[0033] like figure 1 and 2shown, a schematic horizontal and vertical cross-section, respectively, of a screening machine 100 comprising a housing 5 having an inlet 51 and an outlet 52 for the entry of the screening material suspension and the outlet 52 for To receive pulp that has been decontaminated. An outlet 53 or similar structure is provided at the bottom of the casing 5 for discharging the impurities separated from the screening material. Inside the inner chamber 500 of the generally barrel-shaped or cylindrical housing 5, a cylindrical screen basket 2 is coaxially arranged, the screen basket 2 has circular or grooved screening slots 204 for pure pulp The suspension is passed through. Inside the inner chamber 200 of the screen basket 2, a rotor 300 is provided, the rotor 300 is mounted on a central support on a shaft 381 driven by the motor 6, and the rotor 300 rotates around the vertical rotation axis a3. Ribs 382 extend radially from the rotor 300, each rib being provided with a vane 3, at the end of the rib 382 near the screen basket 2, the vane 3 can rotate through the inner surface 20 of the screen basket 2. The screening material is fed into the inner chamber 200 of the screen basket 2 through the inlet 51 under pressure. Since the shape of the rotor 300 is a paraboloid, the cross section of the inner chamber 200 is gradually compressed coaxially downwards. The pulp containing the fiberized material, which has been decontaminated, is formed into a pulp suspension under pressure and passes out through the slits 204 in the screen basket 2 into the inner chamber 500 of the casing 5, which surrounds the screen basket 2 , the suspension is discharged from the outlet 52 of the inner chamber 500 . The size of the slits 204 in the screen basket 2 is designed such that foreign particles in the screening material suspension, such as glass fragments, coarse sand, small stones, metal particles, etc., are retained in the screen basket 2, especially Adsorbed at the screening slot 204 on the inner surface of the screen basket 2 . Without suitable measures, the narrow holes 204 can be blocked and the fibrillated suspension from which impurities have been removed will be prevented from passing through these narrow holes. In order to prevent this from happening, the known blades 3 are made in the shape of an airfoil in cross section, viewed in the direction of rotation dr, due to the distance between the trailing sector of their outer surface 30 and the inner surface 20 of the screen basket 2 The gap increases, thus exerting an adsorption force on the suspension. As a result, a small portion of the suspension, which was first filtered immediately through the screen basket, or squeezed out of the screen basket, was washed again into the screen basket 2, respectively. Due to the rewashing effect, those impurities that block the narrow holes 204 are separated from the inner surface 20 of the screen basket 2 , fall into the bottom of the screen basket 2 , and finally reach the outlet 53 .
[0034] like image 3 As shown, the screening machine 100 works according to the principle of operation, that is, the figure 1 and 2 The screening machine 100 is shown upside down. The bottom of the housing 5 is provided with an inlet 51 for feeding the pulp suspension to be screened, an outlet 52 at the top for discharging the pulp suspension that has been screened to remove impurities, and a relatively high outlet 53 , for the unloading of impurities. Inside the housing 5, a rotor 300 with a conical cross-section is mounted, which is rotatable about the axis a3 with the motor 6. At the top end of the rotor 300 is provided a support disc or arm/rib 382 and extends radially in a star shape. Extending from the support disc or arm/rib 382 there is a blade support 380 pointing downwardly and supporting the inwardly projecting blades 3'. The inner surface 30' of the vanes 3' rotates around the screen basket 2, or around the outer surface 20' of the screen basket 2 with a relatively small gap. Pulp and impurities such as figure 1 and 2 The separation is carried out in the same manner as shown. image 3 The screening machine 100 shown in the known configuration has large airfoil-shaped blades 3', which, as mentioned above, have the disadvantage of high energy consumption and lack of optimal rewashing, resulting in cleaning of the screen basket 2 and removal of clogging of the narrow holes 204 The efficiency of things is very low.
[0035] Figure 4 Shown is a schematic view of a portion of the screen basket 2, which has slits 204 for the passage of the suspension. The radial gap ar between the surface 30 of the vanes 3 facing the screen basket 2 and the inner surface 20 of the screen basket 2 varies along the length of the vanes 3 . A blade 3 with an airfoil-shaped cross-section has a relatively large radial clearance arv at its leading end edge 310 and/or at its most forward starting section 31 . Between this initial section 31 of the blade 3 and its relatively narrow intermediate band 32, the radial clearance ar is reduced to a minimum value arm. From the middle section 32 back to the rear section 33, the radial clearance gradually increases, reaching a maximum value arh at the trailing edge 330. When the blade 3 rotates in the rotational direction dr, at the leading edge 310 and along the starting section 31 there is a pressure build-up, extending towards the intermediate band 32 . Only in the tail section 33 the gap between the surface 30 and the surface 20 of the screen basket 2 is increased, enabling an important suction effect to rewash the impurities. The blade 3 has a flat inner surface 3001 .
