Abstract
A rolled stainless steel object has surface with a raised and indented pattern including a random juxtaposition of at least two types of polygons. Each of the polygons has at least three sides, and is made up of substantially parallel rectilinear scratches, having a depth of from 5 to 30 m separated by ridge lines, the axes of which are from 0.1 to 0.3 mm from each other, and a Fourier transform spectral analysis of which, carried out on a square of at least 100 mm.sup.2, shows that they have an isotropy of at least 40% between the rolling direction and the sideways direction, and two adjacent preferred angular orientations of which scratches, from among the three main preferred angular orientations thereof, are spaced apart by a minimum of 20 and a maximum of 60.
Claims
1. A rolled stainless steel object, wherein the surface thereof has a raised and indented pattern including a random juxtaposition of at least two types of polygons, each of said polygons having at least three sides, a surface area of between 1 and 9 mm.sup.2, and a difference between its smallest and largest dimensions of between 0.5 and 3 mm, each polygon being made up of substantially parallel rectilinear scratches, each separated by 15 relative to the mean orientation of the scratches, having a depth of from 5 to 30 m separated by ridge lines, and the axes of which are from 0.1 to 0.3 mm from each other, each polygon of the pattern has a reference plane, said reference plane represents the orientation of the polygon in space, the scratches have flanks, and a Fourier transform spectral analysis of which, carried out on a square of at least 100 mm.sup.2, shows that they have an isotropy of at least 40% between the rolling direction and the sideways direction, and two adjacent preferred angular orientations of which scratches, from among the three main preferred angular orientations thereof, are spaced apart by a minimum of 20 and a maximum of 60.
2. The object according to claim 1, wherein the reference plane of each polygon is inclined relative to the reference planes of its adjacent polygons, from 1 to 10.
3. The object according to claim 1, wherein the flanks of said scratches have curved surfaces and/or surfaces including unevenness.
4. The object according to claim 1, wherein said object involves a sheet, plate or strip.
5. The object according to claim 4, wherein the sheet, plate or strip, constituting a precursor of said object, is cut and/or shaped.
6. A method for manufacturing an object according to claim 1, wherein said surface having said pattern is obtained during the rolling of the object, or a precursor of said object, by the pressure of a rolling cylinder on the surface of the object or its precursor, said cylinder in turn having, on its surface, a pattern making it possible to obtain said pattern on the surface of the object.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will now be described more precisely, in reference to the following appended figures:
(2) FIG. 1 and FIG. 2, which show the surface of an unetched stainless steel sheet of the prior art, and its spectral analysis diagram, using, as reference direction, the rolling direction (FIG. 1) and the crosswise direction (FIG. 2);
(3) FIGS. 3 and 4, which show the surface of a stainless steel sheet etched in a manner not according to the invention, and its spectral analysis diagram, using the rolling direction as reference direction;
(4) FIGS. 5 to 7, which show examples of isolated polygons, belonging to etching done on a stainless steel sheet according to the invention, with their respective spectral analysis diagrams;
(5) FIG. 8, which shows a perspective view of an example surface portion of a stainless steel sheet etched according to the invention;
(6) FIGS. 9 to 12, which show top views of examples of stainless steel sheet surface portions etched according to the invention, with their respective spectral analysis diagrams;
(7) FIG. 13, which shows the surface of a reference stainless steel sheet with an unetched surface, on which a fingerprint is visible;
(8) FIG. 14, which shows, with the same magnification as FIG. 13, the surface of a reference stainless steel sheet with a surface etched according to FIGS. 3 and 4, on which a fingerprint is visible;
(9) FIG. 15, which shows, with the same magnification as FIG. 13, the surface of a stainless steel sheet etched according to the invention, and on which a fingerprint is substantially not visible.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(10) As references, FIGS. 1 and 2 show sample surfaces of a stainless steel sheet 1 rolled with stainless steel smooth work cylinders, as is typically the case, and which therefore did not have any particular etching. The surfaces of the sheet samples are themselves relatively smooth: only shallow (about 1 to 1.5 m) and very narrow scratches can be seen, oriented cleanly along the rolling direction, and their Fourier transform spectral analysis diagrams, done using a traditional method (for example, see document Techniques de l'Ingnieur, La transforme de Fourier et ses applications [Engineering Techniques, The Fourier transform and its applications], 2007, vol. AFM3, AF1440-1443), are present. In the example of FIG. 1, the analysis is done using, as reference orientation (90), the rolling direction, and in the example of FIG. 2, the analysis is done using, as reference orientation, the crosswise direction, i.e., the direction perpendicular to the rolling direction.
