Effects of Hot Sand and Its Cure by Use of a Sand Cooler: A Case Study

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1 Paper pdf, Page 1 of 10 Effects of Hot Sand and Its Cure by Use of a Sand Cooler: A Case Study M. J. Mroczek, T. S. Wozniak, and C. A. Crespo Weil-McLain, Michigan City, IN S. L. Neltner and V. S. LaFay S&B Industrial Minerals, Cincinnati, OH Copyright 2011 American Foundry Society ABSTRACT For as long as molten metal has been poured into molded sand cavities, foundries have had the problem of that hot molten metal transferring heat into the sand mold. This would not be a problem if it were not for the fact that this sand is re-circulated and is reconstituted with additional materials and water in order to make green sand molds once again. This re-circulating process makes hot sand a problem. When water is added along with additional clay for re-bonding this sand into molds, the water that is used to allow the clay to bond is not as effective at elevated temperatures. So why employ a process with this associated problem? The main reason the green sand system is employed is the fact that it is a very cost-efficient one, because it does recirculate and reuses materials.¹ The only means of eliminating the problem of hot sand is to either discontinue the use of the re-circulating green sand system, change to an alternative sand system that does not re-circulate, or employ some means of cooling the return sand before its reuse¹. Due to cost restraints, most foundries either live with hot sand or take measures to minimize its affects or take the necessary steps to actually cool the sand so that it is at a temperature more conducive to the clay performance temperature range. This paper focuses on one foundry s sand system operating at elevated temperatures prior to any mechanical measures and then looks at this same sand system after steps have been taken to cool the sand and implement improved sand handling systems. Data will be shared to show the effectiveness of sand cooling on the properties of the prepared sand and the reduction of scrap. INTRODUCTION/HISTORY Hot sand is not new to the green sand foundry. Actually, the opposite is true. Rarely does one speak to foundry personnel who do not have some type of problem with hot sand or have taken the necessary steps to minimize the effects of their hot sand. Much has been documented and published on hot sand because it is so prominent in green sand foundries. Many individuals have performed exhaustive studies on the subject of hot sand. So why does this phenomena persist so strongly in the foundry? Simply cost. It is very expensive to generate the energy initially to heat metal into a molten state. In order to minimize this expense of melting metal; foundries employ a recycling molding system to help defer some of the cost of producing a casting. A metal casting facility is made up of various functional areas. These areas include melting capability, molding operation (green sand or other processes), core making, and various mechanical methodologies to separate the metal cast part from the molding media. (See Fig 1.) Simply referred to as Molding, Pouring, Cooling, and Shakeout in a foundry. This publication will focus primarily on the heat transfer during the pouring and cooling stages. This paper is a discussion of the effects of hot sand and most importantly it shares the actual results of an operating foundry and its attempt of controlling and minimizing the negative affects of hot sand primarily by the use of a sand cooler and innovative sand handling practices. Sand Metals & Additives Sand Preparation Sand Test Lab Physical & Chem Lab Sand Handling Core Making Sand Mixing Patterns Melting/Refectories Charging Melting Molding Core Baking Molding Mold Finishing Mold Handling Pouring Metal Handling Shakeout Knockout Cleaning, Finishing Cutoff Trimming Snagging Chipping Blast Cleaning Tumbling Heat Treating Fig. 1. Various functional areas of a foundry. Dimensional NDT Physical Chemical

2 Paper pdf, Page 2 of 10 THE PROBLEM OF THE EFFECTS OF HOT SAND How does the heat transfer from the molten metal to the sand? Depending upon the metal poured and its grade, the temperature of the heats can range from F ( C). When in contact with the green sand mold, these extreme temperatures transfer some portion of that heat by conduction, convection and radiation². Conduction is the heat transfer by actual direct contact. That is, the metal contacting the mold metal interface of the mold and this heat is then transferred from direct contact points between the sand grains. The compaction or compactablity of the prepared sand will affect this heat transfer as the sand becomes more compacted; more contact points are available from sand grain to sand grain. Also as the sand grains become finer, more direct contact points are available for this heat transfer by conduction. One might also consider that as the sand grains become finer, the openness or the permeability of the molded sand decreases and consequently restricts the heat to vent out between the voids in the sand grains as well. (Fig. 2.). Fig. 3. Heat transfer through conduction of contact points and void spaces which allows heat transfer through convection. Less compaction/ less density allows for more venting of heat. Fig. 4. Heat transfer in sand mold by convection and conduction. Fig. 2. Heat transfer by conduction through contact points. Tight compaction/high