The truth about bearing clearance: Don't randomly choose C3 or C4 anymore!

The smaller the clearance, the better. Matching the working conditions is the key

The internal clearance of rolling bearings directly affects the stability, temperature rise, and service life of equipment operation. Seemingly small 0.01mm gap changes may cause systematic failure at high temperatures or speeds. This article uses measured data and practical tools to help you make scientific selections.

1、 What exactly is play? Experiment tells you the answer

🔬  Experiment 1: Visual comparison of different clearance levels (C0-C5)

Install bearings of the same specification but with different clearance levels in the same shaft system, and use a dial gauge to measure the axial runout:

Average axial clearance (mm) of clearance level, degree of hand shaking

C0 (standard) 0.010-0.020 almost imperceptible

C3 0.030-0.050 Slightly perceptible

C4 0.060-0.090 obvious shaking sensation

C5>0.100, easy to perceive shaking

Video slow playback display: C4 bearings have "pre displacement" at the moment of startup, which can easily lead to a decrease in positioning accuracy.

🔥  Experiment 2: The Effect of Temperature on Clearance (-30 ℃~+120 ℃)

Test the variation of clearance of deep groove ball bearings with temperature in a constant temperature chamber:

Room temperature (20 ℃): Initial clearance 0.035mm

High temperature (100 ℃): clearance reduced to 0.012mm (thermal expansion extrusion)

Extreme cold (-30 ℃): clearance expands to 0.068mm (material shrinkage)

⚠️  Conclusion: If standard clearance is used in high temperature environments, it may lead to excessive pre tightening, locking, or even burning.

2、 Real case warning: One gap error, resulting in millions of losses

❌  Case 1: Injection molding machine product thickness out of control

A factory's injection molding machine spindle was originally equipped with C3 clearance bearings, which were mistakenly replaced with C4 during maintenance. After running for one week, the following issues occurred:

The fluctuation of product wall thickness reaches 0.2mm (exceeding the upper tolerance limit)

Production curve shows periodic vibration frequency synchronized with bearing rotation

After being corrected to C3, the product qualification rate increased from 78% to 99.6%

Root cause: Excessive clearance leads to a decrease in mold closing accuracy, affecting the mold closing pressure.

✅  Case 2: Agricultural Machinery Anti Common Sense Longevity Secret

A certain combine harvester gearbox uses C3 clearance instead of the original C2, and in continuous field operation tests:

Average lifespan of C2 bearings: 820 hours

Average lifespan of C3 bearings: 2600 hours (increased by over 3 times)

Analysis: Agricultural machinery is often exposed to dusty environments and operates at high temperatures. C3 reserves space to counteract thermal expansion and avoid early jamming.