Through the hole Figure 1


readings, but the deviation was higher when readings from all four operators were compared. In practice, this would mean if operator 1 takes all readings in a consistent range, but operator 2 takes readings that all are 2-3 seconds higher, the deviation is high even though both operators were consistent on their own. For the purpose of our testing, these were referred to as the operator average and overall average. Operator average shows good agreement (precision) among the operators’ individual measurements, but the overall average, which is of all readings across the operators, shows more variation (accuracy). In a foundry setting, these averages could be interpreted as follows: • Operator average: George on first shift is the only operator who takes viscosity readings in the facility, and therefore his readings are only compared to his other readings.


• Overall average: George on first shift, Pete on second shift, and Kyle on third shift all take viscosity readings. Now their readings are not only compared to their previous readings, but also to the other two operators so that production can continue around the clock.


Endpoint The full data that we reference in this article can be found in the 2019 technical paper titled “A Comprehensive Analysis of Viscosity Measurements.”


® Variables


Operator Cup


Endpoint Slurry


Loadings per Slurry Table 1


For simplicity’s sake, all further results will be relative to each other in a “good, better, best” format. Through the hole and break at the bottom were the most consistent endpoints tested, due to the definitive endpoint of the tests. The one inch below method has a subjective endpoint, resulting in higher deviations. Through the hole did have some subjectivity, though, but only at the highest viscosities with the polymer plus fiber slurry where the hole took much longer to open. For a foundry, this means that using


a 1 inch below endpoint for viscosity on a polymer plus fiber slurry could introduce much more deviation (almost six seconds in our case) if viscosity is assumed as a normal distribution. This six second range is wider than the control range that most foundries use.


Cup The precision of a flow cup is the ability


to measure a viscosity consistently, while the accuracy of a flow cup is proximity of all readings to a target. In this study, cup accuracy was measured by the standard deviation of the readings of all operators with a given flow cup. For the polymer slurry, the readings


by all four operators tended to stay much closer together, resulting in a lower overall deviation across cups. In comparison, the readings of the polymer plus fiber slurry were more spread out. The polymer plus fiber slurry was more difficult to determine the endpoint, especially with the one inch below and break at the bottom methods. This was due to the addition of fiber slightly changing


the slurry rheology and


ultimately affecting how the slurry acted as pressure dropped within the cup as it drained out. As a result, the cups were more accurate on the polymer slurry


Continued on pg 12 April 2020 ❘ 33 #


4 3 3 2 5


Comments SIG, EZ, ISO TTH, 1 in, bottom


Polymer, Polymer plus Fiber L1 (Thickest)…L5 (Thinnest)


One inch below


Break at the bottom


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