2020 AFS Proceedings of the 124th Metalcasting Congress Paper 2020-076 (10 pages)

A Trial to Evaluate Various Chemically Bonded Sand Disc-Shaped Specimens for Surface Finish and Erosion Defects

M. Raval Altair Engineering Inc., Troy, MI

S. Ramrattan Western Michigan University, Kalamazoo, MI

Copyright 2020 American Society

ABSTRACT greatest proportion of sand/metal defects associated with thin and tiny sections in the casting occurs with the Casting issues on thin wall surfaces and in complex chemically bonded sand process. AFS Research geometry interface is not negligible and can result in Committees are studying the troublesome and energy costly defects. prefer chemically bonded sand intensive issues related to sand defects with a plan to mold over green sand when it comes to with thin- minimize or eliminate the concern. This study examines wall sections and complex internal dimensions. Still, various chemically bonded silica sand systems for sand interfacial defects defects in chemically bonded sand erosion and surface finish in cast iron and aluminum process are an issue. This paper addresses chemically castings at different head heights. bonded sand erosion and surface finish issues for aluminum and cast iron castings. Erosion in chemically Erosion defects are major concerns with any casting bonded sand can occur when molten alloy dislodges process involving bonded sand. Erosion usually occurs grains of sand, resulting in a rough as-cast finish. within the gating system and/or at a mold-metal interface of the cavity. Sand erosion is caused when molten Based on a casting trial used to study the erosion in alloy dislodges grains of sand resulting in a rough as-cast alternative green sand specimens; a new trial was finish. This defect is associated with turbulent metal fill. developed to teste to evaluate erosion on multiple This phenomenon of high velocity pouring can cause chemically bonded sand specimens simultaneously. Gray surface defects on casting. The reasons for erosion defects cast iron and an aluminum alloy were delivered from are due to one or a combination of the following: design, controlled head pressures and temperatures to achieve a raw materials (sand, binder and additives), molding and turbulent flow across chemically bonded sand specimens filling technology. Poor sand characteristics such as prior to solidification of the castings. Flow and reactive contaminants, weak sand properties, turbulent solidification simulation of the casting trial model was metal flow, head pressure, cross-sectional area of the conducted. The simulated predictions were evaluated gating system and molding technology are some examples along with results of aluminum and gray cast iron casting that can lead to erosion defects. trials at two different head heights. Results show that in both alloys there are surface differences among the Erosion phenomenon is the relation between a stationary various chemically bonded sand systems studied. entity and fluid flow. In other words, it is the defect caused by the kinetic energy of fluid flow. A sand mold Keywords: casting surface finish, remains stationary while molten metal flows inside the chemically bonded sand, disc-shaped specimens, sand cavity with some definite momentum. This impetus can erosion dislodge sand particles. When the bond between two particles breaks, because of flow momentum a lift occurs, INTRODUCTION and it removes these particles from the surface. This progression causes cavities on the mold surface that leads In the foundry industry, there can be many types and to surface roughness. causes of metal casting defects. These casting defects can be related to the alloy and/or the mold/metal interfacial Solidification simulation is a valuable tool in the foundry issues. There are several publications dedicated to industry. They can be used to predict casting defects. imagining and identifying causes for these defects. Simulations are mainly used for design and sometimes for However, the processing parameters related to such manufacturing problem solving. Nowadays the metal defects are lacking.1,2 Casting issues at the sand/metal casting industry is using a solidification simulation interface result in defects such as inclusions, veining, software to predict casting quality. The rational for using penetration, scabs, scars, erosion, etc.3 Moreover, the this approach would be to identify casting design issues

