Vacuum electron beam welding process and device for stainless steel composite plate blank machining

Abstract

The invention discloses a vacuum electron beam welding process and device for stainless steel composite plate blank processing, and relates to the technical field of stainless steel plate processing, and the vacuum electron beam welding process comprises the following steps: S2, pushing and locking: pressing down a trigger assembly to drive a transmission assembly to move, and further enabling a locking assembly to move to inwards extrude and fit a composite plate blank to lock the composite plate blank. According to the vacuum electron beam welding process and device for machining the stainless steel composite plate blank, the machining table is arranged for bearing the composite plate blank, when the composite plate blank is placed on the machining table, the trigger assembly is pressed down under the gravity effect so as to drive the transmission assembly to move, and then the composite plate blank is welded; further, the locking assembly moves to inwards extrude and fit the composite board blank and then lock the composite board blank, so that the composite board blank is passively pushed to be tightly fit and firmly locked, and poor welding caused by shaking during welding or irregular welding caused by insufficient fit is prevented.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel plate processing, and in particular to a vacuum electron beam welding process and a device for processing stainless steel composite plate blanks. Background Art

[0002] Stainless steel composite slab refers to a composite slab made of a carbon steel base layer and a stainless steel cladding layer. It combines the excellent properties of stainless steel such as corrosion resistance, wear resistance, and anti-magnetic properties, as well as the good weldability, formability, stretchability, and thermal conductivity of carbon steel.

[0003] Vacuum electron beam welding is a welding technology that uses a high-speed electron beam to hit the workpiece in a vacuum environment, converting the kinetic energy of the electrons into heat energy, melting the workpiece to form a weld. Under vacuum conditions, the electron beam emitted from the electron gun is accelerated by high voltage and focused into a high-energy-density electron beam through an electromagnetic lens. When the electron beam bombards the workpiece, the kinetic energy of the electrons is converted into heat energy, melting the workpiece material and achieving welding.

[0004] Under the existing technology, during the welding process, the plate blanks may produce a certain displacement due to thermal expansion or contraction. When the weld is welded by electron beam, the metal at the welding joint will melt rapidly, and the two butted plate blanks will shrink toward the weld, resulting in a certain amount of shrinkage. This shrinkage may cause the plate blanks to shake and displace to a certain extent, resulting in poor welding quality. Summary of the invention

[0005] The purpose of the present invention is to provide a vacuum electron beam welding process and device for processing stainless steel composite plate blanks to solve the above-mentioned shortcomings in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A vacuum electron beam welding process for processing stainless steel composite plate blanks comprises the following steps: S1. Feeding: Push the sheet metal onto the processing table; S2, push and lock: the trigger component is pressed down to drive the transmission component to move, and then the locking component moves to squeeze the composite plate inward to fit and lock the composite plate; S3, vacuuming: close the sliding door and start the vacuum pump to remove the air inside the shell; S4, welding: start the welder and drive the cylinder to make the welder move horizontally for welding; S5, welding completed: turn off the welding machine and the driving cylinder, and open the sliding door; S6. Take out the material: pull the lifting buckle to reset the locking assembly and take out the welded sheet.

[0007] A vacuum electron beam welding device for processing stainless steel composite plate blanks, which is applied to the vacuum electron beam welding process for processing the above-mentioned stainless steel composite plate blanks, comprises a shell and a processing table arranged inside the shell, a base is fixedly connected to the lower surface of the shell, a trigger component and a transmission component are arranged inside the base, the trigger component is connected to the lower surface of the processing table, the transmission component is movably connected to the trigger component, a locking component is also rotatably arranged inside the base, and the transmission component is connected to the locking component; When the composite slab is placed on the processing table, the trigger assembly is pressed down by gravity to drive the transmission assembly to move, thereby causing the locking assembly to move to squeeze the composite slab inward and lock the composite slab.

[0008] As a further preferred solution in the embodiment of the present invention, two conveying racks are fixedly connected to the lower surface of the inner part of the shell, and a plurality of conveying rollers are rotatably connected between the two conveying racks.

