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What Ra Value Is Required for Bathroom Hardware Grinding & Polishing? Industry Standards and Compliance Guide
2026-07-09
Surface roughness Ra is the core quantitative indicator of bathroom hardware appearance quality, directly determining touch, luster and product grade. From rough grinding to fine polishing, each process step corresponds to a clear Ra range, and different markets and product tiers have different acceptance criteria.
Common Roughness Grades in the Bathroom Industry
表格
| Process Stage | Typical Ra Range | Appearance & Touch | Corresponding Grit |
|---|---|---|---|
| Weld rough grinding / stock removal | Ra 3.2 – 6.3 μm | Visible grinding marks, rough feel | 80# – 120# |
| Intermediate grinding | Ra 1.6 – 3.2 μm | Finer marks, visible grain | 180# – 240# |
| Fine grinding / semi-bright | Ra 0.8 – 1.6 μm | Smooth to touch, fine lines visible up close | 320# – 400# |
| Mirror polishing | Ra 0.2 – 0.4 μm | Clear reflection, virtually no tactile grain | 600# + cloth wheel |
| Standard brushing | Ra 0.4 – 0.8 μm | Uniform continuous grain, fine touch | 240# – 320# brushing belts |
Acceptance Requirements by Market & Category
- Commercial / builder-grade: Ra ≤ 1.6 μm after fine grinding; priority is no obvious scratches or burrs, cost-driven.
- Mid-to-high-end domestic brands: Ra ≤ 0.4 μm for polished parts, Ra ≤ 0.8 μm for brushed parts; uniform grain, no uneven shading.
- High-end European & American export orders: Ra ≤ 0.2 μm for mirror finish, with batch Ra variation ≤ 0.1 μm. Extremely high consistency requirements, usually with full inspection or SPC sampling.
- Concealed parts: Non-visible surfaces like valve seats and inlet ports only need Ra ≤ 6.3 μm, focusing on deburring and assembly dimensions.
Key Factors Affecting Roughness Stability
- Belt condition: New vs. worn performance difference, clogging and uneven grit size are the biggest causes of Ra fluctuation.
- Pressure stability: Manual grinding has inconsistent pressure; even robotic grinding suffers uneven local roughness if force control accuracy is poor.
- Surface speed: Too low a speed causes more ploughing than cutting, inducing plastic deformation and worse roughness.
- Upstream process quality: Casting defects and deep rough-grinding scratches are hard to fully remove in subsequent finishing.
Process Solutions for Stable Compliance
- Progressive grit steps, no skipping: Grit ratio between steps should not exceed 1.5×. Each step must fully remove scratches from the previous one to avoid permanent deep marks.
- Full-lifecycle belt management: Fixed-life replacement + wear compensation + in-line cleaning maintains consistent cutting performance.
- Servo constant-force control: Servo force control systems keep contact pressure variation within ±5%, an order of magnitude more accurate than typical pneumatic force control.
- In-line inspection closed loop: High-end lines deploy in-line roughness measurement, with data fed back to auto-tune parameters for closed-loop control.
For bathroom factories, defining Ra targets for each process and matching them with appropriate processes and equipment is the core prerequisite for avoiding over-processing, controlling costs and ensuring quality.