close to the roll 1. An air cylinder is most suitable for actuating the position change of the return trough, because it permits simple control of the trough between its two extreme positions which may as well be the end positions of the air cylinder stroke. On the other hand, a hydraulic cylinder is well suited for keeping the trough upper edge close to the transfer roll 1 during the entire rotational movement of the applicator unit support beam 6. The cylinder 11 is most advantageously placed so that the cylinder piston rod is in its maximally extended position when the return trough 16 is in its operating position and the cylinder capacity is dimensioned to be sufficiently strong to move the trough 16 outward from the surface of the transfer roll 1 when the gap between the roll and the trough is possibly plugged. The same dimensioning rule is also advantageously used in the embodiments illustrated in Figs. 3 and 4.

In Figs. 7 and 8 is shown a construction in which the force-guiding pivotal arm and the pivotal joint of the return trough are replaced by a peg 19 and a guide slot 20, which are adapted into the position of the pivotal joint. The guide slot 20 is mounted on the applicator unit body 3. The peg 19 may be designed into the position of the pivotal joint 10 used in the above-described em- bodiments, and in fact, also connected to the same bearing block hole. The guide slot 20 is curved in a desired manner so that the upper edge of the return trough front wall is brought close to the transfer roll 1 in its operating position and is outdistanced therefrom during the rotation of the applicator unit support beam 6 so that the return trough upper edge will not touch the transfer roll .

In addition to those described above, the present invention may have alternative embodiments.

Advantageously, the loading arm 11 is connected to a point whose position is fixed with regard to the support beam 6 of the applicator unit 5 such as the framework of the transfer roll 1 or the body of the applicator unit 5, 6. Most advantageously, one end of the loading arm 11 is connected close to the center axis of the transfer roll 1 and the other end of the arm is connected to the upper edge of the return trough front wall. Then, the trajectory of the return trough front edge will be as described above, or alternatively, if the pivotal connec- tion point of the loading arm is located exactly at the center axis of the roll 1, the return trough upper edge will remain, during the entire movement of the support beam 5 of the applicator unit, exactly at a distance from the surface of the roll 1 determined by the length of the support arm. If the support arm is connected to the applicator unit body 3, the length and pivotal points of the arm must be dimensioned so that the return trough upper edge stays close to the transfer roll surface in the operating position of the applicator unit and that the trough upper edge cannot touch the roll surface during the rotation of the applicator unit support beam 5. While other pivotal points are also possible, the end of the loading arm 11 which is pivotally connected to the return trough 16 is most advantageously connected as close as possible to the upper edge of the return trough 16. Herein, it is essential that the return trough is supported by means of at least two pivotal joints displaced at a distance from each other and that at least one of the pivotal joints is connected to the loading arm which guides the movement of the return trough upper edge. The loading arm may have a construction which is adjustable, and because of the substantially large cross- machine width of the return trough, its both ends must be provided with said pivotal joints and a loading arm. When required, the return trough may be connected via an arm to the rotatable support beam if the rear edge of the return trough cannot be directly connected via pivotal joint to the support beam and the return trough upper edge is equipped with a flexible lip.

In addition to those mentioned above, the return trough according to the invention is suitable for use in other types of coaters, too. Most applicable herein are blade coaters. The invention is also usable in the collection of excess coat doctored away by doctor blades.

Claims

Claims :

1. A return trough (16) for use in a coat/size applicator comprising

- at least one coat/size applicator roll (1) mounted on bearing blocks (2),

- at least one applicator device, adapted in conjunction with said applicator roll and including at least one applicator unit (5) and a support beam (6) having said applicator unit (5) connected thereto and being rotatably mounted on said body (3) , and

- a coat/size return trough (16) which is adapted into the space remaining between said applicator unit (5, 6) and said coat/size applicator roll and serves to collect the return flow of excess coat or size from said applicator unit, said return trough (16) comprising an upward-open trough (8) with its front wall upper edge located close to the roll (1) and its rear edge located close to said applicator unit,

c h a r a c t e r i z e d in that

- said return trough (16) is supportingly con- nected by at least one end by means of a first pivotal joint (9) to said support beam (6) of said applicator unit (5) and to the coat return trough is connected a guiding element (11 or 19, 20) serving to force-guide the upper edge of the return trough front wall so as to move the trough upper edge toward the coat/size applicator roll (1) when the applicator unit is moved toward the roll (1) and further serving to prevent the upper edge of the return trough (16) from touching the applicator roll during the withdrawal of the applicator unit off from the applicator roll .

2. An assembly as defined in claim 1, c h a r a c t e r i z e d in that said guiding element is a loading arm (11) which is connected by its one pivotal point by means of a second pivotal joint (10) to said coat/size return trough and by its other pivotal point to a stationary point.

3. An assembly as defined in claim 2, c h a r a c - t e r i z e d in that said second end of said loading arm (11) is connected to a structure which is stationary with respect to the support beam (6) in such a manner that makes the loading arm (11) to guide the upper edge of the return trough (16) close to the surface of the applicator roll (1) when the applicator unit (5, 6) is in its operating position.

4. An assembly as defined in claim 3, c h a r a c t e r i z e d in that said second end of said loading arm (11) is connected to a point located outside the area defined by the perimeter of said applicator roll (1) .

5. An assembly as defined in claim 4, c h a r a c t e r i z e d in that said second end of said loading arm is connected by means of a pivotal joint (12) to the bearing block (2) of said applicator roll (1) .

6. An assembly as defined in claim 5, c h a r a c t e r i z e d in that said second end of said loading arm is connected by means of a pivotal joint (12) at the center axis of said applicator roll (1) .

7. An assembly as defined in claim 1, c h a r a c t e r i z e d in that said guiding element is a peg-and- slot combination in which one element (19) is mounted on the coat return trough (16) and the other element to a stationary structure (3) .

8. An assembly as defined in any of foregoing claims, c h a r a c t e r i z e d in that said first pivotal joint (9) is located at the upper edge of the rear wall of said return trough (16)^'.

9. An assembly as defined in claim 7, c h a r a c t e r i z e d in that the rear wall of said coat return trough (16) is formed by a guide lip (15) extending higher than the upper edge of the return trough front wall in the vertical direction.

10. An assembly as defined in any of foregoing claims, c h a r a c t e r i z e d in that the upper edge of said return trough (16) is equipped with a flexible lip.

11. An assembly as defined in claim 1, c h a r a c t e r i z e d in that one end of the loading arm (11) is connected to the applicator unit support beam (6) and that said loading arm (11) is an air or hydraulic cylinder adapted to bring the front wall upper edge of the coat return trough (16) close to the coat/size applicator roll (1) when the applicator unit (5, 6) is moved into its operating position.

12. An assembly as defined in any of claims 1 - 10, c h a r a c t e r i z e d in that said loading arm (11) is comprised of a hydraulic or pneumatic cylinder.

13. An assembly as defined in claim 12, c h a r a c t e r i z e d in that said cylinder (11) is placed so that the cylinder piston rod is in its maximally extended position when the return trough (16) is in its operating position and the cylinder capacity is dimensioned to be sufficient strong to move the trough (16) outward from the surface of the coat/size applicator roll g) when the gap between the roll and the trough is possibly plugged.