Screening design for earplug production

For the apparent density, the contrasts calculated for the seven factors (in gcm ) and their expressions in terms of confounded factorial effects are as follows  

The contrast values for factors A, B, C, F and G fit quite well to a straight line through the origin, and therefore can be interpreted as resulting from experimental error. The values of the other two contrasts, which include the main effects D and E, lie far from the line, especially the value of D. It appears, then, that the reticulate solution flow rate (D) and the mold temperature (E) do affect the apparent density values. The E contrast can be interpreted as the mold temperature effect if one assumes that the two-factor interactions in the definition of contrast Ze are negligible. If a similar assumption is made for Zd, it can be interpreted as the main effect of the reticulate solution flow rate. 

The mold temperature effect is negative, resulting in lower apparent density values, which is desirable for the final product. Since operational constraints did not permit decreasing this temperature below 56 °C, the temperature was held at this value for further experimentation. The reticulate solution flow rate, on the other hand, was varied in subsequent phases of the optimization study (see case studies in Sections 3A.9 and 6A.4). 

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