(11) The isotropy rate between rolling direction and crosswise direction is identical for both images, which is logical since it involves the same sheet, and is 11.6%. This is a low rate, which is normal, since no particular measures were taken in order for the effect of rolling of the sheet on the surface structure to be alleviated, this rolling being carried out in a clearly defined direction. This very low isotropy of the surface is a drawback for the visibility of fingerprints, since it favors the reflection of the light in clearly defined directions in which the fingerprint is particularly visible.
(12) Observed in the rolling direction (FIG. 1), the scratches have favored directions of 90.0, 95.5 and 84.3 relative to the crosswise direction (the 0 and 180 angles corresponding to the two directions of the crosswise direction), which are therefore identical or very close to the rolling direction.
(13) Observed in the crosswise direction (FIG. 2), the scratches have favored directions of 0.289, 5.48 and 174 relative to the crosswise direction, and which are therefore very substantially perpendicular to the crosswise direction and therefore correspond to the rolling direction. The coherence of the results of the measurements of FIGS. 1 and 2 is therefore reasonably well ensured, to within the usual measuring imprecisions.
(14) FIGS. 3 and 4 show a sheet surface etched with a pattern not according to the invention. It includes raised parts according to two interleaved regular arrays.
(15) A first array, oriented along the rolling direction, includes reliefs 2 with a height of 45 m, and a substantially elliptical section whereof, at the base, the large axis measures 1.25 mm and the small axis measures 0.85 mm. They are positioned in staggered rows, along lines separated by 1.13 mm. The section of each raised part decreases gradually along the height of the raised part, and the apices of two adjacent raised parts 2 situated on a same line are separated by 2 mm.
(16) A second array, oriented in the crosswise direction, includes raised parts 3, inserted regularly between the raised parts 2 of the first array. The raised parts 3 have a height of 30 m and a substantially elliptical section whereof, at the base, the large axis measures 0.88 mm and the small axis measures 0.57 mm. They are positioned in staggered rows, along lines separated by 1 mm. The section of each raised part decreases gradually according to the height of the raised part, and the apices of two adjacent raised parts 3 situated on a same line are separated by 2.26 mm.
(17) The spectral analysis diagram of this surface shows that its isotropy is 40.9%, which is relatively high and could be favorable in terms of absence of fingerprint visibility. However, this diagram shows only three favored directions of 16, 89.9 and 160 relative to the crosswise direction. These deviations are very significant, greater than the maximum of 60 required by the invention, and we will see that indeed, the fingerprints remain highly visible on a stainless steel surface with this etching.
(18) FIGS. 5 to 7 show the isolated polygon surfaces 4 belonging to a pattern imparted on the surface of the object, carried out according to the invention. As can be seen, these polygons 4 are, in the illustrated cases, irregular hexagons, within the limits of which rectilinear scratches 5 are arranged, which in turn are separated by ridge lines 6. The axes of each scratch 5 are separated by about 0.2 mm in the illustrated example, and according to the invention, this distance may vary between 0.1 and 0.3 mm. The depth of the scratches 5 relative to the apices of the ridges 6 is about 20 m in the illustrated example. According to the invention, it may be from 5 to 30 m. FIGS. 5 to 7 also show the Fourier transform spectral analysis diagrams of the corresponding isolated polygon 4.
(19) FIG. 5 shows a polygon 4 whereof the axis of the scratches 5 is oriented nearly parallel to the rolling direction. The isotropy rate between the rolling direction and the crosswise direction is 8.36%, and is therefore very low, reflecting a very pronounced orientation of the scratches as a whole. The main favored direction is in fact in the 99.1 direction relative to the crosswise direction, a second favored direction is in the 90 direction, and a third favored direction is in the 84.3 direction.
(20) FIG. 6 shows a polygon 4 identical to that of FIG. 3, for which the axis of the scratches is oblique (about 45) relative to the rolling direction. The isotropy rate is 4.92%. The main favored direction is in the 130 direction relative to the crosswise direction, a second favored direction is in the 136 direction, and a third favored direction is in the 123 direction.
(21) FIG. 7 shows a polygon 4 identical to that of FIG. 3, for which the axis of the scratches 5 is substantially perpendicular to the rolling direction. The isotropy rate is 7.08%. The main favored direction is in the 0.0729 direction relative to the crosswise direction, a second favored direction is in the 171 direction, and a third favored direction is in the 166 direction.
