• Precision Bearing

Precision Bearing

According to the ISO classification standards, precision bearings are divided into: P0, P6, P5, P4, P2. The grades increase in order, among which P0 is ordinary precision, and the other grades are precision grades. Of course, different classification standards, different types of bearings, their classification methods are different, but the meaning is the same. The performance of precision bearings requires the rotating body to have high runout accuracy, high-speed rotation and small friction and friction changes.
Because the precision of the precision bearing itself is within 1μm, it is required to have high dimensional accuracy and shape accuracy with its matching parts (shaft, bearing seat, end cover, retaining ring, etc.), especially the accuracy of the mating surface should be controlled at the same level as the bearing Within the level, this is crucial, and it is most easily overlooked.
It must also be noted that if the matching parts of the precision bearing do not meet the above requirements, the precision bearing will often cause an error that is several times larger than the original bearing error after installation, or even more than 10 times the error. It is completely impossible to be a precision bearing because of the matching machine. The error of the parts is often not simply superimposed on the error of the bearing, but added after being enlarged by different multiples。

Precision Bearing Heat Treatment Process

Preliminary heat treatment:

  • Normalizing

    Normalizing, also known as normalization, is to heat the workpiece to Ac3 (Ac refers to the final temperature at which all free ferrite is transformed into austenite during heating, generally from 727°C to 912°C) or Acm (Acm is the critical temperature line for the complete austenitization of hypereutectoid steel in actual heating) 30~50℃ above, after holding for a period of time, take it out of the furnace and cool the metal in air or by spraying water, spraying or blowing. Craft. Its purpose is to make the grain refinement and carbide distribution uniform. Parameters: The normalizing temperature of different components is slightly different.

  • Spheroidizing Annealing

    Its main purpose is to reduce hardness, improve machinability, and prepare for quenching in the future. This process is conducive to plastic processing and cutting, and can also improve mechanical toughness.

Final heat treatment:

  • Quenching

    Quenching is to heat up the raw material to the austenitizing temperature and keep it for a period of time as needed. Then it is cooled quickly to obtain a structure with higher hardness and strength than the original, so as to enhance the mechanical properties of the material and increase the durability of the material. For example, 45 steel, the original structure is ferrite + pearlite, martensite is obtained after quenching, and the strength and hardness are doubled.

  • Cold Treatment

    Cold treatment: the retained austenite that has not been fully transformed during the quenching process will continue to transform to martensite. In addition to improving the dimensional stability of the parts, it can also slightly improve the hardness and rust resistance of the parts. But it will reduce the toughness of bearing steel. Sometimes, the principle that the martensite is larger than the volume can be used to save the scrapped products due to size reduction with cold treatment.

  • Tempering

    Parts must be tempered after quenching (or cold treatment). Tempering can reduce and stabilize the residual stress, stabilize the structure, avoid cracks and deformation, appropriately reduce the hardness and greatly increase the toughness, so that the parts can finally obtain the best fit, comprehensive toughness and mechanical properties and dimensional stability.

  • Additional tempering (stabilization treatment)

    The role of additional tempering is to eliminate the grinding stress and further stabilize the structure in order to improve the dimensional stability of the parts.

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