How Precise Process Parameters Control the Bearing's "Drawn" Texture

In the bearing industry, the term "wire drawing" doesn't literally mean "drawing into wire." Rather, it refers to a uniform, fine, unidirectional, silk-like texture that appears on the raceway surface after superfinishing. While a byproduct of superfinishing, it's the most intuitive visual indicator of process quality.

I. Formation Mechanism

1. When the oilstone oscillates at a short stroke of 10–25 Hz, the abrasive grains only micro-cut the "peaks," leaving the valleys as regular microgrooves.

2. The oscillation direction is perpendicular to the direction of ring rotation, spreading the cuts into fine lines 0.1–0.3 µm deep.

3. Once the abrasive grains are blunted and the oil film is established, cutting ceases and the friction polishing phase begins. The edges of the microgrooves are slightly rounded, resulting in the "light and dark" silky luster known as wire drawing.

II. Process Window
- Oilstone: GC 400#–800# or WA 600#–1200#, porosity 35–45%, hardness E–G;
- Pressure: 0.2–0.4 MPa for roughing to quickly remove peaks, 0.05–0.15 MPa for fine finishing to produce a fine texture;
- Oscillation Frequency: 15–25 Hz, amplitude 0.8–1.5 mm. Excessive amplitude will blur the texture;
- Workpiece Linear Speed: 20–35 m/min. Too high will skew the grain, too low will cause a foggy surface;
- Lubrication: 5% oily ester + 95% light kerosene, flow rate ≥ 6 L/min, to both flush chips and maintain an oil film.

III. Quality Assessment
- Visual Inspection: Uniform texture, consistent orientation, no visible "white spots" or "meteoric spots";
- Roughness: Ra 0.04–0.08 µm, Rz ≤ 0.5 µm, Rpk ≤ 0.05 µm;
- Waviness: ≤ 0.13 µm/5 mm, 20–30% improvement in ovality;
- Residual Compressive Stress: ≥ –150 MPa, depth 5–10 µm;
- Vibration: 1–2 dB lower than after grinding, noise reduction of 3–6 dB.

IV. Common Defects and Solutions
1. Foggy Texture - The oilstone is too coarse or insufficiently cooled. Replace with an 800# oilstone and increase the flow rate.
2. Meteor Spots - The oilstone pressure is suddenly jumping or there is excessive clearance in the oscillating mechanism. Check the preload on the servo valve and guide rail.
3. No Texture - The oilstone is completely clogged. Use an Al₂O₃ dressing rod to trim the surface online for 2–3 seconds.
4. Wiredrawing Slant - The workpiece and the oilstone guide are not perpendicular. Realign the centering. The V-block angle should be ≤ 0.02 mm.

V. Functional Significance
Although the wiredrawing texture is shallow, it can increase the raceway contact area from 30% after grinding to over 80%, extend the microscopic oil film retention time by 2–3 times, increase the rated life by 20–40%, and significantly reduce vibration and noise. High-end home appliances, high-speed electric spindles, and new energy vehicle reducer bearings almost all have "uniform wire drawing" written into the drawing acceptance standards, making it the fastest "on-site criterion" for whether ultra-precision is qualified.