Shoe in an extended-nip press

Abstract: The invention concerns a shoe (10) in an extended-nip press. The shoe is fitted to be placed in a nip (N) between a back-up roll (K₁) and a belt-mantle roll (K₂) inside the belt mantle (S). The shoe is pressed by means of an actuator, preferably a cylinder device, towards the back-up roll (K₁), while the web (W) / felt or the felts (H₁,H₂) is/are placed between the back-up roll (K₁) and the belt mantle (S). The shoe (10) comprises at least one chamber (12', 12''...) provided for hydraulic fluid, into which chamber the fluid is passed from a duct (15/15', 15'',15'''...). The shoe (10) comprises a first curved face (11), whose curve radius (R₁) is substantially equal to the curve form of the back-up roll (K₁). The shoe (10) comprises a second face (12), which forms the bottom of the chamber (12',12''...) provided for hydraulic fluid and which second face (12) joins said first face (11) and has been made with a larger curve radius (R₂) than the first face (11). According to the invention, at the joint (C) between the first face (11) and the second face (12), the tangents (t₁,t₂) of the faces (11 and 12) are substantially the same.

Description: The invention concerns an extended-nip press of the type disclosed in WO-A-9 117 308, forming the basis of the preamble of claim 1. The optimal shape of the pressure curve in an extended-nip press is a triangle, i.e. the pressure rises in a linear way from zero to its maximal value. In the prior-art shoe solutions for extended-nip presses, the rise of pressure has been unsatisfactory. In the present application, a novel extended-nip press is described by whose means it is possible to come closer to the optimal triangular shape of pressure increase. According to the invention, the novel extended-nip press comprises, in a way known perse, a first face in the area of the trailing side, considered in the direction of running of the web, the radius of said first face corresponding to the curve radius of the back-up roll. The first face is preceded by a second face, which is also curved and which determines the shape of the bottom of the hydrostatic chamber. Said second face has been made with the radius R 2 . At the joint between the first face and the second face, the radii R 1 and R 2 are placed on the same line, while the radius R 2 is slightly longer than the radius R 1 . In relation to the hydrostatic chamber, the area at the inlet side of said chamber comprises a third face, which has been made with the same curve radius R 1 as the first face on the shoe, i.e. said third face corresponds to the curve form of the back-up roll K. In the solution in accordance with the invention, at the joint between the first face and the second face, the tangents of the faces are the same. By means of an arrangement in accordance with the invention, a substantially linear, triangular curve of pressure increase is obtained. The manufacture of a shoe in accordance with the invention takes place so that first the bottom part/parts of the hydrostatic chamber, i.e. hydrostatic pocket, are machined, for example turned, with the radius R 2 and the partition walls of the hydrostatic chamber/chambers with the radius R 1 . After this, the face of the shoe proper, i.e. the first face and the third face, are machined with the radius R 1 . The extended-nip press in accordance with the invention has, more specifically, the characterizing features of claim 1. Further features of the extended-nip press in accordance with the invention are defined in claims 2 to 7. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being not supposed to be confined to said embodiments alone. Figure 1 is a side view of a prior-art extended-nip press. Figure 2 is an axonometric view of a shoe in accordance with the invention for an extended-nip press. Figure 3 is a sectional view taken along the line I-I in Fig. 2. The solution in accordance with the invention will be described based on this figure. Figures 4A and 4B show pressure curves related to a shoe in an extended-nip press according to the invention over the distance of the length of the shoe, while Fig. 4A shows a shoe whose overall length is 250 mm, and Fig. 4B shows a shoe whose overall length is 150 mm. Figure 5 shows the composition of a shoe included in the invention. Figure 6 shows a hydraulic diagram related to a hydrostatic shoe. Figure 1 is a side view of a prior-art extended-nip press. The felts H 1 and H 2 are passed through the nip N while the web W is placed in the middle of the felt draw. The nip N is formed between the rolls mounted on the frame R: the back-up roll K 1 