Mold cooling requirement (chiller capacity)

What is this calculation used for?

Finds how much heat the cooling water must remove from the hot plastic entering the mold. Used to select chiller or tower capacity for a new line, to know the required water flow rate per mold, and to check whether an existing chiller can take on one more machine.

How do I choose temperatures for a new line?

• On a line that is not yet installed, you cannot measure the water’s inlet and outlet temperature; these are design values and you choose them.
• First determine the mold temperature: it is set by the material (the material pages list the recommended mold-temperature range). The cooling water must be lower than the mold temperature.
• Water from the cooling source: a tower delivers roughly 28–32 °C in summer, a chiller typically 8–15 °C depending on its setting.
• Important: the “inlet–outlet difference” is how much the water heats up while passing through the mold; it does not show how many degrees the mold cools. The mold stays at a fixed temperature (a separate target), and the water simply carries heat away from it. Mold temperature is always higher than the water temperature.
• Cold mold (roughly 20–50 °C, e.g. PP, PE, ABS): the water is meant to cool the mold. A chiller or sufficiently cold tower water is used. If the mold temperature is 40 °C or below and tower water rises above 30 °C in summer, tower water will not be enough and a chiller is needed.
• Hot mold (roughly 70–120 °C, e.g. glass-filled PA, PC, PBT, PEEK): the mold is not cooled but kept hot. For this, not a chiller but a mold temperature control unit (working with hot water or oil) is used; water is supplied close to the mold temperature. The heat left behind by the plastic in the mold still has to be removed, and the unit does this with its own cooling water. The heat load and flow rate on this page are still useful when selecting that unit.
• Inside the mold, the inlet–outlet difference is kept small, usually 2–5 °C. If the difference grows, the water-inlet side of the mold stays colder than the outlet side, creating a temperature difference across the mold surface — which means warpage and dimensional problems. You increase the flow rate to keep the difference low.
• The outlet temperature follows automatically: inlet temperature + difference.
• This calculator gives the total water quantity. The distribution of flow across the mold’s cooling circuits, and whether the flow is sufficiently turbulent, is checked per channel by the main calculation tool, the Process analysis page. When selecting a chiller, also rely on the manufacturer’s catalog.

How is it calculated?

• Heat = shot weight × (cp × (T_melt − T_eject) + latent heat) ÷ cycle time × fraction to water
• Water flow rate = heat ÷ (4.186 × water temperature difference)

Results are general engineering estimates; the machine catalog, material data sheet and trial run take precedence.