Page 1 of 10 2020 AFS Proceedings of the 124th Metalcasting Congress Paper 2020-076 (10 pages) and detect metallurgical concerns prior to actual materials and processes, testing will be performed over production. various sand binder systems. The disc-shaped specimens used in this study is identified in Table 1. Current solidification simulation tools contain superior alloy property data but property data for granular media is PUCB Specimens lacking. Real time information such as temperature, The PUCB disc-specimens were prepared by blowing the pressure and fill velocities derived from simulation specimens with a laboratory blower into a core box. software is useful in understanding erosion phenomena. Researchers can make a reasonable argument that either Materials: metal flow or the sand binder properties are responsible The sand was a washed and dried Wisconsin round grain for erosion defects by studying the properties of the silica sand 65 GFN, 3 screen, roundness/sphericity chemically bonded sand and simulation results. (Krumbein) 0.8/0.8, pH 7.1, acid demand 0.8 and the total Polyurethane binder level was 0.9% B.O.S. This chemically bonded sand erosion study uses a casting trial model developed at Western Michigan University Procedure: (WMU) and involves acquired related data from both 1) Add weighed sample of sand to DeLonghi Mixer. casting simulation and laboratory sand testing. The 2) Make two pockets in the sand. purpose of this study was to determine if there are 3) Add Part 1 component into one pocket and Part II to different erosion tendencies among various chemically the other pocket. bonded sands with respect to iron and aluminum castings. 4) Mix for 1 minute. 5) “Flip” mixture and mix for 1 additional minute. OBJECTIVES 6) Using laboratory core blower set at 0.379 MPa (55 1. To measure the surface roughness of a cast psi) for 0.5 seconds and blow the mixed sand into the alloy/chemically bonded sand specimen interface at four cavities of the core box. different head pressures. 7) Cure by gassing with TEA using a Luber gas 2. To measure the volumetric changes occurring at a generator. Gassing parameters: 1 second gassing with cast alloy/chemically bonded sand specimen TEA, followed by an air purge for 6 seconds (gas interfaces at different head pressures. pressure at 0.172 MPa (25 psi) and air purge pressure at 0.103 MPa (15 psi)).

METHODOLOGY Refractory Coated PUCB: Some of the PUCB disc-specimens were refractory An experimental model was designed to perform a casting coated. The coating used in this study were ceramic- trial on chemically bonded sand specimens. The graphite coatings similar to those used by iron sand chemically bonded sand specimens will be used as the casting foundries. A LabWave IV microwave solids mold/metal interfaces during casting. The methodology analyzer was used to determine the solids content and was divided into three areas: deionized water was used to dilute the coating to 38% 1. Preparation of disc-shaped chemically bonded solids. Disc-shaped specimens were manually dipped into sand specimens. the mixed coating to the same depth for two seconds. 2. Gray cast iron and aluminum casting trials. 3. Data gathering, observation and analysis. SHLHB Specimens SHLHB specimens were prepared using a hot-box core Note: All chemically bonded sand systems used in the making technique used in industry when employing resin experiment were tested in controlled laboratory coated sand systems. conditions: the ambient temperature at 70 ± 2˚F (20 ± 1˚C) and relative humidity at 50±2%. Materials: The sand was an Illinois round grain silica sand 60 GFN, DISC SHAPED SPECIMENS 3 screen, roundness/sphericity (Krumbein) 0.7/0.7, pH In the present work, specimens of phenolic urethane 7.1, acid demand 0.8 and the total Phenolic-Novolac amine cold box (PUCB), hot-box shell (SHLHB) and 3D binder level was 1.3% B.O.S. printed furan (FUR3D) were fabricated. Procedure: Specimens (50 mm in diameter by 8 mm thick) were The hot-box cure temperature used for producing provided by three different manufacturers. The specimens was 250°C for 40 seconds. manufacturers all used dissimilar specimen fabrication techniques, sands, binder levels, and chemistries. The FUR3D Specimens chemical sand binder systems used were not optimized for These disc-specimens were 3D printed. the casting alloy, fill temperature, or head-pressure. To ensure the proposed approach is valid across numerous

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Materials: the final casting. This prediction will allow the The sand was a washed and dried round grain silica sand comparison of actual castings to obtain information for 80 GFN, 2 screen, roundness/sphericity (Krumbein) improving the design. Table 1 shows values obtained 0.8/0.8, pH 7.0, acid demand 0.8 and the total Furan from simulation results. binder level was 1.4% B.O.S.