[0036] After a detailed investigation and study, it was found that the airfoil shape is not the optimal shape of the blade 3 in terms of the energy required to rotate the rotor 300, the efficiency of rewashing, and the removal of impurities from the screening slot 204. Since the prior art blade 3 with an airfoil-shaped cross-section has a front section 31 - seen in the direction of rotation dr - the clearance ar decreases as far as the section where the ribs 382 are provided ( figure 1 ), where there is a reaction of dynamic pressure on the pulp suspension, thus hindering the rotation, resulting in increased energy consumption for rotation. Moreover, only a portion of the entire blade surface 30, such as the delicate tail section 33, can obtain a rewash effect to clean the slot 204 of the screen basket.
[0037] FIG. 5 shows a cross-sectional view of a blade 3 installed and designed in accordance with the present invention, the blade 3 having a protruding outer surface 30 that faces the cylindrical shroud surface 20 of the screen basket 2 . The blade 3 is a plate-shaped structure, such as made of metal sheet or composite material, with a thickness of ms. It is more advantageous if the inner surface 3001 is designed parallel to the outer surface 30, ie the two surfaces 30 and 3001 have the same curvature.
[0038] In practice, the thickness of the blades 3 is about 5 to 6 mm, the diameter of the screen basket 2 is usually about 400 to 3000 mm, and the height is about 500 to 1500 mm.
[0039] The smaller secondary sketches in Figure 5 show three examples of optimal shapes for the front edge 310 of the blade 3, the surface ends of which have a rectangular cross-section (schematic a)) and a similar cross-sectional shape in sketch b). It has a rounded edge 3101, which is rounded to 3102 in the sketch c).
[0040] The vane 3 of the present invention is substantially different from the vane of the prior art in that the vane 3 is close to the inner surface 20 of the screen basket 2 and the gap between the surface 30 of the vane 3 and the surface 20 of the screen basket 2 is separated from the vane The leading end edge 310 gradually increases toward the trailing end edge 330, and the radial gap ar also increases from the front end to the rear end. The leading end edge 310 has the smallest radial clearance arv and the trailing end edge 330 has the largest radial clearance arh.
[0041] As shown in FIG. 5 , the radius of curvature rsk of the surface 20 of the screen basket 2 is larger than either of the two radii of curvature rf1 and rf2 of the leading section 31 and the trailing section 33 of the surface 30 of the blade 3 . In fact, it is advantageous to have the surface 30 parallel to the surface 20 near the leading edge 310 . Near the front edge 310, a tangent plane etf is drawn on the guide section 31, which tangent plane etf forms an acute angle ∝ of only a few degrees with respect to the radial tangent plane ets. This acute angle is determined by the radius of curvature rf1 at the leading edge 310 .
[0042] The radial clearance ar of the surface 30 increases continuously from the minimum clearance arv to the maximum clearance arh, due to the "pitch" of the blades 3 in the direction of rotation dr, compared to the screen basket 2, during the rewash, when the blades 3 are opposite When the screen basket 2 rotates, the suction effect that gradually has can exist in the entire span of the blade 3 in the direction of rotation dr.
[0043] According to a particular design shape, the radius of curvature rf1 of the front section 31 of the surface 30 may be smaller than the radius of curvature rf2 of the trailing section 33, forming a transition area on the intermediate zone 32 between the two radii of curvature. It is not desirable to have an edge approximately after the generatrix track of surface 30 between the firm curved leading section 31 and the weak curved tail section 33 of the surface 30 .
[0044] Modification of the degree of curvature of said curvature within the span of the vane 3 allows a favorable change in the flow conditions and a favorable change in the pressure exerted on the suspension. The curvature preferably has a cylindrical shape, but can also be elliptical or ellipsoid.
