Electric spark machining head for cutting sleeve flange in narrow space

Abstract

The invention belongs to the technical field of special maintenance of reactor bodies, and particularly relates to an electric spark machining head for cutting a sleeve flange in a narrow space. Comprising an expansion mechanism, a fine adjustment jacking mechanism, a rotating mechanism, an electrode and a radial servo feeding mechanism, the rotating mechanism provides rotary motion of the electrode and drives the electrode to conduct rotary machining, the radial servo feeding mechanism provides radial feeding motion of the electrode, and the expansion mechanism plays a role in fixing and positioning. The fine adjustment jacking mechanism drives the rotating mechanism, and the radial servo feeding mechanism drives the electrode to do up-down, rotating and radial feeding movement. The method has the beneficial effects that the damage to the pressure-bearing boundary of the primary loop of the nuclear power unit can be avoided under the condition that the heat sleeve is worn out of limits and needs to be replaced aiming at the common problem of wear settlement of the heat sleeve of the control rod driving mechanism of the nuclear power unit, and the whole dismantling work has relatively high safety, reliability and economical efficiency; and greater benefits can be created for the operation of a power plant.

Description

Technical Field

[0001] The invention belongs to the technical field of special maintenance of reactor bodies, and particularly relates to an electric spark machining head for cutting casing flanges in a narrow space. Background Art

[0002] The thermal sleeve is a component of the control rod drive mechanism (CRDM) and is suspended from the CRDM socket on the pressure vessel head. It is installed with a radial clearance fit and no axial constraints. During unit operation, the thermal sleeve is subject to vibrations induced by the primary flow, causing friction between the upper end and the CRDM socket flange, resulting in a drop in the sleeve's height. Over time, wear on the sleeve's end causes the sleeve to drop further. If not addressed, the sleeve will continue to settle, eventually wearing away completely and causing the entire sleeve to fall.

[0003] If preventive measures are not taken, long-term operation will lead to severe wear of the thermal insulation sleeve, resulting in serious failures such as sinking beyond the limit, wall thickness reduction, breakage, etc. Once the problem cannot be alleviated or repaired, it will pose a hidden danger to safe operation and the thermal insulation sleeve needs to be replaced.

[0004] At present, there has been no case of thermal sleeve removal in the nuclear power industry, and the technology of removing from above the top cover is generally adopted.

[0005] The work of removing the thermal insulation sleeve from above the top cover of the in-service unit involves cutting the top CRDM assembly, cutting the lower sealing weld, shaping the groove, cutting the old thermal insulation sleeve and other work steps.

[0006] The reactor pressure vessel top cover has a complex structure. Before replacing and cutting the sealing welds of the control rod drive mechanism pressure hull, the top structure must be dismantled to the maximum extent possible, retaining only the reactor pressure vessel top cover body (including the tube seats), ventilation hood supports, control rod drive mechanism pressure hull components (including the hook components), and the female flange of the thermocouple column. Furthermore, since the pressure vessel and control rod drive mechanism are both Class I nuclear equipment, and the welds involved are also the primary pressure boundary, the operational verification process for removal and reinstallation is complex. The specific replacement work involves cutting the sealing welds of the pressure hull, shaping the grooves, re-welding, non-destructive testing, hydrostatic testing, and automatic welding in a high-radiation environment. The required processes are complex, the construction period is long, and the safety and economic efficiency are poor. Summary of the Invention

[0007] The purpose of the present invention is to provide an electrospark machining head for cutting sleeve flanges in narrow spaces, which is used for removing thermowells. The entire machining head integrates expansion, lifting, rotation, radial feeding, electrodes, and imaging. It is a highly integrated electrospark machining head that can remove defective thermowells from under the top cover of a pressure vessel.

[0008] The technical solution of the present invention is as follows: An electrospark machining head for cutting sleeve flanges in a narrow space, including an expansion mechanism, a fine-tuning lifting mechanism, a rotating mechanism, an electrode and a radial servo feed mechanism. The rotating mechanism provides rotational motion of the electrode, drives the electrode for rotational processing, the radial servo feed mechanism provides radial feed motion of the electrode, the expansion mechanism plays a fixed positioning role, and the fine-tuning lifting mechanism drives the rotating mechanism and the radial servo feed mechanism to drive the electrode to perform up and down, rotation, and radial feed motion respectively.

[0009] The expansion mechanism, fine-tuning lifting mechanism, rotating mechanism, electrode and radial servo feeding mechanism are provided with a metal shell outside, which plays the role of structural support and internal component fixation, and plays a guiding role when the entire processing head passes through the hole in the thermal sleeve.

[0010] The radial servo feeding mechanism includes a gear rack feeding device and cameras. Two cameras are installed on the housing, one lens faces upward to observe the upper condition of the processing head, and the other lens observes the processing condition of the electrode.