density; allows less venting of heat. Convection is the heat transfer done by the motion of airflow. If molding sand is in the area of warm or hot air that is being circulated this can transfer heat to the sand grains. This transfer of heat through air can come from space voids between less compacted sand (Figs. 3. and 4). Radiation is the heat transfer by heat radiating from a high temperature source but without direct physical contact or the assistance of forced air flow. So the returned molding sand gets hot. Two things that need to be discussed are, 1. How hot is too hot?, and 2. What negative effects are the results of hot sand? It is generally accepted from previous works and studies on hot sands that returned sand to the muller should be no hotter than 100F, or no hotter than 15F above ambient temperature. This is considered ideal for green sand preperation³. It has also been documented that having prepared sand exit the muller below 100F (38C) is necessary to prevent temperature buildup, as the sand is reused repetitively 4. The relationship between temperature ranges and sand physical properties is well known. (Fig. 5.)

3 Paper pdf, Page 3 of 10 Sand Temperature Sand Properties 100 F F (38 C 49 C) Stable Green Sand Properties. 120 F -140 F (49 C 60 C) Physical Properties are diminished. Extra Mulling may be required. 140 F 160 F (60 C 71 C) Physical Properties Uncontrollable. High friable sand with weak strengths. Greater than 160 F (71 C) Water evaporates so quickly that mulling is not occurring due to clay not being wetted out or activated. Fig. 5. Sand temperature ranges vs. sand properties. When the return sand approaches the elevated temperatures preparing this hot sand in mullers and mixers becomes more difficult. The moisture that is trying to activate and plasticize the clay in order to make bonds between the sand grains is actually being used to cool the sand. As this water is cooling the sand it drives off the heat through evaporation in the form of steam. In effect, the sand muller will for a period of time act as a sand cooler. The time that it takes to lower this and is then subtracted from the overall mulling time which results in deteriorated sand properties. The sand becomes much more friable which results in sand inclusions, and there is an increase in cut and wash type defects. The friability tests measures the sand s tendency to dry out and become brittle at the mold surface by rotating two prepared sand samples against each other in a rotating basket which abrades of the sands surface. This abraded sand is then measured and reported as a percent of the original sample weights. (Fig. 6.) Even if the sand does appear to be mulled sufficiently, the hot sand when molded tends to dry out and loose sand grains persist as the mold dries out prior to actual metal pour. Besides an increase in friability, hot sand also allows for deterioration in overall strengths. In 1973, J. Scott reported in AFS Transactions that when sands exceeded 100F (38C) that green compression strength, on average decreased by 10%, dry compression strength decreased by 50%, wet tensile values decreased by 30% to 40%, and permeability decreased by 15% 5. PROVEN SOLUTIONS TO COOLING SAND Having an extended cooling table or allowing the poured molds to have enough time to cool below 100F is the ideal solution to the hot sand problem. Unfortunately, many foundries do not have this luxury and due to everincreasing production rate requirements, sufficient cooling time is not always possible. The solidified castings are often shaken out from the molds while they are still described as cherry red hot. Although it is a good idea to have shakeout as soon as possible in order not to have the metal in contact with the sand molds, it is important to take some means of cooling the sand down before returning it to the muller for re-bonding. (Shakeout should not be so premature as to affect casting quality due to castings being too hot and result in batter defects.) In the past, several different systems have proven to be effective in cooling this hot return sand. These systems include altering the sand: metal ratio or more importantly the surface area exposure of the molten metal to the molded sand surface in order to minimize the heat transfer in the first place. Increasing the initial moisture content of the prepared sand also allows for sufficient residual moisture to remain in the sand after shakeout; but new high pressure molding machines tend to prefer drier sands. The use of cooling screens and drums have been effective in cooling return sand as well as the use of alternating plows/discs and logging chains to turn the sand over along transport belts and possibly introduce a moisture source to the sand before it returns to the return sand bin above the muller. 6 Flooding the return sand with quantities of prepared molding sand is another method of cooling this sand (U.S. Patent No ). 7 Another method utilized is the sand cooler. This piece of equipment could be a rotating drum that forces air through hot sand to dissipate the heat and it may also utilize water as well by allowing the evaporated water to expel the heat with it. Fig. 6. Friability test unit. This case study does address the hot sand remedy by use of a manufactured sand cooler. The installation and application as well as the documented results of the sand before and after the addition of this in-line piece of equipment follows.

