Patent Application
20100314065
The present invention relates to a shoe press belt (hereinafter also referred to as “belt”) used for improving the water squeezing capability from a wet paper web and a felt in the press part of a papermaking machine or a similar machine, and more particularly to the groove configuration provided in the felt-side surface of the shoe press belt.
In papermaking, the question of how to increase the dewatering amount from the wet paper web in the press part in order to improve productivity is an important issue. The means adopted for increasing the dewatering amount of the press part include: raising the pressure applied by the press roll, increasing the hardness of the press roll, and other methods; among these, the method of improving the dewatering effect by interposing a shoe press belt to extend the time during which pressure is applied between the roll and the felt during pressing has become widespread in recent years.
Recently, the number of shoe press belts has also increased, in which a plurality of grooves is provided in the felt-side surface for efficiently draining the squeezed water. For example, in the shoe press belt in
Most grooves in the prior art have a rectangular shape for reasons of productivity, cost and because they can be easily manufactured; however, Patent documents 2 and 3 propose grooves with a curved groove bottom part.
Furthermore, in
With this type of discontinuous grooves, the highest pressure in the water inside the grooves occurs when the grooves have completely entered the long nip press shoe; therefore, when, thereafter, the grooves leave the press shoe, water is ejected from the grooves and the pressure subsides rapidly. Consequently, it is considered that a shoe press belt having this type of groove configuration improves the water squeezing capability in papermaking machines operating at a relatively low speed of 300 to 800 m/min.
Patent document 1: Japanese Utility Model Application No. S57-147931 (JP, U, 59-54598) microfilm
Patent document 2: JP, Y, 3104830
Patent document 3: JP, A, 2001-98484
Patent document 4: WO 2005/049917A
Nevertheless, with the shoe press belt according to Patent document 4, cracks tend to occur at the corner parts of the groove end parts when the belt is used because both end parts of the discontinuous grooves in the running direction (machine direction) are in the shape of a rectangle. The object of the present invention, which has been made in view of the above problem, is to provide a shoe press belt for papermaking having good wet paper web dewatering capability and wherein damage (cracks and wear) of the groove end parts does not occur easily.
The present inventors have solved the above-mentioned problem and have arrived at the present invention by making the groove configuration of the water drain grooves into discontinuous grooves and by forming at least one end part in the same groove in the shape of a semicircular arc.
The present invention basically relates to a shoe press belt for papermaking wherein, in a discontinuous groove configuration of water drain grooves, the shape of an end part in the running direction (machine direction) is designed; the present invention is based on the following technology.
(1) Shoe press belt for papermaking which is placed between a press roll and a shoe, which carries a felt for receiving water squeezed from a wet paper web, and which is pressed towards the press roll at high pressure; wherein the water drain grooves provided in the felt-side surface are discontinuous grooves, and wherein at least one end part of the discontinuous grooves in the running direction (machine direction) is in the shape of a semicircular arc.
(2) A shoe press belt for papermaking according to (1); wherein, in the same discontinuous groove, the groove depth is substantially uniform.
(3) A shoe press belt for papermaking according to (1) or (2); wherein the groove bottom of the discontinuous groove is in the shape of a semicircular arc.
(4) A shoe press belt for papermaking according to any one of (1) to (3); wherein the groove length of the discontinuous grooves in the running direction (machine direction) is shorter than the press shoe width (the length of the shoe in the machine direction).
(5) A shoe press belt for papermaking according to any one of (1) to (3); wherein the groove length of the discontinuous grooves in the running direction (machine direction) is identical to the press shoe width or greater to twice its size or shorter.
According to the present invention, by configuring the water drain grooves as discontinuous grooves, water can be forcibly expelled due to the pressing effect at the exit of the long nip press shoe; therefore, even when papermaking machines are operated at relatively low speeds, normal dewatering at the press is possible, and the wet paper web dewatering capability improves. Moreover, since at least one machine direction end part in a discontinuous groove is in the shape of a semicircular arc, it is possible to provide a shoe press belt for papermaking wherein damage (cracks and wear) of said discontinuous groove end part does not occur easily.
Embodiments of the present invention will be described with reference to the drawings.
