moulds | Temperature control
Figure 1: Schematic showing integration of CO2 cooling into injection mould
preceded by a thermal analysis of the mould using an infrared thermal imaging camera. This analysis made it possible to establish precisely where the capillary tubes had to be placed. The cooling process is regulated using a controller unit. This controls the timing and pressure of delivery of the CO2
to the mould and ensures that the areas to be
cooled are maintained at the temperature of the bulk of the mould. The control unit prevents unwanted overcooling of the mould.
component, CO2
Depending on the geometry and material of the cooling can reduce cooling and cycle
times signifi cantly. In some cases it has been possible to reduce the cycle time by more than 50%. Existing moulds can be retrofi tted with the tempera-
during production, resulting in an extended cycle time. The company adopted the Linde CO2
ture control system and, due to the low hardware requirements and the relatively simple installation of the thin and fl exible capillary tubes, the investment costs are low. A typical system comprises a CO2
injection spot mold
cooling process, allowing it to integrate supplementary cooling into the critical fi llet area of its existing mould. The system is essentially simple in implementation. is fed under high pressure through thin,
Liquid CO2
fl exible stainless steel capillary tubes (1/16 inch or less) to the points where cooling is required. The tubes are inserted into small diameter holes drilled or eroded into the mould. The expansion of the CO2
at the end of the
capillary tube in the ‘expansion room’ creates a snow and gas mixture with a temperature of about -109°F
(-78˚C). Due to the high sublimation energy of the CO2 from the solid to gaseous phase, this results in a very high local cooling capacity. The CO2
withdraws heat
from the steel of the mould and escapes out of the expansion room in gaseous form through an annular gap between the hole and capillary tube. The mould for the production of the headlight housing was equipped with numerous capillary tubes per cavity, enabling effective and homogenous cooling to be achieved. The design of the cooling system was
Figure 2: Two CO2 supply system confi gurations for spot cooling
supply,
pipes and capillary tubes, distribution blocks and valves, and a control unit. For repeatable cooling to be achieved, the carbon
dioxide must be supplied at the right pressure and at the right temperature without any gas bubbles. Linde adapts the supply concept to the requirements of the particular application, taking into account consumption, withdrawal profi le and site conditions such as the space available and pipe lengths needed (Figure 2). Small plants can be supplied with cylinder bundles for gas supply. For higher consumptions, a CO2
tank with
suitable pressure boosting equipment would supply the liquid and bubble-free carbon dioxide.
www.lindeplastics.com
About the authors: Mikael Orsén is applications manager and James Stanley program manager industrial applications at Linde’s US operation at Murray Hill, New Jersey, US. Andreas Praller is applications manager for Linde at Unterschleissheim, Germany.
CO2 control unit
CO2 20 bar
(290 psi)
Liquid CO2 e.g. 55 bar
(800 psi)
CO2 cylinder bundle
Tank
Compressor station PRESUS™ C
54 INJECTION WORLD | June 2014
CO2 control unit
Injection moulding machine(s)
www.injectionworld.com
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