In engineering plastics resin and super engineering plastics resin, the types of plastics resin in which case the surface temperature of the cavity exceeds 100°C is increasing. If the surface temperature of the cavity exceeds about 90°C, normally it becomes difficult to increase the temperature when the temperature control is being made using hot water.
In general, the following methods are used.

(1) Temperature control using oil

In the temperature control using oil, oil ejected from a re-circulating pump is re-circulated via a joint hose through a flow path provided in the mold plate and cavity, thereby maintaining a constant temperature. Once the temperature rises up to the set temperature, it is possible to maintain a relatively stable temperature. However, there is the disadvantage that it takes time for the temperature to rise. Further, there is the danger of people suffering burns while handing the oil, and also there is the problem that later treatment of the oil is cumbersome.

(2) Electric heater

In the temperature control using an electric heater (cartridge heater), the temperature is maintained constant using the heater in combination with a temperature sensor (thermocouple, etc.). Since the thermal capacity is high, there is the advantage that the temperature rise is fast.
However, the temperature near the heater is high and the temperature far from the heater is low and hence it becomes difficult to maintain a uniform temperature distribution.
In addition, since a heater has a limited life, it will be necessary to replace the heater periodically.
Mounting holes and clearances will be very important in mounting the heater. If the clearance is too much, the heater will be in the no load condition and hence its life will be shortened.
In order to carry out more accurate temperature control, it is recommended to place a heat insulating plate between the platen of the injection molding machine and the mold installation plate. Or else, it is also possible to provide heat insulating plates surrounding the mold.

Table Example of materials requiring high cavity surface temperatures

In the case of molds for the injection molding of PPS or liquid crystal polymer, since it is necessary to maintain the cavity surface temperature at more than 100°C, temperature control using oil or temperature control using a cartridge heater will be required. The temperature controlling method used very frequently with the cartridge heaters available in the market is the "ON-OFF Control" method in which the temperature is controlled by turning ON and OFF the power supply to the heater.
Since this "ON-OFF Control" can be constructed with a simple switching device, although the price of the controller is relatively low, the variations in the cavity surface temperature are large, and there is the drawback that it is difficult to stabilize the temperature.
If the cavity surface temperature is unstable, it will cause fluctuations in the condition of shrinkage, the dimensions, and the glossiness of the surface in a precision molded item.

In view of this, the "PID Control" method is recommended for stabilizing the cavity surface temperature as much as possible.
The PID Control is a method of controlling that can shorten the time required for the temperature to become stable by using controls of the following types:
Proportional
Integral
Derivative.

Cartridge heaters can have a maximum load of 10 kW with an AC three phase 200V power supply.
Therefore, as an example of use, it is possible to use two three phase 200V 1 kW heaters and to incorporate them at the movable side mold plate and the fixed side mold plate, and to carry out stable control of the cavity surface temperature using PID control.

Heat insulating plates are very important parts for stabilizing the temperature of a mold for injection molding, or for realizing energy savings while maintaining the temperature. They are used as mandatory items in the injection molding of engineering plastics or super engineering plastics.
Misumi offers heat insulating plates as a line up of products, which can be selected suitably depending on the application.
In general, the method of using a heat insulating plate can be of the following two types.
1.Using by fixing to the platen of the injection molding machine.
2.Using by fixing behind the mounting plate of the mold.

The following items are among the criteria for selecting the heat insulating plates.

1.Withstanding temperature

As a guideline, the following recommended usage temperatures are available.

• Recommended usage temperature: Up to 100°C
• Recommended usage temperature: Up to 180°C
• Recommended usage temperature: Up to 220°C
• Recommended usage temperature: Up to 400°C
• Recommended usage temperature: Up to 500°C

2.Material

The material is the factor related to the recommended usage temperature and the compression strength.
The following materials are available.

• Cotton cloth + phenol resin (Bakelite)
• Craft paper + phenol resin (Bakelite)
• Glass fiber + silicate binder
• Glass fiber + ultra high heat resistant epoxy resin
• Glass fiber + phosphate binder
• Glass fiber + borate binder

Asbestos is not handled by Misumi since it is considered to be hazardous to health.