Method for reducing cross strip differences in hot rolled strip

Abstract

The application provides a method for reducing the transverse same-plate difference of hot-rolled strip steel. The application comprises the following steps: slab heating: heating to a preset temperature before hot rolling, and the maximum temperature difference in the thickness direction and the width direction of the slab is kept within a predetermined range; selection of hot-rolling roll shape: for the original roll shape, a roll with a small roll shape concave is selected, specifically, the original roll convexity of the hot-rolling roll is-70 to-90 microns; adjustment of the convexity of the hot-rolling roll: the variable convexity of the hot-rolling CVC roll is adjusted for different rolling stages; hot-rolling tension: different tension adjustments are made for different thicknesses of cold-rolled product supply; hot-rolling bending: the extension length of the bending cylinder is adjusted for different bending pressures of the finishing mill. Through the implementation of the method, the transverse same-plate difference of the hot-rolled strip steel is reduced to 0.018-0.02 mm, which meets the demand of cold-rolled production of high-end products.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot rolling process, in particular to a method for reducing the transverse strip thickness difference of hot rolled strip. BACKGROUND

[0002] The transverse strip thickness difference is the maximum thickness difference between any two points in the width direction of the same strip. The domestic hot rolled strip thickness difference is between 0.025-0.04mm. Reducing the transverse strip thickness difference of hot rolled strip is the key to improving the quality of cold rolled strip. For example, in the production of cold rolled silicon steel sheet for motor and transformer core, the strip thickness difference of the silicon steel sheet is required to be less than 0.007mm. At present, the existing hot rolled strip thickness difference in China is difficult to be less than 0.025mm. The hot rolled strip with large strip thickness difference is difficult to achieve a level of less than 0.007mm after cold rolling, resulting in low yield. SUMMARY

[0003] According to the above technical problems, a method for reducing the transverse strip thickness difference of hot rolled strip is provided. The technical means adopted by the present application is as follows:

[0004] A method for reducing the transverse strip thickness difference of hot rolled strip, comprising the following steps:

[0005] Step 1, slab heating: heated to a preset temperature before hot rolling, and the maximum temperature difference in the thickness direction and width direction of the slab is kept within a predetermined range;

[0006] Step 2, selection of hot rolling roll shape: for the original roll shape, the roll shape with small concave is selected, specifically, the original roll convexity of the hot rolling roll is-70 to-90 microns;

[0007] Step 3, adjustment of hot rolling roll convexity: the variable convexity of the hot rolling CVC roll is adjusted for different rolling stages;

[0008] Step 4, hot rolling tension: different tension adjustments are made for different thickness of cold rolled product supply;

[0009] Step 5, hot rolling bending: the extension length of the bending cylinder is adjusted for different rolling pressures of the finishing mill.

[0010] Further, in step 1, the furnace pressure in the heating furnace is set to 19-21Pa.

[0011] Further, in step 1, the waiting time of the heated slab at the furnace exit position is not more than 4 minutes.

[0012] Further, step 3 is specifically: after the new roll is put into the machine, the CVC roll moves 6-8mm, the variable convexity is -122-130 microns; after 5 rolls are rolled, the CVC roll moves 10-12mm, the variable convexity is -95-100 microns; after 10 rolls are rolled, the CVC roll moves 42-46mm, the variable convexity is -32-40 microns. After 15 rolls are rolled, the CVC roll moves 50-54mm, the variable convexity is -72-80 microns. After 20 rolls are rolled, the CVC roll moves 55-60mm, the variable convexity is -95-100 microns.

[0013] Further, in step 4, the strip tension is increased by 1.8%-2% for the cold-rolled product supply with hot-rolled thickness greater than 5.0mm and less than 6.0mm; the strip tension is increased by 8%-10% for the cold-rolled product supply with hot-rolled thickness greater than 4.0mm and less than 5.0mm; the strip tension is increased by 16%-18% for the cold-rolled product supply with hot-rolled thickness greater than 3.0mm and less than 4.0mm; the strip tension is increased by 19%-21% for the cold-rolled silicon steel product supply with hot-rolled thickness greater than 2.0mm and less than 3.0mm; and the strip tension is increased by 23%-25% for the cold-rolled silicon steel product supply with hot-rolled thickness less than 2.0mm.