[0009] As a further preferred solution in the embodiment of the present invention, a welding groove is provided in the middle of the processing table, and a baffle is connected to the surface of one side of the processing table.

[0010] As a further preferred scheme in the embodiment of the present invention, the trigger assembly includes a connecting rod fixedly connected to the surface of one side of the conveying frame, and one end of the connecting rod is fixedly connected to a sleeve tube, and a connecting strip is slidably sleeved inside the sleeve tube, and the upper end of the connecting strip is fixedly connected to the lower surface of the processing table, and a transmission wheel is arranged at the lower end of the connecting strip.

[0011] As a further preferred scheme in the embodiment of the present invention, the transmission assembly includes a mounting seat fixedly connected to the lower surface of the base and a limiting track, and a transmission block is slidably connected inside the mounting seat, and a transmission inclined surface is provided on the upper surface of the transmission block, and the transmission wheel slides with the transmission inclined surface, and a transmission hole is provided at one end of the mounting seat, and a transmission rod is connected to one end of the transmission block, and a connecting seat is slidably connected in the limiting track, and one end of the transmission rod passes through the transmission hole and is connected to one end of the connecting seat, and a reset spring is connected between the transmission hole and the transmission block, and the reset spring is provided on the surface of the transmission rod.

[0012] As a further preferred scheme in the embodiment of the present invention, the locking assembly includes a first rotating shaft rotatably connected between the two sides of the base, and two pushing blocks are fixedly connected to the surface of the first rotating shaft, and two locking blocks are fixedly connected to one side surface of the two pushing blocks, and a second rotating shaft is rotatably connected between the upper ends of the two pushing blocks, and a transmission bar is connected to the surface of the second rotating shaft, and a third rotating shaft is rotatably connected to the other end of the connecting seat, and the lower end of the transmission bar is connected to the surface of the third rotating shaft.

[0013] As a further preferred scheme in the embodiment of the present invention, a sliding door is slidably connected to the surface of one side of the shell, a sealing groove is provided on the other side of the shell, a reset groove is provided in the sealing groove, a reset rod is also connected to the surface of the second rotating shaft, one end of the reset rod passes through the sealing groove and is connected to a lifting buckle, a sealing spring is connected to the inside of the reset groove, one end of the sealing spring is connected to a sealing block, and the upper end of the sealing block abuts against the lower surface of the reset rod.

[0014] As a further preferred solution in the embodiment of the present invention, a vacuum pump is provided on the upper surface of the shell, and an exhaust pipe and an exhaust pipe are connected to the vacuum pump. One end of the exhaust pipe passes through the upper surface of the shell and is connected to the inside of the shell.

[0015] As a further preferred solution in the embodiment of the present invention, a power connection track is provided on the upper surface of the shell, a welder is slidably connected inside the power connection track, a driving cylinder is provided on one side surface of the shell, and the telescopic end of the driving cylinder is connected to the surface of the welder.

[0016] In the above technical scheme, the vacuum electron beam welding process and device for processing stainless steel composite slab provided by the present invention have the following beneficial effects: The present invention arranges a processing table to carry the composite plate blank. When the composite plate blank is placed on the processing table, the trigger component is pressed down under the action of gravity to drive the transmission component to move, thereby causing the locking component to move to squeeze the composite plate blank inward to fit it and then lock the composite plate blank, so that the composite plate blank is passively pushed to fit tightly and locked firmly, preventing shaking during welding that may cause poor welding or insufficient fitting that may cause uneven welding.

[0017] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

[0018] This application document provides an overview of various implementations or examples of the technology described in the present disclosure, and is not a comprehensive disclosure of the entire scope or all features of the disclosed technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0020] Figure 1 A schematic diagram of the overall structure provided by an embodiment of the present invention; Figure 2 A schematic diagram of a local structure provided by an embodiment of the present invention; Figure 3A schematic diagram of the internal structure provided by an embodiment of the present invention; Figure 4 A partial cross-sectional view provided for an embodiment of the present invention; Figure 5 The embodiment of the present invention provides Figure 4 The enlarged structural diagram at A in the middle; Figure 6 The embodiment of the present invention provides Figure 4 The enlarged structural diagram at B in the middle; Figure 7 A schematic diagram of the internal partial structure when no sheet metal is placed according to an embodiment of the present invention; Figure 8 The embodiment of the present invention provides Figure 7 The enlarged structural diagram at C in the middle; Fig. 9 A schematic diagram of a partial internal structure provided by an embodiment of the present invention; Fig.10 The embodiment of the present invention provides Fig. 9 Enlarged structural diagram at point D in the middle.

