METHOD AT THE MANUFACTURE OF REFINER SEGMENTS

Abstract: Method at the manufacture of refiner segments for refiners. According to the invention, the bars of the segment are given a rough and hard surface by spark machining.

Description: Method at the manufacture of refiner segments This invention relates to a method at the manufacture of refiner segments for the mechanical processing of cellulose-containing material. The invention especially relates to a method of treating the active surfaces of refiner segments in order to provide them with a surface structure and hardness, which facilitate the processing of the cellulose material and provide it with the prop¬ erties desired. Processing of cellulose material can imply defibration of wood chips, beating of already partially defibrated chips or cellulose pulp. Apparatuses for the mechanical processing of cellulose- -containing material can be of different types, for ex¬ ample such with conically designed beating surfaces, so- -called conic refiners, or also so-called disc refiners with beating members of disc configuration. All defibration and refining in these refiners have in common that the result desired is achieved by mechanic¬ ally processing the fibre- material while it is being passed through the refiner. This processing is effected in that fibre material, after having been fed into the refiner by different types of devices, is caused by rot¬ ation forces and pressure differences to pass out of the refiner through a narrow gap between the two processing surfaces. As the rotating beating members at the mechanical proc¬ essing of fibre material are subjected to heavy wear, the members are provided with exchangeable wearing parts, so-called refiner segments, which are designed different¬ ly according to the type of work to which the cellulose material is to be subjected. The surfaces of the refiner segments can be substanti¬ ally plane or formed as a portion of a conic shell surf¬ ace. They can, for example, be designed so as to have, counted in radial direction, differently arranged zones 2,3,4 according to Pig. 1, which have different funct¬ ions in respect of processing and conveying the mater¬ ial. These zones can be provided with patterns of bars and intermediate grooves according to the Figure, but can also be entirely without pattern. The present invention relates to the designing of the processing surfaces, because it was found that, irres¬ pective of the geometric design of the refiner:.- segments, their surface structures and hardness are of essential importance for the quality of the resulting product and for the energy consumption at the refining/beating. It was observed previously that the processing surfaces are of importance in this connection. Our US-PS 4 Oil 150 also includes the- information that the surfaces should have a certain coarseness for bringing about necessary friction. In this case the coarseness was achieved by etching. The importance of the condition of the processing surf¬ aces is apparent also from our US-PS 4 039 15 where it is stated that the surfaces can be worked by etching, electrolysis or grinding. When applied in practice, however, it was found impossible to achieve a suffici¬ ent hardness of the surfaces. Among other proposals can be mentioned the one disclos¬ ed in US-PS 4 023 738, according to which the segment is manufactured of a special alloy containing titanium, which is present in the form of titanium carbide grains having a mean size of at maximum 10 microns. According to US-PS 4 372 495, the processing surfaces of the segment are provided with an abrasive consisting of silicon, aluminium oxide, silicon carbide, zirconium oxide or tungsten carbide. The material grains can have a size of between 140 micrometer and 0.25 cm. The use of such material also had been proposed previously, for example in US-PS 3 482 791. At the manufacture of refiner segments it was found, that the pattern of the segment, i.e. the dimensions of bars and grooves, and also the groove depth, is of decisive importance for the energy consumption. A report thereon is included in our SE-PS 426 294. In order to achieve the accuracy required, we have proposed to produce the • grooves by so-called spark machining. During the development work carried out by us, it was found by surprise that the problems involved with previ¬ ously known segments can be eliminated, in that the proc¬ essing , surfaces according to the present invention are provided with a coarse and simultaneously hard surface by exposing the surfaces to spark machining. The problem of achieving a high hardness of the processing surfaces of the refiner segments also has been covered previously in the literature. According to GB-PS 1 186 6l7 it is proposed to solve this problem by coating the surface with titanium carbide by means of a very troublesome technique. Prom "International Symposium on Wood and Pulping Chemistry" in Japan, May 23-27, 1983, Kano, Twamida and Sumi have reported experiments to develop a mathemetical pattern for the beating process in a refiner. The object had been a.o. to reduce the energy consumption. One measure proposed in this connection is to use refiner segments with a "grinding" surface without bars and grooves. Although the problem, on which the present invention is based and which has been described in the aforesaid patents, is known since long, and in spite of the fact that spark machining