A large-size curved thin-walled neutron beam window and a manufacturing method thereof

Abstract

The present invention belongs to the field of nuclear physics and nuclear technology application, in particular to a large curved thin-walled neutron beam window for a high-resolution neutron diffractometer in spallation neutron source technology and a manufacturing method thereof; the neutron beam window is designed as an integrated curved structure, the thickness of the beam window is designed to be 1.5 mm, and a transverse rib is provided in the middle of the neutron beam window to enhance structural stability without affecting neutron penetration; the present invention is designed as a thin-walled curved structure, so that the neutron beam window can more effectively penetrate neutrons, reduce neutron attenuation during transmission, thereby improving neutron utilization and accuracy of experimental data; at the same time, compared with a traditional planar structure, the curved surface design has better stress distribution, can effectively reduce stress concentration and mechanical deformation, improve the pressure bearing capacity and fatigue life of the neutron beam window, and ensure safe and stable operation of the experimental device.

Description

Technical Field

[0001] The invention belongs to the field of nuclear physics and nuclear technology application, in particular to a large curved thin-wall neutron beam window used for a high-resolution neutron diffractometer in spallation neutron source technology and a manufacturing method thereof. Background Art

[0002] In the spallation neutron source technology, the neutron beam window is a key component in the neutron scattering experiment, and its performance directly affects the neutron transmittance and the safe and stable operation of the experimental device. At present, the large-sized neutron beam windows commonly used at home and abroad are mostly planar, but the planar beam windows are prone to large vacuum deformation, plastic deformation and stress concentration when the thickness is thin, and fatigue fracture is prone to occur under long-term use, posing a potential risk of damage to surrounding detectors. Therefore, the development of a large curved thin-walled neutron beam window that meets the requirements of physical thinness and can ensure sufficient mechanical strength has become an urgent problem to be solved. At the same time, due to the difficulty and high cost of processing large-sized curved beam windows, it is necessary to explore an effective processing technology to solve this technical problem. Summary of the invention

[0003] In response to the above problems, the present invention provides a large-size curved thin-walled neutron beam window and a manufacturing method thereof to resolve the contradiction between thickness and mechanical strength of existing planar neutron beam windows, while improving the neutron transmittance and ensuring the safe and stable operation of the experimental device.

[0004] The technical solution adopted by the present invention is: a large-size curved thin-walled neutron beam window, which is designed as an integrated curved structure. The thickness of the beam window is designed to be 1.5 mm. A transverse rib is provided in the middle of the neutron beam window to enhance structural stability without affecting neutron penetration.

[0005] Two transverse ribs are designed in the detector blind area in the middle of the beam window to equally divide the beam window into three windows: upper, middle and lower.

[0006] The neutron beam window is made of 7075-T651 aluminum alloy to balance neutron transmittance and mechanical strength.

[0007] The cross-sectional dimensions of each window are 620mmx465mm to achieve a balance between neutron transmittance and pressure bearing capacity.

[0008] A method for manufacturing a large-sized curved thin-walled neutron beam window includes the following process steps: firstly, after selecting materials, the materials are subjected to rough processing and stress relief treatment to obtain semi-finished products, then the materials are subjected to semi-finishing and finishing processing to obtain finished products, then the finished products are subjected to quality inspection and fatigue testing to obtain good products, and finally the good products that meet the standards are subjected to final processing and application.

[0009] The rough machining and stress relief treatment steps include: using a 30 mm thick 7075 aluminum alloy plate as a raw material, rough machining to a thickness close to the target thickness, and then performing a secondary aging treatment to remove internal stress.

[0010] The semi-finishing and finishing steps include: using a high-speed milling machine to perform processing, using a special concave-convex mold to pad, and strictly controlling cutting parameters to ensure processing accuracy and quality.

[0011] The quality inspection and fatigue test steps include: performing quality inspection on the processed beam window for indicators such as dimensional accuracy and surface roughness, and performing at least 10,000 vacuum cycle tests to verify fatigue life.

[0012] The final processing and application steps include: performing necessary surface treatment on the tested beam window, such as cleaning and anodizing, and then installing it into the vacuum scattering cavity of a high-resolution neutron diffractometer.

[0013] The method also includes regularly monitoring the performance status of the beam window in actual use to ensure its long-term safe and stable operation.

