A uniformly magnetized plate for magnetic adhesive strips

Abstract

This invention belongs to the field of magnetizing plate technology, specifically a uniform magnetizing plate for magnetic adhesive strips. It includes a magnetizing plate body with multiple magnetizing grooves on its top. A magnetic field homogenizing plate is placed at the bottom of each groove. The bottom of the magnetizing coil is in close contact with the magnetic field homogenizing plate, which homogenizes the magnetic field generated by the magnetizing coil, ensuring a uniform magnetic field distribution. Simultaneously, a moving frame drives the adhesive strip to move at a uniform speed, ensuring that all parts of the adhesive strip fully contact the uniform magnetic field, achieving continuous and uniform magnetization. This effectively solves the problem of uneven magnetization in existing magnetizing plates, improves the magnetization quality of the magnetic adhesive strip, ensures a consistent magnetic field distribution, and meets the requirements for high-precision applications. A dual-positioning clamping structure is incorporated. An electric telescopic rod drives the adhesive strip to press down on the clamping plate, holding the adhesive strip in place. A pressure sensor monitors the clamping force in real time, preventing excessive clamping force from damaging the adhesive strip or insufficient clamping force from causing the adhesive strip to shift.

Description

Technical Field

[0001] This invention relates to the field of magnetizing plate technology, and more particularly to a uniformly magnetizing plate for magnetic adhesive strips. Background Technology

[0002] Magnetic adhesive strips are functional strips made by mixing magnetic materials with base materials such as rubber and plastics. They are widely used in door and window sealing, electronic equipment, and automotive parts. Their magnetic properties directly determine the product's performance and lifespan. The magnetizing plate is a core piece of equipment in the processing of magnetic adhesive strips, used to magnetize them and give them stable magnetism. CN110415914A discloses a uniformly magnetized plate for magnetic adhesive strips, including a base. A rectangular through groove is provided on the upper end surface of the base along its length direction. A magnetizing wire mounting core block is provided in the rectangular through groove. Two parallel magnetizing wire mounting through grooves are provided on the upper end surface of the magnetizing wire mounting core block along its length direction. Magnetizing wires are provided in the mounting through grooves. The two ends of the magnetizing wires extend to the outer sides of the base and the magnetizing wire mounting core block, respectively. The two magnetizing wires are connected together at the outer ends of the tail end of the magnetizing wire mounting core block, and the two magnetizing wires are conductive at this connection point. Multiple height adjustment mechanisms are provided on both side walls of the base along the length direction of the base. Existing uniform magnetizing plates for magnetic adhesive strips suffer from unstable strip positioning during magnetization, leading to misalignment and loosening. This results in insufficient contact between the strip and the magnetizing magnetic field, further exacerbating the uneven magnetization problem. Furthermore, the magnetizing coil generates significant heat during operation. If this heat cannot be dissipated promptly, the coil temperature will become excessively high, affecting magnetic field stability, shortening coil lifespan, and even damaging the magnetizing plate components. Therefore, we propose a uniform magnetizing plate for magnetic adhesive strips. Summary of the Invention

[0003] The purpose of this invention is to provide a uniformly magnetized plate for magnetic adhesive strips, which solves the existing problems.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A uniform magnetizing plate for magnetic adhesive strips includes a magnetizing plate body. The top of the magnetizing plate body has multiple magnetizing grooves, and the bottom of each magnetizing groove has multiple mounting slots. A coil fixing block is fixedly installed inside each mounting slot, and a magnetizing coil is fixedly installed inside each coil fixing block. A magnetic field homogenizing plate is fixedly installed on the bottom inner wall of each magnetizing groove. The bottom of the magnetizing coil abuts against the bottom of the magnetic field homogenizing plate. Heat dissipation fins are fixedly installed on the bottom of the magnetizing coil. A control box is fixedly installed on the rear side of the magnetizing plate body.

[0005] Preferably, a motor is fixedly installed on the right side of the control box, a lead screw is fixedly installed on the output end of the motor, a guide rod is fixedly installed on the inner side of the control box, a movable frame is threaded on the outer side of the lead screw, and the movable frame is slidably installed on the outer side of the guide rod.