[0021] Description of reference numerals: 100, housing; 101, reset groove; 102, sealing groove; 103, sliding door; 200, vacuum pump; 201, exhaust pipe; 202, exhaust pipe; 300, conveyor frame; 301, conveyor roller; 302, processing table; 303, welding groove; 304, baffle; 400, connecting rod; 401, sleeve tube; 402, connecting strip; 403, transmission wheel; 500, mounting seat; 501, transmission hole; 502, transmission block; 503, transmission Moving inclined plane; 504, transmission rod; 505, reset spring; 600, base; 601, first rotating shaft; 602, pushing block; 603, locking block; 604, second rotating shaft; 605, transmission bar; 606, third rotating shaft; 607, connecting seat; 608, limiting rail; 700, reset rod; 701, lifting buckle; 702, sealing block; 703, sealing spring; 800, power supply rail; 801, welding device; 802, driving cylinder. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0023] See also Figure 1 - Fig.10 A vacuum electron beam welding process for processing stainless steel composite slabs comprises the following steps: S1. Feeding: Push the sheet metal onto the processing table; S2, push and lock: the trigger component is pressed down to drive the transmission component to move, and then the locking component moves to squeeze the composite plate inward to fit and lock the composite plate; S3, vacuuming: close the sliding door and start the vacuum pump to remove the air inside the shell; S4, welding: start the welder and drive the cylinder to make the welder move horizontally for welding; S5, welding completed: turn off the welding machine and the driving cylinder, and open the sliding door; S6. Take out the material: pull the lifting buckle to reset the locking assembly and take out the welded sheet.

[0024] The present invention arranges a processing table to carry the composite plate blank. When the composite plate blank is placed on the processing table, the trigger component is pressed down under the action of gravity to drive the transmission component to move, thereby causing the locking component to move to squeeze the composite plate blank inward to fit it and then lock the composite plate blank, so that the composite plate blank is passively pushed to fit tightly and locked firmly, preventing shaking during welding that may cause poor welding or insufficient fitting that may cause uneven welding.

[0025] A vacuum electron beam welding device for processing stainless steel composite slabs, which is applied to the vacuum electron beam welding process for processing the above-mentioned stainless steel composite slabs, comprises a housing 100 and a processing table 302 arranged inside the housing 100, a base 600 is fixedly connected to the lower surface of the housing 100, a trigger assembly and a transmission assembly are arranged inside the base 600, the trigger assembly is connected to the lower surface of the processing table 302, the transmission assembly is movably connected to the trigger assembly, a locking assembly is also rotatably arranged inside the base 600, and the transmission assembly is connected to the locking assembly; When the composite slab is placed on the processing table 302, the trigger assembly is pressed down by gravity to drive the transmission assembly to move, thereby causing the locking assembly to move to squeeze the composite slab inwards and lock the composite slab.

[0026] In an embodiment further provided by the present invention, two conveying racks 300 are fixedly connected to the lower surface of the inner part of the shell 100 , and a plurality of conveying rollers 301 are rotatably connected between the two conveying racks 300 .

[0027] Specifically, the sheet metal is pushed onto the processing table 302 by the conveying roller 301 .

[0028] In an embodiment further provided by the present invention, a welding groove 303 is provided in the middle of the processing table 302 , and a baffle 304 is connected to a surface of one side of the processing table 302 .

[0029] Furthermore, the baffle 304 blocks the board so that the board is aligned front and back.

[0030] Furthermore, the welding groove 303 is hollow to prevent the sheet metal and the processing table 302 from being welded together during welding.