[0014] Further, in step 5, when the hot-rolled roll rolls the cold-rolled product supply, the positive bending extension length is 180-185mm when the finishing mill rolling pressure is greater than 35000KN; the positive bending extension length is 160-165mm when the finishing mill rolling pressure is greater than 30000KN and less than 35000KN; the positive bending extension length is 140-145mm when the finishing mill rolling pressure is greater than 27000KN and less than 30000KN; the positive bending extension length is 120-125mm when the finishing mill rolling pressure is greater than 26000KN and less than 27000KN; the positive bending extension length is 100-105mm when the finishing mill rolling pressure is greater than 25000KN and less than 26000KN; and the positive bending extension length is 80-85mm when the finishing mill rolling pressure is greater than 21000KN and less than 25000KN.

[0015] Through the implementation of the method, the transverse plate difference of the hot-rolled strip is reduced to 0.018-0.02mm, which is more beneficial to the process after cold rolling to reach a level of less than 0.007mm, meets the demand of cold-rolled production of high-end products, and improves the quality and yield of the cold-rolled strip. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings described below are only some embodiments of the present application, and the ordinary skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0017] Figure 1 Flow chart of the present application.

[0018] Figure 2 Variable crown diagram of the present application, where the left is the variable crown decreasing, and the right is the variable crown increasing.

[0019] Figure 3 Bending cylinder positive bending action diagram. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the ordinary skilled in the art without any creative effort are within the protection scope of the present application.

[0021] As shown in Figure 1 The embodiments of the present application disclose a method for reducing the transverse strip difference of hot-rolled strip steel, comprising the following steps:

[0022] Step 1, slab heating: heated to a preset temperature before hot rolling, and the maximum temperature difference in the thickness direction and the width direction of the slab is kept within a predetermined range;

[0023] In the embodiments, the continuous casting slab has a thickness of 70-90 mm, a width of 850-1750 mm, and a length of 10-30 m, and is heated to 1050-1150℃ before hot rolling. The more uniform the slab temperature is, the smaller the transverse strip difference of the hot-rolled and cold-rolled strip steel is. In order to ensure the uniformity of the slab temperature before hot rolling, the maximum temperature difference in the thickness direction of the slab cannot exceed ±7℃, and the maximum temperature difference in the width direction cannot exceed ±7℃.

[0024] If the furnace pressure is set too low, the slab temperature is not uniform due to the cold air suction in the furnace. The furnace pressure of the present application is set to 19-21 Pa.

[0025] The waiting time of the heated slab at the discharge position is reduced. The surface temperature of the slab is reduced due to the excessive waiting time. The present application provides that the time of the hot slab at the discharge waiting position is not more than 4 minutes.

[0026] Step 2, selection of hot rolling roll type: the appropriate roll type is necessary to reduce the strip plate difference, increasing the convexity of the hot rolling original roll type can offset a part of the elastic bending deformation deflection of the roll, thereby reducing the strip width direction middle high both sides low transverse plate difference. For the original roll type, the roll type of the roll with small concave is selected, and the hot rolling roll is designed as a concave roll, that is, the diameter of the middle of the roll body is smaller than the diameter of the two ends of the roll body, in order to compensate the thermal convexity of the roll after the roll is heated in the rolling process. The original roll type data of the hot rolling finishing mill is negative, that is, the concave roll, and the convexity data is-120-140 microns. The original roll of the hot rolling finishing roll is put on the machine, and the roll body generates thermal convexity with the increase of the roll temperature. The original roll convexity of the hot rolling roll is determined as-70-90 microns in the application, which can reduce the strip width direction middle high both sides low transverse plate difference.

[0027] Step 3, adjustment of the convexity of the hot rolling roll: after rolling a stage, the roll will produce thermal expansion. The variable convexity of the hot rolling CVC roll is adjusted for different rolling stages, and the roll gap shape is changed by the relative position change of the axial string movement of the upper and lower rolls; specifically, the hot rolling CVC roll can change the roll gap shape by axial movement, which is equivalent to the variable convexity of the roll. Increasing the variable convexity of different rolling stages is an important option that cannot be ignored to reduce the transverse plate difference of the strip.

