A cooling system uses water or another cooling medium to flow through the cooling circuits of the mold to control the temperature of the metal surfaces that come in contact with the plastic being molded.
The following table lists the most commonly used coolants:
| Coolant | Temperature |
|---|---|
| Ordinary water from mains or a cooling tower | 20°C–25°C |
| Ordinary water from a heater/circulator unit | > 30°C |
| Cold water from a chiller | > 10°C |
| Water mixed with antifreeze from a chiller | > ‒5°C |
| Oil-from a heater/circulator unit | > 80°C |
An important parameter that the mold designer must know is the pressure of coolant available at the plant. If the available pressure is less than the pressure that the cooling channels require, the cooling of the part could be ineffective due to non-turbulent flow of coolant.
Adding glycol (antifreeze) to the coolant will raise its viscosity, resulting in higher pumping pressures being required, or a lower flow rate. Using a chilled water and glycol mix may be less effective cooling than a well-designed circuit with plain tower water circulating at the optimum flow rate. Oil is generally used only when very high mold temperatures are required. The available pump capacity must be greater than that required by the cooling circuits in the mold.