Coating Characterization Findings
Table 2 illustrates that the coating with the highest surfactant level offered the best balance between the transfer and leveling properties. The area of the shear rate versus viscosity curve provides infor- mation about the rate of recovery of the
Table 2 summarizes the findings obtained from the various wet coating characterization tests. The wet coating tests were able to detect the subtle differences in surfactant levels be- tween coatings. This was most prevalent from the findings of the Hercules hi-shear viscometer test. The leveling index describes the ability of a coating to level itself after its appli- cation. It is a measurement of the degree of departure of the coating from Newtonian behavior. Newtonian fluids are flu- ids that flow in a manner similar to water. The leveling index is calculated from the shear rate versus viscosity curve (Figure 3) by dividing the viscosity of the coating at the peak shear rate by the viscosity at lowest shear rate. The low shear viscosity value represents the leveling properties; meanwhile the high shear viscosity value represents the transfer properties of the coating. A high leveling index value de- notes a better balance between the trans- fer and leveling properties of the coat- ing.1
coating. The rate of recovery signifies the change in viscosity due to the change in the shear rate of the coating. Figure 3 clearly illustrates these differences in recovery rate (area of the curve), especially for the lowest surfactant level coating. Ct3 (0.15% surfactant) demonstrated minimal variation in viscosity throughout the shearing process and was found to have the least amount of sedimentation after prolonged stor- age. It is important to note that all three coatings are shear thinning and had different low shear viscosity values (Figure 3) as reflected in the reported values in Table 2.
Figure 3. Shear rate versus viscosity curve obtained from the Hercules hi- shear viscometer.
Table 1. Properties of Silica Sand
Table 2. Coating Characterization Tests Results (Average of 3 Replicates Reported)
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International Journal of Metalcasting/Spring 11
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