4 Paper pdf, Page 4 of 10 CASE STUDY The Foundry Plant in Michigan City, Indiana, manufactures boiler sections cast in green sand molds with cores made in hot-box and cold-box processes. prepared sand also reduces the green compression strength. The moisture has to be increased in the sand proportionally to the sand temperature to compensate for the water loss due to the high sand temperature. The boiler sections are manufactured of cast iron class 25 and meet the ASME Boiler & Pressure Vessel Code. Each section is subject to hydrostatic test and has to meet the minimum wall thickness of 80% of the nominal value; therefore, any deep surface defect or discontinuity that exceeds this requirement would be a reason to scrap the casting. For instance, if the nominal wall thickness were inches (6.35 mm), the maximum permissible surface defect or discontinuity would be only inches (1.27 mm) deep in non-critical areas. In critical areas, any surface discontinuity is not acceptable. The present case study has been conducted on the A-Line, which produces castings of weights between 30lbs to 300lbs ( Kg) and processes approximately 120 tons/hour of green sand. The sand is mixed and mulled in a continuous mixer, which normally operates at a retention time of ~70 seconds. The water and bond addition into the muller is controlled by a Hartley PM 2552 tester, based on feedback measurements of moisture, compactability and green compression strength. BACKGROUND SAND TEMPERATURE The return sand temperature measured before the muller, considerably varied by time. On Fig. 7. are shown typical sand temperature variations within the same day and also between days. At the beginning of the shift, the sand temperature is high (Fig. 7d) because of the stored sand in the silo maintains the temperature overnight even after a weekend shutdown. Then, after a short time of production, the sand temperature starts dropping when cooler sand from molds left overnight are shaken out and put back in the system. After this short period of cool sand, the temperature increases rapidly when hot sand from molds poured in the morning is recycled. After that, the temperature gradually increases during the day. The sand temperature used to go as high as 160F-180F (71-82C) during the shift and at the beginning of the day. If we observe the graphs a) and b) of Fig. 7, the green compression strength (GCS) measured at the muller discharge by the Hartley tester, tends to decrease when the return sand temperature increases. A statistical analysis [displayed below] from one day data shows that the relationship is significant between the two variables (P-value is <0.05), and it indicates that 50% of the variation of the green compression strength is explained by the sand temperature variation. If the moisture is included in the equation, the R-Sq increases to 53%. The increase of moisture in the Fig. 7. Return sand temperature going into the muller and green compression strength [GCS] of prepared sand measured by the Hartley tester: a) and b) Monday GCS and sand temperature after recycling the sand one time on Saturday, c) and d) Wednesday GCS and sand temperature The regression equation is: GREEN STRENGTH = RETURNSANDTEMP (250 cases used, 4 cases contain missing values) Predictor Coef SE Coef T P Constant RETURNSANDTEMP S = R-Sq = 49.5% R-Sq(adj) = 49.3% Analysis of Variance DF SS MS F P Source Regression Residual Error Total GREEN COMPRESSION STRENGTH As it was discussed above, the hot sand reduces the green compression strength. On Fig. 8. it is shown that there is a tendency to increase the proportion of defective parts due to mold-crack as the green compression strength decreases. This mold-crack also may result in sand inclusion defects as it is shown on Fig. 9. On this particular casting, a surface discontinuity deeper than is not acceptable and the part would be rejected. This confirms what already was mentioned in the literature, that the hot sand results in higher percentage of scrap. So, the need of cooling the return sand and