[0028] The CVC hot rolling mill has an S-shaped curve of the upper and lower rolls arranged reversely, and the roll gap shape can be changed by the relative or opposite axial movement of the upper and lower rolls, which is equivalent to the variable convexity of the roll. The CVC roll is axially Figure 2 The greater the trend movement value on the right, the greater the variable convexity. The new roll on the machine is basically the original roll type, and the thermal convexity of the roll gradually increases with the increase of the roll temperature in the rolling process, and the variable convexity gradually decreases to a negative value in order to compensate the convexity generated by the thermal expansion of the roll. In order to reduce the transverse plate difference of the strip width direction middle high both sides low, the variable convexity of different rolling stages is improved in the application.

[0029] Specifically: after the new roll is put on the machine, the CVC roll moves to Figure 2 The right trend moves 6-8mm, and the variable convexity is-122-130 microns; after rolling 5 rolls, the CVC roll moves to Figure 2 The right trend moves 10-12mm, and the variable convexity is-95-100 microns; after rolling 10 rolls, the CVC roll moves to Figure 2 The right trend moves 42-46mm, and the variable convexity is-32-40 microns. After rolling 15 rolls, the CVC roll moves to Figure 2 The right trend moves 50-54mm, and the variable convexity is-72-80 microns. After rolling 20 rolls, the CVC roll moves to Figure 2 The right trend moves 55-60mm, and the variable convexity is-95-100 microns.

[0030] Step 4, hot rolling tension: different tension adjustments are made for different thicknesses of cold-rolled product supply; the strip tension is the tension of the strip in the rolling process, which is established by the speed difference between the front and rear rolling mills. Increasing the strip tension can reduce the rolling pressure, reduce the bending of the roll, and reduce the transverse same plate difference of the strip in which the middle thickness is large and the two edges are small. Due to the increase in tension, the strip is not easy to deviate, which can prevent the transverse same plate difference in which one side of the strip in the width direction is thick and the other side is thin due to the deviation of the strip. Due to the increase in tension, the longitudinal extension resistance of the strip is reduced, and the width direction extension resistance is increased, further reducing the transverse same plate difference in which the middle thickness is large and the two edges are small.

[0031] The strip tension in the rolling process is given a unit area tension of Mpa / mm according to the steel type and the cross-sectional area of the strip. The given unit tension setting value is different if the width of a certain steel type is 1500 mm, the thickness is 5.5 mm, and the given unit tension of the prior art is 25 Mpa / mm. In this embodiment, the given unit tension is increased based on the following principles. In this embodiment, the actual given unit tension is 25.5 Mpa / mm. The principles are as follows: for hot-rolled cold-rolled product supply with a thickness greater than 5.0 mm and less than 6.0 mm, the strip tension is increased by 1.8%-2%; for hot-rolled cold-rolled product supply with a thickness greater than 4.0 mm and less than 5.0 mm, the strip tension is increased by 8%-10%; for hot-rolled cold-rolled product supply with a thickness greater than 3.0 mm and less than 4.0 mm, the strip tension is increased by 16%-18%; for hot-rolled cold-rolled silicon steel product supply with a thickness greater than 2.0 mm and less than 3.0 mm, the strip tension is increased by 19%-21%; and for hot-rolled cold-rolled silicon steel product supply with a thickness less than 2.0 mm, the strip tension is increased by 23%-25%.

[0032] Step 5, hot rolling positive bending: adjust the positive bending extension length of the bending roll cylinder for different rolling pressures of the finishing mill. Specifically, as shown in Figure 3 The bending roll hydraulic cylinder acts on the bearing boxes at both ends of the roll, and generally applies positive bending to offset the elastic bending deformation of the roll caused by the rolling force. Increasing the positive bending extension length of the bending roll cylinder reduces the action of the roll on the two edges of the strip, which can obtain a suitable roll gap shape and reduce the same plate difference of the strip in which the middle is high and the two ends are low in the width direction.

