For the 1.5 mm thick plaques, higher moduli occur as the Graetz number decreases as shown in Fig.
9, may be responsible for the sensitivity of the mechanical properties to the Graetz number. At a 295 [degrees] C melt temperature, VA appears to be near a solid-like state.
the stress and Graetz number, it appears doubtful that the molds could be scaled to a different thickness and yield the same properties.
This equation may be made dimensionless by substitution of 1/2L/U for the contact time, [t.sub.c], of polymer in the center of the mold, and by using the definition for the Graetz number. These substitutions lead to the following form of the equation used in this work:
For a Graetz number of 10 and a dimensionless thickness (y/H) and length (z/L) of 0.447 and 0.5, respectively, the dimensionless temperature ([Theta]), is calculated to be 0.9.
Correlating the flexural moduli to the Graetz number also failed to demonstrate that the optimum properties occurred at the same heat transfer condition.
This transition occurred at a Graetz number of [approximately] 10.
For this blend, it does appear that optimum mechanical properties can be found by changing the injection molding variables so that the Graetz number is in the vicinity of 10.
where Re is a modified Reynolds number, [Rho]U[H.sup.2]/[[Eta].sub.0]L, Gz is the Graetz number, U[H.sup.2]/[Alpha]L, Br is the Brinkman number, [[Eta].sub.0][U.sup.2]/k[Delta]T, and [Alpha] and k are the thermal diffusivity and conductivity, respectively.
The shear stress, residence time, and Graetz number can be compared for molds of the same aspect ratio and for molds with the same length but with different thicknesses.