Mechanical Galvanizing

Mechanical galvanizing is a cold, mechanical process used to apply zinc coatings to fasteners without heat or electrochemical action. The fasteners are tumbled in a rotating barrel with glass beads, zinc powder, water, and chemical promoters. The glass beads impact-peen the zinc powder onto the fastener surface, producing a coating with performance characteristics comparable to hot-dip galvanizing but without thermal or hydrogen embrittlement risks.

Asia Bolts Industries applies mechanical galvanizing per ASTM B695, which covers classes from Class 25 (25 µm minimum) to Class 110 (110 µm minimum), with corresponding coating weight and corrosion performance requirements.

Why Mechanical Galvanizing Over HDG for High-Strength Fasteners:

• Hot-dip galvanizing exposes fasteners to 450°C, which can alter the mechanical properties of high-strength alloy steel bolts

• Electroplating introduces hydrogen into the steel lattice (hydrogen embrittlement risk) — requiring subsequent baking; mechanical galvanizing does not

• For ASTM A490, Grade 10.9, and SAE Grade 8 fasteners, mechanical galvanizing is the preferred zinc coating method

ASTM B695 Class Options:

• Class 25: 25 µm minimum — moderate protection

• Class 40: 40 µm minimum — equivalent to light HDG

• Class 55: 55 µm minimum — equivalent to standard HDG (most common for structural bolts)

• Class 80 / 110: Heavy-duty offshore and marine applications

Supplementary chromate passivation is available to improve initial corrosion resistance and aesthetics.

Applications include high-strength structural bolts (ASTM A490, SAE Grade 8), flange bolts for oil & gas piping systems, heavy anchor bolt assemblies, and all applications where hydrogen embrittlement is a specified design concern.