Special steel bar straightening and bending method with different pass speeds

Abstract

The present application provides a kind of special steel large bar pass speed difference straightening bending method, comprising the following steps: the bending head of the rolling piece to be corrected is sent into the speed difference straightening hole between upper roll and lower roll, in the side of the upper side or the lower side of speed difference straightening hole, the left side of the bending head of the rolling piece is contacted with A point of the inner wall of speed difference straightening hole, the right side of the bending head is contacted with B point of the inner wall of speed difference straightening hole, the vertical height of the A point is lower than the vertical height of B point;In the same section, the metal deformation of A point is faster than the metal deformation of B, the metal at B generates tensile stress to the metal at A, so that the bending of the bending head of the rolling piece to be corrected is corrected under the action of tensile stress.The present application meets the quality requirements of high-end special steel round steel, and realizes the breakthrough of low-cost and high-efficiency square steel rolling.

Description

Technical Field

[0001] This invention relates to the field of special steel rolling technology, and more particularly to a method for straightening and bending large special steel bars by speed difference of the rolling pass. Background Technology

[0002] Special steels include three main categories: high-quality carbon steel, alloy steel, and high-alloy steel. Inadequate design of special steel rolling equipment or improper process control can easily lead to surface defects such as bending at the head of the rolled piece, cracks, wrinkles, hairline cracks, and folds. Optimizing the roll pass design and changing the roll speed difference can effectively prevent bending at the head of the rolled piece after deformation.

[0003] Bending at the head of large bar stock is a persistent problem in the steel rolling process. When the number of stands in a large bar mill is small (generally 3-4 stands), the mill's correction capability is insufficient. Moreover, even if the heating furnace meets the 30°C temperature difference range, bending at the head of the stock can still easily occur. A method to straighten the bent steel by reducing the inner size of the guide at the exit of the final mill unit is to use the guide to force straighten the bent steel. However, this method easily causes surface scratches and other quality defects on the steel, and also results in high guide wear, increasing the cost per ton of steel. Summary of the Invention

[0004] Based on the aforementioned existing technology, this invention addresses the problem of scratches on the steel surface caused by bending at the head of rolled steel bars. Therefore, it provides a special method for straightening bending at the head of rolled steel bars using a speed difference in a special pass. This invention straightens the bent head of the rolled steel bar caused by bending by automatically correcting the steel's bending through a technology that automatically corrects the bending by utilizing the difference in metal deformation speed generated at different metal positions in contact with the pass during rolling.

[0005] The technical means employed in this invention are as follows:

[0006] A special steel bar straightening and bending method using a speed difference straightening hole includes the following steps: The bent head of the workpiece to be straightened is fed into a speed difference straightening hole between the upper and lower rolls; on one side of the speed difference straightening hole, either above or below, the left side of the bent head contacts point A on the inner wall of the speed difference straightening hole, and the right side of the bent head contacts point B on the inner wall of the speed difference straightening hole, wherein the vertical height of point A is lower than the vertical height of point B; in the same cross section, the metal deformation at point A is faster than the metal deformation at point B, and the metal at point B exerts tensile stress on the metal at point A, thereby straightening the bending of the bent head of the workpiece under tensile stress.

[0007] Furthermore, the speed difference straightening hole is symmetrical vertically and horizontally. The speed difference straightening hole on the upper or lower side includes a top arc surface. Each side of the top arc surface is connected to the upper part of a side wall. The lower part of the side wall is connected to a horizontal edge. The side wall is inclined from top to bottom towards the outer side of the top arc surface. The angle between the side wall and the horizontal edge is an obtuse angle.

[0008] Furthermore, the angle between the sidewall and the vertical line ranges from 15° to 22°.

[0009] Furthermore, the angle between the sidewall and the horizontal edge is 112°.

[0010] Furthermore, the formula for calculating the slope of the sidewall is as follows:

[0011] α=0.635η*(D / 2-B k ) / h

[0012] Where α is the sidewall slope, η is the correction coefficient, D is the groove depth, and B k This refers to the width of the hole.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] This invention uses a special die-cutting technique to eliminate the stress difference caused by the asymmetry of rolling stress on both sides of the steel due to temperature difference by generating a reverse force through the speed difference in the bent head of the rolled piece. This solves the problem of head bending defects in large bar stock.