In the present invention, a rotating drill is used for forming the water drain grooves in the felt-side surface of a belt; therefore, the machine direction end parts in the discontinuous grooves can be machined in the groove shape of a semicircular arc.
Firstly, a drill 30 in
Next, the front end (main chip 42) of a helical groove part 41 of a drill 40 in
The method for forming the water drain grooves according to the present invention into discontinuous grooves will be summarized. The required number of drills used in the present invention is mounted in a groove forming device (not shown in the drawings); the front end of the drill is brought into contact with the felt-side surface (external peripheral surface) of a belt into which a groove is to be cut and a groove is cut to the required groove depth. At this time, a circular shape is cut; therefore, one end part of the discontinuous groove to be cut can be formed into a semicircular shape. Next, cutting is performed to the prescribed groove length in the machine direction (MD) by displacing the belt in the machine direction (MD) while the drill is maintained in a fixed position. Then, once the displacement of the belt has been stopped and the front end of the drill is drawn back to a position that is removed from the belt surface, one discontinuous groove is completed. In this case, the other end part of the discontinuous groove is also cut into the shape of a semicircular arc.
Subsequently, after the belt has been displaced by the length of the land part (the portion in which grooves are not cut) in the machine direction (MD), the groove cutting described above is repeated. By thus repeating the same process, the entire peripheral length of the belt is cut. By mounting the required number of drills in a multi-array in the cross-machine direction of the belt, a plurality of discontinuous grooves can be formed in the width direction (cross-machine direction) of the belt by one cutting operation.
Further, discontinuous grooves are grooves which have, in the machine direction (MD), a land part in which grooves are not formed, a groove bottom part in which grooves are formed, a boundary part from the land part to the groove bottom part, and a boundary part from the groove bottom part to the land part.
A first embodiment of the groove configuration according to the present invention is shown in
Furthermore, in a belt 60 shown in
Conversely, it is also possible to form the front end part in the machine direction (MD) at right angles and the rear end part in the shape of a semicircular arc. These shapes may also be formed at random.
The question of whether to form both end parts in the shape of a semicircular arc or to form only one end part in the shape of a semicircular arc may be suitably decided in view of the wet paper web dewatering capability of the shoe press belt, the cracks and wear occurring and the degree thereof.
Moreover, in
A second embodiment of the groove configuration according to the present invention is shown in
Grooves with a discontinuous groove shape 71 as in
A third embodiment of the groove configuration according to the present invention is shown in
Hereinafter, a fourth embodiment of the groove configuration according to the present invention will be described. The fourth embodiment according to the present invention is a discontinuous groove configuration wherein the groove length in the running direction (machine direction) of the discontinuous grooves is shorter than the width of the press shoe.
It is preferred that the machine direction (MD) groove length of the discontinuous grooves according to the present invention is shorter than the width of the press shoe (the machine direction length of the shoe), as mentioned above, because the highest pressure in the water accumulated in the closed grooves occurs when the grooves have completely entered the long nip press shoe. Shoe presses used in the press part of a papermaking machine have press shoes with many different widths; however, generally speaking, widths in the range from 50 to 400 mm are common; therefore, the machine direction (MD) groove length of the discontinuous grooves according to the present invention can be set in the range from 40 to 390 mm which is shorter than the width of the press shoe (the machine direction length of the shoe).
Hereinafter, a fifth embodiment of the groove configuration according to the present invention will be described. In the fifth embodiment according to the present invention, the groove length in the running direction (machine direction) of the discontinuous grooves is identical to the press shoe width or greater to twice its size or shorter.
The groove length which is identical to the press shoe width or greater to twice its size or shorter can be set in the range from 50 to 800 mm.
When a papermaking machine is operated at a medium operating speed of 800 to 1000 m/min, the time it takes for the discontinuous grooves of a belt to pass a long nip press shoe is shorter than the time it takes at a low operating speed. In this case, when discontinuous grooves with a machine direction (MD) length identical to the press shoe width or greater to twice its width or shorter are used, the grooves do not form a groove space that is completely closed in the long nip press shoe; however, due to the dilatancy (Reynolds Phenomenon) occurring as a result of the viscosity effect of the water, a certain degree of high pressure occurs in the accumulated water; therefore, it is possible to maintain the dewatering capability of the wet paper web to a certain degree.
