In addition to the need to maintain cleanliness in the production process, the automotive industry has become increasingly strict in environmental control. Oil particles are very small, and once they are not well diffused due to room differential pressure, or cleaning is not in place, they will contaminate the equipment components. Contaminant particles accumulate on components and can impair their function or cause them to be completely scrapped. Therefore, it is important for automotive equipment components not only to maintain a high degree of cleanliness on the surface, but also to keep the core of the components clean.