METAL SHEET HAVING LOW FRICTION COEFFICIENT AND LOW WAVINESS

Abstract

A metal sheet having a low friction coefficient and a low waviness. Multiple round or roughly-round small pits are distributed on the surface of the metal sheet. The diameter of a single pit ranges from 30 m to 150 m, and the overlap between adjacent pits is lower than 10%. On the surface of the metal sheet where the pits are located, the proportion of the area of pits per square millimeter of surface area is greater than 30%, and the difference between the quantities of pits in any unit square millimeter is less than 20%. By means of the proper design of surface microstructure, the friction coefficient and the waviness can be effectively reduced, thereby improving the forming and painting performance of the material.

Claims

1. A metal sheet having a low friction coefficient and a low waviness, wherein multiple round or roughly-round small pits are distributed on the surface of the metal sheet, the diameter of a single pit ranges from 30 m to 150 m, the overlap between adjacent pits is lower than 10%; and wherein on the surface of the metal sheet where the pits are located, the proportion of the surface area occupied by the pits per square millimeter is greater than 30%, the difference in the number of pits in any unit square millimeter is less than 20%.

2. The metal sheet having a low friction coefficient and a low waviness as claimed in claim 1, wherein the metal sheet is provided with the pits on one surface or both surfaces.

3. The metal sheet having a low friction coefficient and a low waviness as claimed in claim 1, wherein the overlap between adjacent pits is lower than 5%.

4. The metal sheet having a low friction coefficient and a low waviness as claimed in claim 1, wherein the overlap between adjacent pits is 0.

5. The metal sheet having a low friction coefficient and a low waviness as claimed in claim 1, wherein on the surface of the metal sheet where the pits are located, the proportion of the surface area occupied by the pits per square millimeter is greater than 50%.

6. The metal sheet having a low friction coefficient and a low waviness as claimed in claim 1, wherein on the surface of the metal sheet where the pits are located, the difference in the number of pits in any unit square millimeter is less than 10%.

7. The metal sheet having a low friction coefficient and a low waviness as claimed in claim 6, wherein on the surface of the metal sheet where the pits are located, the difference in the number of pits in any unit square millimeter is less than 5%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows the surface microstructure of the metal sheet of Example 1 of the present invention.

[0020] FIG. 2 shows the surface microstructure of the metal sheet of Example 2 of the present invention.

[0021] FIG. 3 shows the surface microstructure of the metal sheet of Example 3 of the present invention.

[0022] FIG. 4 shows the surface microstructure of the metal sheet of Comparative Example 1 of the present invention.

[0023] FIG. 5 shows the surface microstructure of the metal sheet of Comparative Example 2 of the present invention.

[0024] FIG. 6 shows the surface microstructure of the metal sheet of Comparative Example 3 of the present invention.

[0025] FIG. 7 shows the structure diagram of a drawbead tester for measuring the friction coefficient. The meanings of the symbols in FIG. 7 are: 1upper head, 2drawing arm, 3lower head, 4sample.

DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are further described in detail below with reference to the drawings and specific Examples.

[0027] It is an object of the present invention to provide a metal sheet having a low friction coefficient and a low waviness. By means of the proper design of surface microstructure, the friction coefficient and the waviness are effectively reduced, thereby improving the forming and painting performance of the material.

[0028] In order to achieve the above object, the present invention provides a metal sheet having a low friction coefficient and a low waviness, wherein the surface microstructure of the metal sheet has the following characteristics:

[0029] the surface microstructure consists of a large number of tiny pits; the overlap between adjacent pits is lower than 10%; the shape of the pits is round or roughly-round and the diameter of the pits is 30 to 150 m; the proportion of the area occupied by the pits per square millimeter is greater than 30%; the difference in the number of pits in any unit square millimeter of the metal sheet is less than 20%.

[0030] That is, in order to improve the painting effect on the surface of the material, it is necessary to design the microscopic topography of the material surface so that the surface has as low a waviness as possible on the basis of a certain roughness.

[0031] The metal sheet having a low friction coefficient and a low waviness of the present invention is further explained and illustrated below with reference to the drawings and specific Examples and Comparative Examples. However, such explanations and illustrations do not unduly limit the technical solution of the present invention.

Examples 1-3 and Comparative Examples 1-3

[0032] Examples 1-3 are hot-dip galvanized steel sheets having a surface microstructure which has the technical features of the present invention, and Comparative Examples 1-3 are hot-dip galvanized steel sheets having a common surface. The specific surface microstructure parameters of Examples and Comparative Examples are shown in Table 1 below. Since the microstructure of the Comparative Examples has random undulations, it is difficult to accurately distinguish the bosses and the pits. Therefore, it is difficult to obtain the statistics of the pit diameter, the number of pits and the proportion of the pit area for the Comparative Examples. FIGS. 1-6 correspond to the surface microstructures of Examples 1-3 and Comparative Examples 1-3, respectively.

TABLE-US-00001 TABLE 1 Proportion of Number of Microstructure Pit shape Pit diameter pit area pits Example 1 Distributed Round About 80 m 60% 130/mm.sup.2 pits Example 2 Distributed Round About 100 m 62% 110/mm.sup.2 pits Example 3 Distributed Round About 100 m 71% 90/mm.sup.2 pits Comparative Random Irregular Example 1 undulations Comparative Random Irregular Example 2 undulations Comparative Random Irregular Example 3 undulations

[0033] The roughness and waviness of Examples 1 to 3 and Comparative Examples 1 to 3 were tested in accordance with the measurement standard ISO 4287:1997. Gaussian filter was used as the filter. The sampling length was 0.8 mm for the roughness Ra and 40 mm for the waviness Wa. The filtering interval was 0.8 to 8 mm. Then, the friction coefficients of Examples 1 to 3 and Comparative Examples 1 to 3 were measured using the drawbead tester shown in FIG. 7 and compared. Specific test parameters were as follows: sample 4 was placed between the upper head 1 and the lower head 3, the pressure of the upper head 1 was 1500N; drawing arm 2 drew sample 4 at a speed of 150 mm/min and the drawing distance was 100 mm; the size of the sample 4 was 25400 mm for all cases, and the amount of oil applied to the sample was 1.0 g/m.sup.2.

[0034] The data of the test results listed in Table 2 below shows that Examples 1 to 3 having the microscopic surface topography of the material which has the technical features of the present invention have a significantly lower friction coefficient and waviness than Comparative Examples 1-3.

TABLE-US-00002 TABLE 2 Example Example Example Comparative Comparative Comparative 1 2 3 Example 1 Example 2 Example 3 Roughness 1.02 m 1.06 m 0.98 m 1.03 m 1.02 m 0.96 m Waviness 0.183 m 0.193 m 0.211 m 0.246 m 0.235 m 0.251 m Friction 0.119 0.112 0.121 0.130 0.127 0.132 coefficient

[0035] It should be noted that the above listed examples are merely specific embodiments of the invention. It is obvious that the present invention is not limited to the above Examples. Instead, there are many similar variations. All variations that are directly derived or conceived by those skilled in the art from this disclosure of the invention are intended to be within the scope of the present invention.