Swedged Anchor Bolt Galvanizing

The process of preparing and galvanizing swedged anchor bolts to meet ASTM specification F2329 entails several steps:

  1. Wheelabrating:
    Like sandblasting, wheelabrating involves firing steel shot at anchor bolts as they are tumbled, removing surface scale resulting from manufacturing processes such as rolling, heat treating, and forging.
  1. Caustic Soda Bath:
    Anchor bolts are immersed in large tanks of caustic soda to eliminate cutting oil and organic contaminants. Subsequently, they are rinsed with water.
  1. Sulfuric Acid Treatment:
    Anchor bolts undergo submersion in tanks of sulfuric acid to remove light mill scale and etch the steel surface. Afterward, they are rinsed with water.
  1. Flux Application:
    Anchor bolts are submerged in tanks of flux, a chemical aiding in zinc-to-steel bonding, serving as the final preparation step before galvanization.
  1. Galvanization:
    Anchor bolts are placed in baskets or racks and immersed in molten zinc for 2 to 4 minutes. During this process, the zinc bonds to the anchor bolts, forming a robust, corrosion-resistant coating. Upon extraction from the galvanizing tank, excess zinc is removed by spinning. The galvanized anchor bolts are then rapidly cooled in water for handling, inspection, and packaging.

Hot-dip galvanizing is a process designed to apply a zinc coating onto swedged anchor bolts, safeguarding them from corrosion in environments with high moisture levels. Following a meticulous cleaning and preparation procedure, the anchor bolts are submerged in a bath of molten zinc at a scorching temperature of 840°F. This immersion allows the zinc to fuse with the steel, forming a durable and economical protective layer capable of ensuring decades of service life for the anchor bolts. Governed by ASTM specification F2329, this process adds a zinc layer of 2 to 6 mils onto the swedges anchor bolts’ surface. It’s worth noting that contrary to common misconceptions, the threads of galvanized anchor bolts are not reduced in size; they maintain their original threading. Instead, galvanized nuts are slightly oversized to fit snugly onto the threads of the galvanized anchor bolts.

One of the challenges in galvanizing swedged anchor bolts is preventing excessive zinc buildup in the threaded section. As anchor bolt racks or baskets are extracted from the galvanizing tank, the zinc rapidly solidifies. To address this, a specialized centrifuge is employed while the zinc is still in its liquid state to remove excess zinc from the threads. It’s important to note that “chasing” the threads of an anchor bolt (rethreading post-galvanization) is a common but prohibited practice under specification F2329, typically employed by bolt manufacturers and galvanizing companies lacking specialized thread processing systems.