A method for reducing the grinding amount of a support roll of a hot tandem mill

Abstract

The application discloses a method for reducing the grinding amount of a supporting roller of a hot continuous rolling mill, and comprises the following steps: A, confirming the use condition of the supporting roller on the machine; B, checking and recording the roller surface of the supporting roller off the machine; C, grinding the supporting roller on a grinding machine, and detecting by using a grinding machine eddy current flaw detector; D, detecting the hardness of the roller surface after grinding; E, checking the roller body surface, and detecting by using coloring flaw detection if necessary; and F, performing ultrasonic flaw detection on the roller surface. The method solves the problems of crack expansion and peeling of the supporting roller on the machine due to the too small grinding amount of the supporting roller and the waste caused by the too large grinding amount, so that the grinding amount is optimized, and the cost of the rolling mill is reduced.

Description

Technical Field

[0001] This invention relates to a method for determining the amount of grinding of support rolls during the maintenance of hot strip mill rolls, belonging to the field of roll maintenance technology. Background Technology

[0002] Support rolls are crucial components of hot strip mills. They support the work rolls, transmit rolling pressure, and prevent excessive deflection of the work rolls, which could affect the output and quality of the strip. Hot-rolled strip steel is mainly produced by 4-high hot strip mills. Hot strip mill lines typically have 6-7 stands, with each mill consisting of 2 work rolls and 2 support rolls. Each hot strip mill line is equipped with 12-14 support rolls.

[0003] Hot-rolled support rolls are high-value-added products with high technical difficulty, complex processes, many production steps, and long manufacturing cycles. The support rolls are mainly made of high-chromium alloy steel and are produced through casting or forging processes. The roll body has high hardness and good wear resistance. Taking a 40-ton support roll as an example, each roll is worth about 1.5 million yuan.

[0004] The support rolls of hot strip mills operate in harsh environments, subjected to high temperature, high pressure, high speed, and iron oxide scale. They endure extremely high cyclic impact loads, significant friction, and thermal stress, and have a long service life, typically 15-30 days. During this period, fatigue, wear, cracks, spalling, and chipping are common problems that severely impact their service life. Any accident involving the support rolls will inevitably cause production line downtime, and the handling process is lengthy and results in substantial losses.

[0005] After a period of use, the support rollers should be replaced and taken off the machine. The surface of the roller body should be ground and removed by grinding to remove defects such as cracks and fatigue layers. Otherwise, the cracks will expand and cause the roller surface to peel off and break off prematurely.

[0006] Support rolls are prone to surface spalling during use. Spalling can be caused by various factors, such as problems with the support roll's manufacturing and materials, or serious accidents during rolling. However, the most significant factor is inadequate grinding, inspection, and management of the support roll after it leaves the mill, resulting in incomplete repair of cracks. When the roll is reused, the cracks expand, leading to spalling.

[0007] The entire value of a support roller lies in its working layer. Taking a support roller with a total weight of 40 tons as an example, the total value is approximately 1.5 million yuan (the total value increases with the increase in the total weight of the support roller), but the usable working layer thickness is only 150mm (diameter direction, radius direction is 75mm). Therefore, grinding 1mm (diameter direction) is equivalent to a loss of 10,000 yuan.

[0008] To prevent support rolls from spalling and failing due to incomplete repair of cracks, steel mills typically increase the grinding amount after grinding to ensure their safe use. However, excessive grinding inevitably leads to waste. Therefore, controlling the grinding amount of support rolls to achieve the optimal amount is a key issue for hot strip mills to ensure stable production and reduce costs while increasing efficiency. Summary of the Invention

[0009] The purpose of this invention is to provide a method for reducing the grinding amount of support rolls in hot continuous rolling mills, so as to solve the problems of excessive grinding amount leading to crack expansion and peeling on the roll surface of the support roll and excessive grinding amount causing waste, thereby achieving the optimal grinding amount and reducing the cost of production line rolls.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for reducing the amount of grinding on the support rolls of a hot strip mill includes the following steps:

[0012] A. Confirmation of the support roller's usage status in the machine

[0013] It is essential to understand the rolling conditions of the support rolls, the rolling volume, and whether any accidents such as steel piling or clamping have occurred that could affect the service life of the support rolls. Support rolls that have experienced similar accidents should be carefully checked during grinding.

[0014] B. Inspection and recording of the support roller surface at the bottom of the machine.

[0015] The main inspection items for the support roller surface include: cracks, spalling, steel adhesion, pits, peeling, indentations, and bright bands. Defects should be graded according to severity, in descending order of severity: spalling, cracks, pits, peeling, indentations, and bright bands.

[0016] Detailed records of any defects found during inspection should be kept using a drawing method. Unfold the support roller surface into a square and mark the location of the defects and anomalies on the square. For significant defects, mark a line on the corresponding support roller bearing location using a dye penetrant to facilitate inspection during and after grinding.