Procedure: The FUR3D specimen were printed on an ExOne S Max #8. FUR3D printed disc-shaped specimens were produced within the same build-box. Processing parameters such as binder level, recoater angle, and print speed were controlled.

Table 1. Disc-Shaped Specimens Types

Specimens Fabrication Method PUCB Phenolic urethane amine cold box Refractory coated phenolic urethane Coat-PUCB amine cold box Figure 1. CAD image of erosion model.

SHLHB hot-box shell Table 2. Simulation Predictions FUR3D 3D printed furan No. Temperature Velocity (m/s) CASTING TRIALS Aluminum 6” 730 1.4 The casting trial consisted of the following steps: Gray Cast Iron 6” 1511 (℃) 1.37 i. model optimization and simulation, Gray Cast Iron 9” 1513 1.39 ii. an experimental match-plate pattern, iii. preparation of green sand mold, Fig. 2 - 4 shows the bottom view of analysis results taken iv. principle of the gating design, and from simulation. v. melting and pouring

Model Design and Simulation A model was used from previous green sand erosion study. Small amount of optimization was done on the model in terms of well depth and core print. Green sand molds were built using sand from the same mulling cycle. The sand-to-metal weight ratio for all molds was ~3:1. All molds were produced with a pouring sleeve for constant Figure 2. Temperature and Velocity generated during head-pressure and fill velocity. Each mold contained four metal filling in simulation for Aluminum 6”. cavities with core prints but there was no positional effect to be assessed on the casting. This approach allowed possible variation in casting quality to be assigned to only the specimens.

Model optimization was the first step, CAD software was used to regenerate an idea about the erosion model. In gravity casting technology, the value of fluid flow which can cause erosion is considered to be a minimum of 1 3 Figure 3. Temperature and Velocity generated during m/s (~40 inch/sec). Using simulation software, metal filling in simulation for Gray Cast Iron 6”. optimization was done on the CAD model to identify velocities higher than minimum. Altair Inspire Cast was used for simulating model under specific boundary conditions and constant filling parameters. Fig. 1 shows a CAD design for the erosion model with disc specimen imprint.4

Simulation software was used before actual casting trials. The purpose of this tool is to make predictions of some Figure 4. Temperature and velocity generated during factors such as temperature, pressure, shrinkage etc. in metal filling in simulation for gray cast iron 9”.

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EXPERIMENTAL MATCH PLATE symmetrical to the shell core prior to capping with the In this experiment, four different chemically bonded sand cope. A model of the mold assembly is shown in Fig. 8. It specimens (Table 1) were compared using a match-plate is important to point out that both the shell core and the to perform a casting trial. The match-plate was designed shell cone was refractory coated to protect the wetted using CAD software (CREO 3.0). The model was surface against erosion during fill. modified in Altair Inspire Cast such that constant flow and a particular range of velocities could be achieved from a 6 inch head and a 9 inch head. The aim of the experiment was to determine if erosion issues exist at the cast iron and aluminum fill parameters.

The model includes a of match-plate pattern, shell sand plate with runners and shell sand cone on the surface of the parting line. Figures 5 through 7 shows the design of these three important aspects of the models.

Figure 7. Shell cone used to separate flow and encourage turbulence.

Figure 5. Drag side of match plate pattern to create a cavity inside the mold.

The drag side pattern Fig. 5 was used to develop a drag mold. In the four cavities of the drag mold four disc- shaped specimens were arranged such that a small portion Figure 8. Cross-section of the model showing an of their height (~4 mm) was raised above the parting line. assembled mold.