[0014] The beneficial effects of the present invention are as follows: compared with the manufacturing process of the conventional planar neutron beam window, the large-size curved thin-walled neutron beam window and the manufacturing method thereof of the present invention have the following significant beneficial effects: (1) Improving neutron transmittance: by designing a thin-walled curved structure, the neutron beam window can more effectively transmit neutrons, reducing the attenuation of neutrons during transmission, thereby improving the utilization rate of neutrons and the accuracy of experimental data; (2) Enhancing mechanical stability: compared with the conventional planar structure, the curved surface design has better stress distribution, can effectively reduce stress concentration and mechanical deformation, improve the pressure bearing capacity and fatigue life of the neutron beam window, and ensure the safe and stable operation of the experimental device; (3) Optimizing material selection: selecting 7075-T651 aluminum alloy as the material of the neutron beam window, not only It ensures the neutron transmittance while taking into account the mechanical strength, thus achieving a balance between performance and cost; (4) Improving processing efficiency and quality: By optimizing the manufacturing process, including rough processing, stress relief treatment, semi-finishing and finishing steps, not only the processing efficiency is improved, but also the accuracy and quality of the neutron beam window are guaranteed, the scrap rate is reduced, and the cost is saved; (5) Enhanced maintainability: The design of the neutron beam window takes into account the maintainability of long-term use. Through regular monitoring and maintenance, its service life can be extended, the replacement frequency can be reduced, and the maintenance cost can be reduced; (6) Expanding the scope of application: The present invention is not only suitable for scientific research equipment such as high-resolution neutron diffractometers, but can also be promoted and applied to other fields that require efficient neutron transmission, such as neutron scattering experiments, neutron detectors, etc., and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1It is a schematic diagram of the structure when the present invention is used in the vacuum scattering cavity of a CSNS high-resolution neutron diffractometer.

[0016] Figure 2 It is a schematic structural diagram of a large-sized curved thin-walled neutron beam window in the present invention.

[0017] Figure 3 It is a schematic diagram of the partial appearance structure of a planar neutron beam window in the prior art.

[0018] Figure 4 It is a schematic diagram of the partial appearance structure of the curved neutron beam window in the present invention.

[0019] Figure 5 It is the maximum principal stress, maximum principal strain and overall deformation cloud diagram of the plane beam window in the prior art.

[0020] Figure 6 It is the maximum principal stress, maximum principal strain and overall deformation cloud diagram of the curved beam window in the present invention.

[0021] Figure 7 This is a comparison diagram of the experimental results of the measured / calculated maximum principal stress of a 1mm curved beam window.

[0022] Figure 8 This is a comparison diagram of the experimental results of the measured / calculated maximum principal strain of the 1mm curved beam window.

[0023] Fig. 9 This is a diagram showing the experimental measurement / calculation of the maximum principal stress of a 1.5mm curved beam window.

[0024] Fig.10 This is a comparison of the experimental results of the measured / calculated maximum principal strain of the 1.5mm curved beam window. Figure annotation: 1-curved beam window, 2-scattering cavity, 3-interior of the cavity, 4-transverse ribs DETAILED DESCRIPTION

[0025] The specific implementation of the present application is described in detail below in conjunction with the accompanying drawings:

[0026] like Figure 1-10As shown, a large curved thin-walled neutron beam window for high-resolution neutron diffractometer and a manufacturing method thereof are mainly aimed at the problem that the thickness of a large-sized flat neutron beam window is too thick, resulting in reduced neutron transmittance, and the flat beam window is too thin, resulting in large vacuum deformation, plastic deformation and large stress concentration after being subjected to force, and under the action of long-term alternating loads, the stress concentration area is prone to necking or even fatigue rupture, and the impact force brought by the rupture moment may cause damage to the surrounding detectors. The present invention aims to propose a large curved thin-walled neutron beam window, which solves the physical requirement of thinness and meets the mechanical strength requirements. Through finite element calculation and analysis of the flat beam window and the curved beam window 1, it is found that the curved beam window 1 can greatly reduce deformation and stress concentration and extend the service life. However, the processing of a large-area thin-walled curved beam window 1 is difficult, costly and has a long production cycle, and there is no processing experience of similar large thin-walled parts at home and abroad. Through a series of process explorations, a beam window prototype with a cross-sectional size of 1:1 is finally manufactured by using a concave and convex die pad + high-speed milling process. Considering the importance of the beam window and the serious damage that may be caused in the future, the beam window was fatigue tested tens of thousands of times. The stress and deformation obtained by the test were greater than the results of finite element analysis. The main reason for the analysis was that the stress relief process after rough machining and the high aging temperature caused the performance of the material to decrease. The test results showed that the maximum principal stress of the 1mm beam window exceeded the fatigue limit and had a limited life cycle. According to the SN curve, the life of the 1mm beam window is 10 5 The maximum principal stress of the 1.5mm beam window does not exceed the fatigue limit, which means it has an infinite life cycle. The life of the 1.5mm beam window exceeds 10 7 The lifespan of the two thicknesses of beam windows far exceeds the actual service life, but considering the defects of the material itself and processing defects, a 1.5mm thick beam window was finally used. At present, this thickness of beam window has been actually used in the vacuum scattering cavity of high-resolution neutron diffractometers, providing a reference for similar devices.

