Function of cooling channel is to transfer heat from mold to temperature control medium through side wall of channel. The most cost-effective way to control temperature is to use a circular cooling channel to cool down.
Each injection moulded parts should have a separate cooling channel. There are general rules for choosing a cooling channel:
• Channel diameter is usually 6~14mm;
• Multiple small diameter channels are more effective than a few large diameter channels;
• Channels with small diameters and long lengths can cause large pressure losses.

When using tandem cooling (see Figure 5.1), there is only one channel entering and exiting mold. As a result, temperature of cooling medium gradually increases as length of channel extends. In this way, mold temperature will be different in different areas.

 

Using this cooling (see Figure 5.2) method, influent water is divided into multiple parallel tubes to achieve uniform control of mold temperature. Disadvantage of this method is that if there is a channel blockage, its position is difficult to determine.
In general, cooling channel should be located close to mold surface. The smaller distance between channels, the better; the larger area of heat exchange, the better.

Mold temperature is critical to economics of injection molding manufacturing process and quality of injection moulded parts. The latest research results show that temperature difference of entire cavity should not exceed 5℃. This goal can be achieved by correct use of a series of cooling methods.
Temperature difference between inlet and outlet of early mold often exceeds 20℃. This will result in an decrease in quality of injection moulded parts and an increase in cooling time required for solidification of melt, corresponding molding cycle will be extended. Today, mold temperature control is designed to be an alternative heating mode. This is, heating is close to product surface and can be controlled in sub-regions. There are a variety of cooling methods that allow mold to quickly reach release temperature of product. Simply, there is continuous cooling and segmental cooling, as well as intermittent cooling, also known as pulse cooling. It is very important to take away heat when mold temperature is appropriate. When mold temperature is too low, rapid cooling can have a negative impact on product performance. Distribution of temperature and fluidity of plastic should be considered. Ideal mold temperature for various plastics is based on material supplier recommendations, see Table 5.1.

 

Mould cooling has a decisive influence on quality of injection moulded parts and molding cycle. To produce perfect product, all areas of mold surface should be kept at same temperature.

Thermoset injection molding are electrically heated and are completed by heating rods, heater chips, heating coils or hot plates. Hot plate is not incorporated into mold but is part of injection molding machine. Temperature of mold is between 150 and 180℃. Mold temperature was measured by a thermocouple. Thermocouple and heating element are configured to set surface temperature difference to within 5℃. When injection moulded parts require high temperatures, temperature difference needs to be reduced from 5℃ to 2℃. In order to reduce heat loss of mold, a heat insulation plate should be installed on mold.

Elastomeric molding are also electrically heated and completed by heating jackets, heater chips, heating coils or hot plates. Hot plate is not incorporated into mold but is part of injection molding machine. Heat output of thermoset injection molding is 35 to 40 W/kg, and heat output of elastomer molding requires 50 to 60 W/kg. Reason is that elastomer has a lower heat transfer property. And secondly its product structure is relatively weak, so cooling is rapid. Elastomer mold temperature is also measured by a thermocouple. Thermocouple and heating element are configured to control temperature difference to within 5℃. When injection moulded parts are required to be very high, temperature difference can be as low as 2 to 5℃. In order to reduce heat loss of mold, a heat insulation plate should be installed on mold.
Elastomers and thermoset injection molding do not have a cooling system, but all have a heating system. Mold temperature during injection molding is 150~180℃. In order to produce an excellent product, all mold cavity surfaces should be kept at same temperature.