Side trimming method

Abstract

The present invention relates to a method for side trimming a moving steel strip along a cut, comprising: i. a heating step, during which the cutting line is heated to a temperature above Ac1; and ii. a trimming step, during which the steel strip is mechanically cut along the cutting line at a temperature above Ac1.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for trimming steel strip. [Background technology]

[0002] Side trimming refers to the cutting of the sides of a material. In steel production, this operation is usually performed on steel strip after pickling or annealing in a cold rolling line.

[0003] This cutting method has several advantages. First, it allows for a uniform width of the steel strip depending on the product application. Second, it ensures edge quality by eliminating irregular defects on the steel strip edge caused by upstream processes.

[0004] As shown in Figure 1, side trimming is performed by a cutting unit 1 equipped with a pair of trimming knives, an upper trimming knife 2 and a lower trimming knife 2', on either side of the steel strip. The trimming knives, also known as rotary knives, have a disk shape and are configured to rotate in response to the movement of the steel product. The knives generally have a thickness ranging between 20 mm and 40 mm.

[0005] The pair of knives form a shear section defined by two parameters: gap "a" and overlap "b." The gap is the horizontal distance between the two knives, and the overlap is the vertical distance between the top of the lower knife and the bottom of the upper knife.

[0006] Steel products are cut by shearing and tearing at their edges as they pass through the trimming knives. This operation causes wear and tear on the trimming knives, especially on their edges. Unfortunately, worn trimming knives can develop defects such as cracks and / or burrs. This is why worn trimming knives are periodically replaced with ones in good condition. However, this replacement requires the line to be shut down, thus reducing line productivity.

[0007] Therefore, in order to improve the productivity of the line, it is necessary to extend the life of the trimming knife.

[0008] EP 3085465 proposes adding a laser to the cutting unit, i.e., in front of the trimming knife, to preheat the part of the steel product to be cut to a temperature of 400-600°C. This process allows the temperature increase to reduce the yield strength of the steel strip.

[0009] The patent specifies that the temperature of the cut portion must not be below 400°C, otherwise the yield stress will not be reduced sufficiently and it will be impossible to reduce the shear load.

[0010] The patent also discloses that the temperature of the cut portion should not exceed 600°C, otherwise detrimental changes will occur to the material due to transformation after cooling. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent No. 3085465 Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for extending the life of trimming knives used in cutting steel strip. [Means for solving the problem]

[0013] The present invention provides a method for side trimming a moving steel strip along a cutting line, comprising: i. a heating step in which the cutting line is heated to a temperature above Ac1; ii. A trimming step in which the steel strip is mechanically cut along the cutting line at a temperature above Ac1; The present invention relates to a method comprising:

[0014] The cutting line refers to the portion of the steel strip that is subjected to a mechanical cut, where shear and tear forces are applied in the trimming step.

[0015] Ac1 represents the critical temperature at which pearlite transforms to austenite during heating, which can be defined by the following equation by Andrew:

[0016] Ac1[℃]=723-10.7Mn-16.9Ni+29.1Si+16.9Cr+290As+6.38W During the ceremony, Mn, Ni, Si, Cr, As and W are the contents of the corresponding elements in weight percent.

[0017] In contrast to the teaching of EP 3085465, in the present invention the cutting line is heated to a temperature above 600° C., ie above Ac1.

[0018] Surprisingly, we have found that as long as the temperature during trimming is greater than Ac1, transformations after cooling are not detrimental. Although some hard phases would certainly be expected to form on cooling, such phases are inherently brittle. [Brief explanation of the drawings]

[0019] [Figure 1]1 is a diagram already mentioned above and shows a shearing device as known in the prior art; [Figure 2] 1 is a side view of one embodiment of a shearing device according to the present invention. [Figure 3] FIG. 3 is a top perspective view of the embodiment of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] Preferably, the steel is an advanced high strength steel (AHSS) having a tensile strength of at least 500 MPa. The AHSS family includes dual phase (DP) steels, high ductility dual phase (DPHD) steels, complex phase (CP) steels, complex phase high ductility (CPHD) steels, martensitic (MS) steels, transformation induced plasticity (TRIP) steels, hot forming (HF) steels and twinning induced plasticity (TWIP) steels.