[0031] In an embodiment further provided by the present invention, the trigger assembly includes a connecting rod 400 fixedly connected to the surface of one side of the conveying frame 300, and one end of the connecting rod 400 is fixedly connected to a sleeve tube 401, and a connecting strip 402 is slidably sleeved inside the sleeve tube 401, and the upper end of the connecting strip 402 is fixedly connected to the lower surface of the processing table 302, and a transmission wheel 403 is arranged at the lower end of the connecting strip 402.

[0032] Specifically, after the blank is pushed onto the processing table 302, the connecting strip 402 is pressed down by the gravity of the blank.

[0033] Furthermore, under the action of the sleeve 401, the movement direction of the connecting strip 402 is limited to vertical movement.

[0034] In an embodiment further provided by the present invention, the transmission assembly includes a mounting seat 500 fixedly connected to the lower surface of the base 600 and a limiting track 608, and a transmission block 502 is slidably connected inside the mounting seat 500, and a transmission inclined surface 503 is provided on the upper surface of the transmission block 502, and the transmission wheel 403 slides with the transmission inclined surface 503, and a transmission hole 501 is provided at one end of the mounting seat 500, and a transmission rod 504 is connected to one end of the transmission block 502, and a connecting seat 607 is slidably connected in the limiting track 608, and one end of the transmission rod 504 passes through the transmission hole 501 and is connected to one end of the connecting seat 607, and a reset spring 505 is connected between the transmission hole 501 and the transmission block 502, and the reset spring 505 is provided on the surface of the transmission rod 504.

[0035] Specifically, after the connection strip 402 is pressed down, the transmission wheel 403 rolls on the transmission slope 503 to push the transmission block 502 outward, thereby pushing the connection seat 607 to slide outward on the limiting track 608.

[0036] Furthermore, when the transmission block 502 is pushed, the return spring 505 is compressed. After the welding is completed and the sheet metal is pulled apart, the return spring 505 can quickly return the entire device to its original position.

[0037] In an embodiment further provided by the present invention, the locking assembly includes a first rotating shaft 601 rotatably connected between two sides of a base 600, and two pushing blocks 602 are fixedly connected to the surface of the first rotating shaft 601, and two locking blocks 603 are fixedly connected to the surfaces of one side of the two pushing blocks 602, and a second rotating shaft 604 is rotatably connected between the upper ends of the two pushing blocks 602, and a transmission bar 605 is connected to the surface of the second rotating shaft 604, and a third rotating shaft 606 is rotatably connected to the other end of the connecting seat 607, and the lower end of the transmission bar 605 is connected to the surface of the third rotating shaft 606.

[0038] Specifically, the connecting seat 607 slides outward to drive the transmission bar 605 to rotate around the third rotating shaft 606 as the axis, thereby driving the pushing block 602 to rotate around the first rotating shaft 601 as the axis with the cooperation of the second rotating shaft 604, and then the pushing block 602 moves upward and inward, pushing the sheet metal inward to squeeze it tightly, and after the pushing is completed, the locking block 603 is fitted on the upper surface of the sheet metal, so that the sheet metal is firmly locked and will not shake.

[0039] In an embodiment further provided by the present invention, a sliding door 103 is slidably connected to the surface of one side of the shell 100, a sealing groove 102 is provided on the other side of the shell 100, a reset groove 101 is provided in the sealing groove 102, a reset rod 700 is also connected to the surface of the second rotating shaft 604, one end of the reset rod 700 passes through the sealing groove 102 and is connected to a lifting buckle 701, a sealing spring 703 is connected inside the reset groove 101, one end of the sealing spring 703 is connected to a sealing block 702, and the upper end of the sealing block 702 abuts against the lower surface of the reset rod 700.

[0040] Furthermore, when the transmission bar 605 moves, it drives the reset rod 700 to slide upward in the sealing groove 102 , and under the action of the sealing spring 703 , the sealing block 702 always abuts against the lower surface of the reset rod 700 to ensure the vacuum environment inside the housing 100 .