5 Paper pdf, Page 5 of 10 improving the mechanical properties was evident in order to improve the quality of the castings. Proportion of defective parts Scatterplot of Mold-Crack Defect vs Green Compression Strength N = 77 Jan-Aug Green Compression Strength [psi] Fig. 8. Scatter plot of the proportion of defective parts because of mold-crack defect versus the average green compression strength (lab test) on the GOboiler back section marginal increased of the GCS in ~8%. The drawback was the variation increase of the moisture and compactability. After that, and for approximately 45 days prepared sand was diverted and put back into the return sand of the same A-Line system. 7 Initially the green compression strength increased but it was not sustained consistently day-to-day. Also the day-to-day and within the same day variability of the moisture and compactability did not improve. The sand temperature went up to 150F~160F during the day. MOISTURE IN THE PREPARED SAND The prepared sand moisture measured at the molding line averaged 3.44%. The total process variation (6 x Standard Deviation) of the moisture was 1.70% (from 2.60% to 4.30%). Low moisture content resulted in low compactability and more friable mold surface (Fig. 10) Histogram of Moisture [Lab test] Normal Before sand cooler Jan-Aug Mean StDev N Sand inclusion Frequency Causes Cracked molds Fig. 9. Sand inclusions caused by cracked mold surface. GO-boiler back section. To increase the mechanical properties of the sand, the extra mulling time in a continuous mixer was not a viable option, nor the increment of bond. Then, a few different trials were made to try to increase the strength of the molding sand and reduce the sand temperature: Moisture [%] Fig. 10. Green sand moisture distribution before the sand cooler installation. Inefficient mulling because of hot sand also led to increase the moisture content in order to achieve a desired molding sand compactability. Due to the variability of the process, the moisture in the sand went up to the levels that may cause casting defects. It was determined, on a particular casting used for the study, that there is an important relationship between the moisture and the scrap due to burn-on defect, a very severe sand adherence that cannot be removed at the blast. (Fig. 11) One of those was recycling the sand through the muller one time in the weekend and every night before the start of the shift. This practice did not show a significant improvement on the green strength except for Monday morning, but along the day, as it was expected, the return sand temperature increased and the GCS decreased. On the next days of the week, in spite of recycling the sand prior to the start of the shift, the green strength continued declining. Figure 7 shows Monday and Wednesday return sand temperature and the GCS. In addition, it was tried to add approximately 2% of prepared sand into the return sand from the batch muller of B-Line during the production shift. This showed a Fig. 11. An example of typical burn-on defect.

