The following publications from the UNI MCC and AMC staff have been published by the American Foundry Society and can be accessed using AFS member login information.
Evaluation of Emissions in Green Sand and Casting Comparisons / Sairam Ravi, Jerry Thiel and V. LaFay (2019)
For many years, researchers in the foundry industry and universities have been developing testing protocols to evaluate the emission characteristics of prepared green sand during pouring, cooling and shakeout. This paper will review the testing protocol and methods utilized in the collection and evaluation of these emissions that is the result of the entire metalcasting process. An important criterion also is the quality of the casting produced (defect free) when emission characteristics are reduced. This paper will also include the laser imaging evaluation of the castings that are the result of the green sand foundry emissions.
Case Study in Reducing Shrinkage in Aluminum Castings Using Thermal Management / Sairam Ravi, S. Giese, and B. Biersner (2019)
An aluminum foundry collaborated with its resin supplier and the University of Northern Iowa to solve a microshrinkage defect in a complex casting.
Elements within the water used to temper silica-based green sand systems were tested to determine if these elements are contaminants that affect the properties of green sand. Water samples were gathered from different regions throughout the United States and analyzed to for elemental composition, where sodium, calcium, magnesium and chlorine were identified to have higher concentrations. A Taguchi L8 Design of Experiment (DOE) was created to determine the main interaction effects through a low and high level of the four contaminants based on sample composition. Eight green-sand batches were made based on the DOE and tempered to a compactability range of 42–45%. The batches were then subjected to AFS physical property testing. Additionally, class 30 gray iron plate castings were poured to evaluate casting quality. Based on the data collected there were no significant variations in physical properties between the green sand batches.
Research Into the Quantitative Evaluation of Casting Surfaces Using 3-D Laser Scanning / Nate Bryant (2018)
Surface roughness is an integral part of casting quality specifications. Castings with rougher internal surface finishes can decrease the efficiency of material transfer components due to frictional interference. In production facilities, quality engineers are still bound to qualitative forms of surface roughness measurement using cast comparators and visual inspection. The University of Northern Iowa is researching a method to quantitatively describe cast surfaces using a laser scanning device. The results can be represented by industry accepted scales such as root means square (RMS) and roughness average (Ra). Defect analysis and part variation measurement capabilities are also possible with this new method, which is described in detail within.
Does Water Quality Affect Green Sand Properties? / Sairam Ravi, Jerry Thiel and B. Wallace (American Foundry Society) (2018)
Research was conducted to evaluate the effect of contaminants commonly found in tap and well water in the U.S. on green sand properties.
Critical Characteristics Affecting the Surface Finish of Castings / Nate Bryant and Jerry Thiel (2017)
Surface finish is an integral part of casting quality specifications, and a recent study sought to achieve investment casting-level surface finish in sand cast components.
Prediction of Core Gas Pressure from Chemically Bonded Sand Molds Using Process Simulation Software / Sairam Ravi and Jerry Thiel (2017)
Process simulation has developed into a powerful tool for metal casters. It has also provided a valuable research resource. The University of Northern Iowa has completed the first stage of research into developing advanced applied programming interface software code to predict gas porosity defects based on mold and core material property data. The research was partially sponsored by the American Foundry Society and Magma Foundry Software. The code is based on the replacement of the testing methodology for gas pressure and volume with current thermogravimetric analysis technology. The new testing methodology is not only more accurate and repeatable but offers results that are temperature dependent. By using the temperature results generated by commercial process simulation software, data can be entered into off-line equations, solutions processed, and returned to the commercial software for reporting. The paper details the research conducted with phenolic urethane resin used on aluminum alloy castings.
The work presented in this paper investigated the thermophysical properties of green sands. Three experimental sands with different sodium bentonite clay levels were examined, as well as two green sands from industrial production. The industrial sands had a much more complex composition than the experimental sands. Density, as a function of temperature, was determined by dilatometry while specific heat, as a function of temperature, was measured by differential scanning calorimetry. To find the thermal conductivity versus temperature, a series of ingot casting experiments were conducted. Thermocouples were inserted into the ingot mold, and the temperature versus time was recorded. An inverse heat transfer optimization using a commercial solidification simulation package was then performed using the thermocouple, density, and specific heat data to calculate the thermal conductivity. For all the experiments, the sands were tested at the production moisture levels. The thermophysical properties of the molding sands demonstrated complex behavior. The specific heat of the molding sands was dominated by the evolution of water while being heated. This behavior had not been completely realized in previous work. Additionally, there was an indication that phase reactions, such as the ? to ? quartz reaction, could take place at a temperature lower than previously reported. It is certain that continuing to improve simulation accuracy will require foundries to determine their own sand’s thermophysical properties.
