Side trimming method

Abstract

The invention relates to a method for the side trimming of 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; and ii. A finishing step in which the steel strip is mechanically cut along the cutting line at a temperature higher than Ac1.

Description

Technical Field

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

[0002] The side trimming process refers to cutting the sides of a material. In steel manufacturing, this operation is typically performed on a steel strip that has undergone a pickling operation or an annealing treatment in a cold rolling production line.

[0003] This cutting has several advantages. First, this cutting allows for a uniform width of the steel strip according to the product application. Second, this cutting ensures the edge quality by removing irregular defects caused by upstream processes on the strip edges.

[0004] As Figure 1 illustrated, the side trimming is accomplished by a cutting unit 1 that includes a pair of trimming knives, namely an upper trimming knife 2 and a lower trimming knife 2', located on each side of the steel strip. The trimming knives, also referred to as rotary knives, have a disc shape and are configured to rotate according to the movement of the steel product. The knives typically have a thickness between 20 mm and 40 mm.

[0005] This pair of knives defines a shear defined by two parameters: the clearance "a" and the overlap amount "b". The clearance is the horizontal distance between the two knives, and the overlap amount is the vertical distance between the highest point of the lower knife and the lowest point of the upper knife.

[0006] The steel product is cut by being sheared and torn at the edge portion by passing through the trimming knives. This operation causes wear and damage to the trimming knives, especially to the edge portions of the trimming knives. Unfortunately, degraded trimming knives may produce defects such as cracks and / or burrs. This is why it is necessary to regularly replace the degraded trimming knives with well-conditioned trimming knives. However, this replacement requires stopping the production line, thus reducing the production line productivity.

[0007] Therefore, there is a need to extend the life of the trimming knives in order to improve the production line productivity.

[0008] EP 3 085 465 proposes adding a laser in front of the cutting unit, i.e., the trimming knives, to preheat a portion of the steel product to be cut to a temperature between 400°C and 600°C. This process allows for a reduction in the yield strength of the steel strip due to the temperature increase.

[0009] This patent precisely states that the temperature of the cutting portion should not be lower than 400°C, otherwise the yield stress cannot be sufficiently reduced and it is impossible to reduce the shear load.

[0010] It also discloses that the temperature of the cutting portion should not be higher than 600°C, otherwise adverse changes occur to the material due to the transformation after cooling. Summary of the Invention

[0011] The object of the present invention is to provide a method for prolonging the life of a trimming knife used for cutting a steel strip.

[0012] The present invention relates to a method for trimming the side edges of a moving steel strip along a cutting line, which comprises

[0013] i. a heating step in which the cutting line is heated to a temperature higher than Ac1, and

[0014] ii. a trimming step in which the steel strip is mechanically cut along the cutting line at a temperature higher than Ac1.

[0015] The cutting line refers to the part of the strip that is subjected to mechanical cutting, where shear force and tearing force are applied during the trimming step.

[0016] Ac1 represents the critical temperature at which pearlite transforms into austenite during heating. It can be defined by the following formula according to Andrew:

[0017] Ac1 [°C] = 723 - 10.7Mn - 16.9Ni + 29.1Si + 16.9Cr + 290As + 6.38W, where Mn, Ni, Si, Cr, As, and W are the weight percentage contents of the corresponding elements.

[0018] Contrary to the teaching of EP 3 085 465, in the present invention, the cutting line is heated to a temperature higher than 600 °C, i.e., higher than Ac1.

[0019] Surprisingly, the inventors have found that the transformation after cooling is not adverse as long as the temperature during trimming is higher than Ac1. In fact, it can be expected that some hard phases will form upon cooling, and such phases are inherently brittle. Description of the Drawings

[0020] As mentioned above Figure 1 shows a shearing device known from the prior art.

[0021] Figure 2 shows a side view of an embodiment of a shearing device according to the present invention.