6 Paper pdf, Page 6 of 10 Figure12. shows that the increase in moisture will cause an increase in burn-on defect. Proportion of defective parts [Burn on] Scatterplot of Burn on vs Moisture Mean Moist Mean [%] Fig. 12. Scatter plot of the proportion of defective parts because of burn-on (GO-back boiler casting section) versus average of molding sand moisture (lab test) on the GO-boiler back section. Transforming the proportion of defective parts data, we can see a better linear relationship between the burn-on and moisture content in the sand. (Fig. 13) Transf. Burn on Scatterplot of Burn on [transformed data] vs Moist Mean Moist Mean [%] Fits Regress Lowess Fig. 13. Scatter plot of the transformed proportion of defective parts because of burn-on versus average moisture of molding sand. R-Sq=59.4% or r=0.77 The increase in moisture in the sand is also related to the increase of bond addition as preblend. All additives contained in the preblend will absorb water in some degree. This is explained by analyzing the relationship between moisture and active clay (MB clay), which their positive linear relationship also is significant, and the R- Sq is 26% (or r = 0.51). APPLICATION OF THE SAND COOLER BRIEF DESCRIPTION OF THE SAND COOLING SYSTEM In the second half of 2007, it was decided that the installation of a sand cooler was necessary to improve the mechanical properties of the green sand and for improving the quality of our products. 4.0 In September 2008, the installation of the sand cooling system (MU-MUR) manufactured by SPACE SRL of Italy was completed. The system has the following features: Continuous sand weighing system. Complete control of the mixing by moisture, weighing, and temperature sensors installed in the sand stream. Capable to control up to three variable speed screw feeders, for dosing of additives, such as bond. Calculation of the amount of water to be added with automatic compensation of evaporation losses generated by temperature, mixing time, storage time and ambient conditions. All useful information concerning equipment operation is displayed on a screen, including graphic trends of main process variables, and appropriate messages and alarms. The sand cooling system processes the return sand coming straight from the shakeout after passing through a rotary screen. The cooled sand with partial addition of bond is stored for approximately 1-2 hours in a silo prior to the mulling-mixing operation in a continuous mixer controlled by a Hartley system. EFFECT OF THE SAND COOLING ON THE GREEN SAND PROPERTIES The majority of the sand properties that are displayed on the next graphs were taken from the tester. The mean difference between the laboratory and the Hartley testing for green compression strength is expected to be 6-7 psi and for the compactability is expected a mean difference of 12%. Sand temperature The daily average return sand temperature is plotted on Fig. 14. The return sand temperature considerably decreased since the installation of the sand cooler. Average temperature went up to 160F (71C)in summer 2008, as we can see on the graph below, and for similar period in 2009, the maximum average temperature reached 120F (49C). Sand temperature [F degree] Return sand to the Muller Scatterplot of Sand temperature Mean vs Fig. 14. Return sand temperature going into the muller.

7 Paper pdf, Page 7 of 10 GREEN COMPRESSION STRENGTH, MOISTURE, AND MULLER EFFICIENCY The reduction of the return sand temperature resulted in an increase of the green compression strength. This confirms our previous discussion of the negative effect of the sand temperature on the mechanical properties of the green sand. The GCS has increased in approximately 40% measured by the tester and 25% based on laboratory testing. The GCS continuously increased since the installation of the sand cooler. The maximum GCS was obtained with partial addition of bond (50%-70%) into the sand cooler, starting in December This bond addition in the sand cooler, without increasing the amount of active clay in the sand, raised the GCS beyond the maximum desired of 26 psi. (Fig. 15) Green Comp. Strength Mean [psi] Scatterplot of Green Comp. Strength Mean vs [Hartley] Fig. 15. Daily green compression strength mean measured at the muller discharge by the Hartley tester. The working bond follows the GCS pattern. It increased since the sand cooling installation. (Fig. 16) Moisture Mean Scatterplot of Moisture Mean vs [Hartley] Fig. 17. Daily moisture mean measured at the muller discharge by the tester tester The muller efficiency has increased from approximately 55% to 75% (Fig.18.). This 35% increase in efficiency value is mainly driven by the increase in GCS. Muller Efficiency Mean Scatterplot of Muller Efficiency Mean vs Fig. 18. Daily average of muller efficiency. Muller efficiency=working bond/available bond active clay and green compression strength-to-mb clay ratio Working Bond Mean Scatterplot of Working Bond Mean vs [Hartley] The increase in GCS led to reduce the amount of active clay in the prepared sand. As we can see on Fig.19, the amount of active clay (measured by Methylene Blue method) used prior to the sand cooler was approximately 9.0% +/- 1.0, and it has been reduced to 7.5% +/- 1.0 in June This decline of MB clay observed on the right side of Fig. 19 (June) relates to the reduction of GCS and working bond for the same time-period (Fig. 15 and 16 respectively). 2.0 Fig. 16. Daily average of calculated working bond. Working bond = (15.29* GCS)/(132.1-Compactability) The reduction of the sand temperature also resulted in a reduction of moisture in the prepared sand. The average reduction of moisture is approximately 0.6 % [Lab test]. Similar reduction is observed on the Hartley measurements (Fig. 17).