[0006] Preferably, the movable frame is L-shaped, and multiple connecting frames are fixedly installed on the top inner wall of the movable frame. The connecting frames are slidably installed on the inner side of the magnetizing groove. An electric telescopic rod is fixedly installed on the inner side of the connecting frame. A pressure sensor is fixedly installed at the output end of the electric telescopic rod. A rubber strip pressing clamping plate is fixedly installed at the bottom of the pressure sensor.

[0007] Preferably, a plurality of connecting plates are fixedly installed on one side of the movable frame, a fixed cylinder is fixedly installed on the top of the connecting plates, a spring is fixedly installed on the inner wall of the top of the fixed cylinder, a slider is fixedly installed on the bottom of the spring, and the slider is slidably installed on the inner side of the fixed cylinder.

[0008] Preferably, a slide rod is fixedly installed at the bottom of the slider, a mounting bracket is fixedly installed at the bottom of the slide rod, and a lower pressure roller is rotatably installed on the inner side of the mounting bracket, with the lower pressure roller located above the magnetizing groove.

[0009] Preferably, a cooling box is fixedly installed at the bottom of the magnetized plate body, multiple heat dissipation fins are fixedly installed inside the cooling box, a coolant storage tank is fixedly installed at the front of the cooling box, and a condenser and a temperature sensor are fixedly installed inside the coolant storage tank.

[0010] Preferably, a pump is fixedly installed on one side of the coolant storage tank, the suction end of the pump is connected to the coolant storage tank, one end of a cooling coil is fixedly installed on the output end of the pump, the top of the cooling coil abuts against the bottom of the heat dissipation fins, and the other end of the cooling coil is connected to the coolant storage tank.

[0011] Preferably, the cooling coil is serpentine in shape, and both the cooling coil and the heat dissipation fins are made of copper.

[0012] Preferably, the inner wall of the magnetizing groove is provided with a guide groove, and the connecting frame is slidably installed on the inner side of the guide groove.

[0013] Preferably, the mounting frame is U-shaped, and a protective rubber pad is provided on the outer side of the lower pressure roller.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) A uniform magnetizing plate for magnetic adhesive strips of the present invention is provided at the bottom of the magnetizing groove, and the bottom of the magnetizing coil is in close contact with the magnetic field homogenizing plate, which can homogenize the magnetic field generated by the magnetizing coil and ensure that the magnetic field distribution is uniform; at the same time, the moving frame drives the adhesive strip to move at a uniform speed, so that all parts of the adhesive strip can fully contact the uniform magnetic field, realize continuous and uniform magnetization, effectively solve the problem of uneven magnetization of existing magnetizing plates, improve the magnetization quality of magnetic adhesive strips, ensure that the magnetic field distribution of the adhesive strip is consistent, and meet the requirements of high precision use; a dual positioning clamping structure is set, the electric telescopic rod drives the adhesive strip to press down the clamping plate to clamp the adhesive strip, and the pressure sensor can monitor the clamping force in real time to avoid the adhesive strip being damaged by excessive clamping force or the adhesive strip being deviated by insufficient clamping force; the lower pressure roller always adheres to the adhesive strip under the action of spring force, and can automatically adjust the lower pressure according to the thickness of the adhesive strip to further improve the positioning stability; the connecting frame slides along the guide groove on the inner side of the magnetizing groove to ensure that the adhesive strip does not deviate during the movement, and is suitable for magnetic adhesive strips of different thicknesses and specifications, with strong practicality; (2) A uniform magnetizing plate for magnetic adhesive strips according to the present invention has heat dissipation fins at the bottom of the magnetizing coil, which, together with the bottom cooling box, serpentine cooling coil, coolant storage tank, pump and condenser, form a circulating cooling system; the cooling coil and heat dissipation fins are made of copper, which has high thermal conductivity, and the serpentine structure expands the heat dissipation contact area, which can quickly absorb the heat generated by the magnetizing coil and avoid overheating of the coil; the temperature sensor monitors the coolant temperature in real time, and the condenser adjusts the cooling intensity in time to ensure stable equipment temperature, extend the service life of the magnetizing coil and the entire equipment, and improve the stability of equipment operation; the moving frame is driven by the motor, lead screw and guide rod to move at a uniform speed to realize continuous magnetization of the adhesive strip, without the need for frequent manual adjustment of the adhesive strip position, and the operation is convenient; the electric telescopic rod and pressure sensor realize automatic clamping and pressure adjustment of the adhesive strip, further improving the level of automation, reducing the intensity of manual labor, greatly improving the magnetization efficiency, and adapting to the needs of mass production. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a three-dimensional structural schematic diagram of a uniformly magnetized plate for magnetic adhesive strips proposed in this invention. Figure 2 This is a partial three-dimensional structural diagram of a uniformly magnetized plate for magnetic adhesive strips proposed in this invention. Figure 3 This is a partial three-dimensional structural diagram of the heat dissipation fins proposed in this invention; Figure 4 This is a partial three-dimensional structural diagram of the magnetizing groove proposed in this invention; Figure 5 This is a partial three-dimensional structural diagram of the heat dissipation fins proposed in this invention; Figure 6 This is a partial three-dimensional structural diagram of the coil fixing block and the magnetizing coil proposed in this invention; Figure 7 This is a partial three-dimensional structural diagram of the mounting frame and lower pressure roller proposed in this invention.

