Galvanized anchor bolts are manufactured in a variety of configurations. Engineers will determine the appropriate grade, size, and configuration of a galvanized anchor bolt based on its application and the forces acting against it. The various manufacturing processes required to produce a galvanized anchor bolt are described below.
Round bars of steel, typically 20’ – 40’ in length, are melted and rolled at a steel mill. The first labor operation required, regardless of what type of anchor bolt is being manufactured, is to cut the round bar to length. Galvanized anchor bolts can be either sheared or band saw cut. Shears chop the steel like a guillotine and are extremely efficient, while band saws use blades with teeth to cut through the steel. Shears are somewhat limited in the diameters (usually about 2” maximum) and lengths (typically up to about 100”) that they can cut, while band saws essentially have no limitations.
All galvanized anchor bolts, regardless of their configuration, will need a threaded end projecting from the concrete. Threads are either cut or rolled. Cut threads are typically made by chasers, which remove steel from the round bar creating the threaded area. Rolled threads are formed through an extrusion process in which two dies displace the steel to form the threads. Many straight, galvanized anchor rods will also have thread on the embedded end with some combination of a nut(s) and/or plate to provide pull-out resistance.
Some anchor bolts have a forged head on the embedded end, creating pull-out resistance. The unthreaded end of the round bar is heated to around 2,000 degrees Fahrenheit and “upset” in an operation that shapes the heated end into a hex, heavy hex, or square shape. Headed anchor bolts are commonly available through 2½” diameter.
A 90 degree bend, or right angle bend, is a common configuration of galvanized anchor bolt, especially in small, standard sizes. Bending equipment is used to produce a “hook” on the end that will be embedded in the concrete. The bent portion of the anchor bolt provides pull-out resistance.
Swedging is a process in which large dimples or indentations are pressed into the embedded end of a galvanized anchor rod. When the anchor rods are poured into a foundation, the concrete forms around the indentations, preventing the rod from pulling out of the concrete.
Chamfering applies a slight bevel to the threaded end of a galvanized anchor bolt to help facilitate installation of a galvanized nut. The removal of the first thread will also help prevent installation problems.
Galvanized anchor rods often require the welding of steel plates and/or pipe sleeves to nuts or to the embedded end of the anchor rod. Welding is a process in which steel is bonded by heating the components and adding a filler material of molten metal.
Square, round, or rectangular anchor plates are often affixed to the embedded end of galvanized anchor rods to provide pull-out resistance. Steel templates are also used to properly space the anchor bolts during installation. Plates are sheared and punched or burned using a variety of equipment and processes. These plates and templates may or may not be galvanized as part of the anchor bolt assembly.
Many grades of galvanized anchor bolts undergo a heat treating process in which they are quenched and tempered in order to develop the proper strength characteristics of the given specification. After heat treating, bolts must be mechanically tested to ensure compliance with the ASTM specification.
Hot-dip galvanizing is a process in which anchor bolts are submerged in molten zinc for the purpose of applying a corrosion resistant coating. Anchor bolts that will be exposed to the elements will typically be hot-dip galvanized. It is imperative that the company performing the galvanizing process has specialized systems in place to adequately remove the excess zinc form the anchor bolt threads without “recutting” the threads. ASTM F2329 specifically restricts the practice of “chasing threads” in section 5.4.1 of the specification. Galvanizers experienced in processing bolts will typically use centrifugal force to spin the excess zinc out of the threads of galvanized anchor bolts while the zinc is still in a liquid state.