Differences in Core Precision Parameters: The "Key Indicators" Determining Performance

Differences in bearing precision are not abstract concepts but are quantified through specific parameters. The most significant differences between grades are reflected in the following 4 types of core parameters:

Dimensional tolerance refers to the fitting precision between the bearing and the shaft as well as the bearing housing, including the tolerance ranges of inner diameter (d), outer diameter (D) and width (B).

• Low grades (P0/P6): Larger fitting clearances are allowed. For example, the outer diameter tolerance of P0 grade (for bearings with an inner diameter of 50mm) is -0.015mm~0mm, which is suitable for "clearance fit" scenarios (such as the fit between ordinary motor shafts and bearings);
• High grades (P4/P2): "Transition fit" or "interference fit" is adopted, with an extremely narrow tolerance range. For example, the outer diameter tolerance of P4 grade for the same specification is -0.005mm~-0.012mm, which can avoid "relative movement" between the bearing and the shaft during equipment operation and is suitable for high-speed rotation scenarios (such as machine tool spindles).

Form tolerance (e.g., raceway roundness, roller cylindricity) and position tolerance (e.g., coaxiality between inner and outer rings) determine the "eccentricity" of the bearing during rotation:

• P0 grade: Raceway roundness allows ≤15μm, and coaxiality allows ≤20μm. Slight vibration is likely to occur due to "eccentricity" during rotation, so it is only suitable for low speeds (≤3000r/min);
• P4 grade: Raceway roundness is ≤5μm, and coaxiality is ≤8μm. It can still maintain stability without obvious vibration and noise during high-speed rotation (≥10000r/min).

Rotational precision refers to the radial runout (change in radial clearance) and axial runout (end face oscillation) of the bearing during rotation, which directly affects the machining accuracy of equipment:

• General grade (P0): Radial runout ≤30μm, axial runout ≤40μm, with no obvious impact when used in ordinary transmission (such as conveyors);
• Ultra-precision grade (P4): Radial runout ≤10μm, axial runout ≤15μm. When used in CNC machine tool spindles, it can control the roundness error of machined parts within 5μm (while P0 grade may cause an error of more than 15μm).

The surface roughness (Ra value) of bearing raceways and rollers affects the friction coefficient and wear rate:

• P0 grade: The Ra value of the raceway is ≤0.8μm, the friction coefficient is relatively high during operation, and the service life is about 8000 hours (under normal working conditions);
• P4 grade: The Ra value of the raceway is ≤0.2μm, the friction coefficient is reduced by 40%, the service life can be extended to more than 15000 hours, and it is less likely to produce metal debris pollution due to wear.