A cold rolling forming process for zirconium alloy end plugs for nuclear power fuel rods

Abstract

The present invention belongs to the technical field of nuclear power fuel rod processing, and specifically relates to a cold rolling forming process method for zirconium alloy end plugs for nuclear power fuel rods. After the end plug is processed with a straight hole, a rolling wheel is used for cold rolling forming. The rolling path of the rolling wheel is from the side of the end plug to the end plug port. The rolling wheel performs 6-8 rolling along the rolling path. During the cold rolling forming process, the end plug rotates, and the rolling wheel rotates with the end plug. The present invention uses a rolling wheel to perform multiple rolling along the rolling path, so that the port is gradually formed, the deformation is uniform, the deformation amount is controllable, and multiple rolling deformations can improve the port strength, thereby improving the drawing performance.

Description

Technical Field

[0001] The invention relates to a cold rolling forming process method of a zirconium alloy end plug for a nuclear power fuel rod, belonging to the technical field of nuclear power fuel rod processing. Background Art

[0002] Nuclear power fuel rods are the core components of nuclear power reactors. Their performance and reliability are directly related to the safe operation and power generation efficiency of nuclear power plants. As a key component of fuel rods, fuel rod end plugs play an important role in sealing, fixing fuel cores and transferring heat. In addition, the end plug at one end of the fuel rod also serves as a pulling force point during the installation of the fuel rods. The total length of the fuel rods is 4.2-4.4 meters. They are installed in the corresponding grid by pulling. A group of nuclear fuel assemblies has 289 fuel rods. Each fuel rod must be pulled from the upper end of the grid to the tail end. During the pulling and installation of the fuel rods, the friction of about 15 layers of grid springs must be overcome. Therefore, the end plug must be able to withstand sufficient pulling force.

[0003] The end plug used for fuel rod drawing and installation has one end welded to the end of the fuel rod and the other end machined into a drawing hole. The structure of the drawing hole is a shrinkage hole with a large inner diameter and a small orifice diameter. In order to meet the drawing force requirements, the inner hole is required to be formed by plastic forming, and secondary processing is not allowed after forming. Fuel rod end plugs are generally made of zirconium alloy (Zr4). Zirconium alloy material is soft (hardness is 160HV~170HV) and has a low melting point. If pure mechanical processing is used, the material does not form residual compressive stress. When the fuel rod is installed, the end plug may be pulled off during the drawing force, resulting in drawing failure; after the drawing fails, it is necessary to cut off a part of this end of the fuel rod and re-weld the end plug. After the end plug is welded, a series of tests need to be done again to ensure that the fuel rod as a whole meets the product quality requirements before it can be re-installed, resulting in increased processing costs. Moreover, in order to ensure that the lengths of multiple fuel rods in a tube column are uniform, the pulling and installation of each fuel rod is only allowed to fail once. If it fails twice or more, the length of the fuel rod will be significantly shorter than other fuel rods and can only be discarded.

[0004] Therefore, the processing technology of the fuel rod end plug is crucial to ensure the overall performance, service life and successful installation of the fuel rod. The existing processing technology of the fuel rod end plug generally first processes a straight hole in the end plug, and then uses a ball cutter to extrude the port of the straight hole of the end plug to reduce the port diameter of the straight hole, thereby forming a drawing hole structure with a large inner diameter and a small port diameter. In this processing process, due to the large local deformation of the port, the port is very prone to cracks, and the inner arc R is irregular after extrusion, which leads to uneven force on the inner arc, affecting its drawing performance, and low product qualification rate. Summary of the invention

[0005] In view of the defects of the prior art, the present invention provides a cold rolling forming process method for zirconium alloy end plugs for nuclear power fuel rods.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a cold rolling forming process method for zirconium alloy end plugs for nuclear power fuel rods, after the straight hole is processed in the end plug, cold rolling forming is performed using a rolling wheel, the rolling path of the rolling wheel is from the side of the end plug to the end plug port, the rolling wheel rolls 6-8 times along the rolling path, and the end plug rotates during the cold rolling forming process, and the rolling wheel rotates with the end plug.

[0007] On the basis of the above technical solution, the present invention can also make the following improvements:

[0008] Furthermore, the angle between the rolling path and the central axis of the end plug is 40.5°.

[0009] Furthermore, the feed rate of the rolling wheel each time rolling is 0.08mm / r, and the rolling amount is 0.15mm-0.20mm.

[0010] Furthermore, during the rolling process, the rotation speed of the end plug is 800r / min-1000r / min.

