The Radiographic Inspection Technology For Detecting Residual Core Of Blades Based On Digital Subtraction Angiography

Turbine blades are the most critical hot-end components in aircraft engines,the quality of turbine blades not only determines the performance of the whole engine,but also the safety of people during the flight.Because of the extreme high temperature transferred from combustion,nowadays the structure of turbine blades is designed to be hollow and the blades are continuously cooled by low temperature air ins ide.During casting process,the inside of blades are placed with ceramic core,if the casting process is not controlled well enough,the ceramic core may not be able to separated from the blade,leading to less cooling air flowing into the blade or even no cooling air can go through the blade,which will cause pre-failure of the turbine blade and bring enormous safety issue of engine.Therefore,an effective technique has to be used to detect if any residual ceramic core is still inside the blade.This paper proposes a method combined by digital radiographic inspection and image substraction technique o n the basis of present inspecting technique,which achieves effective and reliable detection of residual ceramic core in the blade.The research begins with the equipments and instruments used for experiment,and demonstrates the characteristic parameters of both conventional film and digital radiographic inspection equipments,then introduces the structural feature of inspection object(turbine blade)and analyzes the composition of both turbine blade and ceramic core,and meantime summarizes the process o f removing ceramic core.After that,the specific method and step of detecting residual ceramic core are detailed demonstrated.For the smooth proceeding of other subsequent work,the absorption coeffic ient of both turbine blade and ceramic core are calculated and the interpolation algorithm of tantalum is studied,then according to the calculated absorption coeffic ient of turbine blade,the exposure energy is analyzed to be no less than 105 k V.By comparing argument of substract algorithm,combined with ima ging dealing method like image density enforcement and histogram equalization,it is determined that this substracting enforcement method can increase the recognition capability of weak gray-scale contrast images by human eyes.Three methods including simulation,self-substraction and actual measurement are investigated,the actual blade exposure and image-substraction experimental studies are performed,then analyzes and discusses the advantages and disadvantages of these thre e methods.The results show that actual measurement of detecting residual ceramic core has the best sensitivity,the minimum detectable thickness of ceramic core can be 0.4mm.When actual measurement method is applied to detect naturally formed residual ceramic core,the image of resid ual ceramic core is clear enough.During the experiments,the applicable fixture has been developed.At last,the applicable compensation for the experiment has been developed,the absorption coefficient of three compensations have been analyzed,including metal powder,potassium iodide solution and barium sulfate suspension,all of which are compensation objects that can be used for radiographic inspection.Among them,the metal powder has better image but less efficient,although potassium iodide solut ion and barium sulfate suspension have better efficient,potassium iodide solut ion sha ll be stored away from light,and the deposition issue of barium sulfate suspension shall be further addressed before applying to inspection.