[0015] This invention eliminates the bending defect at the head of steel rolled products, reducing the damage to rolling mill equipment caused by the bending of the rolled product head impacting auxiliary equipment such as guides and rollers.

[0016] This invention solves the problem of scratches caused by steel bending and contact with the roller cover or guide sidewall.

[0017] This invention corrects and controls the bending of the head of large bar stock, ensuring that the bar stock is rolled straight, reducing the straightening cost of the finishing process and the labor intensity of workers, and shortening the contract delivery cycle. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a diagram showing the condition of the workpiece to be corrected in the speed difference straightening hole according to the present invention.

[0020] Figure 2 This is a schematic diagram of the speed difference straightening hole of the present invention.

[0021] Figure 3 This is a diagram showing the straightening of the bent head of the rolled piece in the die.

[0022] In the diagram: 1. Top curved surface; 2. Side wall; 3. Horizontal edge. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0027] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0028] like Figure 1 As shown, this invention provides a special steel bar straightening and bending method using a speed difference straightening hole, comprising the following steps: feeding the bent head of the workpiece to be straightened into a speed difference straightening hole between the upper and lower rolls;

[0029] On one side of the speed difference straightening hole, either above or below, the left side of the bent head contacts point A on the inner wall of the speed difference straightening hole, and the right side of the bent head contacts point B on the inner wall of the speed difference straightening hole. The vertical height of point A is lower than that of point B. In the same cross section, the metal deformation at point A is faster than that at point B. The metal at point B exerts tensile stress on the metal at point A, thereby correcting the bending of the bent head of the workpiece under tensile stress.

[0030] The speed difference straightening hole is symmetrical vertically and horizontally. The speed difference straightening hole on the upper or lower side includes a top arc surface 1. Each side of the top arc surface is connected to the upper part of a side wall 2. The lower part of the side wall is connected to a horizontal edge 3. The side wall is inclined from top to bottom towards the outer side of the top arc surface. The angle between the side wall and the horizontal edge is an obtuse angle.

[0031] I. Reasons for billet head bending due to temperature difference: 1. The billet heating furnace is an end-in, end-out walking beam furnace. The billet exits the furnace in the soaking zone. At the moment the furnace door opens for tapping, heat loss is severe, with a temperature drop of 30℃-40℃. Repeated tapping during production causes the side of the billet facing the exit door to be colder, resulting in a large temperature difference between the billet and the rollers (large yin-yang side). 2. During the process of conveying the billet to the rolling mill, the lower surface of the billet contacts the rollers (with cooling water), causing a temperature drop of 10℃-20℃. This results in a large temperature difference between the upper and lower surfaces of the billet (small yin-yang side), causing uneven elongation of the billet during rolling, thus resulting in head bending deformation. 3. When the billet with a large temperature difference is rolled by the rolling mill, the metal deformation rate on the same cross-section of the billet is different. The metal flow rate on the high-temperature side is higher than that on the low-temperature side (V1 < V2) (see...). Figure 1 This creates tensile stress, causing the steel to bend at the head.

[0032] II. Technical solutions for solving the bending of the rolled piece head: 1. Speed ​​difference analysis

[0033] When a rolled piece has the same cross-section and is in contact with different positions in the elliptical pass, the roll diameter at contact point A and point B will differ. For example, the roll diameter of an 850 rolling mill is Ф900mm. When the rolled piece deforms in the elliptical pass, the roll diameter at point A will differ by D. A =815.6mm, D B =775.6mm, calculated according to the linear velocity formula:

[0034]

[0035] V A =0.299m / s, V B =0.271m / s, so the linear velocity of metal deformation is inconsistent in different parts of the hole.