[0017] C. Grind the support rollers on a grinding machine and inspect them using a grinding machine eddy current flaw detector.

[0018] Before grinding, measure the wear curve of the support roll on the grinding machine and compare it with the historical wear value of the support roll of the mill. Check whether there is local excessive wear (local concave curve). Abnormal wear conditions should be identified, such as excessive wear in local positions (local wear in the diameter direction is more than 0.5mm, which is abnormal). These abnormal positions should be recorded and checked carefully after grinding.

[0019] Calculate the in-machine wear value of the support roller (in-machine wear value = diameter at the center of the wear curve measured after the machine - diameter at the center of the curve measured before the machine). The in-machine wear value of the support roller should generally be less than 1mm. For support rollers with a wear value exceeding 1mm, special attention should be paid during grinding inspection.

[0020] During the grinding of the support roller, after every 0.3~0.5mm of grinding, the roller surface is subjected to eddy current testing using a grinding machine eddy current flaw detector. If the maximum crack value does not have a fixed location and gradually decreases with the increase of grinding amount, it is considered a normal phenomenon and the flaw detection is qualified. If the maximum crack value has a relatively fixed location and tends to increase with the increase of grinding amount, it is considered abnormal and the grinding amount should be increased until the crack value is less than 10.

[0021] If the flaw detection is successful, proceed to the next step; otherwise, continue grinding until the flaw detection is successful.

[0022] D. Test the hardness of the roller surface after grinding.

[0023] After grinding is completed, use a hardness tester to measure the hardness along the roller surface at 100mm intervals. Measure each point 5 times and take the average value. Record the hardness value of each point and compare it with historical data. The hardness value should be reduced to the hardness level after the last grinding, and the deviation should be within 3HSD (HSD is the unit of roller surface hardness, meaning the deviation should be within three units).

[0024] If the surface hardness value of the roller body after grinding is greater than the initial hardness 3HSD, it is considered that the fatigue layer at that position has not been cleaned and needs to be ground for another 0.3~0.5mm before retesting.

[0025] E. Inspect the surface of the roller body, and use dye penetrant testing if necessary.

[0026] The surface of the roller body after grinding must be inspected. There must be no cracks, chips or inclusions on the roller surface. Sand holes and air holes with a diameter not exceeding 3mm are allowed.

[0027] If the surface inspection fails, grind an additional 0.3~0.5mm or perform pitting and grinding on the affected area before retesting.

[0028] Localized pit grinding: Position the angle grinder wheel at a 30° angle to the roller surface and grind the defect location in an elliptical shape, with the major axis of the ellipse parallel to the axial direction of the support roller. The edges of the ground pit should be smooth and without sharp corners. After grinding, use dye penetrant testing to inspect the defect location, ensuring complete removal of the defect. Generally, the major diameter of the ellipse after grinding should be less than 100mm.

[0029] F. Perform ultrasonic flaw detection on the roller surface.

[0030] Use a portable ultrasonic flaw detector to perform ultrasonic flaw detection on the surface of the support roller. Refer to the ultrasonic flaw detection level classification table formulated on site, and achieve Level I or Level II as the qualified standard. After the flaw detection is qualified, it is installed on the machine for use. Otherwise, grind 0.3~0.5mm and retest until the flaw detection is qualified.

[0031] Table 2 Classification of Ultrasonic Flaw Detection Grades

[0032]

[0033] Note: Reaching Level I or II is considered acceptable, while reaching Level III, IV, V, or VI is considered unacceptable and requires further grinding and re-exploration.

[0034] The beneficial effects of this invention are: to achieve precise control of the grinding amount of hot rolling support rolls, to ensure the safe use of support rolls, and to effectively reduce roll consumption. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the method of the present invention.

[0036] Figure 2 This is the wear curve of the support roller in an embodiment of the present invention. Detailed Implementation

[0037] The present invention will be further explained and described below with reference to specific embodiments. Example

[0038] Take the support roller of the F2 stand in the continuous casting and rolling workshop of a steel company as an example.

[0039] A. Confirmation of the support roller's usage status in the machine

[0040] The F2 stand lower support roller (roller number 041501) was inspected and found to have been in use for 20 days, with a steel throughput of 150,000 tons. No steel piling or clamping accidents occurred during its use.

[0041] B. Inspection and recording of the support roller surface at the bottom of the machine.

[0042] 1. Upon inspection after machine removal, wear and peeling were observed on the roller surface at a distance of 450-650mm from the drive side;

[0043] 2. Measure the wear curve of the support roller on the grinding machine and calculate the in-machine wear value; the results are as follows: Figure 2 As shown in Table 3, there is concave abnormal wear in some local areas (the maximum local wear is 0.86 mm).

[0044] Table 3 Roller profile data before grinding

[0045]

[0046] C. Grind the support rollers on a grinding machine and inspect them using a grinding machine eddy current flaw detector.

[0047] After grinding 1 mm, the crack value and soft point value are basically within 10 and tend to stabilize, reaching the qualified standard. The data are listed in Table 4.

