Shape-adaptive magnet yoke equipment

Abstract

Shape self-adaptive magnet yoke equipment comprises a magnet yoke, the magnet yoke comprises a telescopic rod, yoke foot rods are fixedly connected to the two ends of the telescopic rod, magnet exciting coils are wound around the yoke foot rods and connected with a power source, the magnet exciting coils are wrapped with protective sleeves, and self-adaptive mechanisms are arranged at the lower ends of the yoke foot rods. The self-adaptive mechanism comprises an elastic sleeve and a plurality of first magnetic needles, the upper end of the elastic sleeve is fixedly connected with the yoke foot rod, a magnetic head is assembled in the lower end of the elastic sleeve, the magnetic head comprises a pore plate fixedly connected in the elastic sleeve, the pore plate is fixedly connected with an elastic sealing piece, the first magnetic needles penetrate through the sealing piece and the pore plate, and the elastic sealing piece is fixedly connected with the elastic sealing piece. A gap between the pore plate and the first magnetic needle is sealed by a sealing piece, and the elastic sleeve is filled with variable-rigidity magnetorheological fluid. The problems that an existing magnet yoke is poor in shape adaptability and low in magnetic field transmission efficiency are solved.

Description

Technical Field

[0001] The present invention relates to a shape - adaptive magnetic yoke device, which is particularly suitable for fields such as special equipment detection, heavy equipment manufacturing, precision machining, etc., and is used to efficiently apply a magnetic field to detect or process workpieces with complex shapes. Background Art

[0002] A magnetic yoke is an industrial device used to apply a direct current or alternating current magnetic field to external workpieces, and is widely used in fields such as special equipment detection and heavy equipment manufacturing. In special equipment detection, magnetic yokes are often used in magnetic flux leakage testing to detect superficial cracks and defects in ferromagnetic materials. By applying a magnetic field to the surface of the material to be detected, when the magnetic field leaks at surface cracks or defects, the magnetic leakage field can adsorb magnetic fluorescent particles, thereby enhancing the optical contrast between the cracks or defects and the surrounding area, helping engineers quickly obtain the defect characteristics of the material to be detected.

[0003] Traditional magnetic yokes are usually composed of coils wound around ferromagnetic materials, with high stiffness and no deformation ability. This makes traditional magnetic yokes only applicable to workpieces with flat surfaces or very small surface curvatures. However, in actual production activities, many workpieces have complex irregular surfaces, such as the junction area between the wall and the top of a pressure vessel, pipe joints, track bifurcations, etc. Traditional magnetic yokes cannot conform to these irregular surfaces, resulting in a strong lift - off effect, which causes the magnetic field to be unable to be efficiently transmitted to the target position, thus affecting the accuracy and efficiency of detection or processing.

[0004] In recent years, the development of variable - stiffness magnetorheological fluid technology has provided a new idea for solving this problem. Variable - stiffness magnetorheological fluid is a special fluid material whose stiffness can be rapidly changed by external stimuli (such as current, magnetic field, temperature, stress, etc.), changing from a liquid state to a quasi - solid state. For example, by adding ferromagnetic nanoparticles to a gallium - indium alloy, a variable - stiffness magnetorheological fluid with magnetic response can be constructed. This fluid can instantaneously become quasi - solid under the action of a magnetic field and return to its liquid - state characteristics after the magnetic field is removed. At the same time, due to the doping of ferromagnetic nanoparticles inside, this fluid can efficiently conduct magnetic fields, and its magnetic conductivity is even not inferior to that of traditional ferromagnetic materials. Therefore, developing a magnetic yoke with shape - adaptive characteristics using variable - stiffness magnetorheological fluid has become a key direction for solving the limitations of traditional magnetic yokes.