[0027] Example 1: Application to the vacuum scattering cavity of the high-resolution neutron diffractometer (HRD) of the China Spallation Neutron Source (CSNS)

[0028] like Figure 1 As shown, it provides a high vacuum environment for the experimental samples and scattered neutron channels, more specifically a vacuum chamber with a volume of about 10m 3 The interior 3 of the vacuum chamber is used as the scattering cavity 2, and a large-area detector is arranged outside the scattering cavity 2. Therefore, a larger neutron scattering window is required, and the corresponding curved beam window 1 is large in size, which brings great difficulty to the design. It must meet the physical requirements of thinness to ensure that neutrons have good transmittance, and ensure that the curved beam window 1 has sufficient pressure bearing capacity to ensure the safe and stable operation of the entire device.

[0029] At present, domestic and international spallation sources usually use 6061 or 7075 aluminum alloy as beam window material. Under the same wall thickness, the neutron transmittance of 7075 is slightly lower than that of 6061, but the mechanical strength is nearly twice as high as that of 6061. Therefore, 7075 can make the beam window design thinner and minimize the neutron absorption rate. The two most commonly used states of 7075 are T6 and T651. T6 has a large internal stress. The large internal stress generated during the processing makes it easy to deform and warp in subsequent mechanical processing. T651 is stretched on the basis of T6 to eliminate the internal stress, and it is not easy to deform during processing. HRD uses 7075-T651 produced by Kamensk-Uralsky Company in Russia, with a measured tensile strength of 575Mpa, a yield strength of 520Mpa, and an elongation of 12.6%.

[0030] Through a lot of research, it is found that there are many studies on small-sized beam windows at home and abroad, and most of them adopt spherical shapes. For example, the CSNS waste beam station, SNS waste beam station and CSNS proton beam windows all adopt 2mm thick spherical beam windows, the J-PARC proton beam window adopts a 2.5mm thick spherical beam window, and the ISIS proton beam window adopts a 3mm thick spherical beam window. The above spherical beam windows are small in size, and the flanges and thin windows are mostly processed in one piece. For large-sized beam windows, considering time, cost, and processing difficulty, flat beam windows are usually used. For example, the neutron beam window of the J-PARC high-resolution chopper spectrometer (HRC) adopts a sealing structure in which a 1.5mm thin plate is pressed by a pressing frame. The proton beam window of the Korean PEFP adopts a sealing structure in which a 0.5mm thin plate is pressed by a pressing frame. The CSNS general powder diffractometer (GPPD) uses a 5mm thick thin window and a flange to form a flat beam window by milling.

[0031] Large-sized flat beam windows usually experience large vacuum deformation and plastic deformation after evacuation, and large stress concentration occurs at the joint of the flange and the thin window. The beam window usually has a low-cycle fatigue life and needs to be replaced regularly after a certain service life. This paper proposes a large-sized curved thin-walled neutron beam window that can not only meet the physical requirements of thinness, but also meet the mechanical strength requirements.

[0032] Example 2: Manufacturing a large-size curved thin-walled neutron beam window for use in a high-resolution neutron diffractometer (HRD) vacuum scattering cavity

[0033] The principles of manufacturing a large-size curved thin-walled neutron beam window for use in a high-resolution neutron diffractometer (HRD) vacuum scattering cavity include the following:

