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Mold Cooling
Turbulent Flow: Turbulent flow is movement of fluid in all directions and is the desired occurrence in mold cooling lines. With turbulent flow, more heat will be removed from the mold cavity. With laminar flow (the non-desired effect) the liquid heat buildup on the wall of the mold tubular line would act as an insulator so that inside laminar flow would be an inefficient heat remover.
In order to determine if one has achieved laminar flow, the "Reynold's Number" is utilized. This is a ratio that determines whether the flow of a viscous fluid through a passage is laminar or turbulent:
R = 7740VD/n
or
R = 3160Q/Dn
V= fluid viscosity, ft/s (m/s)
D= diameter of passage, in. (cm.)
n= kinematic viscosity, centistokes (see table #1)
Q= flow rate, gpm
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Values of 2100 or lower represent laminar
flow and those above 3000 denote turbulent flow.
Once you have achieved turbulent flow in water
lines, more water flow does very little to carry away more BTU's (the idea of using water in a
tool is to carry away the BTU's which the molten plastic brings into the mold). Therefore, use
larger water lines, with higher capacity pumps.
* Resources: "Rosato's Plastics Encyclopedia
and Dictionary" (Dominick V. Rosato, author); "15 Rules To Live By" (Robert Frey, author)
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