[0036] 2. Features a hole design for straightening steel heads that prevent bending: Due to the symmetrical nature of the elliptical hole design, the diameters on both sides of the central symmetry are generally the same, and the linear velocity is also the same (V). A >V B In elliptical aperture designs, the smooth, rounded sidewalls are transformed into straight sidewalls to increase the linear velocity gradient, with an angle designed between 15° and 22°. Figure 2 As shown.

[0037] The steel head bends due to temperature differences, and at the moment the steel head bites into the die, the contact positions on both sides are asymmetrical, with contact point A on one side and contact point B on the other. (V) A =0.299m / s>V B =0.271 m / s. At the same cross-section, the metal deformation at point A is faster than that at point B, resulting in tensile stress exerted by the metal at point B on the metal at point A. This tensile stress causes the bent end of the steel to correct itself, as... Figure 3 As shown.

[0038] Example 1

[0039] Implementation of the Ф210 hook bending solution:

[0040] The rolling process involved a BD mill for billet preparation, followed by a V1 vertical 850 mill, an H850 flat roll mill, and a V3 vertical 850 mill. This process produced Ф210mm round steel bars with temperatures of 953℃ and 1002℃ on both sides, causing bending during rolling. The #2 elliptical hole had a sidewall angle of 112° and a bottom arc radius of R400mm. The rolling speed was 0.4m / s. The diameter of the roll at point A (contact hole type) was Ф815.5mm. A =0.363m / s, contact point B roll diameter Ф722.2mm, V B =0.322m / s, V A >V BDue to the speed difference, during the rolling deformation process, the deformation speed at point A is faster than that at point B. During the rolling deformation process, the metal flow at point A is subjected to tensile stress from the metal flow at point B. Under the action of tensile stress, the metal at point A flows towards the center of the die, while the metal at point B flows away from the center of the die. Eventually, the metal velocities at points A and B become approximately the same. A ≈V B The rolling deformation stresses are basically symmetrical and equal, and the hook bends basically disappear.

[0041] Example 2

[0042] Implementation of Ф250 hook bending solution:

[0043] The rolling process involved a BD mill for billet preparation, followed by a V1 vertical 850mm mill, an H850 flat roll mill, and a V3 vertical 850mm mill. This process produced Ф250mm round steel bars with temperatures of 933℃ and 1105℃ on both sides, causing bending during rolling. The #2 elliptical bore had a sidewall angle of 112° and a bottom arc radius of R800mm. The rolling speed was 0.430m / s. The roll diameter at point A (contact bore type) was Ф810mm. A =0.387m / s, contact point B roll diameter Ф735.5mm, V B =0.352m / s, V A >V B Due to the speed difference, during the rolling deformation process, the deformation speed at point A is faster than that at point B. During the rolling deformation process, the metal flow at point A is subjected to tensile stress from the metal flow at point B. Under the action of tensile stress, the metal at point A flows towards the center of the die, while the metal at point B flows away from the center of the die. Eventually, the metal velocities at points A and B become approximately the same. A ≈V B The rolling deformation stresses are basically symmetrical and equal, and the hook bends basically disappear.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for straightening and bending special steel large bars using a speed difference in the pass profile, characterized in that, The process includes the following steps: feeding the bent head of the workpiece to be corrected into a speed difference straightening hole between the upper and lower rolls; on one side of the speed difference straightening hole, either above or below, the left side of the bent head contacts point A on the inner wall of the speed difference straightening hole, and the right side of the bent head contacts point B on the inner wall of the speed difference straightening hole, wherein the vertical height of point A is lower than the vertical height of point B; in the same cross section, the metal deformation at point A is faster than the metal deformation at point B, and the metal at point B generates tensile stress on the metal at point A, thereby correcting the bending of the bent head of the workpiece to be corrected under the action of tensile stress; The speed difference straightening hole is symmetrical vertically and horizontally. The speed difference straightening hole on the upper or lower side includes a top arc surface. Each side of the top arc surface is connected to the upper part of a side wall. The lower part of the side wall is connected to a horizontal edge. The side wall is inclined from top to bottom to the outside of the top arc surface. The angle between the side wall and the horizontal edge is an obtuse angle. The angle between the sidewall and the horizontal edge is 112°.

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