8 Paper pdf, Page 8 of 10 MB Clay Mean Scatterplot of MB Clay Mean vs Fig. 19. Daily average percentage of active clay in the prepared sand (MB clay). The GCS-to-MB clay ratio is a very interesting metric. If we observe the trend in June of 2009 (right side of the plot), this trend does not follow the decline of GCS and working bond observed on Fig. 15 and 16. The values of the GCS-to-MB clay are maintained despite the reduction in active clay. It means that for 1% of active clay, the developed GCS has been maintained. (Fig. 20). Compactability/Moisture ratio Scatterplot of Compactability Mean-to-Moisture Mean ratio vs Hartley data Fig. 21. Daily average of Compactability-to-Moisture ratio. PERMEABILITY The green sand permeability has increased significantly by approximately 29%. (Fig. 22) This confirms previous findings mentioned in the literature 5 that the hot sand above 100F negatively affects the permeability. The reduction in bond addition also may have contributed to the permeability increase. Scatterplot of Green Comp. Strength Mean [Hartley]-to -MB Clay ratio vs 180 Scatterplot of Permeability Mean vs Hartley GS Mean/MB Clay Fig. 20. Daily average of Green Compression Strength-to-MB clay ratio. COMPACTABILITY AND COMPACTABILITY-TO- MOISTURE RATIO The desired compactability of the sand at the point of use was maintained at 32% +/- 4% before and after the sand cooler installation. Therefore, the compactability at the tester has not changed either. However, the compactability-to-moisture ratio increased considerably as it is shown on Fig. 21. This means that the mullingmixing system is able to develop the desired temper of the sand with less amount of water. The ratio has increased approximately from 14 to 18 (Hartley data). Based on the laboratory testing, the ratio increment has been from 8-9 range to range. Permeability Mean /1/2008 3/1/2008 4/1/2008 5/1/2008 6/1/2008 7/1/2008 8/1/2008 9/1/2008 1/1/2009 2/1/2009 3/1/2009 4/1/2009 5/1/2009 6/1/2009 7/1/2009 Fig. 22. Daily average of green sand permeability. GREEN COMPRESSION STRENGTH VERSUS SAND TEMPERATURE ANALYSIS The regression analysis of the GCS mean versus the return sand temperature mean, including all data before and after the sand cooler installation, shows that the linear relationship is significant. The variation of sand temperature explains 79.4% of the variation of the GCS (Fig. 23).

9 Paper pdf, Page 9 of 10 Green Comp. Strength Mean Fitted Line Plot Green Comp. Strength Mean4 = Sand temperature Mean2 90 Hartley data through June N= Sand temperature Mean Regression 95% C I 95% PI S R-Sq 79.4% R-Sq(adj) 79.3% Fig. 23. Regression analysis of green compression strength versus return sand temperature. GREEN COMPRESSION STRENGTH VERSUS SAND TEMPERATURE AND ACTIVE CLAY [MB CLAY] AFTER THE SAND COOLER For an average sand temperature range between 85F and 123F, with the sand cooler, the Fig. 24 shows that there is an important linear relationship between two variables: GCS vs. return sand temperature, and GCS vs. active clay content (MB clay). The R-Sq are 42.3% and 37.1% respectively. Green Comp. Strength Mean Scatterplot of GCS vs Sand temperature mean, MB Clay mean Sand temperature Mean MB Clay Mean Fig. 24. Scatter plot of green compression strength, return sand temperature, and active clay [MB clay] after the sand cooler installation. 9 MB clay Mean S = R-Sq = 64.7% R-Sq(adj) = 64.2% Analysis of Variance Source DF SS MS F P Regression Residual Error Total Source DF Seq SS Sand temperature Mean MB clay Mean This analysis is indicating that the green compression strength is also significantly affected by the variation of the active clay content. The interpretation of the regression equation is that if the sand temperature-mean increases by 10F, maintaining the MB clay constant, the GCS mean decreases by 1.34psi. If the MB clay increases by 1%, maintaining the sand temperature constant, the GCS mean increases by 1.94psi. This