According to the present invention, the groove dimensions are adjusted in the ranges of 0.5 to 2 mm groove width, 0.5 to 2 mm groove depth, and 1 to 5 mm space of the land part between adjacent water drain grooves. Damage to the land parts and broken edges can be avoided by chamfering the corner parts of the land part where no grooves are formed.
According to the present invention, the groove arrays may be arranged uniformly in parallel rows as in
Shoe press belts according to the present invention were specifically made for Examples 1 to 9 and Comparative Examples 1 and 2 by the processes described hereinafter.
Process 1: an endless substrate was hanged over 2 rolls and stretched at a prescribed tension.
Process 2: a resin layer (polyurethane layer) was formed on the shoe side of the substrate by applying liquid polyurethane from above the substrate and by curing.
Process 3: after inversing the sides of the substrate, a resin layer (polyurethane layer) was then formed on the felt side of the substrate by applying liquid polyurethane from above the substrate and by curing, whereupon a shoe press belt having a substrate with resin layers on the front and the rear was obtained.
Process 4: a plurality of drills was provided in the groove forming device, the front end of the drill was brought into contact with the felt-side surface of the unmoving shoe press belt, and prescribed discontinuous grooves were formed in the felt-side surface.
Shoe press belts with continuous grooves according to the prior art were specifically made for Comparative Example 3 by the processes described hereinafter.
Process 1 to 3: identical to the processes described above.
Process 4: a plurality of chip saws was provided in the groove forming device, the front end of the chip saw blade was brought into contact with the felt-side surface of the shoe press belt which was displaced in the machine direction (MD), and prescribed continuous grooves were formed in the felt-side surface.
The groove shapes were adjusted in the following ranges.
(1) Groove width: uniformly 1.2 mm
(2) Groove depth: so as to reach 1.5 mm in the deep part of the groove
(3) The space of the land part between adjacent water drain grooves in the cross-machine direction (CMD): uniformly 2.0 mm
(4) The space of the land part between adjacent water drain grooves in the machine direction (MD): uniformly 5.0 mm
(5) Machine direction (MD) length of the discontinuous grooves: the width (shoe length in the machine direction) of a press shoe PS in a test device shown in
Shapes of discontinuous grooves formed are shown in Table 1.
Performance was evaluated by conducting the tests described below with the shoe press belts that were manufactured, and an overall evaluation was made by establishing a ranking.
The device shown in
The frequency until cracks occur was:
Evaluation score A: 300,000 times or more,
Evaluation score B: in the range of 200,000 to 300,000 times,
Evaluation score C: in the range of 100,000 to 200,000 times,
Evaluation score D: 100,000 times or less.
The wet paper web water squeezing test was performed by using the device shown in
The wet paper web moisture content was:
Evaluation score A: 45% or less,
Evaluation score B: in the range of 45% to 49%,
Evaluation score C: in the range of 49% to 53%,
Evaluation score D: 53% or more.
Regarding the test results, the overall evaluation was conducted based on the respective evaluation scores of the above tests, and the ranking was attributed as follows:
Regarding the shoe press belts relating to Examples 1 to 9 and Comparative Examples 1 to 3, crack tests and water squeezing tests were conducted and the performance was evaluated. The results are shown in
According to the results in Table 2, good evaluation scores were obtained in both evaluation tests with the groove shapes of Example 3 and 7, which were the groove shapes with the best balance of properties.
Moreover, in Example 8, in which the machine direction (MD) length of the discontinuous grooves was identical to the press shoe width, even though the evaluation of the water squeezing test was poorer than in corresponding Example 1, the ranking compared favorably. Furthermore, in Example 9, in which the machine direction (MD) length of the discontinuous grooves is greater than the press shoe width, the evaluation of the water squeezing test was lower than in Example 8; however, the ranking was better than in Comparative Example 3, in which the belt had a continuous groove shape.
According to the present invention, it is possible to make a shoe press belt having good water draining capacity in which the occurrence of cracks during use is reduced, and which is therefore extremely useful as shoe press belt used for improving the dewatering capability from a wet paper web and a felt in the press part of a papermaking machine or a similar machine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-300409 | Nov 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP08/71029 | 11/19/2008 | WO | 00 | 5/20/2010 |
