JPH0532076B2 - - Google Patents

Description

Claim 1: A razor blade having a stainless steel cutting edge tip, the shape of its cross-section up to a distance of 40 micrometers from the distal edge is determined by the equation W = ad ^a , where: W is the thickness of the tip (in micrometers) at a distance d (in micrometers) from the distal edge of the blade, a and n
A razor blade, characterized in that: is a constant, a is a proportionality coefficient not greater than 0.8, and n is a power exponent having a value in the range from 0.65 to 0.75.

2. The razor blade of claim 1, wherein at least the tip of the blade is modified to a material having a higher yield strength than stainless steel, wherein the width W obtained from the equation is said yield strength of said razor blade is reduced in inverse proportion to the square root of the ratio of said yield strength to that of stainless steel.

3. The razor blade of claim 1, wherein the tip of the cutting edge is modified by being coated with a material having a yield strength greater than stainless steel, wherein the cross-sectional shape of the tip is defined by the equation W〓
determined by 1/√ma·d ⁿ , where m = the ratio of the yield strength of the hard coating to the yield strength of stainless steel, and W also represents h as the thickness of the coating (micro A razor blade that satisfies the equation W ³ 〓(W−2h)a ² d ²ⁿ .

4. The razor blade of claim 1, wherein the tip of the blade is faceted at a distance between 40 micrometers and 100 micrometers from the distal lip, the facets extending from 7° to 100 micrometers. A razor blade, characterized in that it converges towards said edge at an included angle of up to 12° and preferably in the range from 9° to 11 1/2°.

TECHNICAL FIELD This invention relates to razor blades, and more particularly to cutting edge shaping.

The invention generally resides in a razor blade having a cutting edge whose cross-sectional shape within the first 40 micrometers measured from the distal edge is determined by the formula W = ad ⁿ . where d is the distance from the tip (in micrometers), W = width (i.e. thickness) of the tip at a given distance d (in micrometers), a is the proportionality factor not greater than 0.8, and n
is a power exponent with a value less than 0.75, and from 40 micrometers to 100 micrometers from the terminal edge
The included angle between the tip facets within the micrometer zone is in the range from 7° to 14°, preferably from 9° to 11 1/2°.

For stainless steel blades, n ranges from 0.65 to 0.75 and a ranges from 0.70 to 0.80.

Blades with these tip features were found to have good warpage in comparative warpage tests, but were strong enough to provide a reasonable useful life.

BACKGROUND OF THE INVENTION In order to gain a proper understanding of the features of the present invention, it is convenient to describe and illustrate the background prior art in some detail. In the accompanying drawings: Figure 1 is a highly enlarged view of a typical or average shaped blade tip;

Figure 2 explains the principle of "chord-width" measurement,
It is a diagram of the shape of the tip.

Figure 3 is a very rough depiction of facial whisker amputation.

Figures 4 through 7 are cross-sections of various blades currently commercially available from various manufacturers.

Figure 8 is a view similar to Figures 4 to 7 of the tip configuration described in British Patent Specification No. 1465697;

The cutting edge of a razor blade is sharpened by grinding successive pairs (usually three) of different included corner facets onto a strip of steel by a suitably placed grinding wheel. Ru. A cross-section of such a lip is shown in FIG. 1 with typical values of dimensions and angles, and is conventionally described as a "three-facetted lip." While the last pair of facets is being ground (this step is commonly referred to as "sharpening"), the deflection of the strip in the sharpening machine is due to the mechanical force between the steel and the abrasive grains of the grinding wheel. Together with the interaction, it creates a final facet that is not normally flat but slightly convex. The curvature is a function of the type of steel and grinding wheel used, as well as the adjustment parameters of the grinding machine. Because of this convexity of the last facet, the cross-section of the blade tip in this zone is conventionally called "Gossick-arch". Because of the curvature,
Since this part of the tip of the blade cannot be precisely determined geometrically by a single parameter, the shape can be determined by determining the width of the ``tip'' or ``chord'' at various distances from the edge. It usually represents a characteristic. One alternative method is to apply mathematical equations to the shape of each half of the cross-section of the facet. These methods are illustrated in FIG.

In use, the razor blade is held in the razor at an angle of about 25° and the edge is brought into contact with the skin, and when the edge meets the beard it gradually enters and cuts it, aided by the cutting action. Like, moved over the face. Whiskers (on average about diameter
It is believed that the cut (100 micrometers) is pressed against the facets of the blade far from the facial skin surface to penetrate only about half the diameter of the beard. At this point, the whiskers can curve and tighten away from the blade to reduce the cutting force. Resistance to push through the reaction between the whisker and the blade facets therefore only occurs in the first approximately 50 micrometers of the blade tip from the lip, and the geometry of the blade tip in this zone seems to be the most important from a cutting point of view. This is shown in FIG.

It is clear that reducing the included angle of the facets correspondingly reduces the resistance to successive penetration of the blade tip into the whisker. However, if the angle involved is made too small, the strength of the blade tip will not be able to withstand the bending forces generated at the edge during cutting well, and the tip will deform plastically (or due to the mechanical (by their nature, they are brittle and break) and are permanently damaged, resulting in poor subsequent cutting performance, i.e., the edges become "dull."

