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CN-122007524-A - Automatic nitrogen charging protection brazing process for pipeline of water chiller

CN122007524ACN 122007524 ACN122007524 ACN 122007524ACN-122007524-A

Abstract

The invention discloses an automatic nitrogen charging protection brazing process of a water chiller pipeline, which comprises the steps of S1, automatic butt joint and tightness pre-detection of a workpiece, execution of tightness judgment based on a pressure sensor, S3, dynamic adjustment of pre-charging time based on a workpiece heat capacity coefficient, pulse pre-charging, S4, construction of a feedforward-feedback composite control model containing heating power, nitrogen charging flow and outlet temperature in the brazing process, realization of multi-parameter coupling dynamic nitrogen charging protection, S5, analysis of pressure waveform characteristics in lag gas-off time, online self-detection of nitrogen charging effectiveness, and S6, resetting after the lag gas-off is finished. The invention solves the problems of formalization, parameter statization and incapability of verifying the effectiveness on line in the existing nitrogen charging protection by dynamic nitrogen charging, multiparameter coupling control and on-line self-checking, and remarkably improves the stability and reliability of welding quality.

Inventors

  • GENG LING

Assignees

  • 上海辉卓制冷设备有限公司

Dates

Publication Date
20260512
Application Date
20260407

Claims (10)

