Mar 11,2026
Type selection and matching of mold thermostats: From power calculation to precision requirements
Type selection and matching of mold thermostats: From power calculation to precision requirements
Mold temperature controller, Temperature control unit, Cooling capacity, Heating power, Thermal management
The mold temperature controller (modul thermometer) is the core auxiliary device that maintains the heat balance of the mold. It is responsible for transporting a constant-temperature medium (water or oil) at a certain pressure and flow into the mold‘s cooling/heating channel, taking away the heat released by the plastic melt, or preheating the mold to a specified process temperature. Whether the model selection of the modul thermometer is reasonable directly determines whether the mold can work steadily within the optimal temperature range, thereby affecting the product quality and shaping cycle. Therefore, scientifically performing model selection of the modul thermometer is a systematic engineering undertaking involving thermodynamic calculations and process matching.
The first step in selecting the type is to determine the necessary heat transfer medium. Water is a larger heat capacitor, more efficient in heat transfer, less expensive, and environmentally friendly, and is the preferred cooling medium. However, the boiling point of water is limited by pressure, and the applicable temperature is usually between 10°C and 120°C. When the process temperature exceeds 120°C, or when the mold temperature needs to be steadily controlled at higher temperatures, an oil thermostat must be chosen. Oil has a high boiling point, which can reach above 300°C, but it has only half the heat capacity of water, is less efficient in heat transfer, and is prone to oxidation and carbonization at high temperatures, requiring regular replacement. Therefore, the choice of water or oil depends on the maximum working temperature and temperature control accuracy requirements of the mold.
The core of the type selection is the calculation of the heating power and cooling capacity required. The heating power is used to heat the mold from room temperature to working temperature, or to maintain temperature during production intervals. The calculation formula is usually based on the mass of the mold, relative heat capacity, target temperature rise, and heating time. A rough estimation method is that heating power of about 0.12 kW per kilogram of steel mold to 100°C is required. More precise calculations require consideration of heat radiation loss and heat conduction loss on the surface area of the mold. The cooling capacity is the heat that the modulus must take away during steady-state production. This portion of heat is mainly derived from the heat released by the solidification of molten plastic, which can be calculated by the injection volume of the material, relative heat tolerance, melting heat, and shaping cycle. The cooling capacity of the modulated thermostat must be greater than this value, leaving a certain excess, which is usually chosen as 1.2–1.5 times the calculated value.
Another key parameter for type selection is the flow and lift range of the pump. The flow determines the speed at which the cooling medium flows through the waterway of the mold. To achieve efficient heat transfer, the medium in the waterway should be in a turbulent state (Reynold number > 4000). The minimum required flow can be calculated based on the diameter and length of the waterway. The lift range is the ability of the pump to overcome the waterway resistance. The more complex, longer, and more curved the waterway of the mold, the greater the resistance, and the higher the lift range required. Therefore, when selecting a type, the waterway design diagram of the mold must be provided to the modulated thermostat vendor to accurately calculate the pressure reduction and select the matching pump. The power and type of the pump (centrifugal pump, gear pump) must also be determined based on the medium and working conditions.
Temperature control precision is a core metric for measuring the performance of modulated thermostats. Typical modulated thermostats have a temperature control precision of around ±3°C, suitable for most general-purpose plastics. However, for temperature-sensitive products such as precision optics and medical catheters, ±0.5°C or even higher control precision is required. This requires modulated thermostats to have high-precision PID controllers, high-quality sensors, and fast-responsive heating/cooling switches. High-precision modulated thermostats typically use “proportional valves” or “triple valve” to fine-tune the flow of cooling water, rather than simple “on-off” controls, achieving smooth temperature regulation.
The type of modulated thermostat also needs to consider the need for multi-circuit independent control. For large moulds or moulds with special requirements for temperature distribution, it may be necessary to divide the mould into multiple independent temperature-controlled areas (such as dynamic side, fixed side, slider, form core), each controlled by a separate modulated thermostat. This multi-circuit control can precisely adjust the temperature of different areas, compensate for thermal dissipation differences, and achieve a more uniform modulated temperature distribution. When selecting, the number of circuits required and the power/flow requirements for each circuit should be clear.
In summary, modulating thermostat model selection is a process that accurately matches the thermal characteristics of the mold, process requirements, and equipment performance. The correct model selection not only ensures product quality, but also prevents equipment overload or energy waste, which is an important part of achieving efficient and stable injection molding production.
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