Estimates of the magnitude of the bending stress applied during whisker cutting were made in order to design a suitable shape for the blade tip that is strong enough to prevent failure caused by such bending. Knowing these values and the yield strength of the steel from which the blade is made,
The minimum dimensions of the tip can be calculated. The stress applied during cutting appeared to result from the viscoelastic flow of dense whiskers past the tip of the blade.

Currently manufactured blades have tip geometries of some dimension less than these minimums, and have a normal shaving life (on average, for blades made from conventional razor blade stainless steel) It is known that the edges become dull due to bending within 10 days).

By carefully controlling the tip geometry of a specific zone from 0 micrometers to 40 micrometers from the lip, Applicants have determined that the overall cross-section has a strength suitable for resisting bending failure of the lip. so that cutting performance and warpage satisfaction are improved while maintaining satisfactory durability.
I just discovered that it can be made smaller.

The blade tip shapes of various manufacturers currently on the market are shown in Figures 4 to 7, and Figure 8 shows the blade tip shape described in British Patent No. 1465967. .

The shapes of the tips of these known blades are shown in Figures 10 and 1.
A comparison is made with the preferred blade tip shape of the present invention in Figure 0A.

In one form of the invention, the cross section of the tip of the blade is
The three facets are first narrowed by grinding to a contained corner smaller than that shown in FIG. This has a narrower cross-section throughout;
And importantly, create a blade tip with a narrower cross-section, especially at distances from 0 micrometers to 40 micrometers from the edge, which are required during whisker breaks. Such edges are too weak to withstand stress during warping well and must be further modified. This is accomplished by adding a fourth sharpening step. It is carried out using rotating interlocking discs or spirals of leather or synthetic leather (commonly called "strops") with an abrasive material applied to the periphery. The sharpened blade passes between the strops, which polishes the facets, removes a small amount of steel from their surfaces, and changes the dimensions of the "Gothic arch". This stage is called "sharpening". The flexibility of the strop's leather allows it to somewhat conform to the tip of the sharpened blade, while the abrasive strop increases the curvature of the last facet near the edge, thereby imparting a shape to the far facets. The effect is small.

When the blade is sharpened with a suitably reduced contained corner of a facet and then suitably honed, the shape of the tip is that of a traditionally sharpened rim with the width of the string near the rim. It has been found that the width of the strings further from the lip remains smaller than that of the conventionally sharpened lip, while being varied to become larger. This makes the tip of the blade closer to the edge stronger than normal so it can better resist the bending stress applied to it during beard cutting, while the smaller part further from the edge will not get wedged in during beard cutting. exhibits less resistance, thus making cutting easier.

The radius of the last tip of the lip is less than 1000 Å, and preferably 500 Å, as described for example in patent specification no. 1378550 (US 3761374).
It should be like the conventional one, with a smaller average value. That is, it must be within the normal range of conventionally sharpened edges.

DISCLOSURE OF THE INVENTION Blades according to the present invention were found to have superior shaving performance when compared to conventional blades in reference shaving tests.

One shape of the blade according to the invention and the manner in which it is formed is explained in detail below with reference to FIGS. 9, 10 and 11 by way of example.

FIG. 9 is a schematic diagram of the leather sharpening operation of the tip of the blade.

10 and 10A show the shape of a blade tip according to the invention compared to the known blade tip shape shown in FIGS. 4 to 8. FIG. Figure 10A shows the first
This is a detail enlarged from Figure 0. and FIG. 11 is a graph of chord width "W" at different distances "d" plotted on a logarithmic scale.

A stainless steel razor blade strip having a nominal composition of 13% chromium and 0.6% carbon was hardened and tempered by conventional methods to produce the three-facet configuration of the edge shown in FIG. sharpened by grinding and sharpening, but with included corners that are smaller than those traditionally produced. The blade, like a conventional abrasive sharpener, is passed between a rotating strop of synthetic leather with a fine alumina abrasive on its surface, where it is cut into a corner set in the strop (see Figure 9). The included angle between their tangents at the intersection of the strops (as shown) ranged from 30° to 34°. The facets have a metal coating of an alloy of chromium and platinum (applied by US Pat. No. 3,829,269) with an overcoat of fluorinated hydrocarbon material (as described in British Patent No. 906,005).
It was equipped with

Methods of grinding, sharpening, and sharpening are well known in the art, but less conventional methods may be used, such as forming strips between suitably shaped dies or rollers, or electrolytically or chemically forming the strips. It will be appreciated that deformation by or by ion bombardment can be used to sharpen the tip.

The cross section of the blade tip was measured using optical interferometry. The blade is placed under the objective of a metallurgical microscope fitted with a Michelson interferometer and viewed at approximately 1000x magnification. The interferometer is adjusted to produce fringes oriented perpendicular to the edge of the blade. The blade is tilted at an appropriate angle so that the stripes are moved to reveal the condition of the blade facets. The spacing of the stripes is adjusted so that the movement of the stripes can be easily measured at various distances from the edge. Knowing the angle of inclination, the shape of the tip is calculated from the sum of the movements of these stripes measured at corresponding positions on each side of the blade.

The results of these measurements are shown in Figure 10, where the preferred blade tip cross-sectional extent over the first 40 micrometers is indicated by the darkly shaded band, and the known blade tip cross-sectional extent is It is indicated by a band containing a cross-section line.

In this particular example, the width W of the string at a distance d from the terminal lip was as follows:

dW (Microme Ai Hajime)