FAQs on Bearings and Bearing Housings

Ⅰ. Bearing Selection & Performance

1. What bearing housing is suitable for high-load conditions?
   For heavy-duty applications, double bearing housings (or split-type housings) are recommended. Their symmetrical structure evenly distributes axial/radial loads, enhancing shafting rigidity and preventing deformation or vibration caused by load concentration in single-housing setups. Ideal for heavy machinery, industrial drives, and other high-load scenarios.
2. How do stainless steel bearings compare to standard bearing steel bearings?
   • Material Properties: Stainless steel bearings (e.g., 440 stainless steel, Cr≥12%) offer superior corrosion resistance compared to bearing steel (e.g., GCr15), but have slightly lower hardness (HRC 55-58 vs. HRC 60-62 for bearing steel) and maximum rotational speed.
   • Application Scenarios: Suitable for low-speed (≤10,000 RPM), light-to-medium load environments with moisture, dust, or corrosive media (e.g., food machinery, medical devices). Bearing steel bearings excel in high-speed, heavy-load applications (e.g., motors, machine tools).
3. Are stainless steel bearings completely rust-proof?
   Stainless steel bearings exhibit high corrosion resistance, but are not entirely rust-proof. Their anti-rust performance depends on:
   • Alloy Composition: 304 stainless steel (Cr18Ni8) resists general corrosion, while 440C (Cr17Mo) offers stronger acid/alkali resistance;
   • Environmental Factors: Prolonged exposure to high humidity (>80%RH), saltwater, or strong oxidizers may still cause pitting or stress corrosion.
4. Why do bearings rust, and how to prevent it?
   • Root Causes: Bearing steel (e.g., GCr15) contains only 1.5% chromium, insufficient to form a complete passivation layer. Moisture, salt, or grease degradation accelerates oxidation.
   • Preventive Measures:
     ▶ Material Selection: Use stainless steel or ceramic bearings in wet environments;
     ▶ Environmental Control: Keep installation surfaces dry, avoid liquid splashing, and install protective covers if necessary;
     ▶ Surface Treatment: Apply molybdenum disulfide (MoS₂) anti-rust coatings or hot-dip galvanization;
     ▶ Storage Practices: Store in vacuum packaging with humidity ≤60%, away from corrosive chemicals.

Ⅱ. Installation & Assembly Techniques

5. Key considerations for bearing housing installation?
   • Sequence: Fix the housing first (ensure levelness ≤0.05mm/m), then install the shaft to avoid misalignment-induced load concentration;
   • Surface Requirements: Installation surface roughness ≤Ra1.6μm, flatness error ≤0.02mm. Use a torque wrench to tighten bolts to specified torque;
   • Pre-alignment Check: Measure housing bore concentricity with a dial indicator (tolerance ≤0.01mm) to ensure rotational accuracy.
6. Why do single-row angular contact bearings fail during installation?
   Single-row angular contact bearings can only withstand axial loads in one direction (e.g., right-to-left). Incorrect installation (reverse load direction) causes:
   • Stress concentration on rolling elements and raceways, leading to spalling or fracture;
   • Abnormal internal clearance changes, resulting in overheating or seizing.
     Solution: Verify load direction before installation. For paired use, configure in "back-to-back" or "face-to-face" arrangements to balance axial forces.
7. Installation methods for different fit types?

   Fit Type	Tolerance Class	Installation Method	Application
   Clearance Fit	Shaft g6/h6, Housing H7	Press fit (use manual hydraulic press or sleeve)	Low-speed bearings requiring frequent disassembly
   Transition Fit	Shaft k6/m6, Housing J7	Thermal method (heat bearing to 80-100℃ or cool shaft)	Medium-precision, medium-load rotating parts
   Interference Fit	Shaft n6/p6, Housing N7	Hydraulic fitting or thermal expansion (temperature difference ≥80℃)	High-load, high-precision fixed installations

Ⅲ. Shaft & Housing Tolerance Design

8. What is the recommended shaft tolerance for bearing housings?
   For general applications, shaft tolerance g6 (transition fit) is recommended. The tolerance zone for a φ50mm shaft is -0.007mm~-0.016mm, balancing rotational flexibility and preventing vibration from excessive clearance. For precision equipment (e.g., machine tool spindles), k6 (slight interference fit) may be used to enhance rigidity.
9. Can cast housing dimensions serve as precision positioning references?
   No. Cast bearing housings (e.g., gray cast iron HT200) have a dimensional tolerance of CT9 grade (φ50mm hole tolerance ±0.3mm) and surface roughness Ra≥12.5μm, insufficient for precision assembly. For high-precision scenarios, use machined bearing housings (tolerance IT7, roughness Ra≤3.2μm) or standardized housings with positioning shoulders.

Ⅳ. Technical Analysis of Fit Types

10. Core differences between transition fit and clearance fit?
    • Transition Fit: A slight interference or clearance exists between the bearing inner ring/shaft and outer ring/housing (overlapping tolerance zones). Centering is achieved by controlling interference, suitable for high-precision rotation (e.g., motor rotors) without additional axial fixation;
    • Clearance Fit: A defined gap exists between mating surfaces (shaft tolerance smaller than housing bore tolerance). The bearing can slightly move for self-centering, facilitating disassembly. Used in low-speed, light-load applications or scenarios requiring thermal expansion compensation (e.g., conveyor shafts).

Ⅴ. Maintenance & Lubrication Guidelines

11. Do bearings require regular lubrication?
    • Oil-free self-lubricating bearings (e.g., BBK series): Pre-embedded with solid lubricants (e.g., graphite) at factory. No initial lubrication is needed, but for long-term high-speed operation, replenish lithium-based grease (NLGI 2 grade) every 200 hours;
    • Open/single-sealed bearings: Apply grease (filling 1/3~1/2 of the bearing cavity) before installation. In harsh environments, inspect every 50 hours and replace contaminated or carbonized grease promptly.

Ⅵ. Troubleshooting Guide

12. How to address excessive axial clearance after shaft-housing assembly?
    • Causes: Improper axial fixation of bearings or weak positioning components (e.g., C-clips) leading to looseness;
    • Solutions:
      ▶ Fix the inner ring with shaft retaining rings (GB/T 894) or locknuts (with tab washers);
      ▶ Use housing end covers or snap rings for outer ring positioning, ensuring axial clearance is controlled at 0.02~0.05mm (adjust according to bearing type);
      ▶ Avoid using C-clips for heavy-load bearings, as their positioning accuracy (±0.1mm) cannot meet axial load requirements.