[0022] Figure 3 shows Figure 2 a top perspective view of an embodiment of Detailed Description

[0023] Preferably, the steel is an advanced high-strength steel (AHSS) having a tensile strength of at least 500 MPa. The AHSS series includes dual-phase (DP) steel, dual-phase high-ductility (DP HD) steel, complex-phase (CP) steel, complex-phase high-ductility (CP HD) steel, martensitic (MS) steel, transformation-induced plasticity (TRIP) steel, hot forming (HF), and twinning-induced plasticity (TWIP) steel.

[0024] Preferably, the steel strip is not a press-hardened steel strip.

[0025] Preferably, heating is applied to the upper and lower surfaces of the strip.

[0026] Alternatively, heating is applied to the upper surface or the lower surface. In this embodiment, the surface opposite to the heated surface is indirectly heated by heat transfer.

[0027] Preferably, during the heating step, no grooves are formed. This means that the application of heating does not cause grooves to form at the position of the cutting line.

[0028] 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.

[0029] Ac3 represents the final critical temperature at which free ferrite is completely transformed into austenite during heating. It can be estimated by the following formula:

[0030] Ac3 [°C] = 910 – 203C 1 / 2 – 15.2Ni + 44.7Si + 104V + 31.5Mo + 13.1W –

[0031] 30Mn – 11Cr – 20Cu + 700P + 400Al + 120As + 400Ti, where C, Ni, Si, V, Mo, W, Mn, Cr, Cu, P, Al, As, and Ti are the weight percentage contents of the corresponding elements.

[0032] Preferably, in the heating step, the cutting line is heated to a temperature higher than Ac3, and in the trimming step, the cutting line is mechanically cut at a temperature higher than Ac3. More preferably, the cutting line is heated to a temperature higher than Ac3 + 10 °C. Even more preferably, in the heating step, the cutting line is heated to a temperature higher than Ac3 + 30 °C.

[0033] Preferably, the heating is accomplished by focusing a laser beam onto the cutting line. Even more preferably, the laser beam is controlled to produce a light spot having a circular shape, a linear shape, or an elliptical shape.

[0034] Preferably, the side trimming is performed after the pickling operation in the cold rolling production line. Preferably, the side trimming is performed after the annealing treatment.

[0035] Hereinafter, an apparatus and a method for side trimming a moving steel strip according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0036] As Figure 3 illustrated, the claimed process can be performed by a side trimming apparatus 10, which includes:

[0037] - A laser processing unit 11 that can emit a laser beam 12 toward a cutting line 13 of a conveyed steel strip S to heat the cutting line 13.

[0038] - A cutting unit 14 mounted on the periphery of the steel strip conveying path, wherein the cutting unit can trim the sides of the conveyed steel strip by mechanical cutting.

[0039] In the heating step, as Figure 2 illustrated, the laser processing unit can emit laser beams along the cutting line toward the upper and lower surfaces of the steel strip.

[0040] In this embodiment, the laser processing unit includes a laser oscillator capable of generating a laser beam and an optical focusing head capable of focusing the laser beam on the conveyed steel strip. The laser beam 12 produces a light spot 15 having a circular shape of the steel strip.

[0041] In the trimming step, as Figure 3 illustrated, the steel strip S is mechanically cut by the cutting unit 14 along the cutting line 13. As Figure 2 illustrated, the cutting unit 14 includes an upper trimming knife 14a disposed above the strip conveying path, i.e., the steel strip S, and a lower trimming knife 14b disposed below the strip conveying path. As Figure 3 presented, the cutting unit 14 may further include a bracket 14c that rotatably supports the upper and lower knives.

Claims

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

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

3. The method according to any one of claims 1 to 2, wherein, The heating is accomplished by focusing a laser beam onto the cutting line.

4. The method according to claim 3, wherein The laser beam produces a light spot controlled to have a circular shape or a linear shape or an oval shape.

5. The method according to any one of claims 1 to 4, wherein In the heating step, the cutting line is heated to a temperature in the range of Ac1 + 10 °C to Ac3.

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

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

9. The method according to any one of claims 1 to 7, wherein The side trimming is performed after an annealing treatment.

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