Dynamic Measurement of Constraining Force from Green Sandand Casting Contraction of Gray Cast Iron during Cooling

Seigo Ueno1,+1, Haruki Kashimura1,+2, Yusuke Sano2, Tsuneo Toyoda3,Hiroyasu Makino4 and Makoto Yoshida3

1Graduate School of Modern Mechanical Engineering, Waseda University, Tokyo 169-8555, Japan2Department of Modern Mechanical Engineering, Graduate School of Waseda University, Tokyo 169-8555, Japan3Kagami Memorial Laboratory for Materials Science and Technology, Waseda University, Tokyo 169-0051, Japan4SINTOKOGIO, Ltd., Nagoya 450-6424, Japan

This study investigated the effects of the restraint from green sand mold for cast iron during cooling process. Gray cast iron (JIS FC300,almost identical to ASTM 45) was cast in a green sand mold, and the constraining force to the casting from the sand mold and the contraction ofthe casting were measured dynamically from the beginning of solidification to 200°C. The measurement results obtained using the green sandmold were compared with those using the furan sand mold. The maximum constraining force in the green sand mold case was lower than that inthe furan mold case. The contraction in the green sand mold at 200°C was greater than that in the furan sand mold. The results showed that thegreen sand mold restrains the casting less than the furan sand mold during cooling process. [doi:10.2320/matertrans.F-M2018817]

(Received November 16, 2017; Accepted April 5, 2018; Published May 25, 2018)

Keywords: green sand mold, sand casting, residual stress, distortion, computer aided engineering, gray cast iron

1. Introduction

The casting products such as cylinder blocks and machinetool beds are usually produced by using sand molds. Incasting of these products the residual stress and the warpageare big problems, and T.S.321) reported that their majorcauses are the following three items.(1) The different cooling rates at the thin parts and the thick

parts within a casting.(2) The load to the casting from the sand mold during

cooling.(3) The phase transformation in the solid state during

cooling.This study was conducted to measure the contraction of

the casting and the constraining force to the casting froma green sand mold. In addition, the results obtained for agreen sand mold were compared with those for a furan sandmold reported by Marumoto et al.2) Several recent studieshave been conducted to predict the casting defects usingcomputer-aided engineering (CAE), which incorporates theconsideration of the sand mold restraint and the contractionof the casting. Ahmed and Chandra3) demonstratednumerically that the different mechanical properties of sandmolds affect the residual stress distribution in a copper alloycasting. Jacot et al.4) produced a mathematical model topredict the microstructure and residual stress in the gray castiron casting. Metzger et al.5) and Chang and Dantzig6)

reported a model that expresses the mechanical interactionto consider the restraint force from the sand mold to predictthe residual stress in the casting. Chunsheng and Richard7)

attempted to predict the residual stress and the warpage usingsurface elements developed by Metzger et al..5) and Linet al.,8) and predicted the hot tear position of the steel casting

in a green sand mold using the methods developed byMetzger et al.5) and by Chang and Dantzig.6) Baghani et al.9)

verified the thermal stress analysis using the experimentswith H-shaped steel castings. For modeling the sand mold,the elasto-plastic model is more accurate to predict theresidual stress than elastic model.

As described above, several studies have been conducted topredict the residual stress, hot tear and distortion of thecasting by considering the constraining force to the castingfrom the sand mold. These studies validated the respectiveanalytical methods and the experimental results whichwere obtained only after its cooling process. However, asdescribed above, the permanent deformation of the casting isproduced by the constraining force from the sand mold duringcooling. It remains unclear how the mechanical propertiesand the constitutive equations of the sand mold found inearlier studies can predict the experimentally obtained resultsin the cooling process. Motoyama et al.10,11) developed anew device based on the device presented by Parkins andCowan12) to measure the constraining force and contractionof the casting dynamically during cooling. Using it, theymeasured these values of an aluminum alloy casting fromsolidification to 50°C. Motoyama et al.13) and Inoue et al.14)

compared the measured values and the simulated values ofthe constraining force on the aluminum alloy casting obtainedduring cooling. They tested various mechanical models andmechanical properties of the sand mold, and they reportedabout the necessity of using the temperature-dependentmechanical properties of the sand mold for more accurateprediction instead of the properties which were taken at roomtemperature. Marumoto et al.2) improved the device basedon the methods described by Motoyama et al.10) to measurethe constraining force from the furan sand mold and thecontraction of the cast iron casting dynamically. Green sandmolds have been used widely to fabricate castings, and greensand molds are often made automatically using squeeze

+1Present address: JFE STEEL Corporation, Chiba 260-0835, Japan+2Present address: NISSANMOTOR Co., Ltd., Yokohama 220-8623, Japan

Materials Transactions, Vol. 59, No. 6 (2018) pp. 957 to 962©2018 Japan Foundry Engineering Society

machines. But no report in the relevant literature describes astudy measuring how much the constraining force cast ironcastings receive from the squeezed green sand mold orcontract during cooling. In this study, both the constrainingforce to the casting from the squeezed green sand mold andthe contraction of the gray cast iron casting were measureddynamically from the start of solidification to 200°C usingan improved device based on the device developed byMotoyama et al.10)

2. Experimental Procedures

The schematic illustration of the squeeze machine used inthis study is presented in Fig. 1. The cope and drag werefabricated using this machine. The squeeze pressure was setto 0.8MPa using a hydraulic jack. Natural silica sand wasused for the experiment. Table 1 presents the green sandmold properties, and Fig. 2 portrays the squeezed sand mold.The schematic diagram in Fig. 3 shows the device used formeasuring the constraining force to the casting from thegreen sand mold and the contraction of the casting duringcooling. A quartz rod and the clamp (Fig. 4) were set whenthe cope and drag were assembled. The castings were of graycast iron (JIS FC300, almost identical to ASTM class no. 45;Table 2).