(22) FIG. 8 shows a perspective view of a portion of the surface of a sheet 1 according to the invention, the surface of which has a random juxtaposition of polygons 4 as defined above. One can see therein that the contours and the orientations of the scratches of the different polygons 4 are quite varied, such that it must be expected that the isotropy rate of the surface as a whole will be relatively high, which is confirmed by the measurements that will be seen later. One can also see therein that, according to one preferred alternative of the invention, the polygons 4 are not all situated in the same plane, and that the reference planes of two adjacent polygons are inclined 5 by 1 to 10 relative to one another. FIG. 9 shows a top view of a 400 mm.sup.2 portion of the surface of a sheet 1 according to the invention, with its Fourier transform spectral analysis diagram. The measurements of the isotropy rate between the rolling direction and the crosswise direction and preferred angular orientations are, like in FIGS. 1, 2 and 3, done on the entire depicted surface, and not, as in FIGS. 5 to 7, on isolated polygons. The isotropy is therefore substantially more pronounced, since the favored orientations of the scratches of the various polygons are quite varied: 40.3%. The scratches of the preferred orientations of the surface taken as a whole form a stack of six groups of scratches, these groups having clearly different main orientations. There is therefore no longer one favored, practically unique orientation along the rolling direction like in the reference examples of FIGS. 1 and 2. The three favored orientations are respectively at 97.0, 75.5 and 119, and are therefore quite clearly different from one another, since between two adjacent favored orientations there is a deviation of 21.5 and 22, respectively. However, the deviation between these three favored directions is significantly smaller than in the case of the reference etching, not according to the invention, of FIGS. 3 and 4.
(23) FIG. 10 shows another example surface of a sheet 1 according to the invention. Its isotropy is 53.3%, therefore even better than for the example of FIG. 7. Seven favored orientations are visible on the spectrum, the three main ones of which are separated by 21.8 and 22.2 relative to their neighbor(s), as shown by the data from the diagram.
(24) FIG. 11 shows another example surface of a sheet 1 according to the invention. Its isotropy is 50.2%. Seven favored orientations are visible on the spectrum, the three main ones of which are separated by 22.8 and 30 relative to their neighbor(s), as shown by the data from the diagram.
(25) FIG. 12 shows another example surface of a sheet 1 according to the invention. It in particular shows a large number of polygons having four sides. Its isotropy is 60.5%, therefore even better than those of the other examples shown in FIGS. 7 to 9. Seven favored orientations are visible on the spectrum, the three main ones of which are separated by 54 and 30 relative to their neighbor(s), as shown by the data from the diagram.
(26) FIG. 13 shows the smooth reference surface 7 of a sheet made from a stainless steel of type AISI 304 having undergone glossy annealing, on which a user has left a clearly visible fingerprint.
(27) FIG. 14 shows, with the same magnification as FIG. 13, the surface 8 of a sheet made from a stainless steel of type AISI 304 having undergone glossy annealing, on which a user has also left a clearly visible fingerprint, although this surface 8 has etching according to that shown in FIGS. 3 and 4. It is therefore clear that not any type of etching of the surface of the stainless steel sheet can resolve the problem of alleviating the visibility of fingerprints in a satisfactory manner.
(28) FIG. 15 shows, with the same magnification as FIG. 13, the surface 9 of a stainless steel sheet of the same type as that of FIG. 13 and observed under the same lighting conditions, the surface of which is etched according to the present invention (this is the type of etching of FIG. 12) and on which a user has also placed a finger. Here, this fingerprint is not visible as such, and is reflected only by the presence of a slightly darker zone, which is a sign of a slightly lower light reflection than on the remainder of the surface of the sheet. The aesthetic appearance of the surface 9, in particular its gloss, is therefore not substantially modified for a viewer looking at it from a typical distance.
(29) It is preferable for the flanks of the scratches 5 not to be rectilinear, but to have a curved surface and/or, better still, unevenness. In this way, the diffusion of the light leaving the scratches 5 is more random, which accentuates the desired effect of alleviating the visibility of fingerprints.
(30) The invention may apply to all types of stainless steels, irrespective of their microstructure. It is particularly interesting to use for steels that undergo a glossy annealing, and on which fingerprints are most visible. However, steels treated by traditional annealing, and for which glossiness of the surface is also obtained, may also advantageously benefit from the invention.
