Patent Application
20220118492
The present invention generally relates to a Cold Rolling Mill (CRM). More specifically, the present invention is related to a 4-Hi CRM and a 6-Hi CRM.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.
Cold Rolling Mills (CRMs) are used to reduce thickness of metal strips by pressing them at room temperature. The metal strips are pressed by passing them through a pair of rolls called work rolls. The pair of work rolls are often supported by one or more pairs of supporting rolls, and based on the number of pairs of supporting rolls that are utilized, the CRM are identified as 4-Hi CRM, 6-Hi CRM, 12-Hi CRM, and so on. To obtain a desired thickness of the metal strips, the metal strips are passed through the working rolls for a predefined number of times.
Referring now to
While imparting the stress, the pair of work rolls 104 makes contact with a specific region of the metal strip 102, and such region is called arc of contact 108. During an operational cycle, friction is created and plastic deformation occurs, in the arc of contact 108, while contact occurs between the pair of work rolls 104 that are made of a hard material and the metal strip 102 that is made of a relatively soft material. Due to the friction caused by relative sliding between the work rolls 104 and the metal strip 102 and plastic deformation of the metal strip 102, significant amount of heat is generated around the arc of contact 108. Additionally, heat transfer also occurs from the metal strip 102 to the work rolls 104 because of temperature difference.
The heat will continuously migrate to cooler zones in the work rolls 104 and out of body of the work rolls 104, at localized chill zones created by the coolant sprays 110 (part of a heat exchanger) impingement on the roll surface. The work rolls 104 are subject to thermal fatigue and mechanical fatigue during rolling operations. Thermal fatigue occurs as the work rolls 104 cycle through elevated temperature in the rolling operation and lower temperature zones are cooled under the coolant sprays 110. Mechanical fatigue occurs by mechanical compression (flattening) and physical deflection caused by rolling force and torque applied by a motor running the work rolls 104. Also, if the metal strip 102 is very thin, the top work roll 104-1 and the bottom work roll 104-2 may contact each other beyond the edges of the metal strip 102.
Thus, there remains a need of an improved design of (CRMs) that do not require heat exchangers, have better reduction capability, do not suffer from thermal fatigue and mechanical fatigue, reduces electrical power requirements for running the CRMs, provides metals strips of better shape, and achieve desired thickness in least number of passes.
A general objective of the invention is to provide a CRM that provides an increased transfer of stress on a metal sheet or strip in contact with a pair of working rolls.
Another objective of the invention is to provide a CRM that requires a reduced number of passes/iterations for pressing the metal sheet or strip.
Yet another objective of the invention is to provide a CRM in which less stress remains on the pairs of working rolls.
Yet another objective of the invention is to provide better strip shape.
Still another objective of the invention is to provide a CRM in which less heat is generated, and a requirement of a heat exchanger in the CRM is eliminated.
Still another objective of the invention is to provide a CRM that requires less electrical power for its operation.
This summary is provided to introduce aspects related to a CRM, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
In one embodiment, the CRM comprises a pair of working rolls configured to apply stress on a metal strip for reducing thickness of the metal strip having a width of 1250 mm. Face width of the pair of working rolls is 100 mm to 120 mm greater than a strip width. The CRM further comprises a pair of intermediate rolls configured to provide mechanical support to the pair of working rolls. Face width of the pair of intermediate rolls is 30 mm to 50 mm greater than the strip width. The CRM further comprises a pair of back-up rolls configured to provide mechanical support to the pair of intermediate rolls. Face width of the back-up rolls is 50 mm to 70 mm greater than the strip width.
In one embodiment, the CRM may be a 4-Hi CRM or a 6-Hi CRM. Further, bearing center distance of the CRM (200) is 2170 mm. The CRM transfers more stress on the metal sheet or strip and less stress remains on the pairs of rolls, thereby causing greater reduction in thickness of the metal sheet strip with application of similar Roll Separating Force (RSF).
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
The accompanying drawings constitute a part of the description and are used to provide a further understanding of the present invention.
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.
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.
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.
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.
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.
Referring to
In one implementation, a simulation test was conducted using SOLIDWORKS® Simulation Premium platform, for performing stress analysis of the CRM 200.
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.
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.
The strip stress analysis shown in
Multiple tests were also conducted for performing thermal analysis and observing mechanics of the CRM 200.
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.
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.
In view of the above provided embodiments and their explanations, it is evident that the present invention offers:
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202011045856 | Oct 2020 | IN | national |
