Magnesium alloy plate strip rolling on-line magnetic polishing tension curling integrated device and process

Abstract

The invention discloses an online magnetic polishing and tension curling integrated device and process for rolling a magnesium alloy plate strip, and belongs to the technical field of metal plastic processing surface treatment. The device is arranged between a finish rolling mill and a crimping machine and comprises a magnetic polishing groove body, a tension roller set, a magnetic grinding system and a constant tension crimping mechanism, and integration of online polishing and tension crimping is achieved through cooperation of all the components. According to the process, surface defect removal and regular coiling of the magnesium alloy plate strip are completed by accurately controlling polishing solution parameters, tension values, magnetic field parameters and the plate strip advancing speed. A traditional off-line grinding process is replaced, transfer procedures and magnesium chips are reduced, potential safety hazards are eliminated, the surface roughness Ra is smaller than or equal to 0.8 micrometer, the method is suitable for magnesium alloy plate strips of AZ31B, AZ61, AZ91 and the like with the width of 1600-1800 mm and the thickness of 0.5-6 mm, the production efficiency is improved by 35% or above, the cost is reduced by 50%, universality is high, and the high-quality requirements in the fields of aerospace, automobiles and the like are met.

Description

Technical Field

[0001] This invention relates to the field of metal plastic processing surface treatment technology, specifically to an integrated device and process for online magnetic polishing and tension coiling of magnesium alloy strip rolling, which is suitable for online surface treatment and coiling of magnesium alloy strips of grades such as AZ31B, AZ61, and AZ91 with a width of 1600-1800mm and a thickness of 0.5-6mm after final rolling. Background Technology

[0002] Magnesium alloy sheets and strips are widely used in aerospace and automotive fields due to their lightweight advantages. However, defects such as surface scratches and oxide scale are easily generated during the rolling process. Existing processing methods mostly use grinding or ordinary mechanical polishing: grinding generates a large amount of flammable magnesium shavings, posing a safety hazard and causing serious material waste; ordinary mechanical polishing relies on hard roller friction, which can easily cause scratches and deformation on the surface of magnesium alloy sheets and strips. Moreover, the tension needs to be readjusted after polishing before winding, resulting in poor process continuity.

[0003] While magnetic polishing technology is used in the surface treatment of aluminum alloys, magnesium alloys are chemically reactive and have low hardness (HB30-50). Directly applying the same magnetic polishing fluid and process parameters as aluminum alloys can lead to corrosion and hydrogen embrittlement of the magnesium sheet. Furthermore, existing magnetic polishing equipment cannot be integrated with the tension coiling process of rolling production lines, failing to meet the industrial requirements for online processing of magnesium alloy sheets and strips. Therefore, developing an integrated online magnetic polishing and tension coiling process adapted to the characteristics of magnesium alloys has become an urgent problem to be solved in the industry. Summary of the Invention

[0004] I. Purpose of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an integrated device and process for online magnetic polishing and tension coiling of magnesium alloy strip rolling, which can achieve efficient cleaning of surface scratches after final rolling of magnesium alloy strip, and at the same time complete tension coiling, replacing the traditional grinding process, reducing magnesium shavings and ensuring surface quality.

[0006] II. Technical Solution

[0007] (I) Integrated Online Magnetic Polishing and Tension Coiling Device for Magnesium Alloy Sheet and Strip Rolling

[0008] This device is located between the final mill and the coiling machine in a magnesium alloy sheet and strip rolling production line. It includes a magnetic polishing tank, tension rollers, a magnetic grinding system, and a constant tension coiling mechanism. The components work together to achieve integrated online polishing and tension coiling operations. The specific structure is as follows:

[0009] 1. Magnetic Polishing Tank: A rectangular structure, the main body is made of 316L stainless steel, resistant to corrosion from magnesium alloy polishing fluid. The inner wall is lined with a 0.5mm thick PTFE coating to prevent magnesium ions from displacing into the metal tank. The tank is 3000mm long, ensuring a polishing contact time of ≥2s for the strip; 1900mm wide, suitable for strips 1600~1800mm wide; and 250mm deep, maintaining a polishing fluid level of 200mm, completely immersing the contact area between the magnetic abrasive and the strip. The inlet and outlet are equipped with 30° flared guide ports to prevent scraping of the strip edges; the bottom is inclined at 1°, with a drain and magnetic filter (1μm filtration accuracy) at the lower end to adsorb magnesium shavings and abrasive impurities; an external constant temperature jacket is installed, with temperature control via heat transfer oil, accurate to ±2℃, maintaining a stable polishing fluid temperature.