Research was conducted to evaluate the effect of the addition of specialty aggregates to silica sand.
Testing 1-2-3: Predicting Casting Dimensions With Computer Process Modeling / Jerry Thiel and Sairam Ravi (2016)
Accurately measuring the high temperature dimensional changes in molding materials has shed new light on additional sources of dimensional variation in final casting dimensions.
Use of Specialty Sand Blends to Reduce Veining Defects in Steel Castings / Sairam Ravi and Jerry Thiel (2016)
Metal casters continually strive to produce the highest quality castings at the lowest competitive cost. Unfortunately, they have little control of the cost of the required materials. It’s been well established that molding materials such as chromite, zircon and mullite all exhibit low expansion leading to few casting defects related to expansion and better dimensional accuracy. They also have refractory values significantly higher than silica sand. Although some casting applications require the use of 100% specialty sands, there is a significant amount that requires only modest improvements to the properties of silica sand to yield significant casting quality benefits.
As liquid metal solidifies, it contracts in first volume and then physical size. Accurately predicting the final casting dimensions has been at best accomplished with a set of simple rules along with significant tribal knowledge. Although the age of creating master patterns with wood are mostly behind us, the industry still uses a fair degree of trial and error when producing patterns to meet specific casting dimensions. This method was aided by the use of ‘shrink rules,’ and more recently, Computer-Aided Design (CAD) geometry volume compensation, neither of which accurately predict final casting dimensions. This trial and error method of producing patterns is very costly often requiring as much as 40% of the original pattern cost for dimensional adjustments. Previous researchers have imperially studied the effect of various geometry and areas constrained by cores. Previous research by the University of Northern Iowa in sand expansion has identified several mechanisms whereby changes in the mold and core dimensions render current single volume percentage decreases inaccurate in determining final casting dimensions.1 By understanding the dimensional changes that the sand undergoes during rapid heating and the rigidity of the molding media, accurate predictions can be made to the final casting dimensions given a specific pattern size. Current research by the University of Northern Iowa has detailed a methodology using computer process modeling to accurately determine casting dimensions from room temperature pattern dimensions. Although a preliminary study, it provides the basis of future foundry level tools. As the ability of creating castings true to designs improves, reductions in machine stock can be made to decrease cost, improve reliability and speed production.
New Method for Measuring Gas Evolution in Chemically Bonded Sands / Sairam Ravi & Jerry Thiel (2016)
The gas evolution test has been a valuable tool in determining the volume and pressure of gas emitted by chemically bonded sands during the pouring operations. If the gas pressure is too high, porosity defects will occur. Earlier conventional testing method attempted to measure the volume of gas directly by the use of a graduated burette. Later designs used a sensitive pressure transducer to measure the gas pressure generated. Both of the methods introduced a sand sample container at room temperature by the use of a pushrod for which compensation was needed. The University of Northern Iowa Metal Casting Center has developed a method, which uses a thermos gravimetric analysis unit in conjunction with the atomic weights of the gaseous products to calculate the gas volume and associated gas pressure based on the mold or core permeability. This new test is explained in detail with examples.
Reclaimed Green Sand for Core Room Application / Jerry Thiel, V. Lafay, C. Grefhorst, J. Tibbs (2015)
With the ever changing environmental regulations and foundry waste management coupled with increasing raw material prices, transportation, and disposal costs a challenge for the future of the metalcasting industry has been to find improved methods to reduce/eleminate waste streams from a foundry. These foundry waste streams still contain useful materials that can be lost among the other undesired constituents. A new and innovative wet reclamation process invented by S&B Industrial Minerals (hereafter referenced as Company A) aims to eliminate and aleve these environmental pressures to increase foundry efficiencies, reduce waste and the costs associated with disposal without sacrificing casting quality. The waste materials from foundry green sand systems can now be turned into a valuable new resource to foundries. This innovative process recovers the silica sand from green sand molding operations that can be used in a foundry core room to produce cores with organic binder systems. In addition the Bentonite and carbonaceous materials can be separated and reintroduced into the green sand molding system. The reintroduced bentonite and carbon can replace an equivalent or more of dry bond added to a foundry green sand system. The bentonite exhibits improved molding sand properties because of increased bentonite dispensability.