[0017] In the diagram: 1. Magnetizing plate body; 2. Magnetizing groove; 3. Embedding groove; 4. Coil fixing block; 5. Magnetizing coil; 6. Magnetic field homogenizing plate; 7. Heat dissipation fins; 8. Control box; 9. Motor; 10. Lead screw; 11. Guide rod; 12. Moving frame; 13. Connecting frame; 14. Electric telescopic rod; 15. Pressure sensor; 16. Rubber strip pressing clamping plate; 17. Connecting plate; 18. Fixing cylinder; 19. Spring; 20. Slider; 21. Sliding rod; 22. Mounting frame; 23. Lower pressure roller; 24. Cooling box; 25. Coolant storage tank; 26. Condenser; 27. Pump; 28. Cooling coil; 29. ​​Temperature sensor. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] refer to Figure 1-7A uniformly magnetizing plate for magnetic adhesive strips includes a magnetizing plate body 1. Multiple magnetizing grooves 2 are formed on the top of the magnetizing plate body 1, and multiple mounting grooves 3 are formed on the bottom of the magnetizing grooves 2. A coil fixing block 4 is fixedly installed inside the mounting groove 3, and a magnetizing coil 5 is fixedly installed inside the coil fixing block 4. A magnetic field homogenizing plate 6 is fixedly installed on the bottom inner wall of the magnetizing groove 2. The bottom of the magnetizing coil 5 abuts against the bottom of the magnetic field homogenizing plate 6. Heat dissipation fins 7 are fixedly installed on the bottom of the magnetizing coil 5. A control box 8 is fixedly installed on the rear side of the magnetizing plate body 1. The initial position of the moving frame 12 is adjusted according to the specifications and dimensions of the magnetic adhesive strip. The motor 9 is started. Motor 9 drives lead screw 10 to rotate, and lead screw 10 drives moving frame 12 to slide along guide rod 11, moving moving frame 12 to the starting end of magnetizing groove 2. Motor 9 is turned off, and the position of moving frame 12 is fixed. The magnetic strip to be magnetized is placed in magnetizing groove 2, ensuring that the strip is tightly attached to the magnetic field homogenizing sheet 6 at the bottom of magnetizing groove 2, and that the two ends of the strip are aligned without offset. In this embodiment, motor 9 is fixedly installed on the right side of control box 8, lead screw 10 is fixedly installed on the output end of motor 9, guide rod 11 is fixedly installed on the inner side of control box 8, and moving frame 12 is threaded on the outer side of lead screw 10. Moving frame 12 is slidably installed on the outer side of guide rod 11.

