Casting defects

Process Integrated Detection and Characterization of Casting Defects. 

On industrial applications orientated detection of casting defects... 

Detection of nearsurface casting defects with temperature analysis... 

Detection of casting defects by combination of radioscopy and accoustic emission... 

The aim of defect segmentation is to delimit the detected defect as precise as possible from the background which surrounds the defect (fig. 8). The extracted characteristics of a detected casting defect depend considerable on the threshold value which is used during the defect segmentation. 

The extraction of characteristics contains the determination of properties and characteristics which describe the casting defect. Within this investigations three different groups of characteristics were determined which include information about the geometry, the distribution of gray values, and the contour of the defects (fig. 9). 

The last part, following the method to analyse radioscopy and acoustic emission values, will be to correlate the characteristic values of the radioscopic detection of casting defects with extracted characteristic values of the acoustic emission analysis. The correlation between the time based characteristic values of acoustic emission analysis and the defect characterizing radioscopy values did not come to very satisfactory results referring the low frequency measurements. The reason can be found in the... 

Feiste, K.L. Stegemann, D. Reimehe, W. Three dimensional analysis of growing casting defects. International Symposium on Computerized Tomography for Industrial Applieatlons, 8.10. Junl 1994, Berlin... 

The most remarkable defects, which have been detected and reported to the custumer, are cracks, casting defects (e g. wrinkles) and inside corrosion.(picture 1)... 

In this section results will be presented using test samples to determine the accuracy of our approach. Further on an example is shown using the system to analyse casting defects. For the experiments moderate projective magnifications between 1.1 and 1.4 were chosen. The test samples used to determine the accuracy of calibration, 3D defect position and volume estimation consist of several holes representing internal defects of different but known size and shape. 

Lea.dAnodes. A principal use for lead—calcium—tin alloys is lead anodes for electrowinning. The lead—calcium anodes form a hard, adherent lead dioxide layer during use, resist corrosion, and gready reduce lead contamination of the cathode. Anodes produced from cast lead—calcium (0.03—0.09 wt %) alloys have a tendency to warp owing to low mechanical strength and casting defects. 

Wrought lead—calcium—tin anodes have replaced many cast lead—calcium anodes (14). Superior mechanical properties, uniform grain stmcture, low corrosion rates, and lack of casting defects result in increased life for wrought lead—calcium—tin anodes compared to other lead alloy anodes. 

Casting Defects Handbook, American Eoundrymen s Society, Des Plaines, HI., 1972. 

Bypassing is occurring between volute channels in a double-volute pump casing due to a casting defect or extreme erosion. 

In all cases the number of pinholes and of other types of casting defects is critically dependent on the quality of the support. Even in cases where the same nominal support material is used (but from different batches) varying results are obtained. This sensitivity of support quality could be diminished by adding an organic additive. In our experiments we used polyvinylalcohol, PVA, with a molecular weight of 72,000 and of the type giving a very low residue of ash or tar on pyrolysis. A typical standard solution contains 0.6 mol AlOOH/L (peptized with 0.07 mole HNO3 per mole AlOOH) with about 25-30 wt.% PVA based on dry AljOj (or 20 wt.% based on AlOOH). 

Staff Computed Tomography Details Casting Defects, Advanced Materials Processes, 54 (November 1990). 

M.J. Couper et al Casting defects and the fatigue behaviour of an aluminium casting alloy. Fatigue Fract. Eng. Mat. Struct. 13, 213-227 (1990)... 

---