[0011] Furthermore, before cold rolling forming, the end plug is firstly rough-machined, wherein the end of the end plug is machined into a frustum through the rough-machined process, and the major diameter of the conical surface of the frustum is the starting point of the rolling path.

[0012] Furthermore, a circular arc B is provided at the large diameter end of the conical surface of the frustum, the range of the circular arc B is R5.35mm±0.25mm, and the circular arc B is 3mm-4mm away from the port.

[0013] Furthermore, the rolling wheel includes a wheel cutter and a bearing. The wheel cutter is mounted on a shank via the bearing. The wheel cutter can rotate freely. The shank is connected to a machine tool. During the cold rolling forming process, the wheel cutter contacts the end plug.

[0014] Furthermore, the blade edge of the wheel cutter is provided with an arc-shaped chamfer C, and the range of the chamfer C is R0.9mm-R1.0mm.

[0015] Furthermore, the rolling wheel performs 6-7 rolling operations along the rolling path.

[0016] Furthermore, after cold roll forming, the port and the shape of the end plug are finely processed.

[0017] The beneficial effects of the present invention are as follows: the present invention adopts a cold rolling forming process, and the rolling wheel performs rolling forming according to the designed rolling path. After rolling, the inner arc R of the plug drawing hole is more regular, and no cracks are generated in the inner hole, thereby improving the consistency of the product and thus improving the product qualification rate. During drawing, the inner arc is subjected to more uniform force, thereby improving the drawing performance. The present invention adopts a rolling wheel to perform multiple rolling according to the rolling path, so that the port is gradually formed, the deformation is uniform and controllable, and multiple rolling deformations can improve the port strength, thereby improving the drawing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a rough machining process design diagram of Example 1 of the present invention;

[0019] Figure 2 This is a schematic diagram of a rolling path according to Embodiment 1 of the present invention;

[0020] Figure 3 It is a schematic cross-sectional structure diagram of a rolling wheel according to Embodiment 1 of the present invention;

[0021] Figure 4 This is a schematic diagram of the cold roll forming process of Example 1 of the present invention;

[0022] Figure 5 This is a photo of the dissection of the end plug processed in Example 1 of the present invention;

[0023] Figure 6 This is a metallographic photograph of the end plug of Example 1 of the present invention;

[0024] Figure 7 This is a metallographic photograph of the straight section of the end plug of Example 1 of the present invention;

[0025] Figure 8 This is a macroscopic photograph of the inner arc of the end plug drawing hole of Example 1 of the present invention;

[0026] Fig. 9 This is a photo of the ball knife of Comparative Example 3;

[0027] Fig.10 This is a photo of the dissection of the end plug processed in Comparative Example 3;

[0028] Fig.11 This is a metallographic photograph of the straight section of the end plug of Comparative Example 3;

[0029] Fig.12 This is a macroscopic photograph of the inner arc of the end plug drawing hole of Comparative Example 3;

[0030] Fig.13 It is a cross-sectional view of the internal structure of the end plug drawing hole;

[0031] Fig.14 This is a photo of the end plug appearance of Example 1;

[0032] Fig.15 This is a photo of the end plug appearance of Comparative Example 1.

[0033] The reference numerals are recorded as follows: 11, wheel cutter; 12, through hole. DETAILED DESCRIPTION

[0034] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0035] Example 1

[0036] A cold rolling forming process for zirconium alloy end plugs for nuclear power fuel rods, specifically comprising the following steps:

[0037] 1. Processing straight holes:

[0038] A straight hole is machined at the end of the end plug (diameter φ10.00 mm), the diameter of the straight hole is φ4.19 mm, and the depth is 5.5 mm.

[0039] 2. Rough processing before rolling:

[0040] See also Figure 1 Before cold rolling forming, the end plug is rough-machined, and the end of the end plug is machined into a frustum on a machine tool. Specifically, the rough machining process diagram before rolling is determined according to the relative relationship between the rolling force and the rolling allowance. The rolling allowance refers to the rolling thickness allowance. If the rolling allowance is too much, the material resistance is large. When the rolling force is applied, the force borne by the material in the direction of the inner hole is smaller than the force along the rolling path. The inner hole R arc and the relative position to the port have large deviations after forming, which do not meet the requirements of the drawing; if the rolling allowance is too little, although the inner hole R arc is formed regularly, the port and the outer shape are not fully formed, which cannot meet the requirements of the drawing. It is necessary to determine the rolling allowance requirements through multiple tests. In this embodiment, the rolling allowance is 0.6mm-1.3mm. Specifically, the rolling allowance at the large diameter end of the frustum of the end plug in this embodiment is 0.6mm, and the rolling allowance at the small diameter end is 1.3mm. Among them, the large diameter of the cone surface of the frustum is the starting point of the rolling path ( Figure 1 At A in the figure), the cone angle of the frustum is 21.7° (see Figure 1 ), an arc B is provided at the large diameter end of the conical surface of the frustum, and the design of the arc B is a contour design, that is, it is similar to the shape of the arc R4.75 of the end plug that has been finely machined, and the curvature of the arc B is greater than the arc R4.75. Specifically, in this example, the value of the arc B is R5.35mm, which can enable the wheel cutter to fully contact with the material during rolling by the rolling wheel, which is conducive to the full appearance of the end plug.