[0033] When the hot rolling mill rolls the cold rolling product, the extension length of the positive bending is 180mm when the rolling pressure of the finishing mill is greater than 35000KN; the extension length of the positive bending is 160mm when the rolling pressure of the finishing mill is greater than or equal to 30000KN and less than 35000KN; the extension length of the positive bending is 140mm when the rolling pressure of the finishing mill is greater than or equal to 27000KN and less than 30000KN; the extension length of the positive bending is 120mm when the rolling pressure of the finishing mill is greater than or equal to 26000KN and less than 27000KN; the extension length of the positive bending is 100mm when the rolling pressure of the finishing mill is greater than or equal to 25000KN and less than 26000KN; the extension length of the positive bending is 80mm when the rolling pressure of the finishing mill is greater than or equal to 21000KN and less than 25000KN.

[0034] Example 1

[0035] The rolling is carried out under the following rolling conditions:

[0036] The steel type is 50BW600, the width is 1250mm, and the rolling thickness is 5.5mm. The new roll is put on the machine.

[0037] In step 1, the furnace pressure is controlled at 20Pa.

[0038] In step 2, the original crown of the roll is -88 microns.

[0039] In step 3, the initial rolling, the CVC roll moves 8mm. After rolling 5 rolls, the CVC roll moves 12mm. After rolling 10 rolls, the CVC roll moves 46mm. After rolling 15 rolls, the CVC roll moves 54mm. After rolling 20 rolls, the CVC roll moves 60mm.

[0040] In step 4, in the prior art, the inter-stand tension parameters are as follows: the inter-stand tension between 1-2 stands is 25Mpa / mm; the inter-stand tension between 2-3 stands is 22Mpa / mm; the inter-stand tension between 3-4 stands is 20Mpa / mm; the inter-stand tension between 4-5 stands is 18Mpa / mm. In this embodiment, based on the set principles, the actual given unit tension is: the inter-stand tension between 1-2 stands is 25.5Mpa / mm; the inter-stand tension between 2-3 stands is 22.44Mpa / mm; the inter-stand tension between 3-4 stands is 20.4Mpa / mm; the inter-stand tension between 4-5 stands is 18.36Mpa / mm.

[0041] In step 5, for the extension length of the positive bending: the rolling force of the first stand is 30000KN, and the extension length of the positive bending of the bending roll cylinder is 160mm. The rolling force of the second stand is 28000KN, and the extension length of the positive bending of the bending roll cylinder is 140mm. The rolling force of the third stand is 26000KN, and the extension length of the positive bending of the bending roll cylinder is 120mm. The rolling force of the fourth stand is 24000KN, and the extension length of the positive bending of the bending roll cylinder is 80mm. The rolling force of the fifth stand is 22000KN, and the extension length of the positive bending of the bending roll cylinder is 80mm.

[0042] Finally, the strip after rolling has a strip thickness difference of 0.019 mm. This can lay a good foundation for the requirement of the strip thickness difference of the silicon steel sheet in the subsequent cold rolling process, which is not more than 0.007 mm.

[0043] Comparative Example 1

[0044] The same steel grade and specification as in Example 1 are adopted for rolling according to the prior art.

[0045] In Step 1, the furnace pressure is controlled at 12.5 Pa.

[0046] In Step 2, the original crown of the roll is -140 microns.

[0047] In Step 3, initial rolling, the CVC roll moves 10 mm. After rolling 5 coils, the CVC roll moves 7 mm. After rolling 10 coils, the CVC roll moves 50 mm. After rolling 15 coils, the CVC roll moves 65 mm. After rolling 20 coils, the CVC roll moves 70 mm.

[0048] In Step 4, inter-stand tension. The inter-stand tension between stands 1-2 is 25 MPa / mm. The inter-stand tension between stands 2-3 is 22 MPa / mm. The inter-stand tension between stands 3-4 is 20 MPa / mm. The inter-stand tension between stands 4-5 is 18 MPa / mm.

