轴承上必须有密封件，防止外部的灰尘和水分进入，也防止轴承内部的润滑油脂外漏。
The bearing must be equipped with seals that are able to keep dust and water out and the grease inside the bearing.
含氟塑料作为自润滑和密封材料将被广泛用在汽车零部件上。
As a self lubrication and self sealing material, fluoroplastics is widely used in auto parts.
钢制零件通常涂上润滑脂，以防生锈。(为了防锈，钢制零件通常需涂上润滑脂。)
Steel parts are usually covered with grease for fear that they should rust.
钢制零件通常涂上润滑脂，以防生锈。(为了防锈，钢制零件通常需涂上润滑脂。)
Steel parts are usually covered with grease for fear that they should rust.
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