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VOLUME 3, ISSUE 2 gas, forming the core jet. Compressed air is then added as a jacketed jet to accelerate the snow crystals to supersonic speed. Compared with single-component nozzle systems, the use of compressed air to accelerate the jet significantly increases cleaning performance and also reduces carbon dioxide consumption. The carbon dioxide required by the cleaning system is obtained from processes used in the manufacture of fertilizers and is therefore environmentally neutral. Comprehensive testing to validate cleaning results After selecting the system, the BMW Group carried out extensive tests in collaboration with acp at the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) at the Department of Coating Technology. Firstly, tests were performed to verify that plastic components could be cleaned with carbon dioxide. Then matrix tests were carried out to evaluate how well contaminants such as separating agents, diesel exhaust particulates, various oils, fingerprints and dust could be removed. CO2 snow is harmless and noncombustible and uses a combination of mechanical, chemical and thermal properties to remove particulate and filmy contamination in a drycleaning process without leaving any residues. On impacting on the surface to be cleaned, the snow crystals turn to liquid and then sublime. The resulting sublimation impulse causes any particulate contamination present to be dissolved and removed. In its liquid state, environmentally-neutral carbon dioxide functions as a solvent and removes filmy layers or contamination. Also, the low degree of hardness of the acp system’s tiny snow crystals en-
cleaning nozzles was realized. Depending on the component to be cleaned, the arrays are turned on and off individually via the robot controls, making the system especially economical to operate. Oilfree compressed air and liquid carbon dioxide stored in tanks are fed to the arrays via an inner hollow supply system located inside the robot arm.
sures that surfaces are not damaged during treatment. A third requirement was to develop an optimized system configuration in order to fulfill the demands of the BMW works in Landshut. Robot system with three nozzle arrays To align the process with the range of parts to be cleaned, a robot system with three nozzle arrays, each containing five
The cleaning system was first integrated into a cabinet (approx. the size of a painting booth) and placed in the primer line between the powerwasher und flame treatment booth. Because test results still needed to be confirmed for series operation, the powerwasher and CO2 snow jet cleaning system ran parallel for a while. “As the parts are made of different plastic materials and have varying geometries, we verified the CO2 cleaning process for each workpiece individually by performing particle measurements, optical comparisons and analyses to detect surface residues and also carried out technological