[0020] In this embodiment, the movable frame 12 is L-shaped. Multiple connecting frames 13 are fixedly installed on the top inner wall of the movable frame 12. The connecting frames 13 are slidably installed inside the magnetizing groove 2. An electric telescopic rod 14 is fixedly installed inside the connecting frame 13. A pressure sensor 15 is fixedly installed at the output end of the electric telescopic rod 14. A rubber strip pressing clamping plate 16 is fixedly installed at the bottom of the pressure sensor 15. When the electric telescopic rod 14 is activated, it drives the pressure sensor 15 and the rubber strip pressing clamping plate 16 downwards until the rubber strip pressing clamping plate 16 contacts the magnet. The top of the adhesive strip is in close contact; the pressure sensor 15 detects the clamping force in real time, and adjusts the extension and retraction of the electric telescopic rod 14 according to the thickness and material of the adhesive strip to ensure that the clamping force is moderate; it can fix the adhesive strip and prevent it from shifting during magnetization without damaging the adhesive strip; in this embodiment, multiple connecting plates 17 are fixedly installed on one side of the movable frame 12, a fixed cylinder 18 is fixedly installed on the top of the connecting plate 17, a spring 19 is fixedly installed on the top inner wall of the fixed cylinder 18, and a slider 20 is fixedly installed on the bottom of the spring 19. The slider 20 is slidably installed on the inner side of the fixed cylinder 18.

[0021] In this embodiment, a slide rod 21 is fixedly installed at the bottom of the slider 20, and a mounting bracket 22 is fixedly installed at the bottom of the slide rod 21. A lower pressure roller 23 is rotatably installed on the inner side of the mounting bracket 22, and the lower pressure roller 23 is located above the magnetizing groove 2. The pump 27 and the condenser 26 are started. The pump 27 draws out the coolant from the coolant storage tank 25 and delivers it to the serpentine cooling coil 28. The coolant flows along the serpentine cooling coil 28. Since the cooling coil 28 is in close contact with the bottom of the heat dissipation fins 7, and both are made of copper, the thermal conductivity is high, which can quickly absorb the heat generated by the magnetizing coil 5 and carry the heat away through the coolant. In this embodiment, the magnetizing coil 5 is used to charge the magnetic coil 20 to the bottom of the condenser fins 7. A cooling box 24 is fixedly installed at the bottom of the magnetic plate body 1. Multiple heat dissipation fins 7 are fixedly installed inside the cooling box 24. A coolant storage tank 25 is fixedly installed at the front of the cooling box 24. A condenser 26 and a temperature sensor 29 are fixedly installed inside the coolant storage tank 25. In this embodiment, a pump 27 is fixedly installed on one side of the coolant storage tank 25. The suction end of the pump 27 is connected to the coolant storage tank 25. One end of a cooling coil 28 is fixedly installed at the output end of the pump 27. The top of the cooling coil 28 abuts against the bottom of the heat dissipation fins 7. The other end of the cooling coil 28 is connected to the coolant storage tank 25.

[0022] In this embodiment, the cooling coil 28 is serpentine in shape, and both the cooling coil 28 and the heat dissipation fins 7 are made of copper. The temperature sensor 29 detects the temperature of the coolant in the coolant storage tank 25 in real time. When the temperature is higher than the set threshold, the condenser 26 increases the cooling force to reduce the coolant temperature. The cooled coolant flows back to the coolant storage tank 25 through the cooling coil 28 to form a circulating cooling system, ensuring that the temperature of the magnetizing coil 5 is stable and avoiding the impact of overheating on the uniformity of the magnetic field and the service life of the equipment. In this embodiment, the inner sidewall of the magnetizing groove 2 is provided with a guide groove, and the connecting bracket 13 is slidably installed on the inner side of the guide groove.

[0023] In this embodiment, the mounting bracket 22 is U-shaped, and a protective rubber pad is provided on the outer side of the lower pressure roller 23.

