EP0509873A1 - Slotted screen drum for straining paper pulp and method for making the same - Google Patents

Abstract

Cylindrical screen for pulp scrubber of the thin-sheet type and consisting of a juxtaposition of U-shaped profiled elements (2) made of a metal strip characterized in that the element (2) comprises a first wing ( 3), a bottom (4), followed by a second wing (5) folded towards the outside of the U on itself so as to determine a space (6) in the fold thus formed, intended to receive and hold the first wing (3 ′) of the adjacent element (2 ′).

Description

The present invention relates to a process for producing a cylindrical sieve with slots for purifiers and classifiers of paper pulp obtained from waste paper and the sieve produced according to this process.

In the manufacture of paper pulp from old paper, numerous sieves are used, either to remove impurities or to sort the fibers according to their length.

These sieves are generally perforated cylinders mounted fixed in a closed volume comprising at least one inlet for dirty dough, one outlet for sieved dough, and one outlet for rejects. The dough is stirred by one or more paddles which rotate at high speed in the immediate vicinity of the perforated surface.

Depending on the characteristics of the sifting paste (for example the length of the fibers, the nature and the size of the contaminants), sieves with holes or slits are used. In addition, these perforations are usually accompanied by an obstacle which causes pulsations favoring sieving.

The perforations are usually produced by machining in a sheet of thickness of the order of a centimeter. However, since this machining presents great difficulties, the applicant has produced a screen from a sheet of thin thickness, of the order of 2 millimeters described in EP-A-354 846. This sieve is made up of U-shaped profiles joined next to each other and the bottom of which is perforated. The perforations are still obtained by machining (sawing bore) but the thinness of the wall significantly simplifies these operations.

• lorsque le cylindre est obtenu par juxtaposition de profilés cintrés, les profilés sont joints et maintenus étroitement serrés ensemble par soudage des parois adjacents ou par la pose d'un cavalier qui pince les deux parois. En pratique il n'est possible de réaliser cette liaison que lorsque les parois des profilés en U sont tournés vers l'extérieur du cylindre.
• lorsque l'on prévoit que les ouvertures de tamisage sont associées à un obstacle, l'usinage est tel qu'il est toujours situé du côté extérieur du fond du U.

However, this technique of thin-sheet cylindrical screens still presents difficulties:

• when the cylinder is obtained by juxtaposition of curved profiles, the profiles are joined and held tightly together by welding the adjacent walls or by the installation of a jumper which clamps the two walls. In practice, it is only possible to make this connection when the walls of the U-shaped profiles are turned towards the outside of the cylinder.
• when it is expected that the screening openings are associated with an obstacle, the machining is such that it is always located on the outside of the bottom of the U.

The walls of the U being turned towards the outside of the cylinder, one can practically only produce centrifugal screens.

A first objective of the invention aims to solve this problem. A second objective is to improve the perforation process.

Indeed, on the one hand, the perforation still represents a relatively long work station because the machining of the slots and obstacles comprises two saw passages followed by a deburring operation, on the other hand this machining, even if it removes a small amount of material taking into account the small thickness of the sheet, is important relative to this same thickness and weakens the resistance of the wall.

The subject of the present invention is a cylindrical screen for paper pulp purifier of the thin sheet type and consisting of a juxtaposition of U-shaped profiled elements produced in a metal strip characterized in that the element comprises a first wing , a bottom, followed by a second wing folded towards the outside of the U on itself so as to determine a space in the fold thus formed, intended to receive and hold the first wing of the adjacent element.

The invention also relates to the process for producing such a sieve, characterized in that a plurality of assemblies are assembled elements of the same length, the folded wing of each element engaging on the opposite wing of the neighboring element, the assembly forming a wall which is bent to form a cylinder, then the ends of the elements together.

According to an alternative embodiment, the method is characterized in that the element is wound in a spiral or helix, each turn forming a turn, the turns being assembled by introducing the fold of the second wing on the end of the first wing. of the adjacent turn, or vice versa.

The invention also relates to the process for producing the slots of the sieve, characterized in that the U-shaped metal strip is first put, it is placed on a template and the bottom of the U is punched by means a knife, the end of which has a cutting edge perpendicular to the axis of the strip and a wedge profile, one of the faces of which is perpendicular to the punched surface and in that the punches are made from distance to distance at regular intervals.

In a first variant the punching is not through and only forms a deformation whose profile has a wall perpendicular to the surface of the bottom of the U attacked by the knife followed by an inclined wall, the slot is obtained by a line saw to the right of the vertical wall.

In a second variant, the punching is through, it punctures the strip and cuts the slot, the width of which is determined by the depth of penetration of the knife.

