Abstract
The invention relates to a press belt for a shoe press. A press belt (5) is an endless loop made of elastomeric material and its outer surface (11) is provided with several grooves (13) to remove water. On the outer surface (11) of the press belt, there is at least one section where the depths (GD) of adjacent drain grooves, from the outer surface, change constantly. The invention also relates to an arrangement in a long nip and to a method of manufacturing a press belt.
Claims
1. An arrangement in a long nip of a press section, comprising: a press belt (5) and at least one backup roll (2), wherein an outer surface (11) of the press belt (5) is curved in the crosswise direction (CMD) in such a way that it is thicker in the middle than on the edges, whereby the press belt (5) is positively cambered (M+); wherein the backup roll (2) has a larger outer diameter in the longitudinal middle point than in its end sections, whereby the backup roll (2) is also positively cambered (M+); wherein several adjacent drain grooves (13) are arranged on the outer surface (11) of the press belt (5); and wherein in the crosswise direction (CMD) of the press belt (5), there is at least one section where the depths (GD) of adjacent drain grooves (13), from the outer surface (11), change constantly, decreasing towards the outer edge of the press belt (5,) and where bottoms (19) of the drain grooves (13) are at an equal distance from an inner surface (10) of the press belt (5).
2. A method of manufacturing a press belt by: shaping a frame (16) for the press belt (5) by casting at least one elastomeric material against a mould surface of a rotating mould; providing the frame (16) with several support yarns (17) and covering them with elastomeric material during the casting; curing the frame (16); providing an outer surface (11) of the frame (16) with several drain grooves (13); and finishing the outer surface (11) of the press belt (5) by grinding it after grooving; cambering the outer surface (11) of the press belt (5) by grinding it after grooving, whereby the depths (GD) of the drain grooves (13) on the outer surface (11) of the press belt (5) change constantly in at least one crosswise section (CMD) of the press belt (5), decreasing towards the outer edge of the press belt (5); and whereby bottoms (19) of the drain grooves (13) are at an equal distance from an inner surface (10) of the press belt (5).
Description
BRIEF DESCRIPTION OF THE FIGURES
(1) Some embodiments of the invention are described in greater detail in the accompanying drawings, in which
(2) FIG. 1 is a schematic representation of the principle of a shoe press;
(3) FIG. 2 is a schematic and perspective view of a press belt shaped like a closed loop;
(4) FIG. 3 is a schematic view of the cross-section of a press belt examined in the longitudinal, or machine direction;
(5) FIG. 4 is a schematic view of the cross-section of another press belt examined in the machine direction;
(6) FIG. 5a is a schematic and a highly simplified view of a positively cambered backup roll, and FIG. 5b shows a press belt whose surface facing the web has also been positively cambered;
(7) FIG. 6 is a schematic, machine-direction view of the profile of a partly cambered press belt, where the press belt comprises outermost curved edge sections and a planar middle section;
(8) FIG. 7a is a schematic, machine-direction view of the profile of a grooved press belt blank, and FIG. 7b illustrates a situation after cambering;
(9) FIG. 8a is a schematic, machine-direction view of the profile of a cambered, ungrooved press belt blank, and FIG. 8b illustrates a situation after grooving;
(10) FIG. 9 is a schematic, machine-direction view of a cambered and grooved press belt, which comprises longitudinal mounting sections on the outermost edges;
(11) FIG. 10a is a schematic, machine-direction view of the press belt according to FIG. 9 before a long nip and pressing, FIG. 10b illustrates the situation at the beginning of the long nip, and FIG. 10c illustrates the situation in the most heavily loaded area of the long nip; and
(12) FIG. 11 is a schematic diagram of features relating to the manufacture of a press belt.
(13) For reasons of clarity, some embodiments of the invention are illustrated in the Figures in a simplified form. Similar parts are indicated in the figures by the same reference numbers.
DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION
(14) FIG. 1 shows a highly simplified view of a shoe press 1, which is a drying device typically used in drying a fibre web. The shoe press 1 comprises a press roll or backup roll 2 and a press shoe 3 with a pressing zone 4 between them, through which zone a press belt 5 is arranged to run in the machine direction MD, at least one paper fabric 6, 7 and a fibre web 8 to be dried. The press shoe 3 and backup roll 2 are pressed against each other by force F, whereby the press belt 5, paper machine fabric 6, 7 and fibre web 8 running between them are compressed. The press shoe 3 has a curved sliding surface facing the press roll 2, whereby an elongated contact area, i.e. a so-called long nip, is formed between the press shoe 3 and the backup roll 2. The press belt 5 may be arranged to run around the press shoe 3, supported by a suitable support member 9. An inner surface 10 of the press belt 5 slides against the sliding surface of the press shoe 3, and an outer surface 11 of the belt faces the fibre web 8. The fibre web 8 is guided to the pressing zone 4, typically supported by one or more paper machine fabrics, such as a press felt 7 or wire 6. The paper machine fabric 6, 7 is guided by guide rolls 12 or the like. In the solution of FIG. 1, the upper paper machine fabric may be a press felt 7 and the lower fabric may be a wire 6.