  1. 1. An automatic nitrogen charging protection brazing process for a cold water machine pipeline is applied to an automatic brazing production line, and the production line comprises a workpiece conveying system, a robot flame brazing system and a nitrogen charging protection system connected with a control system, and is characterized by comprising the following steps: step S1, workpiece positioning and feature recognition, wherein model information of a workpiece to be welded is obtained through a visual recognition device or an RFID reader arranged on a workpiece conveying system, and a standard brazing process packet corresponding to the model is called from a database according to the model information, wherein the standard brazing process packet at least comprises pre-filling time T0, main brazing nitrogen filling flow Q1, main brazing nitrogen filling pressure P1 and lag stopping time T2; Step S2, automatic butt joint and tightness pre-detection of a nitrogen charging pipeline are carried out, wherein the control system controls a manipulator to insert a nitrogen charging gun head into a nitrogen charging port of a workpiece, and executes first tightness judgment logic based on a detection value of a pressure sensor in the nitrogen charging pipeline; Step S3, based on the dynamic nitrogen pre-filling of the heat capacity of the workpiece, determining the heat capacity coefficient C of the metal pipeline according to the model of the workpiece identified in the step S1, dynamically adjusting the nitrogen pre-filling time T0 to be T0' according to the heat capacity coefficient C by the control system, and pre-filling nitrogen in a small-pipe-diameter area with constant small flow so as to completely replace air in the pipeline; Step S4, nitrogen charging protection in a multi-parameter coupling brazing process, wherein the control system automatically switches nitrogen charging flow from pre-charging flow to main brazing nitrogen charging flow Q1 and dynamically adjusts nitrogen charging pressure to main brazing nitrogen charging pressure P1 when a robot flame brazing gun is ignited and heated, in the process, the outlet temperature T_out at the head of the nitrogen charging gun is monitored in real time, and a feedforward-feedback composite control model containing heating power W, nitrogen charging flow Q and outlet temperature T_out is constructed so as to maintain micro-positive pressure atmosphere in a pipeline; Step 5, online self-checking of the effectiveness of nitrogen charging, namely after brazing is finished and flame is extinguished, the control system does not immediately close the nitrogen charging, but enters a delay gas-stopping time T2, in the T2 time, judging whether instantaneous pressure fluctuation characteristics caused by solder wetting or molten pool solidification exist or not by analyzing real-time pressure waveforms of the pressure sensor, judging that the nitrogen charging protection fails and marking the product if the characteristic fluctuation is not detected; And S6, delaying gas stopping and resetting, closing a nitrogen valve after the delayed gas stopping time T2 is finished, and pulling out and resetting the nitrogen charging gun head by the manipulator to wait for the next cycle.
  2. 2. The automatic nitrogen charging protection brazing process for the water chiller pipeline according to claim 1 is characterized in that the first tightness judging logic in the step S2 is specifically that after the nitrogen charging gun head is inserted and locked, a nitrogen valve is opened to charge test pressure Pt higher than atmospheric pressure into the pipeline, then the valve is closed, a difference value delta P of the pressure sensor from an initial pressure P_start to P_end is recorded within the dwell time of t1=2-5 seconds, when the delta P is smaller than a preset sealing threshold delta P_set, the sealing is judged to be qualified, when the delta P is larger than or equal to the delta P_set, the sealing is judged to be unqualified, the system automatically increases the locking force of the nitrogen charging gun head to perform one-time compensation resealing attempt, and if the secondary sealing still fails, an alarm is sent.
  3. 3. The process of claim 1, wherein in the step S3, the calculation formula of dynamically adjusting the pre-charging time T0 to T0 'according to the heat capacity coefficient C is T0' =T0× (1+k· (C-C0)/C0), wherein C0 is a standard heat capacity coefficient, k is an adjustment coefficient, and the value range is 0.1-0.5, and the pre-charging process adopts pulse charging, i.e. intermittently opens and closes a charging valve at a fixed frequency, so that nitrogen replaces air in the pipeline with wave-type air flow.
  4. 4. The automatic nitrogen charging protection brazing process for the water chiller pipeline according to claim 1 is characterized in that the feedforward-feedback composite control model in the step S4 comprises the steps of calculating a required basic nitrogen charging flow Q_base through a feedforward model according to the current heating power W, and correcting the basic nitrogen charging flow Q_base by taking deviation between an actual measured value of the outlet temperature T_out and a target temperature interval [ T_min, T_max ] as a feedback quantity to obtain a final main nitrogen charging flow Q1 of brazing, wherein a PID control algorithm is adopted for correction.
  5. 5. The automatic nitrogen charging protection brazing process for the water chiller pipeline according to claim 1 is characterized in that the specific logic for judging the nitrogen charging protection failure in the step S5 is that in the first half section T2a of the lagging air stopping time T2, a control system continuously collects dynamic data of a pressure sensor and carries out frequency spectrum analysis, when the pressure fluctuation amplitude in a specific frequency range (0.5-5 Hz) is detected to exceed a preset fluctuation threshold A_set and the fluctuation duration is greater than 0.5 seconds, the effective fluctuation is judged, namely the nitrogen charging protection is effective, and if the effective fluctuation is not detected in the T2a, the nitrogen charging protection failure is judged.
  6. 6. The automatic nitrogen charging protection brazing process for the water chiller pipeline according to claim 1 is characterized by further comprising the step S7 of self-adaptive learning and process package optimization, wherein the control system records actual nitrogen charging flow, pressure, temperature and heating power data of each qualified workpiece in the brazing process and compares the actual nitrogen charging flow, pressure, temperature and heating power data with theoretical values in the standard brazing process package, a machine learning algorithm is utilized for analyzing welding data of batch workpieces, and when systematic parameter drift caused by ambient temperature, nitrogen source pressure change or equipment aging is found, the reference parameters of the standard brazing process package are automatically corrected.
  7. 7. The automatic nitrogen charging protection brazing process for the water chiller pipeline according to claim 1, wherein the nitrogen charging gun head is a rotary nitrogen charging gun head, and after the nitrogen charging gun head is inserted into a nitrogen charging port of a workpiece, the nitrogen charging gun head is driven by a servo motor to slowly rotate so as to prevent the nitrogen charging gun head from being adhered to a pipe orifice of the workpiece due to long-time static heating.
  8. 8. An automatic nitrogen-charging protection brazing process for a water chiller pipeline according to claim 1 wherein the main nitrogen charging pressure P1 is not a fixed value, but rises linearly or stepwise according to a preset "heat-pressure" curve during the brazing heating process to counteract the tendency of heating to cause gas expansion and overflow in the pipeline.
  9. 9. An automatic nitrogen-charging protection system for performing the automatic nitrogen-charging protection brazing process according to any one of claims 1 to 8, comprising a gas source, a pressure reducing valve, a proportional flow valve, a pressure sensor, a nitrogen-charging gun head, and a controller, wherein the controller comprises: the characteristic recognition module is used for receiving and processing signals of the visual recognition device or the RFID reader and calling corresponding process packages; The seal detection module is used for controlling a seal pre-detection flow and judging qualification; the dynamic nitrogen pre-filling module is used for adjusting nitrogen pre-filling time sequence and flow according to the heat capacity of the workpiece; the coupling control module is used for executing a multi-parameter coupling control algorithm in the brazing process; And the effectiveness self-checking module is used for analyzing the pressure waveform of the delayed gas stopping stage and outputting a detection result.
  10. 10. The automatic nitrogen charging protection system according to claim 9, wherein the effectiveness self-checking module comprises a characteristic waveform database, wherein the characteristic waveform database is pre-stored with standard pressure fluctuation characteristic patterns of workpieces with different pipe diameters and different wall thicknesses under the condition of qualified brazing, the effectiveness self-checking module compares the similarity between the actually measured pressure waveform and the standard characteristic patterns, and the effectiveness self-checking module judges that the nitrogen charging protection fails when the similarity is lower than a preset threshold value.