and the belt-mantle roll K 2 . The shoe 10 in accordance with the invention is placed in the extended-nip press inside the belt mantle S, being pressed against the felt-mantle face S'. Thus, the nip area L becomes long as the resilient belt mantle S follows the curve form and the surface form of the back-up roll K 1 over the entire length L of the shoe 10. Figs. 2 and 3 show a shoe 10 for an extended-nip press in accordance with the invention. The shoe 10 comprises a first face 11, whose curve form R 1 corresponds to the radius, i.e. to the curve form of the back-up roll K. Further, the shoe 10 comprises a second face 12, which forms the bottoms of the hydrostatic pockets or chambers 12',12",12"'. The hydrostatic pockets 12',12"... define a hydrostatic space for pressure fluid. The face 12 has been shaped with the curve radius R 2 . At the joint C between the faces 11 and 12, the tangents t 1 and t 2 of the two faces 11 and 12 are the same. Besides by the curved bottom 12 and by the end wall 15, the hydrostatic chambers 12',12"... are also defined by the partition walls 13',13"... in the transverse direction of the web. The top edges of the partition walls 13',13"... have been made with the curve radius R 1 , which corresponds to the curve form of the back-up roll K 1 . Into each chamber 12',12"..., one or several ducts 15',15",15"' are opened so as to pass pressurized fluid into the chambers 12',12",12"'. The centre of curvature of the top edge of the partition walls 13',13"... is O 1 , i.e. the same as that of the faces 11 and 16. The function of the partition walls 13',13",13'"... is to operate as limiting parts which permit a maximally uniform distribution of the hydrostatic pressure across the length of the shoe without detrimental effects of outside interfering factors and impulses on the pressure formation. By the intermediate of the vertical end wall 14, the face 12 is joined by the third face 16, which has been made, in the corresponding way, with the same curve radius R 1 as the back-up roll K 1 . Fig. 3 is a sectional view taken along the line I-I in Fig. 2. On the basis of this figure, the shoe solution in accordance with the invention is described in more detail. The first face 11 joins the second curved face 12 smoothly at the point C. At the point C, the tangent t 1 of the face 11 is the same as the tangent t 2 of the face 12. Thus, when the radii R 1 and R 2 related to the point C are examined, the centres of curvature O 1 and O 2 of the faces 11 and 12 are placed on the same straight line. The radius R 2 of the face 12 is slightly longer than the curve radius R 1 of the face 11. R 2 /R 1 , i.e. the ratio of the radii, is preferably in the range of 1.05...1.5 and even more advantageously in the range of 1.1...1.3. When the shoe 10 is being designed, the variables are the length L 1 of the first face 11, the length L 2 of the second face 12, and, in the inlet area of the web W, the length L 3 of the face 16 and the length L 4 of the face 17 in the lateral area. The face 17 is preferably a straight face that is connected with the radius R 1 substantially tangentially. Further, the shoe 10 comprises initial and final roundings 18 and 19 related to the faces 11 and 17. The overall length of the shoe is L = L 1 + L 2 + L 3 + L 4 . An advantageous form of the pressure curve is obtained with a solution in which R 2 /R 1 is as little as possible, preferably in the range of 1.1...1.3, and in which solution the length L 2 of the hydrostatic chamber 13 is as large as possible. The overall length of the shoe 10 is preferably in the range of 120...150 mm. Fig. 4A shows the formation of the pressure curve in a case in which the overall length L of the shoe is 250 mm. Fig. 4B shows the formation of the pressure curve in a case in which the overall length L of the shoe is 150 mm. From the figure it is seen that the rise of the pressure curve is substantially linear, and, in a corresponding way, the lowering of the pressure curve is as steep as possible. Fig. 5 shows a mode of composition and formation of the shoe. The bottoms 12 of the hydrostatic pockets 12',12",12"' are first turned with the radius R 2 , and thereupon the partition walls 13',13",13"' are turned with the radius R 1 . The faces 11 and 16 of the lateral parts 20b,20c are turned with the radius R 1 . The parts 20a,20b are fixed, for example by means of screws, to the middle part 20a of the construction, to its side projections 20a',20a", said middle part 20a including the hydrostatic chambers 12',12",12"'. Fig. 6 shows a hydraulic diagram of a hydrostatic loading shoe 10 in accordance with the invention. The