[0024] The specific operation is as follows: Adjust the initial position of the moving frame 12 according to the specifications and dimensions of the magnetic adhesive strip; start the motor 9, which drives the lead screw 10 to rotate, and the lead screw 10 drives the moving frame 12 to slide along the guide rod 11, moving the moving frame 12 to the starting end of the magnetization groove 2; turn off the motor 9 and fix the position of the moving frame 12; place the magnetic adhesive strip to be magnetized in the magnetization groove 2, ensuring that the adhesive strip is tightly attached to the magnetic field homogenization plate 6 at the bottom of the magnetization groove 2, and that both ends of the adhesive strip are aligned without deviation; start the electric telescopic rod 14, which drives the pressure sensor 15 and the adhesive strip pressing clamping plate 16 to move downwards until the adhesive strip pressing clamping plate 16 is in close contact with the top of the magnetic adhesive strip; the pressure sensor 15 detects the clamping force in real time, and adjusts the extension and retraction of the electric telescopic rod 14 according to the thickness and material of the adhesive strip to ensure that the clamping force is moderate; this fixes the adhesive strip, preventing deviation during magnetization, without damaging the adhesive strip. After the adhesive strip is clamped and fixed, the lower pressure roller 23, under the elastic force of the spring 19, presses down through the slider 20 and the slide bar 21, making close contact with the top of the magnetic adhesive strip. The protective rubber pad can prevent damage to the adhesive strip. The spring 19 can automatically adjust the downward pressure according to the thickness of the adhesive strip, ensuring that the lower pressure roller 23 always fits the adhesive strip, further improving the positioning stability of the adhesive strip and preventing the adhesive strip from tilting or shifting during the movement and magnetization process. Start the pump 27 and condenser 26. The pump 27 draws out the coolant from the coolant storage tank 25 and delivers it to the serpentine cooling coil 28. The coolant flows along the serpentine cooling coil 28. Since the cooling coil 28 is in close contact with the bottom of the heat dissipation fins 7 and both are made of copper, the heat conduction efficiency is high. It can quickly absorb the heat generated by the magnetizing coil 5 and carry the heat away through the coolant. Temperature sensor 29 monitors the temperature of coolant in coolant storage tank 25 in real time. When the temperature is higher than the set threshold, condenser 26 increases the cooling force to reduce the coolant temperature. The cooled coolant flows back to coolant storage tank 25 through cooling coil 28 to form a circulating cooling system, ensuring the temperature of magnetizing coil 5 is stable and avoiding the impact of overheating on magnetic field uniformity and equipment lifespan. The magnetizing coil 5 is activated by the control box 8, generating a magnetic field. This magnetic field is homogenized by the magnetic field homogenizer 6, forming a uniformly distributed magnetic field that acts on the magnetic strip within the magnetizing groove 2, achieving initial magnetization. The motor 9 is then activated, driving the lead screw 10 to rotate slowly and uniformly. The lead screw 10 drives the moving frame 12 to slide uniformly along the guide rod 11. The moving frame 12 drives the connecting frame 13 to slide along the guide groove inside the magnetizing groove 2. Under the combined action of the rubber strip pressing clamping plate 16 and the lower pressing roller 23, the rubber strip moves uniformly along the magnetizing groove 2, following the connecting frame 13. During the movement, the strip remains within the uniform magnetic field generated by the magnetizing coil 5, ensuring continuous and uniform magnetization and preventing localized under- or over-magnetization. During magnetization, the pressure sensor 15 continuously monitors the clamping force; if any abnormality occurs, the electric telescopic rod 14 is adjusted promptly to ensure stable positioning of the strip. Based on the magnetization requirements of the magnetic strip, the moving speed of the moving frame 12 and the magnetic field strength of the magnetizing coil 5 are adjusted to ensure the magnetization effect meets the standards. Once the strip has completely passed through the magnetizing groove 2 and the overall magnetization is complete, the magnetizing coil 5 and the motor 9 are turned off.