Description

Automatic nitrogen charging protection brazing process for pipeline of water chiller Technical Field The invention relates to the technical field of water chilling unit manufacturing, in particular to an automatic nitrogen charging protection brazing process for welding copper pipes of a water chilling unit, and particularly relates to an automatic brazing process with online self-learning and self-adaptive control capabilities. Background The water chilling unit is an air conditioning device which is indispensable in cooling of modern large-scale buildings and industrial processes. The core refrigeration circuit comprises a plurality of copper pipe connection points. The quality of the weld at these points directly determines whether the refrigerant is leaking and the long-term operational reliability of the unit. During the brazing process, the interior of the copper tube needs to reach a high temperature of 600-800 ℃. If no protective gas exists, the inner wall of the copper pipe can react with oxygen in the air to generate oxide scale (the main component is copper oxide). These scales can fall off during unit operation, with refrigerant circulation, clog filters (filth plugs), damage compressor bearings, and eventually lead to failure of the entire refrigeration system. Therefore, nitrogen-filled protective brazing is a standard process in the industry. The basic principle is that nitrogen with certain flow is continuously filled into the copper pipe while brazing and heating, and air in the pipe is displaced by utilizing the inertia of the nitrogen to form a micro-positive pressure protective atmosphere, so that the inner wall is prevented from being oxidized. Although a number of automated brazing equipment and nitrogen protection devices have been widely used, the existing automated brazing process still has the following technical bottlenecks: 1. The problems of formalization and blind operation of nitrogen charging protection are that the control logic of the nitrogen charging protection of most of the existing automatic production lines is very simple. After the work piece is in place, the nitrogen filling joint is inserted, and then the nitrogen valve is opened with a preset, constant flow and pressure until the welding is completed. This approach does not truly monitor the effectiveness of the nitrogen charge. For example, when the nitrogen charging pipeline leaks, the nitrogen source pressure is insufficient, or the nitrogen charging gun head is not completely sealed, the system still operates according to a preset program, and the nitrogen charging action is seemingly executed, and in fact, no effective protective atmosphere is established in the pipeline at all, so that batch false welding or oxidation accidents are caused. This "open loop" control mode allows the nitrogen protection to fall into a formalized step rather than a verifiable quality control point. More deeply, this "formalization" problem results from the neglect of the physical nature of the welding process. The prior art only regards nitrogen charging as an independent auxiliary process parallel to welding heating, but does not recognize that a complex nonlinear coupling relationship exists between the nitrogen charging effect and the heating process, material characteristics and sealing state. Thus, the monitoring logic merely remains on confirmation of the actuator action, such as "valve open", "pressure reached", and cannot access the core process objective of "whether the protective atmosphere is actually being effectively established". 2. The problems of "staticization" and "islanding" of process parameters are that the existing process parameters (such as nitrogen charging flow and pressure) are always fixed values set by process personnel according to experience. However, in actual production, the workpiece models are various, the pipe diameters are different from a few millimeters to a few tens of millimeters, and the heat capacity and the complexity of the pipeline are huge. The small-diameter pipeline has the advantages of quick temperature rise, high flow rate and quick evacuation in the early stage, large heat capacity of the large-diameter pipeline, long heating time and continuous and stable flow rate. A static parameter is used for coping with all working conditions, which inevitably leads to small-pipe-diameter nitrogen waste and insufficient large-pipe-diameter protection. In addition, as production proceeds, ambient temperature, nitrogen storage tank pressure, and even the aging of the welding gun all cause the actual working condition to deviate from the preset value, and the static parameters cannot be adjusted in a self-adaptive manner. More importantly, these static parameters are "islanded" with dynamically varying welding heating power, lacking efficient linkage and synergy between the two. The result of this "islanding" is that when the heating power fluctuates (e.g. gun movement, flame regulation), th