Testing 1-2-3: Material of the Future: 3-D Printed Molds Improve Titanium Casting’s Potential / Sairam Ravi and Jerry Thiel (2015)
Researchers developed molding methods and materials to provide exceptional design flexibility while simplifying production.
Developments in additive manufacturing mean engineers have a new set of considerations when designing molds and cores.
Three Dimensional Printed Molds for Titanium Casting Applications / Sairam Ravi and Jerry Thiel (2014)
Titanium alloys continue to remain as some of the most versatile alloys available with high strength to weight ratios and excellent resistance to corrosion. Its use as an engineering material in cast components has been limited due to its high cost, some of which results from the casting process. Because of the strong reactivity with oxygen, current methods of producing titanium castings include rammed graphite molding and investment casting. Both of these methods involve multiple steps and require extensive equipment. Recently, three dimensional printing equipment has become a readily available technology, possessing the accuracy required to produce high quality molds and cores for castings. The University of Northern Iowa under funding provided by the Department of Defense has developed molding methods and materials to enable the casting of titanium in three dimensionally printed molds. This system provides exceptional design flexibility while reducing the time, steps and complexity of producing titanium castings. The system was designed to address the high reactivity of the liquid titanium with the molding materials and minimize alpha case depth. The scope of the research was limited to three dimensional printed molds though the technology developed could be used with conventional molds.
Causes and Solutions to Veining Defects in Iron and Steel Castings / Jerry Thiel and Sairam Ravi (2014)
Studies were conducted at the University of Northern Iowa Metal Casting Center to determine the mechanisms that cause veining defects in iron and steel castings. Advanced testing methods along with computer casting simulations were used to evaluate various sand mixtures for the propensity to form casting veins. It was found that two forces act on the surface of the sand that can either contribute or reduce the defect. The linear expansion of bonded silica sand causes the volume of sand to increase sharply until 573C (1063F), where it changes phase from alpha quartz to beta quartz. Upon further heating, the sand loses its volume due to softening at the surface of the sand grains. This loss of volume at temperatures above 573C (1063F) is the main cause of veining defects. As the temperature of the mold or core surface increases, the length and volume of the sand decreases. The cooler sand directly beneath the surface increases in volume as it passes through the alpha to beta quartz transformation. The combination of contracting sand on the surface with expanding sand directly beneath the surface create tensile failures that fill with liquid metal forming the defect classified as veining. Sand additives that reduce veining defects provide liquid on the surface of the sand grain and favor formation of tridymite or cristobalite and greater expansion of the sand. This secondary expansion reduces the negative strain at the surface of the core and prevents tensile failure and the associated cracks. Through the fluxing action of sand additives, the surfaces of the particles adhere to each other increasing the tensile strength of the sand on the surface of the core or mold. This strength increase reduces the tensile failure on the sands surface and reduces veining defects.
Replacement of Olivine with Silica Sand in Non-Ferrous Foundries / Jerry Thiel, V. Lafay, S. Neltner, M. Ziegler (2012)
Olivine sand is no longer available to the non-ferrous foundry industry and silica sand has been used for many years as the aggregate for non-ferrous foundries. This paper addresses the replacement of silica sand in foundries that have historically utilized olivine sand.
Preliminary Investigation on the Effect of Binder Content and Ratio on Heat Transfer / Sairam Ravi, S. Giese, and B. Biersner (2012)
The goal of the research study was to observe the influence of total binder content and ratio on the solidification time in thin wall aluminum sections for the phenolic urethane no-bake binder system. A356 aluminum was poured in a multiple fin, thin wall casting inserted with thermocouples to measure the thermal profile developed in the mold and the solidification time in a thin wall fin. The solidification time decreased as the total binder phenolic urethane binder content increased. Increasing the Part 1 resin content showed a decrease in the solidification time with a corresponding decrease in the mold temperature profile. The research established the potential heat transfer effect on the solidification time for thin walled aluminum castings, demonstrating the possibility of using a resin binder to control the solidification rate.
Testing was conducted at the University of Northern Iowa to determine the effects of core sand and new sand dilution on the properties and casting performance of a sodium bentonite bonded green sand system. Green system sand and phenolic urethane core sands from operating foundries were used along with new silica sand to develop mixtures that represented the expected dilution levels in foundries. While dilution levels varied from all system sand through all dilution sand, the mulling time was held consistent. Effects of core sand and new sand dilutions are documented with physical property testing and expansion analysis.
