EP1057927B1 - Screen cylinder, especially for paper pulp - Google Patents

Abstract

The cylindrical sieve, especially for processing paper pulp, has two flanges (1,2) held together by a number of bars (3). It has at least one axially rigid and thin filter sieve (10), held in place by supporting rings (11) which also secure it against the bars (3). The cylindrical sieve also has at least one reinforcement ring (20), placed between successive filter sections (10A,10B), with passage openings (20A) for the bars (3) to pass through and lock the assembly together against twisting. The bars (3) are secured to the outer flanges (1,2) with butts (6,7) to maintain a fixed gap between the flanges (1,2). Wedges (12) are inserted between the filter mesh sieve and one or other of the flanges (1,2). The support rings (11) are welded to the filter sieve (10), at their inner or outer surfaces, and their other surfaces are in contact with the support bars (3). The gap between neighboring support rings (11) is about 25 mm.

Description

The present invention relates to a cylindrical screen intended more particularly for pulp processing.

In patent WO97 / 34045 a cylindrical sieve for paper pulp has been described in which the filter elements are clamped between two flanges, keeping them in position being obtained by the fact that their two ends are cut in bevel and fit into grooves also bevelled.

Such an arrangement is costly to implement.

In patent EP 0 707 109, a cylindrical sieve consisting of a stacking hoops of U-section, these hoops being clamped between two flanges by a plurality of tie rods, said screen then being prestressed due to the elasticity U-shaped hoops. However, the cost of the hoops is relatively high, which makes the sieve obtained expensive to manufacture.

Document DE 196 51 643 describes a filtering screen composed of bars arranged in a cage made up of two flanges connected to each other by bars forming tie rods. The wires are clamped between the flanges and connected to the bars by support rings which at their outer edge are welded to the bars and which at their inner rim are provided with recesses receiving the bars by complementarity of form. The bars can thus be placed in the support crowns and extracted from them by removing one of the flanges to have access. However, this screen has a fixed support structure whose crowns are welded to the bars respecting the exact alignment of the recesses from one crown to the next. The establishment of this structure support is thus relatively complicated and therefore expensive.

We know from EP 0 893 536 another sieve for paper pulp comprising a cage composed by two end flanges and an intermediate support ring which are connected to each other by tie rods in the form of bars crossing these three elements. The ends of the bars are threaded to cooperate with nuts arranged on the outer surfaces of the flanges. The filter element consists of two orifice plates which are mounted in grooves arranged on the faces inside of the flanges and on either side of the support ring. For their held in place, the sheets are clamped between the flanges. This sieve thus requires a machining of the flanges and also of the intermediate support ring.

The object of the invention is to propose a screen which is simpler to manufacture and therefore less more expensive than those of the prior art. The sieve according to the invention must particular to avoid the welds between the bars and the crowns of support according to DE 196 51 643, while avoiding the machining of the flanges and the crown of intermediate support according to EP 0 893 536.

The present invention further allows the manufacture of sieves with elements filters made up of wires of appropriate section which are assembled next to the others on load-bearing elements instead of the U-shaped hoops of patent EP 0 707 109.

The sieve according to the present invention is of the type consisting of one or more filter elements arranged between two flanges by means of a plurality of bars, in which the filter element may consist of an assembly on supports regularly spaced with parallel wires, arranged next to each other in leaving little space between them.

Thus, such a filter element is rigid in the axial direction and is arranged upstream said bars relative to the direction of flow of the dough and pressing against them, by the supports of the wires so as to be kept in shape by said bars to against the pressure exerted by the dough.

The object of the invention is a cylindrical sieve, in particular for paper pulp, type comprising two flanges connected to each other by means of a plurality of bars, and at least one thin filter element rigid in the axial direction and constituted by wires arranged side by side, said filter element being carried by circles and disposed upstream of said bars relative to the direction of flow of the dough, characterized in that the filter element bears against the bars by through the circles which are in contact with them, without being attached to them.