lubricant, preferably hydraulic fluid, is passed from the fluid container 21 by means of a fluid pump P, along the duct 22 into the capillary duct 15 / ducts 15',15"... in the shoe 10. Through the capillary duct 15 / ducts 15',15", 15"'..., the fluid is made to flow through the face 12 into the chambers 12',12"... The shoe 10 is loaded hydraulically by means of cylinder devices 24a,24b, by means of their pistons 24a',24b', in relation to the length of the hydrostatic shoe 10, from both ends of the shoe 10. The hydraulic cylinders 24a,24b can be loaded independently from one another, and in this way it is possible to vary the loading of the shoe so as to obtain the desired pressure curve. From the fluid container 21, from the duct 25, the fluid pressure is passed by means of a regulation pump P 2 into the duct 26 and further into the ducts 26a,26b, which ducts 26a,26b comprise, for example, proportionally adjustable valves 27a,27b, by whose means the loads applied by the pistons 24a,24b are regulated. The return ducts 28a,28b from the cylinder 24a,24b join into the duct 29, which comprises a valve 30. When the block 30a of the valve 30 is switched on, the flow passes through the valve 30 into the hydraulic-fluid container 21. When the block 30b of the regulation valve 30 is switched on, the flow is passed from the pump P 2 into the cylinders 24a,24b into the cylinder spaces at the side of the piston rod. As is shown in Fig. 6, the overflow of the fluid is passed from the overflow space 31 along the duct 32 into the fluid container 21.

Claims: Extended-nip press, comprising a nip (N) formed between a back-up roll (K 1 ) and a belt-mantle roll (K 2 ), a shoe (10) being placed inside the belt mantle (S), which shoe is pressed by means of an actuator, preferably a cylinder device, towards the back-up roll (K 1 ), while the web (W) and a felt or felts (H 1 ,H 2 ) is/are passed through the nip between the back-up roll (K 1 ) and the belt mantle (S), and which shoe (10) comprises on its surface pressed against the belt mantle (S) at least one chamber (12',12"...) provided for hydraulic fluid, into which chamber the fluid is passed from a duct (15/15',15",15"'...), and a first curved face (11) on the trailing side of the chamber with respect to the running direction of the web (W), whose curve radius R 1 is substantially equal to the curve form of the back-up roll (K 1 ), characterized in that the shoe (10) comprises a second curved face (12), which forms the bottom of the chamber (12',12"...) provided for hydraulic fluid and which joins said first face (11) and has been made with a larger curve radius R 2 than the first face (11) and so that, at the joint (C) between the first face (11) and the second face (12), the tangents (t 1 ,t 2 ) of the faces (11 and 12) are substantially the same. Extended-nip press as claimed in the preceding claim, charaterized in that, in the area of the web (W) inlet side , the shoe (10) has a third face (16), whose curve radius is equal to the curve radius R 1 of the first face and which precedes said second curved face (12) in the running direction of the web (W). Extended-nip press as claimed in claim 1 or 2, characterized in that the ratio R 2 /R 1 of the curve radii of the first face (11) and of the second face (12) is in the range of 1,05...1,5, preferably in the range of 1,1...1,3. Extended-nip press as claimed in claim 1 or 2, characterized in that the length of the first curved face (11) in the running direction of the web is very small. Extended-nip press as claimed in claim 2, characterized in that the third face (16) is preceded in the running direction of the web (W) by a plane face (17) connected with it substantially tangentially. Extended-nip press as claimed in any of the preceding claims, characterized in that there are provided a number of chambers (12',12",12"'...) for hydraulic fluid arranged in the direction of width of the web, which chambers are separated from one another by partition walls (13',13",13"'...), and that the top edges of the partition walls have been prepared with the curve radius of the back-up roll (K 1 ). Extended-nip press as claimed in any of the preceding claims 2-6, characterized in that the shoe (10) is made of at least three parts (20a,20b, 20c), which are interconnected, the first part (20a) comprising the second curved face (12) and the two other parts (20b,20c) placed at the sides of said first part (20a) comprising the first and third faces (11,16).

Inventors: ILMARINEN ANTTI, ILMARINEN, ANTTI
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1993
Main classification: D21F3
IPC codes: D21F3