EP0509909A1 - Screen for hydrodynamically straining or classifying paper pulp - Google Patents

Abstract

Cylindrical sieve for purification or hydrodynamic classification of paper pulp in a purifier or classifier to pale of the kind bearing on the face opposite to that in front of which the blades circulate a plurality of reinforcing irons characterized in that the sheet is a sheet of thin thickness , of the order of 2 millimeters, perforated by stamping or the like.

Description

The present invention relates to a sieve for purification or hydrodynamic classification of paper pulp, obtained in particular from old paper.

In the waste paper recycling industry, a large number of screens are used, either to separate the fibers forming the pulp from impurities of all kinds called contaminants, or to sort the fibers together. Separation takes place in purifiers and sorting in classifiers.

In conventional devices, the screens consist of a generally cylindrical drum. The cylindrical surface of the drum is perforated with calibrated holes or slots. The dough introduced into the device is filtered through this perforated surface. A blade, parallel to the generator of the cylinder, circulates at high speed in front of the perforated surface, preferably on the upstream side, to avoid clogging of the perforations.

Many specific provisions have been made to improve the performance of the screens, whether in longevity, in filtration quality, or in construction cost.

• la disposition d'obstacles sur la surface amont du tamis, en amont des perforations. Les profils présentent une succession de nervures et de creux ou de rainures, au fond desquelles les perforations sont pratiquées. Ces obstacles, provoquent des pulsations au passage de la pale qui améliorent le rendement tout en évitant le colmatage. Les brevets FR 1.539.846 et FR 88-10684 illustrent par exemple cette disposition;
• la réalisation d'un tamis constitué par la juxtaposition d'éléments à section transversale en U comportant un fond plat de faible épaisseur et perforé. Les éléments sont cintrés et assemblés de telle sorte qu'ils forment une paroi cylindrique mince, perforée, et dont le profil est de préférence du type à obstacles, comme précédemment. De tels tamis présentent l'avantage d'être légers, de construction rapide, tout en offrant des performances similaires à celles des tamis classiques à tôle épaisse et une grande résistance mécanique. Un tel tamis est décrit au brevet EP 354.846.

Among these, the most remarkable are:

• the arrangement of obstacles on the upstream surface of the screen, upstream of the perforations. The profiles have a succession of ribs and hollows or grooves, at the bottom of which the perforations are made. These obstacles cause pulsations during the passage of the blade which improve the yield while preventing clogging. The patents FR 1,539,846 and FR 88-10684 illustrate, for example, this arrangement;
• the realization of a sieve constituted by the juxtaposition of elements with U-shaped cross section having a bottom flat, thin and perforated. The elements are bent and assembled so that they form a thin cylindrical wall, perforated, and whose profile is preferably of the obstacle type, as previously. Such sieves have the advantage of being light, of rapid construction, while offering performances similar to those of conventional sieves with thick sheet and great mechanical resistance. Such a sieve is described in patent EP 354,846.

The present invention relates to a sieve of the thin sheet type, produced according to a new faster process, but giving it however the same resistance as that of traditional sieves and that sieves with juxtaposed elements.

The subject of the invention is a cylindrical sieve for purification or hydrodynamic classification of paper pulp in a purifier or classifier with pale of the kind bearing on the face opposite to that in front of which the blades circulate a plurality of reinforcing irons characterized in that the sheet is a sheet of thin thickness, of the order of 2 millimeters, perforated by stamping or the like.

• il comporte un seul fer enroulé en spirale ou hélice, la spirale s'étendant sur tout le corps du cylindre;
• la tôle est ondulée;
• la découpe de la feuille et son enroulement sont tels que la soudure de jonction des bords n'est pas parallèle à la génératrice du cylindre mais progresse le long du cylindre en formant une hélice;
• le tamis comporte entre deux fers une série de fentes, sensiblement parallèles à la génératrice du cylindre.

The sieve according to the invention is also remarkable for the following characteristics:

• it comprises a single iron wound in a spiral or helix, the spiral extending over the entire body of the cylinder;
• the sheet is corrugated;
• the cutting of the sheet and its winding are such that the weld joining the edges is not parallel to the generatrix of the cylinder but progresses along the cylinder by forming a helix;
• the screen comprises between two irons a series of slots, substantially parallel to the generator of the cylinder.

The invention also relates to the process for producing this sieve, characterized in that the perforations are made in two successive stages by a punching which causes only a deformation without perforation followed by a saw cut.

• les figures 1a et 1b représentent schématiquement en perspective la première étape du procédé de réalisation du tamis selon l'invention;
• la figure 2 représente schématiquement en perspective la deuxième étape du procédé de réalisation du tamis selon l'invention;
• la figure 3 est une vue schématique de profil du tamis selon l'invention muni d'un fer plat enroulé en spirale;
• la figure 4 est une vue partielle de profil du tamis selon l'invention dans une variante de réalisation;
• la figure 5 est une vue en coupe longitudinale partielle de la paroi du tamis selon l'invention;
• la figure 6 est une vue en coupe longitudinale partielle de la paroi du tamis selon l'invention dans une variante de réalisation;

In order to better understand the invention, an exemplary embodiment is shown in the appended drawing in which:

• Figures 1a and 1b schematically show in perspective the first step of the method of producing the sieve according to the invention;
• Figure 2 shows schematically in perspective the second step of the method of producing the sieve according to the invention;
• Figure 3 is a schematic profile view of the screen according to the invention provided with a flat iron wound in a spiral;
• Figure 4 is a partial profile view of the screen according to the invention in an alternative embodiment;
• Figure 5 is a partial longitudinal sectional view of the wall of the screen according to the invention;
• Figure 6 is a partial longitudinal sectional view of the wall of the screen according to the invention in an alternative embodiment;

As can be seen in the drawing, the screen according to the invention is produced by taking a thin sheet 1, of the order of 2 millimeters thick 2.