According to a first embodiment, the bars are fixed to the flanges while being in press against them so that the distance between the two flanges is invariable, this which possibly requires the installation of shims to compensate dimension errors of the filter elements.

According to a second embodiment, the bars are fixed in support of a single bridle and cross each other; so that the filter elements can be tightened by this second flange.

• le tamis comporte en outre au moins un cercle de renfort disposé entre deux éléments de filtrage successifs et pourvu de trous traversant pour recevoir les barreaux afin d'empêcher la flexion de ceux-ci ;
• les barreaux sont fixés aux deux brides en étant en appui contre elles, en butée dans des logements de sorte que la distance séparant les deux brides est invariable ;
• des cales d'épaisseur sont interposées entre l'élément filtrant et l'une ou l'autre des brides ;
• les barreaux sont fixés, en appui, à une seule bride et traversent l'autre de sorte que les éléments filtrants peuvent être serrés par ladite deuxième bride;
• les cercles de support sont à leur rebord intérieur ou extérieur soudés à l'élément filtrant, alors qu'à l'autre rebord, ils sont en contact avec les barreaux ;
• la distance optimale entre deux cercles successifs est de l'ordre de 25 mm.

According to other characteristics of the invention:

• the screen further comprises at least one reinforcing circle disposed between two successive filter elements and provided with through holes for receiving the bars in order to prevent them from bending;
• the bars are fixed to the two flanges by being pressed against them, in abutment in housings so that the distance separating the two flanges is invariable;
• shims are interposed between the filter element and one or the other of the flanges;
• the bars are fixed, in abutment, to a single flange and pass through the other so that the filter elements can be clamped by said second flange;
• the support circles are at their inner or outer rim welded to the filter element, while at the other rim, they are in contact with the bars;
• the optimal distance between two successive circles is around 25 mm.

Figure 1 : une demi vue, en coupe longitudinale, d'un premier mode de réalisation d'un tamis centripète selon l'invention.

Figure 2 : une demi vue, en coupe longitudinale, d'un deuxième mode de réalisation d'un tamis centripète selon l'invention.

Figure 3 : une vue correspondant à la figure 1, en version centrifuge.

Figure 4 : une vue correspondant à la figure 2, en version centrifuge.

Figure 5 : une vue en perspective avec arrachement partiel du tamis de la figure 3.

By way of nonlimiting examples and to facilitate understanding of the invention, the accompanying drawings show:

Figure 1: a half view, in longitudinal section, of a first embodiment of a centripetal sieve according to the invention.

Figure 2: a half view, in longitudinal section, of a second embodiment of a centripetal sieve according to the invention.

Figure 3: a view corresponding to Figure 1, in centrifugal version.

Figure 4: a view corresponding to Figure 2, in centrifugal version.

Figure 5: a perspective view with partial cutaway of the screen of Figure 3.

Referring to Figure 1 we see that the screen is constituted by the assembly, fixed dimensions, of two circular flanges 1 and 2 by means of a plurality of bars 3.

The ends 4 and 5 of each bar 3 are supported at the bottom of housings 6 and 7 formed in the flanges 1 and 2 and the bars are fixed to said flanges by screws 8 and 9.

As a result, the dimensions of the cage thus formed are invariable, which is sometimes essential for the installation of a sieve, in an installation. This cage receives the filter element 10 which in the centripetal embodiment illustrated on Figures 1 and 2 is arranged on the periphery of the cage, and which in the mode of centrifugal embodiment illustrated in Figures 3 and 4 is arranged inside the cage.

The filter element consists of wires arranged side by side and parallel to the generator of the cylinder. The wires are carried by supports which are constituted by circles 11, perpendicular to the wires 10, regularly spaced. When manufacturing procedure the wires are fixed to the circles 11 by welding to define filtration holes between the wires.

The assembly thus obtained is then, in the centrifugal embodiment illustrated in Figures 3 to 5, simply introduced into the cage so that the circles 11 come into contact with the bars 3, which gives a floating mounting between the circles and bars. Then the wires are clamped between the flanges. The assembly for the centripetal embodiment is analogous to that described, but here the whole is placed around the cage.