[0010] 2. Tension Roller Assembly: This includes the inlet tension roller, the in-slot support roller, and the outlet tension roller. The inlet / outlet tension rollers are active tension rollers with a diameter of 200mm and a length of 1900mm. They are equipped with tension sensors (accuracy ±5N) and the tension value is controlled by a PLC closed-loop system. The in-slot support rollers are magnetic guide rollers with a diameter of 150mm and a length of 1900mm. They have built-in electromagnetic coils and are linked with the magnetic polishing system. They not only guide the strip but also enhance the local magnetic field strength, improving polishing uniformity.

[0011] 3. Magnetic Grinding System: Composed of an electromagnetic generator and magnetic abrasive media. The electromagnetic generator is a frequency-converting electromagnetic device installed on the outside of the polishing tank, outputting a magnetic field strength of 0.2–0.6T and a magnetic field frequency of 10–50Hz, which can be adjusted according to the degree of surface defects of the strip. The magnetic abrasive media consists of spherical iron-based abrasive coated with diamond micropowder, with a particle size of 800–1200 mesh, and a filling amount of 30%–40% of the polishing tank volume. Under the action of the magnetic field, it forms a "magnetic brush" that performs high-speed grinding motion on the strip surface, achieving micro-cutting.

[0012] 4. Constant tension winding mechanism: Linked with the exit tension roller, the winding tension value is consistent with the tension of the polishing section. The drum width is 2000mm, which is suitable for winding large-width magnesium alloy strips and ensures that the winding end face is neat.

[0013] (II) Online magnetic polishing and tension coiling process for magnesium alloy sheet and strip rolling

[0014] Based on the aforementioned integrated device, this process includes the following steps:

[0015] S1: The final rolled magnesium alloy strip enters the magnetic polishing tank through the guide port of the magnetic polishing tank. The polishing liquid temperature is maintained at 35±2℃ and the pH value is 5.0±0.2.

[0016] S2: The inlet tension roller sets the tension value according to the thickness of the strip (400-700N for 0.5-2mm strip, 900-1400N for 2-6mm strip), starts the electromagnetic generator of the magnetic grinding system, generates a magnetic field of 0.2-0.6T, drives the magnetic abrasive media to perform high-speed grinding motion on the surface of the strip, and removes surface scratches and oxide scale.

[0017] S3: After being guided by the support rollers in the groove, the strip is kept under stable tension by the exit tension roller. After polishing, it directly enters the constant tension winding mechanism to complete the winding. The strip travel speed is controlled at 4 to 9 m / min to ensure that the grinding time of the magnetic abrasive media is 2 to 5 seconds.

[0018] III. Working Principle

[0019] This device achieves continuous processing of magnesium alloy sheets and strips through the coordinated operation of three functional units: rolling, polishing, and coiling. The working logic of each unit and core component is as follows:

[0020] (I) Overall Work Process

[0021] After being rolled by the final rolling mill, the magnesium alloy strip directly enters the integrated device of this invention, where it sequentially passes through the tension roller group for guidance, the magnetic polishing unit for surface treatment, and the constant tension coiling unit for winding, completing the integrated operation of surface polishing and finished product winding. Throughout the process, the output speed of the rolling unit, the strip throughput speed of the polishing unit, and the winding linear speed of the coiling unit are kept in real time to avoid strip stretching or accumulation.

[0022] (II) Working principle of each unit

[0023] 1. Rolling Unit (connected upstream of this device): The motor outputs power to drive the rollers of the rolling roll system to rotate, which in turn drives the strip forward; the adjusting handwheel adjusts the gap (roll gap) between the upper and lower rollers in the rolling roll system through the screw transmission structure, so as to precisely control the rolling thickness of the strip; the frame provides rigid support for the rolling roll system, motor and other components to ensure the stability of the rolling process.

[0024] 2. Magnetic Polishing Unit (Core Processing Unit): After the electromagnetic generator is powered on, it generates a stable variable magnetic field. The magnetic force drives the magnetic abrasive medium to form a "magnetic brush," which impacts and rubs the surface of the magnesium alloy strip at high speed and uniformly, achieving micro-cutting and removing the oxide layer and minor defects after rolling. The constant temperature jacket of the magnetic polishing tank maintains a stable polishing fluid temperature, and the magnetic filter device adsorbs magnesium shavings and abrasive impurities in real time to avoid secondary pollution. The magnetic guide rollers in the tank not only serve as guides but also enhance the local magnetic field strength, improving the polishing uniformity of the wide strip. Because the polishing medium and the strip are in "flexible contact," it can avoid scratching the soft magnesium alloy. At the same time, the polishing force can be precisely controlled by adjusting the magnetic field strength and frequency.

