Achieving high-quality bearings involves a comprehensive assessment of several parameters, including materials and components, technology and procedures, design and know-how, damages, service, quality assurance, and even price.
In this article, we will focus on the technical parameter of bearing quality – materials.
The choice of materials significantly influences the performance and durability of bearings. The quality of the material used for the production of the bearings directly affects factors such as load-carrying capacity, friction, and heat dissipation. In terms of bearing rings and rolling elements, 4 major materials are used for production:
- High-carbon chromium bearing steel (100Cr6) – up to 2 % chrome, high hardness is achieved by direct quenching, while machinability is improved by spheroidizing annealing
Table 1: High-carbon chromium bearing steel standard equivalents
- Case hardening bearing steel – material with a low level of carbon (below 0,2% carbon), the carbon is added in the special procedure during the heat treatment to the surface of the material which causes the surface to be high-hardened while the core has a lower hardness which allows high-stress capabilities of the surface and toughness of the core
- Stainless bearing steel – materials with higher content of chromium (~18%) with the addition of nickel which is more resistant to surface corrosion. The chromium reacts with oxygen to form a thin layer of oxide on the surface, creating a passive film. Most often used are martensitic stainless steels like AISI 420C, AISI 440C and austenitic AISI 304.
- Medium-carbon bearing steel – materials with medium content of carbon, usually between 0,8 and 2 %, where induction hardening can be applied to portions where high hardness is needed.
- Other materials – special materials used for addressing specific application requirements. Ceramic materials are chosen over stainless steel due to their high corrosion resistance and non-magnetic requirements in application. On the other side, Polymer-Plastic materials (Silicone Nitrate, cages – Phenolic) are used where resistance to corrosion, chemicals and rust as well as a lightweight body with high strength is used.
The essential factor for the quality of the bearings is the selection and purity of the used materials. Therefore, along the supply chain products are accompanied by materials 3.1 certificates which show the chemical composition of used materials.
Table 2: High-carbon chromium bearing steel composition
The selection and purity of materials used in the production of bearings can significantly influence the quality of the final product. Here’s how this may impact manufacturing and bearing performance:
- Workability: The purity of materials determines the type of treatment used for bearing production. For example, if the material has many unwanted components, it is difficult to perform any treatment to achieve specific characteristics.
- Material Strength and Integrity: The purity of the base material is crucial for ensuring the desired mechanical properties. Impurities in the material can weaken its structural integrity, leading to reduced strength and compromised load-carrying capacity. High-quality bearings require materials with consistent and controlled composition to achieve the necessary hardness, toughness, and fatigue resistance.
- Dimensional Stability: Impurities can also affect its dimensional stability, resulting in dimensional variations or deformations during manufacturing or operation. Cleaner materials with controlled composition help maintain the dimensional stability of the bearing, ensuring proper fit, alignment, and smooth operation.
- Surface Finish and Roughness: The presence of impurities or contaminants in the material can result in surface defects or irregularities on the bearing’s surfaces. These imperfections can cause increased friction, wear, and noise during operation. High-purity materials allow for better control over the surface finish and roughness, ensuring smoother and more efficient sliding or rolling contact between the bearing components.
- Corrosion Resistance: Impurities in the material can make the bearing more susceptible to corrosion. Contaminants or alloying elements with low corrosion resistance may lead to premature degradation of the bearing, particularly in harsh or corrosive environments. Utilizing materials with high purity and appropriate alloying elements improves the corrosion resistance of the bearing, ensuring long-term performance and reliability.
- Consistency and Reproducibility: Purity plays a crucial role in achieving consistent and reproducible manufacturing processes. When the material used for bearing production is highly pure and free from contaminants, it allows for better control over the manufacturing parameters, such as heat treatment, machining, and surface finishing. This leads to more consistent bearing quality, tighter tolerances, and improved repeatability in meeting performance specifications.
Overall, bearing materials play a crucial role in achieving a certain level of mechanical strength, dimensional stability, surface quality, corrosion resistance, and overall performance. Materials with high purity provide the foundation for the production of high-quality bearings that can meet the demanding requirements of a wide range of applications and work reliably for long periods of time.
If needed, the producer should be able to provide the certification on the purity and share of elements (%) of the materials. In case you need any assistance, Codex Team is ready to help you with expertise and data.