First, the alloy was melted in argon atmosphere. Thecarbon equivalent (CE = C% + 1/3Si% + 1/3P%) wasadjusted to approximately 3.8% using recarburizer. Beforepouring, 0.2mass% inoculant (including Si, Al, Ca, Ba) wasadded to prevent chilling.

The pouring temperature was approx. 1350°C. Afterpouring the molten alloy, the end of the casting on theopposite side of the flange was held by the clamp. One end ofa quartz rod was cast-in at the center of the flange. During

Fig. 1 Schematic illustration of squeeze machine.

Table 1 Sand mold conditions.

Fig. 2 Squeezed green sand mold.

Fig. 3 Schematic illustration of the device.

Fig. 4 Cooling system of the clamp (ASTM 430 steel).

Table 2 Chemical composition of the alloy (Correspond to JapaneseIndustrial Standards (JIS) FC300 (ASTM class No. 45) gray cast iron).

S. Ueno et al.958

cooling, the longitudinal contraction of the casting wasmeasured dynamically by measuring the displacement of thequartz glass rod that was cast-in at the flange. In addition, theconstraining force to the casting was measured dynamicallyby the load cell connected with the clamp. The experimentalvalues were obtained at 2Hz from the start of solidification(approx. 1210°C) to 200°C. Two concentric cylinderscooled the clamp (Fig. 4) with water whose flow rate wasapproximately 1.0 L/min. A schematic illustration of thecasting and the thermocouple locations is presented in Fig. 5.The size of the flange is 90mm square and 10mm thick.The thermocouples were inserted through the parting line.As shown in Fig. 5 the temperatures at the three positionsof the casting (A, under sprue; B, center of the casting;C, flange (Fig. 5)) were measured using ungrounded type Nthermocouples (stainless steel thermocouple probes with2.3mm outer diameter). The temperatures at the threepositions of the sand mold (D, distance from casting10mm; E, 20mm; F, 30mm (Fig. 5)) were measured usingungrounded type K thermocouples.

3. Results and Discussion

3.1 Green sand moldFigure 6 presents the temperature curves of the casting.

Figure 7 shows the temperature curves of the green sandmold. The comparison of the temperature curves of thecasting reveals that the temperature decreasing rate at thepoint A (under the sprue) was higher than the others,probably as a result of the cooling system at the clamp.The temperature curve of point B (center of the casting)remained constant at around 720°C from 900 s to 1200 sbecause of A1 transformation. This transformation affectedthe temperature curve of the point D (Distance 10mm) in themold, which remained constant from 1000 s to 1300 s. Thehighest temperature of point D (Distance 10mm) reachedapproximately 400°C. The highest temperatures of point E(Distance 20mm) and point F (Distance 30mm) respectivelyreached 250°C and 200°C. As portrayed in Fig. 7, thetemperature curves of points E (Distance 20mm) and F

Fig. 5 Schematic illustration of casting shape and thermocouple locations.

Fig. 6 Temperature curves of casting.

Fig. 7 Temperature curves of green sand mold.

Dynamic Measurement of Force from Green Sand Mold and Contraction of Gray Cast Iron 959

(Distance 30mm) show a constant zones at approximately100°C in their early stages. These zones represent theevaporation of water in the green sand. Figure 8 (firstexperiment) shows the dynamic measurement of theconstraining force to the casting from the green sand moldand the contraction of the casting. The temperature rangeduring the casting cooling can be divided into the shrinkagetemperature range and the expansion temperature range. Inorder to express the temperature-dependent behavior of thecasting, the graphs after Fig. 8 are illustrated with the X-axisof the temperature of casting (point B in Fig. 6). To confirmthe reproducibility, another experiment was conducted underthe identical conditions. Figure 9 and Fig. 10 present thereproducibility of both measurements of constraining forceand contraction. The difference between the measurementvalues in the two experiments was not significant. Figure 11presents an enlarged figure of Fig. 8 (1210°C­1100°C), andit shows that the minimum contraction and the minimumconstraining force reached to ¹0.4mm and ¹0.3 kNrespectively soon after the start of solidification due to the

expanding of the casting. According to Kagawa et al.,15) thefirst expansion (Fig. 11) of the cast iron resulted from thecrystallization of graphite during eutectic solidification. And,as the cooling progressed both the constraining force andthe contraction increased with cooling, but they decreasedat approximately 720°C. Figure 12 presents an enlargedfigure of Fig. 8 (750°C­680°C). The contraction droppedto approximately 0.2mm (from 1.54mm to 1.34mm). Theconstraining force also dropped to approximately 1.7 kN(from 2.45 kN to 0.78 kN). These results also indicate thatthe casting expands in this temperature range. The secondexpansion (Fig. 12) of the cast iron resulted from the A1transformation. Marumoto et al.2) reported their dynamicmeasurement of the constraining force and contraction ofthe gray cast iron casting during cooling indicated similarbehavior in the furan sand mold. After A1 transformation,the constraining force and the contraction increased againwith cooling. The contraction continued to increase up toapproximately 5mm at 200°C. The third decreasing of theconstraining force occurred after it increased approximately

