Preloading refers to the use of the bearing in the play by changing the relative position of the inner and outer rings before the bearing is loaded. For household appliances bearings, the main role of pre-tightening is to improve bearing stiffness and suppress vibration noise.
Preload on the bearing noise
When the bearing is subjected to radial load, due to the radial clearance, only part of the steel ball is subjected to load (ABC in the figure), which is called the bearing area, and the other is called the non-bearing area. During the movement of the steel ball from the D to the D' in the non-bearing zone, the magnitude and direction of the combined force of the self-weight and the centrifugal force of the steel ball constantly change, and the steel balls alternately collide with the inner and outer ring raceways, so that abnormal noise is generated inside the bearing. This abnormal sound can be eliminated by preloading the bearing.
However, if the pre-tightening force is too large, the bearing friction increases, the temperature rises, and the noise life of the bearing decreases. Therefore, it is important to choose a suitable preload.
The structure of NSK common dust cover and sealing ring is shown in the figure below. The dust cover (ZZ) is stamped from a steel plate, and the seal ring is made of rubber covered with steel. Among them, the sealing ring is divided into two types: non-contact type (VV) and contact type (DDU, DDW).
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