In injection molding, three temperatures are said to determine part quality: the melt temperature, the mold temperature and the cooling water temperature. The most neglected of these is the mold temperature — yet it touches everything from gloss to warpage, from cycle time to mechanical strength.
What Does a Mold Temperature Controller Do?
A mold temperature controller (Temperiergerät in German) keeps the mold at the target temperature by passing a fluid at constant temperature through the channels inside the mold — heating it when needed and cooling it when needed. It must not be confused with "cooling": the aim is not a low temperature but a correct and constant temperature.
If the mold temperature is not managed correctly:
- Surface quality falls: matte areas, flow marks and weld lines become pronounced
- The part warps: if the two halves of the mold are at different temperatures, the part shrinks asymmetrically as it cools
- In technical plastics (PA, PBT, POM) crystallization remains incomplete — dimensional stability and strength fall
- The cycle time is either unnecessarily long, or internal stress forms from opening too early
Water-Based Systems (90–160 °C)
Water is an excellent heat carrier: thanks to its high specific heat, it carries far more heat than oil at the same flow rate. Standard atmospheric systems work up to 90 °C; pressurized water systems keep the water under pressure and go up to 120, 140 and 160 °C.
Rummel water temperature control units cover this range in steps:
- [TEMP 90 °C](/en/category/serie-temp-90c-water) — polyolefins, ABS, general-purpose production
- [TEMP 120 °C WDC](/en/category/serie-temp-120c-wdc) — a directly cooled, fast-response system
- [TEMP 140 °C](/en/category/serie-temp-140c-pressurized-water) and [TEMP 160 °C](/en/category/serie-temp-160c-pressurized-water) — technical plastics such as PA, PBT and PC that require a high mold temperature
Oil-Based Systems (200–300 °C)
Above 160 °C water loses its practicality; thermal oil comes into play. Oil-based systems provide temperatures up to 200 °C and 300 °C:
- [TEMP 200 °C OIL](/en/category/serie-temp-200c-oil) — PPS, PSU, high-temperature PA applications
- [TEMP 300 °C OIL](/en/category/serie-temp-300c-oil) — ultra-performance plastics such as PEEK, PEI and LCP
Oil's heat-carrying capacity is lower than water's; so a higher flow rate and more heater power are needed to do the same job. In every application below 160 °C water should be preferred — it is more efficient, cleaner and more economical.
Critical Parameters in Selection
1. Temperature range: Which step does the recommended mold temperature of your material fall into? 2. Heater power (kW): Determines how long it takes to bring the mold mass up to target 3. Pump flow and pressure: Must be able to overcome the pressure drop in molds with narrow channels — turbulent flow is essential 4. Cooling capacity: Being able to remove excess heat is as important as heating 5. Multi-circuit distribution: In large molds, zones can be held at different temperatures with separate circuits
Industry 4.0: The Temperature Controller That Talks to the Machine
A standout feature of modern Rummel units is direct communication with the injection molding machine: via OPC-UA, Profinet, Modbus and serial protocols the machine sends the set value to the temperature control unit, and the actual temperature is monitored and recorded on the machine screen. Temperature becomes a parameter of the process rather than of a separate device — now essential in automotive and medical projects that require traceability.
For all temperature steps and unit models, take a look at our temperature control systems page; for a capacity calculation suited to your mold, contact us.