COLD ROLLING MILL

Abstract

The present application describes a Cold Rolling Mill (CRM) 200. The CRM 200 comprises a pair of working rolls 202 configured to apply stress on a metal strip for reducing thickness of the metal strip. The pair of working rolls 202 have a face width of 1350 mm. The CRM 200 further comprises a pair of intermediate rolls 204 configured to provide mechanical support to the pair of working rolls 202. The pair of intermediate rolls 204 have a face width of 1280 mm. The CRM 200 further comprises a pair of back-up rolls 206 configured to provide mechanical support to the pair of intermediate rolls 204. The back-up rolls 206 have a face width of 1300 mm. Bearing center distance of the CRM 200 is 2170 mm.

Claims

1. A Cold Rolling Mill (CRM) (200) comprising: a pair of working rolls (202) configured to apply stress on a metal strip for reducing thickness of the metal strip, wherein a face width of the pair of working rolls (202) is 100 mm to 120 mm greater than a width of the metal strip; a pair of intermediate rolls (204) configured to provide mechanical support to the pair of working rolls (202), wherein a face width of the pair of intermediate rolls (204) is 30 mm to 50 mm greater than the width of the metal strip; and a pair of back-up rolls (206) configured to provide mechanical support to the pair of intermediate rolls (204), wherein a face width of the pair of back-up rolls (206) is 50 mm to 70 mm greater than the width of the metal strip.

2. The CRM (200) as claimed in claim 1, wherein the CRM (200) is a 4-Hi CRM or a 6-Hi CRM.

3. The CRM (200) as claimed in claim 2, wherein the width of the metal strip is 1250 mm.

4. The CRM (200) as claimed in claim 1, wherein a bearing center distance of the CRM (200) is 2170 mm.

5. The CRM (200) as claimed in claim 1, wherein the CRM (200) is configured to transfers more stress on the metal strip such that less stress remains on each of the pairs of rolls (202, 204, 206) resulting in better strip shape and greater reduction of thickness of the metal strip.

6. A method of reducing thickness of a metal strip using a Cold Rolling Mill (CRM) (200), the method comprising: applying stress on the metal strip via a pair of working rolls (202) of the CRM; mechanically supporting the pair of working rolls (202) via a pair of intermediate rolls (204) of the CRM (200); and mechanically supporting the pair of intermediate rolls (204) via a pair of back-up rolls (206), wherein a face width of the pair of working rolls (202) is 100 mm to 120 mm greater than a width of the metal strip.

7. The method as claimed in claim 6, wherein a face width of the pair of intermediate rolls (204) is 30 mm to 50 mm greater than the width of the metal strip.

8. The method as claimed in claim 6, wherein a face width of the pair of back-up rolls (206) is 50 mm to 70 mm greater than the width of the metal strip.

9. The method as claimed in claim 6, wherein the width of the metal strip is 1250 mm.

10. The method as claimed in claim 6, wherein a bearing center distance of the CRM (200) is 2170 mm.

11. The method as claimed in claim 6, wherein more stress is applied on the metal strip such that less stress remains on each of the pairs of rolls (202, 204, 206).

12. The method as claimed in claim 6, wherein the CRM (200) is a 4-Hi CRM or a 6-Hi CRM.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings constitute a part of the description and are used to provide a further understanding of the present invention.

[0019] FIG. 1 illustrates a side view of a conventional CRM pressing a metal strip, in accordance with prior art.

[0020] FIG. 2 illustrates a front view of proposed CRM having preferred dimensions, in accordance with an embodiment of the present invention.

[0021] FIG. 3a illustrates stress distribution across a metal strip and working rolls processing the metal strip, in accordance with an embodiment of the present invention.

[0022] FIG. 3b illustrates strip stress analysis in proposed CRM, in accordance with an embodiment of the present invention.

[0023] FIG. 4 illustrates thermal and mechanics analysis data for 1250 mm wide strip processed by proposed CRM operated at a speed of 800 MPM, in accordance with an embodiment of the present invention.

[0024] FIG. 5 illustrates thermal and mechanics analysis data for 1250 mm wide strip processed by proposed CRM operated at a speed of 1200 MPM, in accordance with an embodiment of the present invention.

[0025] FIG. 6 illustrates thermal and mechanics analysis data for 1300 mm wide strip processed by proposed CRM operated at a speed of 550 MPM, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0027] Current disclosure provides a roll profile design to achieve significant reductions on a CRM to produce much lighter gauges in the least number of passes, without compromising on strip shape.

[0028] Roll bending and roll flattening are two key phenomenon involved in a cold rolling process. Rolls of a CRM act like beams as the separating force causes the rolls to bend and the amount of bending depends on size and the length of the rolls and width of a metal strip to be processed. In a 6-HI mill, intermediate rolls can be laterally shifted to roll virtually any width of strip with any incoming profile at any roll separating force, to nullify the roll bending movement, but roll bending cannot be eliminated. Roll flattening depends on total Roll Separating Force (RSF), diameter of the roll, and face width of the roll or the roll contact outside the strip edges.

[0029] With the market trends moving towards thinner gauge and high strength steels, it becomes imperative to optimize the cold rolling process to increase the reduction on the strip, without compromising the strip quality.

[0030] The instant application proposes CRMs using work rolls of barrel length ranging from x+100 to x+120, intermediate rolls of barrel length ranging from x+30 to x+50, and back-up rolls having barrel lengths ranging from of x+50 to x+70, while ‘x’ denotes strip width in millimeters. Barrel length of intermediate roll could be designed to accommodate minimum and maximum strip widths to be rolled. Such optimization of the barrel lengths optimized desirable same strip and roll width feature of the CRMs. Reduction in barrel lengths led to reduction of bearing center, i.e., loading points which helped to improve the strip profile significantly.

