Mould Technology Dynamic cavity temperature control requires no water

Editor: Eric Culp

A joint project between three German companies has created a temperature control system in which CO2 replaces H20, according to supplier gwk.

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The use of gas for temperature control can eliminate soiled and corroded cooling channels as well as speed up cycle times.
The use of gas for temperature control can eliminate soiled and corroded cooling channels as well as speed up cycle times.
(Source: gwk)

Brand-new perspectives and possibilities are offered by dynamic temperature control using CO2. This new and environment-friendly procedure provides a solution for heating and cooling of complex and thin-walled moulded parts. By using gaseous media for heating and cooling processes, soiled cooling channels can be eliminated.

CO2, it’s not just for cooling systems anymore

Basically, it is true that gaseous media have the disadvantage of being poor heat carriers. This applies at least to air, which is only used for cooling processes under special circumstances. But in contrast, if the opportunities of CO2 are properly developed and implemented, it offers an interesting alternative to conventional water temperature control.

An application for injection moulding of thick-walled optical lenses made of PMMA for LED lighting employs a waterless cyclic cavity temperature control with CO2. Mould inserts that were produced by means of the company’s integrat 4D-process provide precise and quick heat transfer in the mould, which is operated with high energy efficiency on an all-electric injection moulding machine from Sumitomo Demag.

Compression, proximity let gas work as heating medium

Cooling with CO2 has been sufficiently tested and is well-known. The high enthalpy of evaporation of the injected fluid accompanied by a temperature of -76C offers an extremely efficient heat transfer. As far as cooling of long and thin cores or of narrow bars is concerned, cooling with CO2 has already been applied with great success for many years. Now heating is also possible with gaseous CO2.

Compressed to a suitable pressure and heated close to the mould cavity, the teco vario gt developed by gwk has shown to have excellent heat transfer characteristics and has none of the deposits or corrosion that can form through the use of water and hot steam. These factors make CO2 ideal for dynamic temperature control. The high temperature gradient between hot and cold media is unique and promises minimum cycle times.

Using CO2 is good for the environment, too

The positive environmental effects are also an important benefit: The CO2 used is an extract of by-products from chemical processes, which would normally be emitted directly into the environment. Thanks to a new technique developed by gas supplier Linde, technology firm Iserlohner Kunststoff-Technologie and gwk, however, it is refined and thus becomes suitable for the dynamic temperature control of narrow and otherwise inaccessible mould sections as well as complex part geometries.

Next up: Waterless injection moulds in the clean room

In contrast to all other techniques, this temperature control method does not put any requirements on the cooling system, neither in terms of temperature, pressure, volumetric flow rates or water quality. Thanks to this new technology the operation of water-free injection moulds in clean-room production is now within reach.