significant effect of the active clay on the GCS was not observed prior to the installation of the sand cooler. If we look at again the plots of sand temperature, GCS and MB clay on Fig. 14, 15 and 19 respectively, we can observe that the decline in GCS in June (right side of the plot) corresponds to a reduction in active clay and to a slight increase of sand temperature. IMPACT ON THE QUALITY OF THE PRODUCT Chronic casting defects such as sand inclusions and related defects were significantly reduced after the installation of the sand cooler. See Fig. 25. However, if a multiple linear regression is performed, with the GCS as a response variable, and sand temperature and MB clay as predictor variables, the analysis shows that the relationship is significant and the R-Sq increases up to 64.7%: The regression equation is Green Comp. Strength Mean = Sand temperature Mean MB clay Mean Predictor Coef SE Coef T P VIF Constant Sand Temp Mean Fig. 25. An example of typical sand inclusion defect. The chart below (Fig. 26.) shows that the scrap due to sand inclusions was reduced by 70% on the GO-boiler back section used for the study.

10 Paper pdf, Page 10 of 10 CONCLUSIONS This study has illustrated that cooling the sand prior to the mulling-mixing process increases the green sand properties significantly. The partial addition of bond in the sand cooler improved the sand properties beyond of what was achieved only with the return sand cooling. This was done without an overall increase in the amount of active clay in the sand system. Fig. 26. Scrap reduction of molding sand related defects on the GO-boiler back section. Similarly, the burn-on scrap was reduced on the same part by more than 90% (Fig. 27). On this particular casting no other process change was performed, so the scrap reduction is mainly attributed to the green sand properties improvement. The development of green compression strength by a unit percent of active clay increased significantly in more than 40%. Likewise, the compactability developed by a unit percent of moisture increased in approximately 20%. The improvement in the green sand properties has impacted positively on the reduction of systemic castings defects such as sand inclusions, burn-on and leaks due to inclusions. The reduced sand temperature range after the installation of the cooler still has a significant effect on the green compression strength. The effect of the active clay variation on the green compression strength has become important. Then, the GCS change can be achieved by varying the amount of active clay in the system. The return on investment (ROI) on the installation of this sand cooling system is estimated to be 3 years. ACKNOWLEDGEMENTS The authors would like to thank Weil McLain and S&B Industrial Minerals for permission to publish this work. Fig. 27. Burn-on scrap reduction on GO-boiler back section. All A-Line parts combined, the scrap due to sand related defects was reduced by 39%, as it is shown on Fig. 28. Normalized scrap Sand related defects on A-Line before and after the sand cooler installation Before [Jan-Aug 2008] After [Sep 2008-May 2009] Fig. 28. Scrap reduction of molding sand related defects on all A-Line parts. REFERENCES 1. LaFay, V.S., Neltner, S.L., Greek, D.N., A Study on the Friability of Hot Sand, AFS Transactions, vol. 101, pp (1993) 2. Principles of Sand Control, AFS Green Sand Committee 4M, pp I-12 (2004) 3. Sink, T., The Shakeout brochure, (1992) 4. Heine, R.W., Schumacher, J. S., Green, R.A., Sand/Metal Ratio and Moisture Content for Cooling of Green Sand, AFS Transactions, vol. 84, pp (1976) 5. Scott, J., Hot Sands Properties. Problems, and Remedies Quantified, AFS Transactions, vol. 81, pp (1973) 6. Schumacher, J., Heine, R.W., The Problem of Hot Molding Sands-1958 Revisited, AFS Transactions, vol. 91, pp (1983) 7. Heine, R.W., King, E.H, Schumacher, J., How Molding Sand Moisture Effects Casting Quality, Foundry Magazine, (August 1960)