REFINING ELEMENT

Abstract: A pair of co-operating refining elements (10, 11) intended for a disc refiner with two opposed refining discs, one of which is stationary (stator) and the other one is rotary (rotor), for the working of lignocellulosic fiber material in a refining gap (12) between the co-operating refining elements (10, 11). The refining elements are provided with a pattern of bars (13-16) and intermediate grooves. Each bar is formed with a plurality of high bar portions (13, 15) and intermediate low bar portions (14, 16), counted in radial direction. High bar portions (13, 15) are located directly in front of low bar portions (14, 16) on opposed co-operating refining elements (10, 11). The length of the high bar portions (15) on refining elements (11) of the rotor exceeds the length of the high bar portions (13) on refining elements (10) of the stator.

Description: Refining element This invention relates to working and dispersing refin¬ ing lignocellulosic fiber material, preferably wood pulp containing recycled fiber. The invention, more precise¬ ly, relates to refining elements for use in a disc re¬ finer intended for said refining. A disc refiner comprises: two opposed refining discs, which are rotary relative to each ether and on one of which a plurality of refining elements are arranged. These refining elements are formed with a pattern of bars and intermediate grooves. The refining discs are arranged so that the refining elements form a refining gap, through which the fiber material is intended to pass outward from within whereby the dispersing and re- fing are carried out by the bars of the refining elem¬ ents . In the inner portion of the refining gap the refining elements are formed with coarse bars to initiate the disintegration of the material and to feed it outward to the outer portion of the refining gap where the working proper takes place. For dispersing refining normally the refiner type is used, which comprises one stationary refining disc and one opposed rotary one. This treatment, which is carr¬ ied out with preheated fiber material at high concentrat¬ ion, has the object to bring about by a lenient working a pulp with improved quality. The purpose of dispersing normally is to unbind by mechanical treatment impurit¬ ies in the form of printing ink and so-called hot- melts (plastic and glue particles) from the fibers in the pulp and to disintegrate these impurities to a sub- -visible size without affecting the fibers negatively. The freeness (CSF) of the pulp, thus, must not be red¬ uced appreciably. When conventional refining elements with substantially radial bars are used in the refiner, capacity problems can arise when an effective working of the fiber material is to be obtained. Alternatively, quality problems can arise when the capacity is increased. Furthermore, the freeness of the pulp is reduced. The tensile strength certainly can be improved thereby, but the disintegration of the impurities, the so-called speck reduction, will be relatively poor. By designing the refining elements with toothed working surfaces instead of radial bars, a lenient working with good speck reduction is obtained. The freeness of the pulp is not reduced appreciably, and the strength properties of the pulp are affected only insignificantly. According to the present invention, the co-operating refining elements are designed in a novel way by provid¬ ing them with alternatingly high and low bar portions, which results in effective speck reduction without appreciably reducing the freeness of the pulp and at the same time improving the strength properties of the pulp. In addition, a high capacity is maintained. The charact¬ erizing features of the invention are apparent from the attached claims. The invention is described in greater detail in the foll¬ owing, with reference to the accompanying drawings ill¬ ustrating an embodiment of the invention. Fig. 1 is a cross-sectional view of two co-oper¬ ating refining elements according to the invention , Figs. 2 and 3 show the pattern of the working surface on each refining element, Figs. 2-4 show the results of test runs of different refining elements. The co-operating refining elements 10,11 are intended to be positioned on each of two opposed refining discs in a refiner where one of the refining discs is stationary and the other one rotary. One type of refining elements 10 is intended for the stationary refining disc (stator), and the other type 11 for the rotary one (rotor). These co-operating opposed refining elements 10,11 define betw¬ een themselves a refining gap 12, through which the fiber material is to be passed outward from within, i.e. up¬ ward in the Figure. Each refining element 10,11 is provided with bars 13,14 and, respectively, 15,16 which extend substantially rad¬ ially across the surface of the refining elements. Alt¬ ernatively, the bars can be angled in relation to the radius of the refining elements. Each bar is formed with several high bar portions 13 and, respectively, 15 and intermediate low bar portions 14 and, respectively, 16, counted in radial direction. The bars have such configur¬ ation, that high bar portions 13,15 are located directly in front of low bar portions 14,16 on opposed refining elements. The high bar portions 15 on the refining ele¬ ment 11 of the rotor shall have a length exceeding that of the high bar portions 13 on the refining element 10 of the stator, suitably by 1,5-5 times, preferably by 2-4 times. The transisition between high and low bar portions preferably consists of inclined surfaces.. The height of the low bar portions 14,16 can be some millimeter, preferably 0,5-2 mm. According to the embodiment shown, the upper surface on the high bar portions 15 on the refining element 11 of the rotor shall form an angle f \ with the direction of the refining gap 12, i.e. the axial plane. The angle shall be such, that the height of the bar portions 15 increases radially outward. This angle ^ can vary, but preferably lies in the interval 0 to 10 . Greater angles, however, can be used. The upper surface on the low bar portions 14 of the stator can have a corresponding angle, in such a way that the height of the bar portions 14 decreases outward. The upper surface of the high bar portions 13 of the stator and, respectively, the low bar portions 16 of the rotor may possibly also form an angle with the direction of the refining gap 12 in a similar way. Due to the fact that the co-operating refining elements 10,11 are formed with alternatingly high and low bar portions 13-16, the fiber material is worked very effect¬ ively during its passage through the refining gap 12. By adjusting the refining gap, the axial distance between the bars can be changed, and at the same time the dist¬ ance between opposed inclined transition surfaces between high and low bar portions is changed. Co-operating refin¬ ing elements can thereby be set so that the tops of the bar portions work the fibers effectively and thereby improve the strength properties of the pulp, and that at the same time the inclined transition surfaces of the bar portions knead the pulp softly and force the pulp to move between the rotor and stator. The working isrmade still more effective due to the angled upper surfaces of the bar portions. At the same time as a very effective working is achieved, a high capacity is maintained because the high bar port- ions 15 on the rotor have a greater length than the high bar portions 13 of the stator. This configuration yields a high pump effect and thereby a high capacity. This applies also when the refining elements have a fine pattern, i.e. when the bars and grooves are narrow. The invention, conclusively, provides a possibility to disperse impurities effectively without appreciably reducing the freeness of the pulp, at the same time as the strength properties of the pulp can be improved and a high capacity be maintained. Example Refining elements according to the invention embodiment shown were test run and compared to refining elements with a conventional tooth-patterned working surface. The result proved that refining elements according to the invention yield a high speck reduction for a certain energy consumption and a certain reduction of the pulp freeness. A clear improvement of the tensile strength of the pulp was observed simultaneously. Moreover, with refining elements according to the invention a higher production could be maintained. The results appear from Figs. 4-6 where curve I refers to refining elements of the invention, and curve II refers to the conventional refining elements. Fig. 4 shows the speck reduction in'% for particles ^ "750 i.m as a function of the specific energy consumpt¬ ion in kWh p e r ton bone dry pulp (kWh/BDT). Fig. 5 shows the speck reduction as a function of the freeness decrease in ml CSF. Fig. 6 shows the increase in tensile strength in % as a function of the energy consumption. The invention, of course, is not restricted to the embod¬ iment shown, but can be varied within the scope of the invention idea.

