Comminuting discs having refiner plate bars for cutting and shredding the fibre in pulp slurry are in common use in the paper processing industry. A substantial amount of cost and time delay is involved every time a paper processing machine is down for the sharpening or replacement of the blades or edges on the comminuting bars.
It is, therefore, desirable to reduce the down time to a minimum by providing blades or edges on the bars that are self-sharpening and require replacement less often. Since friction is a major source of wear of the blades or edges, one of the methods that has been tried in the paper processing industry is to make the blades or edges of the bars from an alloy. The alloy may be hardened or very resistant to the friction incurred in the course of processing many gallons of the pulp slurry.
Eventually the wear will, however, become such as to render the blade edge no longer usable or to require re-sharpening of the edge. One way to keep the blade or edge usable for a longer period of time is to form the alloy from two materials, at least one of which is harder and/or more resistant to friction than the other. This has been tried with varying degrees of success in cutting implements by applying in one form or another such as spraying etc. an abrasive material on one of two surfaces that frictionally engage each other a material which will sharpen the edge on the other surface in the course of normal use. This works satisfactorily until the abrasive material wears away.
Another method that has been tried for producing the blades or edges is to mold them from an alloy comprised in part by a traditional metal such as steel and an alloy powder containing titanium, boron, carbon, vanadium, and the like in powder form. This does aid in producing a long lasting blade or edge but it is prohibitively expensive to mold an entire blade in this fashion. These powder alloys are metals that are ordinarily too brittle to use except in some form of alloy wherein the base metal is of a softer type. The softer metal wears away faster thereby providing the possibility for self-sharpening.