FI108877B - Pressko - Google Patents

Description

108877

The press shoe

Pressko 5

The invention relates to a clamping shoe for insertion into a belt sheath roll or the like and loaded in the clamping direction to provide an extended clamping nip.

In long nip presses and calendars, the nip is generally formed between a rotatable cylindrical counter roll and a stationary press shoe having substantially the same curvature, over which a flexible and non-compression strap is imaged. With existing shoe structures, the press shoe must be exactly parallel to the counter roll so that the nip pressure distribution 15 of the press is the same at every point across the web to be pressed. If the direction of the longitudinal axis of the press shoe, for example due to misalignment, deviates substantially from the direction of the axis of the counter roll, the high torsional stiffness of the shoe prevents it from conforming to the shape of the counter roll.

20: ··· 'FI Patent Application 953527 discloses a long nip press in which the machine nip pressure distribution of the press shoe can be adjusted by aligning the shoe • * »; · At the beginning and end of its nip, the collision forces. Slots are formed in the shoe's cross-section to facilitate relative movement of these areas ;; 25 images of the second pressing member. Thus, the shape of the cross-section of the shoe * is changed to adjust the nip pressure distribution. However, the shoe forces the shoe forced into the desired shape cannot freely adapt to the back roll>! 1 _ shape and possible position errors.

[30 DE] 30 30 233 is known from a compressible material

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. a sliding shoe that can adapt to track irregularities and »! 108877 j 2 to the curvature of the counter roll. The shoe rests on a metal foot, which in turn rests on the bracket via a pressurized pressurized pressure pad, which pad may be axially divided into a plurality of pressure zones.

From WO patent application 98/58122 there is known a long nip press which has a plurality of successive loading points in a pressed shoe made of a flexible material, which are subjected to separate adjustable loading forces.

The press shoe of U.S. Patent No. 5,582,689 has two successive hydrostatic-loaded areas in the nip area that provide different pressing pressures at the beginning and end of the nip, if desired. In addition, the shoe may be divided axially into different load areas, which allows for compensation of the deflection.

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The object of the invention is to provide a simple shoe with a structure which minimizes the problems of the prior art.

In particular, the object is to provide a press shoe which, when needed,. The 20 is able to adapt to the off-shoe position of the counter roll and still maintain sufficient bending stiffness to allow even nip pressure • ·.:. achieving a roll across the track to be compressed.

In order to achieve this and the following objects, the compression shoe according to the invention is characterized in what is stated in the characterizing part of claim 1.

The press shoe according to the invention has two slots extending from its end to its end in the longitudinal direction of the shoe. These gaps are in a plane perpendicular to the compression direction: ·· * 30 and are positioned so that they reduce '·]. significantly increases the torsional stiffness around the longitudinal axis of the shoe, but only slightly affects the bending stiffness of the shoe in the compression direction. This is achieved, for example, by positioning the slits at substantially the same height as the neutral plane passing through the surface center (= center of gravity) of the shoe's cross-sectional surface. By a neutral plane is meant a plane substantially perpendicular to the direction of loading of the shoe, on which one side is subject to compression stress while the other is subjected to tensile stress.

The slots formed in the shoe may also be at the same height as the center of rotation of the shoe's cross-sectional surface. The slots may be closed to the shoe surface by opening 10 only at the end by means of supports that limit the elasticity of the shoe in the compression direction. The slits may be 5-20 mm in height and preferably have a common length of about 50-70% of the total machine dimension of the shoe, leaving a single, non-slit area in the center of the shoe accounting for 30-50% of said shoe dimension.

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Preferably, the shoe and the slots therein are dimensioned such that the torque of the shoe's cross-sectional surface is up to twice the torque calculated relative to the axis perpendicular to the compression direction and passing through the center of the cross-sectional area.

