The role of injection molding mold temperature controller

The Purpose of Mold Temperature Control and Its Impact on Molded Parts. In the injection molding process, the primary goals of mold temperature control are to heat the mold to the operating temperature and maintain a constant mold temperature at that temperature. Successfully achieving these two goals optimizes cycle time, ensuring consistently high quality of molded parts.

Mold temperature affects surface quality, flow, shrinkage, injection cycle, and deformation. Excessive or insufficient mold temperature has different effects on different materials. For thermoplastics, higher mold temperatures generally improve surface quality and flow, but increase cooling time and injection cycle time. Lower mold temperatures reduce shrinkage within the mold but increase shrinkage of the molded part after demolding. For thermosets, higher mold temperatures generally reduce cycle time, which is determined by the time required for part cooling. Furthermore, in plastics processing, higher mold temperatures can also reduce plasticizing time and cycle times.

Controlling the thermal balance of the injection mold and heat transfer between the injection molding machine and the mold is crucial to producing molded parts. Inside the mold, heat introduced by plastics (such as thermoplastics) is transferred to the material and mold steel through radiation and to the heat transfer fluid through convection. Heat is also transferred to the atmosphere and mold frame through radiation. Heat absorbed by the heat transfer fluid is removed by the mold temperature controller. The mold's thermal balance can be described as: P = Pm - Ps. Where P is the heat removed by the mold temperature controller; Pm is the heat introduced by the plastic; and Ps is the heat dissipated from the mold to the atmosphere.

Prerequisites for Effective Mold Temperature Control: A temperature control system consists of the mold, the mold temperature controller, and the heat transfer fluid. To ensure heat is applied to and removed from the mold, each component of the system must meet the following requirements: First, within the mold, the surface area of ​​the cooling channels must be sufficiently large, and the flow channel diameter must match the pump capacity (pump pressure).

The temperature distribution within the mold cavity significantly affects part deformation and internal pressure. Properly designed cooling channels can reduce internal pressure, thereby improving the quality of the molded part. It can also shorten cycle time and reduce product costs. Secondly, the mold temperature controller must be able to maintain a constant temperature of the heat transfer fluid within a range of 1°C to 3°C, depending on the quality requirements of the molded parts. Thirdly, the heat transfer fluid must have excellent thermal conductivity. Most importantly, it must be able to transfer large amounts of heat in a short period of time. From a thermodynamic perspective, water is significantly better than oil.

A mold temperature controller consists of a water tank, a heating and cooling system, a power transmission system, a liquid level control system, temperature sensors, an injection port, and other components. Typically, a pump in the power transmission system transports the heat transfer fluid from a water tank equipped with a built-in heater and cooler to the mold and then back to the water tank. A temperature sensor measures the heat transfer fluid temperature and transmits the data to a controller in the control unit. The controller adjusts the heat transfer fluid temperature, thereby indirectly regulating the mold temperature.

If the mold temperature exceeds the controller's set point during production, the controller opens a solenoid valve to connect the water inlet pipe until the heat transfer fluid temperature, and therefore the mold temperature, returns to the set point.