[0041] Specifically, after welding is completed, the pressing and pulling buckle 701 is pulled down, so that the reset rod 700 pulls the transmission bar 605 to move, thereby resetting the push block 602 and the locking block 603, so that the sheet can be taken out smoothly.

[0042] In an embodiment further provided by the present invention, a vacuum pump 200 is provided on the upper surface of the shell 100 , and an exhaust pipe 201 and an exhaust pipe 202 are connected to the vacuum pump 200 . One end of the exhaust pipe 201 passes through the upper surface of the shell 100 and is connected to the inside of the shell 100 .

[0043] In an embodiment further provided by the present invention, a power connection track 800 is provided on the upper surface of the shell 100, a welder 801 is slidably connected inside the power connection track 800, a driving cylinder 802 is provided on one side surface of the shell 100, and the telescopic end of the driving cylinder 802 is connected to the surface of the welder 801.

[0044] In the present invention, the staff first aligns the two composite sheet metals, and then pushes the sheet metals onto the processing table 302 through the conveying roller 301, and ensures that the joint surfaces of the two sheet metals are on the welding groove 303. The baffle 304 blocks the sheet metals so that the sheet metals are aligned front and back. After the sheet metals are pushed onto the processing table 302, the connecting strip 402 is pressed down under the action of the gravity of the sheet metals, thereby driving the transmission wheel 403 to roll on the transmission inclined surface 503, pushing the transmission block 502 outward, thereby pushing the connecting seat 607 to slide outward on the limiting track 608, and then driving the transmission bar 605 to rotate with the third rotating shaft 606 as the axis, thereby driving the pushing block 602 to rotate with the first rotating shaft 601 as the axis with the cooperation of the second rotating shaft 604, thereby making the pushing block 602 move upward and inward, pushing the sheet metals inward to squeeze and fit tightly, and pushing After the movement is completed, the locking block 603 is attached to the upper surface of the sheet metal, so that the sheet metal is securely locked and will not shake; when the transmission bar 605 moves, it drives the reset rod 700 to slide upward in the sealing groove 102, and under the action of the sealing spring 703, the sealing block 702 is always in contact with the lower surface of the reset rod 700 to ensure the vacuum environment inside the shell 100; close the sliding door 103 and start the vacuum pump 200 to extract the air inside the shell 100 to create a vacuum environment, start the welder 801 and the driving cylinder 802, so that the driving cylinder 802 pushes the welder 801 to move horizontally to weld the joint surface of the sheet metal; after welding is completed, pull the downward pressure and pull buckle 701 to make the reset rod 700 pull the transmission bar 605 to move, so that the push block 602 and the locking block 603 are reset, so that the sheet metal can be smoothly taken out.

[0045] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A vacuum electron beam welding process for processing stainless steel composite slabs, characterized in that: The steps include: S1. Feeding: Push the sheet metal onto the processing table; S2, push and lock: the trigger component is pressed down to drive the transmission component to move, and then the locking component moves to squeeze the composite plate inward to fit and lock the composite plate; S3, vacuuming: close the sliding door and start the vacuum pump to remove the air inside the shell; S4, welding: start the welder and drive the cylinder to make the welder move horizontally for welding; S5, welding completed: turn off the welding machine and the driving cylinder, and open the sliding door; S6. Take out the material: pull the lifting buckle to reset the locking assembly and take out the welded sheet.

2. A vacuum electron beam welding device for processing stainless steel composite slabs, which is applied to the vacuum electron beam welding process for processing stainless steel composite slabs as claimed in claim 1, characterized in that: The invention comprises a shell (100) and a processing table (302) arranged inside the shell (100); a base (600) is fixedly connected to the lower surface of the shell (100); a trigger component and a transmission component are arranged inside the base (600); the trigger component is connected to the lower surface of the processing table (302); the transmission component is movably connected to the trigger component; a locking component is also rotatably arranged inside the base (600); and the transmission component is connected to the locking component; When the composite slab is placed on the processing table (302), the trigger component is pressed down under the action of gravity to drive the transmission component to move, thereby causing the locking component to move to press the composite slab inwards to fit and lock the composite slab.

