A METHOD OF MANUFACTURING A SCREEN CYLINDER AND A SCREEN CYLINDER |
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申请号 | EP05771624.3 | 申请日 | 2005-07-12 | 公开(公告)号 | EP1774089B1 | 公开(公告)日 | 2014-09-03 |
申请人 | Aikawa Fiber Technologies Trust; | 发明人 | ASIKAINEN, Aku; | ||||
摘要 | |||||||
权利要求 | |||||||
说明书全文 | The present invention relates to a method of manufacturing a screen cylinder, and a screen cylinder that is particularly suitable for screening, filtering, fractionating, or sorting cellulose pulp suspensions of the pulp and paper making industry, or other similar suspensions. The present invention relates more particularly to screening devices of the type comprising a plurality of screen wires positioned at a small spacing parallel to each other, the plurality of screen wires forming a screening surface facing the pulp suspension to be screened and adjacent wires forming screening openings therebetween allowing an accept portion of the pulp suspension to flow therethrough. For instance, In known screening devices of this type the support elements, which form the supports for the screen wires, are formed of solid bars, mainly rectangular or round in cross section and most typically positioned perpendicular to the screen wires. Additionally, the above-mentioned The screen wires are generally fastened to the support bars by a welding process which gives rise to a number of disadvantages such as variability distortion, thermal stresses and burrs. The heat induced by the welding often causes distortion of the wires and changes in the screening opening width between adjacent wires. It is therefore difficult to get completely uniform screening openings, which means that the efficiency of the screen suffers. Today, when the desired width of screening openings may be as small as 0.1 mm, only minimal distortions (if any) are acceptable. The thermal stresses and the burrs may also lead to failure in operation due to the loading on the screening device in the user's process. Such loading may be either in the form of a constant load or a cyclic loading giving rise to failure by fatigue. Burrs may also catch fibers of the suspension, leading to gradual clogging of the screen or filter, or the formation of so called "strings" which are very detrimental in the user's process. It has also been suggested, e.g. in The above difficulties, among others, tend to result in a poor quality of the screening or in mechanical weaknesses or in high manufacturing costs (for instance, the keyhole clamping needs a very accurate dimensioning of the keyhole groove), it is therefore an object of the present invention to minimize the above-mentioned drawbacks and provide an improved screen cylinder and an improved method of manufacturing such. However, since the use of the keyholes in the support bars, or in the support rings, ensures that the distance between the adjacent screen wires is substantially constant, it should be studied if there are reliable and simple ways of securing the screen wires in the keyhole grooves in such a manner that the wires would not be able to move in the groove. The groove is of the keyhole construction, i.e. machined either entirely inside the support element, or ring or bar, or machined such that the keyhole is open at one side of the support element or bar or ring, the wire is able to move only in the direction of its axis. In other words, the keyhole either clamps the wire substantially tightly, or allows the wire to be slid into the keyhole in the direction of the axis of the wire. Thus it is clear that the keyhole prevents the screen wire from moving in the direction of the pressure pulses created during the screening. It is thereby also an object of the present invention to provide an easily manufactured and assembled screen cylinder without thermally inducing distortion of the screen wires. It is also an object of the present invention to provide an improved strong screen cylinder with accurate and consistent screening openings, i.e. screening slots. It is thereby further an object of the present invention to provide an improved method of manufacturing a screen cylinder, so that uniform screening openings, i.e. good tolerances, are provided, whereby slots with very small widths may be manufactured. It is further an object of the present invention to provide an improved screen cylinder with the minimum of burrs or other protruding elements causing accumulation of fibers on upstream side surfaces of the support rods. In accordance with another preferred embodiment of the invention the support elements are in the form of individual rings arranged at an axial distance from each other. At least one of the support rings is heat-treated such that it bends and clamps the screen wires in openings/grooves in the support ring. A characterizing feature of the method of manufacturing a screen cylinder, said screen cylinder being formed of at least a number of screen wires leaving a screening slot therebetween, and of substantially circular support rings, said support rings having openings/grooves into which said screen wires are installed, is
A characterizing feature of the screen cylinder, said screen cylinder being formed of at least a number of screen wires with a screening slot therebetween, and of substantially circular support rings, said support rings having openings/grooves in which said screen wires are installed, is that at least one of said support rings is bent by heating only one lateral face of said ring so that the ring thermally expands unevenly, and allowing said ring to cool down, whereby said ring retracts unevenly, clamping the screen wires in said openings/grooves. The other characterizing features of the invention will become apparent from the appended claims. In the following the method of manufacturing a screen cylinder and a screen cylinder will be explained in a more detailed manner with reference to the accompanying drawings of which
A common way of fastening the screen wires to the support elements is to use in the support elements 20 substantially transverse grooves or openings into which the screen wires 10 are inserted. A preferred way, but of course not the only way of manufacturing a screen cylinder in accordance with the present invention is such that the support elements 20 in the form of circular rings with appropriate keyhole or dovetail grooves or corresponding openings are attached to a jig. Next, screen wires 10 are pushed through the grooves/openings 30 in the support elements 20. Preferably, the grooves or openings in all the elements/rings are alike. After all the screen wires 10 have been inserted in the grooves/openings 30 of the support elements 20 the screen wires are fastened so that they cannot move in the direction of their axis any more. This is performed by means of heating at least one support element 20 via its one face 25. In other words, the heating is performed unevenly, on one lateral side of the support ring only. The result is that the lower face of the support ring in This kind of heat treatment does not necessarily have to be performed for all support rings of a screen cylinder but, naturally, for at least one of them. However, it is preferable to subject all support rings to the heat treatment as in that case the minor gaps between the wires and the walls of the openings/grooves are removed. A preferable way of treating the support rings is to first position the screen cylinder, after all the wires are inserted into grooves of all support rings, on rolls. Then rotate the cylinder slowly, and heat one face of one support ring at a time so that the temperature of the support ring rises locally and temporarily to between 450 and 900 degrees. The heating has to be temporary so that the characteristics (mainly the corrosion resistance) of the stainless steel do not, however, change (changing the characteristics needs hours, whereas the heat treatment of the invention takes only minutes). In order to be able to heat a very limited area of the surface of the support ring, preferably a welding torch is used either manually or automatically. Also, it is worth consideration if the screen wires need to be covered with some kind of heat insulation so that they will not be heat-treated, too. A preferable heat shield is a strip of metal positioned between two adjacent support rings on screen wires before starting the heating. It should be understood that the above is only an exemplary description of a novel and inventive method of manufacturing a screen cylinder. The above should not be understood as limiting the invention by any means but the entire scope of the invention is defined by the appended claims only. |