Different raw materials with different properties, they have different processing characteristics, mold temperature on the workpiece surface quality fluidity, shrinkage, injection cycle, is a plastic processing and manufacturing must control the factors. Research shows that 24% of the scrap is caused by improper mold temperature. For this reason, mold temperature control systems are widely used in a variety of plastics processing fields from injection molding, blow molding to extrusion molding, in order to heat the mold to the working temperature and keep the mold temperature in a certain range of accuracy.

However, if the mold control system is not properly designed and selected, it will not only fail to improve the molding efficiency, stabilize the product quality and reduce the defective rate, but also make the improvement of other equipment automation meaningless.

Correctly select the appropriate mold temperature control system can be considered from the following aspects.

Determine the mold temperature required by the plastic processing technology

Various plastic raw materials require different processing and molding temperature, mold temperature. “Various plastics processing mold temperature table” gives some of the main plastics processing required mold temperature.

Determine the type of heat transfer medium of the mold temperature controller

A mold temperature control system operates on the principle that a pump-driven heat transfer medium (usually water or oil) travels from a tank with built-in heaters and coolers to the mold, and from the mold back to the tank. The controller regulates the temperature of the thermal fluid and thus the temperature of the mold, based on the temperature of the thermal fluid measured by a temperature sensor, or/and the internal temperature of the mold.

Depending on the type of heat transfer medium used, the mold thermostat is a water mold thermostat, pressurized water mold thermostat, or oil mold thermostat.

Generally, water-type mold thermostats have a lower control temperature range and oil-type mold thermostats have a higher control temperature range. The working temperature of water-type mold thermostat is 120℃, the working temperature of pressurized water-type mold thermostat is 180℃, and the oil-type mold thermostat is used for the working temperature ≥180℃, and the maximum working temperature is 350℃. In terms of the heat transfer medium itself, water as a heat transfer medium is economical and environmentally friendly, even if leakage occurs, it can be discharged directly without polluting the environment, but the water is easy to make the water tank, runner corrosion and scaling, so in addition to the need to do corrosion inhibitor pretreatment, in the use of the rust should also be removed on a regular basis. Heat transfer oil as a heat transfer medium, thermal conductivity is only 1/3 of the water, the cost is relatively high, easy to coking. Special application environment is also a factor to be considered in the selection of mold temperature machine. For example, oil thermostat is limited in the processing of optical lenses, because the oil is evaporated by heat, which will affect the quality of optical lenses.

Temperature control precision

To keep the temperature of the mold in the injection molding process basically constant, the key is to control the balance of heat transfer within the mold. The heat inside the mold, brought about by the thermoplastic, is transferred to the mold through heat conduction. Part of the heat transferred to the mold is dissipated directly in the air through thermal radiation, and the other part is transferred to the heat transfer medium (water or oil) through heat exchange with the mold thermostat.

Mold temperature control is achieved in several ways, including mold temperature control based on thermal fluid temperature, mold temperature control based on mold temperature, and joint mold temperature control. Users should examine the realization of the operation of the mold temperature machine according to the actual situation, and choose the product that can meet their temperature control accuracy requirements.

Based on the thermal fluid temperature mold temperature control, the temperature displayed on the control panel and the mold temperature is not consistent, due to the injection cycle, injection speed, melting temperature and ambient temperature and other factors have not been compensated for, the mold temperature fluctuations are relatively large. Based on the thermal fluid temperature mold temperature control can meet the requirements of most cases, is also the most common method.

Mold temperature control based on mold temperature, by the temperature sensor installed in the mold inside, control panel settings, display temperature mold temperature consistent, applicable to the temperature control precision requirements of the case.

Joint control synthesizes the above methods, suitable for high-precision plastics processing and manufacturing. In the joint control, the placement of temperature sensors in the mold must take into account the shape of the mold, the structure and location of the cooling channel, will be placed in the quality of the processed parts play a decisive role in the place.

At present, the vast majority of mold temperature machine using PID control technology to compensate for various factors affecting the mold temperature.

In the mold temperature machine selection process, the heating power and the pressure and flow of the media cycle are also factors that must be considered.