[0025] 3. Tension winding unit: The drive motor outputs power, which drives the winding roller to rotate through the transmission structure; the tension sensor of the inlet / outlet tension roller detects the tension value of the strip in real time, and the tension is precisely adjusted through PLC closed-loop control to maintain the strip running within the "stable tension range"; the buffer structure buffers the vibration during the winding process to avoid tension fluctuations; the base and support components provide stable support for the entire winding unit to ensure that the winding end face is neat.

[0026] (III) Unit Coordination Logic

[0027] The rolling speed of the rolling unit, the strip passing speed of the magnetic polishing unit, and the winding speed of the tension winding unit are synchronized in real time through the electronic control system. At the same time, the detection signal of the tension adjustment unit is fed back to the rolling unit and the winding unit to fine-tune the rolling output speed and winding speed, ensuring that the strip is always in a stable tension state, and ultimately achieving continuous processing with "high rolling precision, excellent surface quality and regular winding".

[0028] IV. Beneficial Effects

[0029] 1. Process integration advantages: This invention integrates magnetic polishing and tension coiling into a magnesium alloy rolling production line, realizing online surface treatment of wide strips, replacing the traditional offline grinding process, reducing strip transfer steps, increasing production efficiency by more than 35%, and reducing the transfer cost and deformation risk of wide strips.

[0030] 2. Environmental and safety advantages: Magnetic polishing is a micro-cutting process, with magnesium shavings generated being <0.001kg / m². 2 The cost of magnesium shavings processing is reduced by more than 90% compared to traditional grinding processes, and the flammability of magnesium shavings is eliminated. The polishing fluid can be recycled, resulting in high raw material utilization and meeting the requirements of green manufacturing.

[0031] 3. Surface quality advantages: The flexible polishing method of magnetic grinding is adopted, combined with a special polishing fluid for magnesium alloys, to avoid hard contact and scratches on the strip. The surface roughness Ra≤0.8μm, which meets the delivery quality requirements; the polishing uniformity deviation of the wide strip is ≤0.05μm, and the surface is free of defects such as oxide scale and scratches.

[0032] 4. Versatility Advantage: It is compatible with mainstream rolled magnesium alloy grades such as AZ31B, AZ61, and AZ91, as well as strips with widths of 1600-1800mm and thicknesses of 0.5-6mm. It overcomes the limitation of existing magnetic polishing processes that are only compatible with narrow aluminum alloy strips, and has a wide range of applications.

[0033] V. Explanation of Novelty and Inventiveness

[0034] 1. Novelty of process integration: For the first time, magnetic polishing and tension winding are integrated into a magnesium alloy strip rolling production line, realizing online synchronous completion of surface treatment and winding, breaking through the current situation where magnetic polishing equipment is disconnected from the production line; the tension roller group and magnetic guide roller designed for wide magnesium alloy strips solve the problem of poor polishing uniformity of wide strips.

[0035] 2. Novelty of polishing fluid formulation: We developed a weakly acidic magnetic polishing fluid for magnesium alloys, containing ammonium bifluoride corrosion inhibitor and citric acid complexing agent. This is different from the neutral polishing fluid for aluminum alloys, avoiding hydrogen embrittlement and corrosion during the polishing process of magnesium alloys, and providing core chemical support for online magnetic polishing.

[0036] 3. Creativity in parameter design: Targeting the low hardness of magnesium alloys, the magnetic field strength is controlled at 0.2-0.6T (far lower than the 0.8-1.2T required for aluminum alloy polishing), and the tension value is set at 20%-25% of the yield strength. This breaks through the inertia of parameter design in existing magnetic polishing equipment and achieves damage-free polishing of magnesium alloy sheets and strips.

