X-ray Detection Technology For Hollow Turbine Blade Residual Core

In the new Aero-engine Turbine blade,the gas cooling channel is complex and the core is difficult to remove.Related methods of radiographic testing are studied for this problem.The research is divided into three parts: tracer method,image processing method and rule of residual core inspection.Firstly,the tracer was selected according to the attenuation theory of X ray.By comparing the same concentration of sodium tungstate and lead nitrate to X ray attenuation under the same parameter X ray,lead nitrate was determined as the tracer.Then the SEM and EDS were used to observe the micro morphology of the residual core after alkali boiling.It is found that there are many small holes in the residual core,and after the tracer treatment,the hole is filled with another material and formed a layer of crystal on the surface.After analysis,the substance is tracer.Based on capillary mechanics theory,a theoretical model of straight pipe rising is established.Using this model,the maximum height of tracers in different cores can be calculated.When determining the temperature and inclination angle,the relationship between the penetration distance and the time of tracer can be calculated.The model was tested at 20 degree temperature,and then the relationship between permeability and distance was tested under different temperatures and different inclining angles.The results show that the model can well explain the experimental phenomena.The velocity of tracer penetration at different temperatures was tested.It was found that the velocity of tracer penetration decreased with the increase of temperature.The tracing effect of granular core is not sensitive to temperature.Finally,the reasonable tracer temperature was determined to be 30 C°,and the tracer time was determined to be 2min.Image processing is divided into four stages: noise suppression,image enhancement,background filtering and edge detection.For the two types of noise,Poisson White Noise and Gauss noise are respectively suppressed by multi frame superposition and mean filtering.After processing,the noise signal in the image is smoother.The contrast enhancement of linear points,histogram enhancement and adaptive histogram equalization are compared respectively.The results show that histogram enhancement is suitable for local enhancement of images.Manual processing is often better than automatic processing;adaptive histogram equalization can significantly improve image contrast,but it will lead to the loss of some details in the graph.In the detection of residual core,it is reasonable to use linear point operation to preserve details.The image subtraction is used to process the image which has been de-noising and enhanced.Through operation,the information of all gray differenceregions in the image and the standard non residual core image is retained.On this basis,the "Canny" algorithm is used to detect the edge in the image,such as the residual of the core.After processing,the result can be more clear.The shape and position of the residual core are determined.Based on the method of image processing in this paper,the detectable condition of the residual core in different conditions is obtained by testing the thickness,size,wall thickness and residual state of the residual core.The experimental results show that the distinguishability of residual core increases with the increase of core thickness and size,and decreases with the increase of casting wall thickness.In addition,residual sites also affect the distinguishability of core residues,and the possibility of omission increases when there is side core sticking.When the wall thickness of the casting is more than2.6mm,the residual core of the thickness is less than 8.5 ?m can not be detected.When the wall thickness of the casting is less than 3.8mm,the true shape information of the 17?m core can be detected.When the core is attached to the side of the inner cavity and the direction of its thickness is in accordance with the direction of the ray,the residual core with a thickness of more than 1mm can be detected by the method in this article,and the residual core with a thickness of less than 0.5mm can not be detected.