[0005] However, the magnetic yoke devices in the prior art still have the following technical problems to be urgently solved: 1. Poor shape adaptability: Due to high stiffness, traditional magnetic yokes cannot conform to workpieces with irregular surfaces, resulting in low magnetic - field transmission efficiency and unsatisfactory detection effects. 2. Low magnetic - field transmission efficiency: Existing magnetic yokes have a large magnetic loss problem during magnetic - field transmission, especially on the surface of complex workpieces, where the magnetic field is difficult to be efficiently transmitted to the target position. Summary of the Invention

[0006] The object of the present invention is to provide a shape - adaptive magnetic yoke device, which is used to solve the problems of poor shape adaptability and low magnetic field transmission efficiency of the existing magnetic yoke. By introducing variable - stiffness magnetorheological fluid and an adaptive mechanism, the present invention realizes the efficient adaptation of the magnetic yoke to workpieces with complex shapes and the efficient transmission of the magnetic field, while improving the structural stability and dynamic response ability of the device.

[0007] To solve the above problems, the technical solution of the present invention is as follows: A shape - adaptive magnetic yoke device includes a magnetic yoke. The magnetic yoke includes a telescopic rod. Yoke foot rods are fixedly connected to both ends of the telescopic rod. Excitation coils are wound around the yoke foot rods, and the excitation coils are connected to a power supply. A protective sleeve is wrapped outside the excitation coils. An adaptive mechanism is provided at the lower end of the yoke foot rod. The adaptive mechanism includes an elastic sleeve and multiple first magnetic needles. The upper end of the elastic sleeve is fixedly connected to the yoke foot rod. A magnetic head is assembled inside the lower end of the elastic sleeve. The magnetic head includes an orifice plate fixedly connected inside the elastic sleeve. Elastic sealing sheets are fixedly connected to the orifice plate. Multiple first magnetic needles pass through the sealing sheets and the orifice plate, and the gaps between the orifice plate and the first magnetic needles are sealed by the sealing sheets. Variable - stiffness magnetorheological fluid is filled inside the elastic sleeve.

[0008] Further, a cylinder sleeve is fixedly connected between one end of the telescopic rod and one of the yoke foot rods. A piston is arranged inside the cylinder sleeve. The piston is fixedly connected to the other yoke foot rod through a rod. Variable - stiffness magnetorheological fluid is filled inside the cylinder sleeve.

[0009] Further, two groups of second magnetic needles are arranged inside the cylinder sleeve. The two groups of second magnetic needles are respectively fixedly connected to the piston and the yoke foot rod. Each group of second magnetic needles is composed of multiple second magnetic needles, and the two groups of second magnetic needles are staggered with each other in the axial direction of the cylinder sleeve.

[0010] Further, multiple third magnetic needles are arranged inside the elastic sleeve, and the third magnetic needles are fixedly connected to the lower end of the yoke foot rod.

[0011] Further, the elastic sleeve is a silica gel bellows spring sleeve.

[0012] Further, the variable - stiffness magnetorheological fluid includes cobalt - iron nanoparticle liquid, and gallium - indium alloy nanoparticle liquid is doped in the cobalt - iron nanoparticle liquid.

[0013] Further, the weight ratio of cobalt - iron nanoparticles to gallium - indium alloy nanoparticles is 1:0.5 - 0.8.

[0014] Further, the adaptive mechanism has two sealing sheets. The two sealing sheets are made of rubber and are fixedly connected to both end faces of the orifice plate.

[0015] Further, the yoke foot rod is a round rod structure composed of multiple layers of silicon steel sheets stacked together, and an insulating layer made of a polymer material is wrapped outside the round rod structure.

[0016] Furthermore, ball heads are provided at both ends of the first magnetic needle, and the ball diameter of the ball head is greater than the diameter of the through hole on the hole plate.

[0017] The beneficial effects of the present invention are as follows: 1. Shape adaptability: Through the design of the adaptive mechanism, the magnetic yoke can be dynamically adjusted according to the shape of the workpiece, enabling the magnetic head to closely fit the surface of the workpiece, achieving conformal contact with the irregular surface, eliminating the lift-off effect of the traditional magnetic yoke, and significantly improving the magnetic field transfer efficiency and the accuracy of detection or processing.

[0018] 2. High magnetic field transfer efficiency: Variable stiffness magnetorheological fluid is filled in the cylinder liner and the elastic sleeve, and multiple groups of magnetic needle arrays are provided. The magnetic nanoparticles in the magnetorheological fluid are rearranged under the action of the magnetic field, enhancing the magnetic field transfer efficiency. At the same time, multiple groups of magnetic needle arrays can continuously transfer the magnetic induction lines to the external workpiece, reducing magnetic loss and further improving the magnetic field loading efficiency.

