postgalvanizing

Postgalvanizing refers to applying a protective zinc coating to steel or iron components after they have been formed, fabricated, or assembled. This contrasts with galvanizing of raw stock or sheet metal before shaping. Post-fabrication galvanizing is commonly used for structural members, hardware, and assembled parts where pre-coated stock is impractical or where corrosion protection is needed after fabrication.

The most common postgalvanizing method is hot-dip galvanizing (HDG). In HDG, cleaned and prepared parts are immersed in molten zinc, producing a metallurgical bond and a uniform coating that follows contours and complex geometries. Other methods include electrogalvanizing, which uses electrical current to deposit zinc, and zinc-based thermal spray or spray-on coatings for certain shapes or repair work. Some processes may combine coating with post-weld treatment, since welding can compromise zinc coverage in welded areas.

Standards and specifications for postgalvanizing are set by organizations such as ISO and ASTM. Examples include ISO 1461 for galvanized coatings on iron or steel and ASTM A123/A123M for hot-dip galvanizing of structural steel. Fasteners may fall under ASTM A153/A153M, while smaller parts and hardware have their own applicable standards. Coating thickness typically ranges from about 45 to 100 micrometers, depending on the process, required corrosion resistance, and applicable standard.

Advantages of postgalvanizing include excellent long-term corrosion protection, even coating on complex geometries, and the ability to retrofit protection onto already assembled structures. Limitations include potential distortion in large parts, the need for surface preparation and coating cure times, possible weld area coverage issues requiring repair, and higher processing costs for some geometries.

Applications span construction (bridges, buildings, and pipelines), industrial equipment, fence posts, and hardware components where reinforced rust resistance is desirable after assembly.