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 advantages 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 sig- nificant in-kind effort by the foundry conducting the work and the steering committee, 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 com- plete and analysis of slag and compositional results is being compiled into a final report. 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 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-
International Journal of Metalcasting/Fall 2011
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-
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