20th ... j When the shoe is formed with slits as shown, its torsional stiffness with respect to the • i. longitudinal axis of the shoe is less than that of a conventional non-slit; '·, · In a shoe. In this case, the shoe may be more easily warped about its longitudinal axis and thus adapted to the counter roll if, for example, the axis of the counter roll is not parallel: with the longitudinal axis of the shoe or when the press roll axis and shoe

With the solution of the invention, the torsional stiffness of the shoe can be substantially • - · reduced without any significant loss of tensile stiffness important for the transverse line pressure distribution of the nip. With a simple structural solution, it is possible to achieve * »4 108877 essentially identical machine direction nip pressure distribution at various points on the web.

In the following, the invention will be described in more detail with reference to the figures in the accompanying drawings, in which details, however, are not intended to be narrowly limited.

Figure 1 is a cross-sectional view of a press shoe according to the invention fitted to a long nip press.

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Figure 2 is a more detailed cross-sectional view of a press shoe according to the invention.

Figure 3 shows a cross-section of a prior art press shoe.

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Figure 4 shows a cross-section of a press shoe according to the invention.

The long nip press of Fig. 1 comprises a press shoe 10 and a counter roll 11 between which an elongated compression zone or nip N is formed. The arrow 12 indicates the direction of rotation of the. 20 counter roll 11 and also the direction of the web W being compressed through the nip N. Over the front face of the press shoe 10 is a pressure roller, · forming a shoe made of a flexible and non-compressible material;

13. Wrapped paper or board web W is guided through nip N

through, together with the water-receiving press fabric 14, which may pass 25 optionally below or above the web W, or alternatively there may be one press fabric on each side of the web.

A press shoe 10 housed within an endless belt loop 13 is loaded; · · * Is pressed in the compression direction P against the counter roll 11 by means of hydraulic loading members 15 '*: 30 which are only one in the direction of travel of the web but in the width of the web. ,: several in parallel. The loading means 15 are supported on the support members 17 of the press shoe 10, which remain substantially stationary as the belt 13 rotates an endless web during compression. The loading members 15 comprise a two-piece outer cylinder 15a, 15b and an inner cylinder 16 disposed therein. The upper portion 15a of the outer cylinder is secured by clamping members 18 to the press shoe 10 and to which pressure medium is fed through the channel 19 in the support beam 17 to load the press shoe 10 in the pressing direction P against the counter roll 11. The outer surface of the inner cylinder 16 is sealed against the inner surface of the outer cylinder parts 15a, 15b by two sealing rings 20.

The face of the press shoe 10 has a hydrostatic chamber 21, into which pressure medium is introduced through a passageway 22. The nip N of the press thus comprises a hydrostatically loaded area in the center of the shoe, preceded and followed by hydrodynamically lubricated areas at the front and rear of the shoe 15.

Figure 2 shows in more detail the cross-sectional shape of the press shoe 10 according to the invention. The press shoe 10 is formed as a single piece of material of relatively high stiffness. Reducing torsional stiffness; 20 sex in shoe 10 is two in its longitudinal direction, ie in the cross machine direction * ·

Mli., ..; end-to-end slots 23 and 24 of the shoe, the first 23 starting from the front of the shoe 25 and the second 24 from the rear of the shoe 26. The height h of the slots 23,24 is? 5 mm. Both slots 23,24 extend in the same plane perpendicular to the compression direction P from the side surface of the shoe 25.26 towards the unidirectional central portion of the shoe. Preferably, the length of the gapless area s in the center of the press shoe 10 is 30% to 50% of the total machine dimension L of the shoe.

The support members 27 are of rigid material and have substantially the same height: * · 30 of the slots 23 and 24.

6 108877

Figs. is substantially parallel to the y-axis. The longitudinal axis of the shoe, not shown in the figures, extends perpendicularly outward from the plane of the cross section.

In the optimum case, the press shoe and counter roll are exactly parallel, i ...

j 10 whereby the profile of the compression pressure acting between them is constant over the entire width j of the web. If the axial directions of the press shoe and the counter roll are different, the forces and moments acting on the shoe cross-section at different points in the longitudinal direction of the shoe will be different. In this case, the shoe is subjected to torque and bending moments, which tend to alter the geometry of the shoe.

