Method for reducing vibrations in web cutting blades
The invention relates to a method for reducing vibrations in revolving disc cutters used for cutting a running web. 
     The disc cutters used for cutting a running web are arranged in pairs against each other in such a manner that the web runs through between them. A cutting device usually includes several disc cutter pairs. 
     One substantial problem in web cutting is the high noise level. Noise is caused, for example, by the operating motors of the cutting device as well as by the friction between the two revolving disc cutters of a cutter pair. Further, the cutting of a web causes vibrations in the cutter discs, which gives rise to troublesome high-frequency overtone noise and increases the wear of the cutter discs. There have been attempts to reduce the harm caused by vibrations by making disc cutters with a considerably greater mass, which, however, has resulted in a substantial increase in the manufacturing costs. 
     One object of the invention is to provide an advantageous and effective way of reducing the harm caused by cutter vibration. The invention is characterized in that the disc cutters are at least partly coated with a layer having substance components with a high internal friction. By this means is achieved, without large costs, that the vibrations of the disc cutters are absorbed by the damping layer which results in a remarkable decrease in the noise level. 
     The cutters can with advantage be cup-formed or shaped so that they have a convex side and a concave side. As regards the adhesion of the layer, it is of advantage to have the coating on the concave side of the disc cutter. The adhesion may be further improved by providing that part of the disc cutters which is to be coated, with grooves before the coating is applied. 
     Tough plastic, preferably epoxy resin or rubber, mixed with metal powder can be used as a coating layer. The substance must not be too brittle, because it could then split off. In the mixture 50-95 percent by weight metal powder can be used. A suitable metal is, for example, iron, lead or any other heavy metal powder. The coating layer can be applied to the surface to be coated by casting, spraying or painting. The thickness of the coating layer can be 1-5 mm, preferably 2-3 mm. Experiments have shown that the decrease in the noise level is substantial, especially within the frequency range of 2000-16000 Hz, when a coating substance including iron powder and epoxy resin is used. Naturally, the somewhat increased mass of the disc cutter, due to the coating layer, contributes to absorb the vibration energy. However, the increase in mass per se is not great enough to have any substantial influence on the damping of the vibrations. 
     The invention also relates to a disc cutter for cutting a running web, which cutter is manufactured by applying the features mentioned above and is characterized in that it is at least partly provided with a coating layer having a high internal friction. The relation between the axial width and the outer diameter of the cutter can be 0.015-0.2. The axial width means the total depth of the disc cutter. For its attachment to a cutting device, the cutter is provided with an attachment opening, and the relation between the outer diameter of the cutter and the diameter of the attachment opening can with advantage be 2-4. 
    
    
     The invention is illustrated in the attached drawing, in which 
     FIG. 1 shows a disc cutter according to the invention viewed from its concave side, 
     FIG. 2 shows the section II--II of FIG. 1, 
     FIG. 3 shows on a larger scale the portion III of FIG. 2. 
    
    
     In the drawing, numeral 1 indicates a disc cutter made of tool steel, stellite, heat treated carbon steel, sintered carbide or any other material suitable for this purpose, the concave side of which cutter is coated with a coating layer 2 for damping vibrations induced in the cutter when cutting a running web. For obtaining a better adhesion of the coating layer the cutter is provided with grooves 3. The cutter is mounted in a cutting device by means of its central opening 4 and borings 5 for the attachment members. 
     The invention is not limited to the embodiment described, but several modifications are feasible within the scope of the attached claims.