[0011] The electrode is mounted on a rack of a gear-rack feeding device. The feeding electrode drives the gear to rotate, and the gear drives the rack to move laterally, thereby driving the electrode to move radially.

[0012] The rotating mechanism includes a rotating reducer, a limit switch and a fixed shaft. The rotating reducer is equipped with a limit switch, which controls the rotation angle of the rotating reducer. The output shaft of the rotating reducer is fixed to the fixed shaft.

[0013] The flange of the rotary reducer is connected to the housing, and the housing is connected to the electrode and the radial servo feed mechanism. When the rotary reducer rotates, the flange drives the electrode and the radial servo feed mechanism to rotate.

[0014] The fine-tuning jacking mechanism includes a gear pair, a first rotary reducer and a threaded screw pair. The first rotary reducer drives the threaded screw pair to rotate through the gear pair.

[0015] The expansion mechanism includes an expansion electrode, a wedge-shaped driving head and an expanding head. The expansion electrode provides up and down movement of the output shaft, driving the wedge-shaped driving head to move up and down. The wedge-shaped driving head is evenly arranged with three "convex" wedge-shaped grooves around the circumference. The three expanding heads are inserted into the wedge-shaped grooves of the wedge-shaped driving head through "convex" wedge blocks. When the wedge-shaped driving head moves up, the three expanding heads are driven to open outward, supporting the inner wall of the thermowell and playing a centering and fixing role.

[0016] The expansion mechanism realizes radial fixation between the electric spark machining head and the thermal sleeve through a wedge-shaped expansion block structure.

[0017] The present invention addresses the common problem of wear and sedimentation of thermowells in control rod drive mechanisms of nuclear power plants. When thermowells exceed specified wear limits and require replacement, damage to the primary pressure-bearing boundary of the nuclear power plant is avoided. This makes the entire dismantling operation highly safe, reliable, and economical, creating greater benefits for power plant operations. The method utilizes a rotating block graphite electrode coupled with radial feed motion for electrical discharge machining, making it safe and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of an EDM head for cutting casing flanges in narrow spaces provided by the present invention; Figure 2 This is a processing diagram of an EDM head for cutting casing flanges in narrow spaces provided by the present invention; Figure 3 This is a partial enlarged view of an electrospark machining head for cutting casing flanges in narrow spaces provided by the present invention; Figure 4 An exploded view of an EDM head for cutting sleeve flanges in narrow spaces provided by the present invention (with the outer shell removed); Figure 5 This is the schematic diagram of the radial servo feed mechanism; Figure 6 This is the principle diagram of the rotating mechanism; Figure 7 This is the schematic diagram of the fine-tuning jacking mechanism; Figure 8 This is the schematic diagram of the expansion mechanism.

[0019] In the figure: 1. Expansion mechanism; 2. Fine-tuning lifting mechanism; 3. Rotation mechanism; 4. Electrode; 5. Radial servo feed mechanism; 8. EDM head; 9. Thermal sleeve; 11. Expansion electrode; 12. Wedge-shaped drive head; 13. Expansion head; 21. Gear pair; 22. First rotary reducer; 23. Threaded screw pair; 24. Fixed nut; 31. Rotation reducer; 32. Limit switch; 33. Fixed shaft; 51. Rack and pinion feed device; 52. Camera. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The present invention provides an electrospark machining head for cutting casing flanges in narrow spaces. The head is used to remove the thermal sleeve when the wear and settlement of the thermal insulation sleeve of the control rod drive mechanism of a pressurized water reactor nuclear power unit exceeds the standard. The removal process is carried out under the top cover.

[0022] Given the thermowell's "large ends, small center" shape and suspended mounting method, the lack of access and space inside the equipment necessitates utilizing the internal channels of the sleeve to move the machining head to the desired area for cutting. Therefore, EDM (Electrodischarge Machining) was chosen as the cutting method. This method, without the reactive forces of EDM, allows for a smaller machining head. Furthermore, EDM provides monitoring and protection features, preventing damage to the surrounding equipment and generating the large amounts of dust and iron chips typically associated with machining, thus facilitating equipment cleanliness.

[0023] Electric spark cutting needs to consider functions such as positioning, clamping, lifting, rotation, servo feeding, and real-time camera, and the present invention integrates these functions.

[0024] like Figure 1 As shown, an EDM head 8 for cutting sleeve flanges in a narrow space includes an expansion mechanism 1, a fine-tuning lifting mechanism 2, a rotation mechanism 3, an electrode 4 and a radial servo feeding mechanism 5, which work together to realize the functions of the EDM head 8.

