This paper describes the development of high efficiency and compact bumper recycling equipment for facilitating bumper recycling globally. Various equipment to remove paint coat from bumper has been developed since 90s', using mechanical, physical or chemical method. However, it is difficult to promote bumper recycling without realizing cost effective overall system from paint coat removal to pelletizing.
Our company jointly developed method of mechanically removing paint coat and has committed to bumper recycling in the form of outsourcing since 2000. In 2010, a dedicated plant for recycling bumpers was launched on the premises of our Oppama Assembly Plant in Japan.
In the future, promoting bumper recycling at other overseas assembly plants is necessary as vehicle production will expand globally. Having more compact and cost effective recycling system compared to the one at the Oppama plant is required since the scale of the system including bumper crushing, paint coat removal, and pelletizing has to match processing capacity at these plants rather than equipping large one like Oppama's.
With this reason, the newly developed equipment includes renewed machines for bumper crushing, paint coat removal and pelletizing. The paint coat removal process was developed on the basis of an environmentally friendly mechanical technology that Nissan developed approximately ten years ago. This process makes use of differences in material property changes of the polypropylene base material, paint coat and primer that occur accompanying a temperature rise during the churning of crushed bumper fragments. Optimum temperature control in the churning vessel enabled the equipment to be downsized and to achieve highly efficient paint removal. The geometry of the extruder screw used in the pelletizing process was optimized along with optimizing the conditions for suppressing vent-up resin flow due to a pressure rise in the vessel. These improvements made possible more compact equipment than the existing bumper recycling system. The newly developed equipment combined with more simplified auxiliary units enabled the entire recycling process from bumper crushing through paint removal to pelletizing to be substantially downsized.