Phase II—Development Core Gas Venting Guidelines Performance (11-12#02a/b)


Coordinator: Andrei Starobin, Alchemcast, and AFS Engi- neering Division (1)


Venting of chemically bonded sand cores and molds is neces- sary to prevent excessive binder gas blow into a poured casting. All organic binders currently in use in foundry core making practice outgas significantly and produce internal core gas pres- sures up to 1 psi in moderately sized cores. There is also evi- dence that the newer inorganic binders used effectively only in Aluminum castings, while outgassing fewer hazardous volatiles, still outgas enough to potentially compromise casting quality. Thus the problem of core/mold venting remains an engineer- ing foundry challenge.


Venting techniques practiced today involve forming vent chan- nels in molds drilled to core prints, forming vent channels in cores during core blowing, forming blind core vents in multi- core assemblies, coarsening sand for better permeability reducing binder content and coating cores. In cases where explicit core venting is not feasible, or is limited, the engineer needs to assess the amount, location and timing of the gas pressure. Specifically, one wants to know at what metal head the gas is sealed and espe- cially if the gas has been sealed at the highest metal head achiev- able in a given casting. One can also look into regating possibili- ties that might drop peak gas pressure with a given amount of venting. This might involve not gating into areas of the casting with thin core sections, or orientating the casting so the last area of the core to be submerged by the metal is the core print.


The available means of control of core gas pressure generate a large engineering design space where one would like to make quick and balanced choices to mitigate gas pressures while main- taining core mechanical strength. A unique modeling 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 degradation and gas transport and computes amounts of gas blow into metal. The model is undergoing vali- dation 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 temperatures, 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, the VOCs, HAPs and gas con- stants of gases given off from two binder systems were mea- sured. This information is being used for validation of the core gas model in FLOW-3D®, a Core Venting Design; the Guide- line Development and Technology document along with the initial version of Peak Gas Pressure Calculator. This is being validated and refined in Phase II and then will be transferred to the industry. This work is being monitored by the AFS Process


Design and Modeling Committee (1F). Those wishing to par- ticipate should contact Krishnan Venkatesan, Stahl Specialty, at venkatesank@stahlspecialty.com.


Studies of a Quenched Cupola Part IV: Behavior of Coke (11-12#01)


Coordinator: University of Antiqua, S. Katz Associates and AFS Melting Methods & Materials Division (8)


The cupola furnace produces about 60% of liquid iron used for castings. Despite the age of the process, over 200 years, the cu- pola has maintained its position as the predominant melting fur- nace because it is able to melt a much wider variety of scrap than the more modern electric furnaces, hence providing iron at lower cost. Today’s cupolas are far different than the original furnaces which were carried on the back of a horse drawn platform to produce iron for itinerant pot-makers. The virtue of this furnace is its ability to transform itself to meet current needs.


Today the cupola furnace must transform itself once more to insure its continued use. There are two major problems that need to be solved: (1) the cupola furnace burns coke which gen- erates more carbon emissions than any other foundry process. As a result, future emissions legislation could impose severe penalties on cupola melting. Since the thermal efficiency of coke-combustion is only 50% - 65%, a significant reduction in emissions could be provided by improving the combustion ef- ficiency. (2) The cupola furnace supplies a large fraction of the carbon for alloying, however the efficiency of coke dissolution is very low (5% - 10%). As a result the required amount of coke required for iron production increases significantly when there is a need for alloy-carbon.


The cupola furnace is among the most complex processes employed in the foundry. All the easy improvements have al- ready been made. Further improvements will require a more sophisticated understanding of the complex internal process- es. To this end, the Department of Energy and the Ameri- can Foundry Society sponsored a project to water-quench a cupola furnace while in full operation and then to conduct an archeological examination of the contents. Three papers were published in 2009 covering the details of the quenching experiment, and tracing the changes in the iron, steel, silicon carbide and slag from the charge door to the tap-hole. The current and final paper covers the corresponding changes in coke, the material whose use must be reduced in order to re- duce carbon emissions. It is anticipated that this study will generate ideas for the improvement of cupola performance which includes cost and energy savings and improved com- bustion efficiency.


A recent research project, commissioned by Committee 8K, measured all of the properties used to describe both foundry and blast furnace coke. It included coke from all the current foundry coke producers. No available cupola studies have examined the importance of the additional properties


International Journal of Metalcasting/Winter 2012


65


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