Fig. 8 Constraining force and contraction. (First experiment)

Fig. 9 Reproducibility of constraining force.

Fig. 10 Reproducibility of contraction.

Fig. 11 Enlarged curves of the constraining force to the casting and castingcontraction (1200°C­1100°C).

S. Ueno et al.960

2.5 kN. This decrease of the constraining force is consideredto result from the expansion of the moisture condensationlayer and from sand mold fracture. Marek16) reported thatthe position and length of the vapor transporting zone changecontinuously with the progress of solidification. Katashimaet al.17) reported that the moisture condensation layerthickness in the green sand mold increased and that theposition of that layer moved in the outward directionbecause the evaporated water moved from the area withhigh temperature (above 100°C) to the area with lowtemperature (below 100°C). Additionally, Katashimaet al.18) found that the compressive strength and thedeformation modulus of the moisture condensed layer aremuch lower than those of the green sand mold. Figure 13portrays a crack in the sand mold surface at 200°C. Thiscracking was found in every experiment. However, whetherthe reason for the cracking is the decrease of the strengthof the mold because of the expansion of the moisturecondensed layer, or not, remains unknown.

3.2 Comparison between the green sand mold and thefuran sand mold

Figure 14 and Figure 15 present the comparisons of theconstraining force and the contraction data obtained fromour experiment (green sand mold) and reported by Marumotoet al.2) (furan sand mold). During solidification, themaximum expansion of the casting in the green sand mold(0.4mm) was greater than that in the furan sand mold(0.2mm), and the minimum constraining force to the castingin the green sand mold (¹0.3 kN) was lower than that in thefuran sand mold (¹0.9 kN). During the casting cooling to200°C, while the maximum constraining force to the castingwas 2.5 kN in the green sand mold, it was as large as 13 kN inthe furan sand mold. Additionally, the temperature range thatthe casting receives lower constraining force from the greensand mold is wider than that of the furan sand mold. The finalcontraction value (at 200°C) of the casting in the green sandmold (5mm) was greater than that in the furan sand mold(4mm). These results mentioned above indicate that the furan

Fig. 12 Enlarged curves of the constraining force to the casting and castingcontraction (750°C­680°C).

Fig. 13 Crack of the green sand mold surface.

Fig. 14 Constraining forces to casting with the green sand mold and thefuran sand mold.

Fig. 15 Contraction of castings with the green sand mold and the furansand mold.

Dynamic Measurement of Force from Green Sand Mold and Contraction of Gray Cast Iron 961

sand mold restrains the casting more than the green sandmold during the cooling process. The furan sand mold isknown to have higher strength than that of the green sandmold. However, according to Hirakata19) and Yamamotoet al.,20) in the temperature range higher than 600°C thecompressive strength of a green sand mold was higher thanthat of a furan sand mold. Hirakata19) reported that thecompressive strength of a green sand mold at 200°C wasapproximately 0.18MPa. Yamamoto et al.20) reported thatthe compressive strength of a furan sand mold at 200°Cwas approximately 1.27MPa. They also reported that thecompressive strength of a furan sand mold wasapproximately 0.2MPa and that of a green sand mold wasapproximately 0.24MPa at 600°C. As portrayed in Fig. 7,the highest temperature of the point D (Distance 10mm)reached up was approximately 400°C. Therefore, in the greensand mold of this study, the area whose highest temperaturehad reached up 600°C was only a part of the inside ofpoint D (Distance 10mm), so that the area of the green sandmold whose strength is higher than that of the fran sand moldis considered to be relatively small. That is considered to beone of the reason that Fig. 14 shows that the constrainingforce of the furan sand mold was greater than that of thegreen sand mold.

4. Conclusion

For this study, based on the method described byMotoyama,10) a device was developed for dynamicmeasurement of both the constraining force from a greensand mold and the contraction of the cast iron casting.The constraining forces to the casting from the green sandmold and the casting contraction were measured dynamicallyfrom the start of solidification to 200°C. Comparing withthe results reported by Marumoto et al.2), and the followingconclusions were obtained.(1) During solidification, the casting expansion of the

casting in the green sand mold was recognized to begreater than that in the furan sand mold.

(2) During cooling, the furan sand mold constrains thecasting more than the green sand mold. The contractionof the casting during the cooling was recognized to be

greater in the green sand mold than in the furan sandmold.

Acknowledgements

This research is supported by Kimura Foundry Co., Ltd.

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