[0041] In this embodiment, the design principle of the rough machining process diagram is:

[0042] 1) According to the principle of plastic deformation of materials and the principle that the volume of materials remains unchanged before and after deformation, the total margin requirement is determined. In this embodiment, in the rolling deformation area, no margin is left for the inner hole, but a rolling margin is left for the outer shape. Ensure that the inner hole meets the size requirements of the drawing after rolling, and no secondary processing is performed;

[0043] 2) According to the product structure, combined with the relationship between rolling deformation and wall thickness, determine the wall thickness rolling allowance of the deformed part. In this embodiment, the deformation volume is about 128mm 3 According to the deformation volume, the rolling allowance of the rough-machined conical surface wall thickness is determined as follows: the large diameter end and the conical surface shape have a rolling allowance of 0.6mm, and the small diameter end has a rolling allowance of 1.3mm.

[0044] 3. Cold rolling forming:

[0045] See also Figure 2 , a rolling wheel is used for cold rolling forming. First, a rolling route is designed. The rolling path of the rolling wheel is from point A on the side of the end plug to the end plug port. The rolling wheel rolls 6-8 times along the rolling path. Specifically, in this embodiment, the rolling wheel rolls 7 times along the rolling path. In order to facilitate the formation of the inner arc of the drawing hole, an inner arc avoidance section is provided in the middle section of the rolling path each time the rolling is performed. The inner arc avoidance section is an arc-shaped path section protruding outward. During the cold rolling forming process, the product rotates at a speed of 800r / min-1000r / min. The rolling wheel rotates with the product. The rolling feed amount of the rolling wheel each time is 0.08mm / r, and the rolling amount is 0.15mm-0.20mm. Specifically, in this embodiment, the rolling amount of the rolling wheel each time is 0.15mm, and the angle between the rolling path and the central axis of the end plug is 40.5° (see Figure 2 ). Among them, the feed amount of the rolling wheel refers to the distance that the rolling wheel feeds along the length direction of the end plug for each rotation of the end plug; the rolling amount of the rolling wheel refers to the distance that the rolling wheel feeds in the direction perpendicular to the end plug processing surface, that is, the feed amount of the rolling wheel.

[0046] Specifically, in this embodiment, see Figure 3 The rolling wheel includes a wheel cutter 11 and a bearing (not shown in the figure). The wheel cutter 11 is installed on a shank (not shown in the figure) through a bearing. The wheel cutter 11 is provided with a through hole 12 for installing the bearing. The bearing is installed in the through hole 12. The end of the shank is inserted into the inner hole of the bearing. The shank is connected to a machine tool. During the cold rolling forming process, the shank is driven by the machine tool to drive the rolling wheel close to the end plug, and cold rolling is performed according to a preset angle, feed amount and rolling amount. The wheel cutter contacts the end plug, and cold rolling is performed on the end plug according to a preset rolling path (see Figure 4), in this process, the end plug rotates under the drive of the power mechanism, the end plug speed is 1000r / min, the rolling wheel is in contact with the end plug, so the rolling wheel will follow the rotation of the end plug. Since the rolling wheel rolls multiple times along the rolling path, see Figure 4 The rolling wheel is processed along the rolling path. During the initial rolling, although the rolling wheel starts to feed from the large diameter end of the end plug cone, the rolling wheel does not contact the end plug when feeding at the large diameter end, but contacts the end plug when feeding at the small diameter end, that is, the rolling wheel first processes the small diameter end, and in the intermediate rolling process, the rolling wheel gradually contacts the large diameter end of the end plug. In this way, 7 rollings are performed along the rolling path until the final rolling is completed, so that the port is gradually formed, the port of the end plug will not undergo large local deformation, the inner arc of the end plug is neatly formed, the material is deformed evenly, without cracks or folds, and the rolling wheel moves with the rotation of the end plug, the contact surface between the end plug and the rolling wheel will not generate large friction, and there is no ablation on the surface of the end plug.

