Detail of Bumper - to - bumper recycling
In response to growing concern over environmental issues and recycling of resources, automobile manufacturers are increasingly collecting and recycling damaged bumpers. Since 1992, Mazda has been collecting used bumpers and recycling them for use as vehicle undercovers. In 2001, Mazda began removing the paint—which causes deterioration of mechanical properties—from damaged bumpers and incorporating the recycled material in new bumper plastic. However, with the advent of mirror-finished bumpers, it became necessary to improve the degree of paint removal in order to ensure the recycled bumpers exhibit the required paint quality. This led Mazda to develop its new paint removal process.
The new process to raise the degree of paint removal was developed in collaboration with local machinery maker Satake Corporation. After using a conventional mechanical paint stripping process, optical selection technology is employed to detect and remove pellets of the crushed bumpers that still hold paint. As well as raising the average rate of paint removal, the system also reduces the variance in paint removal rate to less than one quarter of the previous system and therefore ensures reliable attainment of the target ratio.
- Target paint removal rate
The paint removal rate for materials recycled with the conventional process is 98.50 percent, which means a 1.50 percent residual rate. With this method, new bumpers made from 30 percent recycled material do not possess sufficient surface quality to be painted. The recycled material content must be lowered to just three percent to satisfy the criteria. In order to achieve the desired 30 percent recycled material content, we first had to reduce the paint residual rate from 1.50 to 0.15 percent. This led to our target paint removal rate of 99.85 percent.
- How the paint removal rate was improved
Mazda conducted a detailed examination of crushed bumper pellets to determine the paint removal rat
e of the conventional process, and found that only a small proportion (14 percent) of the pellets still had residual paint; 86 percent were paint free.
Given this, we surmised that if we could detect and remove bumper pellets with an area of residual paint over 10 mm2, we would achieve a high yield of recycled material at the target paint removal rate. (Yield is defined as: 'the number of paint-free pellets/the total number of crushed pellets x 100.'
- Selection mechanism
Crushed bumper pellets are subjected to the paint stripping process, then collected in a hopper and passed through a shooter. As they exit the shooter, light is shone on them from various angles. Any paint adhered to the fragments reflects light more intensely than the (black) bumper material. Charged-coupled device (CCD) sensors detect the reflected light and an air jet immediately removes the unwanted pellets.
This mechanism to separate crushed bumper pellets successfully improves the average rate of paint removal from 98.50 to 99.85 percent.