A three year study funded by the Department of Energy has yielded two new bio-urethane foundry binders. These binders were developed at the University of Northern Iowa Center for Advanced Bio-based Binders (CABB) to help replace petrochemical derived foundry products, reduce their environmental burden and improve casting quality. The biourethane binders that were developed replace the phenolformaldehyde component of phenolic urethane binders with saccharides and humic containing substances. The binders have the ability to utilize conventional or modified isocyanate and catalyst components and are compatible with current foundry equipment and procedures. Evaluations of the new binders include physical properties, elevated temperature physical properties, thermogravimetric analysis, step cone casting evaluation, emissions and foundry trials. Results show that the bio-urethane binders exhibit comparable core strengths, curing rates and casting finish. The new binders exhibited higher elevated strength properties along with improved shakeout. Results of emission testing compared favorably with conventional phenolic urethane binders.
The expansion of silica sands has long been misunderstood as the cause of several casting defects. It’s equally misunderstood that we can’t change the way silica sands expands. The research studies in depth the expansion of silica sands and the effect of phase changes in the sands. It was found that several materials change the high temperature phases of silica sand and corresponding expansion. These phase changes give us a view into several casting defects and methodologies to correct them. The results also give us a better understanding of the difficulty and complexity in providing castings with lower dimensional variation and higher degrees of dimensional predictability.
Iron Oxide in Molds and Cores for the Production of Iron and Steel Castings / Jerry Thiel, R. Monroe, J.Andrews (2010)
Iron oxide is a common addition to mold and core sand mixtures used in the production of iron and steel castings. The AFS Cured Sand Committee 4-I-1 conducted a survey over 25 years ago to document the use of iron oxide. This is an update to the paper reporting on the work done by the Committee.1 At that time, the dominant reason given for the use of iron oxide was to prevent sand expansion defects. As subsequent work has shown, iron oxide does help prevent many of the undesirable defects associated with the mold-metal interaction but does this through more complex means than preventing expansion.
The ability to produce dimensionally accurate cast components depends on your understanding of the physical characteristics of the molding materials. To further that understanding, a study recently was conducted on three commercially available chemically bonded sands. Phenolic urethane cold box (PUCB), epoxy acrylic cold box (EACB) and resin coated sands each were evaluated during 15, 30 and 60 minute heating cycles for high temperature strength, expansion and stiffness (see sidebar for more on the methods used to evaluate the core sands). Following is a look at the results of those tests and what they mean for the use of the binders in commercial metal casting facilities.
High-Temperature Physical Properties of Chemically Bonded Sands Provide Insight into Core Distortion and Provides New Data for Casting Process Simulation / Jerry Thiel, L.Stahl, and S. Dutler (2009)
The ability to produce dimensionally accurate cast components is dependent on our understanding of the physical characteristics of the molding materials. A study performed at the University of Northern Iowa measured the high temperature properties of three commercially available chemically bonded sands. Epoxy Acrylic, Phenolic Urethane Cold Box and Resin Coated Sands were evaluated for high temperature strength, expansion and stiffness. Studies of cast components show that the high temperature properties of the molding sands helped explain core distortion defects. New data developed in the study will allow casting process modelers to determine when and if cores may fail in the casting process.
Reinventing Shell Technology: Making Good Scents of an Ageless Process / Jerry Thiel and K. Kerns (2009)
New developments in shell technology have made it cleaner and faster. A review of the attributes that have sustained the utility of the technology as well as new data is presented on environmental and casting performance as compared to phenolic urethane cold box.
High Strength Low Alloy (HSLA) Steels for High-Performance Steel Casting High Strength Low Alloy Applications / Jerry Thiel and A.Ghosh (2009)
Higher strength casting alloys can allow metal casters to lighten casting designs by reducing section thicknesses. By using these high strength alloys, steel castings can achieve strength to weight ratios as high as titanium castings at a fraction of the cost with reduced lead times and overall cost. A study conducted at the University of Northern Iowa evaluated the physical properties of three commercially available low alloy steels and their ability to achieve properties above 956MPa (140 ksi) yield strength while maintaining necessary ductility and toughness. These low alloy compositions were evaluated for their ability to meet 956MPa (140 ksi) yield strength, 6% elongation and 12% reduction of area. The paper discusses induction melting and casting techniques and includes methods for heat treatment and testing. Mechanical testing results are shown for varying tempering temperatures and various heat treatments including standard quench and temper. Results of the mechanical testing show that conventional 4300 series alloys can be effectively heat treated to high strength levels without loss of ductility and toughness. Carbon content was found to be critical in obtaining these high strength levels.