[0021] Preferably, the strip steel is not press hardened steel strip.

[0022] Preferably, heat is applied to the top and bottom surfaces of the strip.

[0023] Alternatively, heating is applied to the top or bottom surface. In this embodiment, the surface opposite the heated surface is indirectly heated by heat transfer.

[0024] Preferably, no grooves are formed during said heating step, meaning that the application of heat does not lead to the formation of grooves at the locations of the cutting lines.

[0025] Preferably, in the heating step, the cutting line is heated to a temperature in the range of Ac1+10° C. to Ac3. Even more preferably, in the heating step, the cutting line is heated to a temperature in the range of Ac1+30° C. to Ac3.

[0026] Ac3 represents the final critical temperature at which free ferrite completely transforms to austenite during heating, which can be estimated by the following formula:

[0027] Ac3[℃]=910-203C 1 / 2 -15.2Ni+44.7Si+104V+31.5Mo+13.1W-30Mn-11Cr-20Cu+700P+400Al+120As+400Ti, During the ceremony, C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As and Ti are the contents of the corresponding elements in weight percent.

[0028] Preferably, in the heating step, the cutting wire is heated to a temperature above Ac3, and in the trimming step, the cutting wire is mechanically cut at a temperature above Ac3. More preferably, the cutting wire is heated to a temperature above Ac3+10°C. Even more preferably, in the heating step, the cutting wire is heated to a temperature above Ac3+30°C.

[0029] Preferably, said heating is performed by focusing a laser beam onto said cutting line, and even more preferably said laser beam produces a spot that is controlled to have a circular, linear or elliptical shape.

[0030] Preferably, the side trimming is performed after a pickling operation in a cold rolling line. Preferably, the side trimming is performed after an annealing treatment.

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a side trimming device and a side trimming method for a moving steel strip according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0032] As shown in FIG. 3, the claimed method can be performed by a side trimming device 10, which includes: a laser processing unit 11 capable of irradiating a cutting line 13 of a conveyed steel strip S with a laser beam 12 so as to heat the cutting line 13; - a cutting unit 14 installed around the steel strip transport path, capable of trimming the sides of the transported steel strip by mechanical cutting.

[0033] In the heating step, as shown in FIG. 2, the laser processing unit can irradiate the upper and lower surfaces of the steel strip with a laser beam along the cutting line.

[0034] In this embodiment, the laser processing unit includes a laser oscillator capable of generating a laser beam 12 and an optical focusing head capable of focusing the laser beam on the steel strip being transported. The laser beam 12 generates a spot 15 having the circular shape of the steel strip.

[0035] In the trimming step as shown in Fig. 3, the steel strip S is mechanically cut along the cutting line 13 by a cutting unit 14. As shown in Fig. 2, the cutting unit 14 includes an upper trimming knife 14a disposed above the steel strip conveying path and a lower trimming knife 14b disposed below the steel strip conveying path, i.e., the steel strip S. As shown in Fig. 3, the cutting unit 14 may also include a stand 14c that rotatably supports the upper and lower knives.

Claims

1. 1. A method for side trimming a moving steel strip along a cutting line, comprising: i. a heating step in which the cutting line is heated to a temperature above Ac1; ii. A trimming step in which the steel strip is mechanically cut along the cutting line at a temperature above Ac1; A method comprising:

2. 2. The method of claim 1, wherein the steel is an advanced high strength steel having a tensile strength of at least 500 MPa.

3. 3. The method according to claim 1, wherein the heating is performed by focusing a laser beam on the cutting line.

4. The method of claim 3 , wherein the laser beam produces a spot that is controlled to have a circular, linear, or elliptical shape.

5. 5. The method according to claim 1, wherein in the heating step, the cutting line is heated to a temperature in the range of Ac1+10°C to Ac3.

6. 6. The method of claim 5, wherein in the heating step, the cutting line is heated to a temperature in the range of Ac1+30° C. to Ac3.

7. 7. The method according to any one of claims 1 to 6, wherein the strip steel is not a press-hardened steel strip.

8. 8. The method of any one of claims 1 to 7, wherein the side trimming is performed after a pickling operation in a cold rolling line.

9. 8. The method according to claim 1, wherein the side trimming is performed after an annealing treatment.

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