A special electromagnetic casting roll for magnesium alloy casting and rolling

Abstract

The solidification weld line is a comprehensive manifestation of the casting and rolling process. Addressing the "Ɔ"-shaped phenomenon of the solidification weld line in traditional casting and rolling processes, which leads to edge cracking and low yield in conventional cast and rolled sheets, this invention discloses a special electromagnetic casting roll for magnesium alloy casting and rolling. The roll includes a roll core, a roll sleeve, and end caps. A coil is uniformly wound between each water channel on the roll core, and a coil is uniformly wound inside the roll sleeve. The end caps are made of composite ceramic material, and an insulating gasket is placed between the end caps and the coils to ensure good insulation. A pre-reserved groove on the end caps is used to adjust the energization of the coils on the roll core. The annular coil is connected to a brush to ensure smooth external power supply to the roll core and roll sleeve. The end caps are used to fix the roll core and roll sleeve. This invention can directionally and quantitatively improve the morphology of the solidification weld line and control the temperature of the casting and rolling zone by adjusting the parameters of the pulse current and the casting and rolling process parameters. This effectively reduces segregation, refines grains, and homogenizes the microstructure in cast and rolled strips, thereby improving the yield and product performance of magnesium alloy cast and rolled strips.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy material processing, specifically relating to an electromagnetic casting roll for magnesium alloy casting and rolling. Background Technology

[0002] Magnesium alloys are widely used in the automotive, military, aerospace, electronics, biomedical and energy fields due to their high specific strength and specific stiffness, as well as their good damping and shock absorption properties, good biocompatibility, good electromagnetic interference shielding, easy machining, recyclability and environmental friendliness. They are hailed as the green engineering material of the 21st century.

[0003] Casting and rolling integrates casting and rolling, enabling short-process, high-efficiency, and low-cost production of magnesium alloys. Traditional casting and rolling suffers from uneven cooling rates, with the magnesium alloy melt at the edges of the casting zone and near the surface of the rolls solidifying first. This results in an "Ɔ"-shaped solidification weld line along the width of the plate within the casting zone, making edge cracking highly likely during the casting and rolling process. Simultaneously, the cast-rolled plate exhibits uneven microstructure and segregation. The solidification weld line is a comprehensive reflection of the casting and rolling process parameters; its position and shape significantly influence the performance of the cast-rolled slab. Currently, research on adjusting the solidification weld line in magnesium alloy casting and rolling is limited, and simply changing the casting and rolling process parameters has limited effect on its shape control.

[0004] Based on the Lorentz force effect and Joule heating effect of pulsed magnetic field, this invention develops an electromagnetic roller specifically for magnesium alloy casting and rolling. By using the Lorentz force of pulsed magnetic field to adjust the shape of solidification weld line in magnesium alloy casting and rolling, the solidification weld line can be transformed from an "Ɔ" shape to an "I" shape, thereby achieving the purpose of suppressing edge cracks, refining grains, and homogenizing the microstructure of magnesium alloy casting and rolling. Summary of the Invention

[0005] To address the bottlenecks in existing technologies, this invention introduces a pulsed electromagnetic field into the rolling mill rolls to adjust the position and shape of the solidification weld line, thereby reducing edge cracking in magnesium alloys, refining grains, and homogenizing the microstructure. This invention aims to provide a pulsed magnetic field-assisted synergistic control technology for the shape of cast-rolled magnesium alloy sheets. By optimizing the structure and developing the functions of existing casting rolls, directional and quantitatively controllable Lorentz forces and Joule heating effects are obtained in the casting zone. The Lorentz force increases the metal flow rate in the casting zone, promoting the melting and secondary nucleation of dendrites, thus achieving grain refinement and microstructure homogenization. Controlling the Joule heating effect achieves uniform temperature across the entire sheet width in the solidification zone. The coupling effect of these two factors with the casting process parameters enables the control of the position and shape of the solidification weld line, aiming to achieve portable, high-quality, low-cost, and short-process magnesium alloy sheet production.

[0006] To achieve the above objectives, the present invention provides the following solution: a special electromagnetic casting roll for magnesium alloy casting and rolling, the equipment comprising: an end cover (1), a roll core (2), and a roll sleeve (3), wherein an annular coil positioning groove is reserved on the end cover (1), and the roll sleeve (3) and the roll core (2) are fixed to the end cover (1) by bolts. The roll core comprises: a water inlet (10), a water inlet branch (6), a water outlet branch (8), a water outlet (5), a coil winding, and a guide wire (13); the roll sleeve comprises: a composite ceramic coating, an embedded coil winding (14), and an annular coil (4); the pulse power supply comprises: a low-frequency pulse generator and a brush.

