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Volkswagen Plastics Technology applies CO2 snow jet system for clean coating

Volkswagen Plastics Technology in Braunschweig, Germany has been using the CO2 snow jet technique developed by acp to clean interior

components before painting for about a year now, the company said in a press release.

Apart from aiming to improve quality, the main reasons behind the investment were cost-efficiency, sustainability, ease of automation and the low space requirements of the cleaning system, according to Volkswagen Plastics Technology.

In addition, the process also enables high-gloss injection molded components to be cleaned gently and efficiently before a single layer of metallic paint is applied.

Volkswagen Plastics Technology said it can now develop and manufacture interior components such as panels, trims, ventilation grilles and air diffusers without painting or applying only a single layer of paint.

One of the components produced is a decorative panel made of ABS-PC blend. Although the part already has a high-gloss surface on leaving the injection-molding machine, it is subsequently coated with a layer of high-gloss metallic paint to give it a sophisticated finish.

As the paint is applied without an undercoat, the tiniest dust particles or water marks would cause rejects. Thus a cleaning solution was needed which was not only fast, economical and reproducible, but also dry and gentle on materials. At the same time, the cleaning system had to fit into a small space and be integrable into the painting process.

The CO2 snow jet technology was sourced from acp, advanced clean production GmbH. Volkswagen Plastics Technology said that extensive series of tests on high-gloss components and “conventional” plastic parts showed that the cleaning process was capable of attaining the level of cleanliness required to pre-treat the entire spectrum of components to be painted.

The cleaning technique uses liquid carbon dioxide as a medium which is stored in tanks at Volkswagen Plastics Technology. Produced as a by-product in the chemical industry, it is said to be environmentally neutral and gentle on resources.

According to the press release, the supersonic two-component ring nozzle located in the compact cleaning head, the modularly-constructed CO2 snow jet system manufactured by acp has a high cleaning power despite relatively low carbon dioxide requirements.

Liquid carbon dioxide expands on exiting the nozzle to form a mixture of snow and gas which is the core jet. Oil-free compressed air is fed to the core jet as a jacketed jet, accelerating the non-toxic, non-combustible snow crystals to supersonic speed. When the easily focused jet impacts on the surface of a component, the combination of mechanical, chemical and thermal forces cleans off particulate and filmy contamination without leaving any residues. In the process, the low degree of hardness of the tiny non-abrasive snow crystals ensures that even high-gloss surfaces keep their quality and remain undamaged during cleaning.

The CO2 snow jet system has been running in three-shift series operation at the Volkswagen works in Braunschweig since August last year. Several thousand plastic parts are cleaned by it every day. It has also enabled reject rates to be lowered by around 3%, according to Volkswagen Plastics Technology.


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