[0037] 4. Significant improvement in technical performance: Magnesium shavings generated after polishing <0.001 kg / m³ 2 It is far lower than the 0.05 kg / m of traditional grinding processes. 2 Eliminates safety hazards; surface roughness Ra≤0.8μm, meeting delivery quality requirements; production efficiency increased by 35%, cost reduced by 50%, adaptable to multiple grades of magnesium alloy plates and strips, with strong versatility. Attached Figure Description

[0038] Figure 1 Schematic diagram of an integrated online magnetic polishing and tension coiling device for magnesium alloy sheet and strip rolling;

[0039] Explanation of component labels in the diagram: ①-Adjusting handwheel, ②-Motor, ③-Frame, ④-Drive motor, ⑤-Rolling roll system, ⑥-Magnetic polishing assembly, ⑦-Polishing medium, ⑧-Tension adjustment unit, ⑨-Transmission gear set, ⑩-Take-up roll. -Support shaft, - Buffer spring, - Base.

[0040] Figure 2 Flowchart of the integrated online magnetic polishing and tension coiling process for magnesium alloy sheet and strip rolling. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0042] Example 1: In-line magnetic polishing and coiling of AZ31B magnesium alloy thin strip (thickness 0.5mm, width 1600mm)

[0043] Using the integrated device of this invention, the magnetic polishing fluid, by mass fraction, consists of 5% ammonium dihydrogen phosphate, 2% citric acid, 1.5% ammonium bifluoride, 0.8% polyethylene glycol, 0.5% sodium dodecyl sulfate, and 90.2% deionized water. The temperature is controlled at 35℃, and the pH value is 5.0. The electromagnetic generator has a magnetic field strength of 0.2T and a magnetic field frequency of 10Hz. The magnetic abrasive medium is 800-mesh diamond-coated iron-based abrasive, and the filling amount is 30% of the polishing tank volume. The inlet / outlet tension rollers are set to a tension value of 400N, the strip travel speed is 4m / min, and the grinding time is 5s. After treatment, the surface scratches of the AZ31B magnesium alloy strip are completely removed, the surface roughness Ra is 0.8μm, the strip has no tensile deformation, the perpendicularity error of the winding end face is ≤0.5mm, and the amount of magnesium chips generated is <0.0005kg / m. 2 .

[0044] Example 2: Online magnetic polishing and coiling of AZ31B magnesium alloy strip (thickness 1.2mm, width 1700mm). The polishing slurry formula and temperature were the same as in Example 1. The electromagnetic generator had a magnetic field strength of 0.3T and a magnetic field frequency of 20Hz. The magnetic abrasive medium was 1000-mesh diamond-coated iron-based abrasive with a filling amount of 35%. The tension was set to 550N, the strip travel speed was 6m / min, and the polishing time was 3.5s. After treatment, the surface roughness Ra of the AZ31B magnesium alloy strip was 0.6μm, the width direction roughness deviation was ≤0.04μm, there was no oxide scale on the surface, and the strip had no interlayer scratches after coiling.

[0045] Example 3: Online magnetic polishing and coiling of AZ61 magnesium alloy medium-thick strip (thickness 3mm, width 1750mm). The polishing slurry formula and temperature were the same as in Example 1. The electromagnetic generator had a magnetic field strength of 0.4T and a magnetic field frequency of 30Hz. The magnetic abrasive medium was 1000-mesh diamond-coated iron-based abrasive with a filling amount of 35%. The tension was set to 900N, the strip travel speed was 7m / min, and the polishing time was 3s. After treatment, the surface roughness Ra of the AZ61 magnesium alloy strip was 0.5μm, the surface flatness error was ≤0.02mm / 100mm, and the magnesium chip generation was <0.0008kg / m. 2 This meets the delivery requirements for lightweight automotive components.

[0046] Example 4: Online magnetic polishing and coiling of AZ61 magnesium alloy medium-thick strip (thickness 4.5mm, width 1800mm). The polishing slurry formula and temperature were the same as in Example 1. The electromagnetic generator had a magnetic field strength of 0.5T and a magnetic field frequency of 40Hz. The magnetic abrasive medium was 1200-mesh diamond-coated iron-based abrasive with a filling amount of 40%. The tension was set to 1200N, the strip travel speed was 8m / min, and the polishing time was 2.5s. After treatment, the surface roughness Ra of the AZ61 magnesium alloy strip was 0.4μm, with no indentations, cracks, or other defects. The coiled strip end face was neat, and the perpendicularity error was ≤0.8mm.

