Bearing rollers are key components in mechanical transmissions, rolling bearings, and other equipment. Their material and quality grade directly affect the service life, load-carrying capacity, and operational stability of the equipment. The following is a detailed explanation from the aspects of material classification and quality grade:
The material of bearing rollers needs to meet the requirements of high strength, high wear resistance, good toughness, and fatigue resistance. Common materials include:
High-carbon chromium bearing steel (e.g., GCr15, SUJ2)
- Characteristics: Carbon content is about 1%, chromium content is about 1.5%. After quenching and low-temperature tempering, the hardness can reach HRC 60-65, with excellent wear resistance and fatigue resistance.
- Applications: Suitable for most general-purpose bearing rollers, such as deep groove ball bearings and cylindrical roller bearings, which can bear medium loads and speeds.
Carburized bearing steel (e.g., 20CrMnTi, 12Cr2Ni4)
- Characteristics: Low-carbon alloy structural steel. After carburizing and quenching, the surface hardness reaches HRC 58-62 (wear-resistant), and the core hardness is HRC 30-45 (good toughness).
- Applications: Suitable for rollers bearing impact loads, such as automobile gearbox bearings and large mechanical bearings.
- Characteristics: Added with molybdenum, vanadium, and other elements, it is resistant to high temperatures (up to 300-500°C) and maintains high hardness and strength at high temperatures.
- Applications: Rollers in high-temperature environments such as aero-engines and steam turbines.
9Cr18, 440C
- Characteristics: Chromium content ≥ 12%, with good corrosion resistance and oxidation resistance, and hardness up to HRC 58-60.
- Applications: Rollers in humid or corrosive environments such as medical equipment, food machinery, and marine engineering.
Silicon nitride (Si₃N₄), zirconia (ZrO₂)
- Characteristics: Low density (about 1/3 of steel), low friction coefficient, high temperature resistance, corrosion resistance, good insulation, and non-magnetic.
- Applications: High-speed precision machine tools, semiconductor equipment, high-temperature bearings, and other scenarios requiring lightweight and corrosion resistance.
- Tool steel (e.g., T10A): Suitable for low-load and low-speed occasions with low cost.
- Composite materials: Such as metal matrix composites (added with ceramic particles), which can balance strength and wear resistance, suitable for special working conditions.
The quality grade of bearing rollers is mainly divided based on dimensional accuracy, form tolerance, surface quality, and internal quality. There are relevant international and domestic standards (such as ISO, GB/T), and common grades are as follows:
- Main Indicators: Roller diameter deviation, length deviation, ellipticity, taper, etc.
- Grade Classification (Taking GB/T as an Example):
- Grade 0: Highest precision, dimensional deviation ≤ ±1μm, suitable for high-precision equipment such as precision machine tools and aerospace.
- Grade I: High precision, dimensional deviation ≤ ±3μm, suitable for high-speed motors and precision instrument bearings.
- Grade II: Medium precision, dimensional deviation ≤ ±5μm, suitable for general machinery, automobile bearings, etc.
- Grade III: Ordinary precision, dimensional deviation ≤ ±10μm, suitable for general machinery with low speed and low load.
- Main Indicators: Surface roughness (Ra value), surface defects (such as scratches, cracks, pitting).
- Grade Requirements:
- High-precision rollers: Ra ≤ 0.02μm (mirror level), no visible defects, suitable for high-speed and low-noise occasions.
- Ordinary rollers: Ra ≤ 0.1-0.2μm, allowing slight defects to meet general working condition requirements.
- Main Indicators: Content of non-metallic inclusions, depth of decarburized layer, uniformity of microstructure (such as martensite grade).
- Grade Classification:
- High-grade rollers: Inclusion grade ≤ 0.5 (according to ISO 4967 standard), no decarburized layer, uniform structure, and long fatigue life.
- Ordinary rollers: Inclusion grade ≤ 2, decarburized layer depth ≤ 0.02mm, suitable for conventional load scenarios.
- International standards: Such as ISO 3096 (Rolling bearings - Rollers - Dimensions and tolerances), ISO 4963 (Rolling bearings - Rollers - Surface quality).
- Domestic standards: Such as GB/T 307.3 (Rolling bearings - Tolerances for rollers), which divides rollers into four grades: 0, I, II, and III, corresponding to dimensional accuracy grades.
When selecting bearing rollers, it is necessary to match the material according to specific working conditions (load, speed, temperature, environment), and determine the quality grade according to the equipment accuracy requirements. Although high-quality rollers have higher costs, they can significantly improve the reliability and service life of equipment and are the core guarantee for key mechanical components.