These support circles 11 thus remain in contact with the bars 3, in order to allow the filter element to resist the pressure exerted by the paste since in this way, the filter element is in fact in abutment against the bars, by through the circles forming supports. The optimal distance between two circles successive is of the order of 25 mm, which means that their number depends on the total length of the filter element.

The screen must operate in centripetal regime, that is to say the flow of the dough being made from the outside towards the inside, the bars 3 are, as already mentioned, inside the filter element so as to support it. In in other words, the filter element is upstream of the bars 3 relative to the direction of the flow of the dough.

As it may happen that the length of the filter element 10 does not correspond exactly at the distance separating the two flanges 1 and 2, which is invariable on plans to be able to put shims such as 12 between one end of the cylinder and either flange 1 or 2.

FIG. 2 represents an alternative embodiment of the centripetal sieve of FIG. 1, the same elements with the same references. Unlike Figure 1, the sieve here has three filter elements 10A, 10B and 10C which are placed one after the others with the interposition of reinforcing circles 20, which support the bars 3 to prevent bending.

Each reinforcing circle 20 has a number of through holes 20A to receive the bars 3 and the number of holes thus corresponds to the number of bars. Each reinforcing circle 20 is thus a separate element which is placed directly on a filter element and threaded onto the bars 3 before the next filter element is not in place. The reinforcement circle has the sole function of connect the bars to each other to stiffen them together.

Furthermore, in this variant one of the ends 15 of the bars 3 crosses the flange 2 by holes 17. These ends of the bars 3 are threaded, so that it it is possible to tighten the flange 2 and therefore to keep the filter element 10 in place by tightening between the flanges.

FIGS. 3 to 5 represent the application of the invention to centrifugal screens, i.e. in which the flow of the dough goes from inside the sieve to outside.

In these figures, the elements identical to those of FIGS. 1 and 2 bear the same references.

The difference comes mainly from the fact that in Figures 1 and 2 the bars 3 are inside the filter element 10 to maintain it. in Figures 3 to 5, they are found outside.

In Figures 3 and 5 which show the same arrangement of the elements, two filter elements 10A and 10B are used and therefore only one reinforcing circle 20 is required. More specifically, the number of reinforcing circles 20 is a function direct of the number of filter elements and one could for example implement a sieve with five filter elements and therefore four reinforcing circles.

In the examples shown in Figures 1 to 5, the filter element consists of an assembly of wires 10 on supports 11; but the invention is not limited to this particular mode of the filter element.

Claims (6)

1. Screen cylinder, in particular for paper pulp, of the type comprising two flanges (1, 2) which are connected to each other by means of a plurality of bars (3), and at least one thin filter element (10) which is rigid in the axial direction, said filter element being carried by support circles (11) and being disposed upstream of said bars (3) with respect to the direction of flow of the pulp, characterised in that the filter element is supported on the bars (3) by means of the support circles (11) which are situated in contact with the latter, without being fixed thereon.
2. Screen according to claim 1, in which the screen comprises furthermore at least one reinforcement circle (20) which is disposed between two successive filter elements (10A, 10B, 10C) and is provided with traversing holes (20A) in order to receive the bars (3) so as to fix them together in order to prevent them from deflecting.
3. Screen according to claim 1 or 2, in which the bars (3) are fixed to the two flanges (1, 2) by being supported on them, abutting in housings (6, 7) such that the distance separating the two flanges is invariable.
4. Screen according to claim 3, in which shims (12) are interposed between the filter element and one or the other of said flanges (1, 2).
5. Screen according to any of the preceding claims, in which the support circles (11) are welded to the filter element (10) at their interior or exterior shoulder, whilst at the other shoulder they are in contact with the bars (3).
6. Screen according to any of the preceding claims, in which the distance between two successive support circles (11) is of the order of 25 mm.

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