Preparation of Disc-Shaped PUCB Specimens
PUCB specimens were prepared using washed and dried round grain silica sands (Table 1). Sand systems were se- lected to represent distributions that have coarse, medium, and fine AFS Grain Fineness Numbers (GFNs).
The PUCB disc specimens were prepared by blowing them with a laboratory core blower into a three-cavity disc core box (Figure 2). Each cavity had its own gate opening and a vent opposite the gate.
Materials:
Silica sand (see Table 1), PUCB binder system Part 1 and Part 2 (mixture ratio 54 Part 1: 46 Part 2).
Equipment: DeLonghi mixer, core box, core blower.
Procedure: 1. Add weighed sample of sand to DeLonghi mixer. 2. Make two pockets in the sand. 3. Add Part 1 component into one pocket and Part II to the other pocket.
4. Mix for one minute. 5. “Flip” mixture and mix for one additional minute. 6. Using laboratory core blower set at 0.414 MPa for 0.5 seconds, blow the mixed sand into the three cavities of the core box (Figure 2).
7. Cure by gassing with triethylamine (TEA) using a Luber gas generator. Gassing parameters: 0.5 seconds gassing with TEA, followed by an air purge for 10 seconds. (Gas pressure was 0.138 MPa and air purge pressure was 0.207 MPa.)
Preparation and Characterization of the Coatings
The coatings used in this study were ceramic-graphite coat- ings similar to those used by iron sand casting foundries. The coating formulations were identical except for different levels of surfactant. Surfactants are chemical agents that serve two purposes in the coating. First, they serve as a wetting agent that contributes to the reduction in surface tension of the wa- ter based coating. Second they reduce the interfacial tension between two liquids,1
which were water and oil in this study.
The coatings were received at 46% solids and diluted to 38% as recommended by the coating supplier. A Lab- Wave IV microwave solids analyzer was used to deter- mine the solids content and deionized water was used to dilute the coating to 38% solids. Deionized water limits the variability that may be caused by the impuri- ties in tap water. Tap water contents may vary from one geographical location to another which could cause in- explicable inconsistencies in the experimental results. In addition to the solids content, the wet coatings were fully characterized using the tests identified in Phase I of this study; gravimetric cup density, hydrometer (Baumé), surface tension, and the Hercules hi-shear viscosity tests.1, 5
Materials: Coatings: Ct1 (0.35% surfactant), Ct2 (0.25% surfactant), and Ct3 (0.15% surfactant); deionized water.
Equipment:
CEM SmartTrac 4, rapid moisture analyzer, mixer (vari- able speed).
Procedure:
The coating was stirred manually to disperse the par- ticles that settled to the bottom of the container during transport and storage. The coating then was placed un- der a mixer at low speed for 20 minutes to uniformly disperse the coating. The mixer was set at low speed to avoid vortexing which would draw unwanted air into the coating. After mixing, the solids of the coating were checked using the microwave solids analyzer. Deion- ized water then was added to dilute the coating to the desired 38% (± .03%) solids level. The diluted coating then was placed back under the mixer and allowed to mix for 15-20 minutes before the solids level was re- checked. The coating then was removed and placed in an airtight plastic container to prevent any evaporation or absorption of moisture from the surrounding envi- ronment. Three samples of the diluted coating were taken and used to perform the gravimetric cup density, hydrometer (Baumé), surface tension, and the Hercules hi-shear viscosity tests following Technical Associa- tion of the Pulp and Paper Industry (TAPPI) standard testing procedure.5
Figure 2. Core box for disc specimens. International Journal of Metalcasting/Spring 11 9
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