A cope mold with a sleeve was developed to receive a Preparation of Green Sand Mold specialized shell core. The sleeve from the cope aligns It was important to keep the green sand formulation with the shell core to simultaneously deliver the molten simple so that potential errors in preparation would not metal over the specimen surfaces (Fig. 6). affect the analysis. Apart from sand, clay, and water, no additives were introduced to the green sand systems used in this study. Compactability was monitored continuously. The water additions were then raised or lowered accordingly on that batch of sand to produce the 35% target compactability. The sand was not discharged until the compactability was on target. Thus, the green sand systems used in this study were tempered to a desired compactability, and property tested (as-mulled). The silica base aggregate (lake sand 62 [4] GFN) used in the study came from Michigan. The green sand system used in the study was mulled (200 kg Simpson Sand Muller) at WMU Metal Casting Laboratory. The green sand system used a clay bond pre-blend made up of 20 % Figure 6. Shell core used to deliver molten metal over Southern Bentonite / 80 % Western Bentonite where total the specimen surfaces. clay added was 8.0% BOS (methylene blue clay was 7.45%), and water added to produce the desired The shell core was fitted onto the four specimens. In compactability. addition, a shell cone (Fig. 7) was affixed to the drag and

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Principle of Gating Design Melting and Pouring: A pressurized gating design was used to control the fill The mold was poured where the AFS standard chemically of the casting (Fig. 9). The gating ratio is Area of : bonded sand specimens (4) were set into the drag. The Area of runners: Area of ingates and was measured 23.4: drag mold contained four symmetrical cavities with no 1.0: 1.8 (area units are mm2/100). This design allowed a positional effect to be assessed on the casting. This constant fill time (~9 sec.) with the turbulent metal flow approach allowed possible variation in casting surface over the green sand specimens. This allowed the quality (specimen/metal interface) to be assigned to the researchers to investigate potential erosion issues. The sand specimens. The sand-to-metal ratio for the casting parameters of temperature, pressure and velocity of fill was ~3:1. were discussed under the sub-heading “Model Design and Simulation.” The mold was manually poured, and gray cast iron (Table 3) was (average pouring time ~9 and sec., temperature at pour ladle 1510ºC (2642ºF), CE = 4.16 and = 0.021”) delivered through a direct pouring sleeve fitted. The mold was poured to a 9-inch (228.6) and a 6-inch (152.4 mm) head-height. Similarly, aluminum 356 (Table 4) was poured from a 6 inch at 730ºC. The mold was prepared and poured at WMU Metal Casting Laboratory. The casting was allowed to solidify under an ambient temperature. After air-cooling and shakeout the casting was sectioned near the specimen/metal interfaces.

Figure 9. Cut-section of erosion model showing gating design in relation to specimens.

Table 3. Gray Iron Chemistry

C Mn P Si Cr S Al Pb Ti Mo Cu Ni Sn Sb Mg Fe

3.59 0.65 .097 2.39 0.103 0.101 0.001 <0.001 0.011 0.02 0.13 0.06 0.009 0.002 0.0025 92.94

Table 4. Aluminum (356) Chemistry

Al Si Fe Cu Mn Mg Cr Ni Zn Ti Ca Cd Na Pb Sr 92.2 7.07 0.163 0.046 0.018 0.331 0.007 0.006 0.018 0.098 0.0007 0.002 0.001 0.016 0.008

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DATA GATHERING and shakeout, the as-cast runner interfaces with the Data gathering is divided into two steps: specimens was measured using the 3D Macroscope. 1. Shakeout and Observations 2. Analysis using 3D-Macroscope • Disc-shaped specimen surfaces • As-cast surfaces

Shakeout and Observations After solidification and cool-down of the casting, the next step was to shakeout from the green sand mold manually (Fig. 10). The researchers took care in removing the cope from the drag to observe how the various disc-shaped sand specimens collapsed from the runners’ interface of the casting. As-cast surfaces particularly the runners were gently cleaned using a wire brush. Figure 11. 3D-Macroscope.

RESULTS AND DISCUSSION

The observations and findings in this study are shown in Table 5, 6 and 7. All chemically bonded disc-shaped specimens tested showed some erosion tendency and surface finish differences. Both alloys at the respective head height showed difference in as-cast surface and volumetric change among the four disc-shaped specimens. It is important to recognize that an as-cast surface roughness will be better than the specimen surface. Further, the researchers are considering an 8 µm change in roughness as significant.