[0048] Table 4. Changes in eddy current testing values ​​after each grinding increment of 0.5 mm.

[0049]

[0050] D. Test the hardness of the roller surface after grinding.

[0051] Since hardness can reflect the performance of a material, the hardness of a roll will change accordingly after a fatigue layer is formed on its surface. Therefore, the hardness of the support roll is tracked during grinding.

[0052] Table 5. Hardness changes before and after grinding

[0053]

[0054] As shown in Table 5, the hardness measurement value is the smallest when the grinding amount exceeds 1.5 mm, which means that the fatigue layer on the roll surface has been removed at this time. Therefore, the grinding amount of 2.0 mm is a bit too large, and it is recommended to grind the roll to 1.5 mm in the future.

[0055] E. Inspect the surface of the roller body, and use dye penetrant testing if necessary.

[0056] The surface of the roller body after grinding must be inspected. There must be no cracks, chips or inclusions on the roller surface. Sand holes and air holes with a diameter not exceeding 3mm are allowed.

[0057] If the surface inspection fails, grind an additional 0.3~0.5mm or perform pitting and grinding on the affected area before retesting.

[0058] Localized pit grinding: Position the angle grinder wheel at a 30° angle to the roller surface and grind the defect location in an elliptical shape, with the major axis of the ellipse parallel to the axial direction of the support roller. The edges of the ground pit should be smooth and without sharp corners. After grinding, use dye penetrant testing to inspect the defect location, ensuring complete removal of the defect. Generally, the major diameter of the ellipse after grinding should be less than 100mm.

[0059] F. Perform ultrasonic flaw detection on the roller surface.

[0060] Using a portable ultrasonic flaw detector, ultrasonic testing was performed on the surface of the support roller. Obvious defect echoes were found on the roller surface, and the bottom of the defect echoes contained numerous stray waves, initially identified as inclusions or shrinkage cavities. After grinding 2mm, ultrasonic surface wave testing of the roller surface showed no abnormal defect reflection echoes. A visual inspection of the original defect area revealed no defects, indicating that the roller was ready for installation and use.

[0061] By implementing the above methods, precise control of the grinding amount of hot rolling support rolls is achieved, ensuring the safe use of support rolls and effectively reducing roll consumption. The average grinding amount of support rolls is reduced from 3.0mm to 2.0mm, a reduction of 1mm per roll, with each millimeter representing a value of 10,000 yuan. A certain hot strip mill has a 6-stand hot strip mill with a total of 12 support rolls. Each replacement reduces the grinding amount by 12mm, and each replacement reduces losses by 120,000 yuan. Calculated based on an average replacement every 20 days, there are 18.25 replacements per year (=365 / 120), resulting in an annual reduction of 219mm in support roll grinding amount (=12*18.25), and a reduction in support roll losses of 2.19 million yuan per year.

Claims

1. A method for reducing the grinding amount of support rolls in a hot continuous rolling mill, characterized in that, Includes the following steps: A. Confirmation of the support roller's usage status in the machine B. Inspection and recording of the support roller surface at the bottom of the machine. C. Grind the support rollers on a grinding machine and inspect them using a grinding machine eddy current flaw detector. During the grinding of the support roller, after every 0.3~0.5mm of grinding, an eddy current flaw detector is used to perform eddy current flaw detection on the roller surface. If the maximum crack value does not have a fixed location and gradually decreases with the increase of grinding amount, it is considered a normal phenomenon, the flaw detection is qualified, and the next step is continued; if the maximum crack value has a relatively fixed location and tends to increase with the increase of grinding amount, it is considered abnormal, and grinding should continue until the crack value is less than 10. D. Test the hardness of the roller surface after grinding. After grinding, use a hardness tester to measure the hardness along the roller surface at 100mm intervals. Measure each point 5 times and take the average value. Record the hardness value of each point and compare it with historical data. The hardness value should be reduced to the hardness level after the last grinding, and the deviation should be within 3HSD. If the surface hardness value of the roller body after grinding is greater than the initial hardness 3HSD, it is considered that the fatigue layer at that position has not been cleaned and needs to be ground for another 0.3~0.5mm before retesting. E. Inspect the surface of the roller body, and use dye penetrant testing if necessary. The surface of the roller body after grinding shall be inspected. There shall be no cracks, chips or inclusions on the roller surface. Sand holes and air holes with a diameter not exceeding 3mm are allowed. If the surface inspection fails, grind an additional 0.3~0.5mm or perform pitting and grinding on the affected area before retesting. F. Perform ultrasonic flaw detection on the roller surface. Use a portable ultrasonic flaw detector to perform ultrasonic flaw detection on the surface of the support roller. Refer to the ultrasonic flaw detection level classification table formulated on site, and take Level I and Level II as the qualified standard. After the flaw detection is qualified, it is installed on the machine for use. Otherwise, grind 0.3~0.5mm and retest until the flaw detection is qualified.

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