[0025] like Figure 1 As shown, the expansion mechanism 1, the fine-tuning lifting mechanism 2, the rotating mechanism 3, the electrode 4 and the radial servo feeding mechanism 5 are all surrounded by a metal shell, which plays a role in structural support and fixing the internal components. At the same time, it plays a guiding role when the entire EDM head 8 passes through the hole in the thermal sleeve 9.

[0026] The expansion mechanism 1, the fine-tuning lifting mechanism 2, the rotating mechanism 3, the electrode 4 and the radial servo feeding mechanism 5 cooperate with each other to respectively realize the functions of clamping, lifting, rotation, lateral feeding and discharge machining, and work together to complete the machining and cutting of the upper end of the thermowell 9 by the electrode 4.

[0027] The expansion mechanism 1 realizes radial fixation between the EDM head 8 and the thermal sleeve 9 through a wedge-shaped expansion block structure, providing positioning guarantee for subsequent other actions.

[0028] The fine-tuning lifting mechanism 2 can drive the rotating mechanism 3, the electrode 4 and the radial servo feed mechanism 5 to move up and down within a certain range. Because the electrode 4 needs to be adjusted up and down during the processing of the thermowell 9, the fine-tuning lifting mechanism 2 provides the up and down movement of the electrode 4.

[0029] The rotating mechanism 3 provides the electrode 4 with a rotational motion, driving the electrode 4 to perform rotational processing.

[0030] The radial servo feed mechanism 5 provides radial feed motion of the electrode 4 .

[0031] The expansion mechanism 1 plays a role in fixing and positioning, and the fine-tuning lifting mechanism 2, the driving rotation mechanism 3, and the radial servo feeding mechanism 5 respectively drive the electrode 4 to perform up and down, rotation, and radial feeding movements, providing all-round action guarantees for the electrode 4 to discharge and cut the upper end of the thermal sleeve 9.

[0032] like Figure 5 As shown, the radial servo feeding mechanism 5 includes a gear rack feeding device 51 and a camera 52. Two cameras 52 are installed on the housing, one lens faces upward to observe the upper part of the EDM head 8, and the other lens observes the processing condition of the electrode 4.

[0033] The rack and pinion feeding device 51 is fixed on a supporting structure connected to the housing.

[0034] The electrode 4 is mounted on the rack of the gear-rack feeding device 51 . The feeding electrode drives the gear to rotate, and the gear drives the rack to move laterally, thereby driving the electrode 4 to move radially.

[0035] like Figure 6 The rotating mechanism 3 includes a rotating reducer 31, a limit switch 32 and a fixed shaft 33. The limit switch 32 is installed on the rotating reducer 31. The limit switch 32 controls the rotation angle of the rotating reducer. The output shaft of the rotating reducer 31 is fixed to the fixed shaft 33.

[0036] The flange of the rotary reducer 31 is connected to the outer shell, and the outer shell is connected to the supporting structure of the upper electrode 4 and the radial servo feed mechanism 5. When the rotary reducer 31 rotates, since the motor output shaft is stationary, the rotary reducer 31 rotates, driving the upper outer shell to rotate through the flange, thereby driving the electrode 4 and the radial servo feed mechanism 5 to rotate through the internal support structure.

[0037] like Figure 7 As shown, the fine-tuning jacking mechanism 2 includes a gear pair 21, a first rotary reducer 22 and a threaded screw pair 23. The first rotary reducer 22 drives the threaded screw pair 23 to rotate through the gear pair 21.

[0038] The threaded screw pair 23 cooperates with the fixing nut 24, which is connected to the outer housing. The rotation of the threaded screw pair 23 drives the fixing nut 24 to move up and down, thereby driving the outer housing up and down. The outer housing here is connected to the housings of other functional components above, thus achieving fine-tuning and lifting of the processing head.

[0039] like Figure 8As shown, the expansion mechanism 1 includes an expansion electrode 11, a wedge-shaped drive head 12, and an expansion head 13. The expansion electrode 11 provides the up-and-down motion of the output shaft, thereby driving the wedge-shaped drive head 12 up and down. The wedge-shaped drive head 12 has three convex wedge-shaped slots evenly spaced around its circumference. The three expansion heads 13 are inserted into the wedge-shaped slots of the wedge-shaped drive head 12 via convex wedge blocks. When the wedge-shaped drive head 12 moves upward, it drives the three expansion heads outward, supporting the inner wall of the thermowell 9 and providing centering and fixation.

[0040] The working principle of the present invention is as follows: The function of the expansion mechanism 1 is to axially secure the EDM head 8 after it has been inserted into the specified position of the thermowell 9. The operating principle is that the expansion electrode 11 drives the wedge-shaped drive head 12 to move up and down. The wedge-shaped surfaces between the wedge-shaped drive head 12 and the expansion head 13 cooperate to convert the up and down motion of the wedge-shaped drive head 12 into radial motion of the three expansion heads 13. These three expansion heads contact the inner wall of the thermowell 9, thus achieving expansion and release.

