Effects of Varying SiC Purity on Cupola Performance (09-10#03)
Coordinator: Grede, S. Katz Associates and AFS Melting Methods & Materials Division (8)
Nearly 8 million tons of cast iron products were produced in the U.S. in 2007. This required the production of about 16 million tons of liquid iron. About 60% of the liquid iron was generated in cupola furnaces. The major materials charged to the cupola are cast iron and steel. On average, about 50% of the charge is steel, which makes it necessary to add large amounts of silicon alloy to achieve the desired cast iron composition (~2.5% Si). To meet this level of demand, cupolas consume about 4x105 silicon/year, of which about 10% is oxidized (4x104
tons of tons of Si).
This loss represents not only a large added cost to the foundry ($40x106
/year), but also a large waste of energy.
The overall goal of this study is to demonstrate the relative ad- vantages and disadvantages of 36% and 65% SiC so as to provide foundries with the information required to optimize the use of SiC at their facilities. The project will involve significant in-kind effort by the foundry conducting the work and the steering com- mittee, with AFS support to fund for slag and off-gas analyses and a consultant to assist with data collection and analysis.
Status Update: The plant trial phase of this project is complete and analysis of slag and compositional results is being compiled into a final report by August. The work is being monitored by the AFS Melting Methods & Materials Cupola Committee (8F). Those wishing to participate should contact Jim Cree, Grede, at
JCree@grede.com.
Phase I—Development Core Gas Venting Guidelines Performance (10-11#03a/b)
Coordinator: Andrei Starobin, Alchemcast, and AFS Engi- neering Division (1)
Venting of chemically bonded sand cores and molds is nec- essary to prevent excessive binder gas blow into a poured casting. All organic binders currently in use in the foundry core practice outgas significantly and produce internal core pressures up to a psi in moderately sized cores. There is also evidence that the newer inorganic binders used and effective only in Aluminum castings, while outgassing fewer hazardous volatiles, still outgas enough to potentially compromise cast- ing quality. Thus the problem of core/mold venting remains an engineering foundry challenge.
Venting techniques practiced today involve forming vent channels in molds drilled to core prints, forming vent chan- nels in cores during core blowing, forming blind core vents in multi-core assemblies, coarsening sand for better per- meability and reducing binder content. In cases where ex- plicit core venting is not feasible, or is limited, the engineer needs to assess the amount, location and timing of the gas blow. Specifically, one wants to know at what metal head the gas is sealed and especially if the gas has been sealed at the highest metal head achievable in a given casting. One can also look into regating possibilities that might drop peak gas pressure with a given amount of venting. This might involve regating away from thin core sections, or re- orienting cores so that last place of the core to submerge is placed near core print.
The available means of control of core gas pressure gener- ate a large engineering design space where one would like to make quick and balanced choices to mitigate gas pressures while maintaining core mechanical strength. A unique mod- eling tool has been developed at Flow Science Inc. which will allow the designer to evaluate various core and mold venting choices. The core gas model tracks binder degrada- tion and gas transport and computes amounts of gas blow into metal. The model is undergoing validation and has been shown to give reasonable predictions of gas pressures in PUCB Isocure® bonded water jacket cores. It is the intent of this research program to A) develop necessary data for other binder systems both at Al and Iron casting tempera- tures, B) Validate the numerical model in FLOW3D® under this new set of casting conditions and C) Develop general core venting design guidelines for Iron and Al castings with cores bonded by either PUCB Isocure®, or Acrylic Epoxy Isoset® binders.
Status Update: During Phase I, work has been started to mea- sure VOCs, HAPs and gas constants of gases given off from two binder systems. The samples will be immersed in both aluminum and iron, the systems being analyzed are PUCB and Acrylic Ep- oxy binders. Gas Chromatography/Mass Spectrometry on the gases from samples immersed in iron is being performed by Core Labs, Houston, TX. This information will be used for validation of the core gas model in FLOW-3D®, a Core Venting Design; the Guideline Development and Technology document will be transferred to industry. This work is being monitored by the AFS Process Design and Modeling Committee (1F). Those wishing to participate should contact Krishnan Venkatesan, Stahl Specialty at
venkatesank@stahlspecialty.com.
International Journal of Metalcasting/Summer 2011
67
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