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When a shoe is subjected to a torque, its successive longitudinal cross-sections tend to slide relative to one another, rotating about the torsion center Vk. The torsional stiffness of the shoe depends on the size and geometry of its cross section and is described by the torque square.

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The bending moment on the shoe creates a tension in it that tends to stretch the shoe in the longitudinal direction and compress it »i · '. size in the same direction. There is thus always one plane perpendicular to the direction of action of the bending force in the shoe, where the bending stress is zero. This plane ''; 25 generally passes through the center of gravity of the shoe's cross-section, i.e. the center of gravity Pk, and is called the neutral plane. When the shoe is only loaded with a nip load; through the center of the surface Pk of the cross-section, approximately parallel to the x-axis, whereby the bending stiffness in the compression • · j 30 direction P is proportional to the square moment Ix calculated with respect to the x-axis.

7 108877

The shoe 30 of Fig. 3 has a torque Ix relative to the x-axis passing through the surface center Pk of 3.225 x 10'5 and a torque of 1.035 x 10'4 relative to the longitudinal axis of the shoe 30. In the shoe according to Fig. 4, the square of torque 10 is equal to 3.215 x 10'5 and the torque is 3.747 x 10'5. From this, it can be calculated that when the shoe structure of Fig. 3 is provided with the gaps shown in Fig. 4, the torque of the shoe is reduced by as much as 64%, while the square torque Ix relative to the x-axis is reduced by only 0.3%. It follows that the shoe of Fig. 4 rotates appreciably about its longitudinal axis 10 is easier than the shoe in Figure 3, but as the shoe is twisted it cross-sectioned! the shape of the cup, and hence the nip pressure distribution, remains almost unchanged Mana.

The ratio of the torque square to the square torque Ix calculated with respect to the x-axis is 15 in Figure 3 shoe 3.21 and in Figure 4 shoe only 1.17. It has been found advantageous for the shoe to have a torque of up to twice the cross-sectional torque compared to the square torque Ix calculated with respect to the x-axis through the cross-sectional surface center Pk.

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Claims (7)

1. Pressure shoe (10) intended to be placed inside a belt mantle or equivalent and loaded in the press direction (P) against a counter-roll (11) for providing an extended press nip, characterized in that a cross-section of the shoe (10) has a the pane perpendicular to the pressing direction (P) two slots (23,24) extending in the longitudinal direction of the shoe (10) from one end to the other end and positioned in such a position that they substantially reduce the torsional stiffness of the shoe ( 10) around its longitudinal axis, but only slightly affects the bending stiffness of the shoe (10) in the pressing direction (P). Pressure shoe according to claim 1, characterized in that the slots (23,24) are substantially at the same height as a neutral plane running through the surface center (Pk) of the cross-sectional surface of the shoe (10), which is a substantially perpendicular to the shoe's (10) load direction lying on the side of which one side exerts a compressive tension and on the other side a tensile tension where the shoe is bent. Pressing shoe according to claim 1 or 2, characterized in that the slots' (23,24) are substantially at the same height as the center of rotation (Vk) of the cross-sectional surface I. ·· 20 of shoes (10). Pressure shoe according to any of the preceding claims, characterized in that the end of each gap (23,24) which opens at the surface (25,26) of the shoe has a support piece (27), the purpose of which is to limit the suspension of the shoe (10): 25 in the press direction (P). > i > ... 5. Pressure shoe according to any of the preceding claims, characterized in that the height of the slots (23,24) is 5-20 mm. 108877 Press shoe according to any of the preceding claims, characterized in that the total length of the slots (23,24) is 50-70% of the total machine-directed length (L) of the cross-section of the shoe (10). Pressing shoe according to any of the preceding claims, characterized in that the moment of inertia of the cross-sectional area of the shoe (10) is at most double compared to an inertia moment calculated with respect to an axis perpendicular to the direction of pressure (P) and extending through the center of the surface (P). of the cross section. ! j * 1 * 1 • · * · · t · · »· · I I 1 1