[0034] (1) Design and analyze beam windows according to requirements: HRD has two sizes of beam windows, the medium and low angle beam windows are 1570mmx740mm, and the high angle beam windows are 1070mmx750mm. This article mainly introduces the design of medium and low angle beam windows. The initial design thickness is 1mm. Since the medium and low angle beam windows are large and thin, the processing is extremely difficult. Therefore, two horizontal ribs 4 are designed in the blind area of ​​the detector in the middle of the beam window to divide the beam window into three windows: upper, middle and lower. Figure 2 As shown, the cross-sectional dimensions of each window are 620mmx465mm. Finite element analysis is performed to compare the 1mm thick flat beam window and the curved beam window. The specific structure is as follows Figure 3 To improve the computational efficiency, one of the windows is selected for finite element analysis. Figure 4 It can be seen that the root of the plane beam window produces very high stress concentration, with the maximum principal stress reaching 609MPa, the maximum principal strain reaching 0.95%, and the overall deformation of the beam window being 14.2mm. The maximum principal stress exceeds the tensile strength of the material, and there is a risk of fracture. Figure 5 It can be seen that the maximum principal stress at the root of the curved beam window 1 is 282MPa, the maximum principal strain is 0.32%, the overall deformation of the beam window is 3.9mm, and the maximum principal stress is much lower than the yield strength of the material, with a high safety factor. Through analysis and comparison, the curved beam window 1 can greatly reduce the stress, strain and overall deformation at the root of the beam window, and can extend the service life of the beam window.

[0035] (2) Determine the beam window processing technology: At present, large-sized beam windows of spallation neutron sources at home and abroad are all flat, mainly because the flat beam window processing technology is simple. However, large-sized curved beam windows are difficult to process, with complex processes, high costs and long cycles.

[0036] Main processing difficulties: First, the beam window is made of 30mm thick aluminum plate, and the final milling process is 1mm thick. The internal stress release during the processing will cause the beam window to warp and deform. Secondly, the front and back sides of the beam window are curved surfaces, and both sides need to be processed. The final thickness of the formed surface is only 1mm. The processing process is prone to vibration of the knife, resulting in obvious knife marks, uneven transition dents, and even cracks. The notch sensitivity of 7075 requires that the beam window must have a very good surface processing quality.

[0037] The solution provided by this embodiment is: after the rough machining of the beam window, a secondary aging treatment is performed to remove the internal stress generated by the rough machining. In addition, semi-finishing and finishing should be processed by a high-speed milling machine to ensure high feed speed and small cutting parameters, so that the processing efficiency is higher and the surface accuracy and quality are better. At the same time, a special concave and convex mold is used in the processing process to ensure seamless fit with the beam window and avoid surface quality problems caused by vibration.

[0038] (3) Conduct beam window fatigue test: The neutron beam window described in this article needs to operate for 30 years under alternating loads and should have a life cycle of more than 6,000 times. Considering that the beam window is prone to fatigue rupture under long-term alternating loads, a fatigue test was performed on it. 1mm and 1.5mm beam window prototypes and simple vacuum chambers were manufactured respectively, and the stress and strain of the beam window were tested using a contact strain gauge, as shown in the figure. Based on time and cost considerations, the beam window was subjected to a vacuum cycle test of 10,000 times, and the beam window did not rupture. The maximum principal stress of the 1mm beam window is 330MPa, and the maximum principal strain is 0.47%. The maximum principal stress of the 1.5mm beam window is 214MPa, and the maximum principal strain is 0.3%. It proves that the beam window structure design and processing plan are feasible and can meet the needs of 30 years of use.

[0039] (4) Comparison between actual measurement and finite element analysis: The measured data are compared with the finite element calculation results. As shown in the figure, the stress and strain trends of the two are basically consistent. The calculated results are slightly lower than the measured results. The main reason is that the secondary aging temperature after rough machining is too high, which causes the performance of the material to decline.

[0040] (5) Beam window life evaluation: According to the research of Gao et al., the fatigue limit (260MPa) of 7075-T651 is half of the yield limit. The maximum principal stress of the 1mm beam window is 330MPa, and the maximum principal stress of the 1.5mm beam window is 214MPa. The maximum principal stress of the 1mm beam window exceeds the fatigue limit and has a limited life cycle. The maximum principal stress of the 1.5mm beam window does not exceed the fatigue limit and has an infinite life cycle. According to the SN curve of 7075-T651, the life of the 1mm beam window is close to 105, and the life of the 1.5mm beam window exceeds 107. Therefore, the theoretical service life of the 1mm and 1.5mm thick beam windows is far more than 30 years, but considering the defects of the material itself and processing defects, the 1.5mm thick beam window was finally used.

[0041] Embodiment 3: Application of the present invention to an experimental device

[0042] In summary, the present invention provides a large-size curved thin-walled neutron beam window and a manufacturing method thereof for application in an experimental device to resolve the contradiction between thickness and mechanical strength of the existing planar neutron beam window, while improving the neutron transmittance and ensuring the safe and stable operation of the experimental device.

