Mould temperature regulation

Figure 3.14 Mould temperature regulation in nozzle zone...

Before an HR mould commences operation, the following preparations are needed connection and checking of the mould temperature regulation system ... 

Mould temperature regulation can be used to reduce the effects of these interference factors considerably. A temperature sensor in the mould acts as an actual value pick-up, and signals the actual mould temperature to the temperature control imit. The flow temperature is now no longer kept at a constant value, but is adjusted by means of a regulator until the actual temperature in the mould corresponds to the theoretical temperature for the mould set on the temperature control unit. 

Another limitation to the operation of the system may by a badly-designed mould e.g., without zonal temperature regulation, or contaminated raw material, and so on. 

The nozzle ends were adapted to the shape of the moulding. The manifold is equipped with 11 temperature regulation circuits. To compensate for the thermal expansion in a large manifold, nozzles set in intermediate blocks were used in this design. 

A measurement point position like this is not suitable for regulating the mould temperature, because of the temperature variations referred to. The temperature gauge should therefore be sufficiently far away from the mould wall, so that at the measuring point the temperature variations have already been sufficiently dampened. But it should also be an adequate distance away from the temperature control channels, so as to exclude reverse effects from this side. A middle position between the mould wall and the temperature control channels is recommended. Because the temperature falls towards the clamping surface, the measuring point should naturally not he too close to this. It is in any case advisable to insulate the mould halves from the clamping surface, so as to reduce the interference factors. For high mould temperatures, economic considerations also require this. 

For temperature control (regulated flow temperatures), the variations in the cycle temperatures should be less than 5 °C, in order to reach a suitable temporal constancy in the mould temperatures. 

The whole HR system is divided into temperature control zones temperature measurement and control are carried out with the aid of automatic regulators separated from the mould. 

The thermal equilibrium of any HR system is governed by variable and fixed values of all components of the thermal balance of the mould/injection moulding machine/ambient conditions system. The fact that variable factors are always present means that automatic temperature control and regulation of the HR system must be used to keep deviations from the required temperature to a minimum. The following initial conditions must be fulfilled ... 

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