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Metal Casting Technologies : Whos who September 2011
52 www.metals.rala.com.au TECHNICAL FEATURE sand casting mold for certain time, after which it was taken out to complete its solidification and building its microstructure. Taking the casting sample out to solidify at faster rate acted as quenching process. The first, second up to the ninth casting samples were left inside the mold for 5, 10, 12.5, 15, 17.5, 20, 22.5, 25 and 30 minutes respectively. The surrounding temperature was same for all samples and it was 25 C. After the nine samples of different solidification rates were obtained, their surface and subsurface defects were investigated using the penetrant testing (PT) and the ultrasonic testing (UT), respectively. Testing casting samples using liquid penetrant testing (PT). The first step of liquid penetrant testing is to ensure the tested surfaces are free of dirt, rust, scale, oil, and grease by cleaning. The second step is the application of the penetrant by spraying method, leaving it for around ten minutes so that the penetrant solution can be allowed to penetrate the surface of the sample to fill any defects that exist there. Those 10 minutes are called the dwell time. The approximate dwell time needed was obtained from the following table reported in Reference . The third step is the removal of the excess penetrant. This technique depends upon the type of penetrant used. In this research solvent removable with dry cloth to remove the bulk of the excess penetrant was used. Cloth lightly dampened with solvent is used to remove any remaining penetrant on the surface in one direction. Aluminium: Source: From: Discontinuity: Dwell-Time-for-Water- Washable- (minutes) Dwell-Time-for-Post- Emulsifiable- (minutes) Military- Technical- Order-33B-1-1 Castings Porosity 5-to-10 5 Cold-Shuts 5-to-15 5 Extrusions/Forgings Laps *NR 10 Welds Lack-of-Fusion 30 5 Porosity 30 5 All Cracks 30 10 All Fatigue-Cracks *NR 30 ASME-Boiler- and-Pressure- Vessel-Code Castings Porosity 5-to-15 Cold-Shuts 5-to-15 Extrusions/Forgings Laps 30 Welds Lack-of-Fusion 30 Porosity 30 All Cracks 30 ASTM-E1209/- E-1210 Castings Porosity 5 5 Cold-Shuts 5 5 Extrusions/Forgings/- and-Plate Laps/Cracks 10 10 Welds Lack-of-Fusion 5 5 Porosity 5 5 All Cracks 5 5 *NR: Not reliable data available. Table 1. Dwell time for penetrant testing of aluminum samples 
Whos who September 2012