Investigation into the Technical Limitations of Silica Sand Due to Thermal Expansion / Jerry Thiel, M. Ziegler, P. Dziekonski, S. Joyce (2007)
Casting defects that are a result of the thermal expansion of silica sand have always posed difficulties for the metal caster. Veining, scabs, rattails and castings out of dimensional tolerances are only a few of the defects that are associated with the detrimental expansion silica sand. The following study was funded by multiple member companies of the National Industrial Sand Association. The study reviewed how the expansion of sand had previously been tested and covers the development of new testing equipment to increase sensitivity and accuracy of the results. The new equipment was utilized to measure the expansion of loose unbonded silica sands with relation to mesh size, grain shape, screen distribution, chemistry and density. The study also investigates the influence of chemical binder systems including phenolic urethane cold box, ester cured phenolic, furan and modified sodium silicate on the thermal expansion of bonded sand samples. The study also investigated the expansion of bonded sands with additives that included red iron oxide, black iron oxide and engineered sand additives.
An evaluation technique for assessing veining and metal penetration defect formation using the step cone casting is proposed. Casting experiments were conducted to verify the ability of the analysis technique to accurately identify defect formation trends based on known tendencies observed by the foundry industry. This was accomplished by evaluating step cones produced from lake and silica sand by varying the % solids content of a graphite coating. Lake sand, with a lower thermal expansion characteristic than silica sand, has been observed by the foundry industry to reduce the propensity for forming veining defects. It is also known that increasing the solids % content of a coating provides greater protection to metal penetration formation. Using these two variables as a control group, the proposed analysis technique should clearly identify their influence on casting surface quality. Experimental results obtained from five inspectors with varying experience in evaluating being and penetration defects validated the proposed evaluation methodology. Though the defect severity value spread obtained by individual inspectors is large, the research showed the casting ranking for a particular defect evaluation between inspectors were close to the ranking based on the average defect severity value between the inspectors. Variability between casting heats showed minimal influence between the overall rank. The defect analysis technique was demonstrated to be a viable procedure as an evaluation tool in assessing foundry materials to prevent core related defects.
Effects of Using Causticized Lignite as a Seacoal Replacement on Mold Gas Emissions / Jerry Thiel, S. Giese, V.Losacco, J. Darlington, and M. Van Leirsburg (American Colloid Co.) (2005)
Emission testing was conducted to determine the effect of substituting causticized lignite for seacoal in a green sand molding system. During the testing, emissions were first collected from a typical baseline system sand containing seacoal. These results were then compared to the emissions resulting from increasing amounts of causticized lignite substituted for the seacoal in experimental green sand systems. In addition to the collection of CO/CO2 samples, 63 different Hazardous Air Pollutants (HAPs) and Volatile Organic Compounds (VOCs) were also collected and evaluated. The results of the testing demonstrated that the total substitution of seacoal with causticized lignite reduced mold gas emissions of HAPs and VOCs by more than 45%. Proportional reductions in both HAPs and VOCs were observed with partial replacements of causticized lignite for seacoal in the different green sand mixtures. Other results of the testing included a decrease of 18% in bond requirement in the sand mixtures containing all caustisized lignite.
Influence of Protein-Based Biopolymer-Coated Olivine Core Sands on Olivine Green Sand Molding Properties / Jerry Thiel, S. Giese, R.M. Herreid and J.D. Eastman (Hormel Foods) (2002)
An applied research study was undertaken to assess the influence of protein based biopolymer coated, olivine sand cores on olivine green sand molding properties. Green sand molds were made to assess the green sand properties as used biopolymer cores were continually introduced into the molding system. Aluminum castings were poured to observe the casting quality after each cycle diluted with the biopolymer coated cores. The research work showed an increase in water capacity but stabilized toward the end of the experiment as the amount of returned olivine core sand increased. The green sand properties exhibited an initial decrease but stabilized as the olivine green sand matured with the addition of biopolymer coated cores. An indirect result of the feasibility study was the reduction of free silica in the workplace and exposure to hazardous air pollutants associated with organic binder processes.