is a well-known technique, the person skilled in the art in this field has not deemed it possible to provide the refiner segments by such a_ working method with properties solving the problem. According to one embodiment of the method according to the invention, a refiner segment is provided with a pattern, which in principle can be designed as shown in Figs. 1 and 2. The segment 1 shown comprises three zones 2, 3 and 4, respectively, defined in radial dir¬ ection, where the final processing of the cellulose material takes place in the outer zone 4. The design of the bars 5 and grooves 6 appears more clearly from Fig. 2 where the width of the bars, the width of the grooves and, respectively, the depth of the grooves are designated by B, S and, respectively,D It is also important that the refiner segments are man¬ ufactured of a material, which is highly resistive to wear, corrosion and erosion. As an example of such a material, a steel material can be mentioned which cont¬ ains the alloying elements as follows: Alloying element % by weight C 0,5 - 1,7 Si 0,5 - 1,0 Mn 0,3 - 0,8 Cr 16 - 19 Ni 1,0 - 2,1 Mo 0,7 - 1,0 The steel material can also contain a certain amount of titanium, preferably 1-5% by weight, in the form of very small titanium carbide grains. The bars and grooves usually are formed in connection with the casting of the refiner segments. The beating surface of the bars thereafter is produced convention¬ ally by face grinding. It was found essential accord¬ ing to the invention, that especially the surface and edges of the bars are provided with a special structure and hardness. This is important for processing the cellulose material in the manner desired and to fac¬ ilitate the transfer of energy to the material. In view of the great stresses, to which the refiner segments are subjected during-the refining process, it is important that the surface structure suitable for the beating work has a sufficient hardness, and that this hardness extends sufficiently deep down into the material. By selecting a suitable material, refiner segments are obtained which are sufficiently resistant to wear, so that the original surface structure suitable for the beating work is maintained efficient during a sufficiently long operat¬ ing time of the segments. It was not possible to achieve this by using the con¬ ventional manufacturing technique of casting and grinding. By spark machining a structure is obtained, which in the direction of its- depth can be divided into separate zones, viz. a melting zone, a hardened or re-hardened zone, and beneath it an annealed zone, which gradually transforms to the unaffected matrix in the material. For obtaining the surface structure desired according to the invention, the parameter combination at the spark machining must be chosen in a special way. The parameters in question are impulse time, interval time, period, open circuit voltage, working voltage and current intensity. Of these parameters the impulse time must be deemed the most im¬ portant factor for determining the thickness of the diff¬ erent zones. The longer the burning time used, the greater is the depth obtained. This is illustrated by the values as follows: Impulse time Melting depth 10 10 μ 100 30 u By a suitable parameter combination a substantially higher hardness in the molten zone, but also a higher hardness in the re-hardened zone is obtained. The resulting surface roughness is of decisive import¬ ance in the present connection. In the accompanying Fig. 3 a surface structure is shown schematically, where Rme„_ι. designates the greatest depth and Rα, designates the arithmetic mean value. By combining the parameteis current intensity and impulse time, R m ma, v x and Ra„ can be varied. The thickness of the molten zone substantially is in¬ dependent of the material. At the experiments carried out for obtaining a hard and rough surface structure on the surface of the bars by spark machining according to the invention, the follow¬ ing results were obtained: Sample Current Voltage Impulse time R R intensity a max A V μs ' μ μ 1 3 270 45 4 20 2 1 270 45 3 15 3 5 270 100 6 3C 4 1 270 45 2 10 5 ± 270 100 ~ 25 The invention, of course, is not restricted to the examples described, but can be varied within the scope of the invention idea.

Claims: . . original claims 1-4 replaced by new claims 1-3 (1 page)] 1. A method at the manufacture of refiner segments intended for the mechanical processing, for example defibration or refining of cellulose-containing mater¬ ial, which segments comprise bars and intermediate groov¬ es arranged in special pattern, c h a r a c t e r ¬ i z e d i n that the bars or portions thereof are given a rough and/or hard surface by spark machining previously known per se. _> 2. A method as defined in claim 1, c h a r a c t e r ¬ i z e d i n that as material a steel material is used which contains the alloying elements as follows. c 0,5 - 1,7 % by weight Si 0,5 - 1,0 It n 0,5 - 0,8 tt Cr 16 - 19 π Ni 1,0 - 2,1 II Mo 0,7 - 1,0 It 3. A method as defined in claim " 2^ c h a r a c t e r ¬ i z e d i n that the steel material in addition contains titanium, preferably in an amount of 1 - 5 % by weight, for example in the form of small titanium carbide grains.

Inventors: PETERSON PER VIKING, PETERSON, PER, VIKING
Applicants: SCA DEVELOPMENT AB, SCA DEVELOPMENT AKTIEBOLAG
Application year: 1985
Main classification: B02C7
IPC codes: B02C7, D21D1