[0041] The fine-tuning lifting mechanism 2 consists of a first rotary reducer 22, a gear pair 21, and a threaded screw pair 23. The first rotary reducer 22 drives the threaded screw pair 23 to rotate through the gear pair 21. Since the screw only rotates and does not move axially, the nut will move up and down along with the rotation of the screw. The upper part of the processing head is connected to the nut through the outer shell and also follows the lifting movement.

[0042] Rotating mechanism 3 consists of a fixed shaft 33, a rotary reducer 31, and a limit switch 32. The output shaft of rotary reducer 31 is fixed to fixed shaft 33 and cannot rotate. When rotary reducer 31 rotates, the motor rotates because the output shaft is fixed. Due to winding considerations, the motor can only rotate 360°, and the rotation angle is controlled by limit switch 32.

[0043] The electrode 4 is in a block shape and is mounted on a radial servo feed mechanism 5 for radial movement. There are many drainage holes distributed on the electrode 4 for spraying the EDM fluid.

[0044] The radial servo feeding mechanism 5 is a set of gear rack feeding device 51. The motor drives the gear to rotate, which is converted into the in and out movement of the rack in the radial feeding direction, and the rack drives the electrode 4.

[0045] There are also two cameras installed on the processing head, one looking upwards and the other observing the EDM position for real-time monitoring.

Claims

1. An electrospark machining head for cutting casing flanges in narrow spaces, characterized by: It includes an expansion mechanism, a fine-tuning lifting mechanism, a rotating mechanism, an electrode and a radial servo feed mechanism. The rotating mechanism provides the electrode with rotational motion and drives the electrode to perform rotational processing. The radial servo feed mechanism provides the electrode with radial feed motion. The expansion mechanism plays a fixed positioning role. The fine-tuning lifting mechanism drives the rotating mechanism and the radial servo feed mechanism to drive the electrode to perform up and down, rotation and radial feed motion respectively.

2. The electrospark machining head for cutting casing flanges in narrow spaces according to claim 1, characterized in that: The expansion mechanism, fine-tuning lifting mechanism, rotating mechanism, electrode and radial servo feeding mechanism are provided with a metal shell outside, which plays the role of structural support and internal component fixation, and plays a guiding role when the entire processing head passes through the hole in the thermal sleeve.

3. The electrospark machining head for cutting casing flanges in narrow spaces according to claim 1, characterized in that: The radial servo feeding mechanism includes a gear rack feeding device and cameras. Two cameras are installed on the housing, one lens faces upward to observe the upper condition of the processing head, and the other lens observes the processing condition of the electrode.

4. The electrospark machining head for cutting casing flanges in narrow spaces as claimed in claim 3, characterized in that: The electrode is mounted on a rack of a gear-rack feeding device. The feeding electrode drives the gear to rotate, and the gear drives the rack to move laterally, thereby driving the electrode to move radially.

5. The electrospark machining head for cutting casing flanges in narrow spaces as claimed in claim 1, characterized in that: The rotating mechanism includes a rotating reducer, a limit switch and a fixed shaft. The rotating reducer is equipped with a limit switch, which controls the rotation angle of the rotating reducer. The output shaft of the rotating reducer is fixed to the fixed shaft.

6. The electrospark machining head for cutting casing flanges in narrow spaces as claimed in claim 5, characterized in that: The flange of the rotary reducer is connected to the housing, and the housing is connected to the electrode and the radial servo feed mechanism. When the rotary reducer rotates, the flange drives the electrode and the radial servo feed mechanism to rotate.

7. The electrospark machining head for cutting casing flanges in narrow spaces as claimed in claim 1, characterized in that: The fine-tuning jacking mechanism includes a gear pair, a first rotary reducer and a threaded screw pair. The first rotary reducer drives the threaded screw pair to rotate through the gear pair.

8. The electrospark machining head for cutting casing flanges in narrow spaces as claimed in claim 1, characterized in that: The expansion mechanism includes an expansion electrode, a wedge-shaped driving head and an expanding head. The expansion electrode provides the up and down movement of the output shaft, driving the wedge-shaped driving head to move up and down. The wedge-shaped driving head is evenly arranged with three "convex" wedge-shaped slots around the circumference. The three expanding heads are inserted into the wedge-shaped slots of the wedge-shaped driving head through "convex" wedge blocks. When the wedge-shaped driving head moves up, the three expanding heads are driven to open outward, supporting the inner wall of the thermowell and playing a centering and fixing role.

9. The electrospark machining head for cutting casing flanges in narrow spaces as claimed in claim 8, characterized in that: The expansion mechanism realizes radial fixation between the electric spark machining head and the thermal sleeve through a wedge-shaped expansion block structure.

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