Welded conical grinding cutter
BACKGROUND OF THE INVENTION 
     The present invention concerns a conical grinding cutter for use in grinding, or refining, wood pulp, wherein the cutting part constituted by the mantle surface of a cone is assembled of a plurality of separate sectors. A grinder, or refiner, of this type comprises two cone-shaped cutters, the outer and the inner, of which one at least rotates, and their surface facing each other having been provided with an appropriate furrow pattern so that when the cutter is rotating the ridges following each other with a small interval will grind the wood to fine pulp. 
     In the prior art such conical grinding cutters are known which have been produced by casting in one place. The problem is then, however, that it is difficult to achieve good casting quality; therefore the reject percentage is high, the casting process expensive and the delivery time objectionably long. Causes of foundry technology alone impose major restrictions on the casting of objects of this size and shape, and it is not possible to produce a surface patterning meeting high enough quality standards. Morever, manufacturing of the pattern equipment needed in mold preparation is expensive and time-consuming. In practice, there are furthermore restrictions regarding choice of material. 
     It is also known to manufacture conical grinding cutters by welding the ridges fast to the mantle one by one. This procedure, too, is expensive and time-consuming, as anybody will realize. Morever, steel ridges of weldable material have no long service life. 
     Through the Finnish Pat. No. 54,351 is also known a conical grinding cutter assembled of separate steel sectors. By forming the conical grinding cutter of separate cutter sectors one gains the advantage that the casting process is facilitated and rather more fine-feathered cutter patterns can be cast. It is also a remarkable improvement that the casting quality improves and hereby the reject percentage goes down. In addition, the time consumed in preparing the pattern equpiment needed in mold making is short and the work is comparatively inexpensive. However, the drawback is present that the cutter sectors have been interconnected with flanges at their ends only, whereby the construction of the conical grinding cutter is not made rigid enough. We have observed that in the case of cutters requiring such high manufacturing accuracy, where the distance between the cutter surfaces facing each other is only a fractoin of one millimetre, the grinding efficiency is substantially impaired by the least yielding of an inadequately stiffened cutter sector. 
     OBJECT OF THE INVENTION 
     The object of the present invention is to achieve an improvement in respect of the drawbacks mentioned above. 
     The invention is mainly characterized in that the cutter sectors have been welded together by their sides in order to obtain a rigid juncture substantially over the entire length of the grinding cutter. In this way the construction of the grinding cutter is made rigid enough and good grinding efficiency is achieved. 
     An advantageous embodiment of the invention is characterized in that the cutter sectors of the grinding cutter have been joined with each other with a continuous weld. In this way the structure of the grinding cutter becomes tightly sealed, that is, the corrosive substance flowing within the cutter cannot through the interstices of the sectors come into contact with structures outside the grinding cutter and thereby inflict corrosion damage on them. 
     An advantageous embodiment of the invention is also characterized in that the cutter sectors of the grinding cutter have been joined together with an interrupted weld. In frequent instances a rigid enough structure of the grinding cutter is obtained with an interrupted weld, and it makes for faster assembly. 
     An advantageous embodiment of the invention is also characterized in that the cutter sectors have been made of weldable material. 
     An advantageous additional embodiment of the invention is characerized in that on the sides of the cutter sectors have been cast, or in another way produced, one or several junction pieces consisting of weldable material. The advantage is hereby gained that the cutter sectors may be cast of the material which is most appropriate for cutter material in each instance. It is furthermore characteristic that the junction pieces are provided with anchoring holes extending all the way through the piece. The junction pieces are by their action better anchored in the casting, and in this case the casting is not cooled at excessive rate by the junction pieces. It is furthermore characteristic that on the junction pieces casting lugs have been provided. The junction piece or pieces are held in their proper place during the casting process. These lugs are removed on completed casting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is in the following described in detail with reference made to the attached drawings. 
     FIG. 1 presents a section of a rotating conical grinder inner cutter of the prior art, this cutter consisting of separate cutter sectors which have been interconnected at their ends. 
     FIG. 2 presents the outer cutter sector of a static conical grinder&#39;s counter-cutter according to the invention, this sector having been cast of weldable material. 
     FIG. 3 presents the outer cutter sector of a static concial grinder&#39;s counter-cutter according to the invention to the sides of which have been cast junction pieces consisting of weldable material. 
     FIG. 4 presents the cross section of the outer cutter sector of the preceding figure. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIG. 1 is depicted a concial grinding cutter as known in the prior art, longitudinally sectioned. Weldable pieces 5 have been mounted on the ends of the cone. With the aid of these pieces, the cutter sectors 4 have been connected with the flanges 2, 3, which are rotated by the shaft 1. 
     In FIG. 2 is depicted the outer cutter section 6 of a conical grinding cutter, made of weldable material. These cutter sectors 6 are mutually joined by welding them by their sides substantially over their entire length. The cutter sector 6 carries steel ridges 7. 
     Attached to the cutter sectors depicted in FIGS. 3 and 4 during, or nearly concurrently with, the casting process are junction pieces 9 consisting of weldable material. With the aid of these junction pieces 9, the cutter sectors 8 can be joined along their sides. The junction pieces 9 carry casting lugs 10, by the aid of which the junction pieces are properly positioned prior to casting. The casting lugs are removed on completed casting. The junction pieces have also been provided with piercing holes 11, through which the casting material flows, thereby producing better anchoring to the junction piece 9. 
     It is obvious to a person skilled in the art that the invention is not confined to the examples presented above and that it may rather vary within the scope of the claims following below.