[0019] 3. Strong structural stability: The stiffness of the magnetorheological fluid rapidly increases under the excitation of the magnetic field, which can improve the overall structural stability of the magnetic yoke. At the same time, the design of the piston in the cylinder liner and the elastic sleeve makes the magnetic yoke more reliable during operation and adaptable to various complex working conditions.

[0020] 4. Fast response and cyclic stability: The variable stiffness magnetorheological fluid with a special formula achieves the best balance between its magnetic properties and variable stiffness properties, enabling it to quickly respond to magnetic field changes in a short time and having good cyclic stability, ensuring the stable performance of the magnetic yoke during long-term use.

[0021] 5. Wide application range: The magnetic yoke device of the present invention is not only applicable to the detection and processing of traditional regular surface workpieces, but also can be efficiently applied to workpieces with complex irregular surfaces, such as pressure vessels, pipe joints, track bifurcations, etc., significantly expanding the application range of the magnetic yoke.

[0022] 6. Simple operation and low maintenance cost: The installation and use process of the device is simple, and the magnetic field intensity and the shape of the magnetic yoke can be quickly adjusted by adjusting the current in the excitation coil. At the same time, the device has low maintenance cost and long service life, with good economic efficiency and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below with reference to the accompanying drawings: Figure 1 is a three-dimensional structural schematic diagram of the present invention, Figure 2 is a sectional structural schematic diagram of the present invention, Figure 3 is a partial structural schematic diagram of the present invention, Figure 4 isFigure 3 Schematic cross-sectional structure diagram at A-A in Figure 5 Schematic three-dimensional structure diagram of the present invention Figure 6 Schematic structure diagram when the present invention is implemented Figure 7 Schematic structure diagram when the present invention is implemented.

[0024] In the figure: 1 is the first magnetic needle, 2 is the elastic sleeve, 3 is the protective sleeve, 4 is the yoke foot rod, 5 is the rod member, 6 is the cylinder liner, 7 is the piston, 8 is the sealing piece, 9 is the orifice plate, 10 is the third magnetic needle, 11 is the exciting coil, 12 is the piston, 13 is the second magnetic needle, 14 is the ball head, 15 is the magnetorheological fluid, and 16 is the workpiece. Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] As Figures 1 to 5 shown, a shape-adaptive magnetic yoke device includes a magnetic yoke. The magnetic yoke includes a telescopic rod, and yoke foot rods 4 are fixedly connected to both ends of the telescopic rod. An exciting coil 11 is wound around the yoke foot rods 4, and the exciting coil 11 is connected to a power source. A protective sleeve 3 is wrapped outside the exciting coil 11. An adaptive mechanism is provided at the lower end of the yoke foot rod 4. The adaptive mechanism includes an elastic sleeve 2 and multiple first magnetic needles 1. The upper end of the elastic sleeve 2 is fixedly connected to the yoke foot rod 4. A magnetic head is assembled inside the lower end of the elastic sleeve 2. The magnetic head includes an orifice plate 9 fixedly connected inside the elastic sleeve 2. An elastic sealing piece 8 is fixedly connected to the orifice plate 9. Multiple first magnetic needles 1 pass through the sealing piece and the orifice plate 9, and the gap between the orifice plate 9 and the first magnetic needles 1 is sealed by the sealing piece 8. A variable-stiffness magnetorheological fluid 15 is filled inside the elastic sleeve 2. When the magnetorheological fluid 15 is subjected to a magnetic field, the stiffness of the variable-stiffness magnetorheological fluid 15 will change, thereby affecting the shape and position of the magnetic head. At the same time, the first magnetic needles 1 move freely in the variable-stiffness magnetorheological fluid 15, and arrayed contact is achieved through the cooperation of the ball head 14 and the orifice plate 9.

[0027] Thus, through the design of the adaptive mechanism, as Figure 6 and 7 shown, the magnetic yoke can be adjusted according to different workpiece shapes, improving the adaptability of the magnetic yoke to workpieces with irregular surfaces, solving the problem that traditional magnetic yokes cannot conform to irregular surfaces, achieving conformal contact between the magnetic yoke and irregular surfaces, and eliminating the lift-off effect.

