1. Appearance inspection (preliminary screening)
Surface finish
High-quality bearings: smooth inner and outer rings, rolling element surfaces without burrs, and no mechanical damage (scratches, indentations).
Poor-quality bearings: rough surface, may have rust spots or oxidation marks (indicating poor anti-rust process).
Engraving and logo
Authentic bearings: brand, model, precision grade (such as ABEC-5), origin, etc. laser engraving is clear and uniform, without repeated engraving marks.
Poor-quality bearings: fuzzy fonts, different depths, and even missing key parameters.
Clearance and shaking
Axial clearance test: pinch the inner ring by hand, shake it up and down, the clearance should be less than 0.1mm (precision bearings are smaller).
Radial clearance test: turn the outer ring, there should be no sense of jamming, no obvious jumping.
2. Materials and processes (core indicators)
Material testing
High-quality bearing steel: generally GCr15 (SUJ2), high and uniform hardness (Rockwell hardness HRC 58-62).
Simple test: Use a file to lightly file the non-working surface, inferior steel will leave obvious scratches.
Heat treatment process
Genuine bearings: After vacuum quenching + low-temperature tempering, the metallographic structure is uniform (martensite + fine carbide).
Inferior bearings: uneven hardness, prone to cracking or premature wear.
Cage material
High-end bearings: copper alloy or engineering plastics (such as PEEK), high temperature resistance and deformation resistance.
Low-end bearings: Use inferior steel plates or nylon, which are easy to break and melt (can be ignited for testing, nylon cages have a pungent smell when burning).
3. Accuracy and performance test
Rotation flexibility
Manually rotate the bearing, high-quality products should be smooth and unobstructed, and slow down when stopping (grease filling is uniform).
Inferior bearings: jerky rotation or sudden stop (may be due to rough raceways or poor assembly).
Noise test
High-quality bearings: The sound is continuous and slight when idling, and there is no abnormal sound of metal friction.
Professional method: Use a decibel meter to test at 1500rpm, the noise value should be less than 45dB (lower for precision bearings).
Temperature rise test
Run without load for 30 minutes, the temperature of the outer ring should not rise more than 15℃ (poor lubrication or high internal friction will cause overheating).
Precision grade verification
Reference standard:
ABEC standard (USA): ABEC-1 to ABEC-9, the higher the grade, the smaller the tolerance.
ISO standard: P0 (ordinary) to P6 (ultra-precision).
Professional instruments are required to measure the radial runout of the inner and outer rings (such as micrometers), for example:
The radial runout of ABEC-5 bearings should be ≤0.005mm.
IV. Seal and lubrication
Seal quality
Rubber seal ring: good elasticity, no aging cracks (inferior seal rings are prone to hardening and oil leakage).
Contact seal: Move the sealing lip by hand, it should rebound quickly without deformation.
Grease detection
High-quality grease: uniform color (usually light yellow or blue), no odor.
Poor quality grease: easy to dry and clump, black sludge will flow out at high temperature.
5. Brand and certification
Famous brand reference
International first-line: SKF (Sweden), NSK (Japan), FAG (Germany), TIMKEN (USA).
Domestic high-quality: C&U, HRB, ZWZ.
Certification mark
Required certification: ISO 9001 (quality management system), ISO/TS 16949 (automotive industry).
Special fields: CE (EU), RoHS (environmental certification).
6. Practical skills (when there are no professional tools)
Magnetic test
Put a magnet close to the bearing, high-quality stainless steel bearings are non-magnetic (except martensitic stainless steel).
Landing test
Let the bearing fall freely from a height of 1 meter to the wooden floor. The sound of the genuine product is crisp and short, and the sound of the inferior product is dull (the internal structure is loose).
Packaging and anti-counterfeiting
Authentic packaging: The box is sturdy, printed with anti-counterfeiting code, batch number, and comes with instructions and certificate of conformity.
Imitation packaging: Blurred printing, no anti-counterfeiting label or label can be easily torn off.
VII. Common characteristics of inferior bearings
The price is significantly lower than the market average price (for example, the price of SKF bearings is only 1/3 of the genuine ones).
The outer packaging has no brand LOGO or the LOGO is rough.
It feels astringent when rotating, and the position of the ball is random after stopping (the genuine product will stop at a fixed position due to precision processing).
Summary:
Short-term judgment depends on appearance, rotation flexibility and brand logo;
Long-term verification requires testing of wear resistance (continuous operation for 72 hours without abnormal temperature rise and noise).
It is recommended to ask the supplier to provide material report (MTC) and third-party inspection certificate (such as SGS) for the first cooperation.
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