Table 3. Digital Images of a PUCB Specimen Before and After TDTng Description


Scanned Images


of sand where contact was made with the hot surface and any other discol- orations. Losses at the heat affected zone may be indicative of the tendency to produce cuts, washes and erosion/ inclusion type defects. To interpret this data, the components causing the change in mass are identified. Te percent change in mass was calculated based upon the difference between the weight before and after as a percent of the before weight. All the percent changes in mass values represent the percentage of weight lost.


Initial Trials Positive Te thermal distortion curves for


all systems tested showed undula- tion that indicate thermo-mechanical and thermo-chemical changes in the binder system at elevated tem- peratures. Te longitudinal distortion curves showed an initial expansion before plastic deformation. Te radial distortion clearly indicated an expan- sion trend. For specimens tested at 1,832F,


expansion for 15 seconds was followed by plastic deformation for the duration of the test. All specimens had similar thermal distortion curves, and the two binder levels (0.9% and 1.4%) were not significantly different. Longitudinal dis- tortions from the TDTng supports the trends observed with the original TDT. Considerable heat-induced


thermo-mechanical reactions occurred in the PUCB samples, as is evident from the surface cracks found on tested specimens and percent change in mass value (Table 2). Expansion cracks were macroscopically evident on certain specimens. Te crack propagation was more pronounced in 1.4% PUCB specimens. Craters were evident at the hot surface/specimen interface where binder bridges pyro- lyzed and sand grains broke loose. Te loose sand at the hot surface/specimen interface was white. Expansion cracks were macroscopically evident. Comparing surface deviation was


problematic with the original TDT. Te alignment of the cylindrical sam- ples before and after testing could have been compromised between scans. Te new holder incorporates a set of reference points. As long as the sample


Before TDTng


After TDTng


After TDTng - and 0.07 MPa air blow


Deviation plot After TDTng


After TDTng


is not moved in the holder, the surface deviation can be tracked at each stage of testing. A white light digital scanner took images of the specimen’s surface as it sat in the holder before thermal distortion testing, immediately after testing, and after the loose material was blown away (Table 3)). Te images were used to develop


deviation plots. Te specimen surface before TDTng was set as reference and the other two surfaces were analyzed for deviations from the reference. Te holder at the base of the specimen shows no deviation and most of the specimen’s surface shows little deviation with the exception of the region which was in contact with the hot surface. Following its initial development


and testing, the relationship between TDTng data and cast dimensions will require actual casting trials to validate the test data. Additional chemically bonded sand systems should be studied, and further work could be done at different loads and temperatures to simulate other alloys and pressures. The develop- ers of the TDTng recommend using thermal imaging to investigate the radial deviation with respect to heat transfer.


Research for the Next Generation Ter- mal Distortion Tester was supported by the AFS 4F committee. For the original paper (13-1454) presented on the tester at the 117th Metalcasting Congress, go to www.moderncasting.com.


July 2013 MODERN CASTING | 35


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