GB674446A - Improvements in or relating to knives - Google Patents

Abstract

674,446. Making knives. BISS, R. Nov. 7, 1950 [April 18, 1950], No. 9481/50. Class 83 (ii). [Also in Group VIII] A method of making a steel knife blade 10, e.g. a band-knife or cutting rule, consists in effecting localized heating of one edge of a hardenable steel strip having a thickness of from 20 to 160 thousandths of an inch and a hardness not exceeding 38 Rockwell C and quenching the edge so as to effect hardening to diminishing degrees of hardness from the edge towards the body of the blade, and subsequently grinding bevels to such an extent as to produce a blade in which the crystalline structure of the bevelled part becomes of the same type as that of the body of the blade before passing the plane of junction 15 of the body with the bevels, e.g. at the plane 13. The crystalline structure at the extreme cutting edge 16 of the bevelled part is of the same type as that of a piece of steel of the same composition hardened to between 42 and 63 Rockwell C while the body of the blade has a hardness between 60 Rockwell B and 38 Rockwell C. The knife blade may be made from plain steel or alloy steel with a carbon content of between 0.5 and 1.4 per cent. Secondary bevels 30 may be provided to remove material of insufficient elongation, i.e. in a case where the position of the planes 13, 15 is transposed to 130, 150 respectively. In one method of making the blade, a strip 10, Fig. 5, is fed between watercooled blocks 34, 35, a small part of the protruding edge 11 of the blade is heated by a flame from a burner pipe 40, and the edge is cooled and quenched by the parts 41 of the blocks which extend over the edge of the strip. If desired, quenching may be effected by jets of cooling media applied adjacent to the blocks 34, 35. The strip is then ground to produce the bevels. Preferably, the hardening is effected from the edge widthwise of the strip to a depth not exceeding four times the thickness of the strip. The feed rollers 32, 33 may be used to pre-stretch the edge of the strip to be hardened. In another method of quenching, Fig. 6 (not shown), the edge of the strip to be hardened is contacted by a cooling block which has the effect of producing a head on the edge of the strip, Fig. 8 (not shown). In a further method, both edges of a wide strip, Fig. 9 (not shown), are hardened and the strip is then cut to form two strips each having a hardened edge. In a still further modification, Fig. 7 (not shown), the strip has its edge passed between two pairs of spaced cooling blocks connected electrically.