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Topic: CO2 snow jet cleaning runs in series at the BMW Group

To clean exterior plastic parts before applying a primer, the BMW works in Landshut has replaced its powerwash system with a CO2 snow jet system made by acp. Reasons for this include improved cost-effectiveness, sustainability and quality as well as a reduced footprint. A further benefit is an increase in design freedom. This is because water-drawing component geometries and the associated displacement of media to painting processes are no longer a problem as far as the efficient dry-cleaning technique is concerned.

The BMW Group doesn’t just implement innovative technologies in its cars but also in production processes, enabling it to improve cost-efficiency, sustainability and environmental friendliness. For this reason, the Bavarian car manufacturer looked around for an alternative to powerwash cleaning for its works in Landshut - a process traditionally used before painting plastic components. The BMW works in Landshut rejected wet-chemical processes for two reasons: firstly, because it wanted to reduce energy and water consumption and waste water production and secondly, to increase cost-effectiveness and component quality. With the dry, environmentally-neutral CO2 snow jet technology it has developed, acp – advanced clean production GmbH provides a cleaning technique which not only fulfills BMW’s cleaning quality requirements but also its demands regarding reliability and availability.

Efficient cleaning – even in delicate cavities

The CO2 snow jet system‘s high cleaning performance combined with a relatively low carbon dioxide consumption is due to the supersonic two-component cleaning head which has been designed and patented by the Esslingen-based company. Liquid carbon dioxide expands on exiting the nozzle to from a mixture of snow and gas, forming a core jet. Compressed air is then added as a jacketed jet to accelerate the tiny, non-abrasive snow crystals to supersonic speed. At the same time, the compact design of the cleaning head ensures that the non-toxic incombustible CO2 snow jet is also capable of reliably cleaning highly delicate component cavities and undercuts such as those found in fenders, rear and side panels and spoilers. In the process, through the combined use of mechanical, chemical and thermal properties, particulate and filmy contamination can be removed without leaving any residues. The carbon dioxide for the cleaning system originates from processes used to manufacture fertilizers and is therefore environmentally neutral.

For serial operation, the CO2 cleaning system has been designed to clean components of all shapes and sizes made of a range of different plastics. This was proved by carrying out particle measurements and making optical comparisons and analyses to detect residues on the surfaces as well as by performing technological tests to assess paint adhesion and optical appearance.

Optimally aligned system configuration

Working together, project members of the BMW works in Landshut and acp developed a customized system configuration in line with the spectrum of parts requiring cleaning. The result is a robot system fitted with three nozzle arrays each containing five cleaning heads. Depending on the part to be cleaned, via the robot controls the arrays are automatically turned on and off individually according to a component-specific cleaning program stored in the control system. The arrays are supplied with liquid carbon dioxide and oil-free compressed air via an inner hollow supply system located inside the robot arm. The cleaning system has been integrated into a cabinet the size of a painting booth.

Cost-efficient serial operation with significant space gain

The CO2 cleaning system has been running in series in the primer line of the Landshut BMW works since the beginning of 2009. Several thousand parts are cleaned and painted here every day in two-shift operation. By replacing the powerwash system with the snow jet process developed by acp, cleaning hasn’t just become more economical and kinder on resources - valuable production space has also been gained. The space gain resulting from the removal of the powerwash system and accompanying energy-consuming drying machine is now available for production and assembly tasks. It has been viewed as a milestone for integrating different fender pre-assemblies in the BMW works in Landshut. An additional benefit of dry cleaning has been an increase in design freedom as far as parts construction is concerned. This is because it doesn’t matter anymore if exterior parts made of plastic have water-drawing geometries.

CO2 cleaning for the topcoat line

As a result of the good experience made with the first acp snow jet cleaning system, the BMW works in Landshut is now pursuing this strategy even further. In the next step, a topcoat line is going to be fitted with the efficient dry-cleaning process. www.acp-micron.com