[0031] Referring to FIG. 2, a 6-Hi CRM 200 of preferred dimensions is described. The CRM 200 comprises a pair of working rolls 202 configured to apply stress on a metal strip for reducing thickness of the metal strip of width 1250 mm. The pair of working rolls 202 have a face width/barrel length of 1350 mm. A pair of intermediate rolls 204 is configured to provide mechanical support to the pair of working rolls 202. The pair of intermediate rolls 204 have a face width/barrel length of 1280 mm. Further, a pair of back-up rolls 206 is configured to provide mechanical support to the pair of intermediate rolls 204. The back-up rolls 206 have a face width/barrel length of 1300 mm. Bearing center distance of the CRM 200 is 2170 mm.

[0032] In one implementation, a simulation test was conducted using SOLIDWORKS® Simulation Premium platform, for performing stress analysis of the CRM 200.

[0033] Specifically, the simulation test was conducted to analyze effect of the roll profile and load centers on actual stress distribution on the metal strip and the working rolls 202. The simulation test revealed the following results in Table 1 below.

TABLE-US-00001 TABLE 1 Analysis Type Static Mesh Type Solid Mesh Mesher Used Blended curvature-based mesh Jacobian Points 16 Maximum Element Size 80 mm Minimum Element Size 16 mm Mesh Quality Plot High Solver Type Direct Sparse Solver Soft Spring On

[0034] During the simulation test, a total load of 250,000 Kgf×4, i.e., 1,000,000 Kgf was applied on the 1250 mm wide and 0.5 mm thick metal strip on two models. One model was based on conventional roll profile used in 6-HI CRM and other model was based on the proposed design of 6-HI CRM 200.

[0035] FIG. 3a illustrates stress distribution across the metal strip and the working rolls 202. Curve 302 provides stress distribution on a metal strip processed using conventional CRMs. Curve 304 provides stress distribution on a similar metal strip processed using proposed CRM 200. Curve 306 provides stress distribution on a working roll of conventional CRMs. Curve 308 provides stress distribution on the working rolls 202 of the proposed CRM 200. From the curves 302 and 304, it is evident that the stress distribution across the metal strip on the proposed CRM 200 is quite uniform. It is also notable to observe that there is sharp edge drop-off on the conventional mill due to more bending movement of working rolls. FIG. 3b illustrates strip stress analysis conducted on the conventional CRMs and the proposed CRM 200. Block 320 corresponds to strip stress in a conventional CRM and block 322 corresponds to strip stress in the proposed CRM 200. The stress distribution illustrated in FIG. 3a indicates that stress on the working rolls 202 of the proposed CRM 200 is lower, i.e., the working rolls 202 are subject to lower mechanical and thermal fatigue.

[0036] The strip stress analysis shown in FIG. 3b suggests that optimization of the roll profile results in 15% more stress on the metal strip, and thus reduction in number of passes of the metal strip through the CRM, and a uniform stress distribution across width of the metal strip, which would ensure a better strip profile.

[0037] Multiple tests were also conducted for performing thermal analysis and observing mechanics of the CRM 200. FIG. 4 illustrates thermal and mechanics analysis data for 1250 mm wide strip processed by the CRM 200 operated at a speed of 800 MPM. FIG. 5 illustrates thermal and mechanics analysis data for 1250 mm wide strip processed by the CRM 200 operated at a speed of 1200 MPM. FIG. 6 illustrates thermal and mechanics analysis data for 1300 mm wide strip processed by the CRM 200 operated at a speed of 550 MPM. From data illustrated in FIGS. 4 through 6, it could be observed that energy going in to strip reduction in CRM 200 was between 50 to 80 percent compared to 48 to 59 percent in conventional CRMs.

[0038] Also, energy going in to the friction and conduction in the CRM 200 is significantly lower compared to conventional CRMs. The more the reduction in energy going in to the strip implies higher strip temperature. Such increase in strip temperature will cause decrease in material yield stress which is result of the increase in strain rate. Further, more energy going in to the strip means more reduction on the strip and hence, less number of passes are required to obtain final thickness from similar input thickness. It is to be noted that more number of passes result in higher yield stresses in the strip and greater conduction occurs between the strip and the rolls. Hence, the energy going in to the strip is less than the reduction energy and half the friction energy. The more energy going in to the strip means less rise in roll coolant temperature, and thereby eliminating the heat exchanger used for roll coolant cooling.

[0039] As the strip thickness becomes smaller, flattening of the rolls and axial bending of the rolls become proportionally larger. At some stage, depending on roll force, strip width, roll crown, and roll bending force, the top and bottom work rolls will come in contact outside the strip edges. A higher roll force has a tendency to make the strip shape poorer but the edge contact force in the work rolls plays an important role in thin strip rolling process. In case the edge contact force between two work rolls is controlled between 11 to 15 percent, it can improve the strip shape. During roll flattening, force applied to the strip will approach a fixed ratio of the total roll separating force and can be controlled to improve the strip profile.

[0040] In view of the above provided embodiments and their explanations, it is evident that the present invention offers: [0041] 12-15% more reduction on the strip and hence lesser number of passes are required to achieve a desired thickness of the strip; [0042] lesser yield stresses on the strip due as a result of the reduced number of passes; [0043] better strip shape profile on account of controlled work roll edge contact force; [0044] reduced thermal and mechanical fatigue on working rolls; [0045] elimination of cooling arrangement for emulsion system; and [0046] 2-3% reduction in rolling power consumption.

[0047] Although implementations of CRMs have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features are disclosed as examples of the CRMs.