3. The vacuum electron beam welding device for processing stainless steel composite plate blank according to claim 2, characterized in that: Two conveying racks (300) are also fixedly connected to the inner lower surface of the shell (100), and a plurality of conveying rollers (301) are rotatably connected between the two conveying racks (300).

4. The vacuum electron beam welding device for processing stainless steel composite plate blank according to claim 3, characterized in that: A welding groove (303) is provided in the middle of the processing table (302), and a baffle (304) is connected to a surface of one side of the processing table (302).

5. The vacuum electron beam welding device for processing stainless steel composite plate blank according to claim 4, characterized in that: The trigger assembly comprises a connecting rod (400) fixedly connected to a side surface of a conveying frame (300), one end of the connecting rod (400) is fixedly connected to a sleeve tube (401), a connecting strip (402) is slidably sleeved inside the sleeve tube (401), an upper end of the connecting strip (402) is fixedly connected to a lower surface of a processing table (302), and a transmission wheel (403) is provided at the lower end of the connecting strip (402).

6. The vacuum electron beam welding device for processing stainless steel composite plate blanks according to claim 5, characterized in that: The transmission assembly comprises a mounting seat (500) fixedly connected to the lower surface of the base (600) and a limiting track (608), and a transmission block (502) is slidably connected inside the mounting seat (500), and a transmission inclined surface (503) is provided on the upper surface of the transmission block (502), and the transmission wheel (403) is slidably matched with the transmission inclined surface (503), and a transmission hole (501) is provided at one end of the mounting seat (500), and a transmission rod (504) is connected to one end of the transmission block (502), and a connecting seat (607) is slidably connected inside the limiting track (608), and one end of the transmission rod (504) passes through the transmission hole (501) and is connected to one end of the connecting seat (607), and a return spring (505) is connected between the transmission hole (501) and the transmission block (502), and the return spring (505) is provided on the surface of the transmission rod (504).

7. The vacuum electron beam welding device for processing stainless steel composite plate blank according to claim 6, characterized in that: The locking assembly comprises a first rotating shaft (601) rotatably connected between two sides of the base (600), and two pushing blocks (602) are fixedly connected to the surface of the first rotating shaft (601), and two locking blocks (603) are fixedly connected to the surfaces of one side of the two pushing blocks (602), and a second rotating shaft (604) is rotatably connected between the upper ends of the two pushing blocks (602), and a transmission bar (605) is connected to the surface of the second rotating shaft (604), and a third rotating shaft (606) is rotatably connected to the other end of the connecting seat (607), and the lower end of the transmission bar (605) is connected to the surface of the third rotating shaft (606).

8. The vacuum electron beam welding device for processing stainless steel composite plate blanks according to claim 7, characterized in that: A sliding door (103) is slidably connected to the surface of one side of the shell (100), a sealing groove (102) is provided on the other side of the shell (100), a reset groove (101) is provided in the sealing groove (102), a reset rod (700) is also connected to the surface of the second rotating shaft (604), one end of the reset rod (700) passes through the sealing groove (102) and is connected to a lifting buckle (701), a sealing spring (703) is connected inside the reset groove (101), one end of the sealing spring (703) is connected to a sealing block (702), and the upper end of the sealing block (702) abuts against the lower surface of the reset rod (700).

9. The vacuum electron beam welding device for processing stainless steel composite plate blanks according to claim 8, characterized in that: A vacuum pump (200) is provided on the upper surface of the shell (100), and an air extraction pipe (201) and an exhaust pipe (202) are connected to the vacuum pump (200), and one end of the air extraction pipe (201) passes through the upper surface of the shell (100) and is connected to the interior of the shell (100).

10. The vacuum electron beam welding device for processing stainless steel composite plate blank according to claim 9, characterized in that: An electric connection track (800) is provided on the upper surface of the shell (100), a welder (801) is slidably connected to the inside of the electric connection track (800), and a driving cylinder (802) is provided on one side surface of the inside of the shell (100), the telescopic end of the driving cylinder (802) is connected to the surface of the welder (801).

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