technical case study
• Bead blasting uses small glass beads projected at high velocity onto the surface. This produces a uniform matte, non-reflective finish. While visually consistent, bead blasted surfaces have relatively high surface roughness, which can create sites where moisture and contaminants accumulate, potentially initiating corrosion under certain conditions. Chemical Treatments • Chemical methods are primarily used to remove heat tint caused by welding and other fabrication processes. Heat discoloration often indicates chromium depletion in the near-surface layers. Chromium is essential for corrosion resistance, and heat-tinted material must be removed to expose sound stainless steel. While mechanical removal is possible, chemical treatments are generally more effective. The process typically involves two steps: pickling and passivation. Passivation is not always required, as the passive layer reforms naturally in a clean environment. • Pickling r emoves heat tint and scale using acid, leaving a clean surface free from iron contamination and chromium-depleted material. The resulting appearance is generally uniform and dull. • Passivation is also acid-based and promotes the formation of a stable passive layer. It helps restore brightness and stabilise the surface appearance. Uniform passivation supports consistent sheen, while contamination or disruption of the passive film can result in discoloration and uneven appearance. Electropolishing Electropolishing is an electrochemical process that produces a bright, smooth, highly reflective surface. The smoothness achieved through electropolishing
• Cleanability and sanitation - Smoother finishes are easier to clean and less likely to harbour bacteria, making them suitable for food processing, pharmaceutical, and medical applications. • Friction and wear - Surface roughness affects the coefficient of friction and therefore influences wear performance. Smoother finishes generally provide lower friction and improved wear resistance. • Adhesion of coatings - Surface roughness affects the adhesion and durability of coatings or paints. Although stainless steel rarely requires coating, it is worth noting that it has strong resistance to filiform corrosion, which can cause coatings to peel from other base materials. 2. Finish Type Different processing routes can dramatically alter the appearance of stainless steel surfaces. • Mechanical Finishes Mechanical processes such as grinding, brushing, and polishing use wet or dry abrasives, typically in belt or stone form, applied at relatively high speeds. These processes create directional grain marks or a smooth directional sheen. Surface quality depends on abrasive type, grit size, application speed, and applied pressure. Many of these operations are manual, which makes consistency difficult to control. Nevertheless, reasonably high levels of smoothness can be achieved. • Directional finishes , such as brushed No.4, produce a visible linear grain that affects perceived brightness and texture. Grain direction strongly influences reflectivity and shading. Highly polished or Bright Annealed (BA) finishes have little or no visible directionality.
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Issue 1 – 2026
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