[0047] Example 5: Online magnetic polishing and coiling of AZ91 magnesium alloy thick strip (thickness 6mm, width 1800mm). The polishing slurry formula and temperature were the same as in Example 1. The electromagnetic generator had a magnetic field strength of 0.6T and a magnetic field frequency of 50Hz. The magnetic abrasive medium was 1200-mesh diamond-coated iron-based abrasive with a filling amount of 40%. The tension was set to 1400N, the strip travel speed was 9m / min, and the polishing time was 2s. After treatment, the surface roughness Ra of the AZ91 magnesium alloy strip was 0.3μm, the surface was bright and uniform, there were no polishing scratches, and the amount of magnesium chips generated was <0.001kg / m. 2 This meets the delivery requirements for rail transit equipment components.

[0048] Example 6: Online magnetic polishing and coiling of AZ91 magnesium alloy thick strip (thickness 5mm, width 1650mm). The polishing slurry formula and temperature were the same as in Example 1. The electromagnetic generator had a magnetic field strength of 0.55T and a magnetic field frequency of 45Hz. The magnetic abrasive medium was 1100-mesh diamond-coated iron-based abrasive with a filling amount of 38%. The tension was set to 1100N, the strip travel speed was 7.5m / min, and the polishing time was 2.8s. After treatment, the surface roughness Ra of the AZ91 magnesium alloy strip was 0.35μm, the polishing uniformity deviation in the width direction was ≤0.03μm, and the overall performance of the coiled strip met the delivery standards for high-end equipment manufacturing.

Claims

1. An integrated online magnetic polishing and tension coiling device for magnesium alloy sheet and strip rolling, characterized in that: Located between the final rolling mill and the coiling machine in a magnesium alloy sheet and strip rolling production line, the system includes a magnetic polishing tank, a tension roller assembly, a magnetic grinding system, and a constant tension coiling mechanism. The magnetic polishing tank is a rectangular structure, primarily made of 316L stainless steel, with a 0.5mm thick polytetrafluoroethylene coating on the inner wall. The tank is 3000mm long, 1900mm wide, and 250mm deep. It features 30° flared guide ports at the inlet and outlet, a 1° inclined bottom with a drain outlet and a 1μm precision magnetic filter at the lower end, and a constant-temperature jacket for heat-conducting oil on the outer side. The tension roller assembly includes an inlet tension roller, an in-tank support roller, and an outlet tension roller. The inlet / outlet tension rollers have a diameter of 200mm. An active tension roller with a length of 1900mm is equipped with a tension sensor with an accuracy of ±5N; the inner support roller is a magnetic guide roller with a diameter of 150mm and a length of 1900mm, with an internal electromagnetic coil and linked to the magnetic polishing system; the magnetic polishing system consists of a frequency conversion electromagnetic generator and magnetic abrasive media. The electromagnetic generator is installed on the outside of the polishing tank, outputting a magnetic field strength of 0.2~0.6T and a magnetic field frequency of 10~50Hz. The magnetic abrasive media is spherical iron-based abrasive coated with diamond micro powder, with a particle size of 800~1200 mesh, and a filling amount of 30%~40% of the polishing tank volume; the constant tension winding mechanism is linked to the exit tension roller, and the winding width is 2000mm.

2. The online magnetic polishing tension coiling process for magnesium alloy strip rolling based on the device described in claim 1, characterized in that: Includes the following steps: S1: The final rolled magnesium alloy strip enters the magnetic polishing tank through the guide port. The polishing liquid temperature is maintained at 35±2℃ and the pH value is 5.0±0.

2. S2: The inlet tension roller is set with a tension value according to the strip thickness. The tension value is set to 400~700N for 0.5~2mm strip and 900~1400N for 2~6mm strip. The electromagnetic generator is started to generate a magnetic field of 0.2~0.6T, which drives the magnetic abrasive media to grind the strip surface and remove scratches and oxide scale. S3: After the strip is guided by the support roller in the groove, the tension is maintained by the exit tension roller. After polishing, it directly enters the constant tension winding mechanism for winding. The strip travel speed is controlled at 4 to 9 m / min and the grinding time is 2 to 5 s.

3. The integrated device according to claim 1, characterized in that: The temperature control accuracy of the thermostatic jacket is ±2℃.

4. The process according to claim 2, characterized in that: The polishing solution contains, by mass fraction, 5% ammonium dihydrogen phosphate, 2% citric acid, 1.5% ammonium bifluoride, 0.8% polyethylene glycol, 0.5% sodium dodecyl sulfate, and 90.2% deionized water.

5. The integrated device according to claim 1, characterized in that: The constant tension winding mechanism maintains the same winding tension value as the polishing section tension.

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