• le poinçonnage est effectué sur la face extérieure du fond du U vers l'intérieur. La surface du tamis étant déterminée par la face extérieure du fond du U, cette surface présente alors une pluralité de creux perforés.
• l'intervalle entre deux poinçons successifs est réduit de façon que, considéré dans le sens d'écoulement de la pâte, la face inclinée d'une déformation soit immédiatement suivie de la paroi verticale, le profil étant alors en dents de scie.
• le poinçonnage est effectué sur la face intérieure du fond du U vers l'extérieur; la surface du tamis présente alors une pluralité d'obstacles en relief.
• le poinçonnage donnant un obstacle en relief est déterminé de façon que les extrémités latérales voisines et opposées de deux obstacles adjacents forment, lors de la juxtaposition des éléments en U, une rainure de forme approximativement concave.

The process is also remarkable for the following characteristics:

• punching is carried out on the outside of the bottom of the U towards the inside. The surface of the screen being determined by the outer face of the bottom of the U, this surface then has a plurality of perforated hollows.
• the interval between two successive punches is reduced so that, considered in the direction of flow of the dough, the inclined face of a deformation is immediately followed by the vertical wall, the profile then being jagged.
• the punching is carried out on the inside face of the bottom of the U towards the outside; the surface of the screen then presents a plurality of obstacles in relief.
• the punching giving an obstacle in relief is determined so that the adjacent and opposite lateral ends of two adjacent obstacles form, when the juxtaposition of the U-shaped elements, a groove of approximately concave shape.

• la figure 1 représente une vue schématique d'un profil du tamis selon l'invention,
• la figure 2 représente une vue en coupe transversale d'un élément en U selon l'invention;
• la figure 3 représente une vue schématique en coupe d'une première variante de réalisation d'un tamis cylindrique selon l'invention,
• la figure 4 représente une vue schématique en coupe d'une seconde variante de réalisation d'un tamis cylindrique selon l'invention,
• la figure 5 représente une vue de profil longitudinal d'un élément perforé par poinçonnage en creux,
• la figure 6 représente une vue en coupe transversale selon VI-VI de l'assemblage de la figure 5,
• la figure 7 représente une vue de profil longitudinal d'un élément perforé par poinçonnage en relief,
• la figure 8 représente une vue en coupe transversale selon VIII-VIII de l'assemblage de la figure 7.

In order to better understand the invention and the advantages which it brings, an exemplary embodiment of the sieve according to the invention is shown in the appended drawing in which:

• FIG. 1 represents a schematic view of a profile of the screen according to the invention,
• Figure 2 shows a cross-sectional view of a U-shaped element according to the invention;
• FIG. 3 represents a schematic sectional view of a first alternative embodiment of a cylindrical screen according to the invention,
• FIG. 4 represents a schematic sectional view of a second alternative embodiment of a cylindrical screen according to the invention,
• FIG. 5 represents a longitudinal profile view of an element perforated by hollow punching,
• FIG. 6 represents a cross-sectional view along VI-VI of the assembly of FIG. 5,
• FIG. 7 represents a longitudinal profile view of a perforated element by punching in relief,
• FIG. 8 represents a cross-sectional view along VIII-VIII of the assembly of FIG. 7.

As shown in FIG. 1, the sieve is a cylinder 1 made up of identical, curved and juxtaposed longitudinal metal elements 2 in a U shape.

Element 2 is made of a thin metal strip or strip. The strip is folded so that, in cross section, the element has a first wing 3, a bottom 4, followed by a second wing 5 folded outwards from the U on itself so as to determine a space 6 in the fold thus formed, intended to receive and hold the first wing 3 ′ of the adjacent element 2 ′.

The folded part 7 or flap of the second wing substantially covers the first adjacent wing 3 ′. Preferably the flap extends over the entire height 8 of the flat part of the wing 3 ′. In this way the first wing is held in the fold of the adjacent second over its entire flat part.

In a first embodiment not shown, a plurality of elements 2 of the same length are assembled, the folded wing 5 of each element engaging on the wing 3 ′ opposite to the neighboring element 2 ′; the assembly forms a wall which is bent to form a cylinder, then the ends of the elements are welded together.

In a second variant, the element 2 is wound in a spiral or helix, each turn forming a turn, the turns being assembled by introducing the space 6 of the fold of the second wing 5 onto the end of the first wing 3 ′ of the adjacent turn or vice versa.

As seen in Figures 3 and 4 the assembly can then be done both by bending the U-shaped element, the wings being oriented towards the outside of the cylinder (fig.3), that by bending it, the wings being oriented inward (fig. 4), which allows for indifferently a centrifugal or centripetal sieve, and this without needing to carry out a single welding.

The elements, before the bending and assembly operations, are perforated, the perforations possibly being holes or slots.

For slotted sieves, EP-A-0.354.846 discloses a perforation process by successive sawing. This process not only makes it possible to obtain a calibrated and very fine slit but also to produce a profile forming an obstacle.