(15) The outer surface 11 of the press belt 5 may comprise several grooves 13 for removal of water. When the fibre web 8 runs through the relatively long pressing zone 4 formed by the press roll 2 and the press shoe 3, water will be squeezed out. At least some water may run through the press felt 7 into drain grooves 13 made on the outer surface 11 of the press belt 5 and providing additional space for the draining water. The water volume that the pressed press felt 7 cannot receive may then drip into the water space provided by the press belt 5. Should the press belt 5 not provide any additional water space, the water may move towards the beginning of the pressing zone 4 and create running problems. Drain grooves 13 provided on the outer surface 11 of the press belt 5 prevent flooding and control water removal. One or more water collecting devices 14 or the like may be arranged in connection with the press felt 7 circulation path, whereby water can be removed from the press felt 7 before the felt returns to pressing zone 4.
(16) It should be noted that the press belt according to the invention may also be used in other types of shoe presses. The idea of an embodiment is that the shoe press comprises a rotating press or backup roll against which a press shoe provided with a curved surface is pressed, which forms an elongated nip. Guided by guide rolls or the like, a separate press belt may be run to the space between the press roll and the press shoe. Further, a fibre web, supported by a paper machine fabric, is run to the pressing zone. Furthermore, the separate press belt may be arranged on top of the press roll and the press shoe may be pressed towards the press belt forming the outer surface of the press roll. A common feature of the above embodiments is that the press belt is always a separately manufactured component shaped like an endless loop, which is or can be arranged in a shoe press in such a way that it runs through a long nip between at least one roll and a press shoe.
(17) FIG. 2 shows a press belt 5 shaped like an endless loop, comprising an inner surface 10 and an outer surface 11. The press belt 5 is arranged in a shoe press 1 in such a way that its outer surface (11) faces a fibre web 8. The outer surface 11 comprises several parallel drain grooves 13. The drain grooves 13 may be endless and they may be arranged substantially in the machine direction MD. Between adjacent drain grooves 13, there is a longitudinal neck 15. The drain grooves 13 may go around the press belt 5 or they may be continuous spiral grooves.
(18) FIG. 3 illustrates a cross-section of a press belt 5, seen in the machine direction MD. The press belt 5 comprises an elastic frame 16 having sufficient elasticity and ability to return to its original shape after pressing. The frame 16 may be mainly of elastomeric material, such as rubber fit for purpose, or it may be made of a polymer, such as polyurethane. Further, the press belt 5 may have a support structure potentially comprising several support yarns 17 arranged in one, two or more layers inside the frame 16. The yarn layers on top of each other may be separate or they may be tied together. An inner surface 10 of the press belt 5 may be substantially smooth. An outer surface 11 of the press belt 5, however, comprises several parallel drain grooves 13 with necks 15 between them. The drain grooves 13 are typically arranged in the machine direction MD.
(19) The cross-section of the drain grooves 13 may be of a rectangular shape as illustrated in the figure, but they may also be substantially U-shaped or of the shape of a cut triangle. The groove 13 has side surfaces 18 and a bottom 19. The section between the bottom 19 and the sides 18 may be rounded or bevelled to improve durability. Further, the greatest depth GD of each groove 13 is determined from the outer surface 11 to the deepest point of the bottom 19. The width GW of the grooves 13 in the figure is constant, but the groove depth GD, on the other hand, changes constantly. The bottoms 19 of the grooves are in a straight line 20, which clearly illustrates the continuously changing depths in the section examined. The grooves on the outer surface 11 may be made with a chipping tool, whose depth position will be set, for the duration of the machining, as required by each individual groove. In FIG. 3, the outer surface 11 of the press belt 5 is planar.
(20) FIG. 4 shows a press belt 5 with a cambered outer surface 11, whereby the surface is curved. The curvature is illustrated, in an exaggerated manner, with a profile line 21. The outer surface 11 comprises drain grooves 13, whose bottoms 19 are at an equal distance from an inner surface 10. A broken line in the figure illustrates a plane 20 passing through the bottoms 19. The depth GD of the grooves 13 changes constantly, and so does the width LW of necks 15. Further, as the cross-sectional shape of the grooves 13 is that of a triangle with a cut corner and comprises bevelled side surfaces 18, the cross-sectional shape of the grooves 13 changes constantly.