[0043] Firstly, the present invention provides a large-sized curved thin-walled neutron beam window. The overall design of the beam window is curved to reduce stress concentration, reduce deformation, and improve neutron transmittance. The beam window material is 7075-T651 aluminum alloy to balance neutron transmittance and mechanical strength. The thickness of the beam window is designed to be 1.5 mm, which not only ensures good neutron transmittance, but also ensures sufficient pressure-bearing capacity. Transverse ribs are designed in the blind area of ​​the detector in the middle of the beam window to enhance structural stability without affecting neutron transmittance.

[0044] Through curved surface design, the vacuum deformation, plastic deformation and stress concentration of the beam window when subjected to stress are effectively reduced; the fatigue life of the beam window is improved to ensure long-term safe and stable operation; the neutron transmittance is optimized, and the accuracy and reliability of the experimental data are improved.

[0045] Secondly, the present invention provides a method for manufacturing a large-sized curved thin-walled neutron beam window, including the following implementation steps: (1) Rough machining and stress relief treatment: Use 30mm thick 7075 aluminum alloy plate as raw material; Rough machining to close to the target thickness, and then perform secondary aging treatment to remove the internal stress generated during the machining process. (2) Semi-finishing and finishing: Use high-speed milling machines for semi-finishing and finishing to ensure machining efficiency and surface quality; Use special concave and convex molds to pad during machining to avoid surface quality problems caused by vibration of the knife; Strictly control cutting parameters to ensure the surface accuracy and quality of the beam window. (3) Quality inspection and fatigue testing: Perform quality inspection on the finished beam window, including indicators such as dimensional accuracy and surface roughness; Perform at least 10,000 vacuum cycle tests to verify the fatigue life of the beam window; Adjust the processing parameters according to the test results to optimize product quality. (4) Final processing and application: Perform necessary surface treatment on the tested beam window, such as cleaning and passivation; install the beam window into the vacuum scattering cavity 2 of the high-resolution neutron diffractometer to ensure its sealing and stability; regularly monitor the performance status of the beam window in actual use to ensure its long-term safe and stable operation.

[0046] This embodiment successfully solves the contradiction between thickness and mechanical strength of a large-sized neutron beam window through a unique curved surface design and an optimized processing technology, thereby improving the neutron transmittance and the safety and stability of the experimental device.

Claims

1. A large-sized curved thin-walled neutron beam window, characterized in that: The neutron beam window is designed as an integrated curved structure, the thickness of the beam window is designed to be 1.5 mm, and a transverse rib is provided in the middle of the neutron beam window to enhance the structural stability without affecting the neutron penetration; The method for manufacturing a large-size curved thin-walled neutron beam window comprises the following steps: First, after material selection, the material is subjected to rough machining and stress relief treatment to obtain a semi-finished product, wherein the rough machining and stress relief treatment steps include: using a 30 mm thick 7075 aluminum alloy plate as a raw material, rough machining to a thickness close to the target thickness, and then performing a secondary aging treatment to remove internal stress; Then, the material is semi-finished and finished to obtain a finished product, wherein the semi-finished and finished steps include: using a high-speed milling machine to perform processing, using a special concave-convex mold to pad, and strictly controlling cutting parameters to ensure processing accuracy and quality; Then, quality inspection and fatigue test are performed on the finished product to obtain a good product. The quality inspection and fatigue test steps include: performing quality inspection on the processed beam window for indicators such as dimensional accuracy and surface roughness, and performing a vacuum cycle test for at least 10,000 times to verify fatigue life; Finally, the qualified products that meet the standards are subjected to final processing and application, which includes: performing necessary surface treatment on the beam window that has passed the test, i.e., cleaning and anodizing, and then installing it in the vacuum scattering cavity of a high-resolution neutron diffractometer.

2. The large-size curved thin-walled neutron beam window according to claim 1, characterized in that: Two transverse ribs are designed in the detector blind area in the middle of the beam window to equally divide the beam window into three windows: upper, middle and lower.

3. The large-size curved thin-walled neutron beam window according to claim 1, characterized in that: The neutron beam window is made of 7075-T651 aluminum alloy to balance neutron transmittance and mechanical strength.

4. The large-size curved thin-walled neutron beam window according to claim 2, characterized in that: The cross-sectional dimensions of each window are 620mmx465mm to achieve a balance between neutron transmittance and pressure bearing capacity.

5. The large-size curved thin-walled neutron beam window according to any one of claims 1 to 4, characterized in that: The method also includes regularly monitoring the performance status of the beam window in actual use to ensure its long-term safe and stable operation.

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