As would be expected the refractory coated specimens (Coat-PUCB) had the superior surface finishes regardless of alloy. In general the uncoated disc-shaped specimens had better finishes at the lowered gray cast iron head

height. For aluminum the surface finishes were no Figure 10. Casting product after shakeout of green different among the coated and uncoated specimens and sand from the mold. superior to gray cast iron. With respect to sand erosion, the uncoated PUCB specimen showed significant Analysis using 3D-Macroscope volumetric change on the as-cast surfaces of both alloys. To evaluate the disc-shaped sand specimen surfaces and the as-cast surfaces a non-contact 3D Measuring Macroscope (Fig. 11) was used. The 3D Measuring LIMITATIONS Macroscope allows the surface of specimens as well as as-cast surfaces (metal runners) to be captured (at ambient This model can focus on just four chemically bonded sand or elevated temperature). Using the 3D-Macroscope and systems that can be used in the foundry industry. There its accompanying software, high-speed, high-accuracy 3D are many other binders, refractory coating, molding measurement of surface finish and volumetric change processes and alternative granular media that are under were documented. development.

Before performing the actual casting trial, surface texture and roughness of the disc-shaped specimens was measured using the 3D Macroscope. After the casting trial

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Table 5. Chemically Bonded Sand and As-Cast Metal Surface Analysis for Gray Cast Iron 6” Head

Specimen As-Cast Volumetric Disc-Shaped Specimen Surface Surface Change Specimen As- Cast Surface Surface Roughness Roughness (µm) (µm) (mm3)

PUCB 43 18 25

Coat-PUCB 20 21 15

SHLHB 45 41 25

FUR3D 31 29 30

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Table 6. Chemically Bonded Sand and As-Cast Metal Surface Analysis for Gray Cast Iron 9” Head

Specimen As-Cast Volumetric Disc-Shaped Specimen Surface Surface Change Specimen As- Cast Surface Surface Roughness Roughness (µm) (µm) (mm3)

PUCB 49 66 48

Coat-PUCB 20 30 25

SHLHB 40 33 19

FUR3D 28 28 20

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Table 7. Chemically Bonded Sand and As-Cast Metal Surface Analysis for 356 Aluminum 6” Head

Specimen As-Cast Volumetric Disc-Shaped Specimen Surface Surface Change Specimen As- Cast Surface Surface Roughness Roughness (µm) (µm) (mm3)

PUCB 46 12 75

Coat-PUCB 19 14 12

SHLHB 50 16 8

FUR3D 29 20 19

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CONCLUSION AND RECOMMENDATIONS

A practical casting trial was developed to compare and evaluate chemically bonded sand systems for erosion and surface finish with respect to cast iron and aluminum. The research reinforces a need to study sand erosion with respect to chemically bonded sand and potential need for a refractory coating.

Results of this study show that a casting trial can be used to discriminate among the surface finish and erosion tendency for various chemically bonded sand systems. Further, the results from such casting trials can be related to laboratory test data on disc-shaped specimen and ultimately for the enhancement of solidification simulation tools.

ACKNOWLEDGMENTS

The authors thank Mr. Mayank Patel and Mr. Michael Konkel from the WMU Metal Casting Laboratory for their technical support.

REFERENCES

1. “Analysis of Casting Defects,” American Foundry Society, Schaumburg, IL, ISBN-10: 0874330041 (1974, 2002). 2. Rajkolhe, R., and Khan, J. G., “Defects, Causes and Their Remedies in Casting Process: A Review,” International Journal of Research in Advent Technology, E-ISSN: 2321-9637, Vol.2, No.3 (March 2014). 3. Pike, A., Ramrattan, S., and Shah, R., “Comparing Simulation with Gray Iron Casting Trials using PUCB Disc-Shaped Sand Specimens,” AFS Transactions, Paper 18-036, (2018). 4. www.solidThinking.com

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