1. Material Preparation
Material Selection: High-density bronze alloy sheets are selected, commonly grades CuSn8 (tin bronze) or CuSn6, with thickness determined by bearing specifications (typically 0.5–3mm).
Blanking: The bronze sheet is cut according to the bearing's developed dimensions, with allowances reserved for welding and machining.
2. Winding/Forming
This is the core process, which follows two main routes:
Route A: Direct Winding Method (for thin-wall bearings)
Pre-bending: Both ends of the bronze sheet are pre-bent into an arc to facilitate rolling.
Cylindrical Rolling: The flat sheet is rolled into a cylindrical shape on a rolling machine, controlling roundness and seam gap.
Welding: The seam is welded using TIG or laser welding to form a continuous cylinder. Post-weld, the weld seam is cleaned and stress relief treatment is performed.
Sizing: The rolled blank is placed in a dedicated die for press sizing to correct roundness and ensure dimensional accuracy.
Route B: Composite Winding Method (for self-lubricating bearings)
Surface Structuring: The bronze sheet surface is machined with ordered oil holes, oil pockets, or oil reservoirs, typically φ1–3mm in diameter.
Powder Sintering (for composite self-lubricating types):
Spherical bronze powder is evenly dispersed on a steel backing sheet and sintered in a tunnel furnace (850–900°C) to form a porous bronze layer.
Modified PEEK or PTFE particles are then spread and secondarily sintered to embed the lubricating material into the pores.
Composite Rolling: The three-layer structure (steel back + bronze layer + lubricating layer) is firmly bonded via rolling mill at 200–300 MPa pressure.
Cylindrical Forming: The composite sheet undergoes the same rolling and welding processes to form a cylinder.
3. Precision Machining
Turning or Grinding:
Rough machining of inner and outer diameters, leaving a finishing allowance of 0.1–0.2mm.
Finish turning of ID and OD to design dimensions, with tolerance grades controlled to IT7–IT8.
Oil Hole Machining: Oil injection holes are drilled or punched, with chamfering and deburring required at hole edges.
Segmenting: Cut into individual bearings or kept as retaining sleeves based on requirements.
4. Post-Processing and Quality Inspection
Heat Treatment (optional):
Stress relief annealing at 300–400°C for 1–2 hours to eliminate rolling and welding stresses.
For oil-impregnated bearings, oil impregnation is performed under vacuum or protective atmosphere.
Oil Impregnation (oil-impregnated bearings only):
Bearings are immersed in lubricating oil (ISO VG100) at 80–100°C; oil penetrates pores via capillary action for 2–4 hours.
Surface Treatment:
Inner and outer surfaces are polished to a roughness of Ra ≤ 0.8 μm.
Optional tin plating or anti-corrosion coating.
Quality Inspection:
Dimensional accuracy: Measurement of ID, OD, roundness, and cylindricity.
Performance testing: Crush strength (≥150 MPa), porosity (18–22%), oil content.
Visual inspection: Weld seam quality and surface defects.
Marking and Packaging: Laser marking of model and batch numbers, followed by cleaning, anti-rust oil application, and packaging.
5. Special Process Notes
Self-lubricating bearings: Oil reservoirs must be rolled on the bronze layer surface before winding; the reservoir opening is smaller than its cavity to prevent oil expulsion.
Large-diameter bearings: Require segmented rolling using dedicated dies, followed by overall sizing after welding.
Thin-wall bearings (wall thickness <1mm): Mandrel-free rolling technology must be used to prevent sheet cracking.
Summary of Key Process Parameters
| Process | Temperature | Pressure/Time | Quality Control Index |
|---|---|---|---|
| Cylindrical Rolling | Room temp. | – | Roundness ≤ 0.05 mm |
| Sintering | 850–900°C | 1–2 h | Porosity 18–22% |
| Rolling | – | 200–300 MPa | Bond strength ≥ 70 N/mm² |
| Oil Impregnation | 80–100°C | 2–4 h | Oil content ≥ 12% |
This process combines metal plastic forming and powder metallurgy technologies, offering high material utilization, low cost, and suitability for mass production. It is particularly ideal for medium-load, low-speed applications such as conveying machinery and lifting equipment.
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