TABLE OF CONTENTS Some of the heat supplied to the material during the plasticising and injection phase must be removed from the tool before ejection of the parts can take place. However, not only is it unnecessary it is also wasteful to continue cooling the tool until the part has reached ambient temperature, as many materials may be safely ejected at temperatures up to 50 C or more.
The cooling phase can be up to 80% of the overall cycle and often the most expensive cost component of the moulding. Clearly it is highly desirable to minimise the cooling cycle, and in order to do this it is essential to pay sufficient attention to the design and efficiency of all cooling systems.
The overall requirement is to cool the moulding as quickly as possible while preserving the physical properties of the material and the required quality of the moulding. When molten material is injected into the cavities of a mould it has to be allowed to solidify before the resulting mouldings can be ejected. As the ejection temperature may be 200-300 C lower than that of the molten material, heat must be removed from the mould to reach ejection temperature as soon as possible.
A mould tool, is in effect, a highly stressed heat exchanger and the cooling phase of the injection moulding cycle is extremely important. The overall objective is to cool the polymer as quickly as possible to a temperature at which the moulding can be safely ejected. In...
