Metal tools and implements – making – Blank or process – Cutlery
Patent
1998-01-06
2000-08-29
Rachuba, M.
Metal tools and implements, making
Blank or process
Cutlery
30350, B21K 1100, B26B 900
Patent
active
061091383
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to knife blades and to a method of their production.
It has long been known that the surface hardness and wear resistant properties of metal objects can be enhanced by the provision of a hard surface on the metal objects. Thus it is known to generate a carbide and/or nitride enriched or transformed surface, by an appropriate heat treatment, and also known to provide a hard surface coating such as by carburising or nitriding, chemical or physical vapour deposition, electroplating, plasma arc spraying, and other processes.
When considering a knife blade, providing a hard surface particularly at the cutting edge, is difficult to put into practice by any of the techniques outlined above, as a consequence of the very thin sections of blanks ordinarily employed in knife blade construction, and the acute angle to be found at the cutting tip. To take a finished enriched, or transformed hard surface layer, there is the inevitable depletion of carbon from the body of the blade, leaving a blade of thin section with insufficient strength. With surface coatings with a finished blade the relatively small included angle formed at the cutting edge is such that there is an inevitable build-up of coating material at the actual cutting tip and which has a major adverse effect on the sharpness of the blade.
Attempts have been made hitherto to apply a hardened surface to a knife blade such as by a diffusion heat treatment and by vapour deposition of carbides or nitrides. In one known form of construction there has been the treatment of a tapered blank followed by a single wetting or grinding to form a single edge ground or chisel cutting edge that puts the cutting edge in line with one side face of the blank. When subjected to recognised edge testing procedures, such knives have demonstrated no significant improvement in their cutting characteristics in comparison with untreated blades of the same configuration.
Improvements of considerable note have been achieved where a knife blade comprises a V-shaped cutting edge formed on a blank and such that the cutting tip lies substantially centrally of the width of the blank, one side face of the V-shaped cutting edge being provided with a coating of a material harder than the material of the blank, the actual cutting edge being formed wholly of the harder material. EP 92908829.2 discloses a method of forming a blade where a blank is first ground with one face of the V-shaped edge, the ground face is then provided with a hard coating, and the blank is then ground with the other face of the V-shaped edge. EP 93303062.9 improves on this by providing a hard coating having a columnar crystal structure that extends away from the surface of the blank and to the outer face of the coating.
SUMMARY OF THE INVENTION
The object of the present invention is to provide still further improvements in the cutting and edge retention characteristics.
According to the present invention, a knife blade comprises a cutting edge formed on a blank, one side of the edge being provided with a coating formed by a particulate material in a matrix, the matrix being softer than the particulate material, and the coating being such that a considerable number of the particules project from the matrix in the vicinity of the cutting tip of the blade edge, to form the cutting tip.
Preferably, the cutting edge of the knife blade is of generally V shape, and the coating of particulate material and matrix provided on one side only of the V-shaped edge. Thus, a first face of the edge may be ground and coated, and following that, the second face of the edge is ground. Equally, both of the first and second faces of the V-shaped edge can be ground, one side only of the V-shaped edge being provided with a coating, the uncoated side of the V-shaped edge being re-ground after coating has been applied. The generally V-shaped edge may be formed by plunge or flat grinding to both sides, edge grinding to both sides, hollowgrinding to both sides, or the edge may be formed by one g
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Corresponding Preliminary Examination Report, International Application No. PCT/GB 96/00752, Jan. 30, 1997.
Choi Stephen
McPherson's Limited
Rachuba M.
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