[0028] Furthermore, one end of the telescopic rod is fixedly connected with a cylinder sleeve 6 to one of the yoke rods 4. A piston 12 is arranged inside the cylinder sleeve 6. The piston 12 is fixedly connected with the other yoke rod 4 through a rod member 5. A variable stiffness magnetorheological fluid 15 is filled inside the cylinder sleeve 6. A liquid injection hole is opened on the cylinder sleeve 6, and a sealing plug is installed on the liquid injection hole. This further enhances the shape adaptability of the magnetic yoke. Through the movement of the piston 12 inside the cylinder sleeve 6, the size and shape of the magnetic yoke can be adjusted more flexibly to better adapt to the surface features of different workpieces, further improving the application range and working efficiency of the magnetic yoke.

[0029] Furthermore, two groups of second magnetic needles 13 are arranged inside the cylinder sleeve 6. The two groups of second magnetic needles are respectively fixedly connected with the piston 12 and the yoke rod 4. Each group of second magnetic needles 13 is composed of multiple second magnetic needles 13. The two groups of second magnetic needles are staggered with each other in the axial direction of the cylinder sleeve 6. After staggering, when the piston 12 retracts, the two groups of second magnetic needles 13 will not collide with each other, and the staggered arrangement also enhances the magnetic field continuity. In this way, the second magnetic needles 13 will generate magnetic induction under the action of the magnetic field and interact with the magnetic nanoparticles in the magnetorheological fluid 15, enhancing the transmission efficiency and stability of the magnetic field, enabling it to more effectively guide the transmission of the magnetic field, reducing magnetic loss, improving the magnetic field loading efficiency, and at the same time enhancing the overall structural stability of the magnetic yoke, making it more reliable during the working process.

[0030] Furthermore, multiple third magnetic needles 10 are arranged inside the elastic sleeve 2. The third magnetic needles 10 are fixedly connected with the lower end of the yoke rod 4. When the stiffness of the magnetorheological fluid 15 changes, the third magnetic needles 10 can better transmit the magnetic field to the magnetic head part inside the elastic sleeve 2, ensuring the uniform distribution and efficient transmission of the magnetic field. Thereby, the transmission path of the magnetic field is further optimized, improving the uniformity and stability of the magnetic field, enabling the magnetic yoke to more effectively apply the magnetic field to the workpiece during operation, and improving the quality and efficiency of detection or processing.

[0031] Furthermore, the elastic sleeve 2 is a silicone accordion spring sleeve 2. This sleeve 2 can freely flex within a range of ±30°, significantly enhancing the shape adaptability to complex surfaces such as the curved surface of a pressure vessel, a pipe elbow, and a weld, ensuring conformal contact between the magnetic head and the workpiece.

[0032] Furthermore, the variable-stiffness magnetorheological fluid 15 includes a cobalt-iron nanoparticle fluid, which is prepared by chemical co-precipitation method and modified with oleic acid. A gallium-indium alloy nanoparticle fluid is doped in the cobalt-iron nanoparticle fluid. The cobalt-iron nanoparticles have good magnetic properties, while the gallium-indium alloy nanoparticles have special physical characteristics. When the excitation coil 11 is energized to generate a magnetic field, the nanoparticles in the magnetorheological fluid 15 are rearranged under the action of the magnetic field, resulting in a change in its stiffness, thereby realizing the variable-stiffness characteristic of the magnetorheological fluid 15. This special magnetorheological fluid 15 formulation can provide better magnetic field response ability and variable-stiffness performance, enabling the magnetic yoke to more quickly adapt to different workpiece shapes during operation, while improving the magnetic field transfer efficiency and stability, and further optimizing the performance of the magnetic yoke.

[0033] Furthermore, the weight ratio of the cobalt-iron nanoparticles to the gallium-indium alloy nanoparticles is 1:0.5 - 0.8. Within this ratio range, the magnetic properties and variable-stiffness performance of the magnetorheological fluid 15 can reach the best balance, ensuring that the magnetic yoke can efficiently transfer the magnetic field during operation, while having good shape adaptability, making it show better adaptability and stability in practical applications, and further improving the performance and reliability of the magnetic yoke.