[0007] Preferably, the total length of the roller core plate in the width direction (axial direction) is 400mm and the diameter is 880mm. The roller core circulating cooling water channel adopts a rectangular cross section of 10*5mm and the material is aluminum alloy.

[0008] Preferably, the number of turns of the roller core water channel is 10 turns, and the coil is evenly wound between each turn of the water channel for a total of 80 turns. The circulating cooling water pressure in the water channel is 0.5 to 1 MPa, and the flow rate is 80 to 110 L / min.

[0009] Preferably, a coil is embedded in the roller sleeve, with the coil and water channel arranged alternately. The embedded coil is uniformly wound with 120*2 turns (240 turns in total) from both ends into a 100mm range along the width of the plate.

[0010] Preferably, the coil current is a sinusoidal pulse current with a current frequency of 1 to 10 Hz and a current peak value of 180 to 220 A.

[0011] Preferably, an annular coil is embedded on the outside of the roll end cover. The annular coil is connected to an external energy source through a brush to ensure that the external current is smoothly introduced into the coil. There is an insulating gasket between the annular coil and the end cover to ensure good insulation between the annular coil and the end cover.

[0012] Preferably, the end cap has a pre-reserved groove, and the guide wire of the roller core can contact the annular coil through the groove to control whether the roller core current is connected, which is used to adjust the magnetic field strength generated by the casting roll.

[0013] Selection of casting and rolling process parameters: casting temperature in the casting and rolling zone is 905-940K, casting and rolling speed is 1-3.5m / min, and exit height of the casting and rolling zone is 3-8mm.

[0014] This invention has advantages and positive effects:

[0015] 1. This invention enables the adjustment of the solidification weld line temperature gradient by a pulsed magnetic field, transforming it from an "Ɔ" shape to an "1" shape, which can suppress edge cracking in magnesium alloy casting and rolling.

[0016] 2. This invention applies a pulsed magnetic field to the entire casting and rolling zone, thereby achieving forced disturbance of the melt in the casting and rolling zone by electromagnetic force and alleviating the segregation phenomenon caused by uneven microstructure in the cast and rolled sheet.

[0017] 3. This invention utilizes the Lorentz force effect of a pulsed magnetic field to achieve fine-grain strengthening of the melt, thereby improving the yield and mechanical properties of cast and rolled slabs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the electromagnetic casting roll.

[0019] Figure 2 This is a schematic diagram of the roller sleeve;

[0020] Figure 3 Schematic diagram of the inner coil of the roller sleeve;

[0021] Figure 4 This is a schematic diagram of the roller core;

[0022] Figure 5 A schematic diagram of the coil wound between each turn of the water channel in the roller core;

[0023] Figure 6 This is a schematic diagram of the end cap;

[0024] Figure 7 This is a schematic diagram of the simulation model;

[0025] Figure 8 A comparative schematic diagram showing the simulation results of solidification weld lines.

[0026] Figure 9 A schematic diagram of the magnetic field acting on the casting and rolling zone (arrows indicate the direction of magnetic induction intensity).

[0027] Among them, 1. End cap; 2. Roller core; 3. Roller sleeve; 4. Ring coil; 5. Water outlet; 6. Water inlet branch; 7. Cooling water channel; 8. Water outlet branch; 9. Coil; 10. Water inlet; 11. Insulating gasket; 12. Slide groove; 13. Drain wire; 14. Embedded coil winding. Detailed Implementation

[0028] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Reference Figure 1-6This example provides a special electromagnetic casting roll for magnesium alloy casting and rolling. The equipment includes: end cover (1), roll core (2), and roll sleeve (3). Working principle: The roll diameter is 880mm and the total length is 400mm. The roll core (2) and the roll sleeve (3) are fixed on the end cover (1) by bolts to ensure that the roll core and the roll sleeve rotate synchronously. The external power supply is selected as sinusoidal pulse current with a current frequency of 1 to 10Hz and a current peak value of 180 to 220A. The positive and negative poles of the power supply are connected to the ring coil (4) through the brush. The current enters the embedded coil (14) of the roll sleeve (3). At this time, the current can be connected to the roll core coil by adjusting the guide wire (13). There is an insulating pad between the ring coil and the end cover to ensure the good insulation of the ring coil. The current generates a magnetic field strength of 0.3T with a frequency of 1 to 10Hz.