Claims: Claims 1. A pair of co-operating refining elements (10,11) intended for a disc refiner with two opposed refining discs, one of which is stationary (stator) and the other one rotary (rotor), for working lignocellulosic fiber material in a refining gap (12) between the co-operating refining elements (10,11), which are provided with a pattern of bars (13-16) and intermediate grooves, c h a r a c t e r i z e d i n that each bar is formed with a plurality of high bar portions (13,15) and inter¬ mediate low bar portions (14,16), counted in radial direction, that high bar portions (13,15) are located directly in front of low bar portions (14, 15) on opposed co-operating refining elements (10,11), and that the length of the high bar portions (15) on refin¬ ing elements (11) of the rotor exceeds the length of the high bar portions (13) on refining elements (10) of the stator. 2. A pair of refining elements as defined in claim 1, c h a r a c t e r i z e d i n that the upper surface on the high bar portions (15) at least on refining ele¬ ments (11) of the rotor forms an angle (ø with the direction of the refining gap (12), and that the height of the bar portions (15) increases radially outward. 3. A pair of refining elements as defined in claim 1 or 2, c h a r a c t e r i z e d i n that the transition between high bar portions (13,15) and low bar portions (14,16) consists of inclined surfaces.

Inventors: FROEBERG PER, KANKAANPAEAE VEIKKO, MAEKIVAARA JUHA, FROEBERG, PER, KANKAANPAEAE, VEIKKO, MAEKIVAARA, JUHA
Applicants: FROEBERG PER, KANKAANPAEAE VEIKKO, MAEKIVAARA JUHA, SUNDS DEFIBRATOR IND AB, FROEBERG, PER, KANKAANPAEAE, VEIKKO, MAEKIVAARA, JUHA, SUNDS DEFIBRATOR INDUSTRIES AB
Application year: 1995
Main classification: B02C7
IPC codes: B02C7, D21D1