When Southeast Asian manufacturers list industrial components on Alibaba.com, surface treatment specifications often become a key differentiator in buyer decision-making. Polished mirror finish represents the highest grade of surface refinement in metal fabrication, but its technical definition varies significantly across industries and applications.
For manufacturers in the testing instrument and equipment category (including crane scales, weighing systems, and precision instruments), understanding these standards is essential for matching buyer expectations in medical, food processing, pharmaceutical, and high-end industrial markets.
According to industry standards documented in technical specifications, stainless steel surface finishes are classified into numbered grades:
- No.1 (Hot Rolled Annealed): Rough, dull surface, lowest cost
- No.2B (Cold Rolled): Standard mill finish, smooth but not reflective
- No.3 (Coarse Polished): Ra 0.8-1.0μm, visible polishing lines
- No.4 (Brushed/Satin): Ra 0.2-0.6μm, directional grain pattern, most common for appliances
- BA (Bright Annealed): Ra 0.1-0.2μm, highly reflective without mechanical polishing
- No.7 (Semi-Mirror): Ra 0.1-0.15μm, near-mirror reflection with faint polishing lines
- No.8 (Mirror): Ra<0.1μm, true mirror reflection, highest grade [2][5]
Surface Finish Grade Comparison: Technical Specifications and Applications
| Finish Grade | Ra Value (μm) | Reflectivity | Cost Premium | Typical Applications |
|---|---|---|---|---|
| No.2B (Standard) | 0.4-0.8 | Low | Baseline | General industrial, structural |
| No.4 (Brushed) | 0.2-0.6 | Medium | +20-30% | Appliances, architectural, food equipment |
| BA (Bright Annealed) | 0.1-0.2 | High | +50-80% | Decorative trim, elevator panels |
| No.7 (Semi-Mirror) | 0.1-0.15 | Very High | +100-150% | High-end appliances, signage |
| No.8 (Mirror) | <0.1 | Mirror | +200-300% | Medical, pharmaceutical, luxury applications |
For crane scales and weighing equipment specifically, the hook component often receives higher-grade polish than the housing. This is not merely aesthetic—hygiene and cleanability become critical factors when equipment is used in food processing, pharmaceutical, or laboratory environments where contamination control is paramount.
Three primary polishing methods achieve mirror finish:
Mechanical Polishing: Progressive grit sanding (220→400→600→800→1000→1500→2000+) followed by buffing compound. Most common, cost-effective for large parts [1].
Electropolishing: Electrochemical process that removes surface material uniformly. Achieves Ra 0.1-0.25μm, excellent for complex geometries and medical components [1].
Chemical Polishing: Acid-based solutions dissolve surface peaks. Less common, typically used for small parts or specific alloys [1].