(21) FIGS. 5a to 8b show a highly simplified view of a press belt 5 seen from the machine direction. The contour of the press belt is exaggerated and, for the sake of clarity, cross-sectional lines and drain grooves have been left out. However, a line 20 passing through the bottoms of the drain grooves is shown to illustrate the grooves and their features.
(22) FIG. 5a shows a simplified and an exaggeratedly reduced view of a backup roll 2 provided with positive cambering M+. FIG. 5b illustrates a press belt 5 whose outer surface 11 facing the web is also positively cambered M+. The arrangement thus comprises positively cambered M+ components 2 and 5 facing each other. FIG. 5b also illustrates a line 20 passing through the bottoms of the drain grooves, which line may be straight or a curved line illustrated in the figure.
(23) A press belt 5 of FIG. 6 comprises curved edge sections B in the pressing section P and a middle section A between them. The edge sections B are positively cambered M+ and the middle section has a planar surface T. The bottoms of all the grooves are in line 20. On account of the cambering of the edge sections B, the groove depth changes constantly in accordance with the curvature of the cambering.
(24) FIG. 7a shows a profile of a grooved press belt blank 5a, and FIG. 7b shows a finished press belt 5 when an outer surface 11 has been provided with positive cambering M+. In this embodiment, grooves of a standard depth are made first, and the outer surface will then be curved.
(25) FIG. 8a shows a profile of a cambered, ungrooved press belt blank 5a, and FIG. 8b shows a finished press belt after grooving. In this embodiment, positive cambering M+ is performed first, and grooves of varying depths will then be made.
(26) FIG. 9 shows a cambered and grooved press belt 5 having longitudinal mounting sections R on the outermost edges outside the press section P. The middle section A may comprise a planar section T, and the edge sections B may be positively cambered M+.
(27) FIGS. 10a-10c show a simplified arrangement in a long nip, without a fibre web and press felt between a press belt 5 and a backup roll 2. In addition, only part of the backup roll 2 is shown in the figure. FIG. 10a shows the press belt 5 according to FIG. 9 before it is compressed in the long nip. FIG. 10b illustrates a situation at the beginning of the long nip, whereas FIG. 10c illustrates a situation in the most heavily loaded area of the long nip. As shown in FIGS. 10a and 10b, before the press belt 5 is compressed, the drain grooves 13 are clearly deeper and larger in the middle section of the press belt 5 than on the edges. In FIG. 10c, on the other hand, the press belt structure is compressed, particularly in the middle section, on account of a positively cambered M+ backup roll 2, which puts most pressure on the middle section. As in the starting situation the grooves in the middle section of the press belt 5 have the largest free cross-sectional area, they are sufficiently large for water removal even after the structure has been compressed. The differences in the depths and water volumes of the grooves on the outer surface of the press belt will level out during the pressing on account of the cambered backup roll.
(28) FIG. 11 shows a schematic diagram of features relating to the manufacture of a press belt and some alternative manufacturing methods. These details relating to the manufacture have been described earlier in this application, but they can be summarised by stating that a method of manufacturing a press belt comprises the following features: shaping a frame for a press belt by casting at least one elastomeric material against a mould surface of a rotating mould; providing the frame with several support yarns and covering them with elastomeric material during the casting; curing the frame; providing the outer surface of the frame with several drain grooves; finishing the outer surface of the press belt by grinding it after grooving; and cambering the outer surface of the press belt by grinding it after grooving, whereby the depths of the drain grooves on the outer surface of the press belt vary constantly in at least one crosswise section of the press belt.
(29) Furthermore, calender presses, using which the surface of a web to be treated can be polished, are previously known. Such calender presses comprise a long nip with shoe and backup rolls. The backup roll of a calender press may be cambered and, similarly, the press felt used may also be cambered. The press belt may have been cambered taking account of the features disclosed in this application. However, the cambered press belt used in a calender press does not comprise drain grooves. In addition to a calender press, such ungrooved, cambered press belts can also be used in slow-speed board machines, pulp dryer machines or other slow-speed machines. The embodiments described in this paragraph are not in line with the independent claims of this application, as grooves are lacking.
(30) In some cases, features disclosed in this application can be used as such, independently of other features. On the other hand, features disclosed in this application can be combined, if necessary, to form various combinations.
(31) The drawings and their description are intended only to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.
