Research On Products Air Tightness Detection Technique

This project developed from the engineering reality of aircraft manufacture, andaccording to the different states of the products, it selected different ways to take theair-tightness detection. Then it carried out a test research on the typical assemblies ofconduit connector, the weld and tightness of the oil storage tank and the tightness of thetank containing riveted structure. Finally it could ensure the tightness qualification ofthe whole product for one time.(a) Differential pressure method was substituted for direct pressure method, and aleakage comparative detection experiment was carried out. In accordance with thedesign requirements, pipeline system’s air tightness detection was specifically measuredby pressure changes, took direct pressure method and daubing liquid leak detectionmethod to detect. The conventional direct pressure method detection, with goodintuitive, simple configuration of the test system, can determine the leakage accordingto pressure changes. Air-tightness is mostly to be ensured by tightening torque andworkers operating experience, and its detection accuracy is not high. Considering theabove factors, differential pressure method was substituted for direct pressure method,and a leakage comparative detection experiment which corresponded to the designrequirements was carried out. The article introduced the detection principle ofdifferential pressure method in detail, for non-symmetrical differential pressure leakdetection system, specially designed samples, and considered the temperaturecompensation, internal standard substance, rational arrangement of measurement pointsand other means to prove that differential pressure leak detection of small volume tolarge volume is feasible.(b) Helium mass vacuum jetting leak detection method was substituted for bubblesmethod, and a leakage comparative detection experiment was carried out. In accordancewith the design requirements, bubble method was used for oil storage tank pipelineweld’s air-tightness detection, after installed blanking covers, blocking caps, the jointsand other workpieces on the seized items, connected aerating conduit, and inflated theseized items, its pressure rise was made to a predetermined value, then generated thepressure difference inside and outside, the bubble would blow up from the leak, therebythe leak position and size of the leak rate was displayed. In order to improve theaccuracy and efficiency of oil storage tank pipeline weld detection, we carried out helium mass leak detection methods investigation. This paper introduced the principleof helium mass detection method, for the requirements of oil storage tank pipelineweld’s air-tightness detection, and carried out a standard leak oil test and standard leakbubble test. Compared to the conventional bubble method, the choice of he lium massleak detection method can improve accuracy of leak detection and ensure the reliabilitymore effectively.(c) The air-tightness detection methods of the overall system was described. For asystem combined in place, in order to ensure air-tightness to be qualified afterintegrating the system, we need to strictly ensure air-tightness of sub-systems andvarious components. This article took integral fuel tank with riveted structure form as anexample, based on different states in fuel tank combining process, and carried out rivetsoiltight experiment. For the state of the workpieces in fuel tank riveting process,established a detection model, applied the suction gun cover cartridge vacuum detectionmethod to the specific detection, and carried out a variety of tests to determine thedetection indicators and detection accuracy, and ensured overall tank air-tightnessdetection once-through. Meanwhile, the application test for different concentrations ofhelium gas mixture which can reduce test costs was carried out. For a typical sample offuel tank simulation, system air-tightness detection test was carried out, using directdetection method, the detection process: first gas mixture helium with certain pressureand certain concentration of helium was filled into analog parts of the whole fuel tank,helium mass suck marksmanship was applied to detect suspicious leak source, and theleakage rate was determined. Then helium mass suck marksmanship was applied todetect standard leak, to obtain a response value of standard leak which the leak rate isknown, thus the leakage rate value of leak source can be calculated, and to determinequalified leak rate indicator based on test results.