It is preferably flat but, according to the variant shown in FIG. 6, it can be wavy, this arrangement making it possible to substantially increase the filtration surface.

In a first step, the sheet 1 which is in the form of a plate, is perforated (Figure 1a). The perforations 3 are calibrated holes or slots.

Preferably the perforations are regularly distributed over the surface of the sheet so as to form precise alignments 4, 20, 21.

According to the invention, the perforations are produced by stamping or punching with a tool 5 with a sharp edge 6: the sheet is placed flat on a table 7 having recesses 8 in which the metal can penetrate under the action of the tool.

• dans une première variante le poinçonnage n'est pas traversant et ne forme qu'une déformation dont le profil présente une paroi perpendiculaire à la surface de référence de la plaque attaquée par l'outil, suivie d'une paroi inclinée; la fente est ensuite obtenue par un trait de scie au droit de la paroi verticale.
• dans une seconde variante le poinçonnage est traversant, il crève la tôle et découpe la fente dont la largeur est déterminée par la profondeur de la pénétration de l'outil. Dans cette variante on utilise comme outil un couteau à bord tranchant droit de sorte que la longueur de la fente est constant et ne varie pas selon la pénétration du couteau.

When the perforations are slots 14, these can be produced according to two variants:

• in a first variant, the punching is not through and only forms a deformation, the profile of which has a wall perpendicular to the reference surface of the plate attacked by the tool, followed by an inclined wall; the slit is then obtained by a saw cut in line with the vertical wall.
• in a second variant, the punching is through, it punctures the sheet and cuts the slot, the width of which is determined by the depth of the penetration of the tool. In this variant, a knife with a straight cutting edge is used as a tool so that the length of the slot is constant and does not vary according to the penetration of the knife.

In one as in the other of the variants the slots 14 are all parallel to each other.

When the perforations are completed the sheet is rolled into a cylinder 15 of circular section, the edges 9 joined and welded 10. Preferably the cutting of the sheet and its winding are such that the weld is not parallel to the generator of the cylinder but progresses along the cylinder forming a helix.

Then on this cylindrical body, on the side which will be the downstream side 13 during operation, flat irons 11 on edge, intended to constitute stiffening ribs.

The irons are curved and extend over at least 360 °.

In a first variant (FIG. 4) the irons 11 form closed circles, they are introduced hot by expansion and are kept tight by cooling. It's the strapping. They can also be welded.

In a second variant (FIG. 3) the irons 11 extend over more than 360 ° and develop in a helix 12 over the entire length of the cylinder 15. It is then possible to use only one iron. This iron is welded to the cylinder.

In the example illustrated, the cylinder comprises between two flat bars a single series of identical slots, the slots 14 being substantially parallel to the generator of the cylinder or inclined by a few degrees relative to said generator.

According to the invention, the slots, from one row to another can be aligned 20 (FIG. 2) along the axis of the slot or regularly offset, then forming helical alignments 21 (FIG. 3).

It is of course possible within the meaning of the invention to provide several parallel series of perforations (holes or slots) between two irons.

In addition, the bars are regularly arranged along the cylinder so that the space 16 between the bars is of constant width; in the case of a spiral iron, the pitch is constant.

• la perforation est très rapide car l'épaisseur à traverser est faible;
• les gains sur les coûts matière sont importants car la tôle est mince et les pertes de matière sont moindres car il y a moins de retrait de matière lors des perforations;
• la résistance générale mécanique du tamis est facilement contrôlable car elle ne dépend pratiquement plus que des dimensions du ou des fers plats;
• enfin le tamis est très simple et très rapide à réaliser.

This invention provides many advantages, including the following:

• the perforation is very fast because the thickness to be crossed is small;
• the savings on material costs are significant because the sheet is thin and the losses of material are less because there is less shrinkage of material during perforations;
• the general mechanical resistance of the sieve is easily controllable because it practically depends only on the dimensions of the flat iron (s);
• finally the sieve is very simple and very quick to make.

Claims (6)

1- Cylindrical sieve for purification or hydrodynamic classification of paper pulp in a purifier or classifier to pale of the kind bearing on the face opposite to that in front of which the pale circulates a plurality of reinforcing irons (11) characterized in that the sheet ( 1) is a thin sheet (2), of the order of 2 millimeters, perforated (3) by stamping or the like. 2- Sieve according to the preceding claim characterized in that it comprises a single iron wound in a spiral or helix (12), the spiral extending over the entire body of the cylinder. 3- Sieve according to any one of claims 1 or 2 characterized in that the sheet (1) is corrugated. 4- sieve according to any one of the preceding claims, characterized in that the cutting of the sheet and its winding are such that the weld (10) joining the edges (9) is not parallel to the generator of the cylinder but progresses along the cylinder forming a helix. 5- screen according to any one of the preceding claims, characterized in that it comprises between two irons (11) a series of slots (14), substantially parallel to the generator of the cylinder. 6- A method of producing this sieve, characterized in that the perforations (3) are produced in two successive stages by punching which only causes deformation without perforation, followed by a saw cut.

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