[0034] The preparation method of the variable-stiffness magnetorheological fluid 15 is as follows: First, cobalt-iron nanoparticles are synthesized by co-precipitation method and modified with oleic acid. At the same time, gallium-indium alloy nanoparticles are prepared by ultrasonic-assisted method. After mixing the two kinds of nanoparticles according to the weight ratio of 1:0.5 - 0.8, silicone oil or deionized water is added as the carrier fluid, and 1.5 - 3% of dispersant (oleic acid / PVP) is added. Uniform dispersion is achieved through a high-shear disperser and ultrasonic treatment. Finally, 0.5% of nano-SiO2 is added for thickening and magnetic field pretreatment to form a fluid material with both high magnetic permeability (μ r = 8 - 12), fast response (<10 ms) and cyclic stability (>10 4 times). Its zero-field viscosity can be regulated within the range of 5 - 50 Pa / s by adjusting the carrier fluid ratio.

[0035] Furthermore, the adaptive mechanism has two sealing sheets 8, which are made of rubber and fixedly connected to the two end faces of the orifice plate 9. The two sealing sheets 8 can better prevent the leakage of the magnetorheological fluid 15. At the same time, when the stiffness of the magnetorheological fluid 15 changes, the sealing sheets 8 can provide certain elastic support to ensure the structural stability of the magnetic head.

[0036] Further, the yoke foot rod 4 and the rod member 5 are round rod structures composed of multiple layers of silicon steel sheets stacked together. An insulating layer made of a polymer material is wrapped outside the round rod structure. During processing, epoxy resin is used to bond and fix the multiple layers of silicon steel sheets, and then it is turned into a round rod by turning. After that, a heat shrinkable tube is wrapped outside to wrap the round rod. This structural design can improve the magnetic performance and insulation performance of the yoke foot rod 4, enabling it to conduct the magnetic field more efficiently during operation, while ensuring the safety and reliability of the magnetic yoke and further optimizing the overall performance of the magnetic yoke.

[0037] Further, spherical heads 14 are provided at both ends of the first magnetic needle 1, and the spherical diameter of the spherical heads 14 is larger than the diameter of the through holes on the hole plate 9. The design of the spherical heads 14 enables the first magnetic needle 1 to better adapt to different angular and positional changes when cooperating with the hole plate 9, while preventing the magnetic needle from falling off the hole plate 9 and ensuring the stability and reliability of the magnetic needle.

[0038] The usage method of the shape-adaptive magnetic yoke device of the present invention is as follows: 1. Fix the magnetic yoke device near the workpiece that needs to be applied with a magnetic field, and ensure that the contact surface or gap between the device and the workpiece meets the detection or processing requirements. Connect the excitation coil 11 to the power supply, and the power supply should have the function of adjustable current to adjust the magnetic field strength as needed. By adjusting the power supply current, observe the response of the magnetorheological fluid 15 to ensure that the device is in a soft state without a magnetic field and can quickly harden and transmit the magnetic field after being energized.

[0039] 2. Clean the surface of the workpiece to be detected or processed to ensure that its surface is clean and free of impurities, so that the magnetic yoke can be in good contact with the workpiece surface. According to the shape of the workpiece and the detection or processing requirements, adjust the adaptive mechanism of the magnetic yoke to make the magnetic head closely fit the workpiece surface. By adjusting the current, make the magnetorheological fluid 15 harden under the action of the magnetic field, so as to efficiently transmit the magnetic field to the workpiece surface. During the detection process, use the magnetic flux leakage method to detect cracks or defects on the workpiece surface.

[0040] For example: A. When detecting cracks on the surface of a pressure vessel, fix the magnetic yoke device on the surface of the pressure vessel, adjust the current of the excitation coil to 10 A, make the magnetorheological fluid harden, and ensure that the magnetic head is closely attached to the surface of the pressure vessel.

[0041] B. In the detection of a pipeline joint, fix the magnetic yoke device at the pipeline joint, adjust the current of the excitation coil to 15 A, and adjust the shape of the magnetic head through the adaptive mechanism to ensure that the magnetic field is evenly transmitted to the surface of the pipeline joint.