[0025] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0026] The above provides a detailed description of a uniformly magnetized plate for magnetic adhesive strips provided by the present invention. Specific embodiments have been used to illustrate the principles and implementation methods of the invention. These embodiments are merely illustrative and are intended to aid in understanding the method and core concepts of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A uniformly magnetized plate for magnetic adhesive strips, characterized in that, include: A magnetizing plate body (1) has multiple magnetizing grooves (2) on its top and multiple mounting grooves (3) on its bottom. A coil fixing block (4) is fixedly installed inside the mounting groove (3). A magnetizing coil (5) is fixedly installed inside the coil fixing block (4). A magnetic field homogenizing plate (6) is fixedly installed on the bottom inner wall of the magnetizing groove (2). The bottom of the magnetizing coil (5) abuts against the bottom of the magnetic field homogenizing plate (6). A heat dissipation fin (7) is fixedly installed on the bottom of the magnetizing coil (5). A control box (8) is fixedly installed on the rear side of the magnetizing plate body (1).

2. The uniformly magnetized plate for magnetic adhesive strips according to claim 1, characterized in that, A motor (9) is fixedly installed on the right side of the control box (8), a lead screw (10) is fixedly installed at the output end of the motor (9), a guide rod (11) is fixedly installed on the inner side of the control box (8), a movable frame (12) is threadedly installed on the outer side of the lead screw (10), and the movable frame (12) is slidably installed on the outer side of the guide rod (11).

3. The uniformly magnetized plate for magnetic adhesive strips according to claim 2, characterized in that, The movable frame (12) is L-shaped. Multiple connecting frames (13) are fixedly installed on the top inner wall of the movable frame (12). The connecting frames (13) are slidably installed on the inner side of the magnetizing groove (2). An electric telescopic rod (14) is fixedly installed on the inner side of the connecting frame (13). A pressure sensor (15) is fixedly installed at the output end of the electric telescopic rod (14). A rubber strip pressing clamping plate (16) is fixedly installed at the bottom of the pressure sensor (15).

4. A uniformly magnetized plate for magnetic adhesive strips according to claim 2, characterized in that, Multiple connecting plates (17) are fixedly installed on one side of the mobile frame (12). A fixed cylinder (18) is fixedly installed on the top of the connecting plate (17). A spring (19) is fixedly installed on the inner wall of the top of the fixed cylinder (18). A slider (20) is fixedly installed on the bottom of the spring (19). The slider (20) is slidably installed on the inner side of the fixed cylinder (18).

5. A uniformly magnetized plate for magnetic adhesive strips according to claim 4, characterized in that, The bottom of the slider (20) is fixedly mounted with a slide rod (21), and the bottom of the slide rod (21) is fixedly mounted with a mounting bracket (22). A lower pressure roller (23) is rotatably mounted on the inner side of the mounting bracket (22), and the lower pressure roller (23) is located above the magnetizing groove (2).

6. A uniformly magnetized plate for magnetic adhesive strips according to claim 1, characterized in that, A cooling box (24) is fixedly installed at the bottom of the magnetized plate body (1), and multiple heat dissipation fins (7) are fixedly installed on the inner side of the cooling box (24). A coolant storage tank (25) is fixedly installed on the front side of the cooling box (24), and a condenser (26) and a temperature sensor (29) are fixedly installed on the inner side of the coolant storage tank (25).

7. A uniformly magnetized plate for magnetic adhesive strips according to claim 6, characterized in that, A pump (27) is fixedly installed on one side of the coolant storage tank (25). The suction end of the pump (27) is connected to the coolant storage tank (25). One end of the cooling coil (28) is fixedly installed at the output end of the pump (27). The top of the cooling coil (28) abuts against the bottom of the heat dissipation fins (7). The other end of the cooling coil (28) is connected to the coolant storage tank (25).

8. A uniformly magnetized plate for magnetic adhesive strips according to claim 7, characterized in that, The cooling coil (28) is serpentine in shape, and both the cooling coil (28) and the heat dissipation fins (7) are made of copper.

9. A uniformly magnetized plate for magnetic adhesive strips according to claim 3, characterized in that, The inner wall of the magnetizing groove (2) is provided with a guide groove, and the connecting frame (13) is slidably installed on the inner side of the guide groove.

10. A uniformly magnetized plate for magnetic adhesive strips according to claim 5, characterized in that, The mounting bracket (22) is U-shaped, and a protective rubber pad is provided on the outside of the lower pressure roller (23).

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