[0049] In Step 5, in the specification, when the hot rolling rolling cold rolling product supply, the bending roll cylinder positive bending extension length is 160 mm when the finishing mill rolling pressure is greater than 35,000 KN; the bending roll cylinder positive bending extension length is 140 mm when the finishing mill rolling pressure is greater than 30,000 KN and less than 35,000 KN; the bending roll cylinder positive bending extension length is 120 mm when the finishing mill rolling pressure is greater than 27,000 KN and less than 30,000 KN; the bending roll cylinder positive bending extension length is 100 mm when the finishing mill rolling pressure is greater than 26,000 KN and less than 27,000 KN; the bending roll cylinder positive bending extension length is 80 mm when the finishing mill rolling pressure is greater than 25,000 KN and less than 26,000 KN; the bending roll cylinder positive bending extension length is 60 mm when the finishing mill rolling pressure is greater than 21,000 KN and less than 25,000 KN.

[0050] In the actual operation process of Step 5, the first stand rolling force is 30,000 KN, and the bending roll cylinder positive bending extension length is 140 mm. The second stand rolling force is 28,000 KN, and the bending roll cylinder positive bending extension length is 120 mm. The third stand rolling force is 26,000 KN, and the bending roll cylinder positive bending extension length is 100 mm. The fourth stand rolling force is 24,000 KN, and the bending roll cylinder positive bending extension length is 60 mm. The fifth stand rolling force is 22,000 KN, and the bending roll cylinder positive bending extension length is 60 mm.

[0051] Finally, the strip after rolling the same plate difference is 0.032mm. Lead to cold rolling after it is difficult to achieve less than 0.007mm level.

[0052] Finally, it should be noted that: the above examples are used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still be modified to the technical solutions recorded in the foregoing examples, or part or all of the technical features are replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for reducing transverse thickness variation in hot-rolled strip, characterized in that, Includes the following steps: Step 1, Slab heating: Before hot rolling, heat the slab to 1050℃~1150℃, and the maximum temperature difference in the thickness and width directions should not exceed ±7℃; the furnace pressure in the heating furnace should be set to 19~21Pa; the waiting time for the heated steel billet at the exit position should not exceed 4 minutes; Step 2, Selection of hot rolling roll type: For the original roll type, select a roll with a small roll concavity. Specifically, the original roll crown of the hot rolling roll is -70 to -90 micrometers. Step 3: Adjustment of hot rolling roll crown: Adjust the variable crown of the hot rolling CVC roll for different rolling stages; specifically: after a new roll is installed, the CVC roll moves 6~8mm, with a variable crown of -122~-130 micrometers; after rolling 5 coils, the CVC roll moves 10~12mm, with a variable crown of -95~-100 micrometers; after rolling 10 coils, the CVC roll moves 42~46mm, with a variable crown of -32~-40 micrometers; after rolling 15 coils, the CVC roll moves 50~54mm, with a variable crown of -72~-80 micrometers; after rolling 20 coils, the CVC roll moves 55~60mm, with a variable crown of -95~-100 micrometers. Step 4, Hot Rolling Tension: Adjust the tension differently for cold-rolled products of varying thicknesses. For cold-rolled products with a hot-rolled thickness greater than 5.0mm and less than 6.0mm, increase the strip tension by 1.8%~2%; for cold-rolled products with a hot-rolled thickness greater than 4.0mm and less than 5.0mm, increase the strip tension by 8%~10%; for cold-rolled products with a hot-rolled thickness greater than 3.0mm and less than 4.0mm, increase the strip tension by 16%~18%; for cold-rolled silicon steel products with a hot-rolled thickness greater than 2.0mm and less than 3.0mm, increase the strip tension by 19%~21%; for cold-rolled silicon steel products with a hot-rolled thickness less than 2.0mm, increase the strip tension by 23%~25%. Step 5, Hot-rolled positive bending: Adjust the positive bending extension length of the bending roll cylinder according to different finishing mill rolling pressures; When hot-rolled and cold-rolled products are fed, the positive bending extension length is 180~185mm when the finishing mill rolling pressure is greater than 35000KN; 160~165mm when the finishing mill rolling pressure is greater than 30000KN and less than 35000KN; 140~145mm when the finishing mill rolling pressure is greater than 27000KN and less than 30000KN; 120~125mm when the finishing mill rolling pressure is greater than 26000KN and less than 27000KN; 100~105mm when the finishing mill rolling pressure is greater than 25000KN and less than 26000KN; and 80~85mm when the finishing mill rolling pressure is greater than 21000KN and less than 25000KN.

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