[0045] If the tangent plane etf is drawn at the guide section 31 of the surface 30 , 30 ′ facing the screen basket, or at the tip region of the front edge 310 of the vanes 3 , 3 ′, at the facing vane corresponding to the screen basket 2 3. The tangent plane ets drawn at the radial generatrix ezs of the surfaces 20 and 20' of 3' forms an angle of 0° to 15° between the two tangent planes, preferably between 0° and 8°. It is preferably between 0° and 2°, which is particularly advantageous. As a result, the defined surface 30 has better hydrodynamic properties and the suction effect is also increased. Such dimensioning also applies to the blades 3, 3' rotating inside and/or outside the screen basket 2.
[0046] Provided that the curvature at the front or guide section 31 of the surface 30 of the blade 3 adjacent to the screen basket is 5 to 20% greater than the curvature of the facing surface 20 of the screen basket 2, preferably 10 to 15%, and, It is advantageous if the curvature at the rear or trailing end section 33 of the surface 30 of the blade 3 is 0 to 9%, preferably 0 to 4% greater than the curvature of the surface 20 of the screen basket 2 .
[0047] FIG. 6 shows a schematic view of the screen basket 2 of a centripetal screening machine. The blades 3 ′ of the screening machine rotate around the outside of the screen basket 2 , and the curvature of the surface 30 of the blades 3 ′ is greater than the curvature of the outer surface 20 of the screen basket 2 Small, the protruding surface 30 ′ of the vane 3 ′ faces the outer surface 20 ′ of the screen basket 2 . The dashed line indicates that the curvature of the blade 3' may also be as "infinite" as possible in the front section 31', eg the angle ∝ at the front edge 310 may be equal to the limit value 0°.
[0048] FIG. 7 shows a rotor 300 designed according to the present invention, the blades 3 of which are offset from each other in the height direction, and are arranged meandering in a zigzag shape. In contrast, in the rotor 300 shown in FIG. 8 , the blades 3 are arranged offset from each other in the circumferential direction. The rotor 300 of the present invention shown in FIG. 9 has the blades 3 arranged along an ascending helix.
[0049] Figures 10 to 16 show in sequence the vanes 3, 3' of the invention having a trapezoidal, triangular and substantially trapezoidal overall profile. As shown in FIG. 12 , the surface 30 of the blade 3 has a strip-shaped protruding strip 308 in the shape of a vortex, which is arranged in a direction of an angle γ with the blade generatrix ezf and is substantially parallel to the bottom edge 35 . Instead of these protruding strips 308 , groove-shaped indentations can also be used on the blade 3 .
[0050] The angle ω formed by the crossing of the side edges 35 against the rotational direction dr is between 20 and 60°, preferably 25 to 50°. When the blade 3 rotates, the generally strip-shaped protruding strips 308 or groove-shaped indentations on the surface 30 of the blade 3 can induce local negative pressure eddies, which help to separate the foreign particles adhering to the screen basket 2 .
[0051] As shown in FIG. 13 , the sides 35 of the blade 3 protrude to form an obtuse angle, and the sections 351 directly adjacent to the short front edge 310 together form an angle ω. As shown in FIG. 14 , the side edges 35 of the blade 3 are designed as regular steps 352 . The graded side edges 35 increase substantially over their entire length, thus increasing the vortex effect in the pulp suspension when the blades 3 rotate.
[0052] As shown in Fig. 15, the profile shape of the blade 3 has intersecting sides 35 in its forward section, which then begins to deflect inwards approximately at the distal third of the surface 30, and then angularly outwards towards each other Two short branches extend to the rear and terminate at the rear edge 330 . As shown in FIG. 16 , the blade 3 has a tongue-and-groove profile with a short front edge 310 .
[0053] Figure 17 , 18and 19 represent schematic views of the blades 3, 3' The vanes 3, 3' are made of curved sheet metal, in particular having an outer surface 30 and an inner surface 3001 parallel to each other. like Figure 17 and 18 As shown, a base 383 is provided on the blades 3, 3'. Figure 17 The illustrated base 383 has an inwardly facing sleeve-shaped recess 385 into which the protrusion 386 of the bracket 382 is inserted. The side protrusions 387 of the bracket 382 enclose the side limits 388 of the recess 385 . The protrusions 386 and the recesses 385 are connected to each other by well-known screws.
[0054] like Figure 18 As shown, the rear section of the base 383 of the blades 3, 3' Tabs 389 and 390 are interconnected at 384 by well-known screws.
[0055] like Figure 19 As shown, the vanes 3, 3' may be screwed together at 384 to the bracket or rib 382 via a support 391.
[0056] The above-described design allows simple and easy modification of the blades 3, 3', so that screening machines fitted with blades of this type can be quickly adapted to different operating conditions.