[0030] The cooling water pressure is 0.5-1MPa and the flow rate is 80-110L / min. Changing the cooling water flow rate can change the heat exchange rate. The cooling water enters through the inlet (10) and fills the entire water channel through the water inlet branch (6). Each water channel exchanges heat with the casting and rolling zone through the roller sleeve to achieve solidification of the magnesium alloy melt. The water channel also ensures the cooling of the coil embedded in the roller sleeve and the coil wound between the water channels, so as to cool the coil and ensure good conductivity of the coil.

[0031] The magnetic field generated by the casting rolls acts on the melt in the casting zone, causing the melt to generate an electromagnetic force along the width of the plate. The electromagnetic force generates a velocity in the width of the melt. The melt moves in the magnetic field, generating current and then Joule heating. Joule heating enhances the fluidity of the edges. The electromagnetic force and Joule heating together cause the solidification weld line to change from an "Ɔ" shape to an "1" shape.

[0032] Further optimization of the scheme: the outer surface of the roller sleeve (2) is coated with iron-nickel alloy and ceramic composite material to form a metal-ceramic composite material with magnetic conductivity and high temperature resistance; the coil has an insulating skin made of high temperature resistant asbestos silicone rubber.

[0033] Further optimization of the scheme: the inner surface of the roller sleeve (3) has a water channel groove, the groove matches the cooling water channel of the roller core (2), the end face of the roller sleeve has 8*M10 bolt holes, the roller sleeve (3) and the ring coil (4) are integrated, and the Lorentz force generated by the roller sleeve coil is precisely applied to the solidification and welding line area of ​​the casting and rolling zone.

[0034] Further optimization scheme: the roller core (2) is wound with coil windings between each water channel, and each winding is wrapped with an insulation layer. The lead wire (13) at the end of the coil contacts the ring coil (4) through the slide groove (12) so that the external current is introduced into the roller core to complete the magnetic field enhancement of the casting and rolling roll. The roller core is reserved with 6*M10 holes.

[0035] Further optimization of the scheme: the end cap (1) is reserved with a sliding groove (12) and a positioning groove for the annular coil. The positioning groove is made of elastic rubber-metal composite material, and there is an insulating pad between the annular coil and the positioning groove.

[0036] The implementation method includes the following steps:

[0037] a. The magnesium alloy billet is placed in a melting furnace for melting. The molten material enters the casting nozzle from the melting furnace and then reaches the casting and rolling zone for casting and rolling. The model of the casting and rolling zone is as follows: Figure 7 As shown;

[0038] b. The ring coil 4 is connected to the positive and negative terminals of the power supply via brushes. The lead wire 13 contacts the ring coil 4, energizing the roller core. The pulsed current generates a pulsed magnetic field that acts on the casting and rolling zone. The molten material moves in the casting and rolling zone under electromagnetic force, and the direction of movement changes with time. Joule heating is also generated simultaneously. The electromagnetic force acting on the casting and rolling zone is as follows: Figure 9 As shown;

[0039] c. Cooling water circulates from inlet (10) - inlet branch (6) - outlet branch (8) - outlet (5) to cool the casting rolls and solidify the melt in the casting zone, and cools the coils to ensure their conductivity. The cooling water model is as follows: Figure 5 As shown;

[0040] d. The molten material is subjected to electromagnetic force and Joule heating in the casting and rolling zone, causing the solidification weld line to change from an "Ɔ" shape to an "1" shape. The transformation of the solidification weld line is as follows: Figure 8 As shown;

[0041] e. The adjustment of the magnesium alloy casting-rolling solidification welding line can be completed by continuously repeating processes a to d.

[0042] A simulation was performed for this invention, and the casting and rolling zone model is as follows: Figure 7 As shown in Table 1, the casting and rolling process parameters are simulated. The simulated material is AZ31 magnesium alloy. The magnetic field strength applied to the roll is 0.3T, and the frequency is 8Hz. The simulation results are shown in the figure. Figure 8 It can be seen that applying a pulsed magnetic field can adjust the solidification weld line from an "Ɔ" shape to an "1" shape.

