In the plastics industry, you face a constant balance between increasing output and maintaining quality. Reducing cooling times can cause product distortion and surface imperfections because of excess heat. Constantly pushing the limits leads to inconsistent quality. You need a different approach.
It’s not always possible to water cool injection mould tools. If they have narrow cores or sections, water cooling channels in these areas can become clogged with lime scale and corrosion, rendering them ineffective. Hotspots form where cooling channels are absent or blocked, dictating the total cooling cycle time of the part.
However, feeding carbon dioxide (CO2) into the mould through capillary tubes with an external diameter of just 0.8 mm, will allow some of the narrowest areas to be spot cooled. Used in tandem with water cooling in other areas, it can reduce your production cycle time by up to 40% (easing your productivity pressure) and provides a more controlled and uniform cooling system for the plastic part within the mould, reducing warping and eliminating sink marks.
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Ensure high quality finishes
Using CO2 can also simplify your cooling processes, particularly when you want a high quality gloss finish. When the molten polymer enters the mould, it’s imperative the internal surface temperature of the mould cavity matches the polymer at the moment of contact. If not, a skin can form on the polymer’s surface, reducing its gloss finish due to ‘near surface’ crystallising. Then the mould has to be cooled to solidify the plastic part inside.
Conventional ways of achieving this involve a complex mix of hot water, oil or steam, plus the use of induction and electrical heating, followed by cold water or oil. This not only costs time and money but also requires the whole mould to be heated and then cooled. All of this can now be replaced by a far more accurate distribution of just one material – hot gaseous CO2 followed by liquid CO2. Simple, efficient, effective and fast. CO2 works so well because it is easy to distribute but, under pressure, its density increases rapidly giving it excellent cooling properties.
Avoid product distortion
CO2 gas assisted injection moulding is also invaluable when producing plastic parts with thicker walled sections, for example where a rib or post merges onto a main wall of a component. This leads to a difference in cooling behaviour, with thicker sections tending to shrink more, producing sink marks.
Nitrogen or liquid CO2 can be pumped into the thick sections where its internal pressure will compensate for the shrinkage to eliminate distortions. Our enhanced CO2 technology significantly improves cooling, thus improving the cycle time by up to 40%.
If you want to eliminate common heat-related production faults, BOC can offer a free trial to show you how to maximise both quality and productivity with our PLASTINUM® gas solutions for plastics manufacturing.
Could BOC’s advanced gas techniques boost your injection moulding productivity? Download our e-book for more detail on the cycle time and profitability improvements you could achieve by making the switch.