According to the invention, the slots are no longer obtained solely by sawing but essentially by punching: first the metal strip is U-shaped, it is placed on a template 9 and the bottom of the U is punched by means of '' a knife 10, the end of which has a cutting edge 11 perpendicular to the axis of the strip and a wedge profile, one of the faces 12 of which is perpendicular to the punched surface and in that the punches are produced from distance to distance at intervals regular.

In a first variant, the punching is not through and only forms a deformation 13 whose profile has a wall 14 perpendicular to the surface 15 of the bottom of the U followed by an inclined wall 16, the slot 17 is obtained by a saw cut 18 to the right of the vertical wall.

In a second variant, not shown, the punching is through, it punctures the strip and cuts the slot, the width of which is determined by the depth of penetration of the knife 10.

The interval between two successive punches is reduced so that the inclined face 16 of a deformation is immediately followed by the vertical wall 14 of the next deformation, the profile then being jagged.

The punching member can be a simple hammer with reciprocating motion or a knurled wheel, which makes it possible to achieve a high rate of perforation.

In the variant shown in FIGS. 5 and 6, the punching is carried out on the outside face of the bottom of the U towards the inside 20. The screening surface being determined by the outside face of the bottom of the U, this surface then has a plurality of hollows perforated: the screen is perforated hollow.

In the variant shown in Figures 7 and 8 the punching is carried out on the inner face 21 of the bottom of the U outwards 22; the surface of the screen then presents a plurality of obstacles in relief: the screen is perforated in relief.

The punching giving an obstacle in relief is determined so that during the juxtaposition of two adjacent elements 2, 2 ′ mounted in a spiral the adjacent and opposite lateral ends 23, 24 of two adjacent obstacles 25, 26 are approximately aligned and form a groove 27. This forms a helical path which has the function of receiving and guiding the fraction of the rejected pulp towards the discharge outlet.

• . grande solidité du fait de la triple épaisseur des ailes, et aussi du fait qu'il n'y a pratiquement pas de perte de matière par usinage;
• . grande souplesse du fait qu'il n'y a pas de point de soudure;
• . durée du poste de perforation par poinçonnage très brève.

This process for producing a cylindrical screen has many advantages:

• . great strength due to the triple thickness of the wings, and also because there is practically no loss of material by machining;
• . great flexibility due to the fact that there is no welding point;
• . duration of the very short punching station.

Claims (10)

1 - Cylindrical sieve for paper pulp purifier of the thin sheet type and consisting of a juxtaposition of U-shaped profiled elements (2) produced in a metal strip characterized in that the element (2) comprises a first wing (3), a bottom (4), followed by a second wing (5) folded towards the outside of the U on itself so as to determine a space (6) in the fold thus formed, intended to receive and hold the first wing (3 ′) of the adjacent element (2 ′). 2 - A method of producing the screen according to claim 1 characterized in that a plurality of elements (2) of the same length are assembled, the folded wing (5) of each element engaging on the opposite wing ( 3 ′) of the neighboring element, the assembly forming a wall which is bent to form a cylinder, then the ends of the elements are welded together. 3 - A method of producing the sieve according to claim 1 characterized in that the element (2) is wound in a spiral or helix, each turn forming a turn, the turns being assembled by introduction of the fold of the second wing (5 ) on the end of the first wing (3 ′) of the adjacent turn (2 ′), or vice versa. 4 - A method of producing the sieve slots according to any one of claims 1 to 3 characterized in that one first puts the metal strip in the shape of a U, it is placed on a template (9) and the bottom of the U is punched by means of a knife (10), the end of which has a cutting edge (11) perpendicular to the axis of the strip and a wedge profile, one of the faces (12) of which is perpendicular to the surface punched (15) and in that the punches are made from distance to distance at regular intervals. 5 - A method according to claim 4 characterized in that the punching is not through and forms only one deformation (13) whose profile has a wall perpendicular (14) to the surface (15) attacked by the knife (10) of the bottom of the U followed by an inclined wall (16), the slot (17) being obtained by a saw cut to the right of the vertical wall. 6 - A method according to claim 4 characterized in that the punching is through, it punctures the strip and cuts the slot whose width is determined by the depth of penetration of the knife. 7 - Method according to claim 4 characterized in that the punching is carried out on the outer face (19) of the bottom of the U inward (20), so as to form recesses on the reference surface of the screen. 8 - Method according to claim 4 characterized in that the interval (30) between two successive punches is reduced so that, in the direction (31) of flow of the dough, the inclined face (16) is immediately followed by the vertical wall (14), the profile then being jagged. 9 - Method according to claim 4 characterized in that the punching is carried out on the inner face (21) of the bottom of the U outward (22). 10 - A method according to claim 9 characterized in that the obstacle in relief is determined so that the adjacent side ends (23, 24) and opposite of two adjacent obstacles (25, 26) form, when juxtaposing elements in U, a groove (27).

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