[0043] Traditional casting can only change the position of the solidification weld line by altering the casting and rolling process parameters, but cannot change its shape. This invention utilizes the Lorentz force and Joule heat generated by a pulsed magnetic field to adjust the shape of the solidification weld line to tend towards an "I" shape, making the cooling and solidification rate in the width direction of the plate more uniform, thereby suppressing edge cracking in magnesium alloy casting and rolling. At the same time, the melt is forced to oscillate, promoting the homogenization of the microstructure and improving the segregation phenomenon of the cast and rolled plate. The pulsed magnetic field generates a non-contact electromagnetic force on the melt, which also avoids the introduction of impurities. The yield and product performance of magnesium alloy cast and rolled plates are both improved.

[0044]

Claims

1. A method of regulating the solidification of a magnesium alloy weld bead using an electromagnetic casting roll, the method using a casting roll comprising: End cap (1), roller core (2), roller sleeve (3): The roller core (2) and roller sleeve (3) are fixed to the end cover (1) by bolts; The roller core includes: an inlet (10), an inlet branch (6), an outlet branch (8), an outlet (5), a coil winding, and a guide wire (13). The roller sleeve includes: a composite ceramic coating, an embedded coil winding (14), and a ring coil (4); the pulse power supply includes: a low-frequency pulse generator and a brush; The electromagnetic casting roll current input method is as follows: the casting roll is connected to the positive and negative poles of an external low-frequency pulse power supply through a brush, the external current is input to the ring coil (4) through the brush, the guide wire (13) is in direct contact with the ring coil (4) through the slide groove (12), and the current is input to the coil of the roll core (2); Specifically, the steps include the following: a. The magnesium alloy billet is placed in a melting furnace for melting. The melt enters the casting nozzle from the melting furnace and then reaches the casting and rolling zone for casting and rolling. b. The ring coil (4) is connected to the positive and negative terminals of the power supply through the brush. The lead wire (13) contacts the ring coil (4). The roller core is energized, and the pulse current generates a pulse magnetic field that acts on the casting and rolling zone. The melt moves in the casting and rolling zone under electromagnetic force. The direction of movement changes with time, and Joule heat is generated at the same time. c. Cooling water circulates from inlet (10) - inlet branch (6) - outlet branch (8) - outlet (5) to cool the casting rolls and solidify the melt in the casting zone, and cools the coils to ensure their conductivity. d. The molten material is subjected to electromagnetic force and Joule heating in the casting and rolling zone, and the solidification weld line changes from an "Ɔ" shape to an "1" shape; e. The control of the magnesium alloy casting-rolling solidification welding line can be completed by continuously repeating processes a to d.

2. The method for controlling the solidification weld line of magnesium alloys according to claim 1, characterized in that: The roller core (2) has a coil wound evenly between each water channel. The coil is provided with an insulating layer. The end lead wire (13) of the roller core (2) contacts the annular coil (4) through the slide groove (12). When the roller core current is connected, the roller core is de-energized. The coil can be quantitatively set according to the required position, magnetic field strength and temperature.

3. The method for controlling the solidification weld line of magnesium alloys according to claim 1, characterized in that: The cooling water of the roller core (2) is rapidly filled into each water channel through multiple water inlet branches (6) and flows out rapidly from multiple water outlet branches (8). The flow rate of the cooling water is adjustable and is used for rapid cooling of the casting roll and the coil winding.

4. The method for controlling the solidification weld line of magnesium alloy according to claim 1, characterized in that: The roller sleeve (3) is uniformly wound with coils from both ends into a range of 100mm. The magnetic field generated by the coil can accurately act on the "Ɔ"-shaped arc area of ​​the solidification weld line in the casting and rolling zone, producing an electromagnetic stirring effect.

5. The method for controlling the solidification weld line of magnesium alloys according to claim 1, characterized in that: The end cap (1) has a reserved sliding groove (12) and a reserved positioning groove for placing the ring coil (4). There is an insulating pad between the ring coil (4) and the positioning groove. The ring coil introduces external current into the casting roll, and the insulating pad ensures good insulation between the end cap and the ring coil.

6. The method for controlling the solidification weld line of magnesium alloys according to claim 1, characterized in that: The roller core (2) and roller sleeve (3) are fixed to the end cover (1) by bolts, so that the roller core and roller sleeve rotate synchronously and facilitate the later maintenance and replacement of the casting roll.

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