[0042] 3. The magnetic field strength is controlled by adjusting the current in the excitation coil 11. The larger the current, the stronger the magnetic field, and the higher the stiffness of the magnetorheological fluid 15, which is suitable for workpiece inspection or processing that requires a higher magnetic field strength. In actual operation, the current can be dynamically adjusted according to the complexity of the workpiece and the progress of the inspection to achieve the best magnetic field application effect.

[0043] 4. After use, clean the residual magnetorheological fluid 15 and impurities on the yoke equipment in time to prevent them from affecting the performance and service life of the equipment.

[0044] Through the above-mentioned usage method, the shape adaptive yoke device of the present invention can efficiently apply a magnetic field to various workpieces, is suitable for special equipment detection, precision machining and other fields, and has good practicality and reliability.

[0045] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A shape-adaptive yoke device, characterized in that: It includes a yoke, the yoke includes a telescopic rod, yoke foot rods are fixedly connected to both ends of the telescopic rod, excitation coils are wound around the yoke foot rods, the excitation coils are connected to a power source, a protective sleeve is wrapped outside the excitation coils, an adaptive mechanism is provided at the lower end of the yoke foot rod, the adaptive mechanism includes an elastic sleeve and multiple first magnetic needles, the upper end of the elastic sleeve is fixedly connected to the yoke foot rod, a magnetic head is assembled inside the lower end of the elastic sleeve, the magnetic head includes an orifice plate fixedly connected inside the elastic sleeve, an elastic sealing sheet is fixedly connected to the orifice plate, multiple first magnetic needles pass through the sealing sheet and the orifice plate, the gap between the orifice plate and the first magnetic needles is sealed by the sealing sheet, and variable stiffness magnetorheological fluid is filled inside the elastic sleeve.

2. The shape-adaptive magnetic yoke device according to claim 1, characterized in that: A cylinder sleeve is fixedly connected between one end of the telescopic rod and one of the yoke foot rods, a piston is arranged inside the cylinder sleeve, the piston is fixedly connected to the other yoke foot rod through a rod, and variable stiffness magnetorheological fluid is filled inside the cylinder sleeve.

3. The shape-adaptive magnetic yoke device according to claim 2, wherein: Two groups of second magnetic needles are arranged inside the cylinder sleeve, the two groups of second magnetic needles are respectively fixedly connected to the piston and the yoke foot rod, each group of second magnetic needles is composed of multiple second magnetic needles, and the two groups of second magnetic needles are staggered with each other in the axial direction of the cylinder sleeve.

4. The shape - adaptive magnetic yoke device according to claim 2, characterized in that: Multiple third magnetic needles are arranged inside the elastic sleeve, and the third magnetic needles are fixedly connected to the lower end of the yoke foot rod.

5. A shape-adaptive magnetic yoke device according to any one of claims 2 to 4, characterized in that: The elastic sleeve is a silica gel bellows spring sleeve.

6. A shape-adaptive magnetic yoke device according to any one of claims 2 to 4, characterized in that: The variable stiffness magnetorheological fluid includes cobalt iron nanoparticle liquid, and gallium indium alloy nanoparticle liquid is doped in the cobalt iron nanoparticle liquid.

7. The shape - adaptable yoke device according to claim 6, wherein: The weight ratio of cobalt iron nanoparticles to gallium indium alloy nanoparticles is 1:0.5 - 0.

8.

8. A shape-adaptive magnetic yoke device according to any one of claims 1 to 4, characterized in that: The adaptive mechanism has two sealing sheets, the two sealing sheets are made of rubber, and the two sealing sheets are fixedly connected to both end faces of the orifice plate.

9. A shape-adaptive magnetic yoke device according to any one of claims 1 to 4, characterized in that: The yoke foot rod is a round rod structure composed of multiple layers of silicon steel sheets stacked together, and an insulating layer made of a polymer material is wrapped outside the round rod structure.

10. A shape-adaptive magnetic yoke device according to any one of claims 1 to 4, characterized in that: Ball heads are provided at both ends of the first magnetic needle, and the ball head diameter is larger than the diameter of the through hole on the orifice plate.

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