The gas blow curve in Figure 4 can be seen to track submer- sion and seal events. It also shows that the lower part of the jacket has a lower peak blow rate, seals faster and overall blows less gas to metal than the upper portion of the core. As a result only one vent per core leg was needed in the lower jacket to fully evacuate the gas, while two were needed for upper core legs.
Computations for the vented geometry showed no gas blow to metal when the surface tension threshold was set to 570 Pa. This is somewhat higher than the expected value of 450 Pa and could be due to the increase of the metal surface ten- sion in the presence of an oxide skin.
Conclusions
Gas formed during pyrolysis of sand binder can be a seri- ous source of defects in castings. Foundry core submersion tests show that gas pressure in an Al block water jacket core during casting is sufficiently low that all gas can be evacu- ated with proper venting. These tests further yield reference gas pressures that are used to check the accuracy of the pro- posed physical model for binder pyrolysis and gas transport in cores. The level of agreement between computed and measured gas pressures indicates that the model can be used to assess both the likelihood of gas blow to metal and the effectiveness of venting in complex cores.
Acknowledgements
We would like to thank Charles Bates, Harry Littleton, Tony Hirt and Michael Barkhudarov. Special thanks go to Amanda Hayes for pointing out the work of Marvin McKinley. Andrei Starobin would like to thank Flow Science Inc. and the Amer- ican Foundry Society for sponsoring portions of this work.
REFERENCES 1. Lytle, C.A., Bertsch, W., McKinley, M.D., “Determination of Thermal Decomposition Products from a Phenolic Urethane Resin by Pyrolysis-Gas Chromatography-
Mass Spectrometry,” Journal of High Resolution Chromatography, vol. 21, issue 2, pp. 128-132 (1998).
2. Starobin, A., Hirt, C.W., Goettsch, D. “A Model for Binder Gas Generation and Transport in Sand Cores and Molds,” Modeling of Casting, Welding, and Solidification Processes XII, TMS (The Minerals, Metals & Minerals Society), Warrendale, PA (2009).
3. McKinley, M.D., “Modeling of Casting Process Combustion Products,” Technical Management Concepts Inc., Beavercreek, OH (1997).
4. Winardi, L., Littleton, H., Bates, C.E., “Variables Affecting Gas-Evolution Rates from Cores in Contact with Aluminum,” Foundry Management and Technology, August (2007).
5. FLOW-3D User Manual, v9.4 (available upon request from Flow Science, Inc., Santa Fe, NM,
www.flow3d.com). 6. Campbell J., Castings, 2nd Heinemann, Oxford (2003).
Ed., Butterworth-
7. “Perry’s Chemical Engineers’ Handbook,” 6th 3:247-250, McGraw-Hill.
ed., pp.
8. Hwang, J.C. et al., “Measurement of Heat Transfer Coefficient at Metal/Mold Interface During Casting,” AFS Transactions, vol. 102, pp. 877-883 (1994).
9. Pehlke, R.D., Jearajan, A., Wada, H., “Summary of Thermal Properties for Casting Alloys and Mold Materials,” University of Michigan (1982).
10. ThermTest Inc., “Temperature Dependent Thermal Conductivity of AFS63 1.3 wt % PUCB Core Sand” (2011).
11. Hirschfelder, J.O., Curtiss, C.F., Bird, R.B., “The Molecular Theory of Gases and Liquids,” John Wiley & Sons (1954).
12. Bear J., “Dynamics of Fluids in Porous Media,” Dover Pub., N.Y. (1972).
13. Harlow, F.H. and Amsden, A.A., “A Numerical Fluid Dynamics Calculation Method for All Flow Speeds,” Journal of Computational Physics, vol. 8, issue 2, p. 197 (1971).
14. Winardi, L., Scarber, P., Bates, C., “Gas Flow Permeability of AFS Sands”, private com. (2006).
Technical Review and Discussion
Gas Pressure in Aluminum Block Water Jacket Cores
A. Starobin, Flow Science, Inc., Santa Fe, NM D. Goettsch, GM Powertrain Pontiac, MI, USA M. Walker, GM R&D Center, Warren, MI, USA D. Burch, Alchemcast LLC, Birmingham, AL, USA
Reviewers: The authors seem to make some assumptions re- lating to the thermal conductivity, based on Pehlke’s green- sand results, which would be significantly higher as a result of the water content in greensand. This issue error would benefit from greater emphasis.
64
Authors: We have performed direct measurements of bond- ed core thermal conductivity up to 600 C. The measure- ments were performed at and outside lab1
with the aid of
transient plane source thermal conductivity system TPS2500 S. The values, perhaps somewhat surprisingly, were found to track thermal conductivity of the green molding sand to 300 C. Above 300 C PUCB bonded core sand had lower thermal conductivity with the largest difference of 30% at 500 C. All the computations reported in this draft were performed with temperature dependent thermal conductivities and heat ca- pacities (also see text)
1
ThermTest Inc, 34 Melissa St., Unit #1, Fredericton, NB E3A 6W1, Canada.
International Journal of Metalcasting/Summer 2011
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