[0047] 4. Finishing

[0048] After rolling, the port and shape are machined to meet the accuracy requirements of the drawing. The processed parts include the end shape of the end plug, the end face and the straight mouth of the drawing hole.

[0049] Dissect the end plug obtained after processing (such as Figure 5 As shown), and metallographic examination was performed, the results are as follows Figure 6-8 As shown. Figure 5 , Figure 6 and Figure 8 As shown, the end plug processed by the process method of the present invention undergoes plastic deformation multiple times along the contour rolling path, the material deforms evenly, without cracks or folds, the inner arc is formed regularly, and the inner arc of the drawing hole of the end plug is symmetrical and regular. Figure 7 As shown in the figure, the straight section of the end plug has good continuity, full molding, and no ablation, which better meets the requirements of subsequent finishing. Fig.14 As shown, the end plug has a smooth appearance and meets the requirements for finishing allowance.

[0050] Example 2

[0051] Different from the first embodiment, the rolling amount of the rolling wheel in this embodiment is 0.20 mm each time, and the rest is the same as the first embodiment and will not be described again.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that the angle between the rolling path and the central axis of the end plug in this comparative example is 41°. Fig.15 As shown, it can be seen that there is no machining allowance in part of the shape of the end plug, especially on the outer side of the port of the end plug.

[0054] Comparative Example 2

[0055] The difference from Example 2 is that the angle between the rolling path of this comparative example and the central axis of the end plug is 41°.

[0056] The rolling process parameters of Example 1-2 and Comparative Example 1-2 are shown in the following table:

[0057] Table 1 Rolling process parameters

[0058]

[0059] Comparative Example 3

[0060] The difference from Example 1 is that the third step of this comparative example adopts Fig. 9 The ball cutter shown extrude the end plug for 1-2 times. During the extrusion process, the end plug rotates but the ball cutter does not rotate.

[0061] The end plug obtained after processing in this comparative example was dissected (such as Fig.10 As shown), and metallographic examination was performed, the results are as follows Figure 11-12 As shown, the local deformation of the metal material end portion processed by the extrusion molding process of this comparative example is large, and it is easy to produce cracks and folds, and the inner arc molding is irregular (see Fig.12 ), and local material shortage or ablation occurs (see Fig.11 ).

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A cold rolling forming process for zirconium alloy end plugs for nuclear power fuel rods, characterized in that: After the straight hole is processed in the end plug, a rolling wheel is used for cold rolling forming. The rolling path of the rolling wheel is from the side of the end plug to the end plug port. The rolling wheel rolls 6-8 times along the rolling path. During the cold rolling forming process, the end plug rotates, and the rolling wheel rotates with the end plug; the angle between the rolling path and the center axis of the end plug is 40.5°; the feed amount of the rolling wheel each time is 0.08mm / r, and the rolling amount is 0.15mm-0.20mm; during the rolling process, the rotation speed of the end plug is 800r / min-1000r / min.

2. The cold rolling forming process of zirconium alloy end plugs for nuclear power fuel rods according to claim 1 is characterized in that: Before cold rolling forming, the end plug is firstly rough-machined, wherein the rough-machined process is to machine the end of the end plug into a frustum, and the major diameter of the conical surface of the frustum is the starting point of the rolling path.

3. The cold rolling forming process of zirconium alloy end plugs for nuclear power fuel rods according to claim 2 is characterized in that: An arc B is provided at the large diameter end of the conical surface of the frustum, the range of the arc B is R5.35mm±0.25mm, and the arc B is 3mm-4mm away from the port.

4. The cold rolling forming process of zirconium alloy end plugs for nuclear power fuel rods according to claim 3 is characterized in that: The rolling wheel comprises a wheel cutter and a bearing. The wheel cutter is mounted on a shank through the bearing. The wheel cutter can rotate freely. The shank is connected to a machine tool. During the cold rolling forming process, the wheel cutter contacts the end plug.

5. The cold rolling forming process of zirconium alloy end plugs for nuclear power fuel rods according to claim 4 is characterized in that: The blade edge of the wheel cutter is provided with an arc-shaped chamfer C, and the range of the chamfer C is R0.9mm-R1.0mm.

6. The cold rolling forming process of zirconium alloy end plugs for nuclear power fuel rods according to claim 5 is characterized in that: After cold roll forming, the end plugs are finished in terms of port and shape.

7. The cold rolling forming process of zirconium alloy end plugs for nuclear power fuel rods according to claim 6 is characterized in that: The rolling wheel rolls 6-7 times along the rolling path.

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