Correct selection of mold temperature control system for processing technology characteristics
Different raw materials have different properties. They have different processing characteristics. The influence of mold temperature on the mass flowability, shrinkage rate and injection cycle of the workpiece is a factor that must be controlled in plastic processing and manufacturing. Studies have shown that 24% of scrap is caused by improper mold temperature. To this end, mold temperature control systems are widely used in various plastic processing fields, from injection molding to blow molding to extrusion, to heat the mold to the operating temperature and maintain the mold temperature within a certain accuracy range.
However, if the mold control system is designed and improperly selected, it will not only improve the molding efficiency of the product, stabilize the product quality and reduce the defect rate, but also cause the improvement of automation of other equipment to lose its meaning.
Proper selection of the appropriate mold temperature control system can be considered from the following aspects.
Determine the mold temperature required for plastic processing
The processing temperature and mold temperature required for various plastic raw materials are different. "A variety of plastic processing mold thermometers" gives the mold temperatures required for some major plastics processing.
Determine the type of heat transfer medium for the mold temperature machine
The mold temperature control system works by pumping a heat transfer medium (usually water or oil) from a tank containing a built-in heater and cooler to the mold and back from the mold to the tank. The controller adjusts the temperature of the hot fluid to adjust the temperature of the mold based on the temperature of the hot fluid measured by the temperature sensor, or/and the temperature inside the mold.
The mold temperature machine is a water mold temperature machine, a pressurized water mold temperature machine or an oil mold temperature machine depending on the type of heat transfer medium used.
Generally, the water temperature control unit has a lower control temperature range, and the oil type mold temperature machine has a higher control temperature range. The working temperature of the water mold temperature machine is 90 °C, the working temperature of the pressurized water mold temperature machine is 160 °C~180 °C, and the oil type mold temperature machine is used for the working temperature ≥150 °C, the maximum working temperature is 350 °C. .
As far as the heat transfer medium itself is concerned, water is used as a heat transfer medium, which is economical and environmentally friendly. Even if a leak occurs, it can be directly discharged without polluting the environment, but the water easily causes corrosion and scaling of the water tank and the flow path, so in addition to the anticorrosive agent In addition to pretreatment, it is also regularly rusted during use. The heat transfer oil is used as the heat transfer medium, and the thermal conductivity is only 1/3 of water, the cost is relatively high, and it is easy to coke.
The special application environment is also a factor to consider when choosing a mold temperature machine. For example, the oil temperature machine is limited in the processing of optical lenses, because the oil is evaporated by heat, which will affect the quality of the optical lens.
Temperature control accuracy
To keep the temperature of the mold in the injection molding process substantially constant, the key is to control the heat transfer balance within the mold. The heat generated by the thermoplastic inside the mold is transferred to the mold through heat conduction, part of the heat transferred to the mold is directly dissipated in the air by heat radiation, and the other part is transferred to the heat transfer medium (heat or water) through heat exchange with the mold temperature machine. oil).
The realization of mold temperature control includes mold temperature control based on hot fluid temperature, mold temperature control based on mold temperature, and joint mode temperature control. The user should investigate the realization of the operation of the mold temperature machine according to the actual situation, and select the product that can meet the requirements of its own temperature control accuracy.
Based on the temperature control of the hot fluid temperature, the temperature displayed on the control panel is not consistent with the mold temperature. The temperature fluctuation of the mold is relatively large due to factors such as injection cycle, injection speed, melting temperature and ambient temperature. Temperature temperature control based on hot fluid temperature can meet most of the requirements and is the most common method.
The mold temperature control based on the mold temperature is installed in the mold by the temperature sensor, and the temperature of the mold is set and displayed on the control panel, which is suitable for the case where the temperature control accuracy is high.
The combined control combines the above methods and is suitable for high precision plastics processing and manufacturing. In joint control, the position of the temperature sensor in the mold must take into account the shape of the mold, the structure and the location of the cooling passages, and place them in a decisive role in the quality of the workpiece.
At present, most mold temperature machines use PID control technology to compensate for various factors affecting mold temperature.
During the mold temperature machine selection process, the heating power and the pressure and flow rate of the media cycle are also factors that must be considered.
Calculation of heating energy
among them:
P mold heating energy (kW)
W mold weight (kg)
C mold specific heat (kcal / kg ° C)
T1 required mold temperature (°C)
Mode temperature (°C) when T2 starts production
S safety factor, value 1.5~2
t time from the start of production to the desired mold temperature (h)
Media cycle pressure
The finer the mold, the greater the pressure required and the impedance of the runner.
P = 0.1 × H × α
P pressure (kg/cm2)
H head height (m)
The specific heat of the alpha heat transfer medium. Water=1; oil=0.7~0.9
Media loop required traffic
The greater the flow rate, the better the heat transfer effect.
L media loop required traffic (L / min)
Q mold heat to be removed or moved in (kcal/h)
c specific heat of the heat transfer medium. Water=1; oil=0.7~0.9
Temperature difference between ΔT cycle media entering and exiting the mold (°C)
The proportion of the alpha media cycle
Usually, mold temperature machine manufacturers will provide the pump characteristics of their products and the comparison of the model temperature of the mold temperature. These are the references for selecting the mold temperature machine. Explain the products of Shan State.
· Determine the temperature range that needs to be reached: "Various plastic processing mold temperature gauges" provide some mold temperatures required for major plastic processing. The user needs to determine the temperature range to be achieved according to the processing requirements.
· Choice of heat transfer medium: The general water temperature machine controls the temperature range is low, and the oil temperature machine controls the temperature range is high. For the mold temperature machine, if water is required as the heat transfer medium, the YBM-D series should be selected; if oil or water is used as the heat transfer medium, the YBM-I type should be selected.
• According to the "Model Function Table", select the most suitable model for the maximum allowable heating time.
For example: the mold weight is 120kg, the mold temperature needs to reach 120 °C in 25 minutes, YBM-1IH (high temperature type) is the best choice;
The mold weight is 120kg, the mold temperature needs to reach 120 °C in 10 minutes, and YBM-2IH (high temperature type) is the best choice;
The mold weight is 120kg, the mold temperature needs to reach 80 °C in 25 minutes, and YBM-1D or YBM-1I (general type) is the best choice.
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