The first step in the production of headed anchor bolts is cutting the material. Calculations are performed to determine the length of round bar to be cut considering the head style so the finished fastener will be the correct length.
Watch cutting operations at Portland Bolt
Once the material has been cut to length, the anchor bolts are ready to be headed. One end of the round bar is heated to around 2000 degrees Fahrenheit using induction heating coils. The hot end of the rod is then placed into an Upsetter to forge the head into the required shape.
After the raw material is cut to length, threads of a headed anchor bolt can be produced by either cutting or rolling. Portland bolt is capable of cut threading through 6″ diameter and roll threading through 1″ diameter. Cut threading is a process by which steel is cut away, or physically removed, from a round bar of steel to form the threads. Roll threading is an extrusion process in which steel round bar is forced between two dies to form the threaded portion of a fastener, instead of being removed as in cut threading. Roll threading is an extremely efficient process and often results in significant cost savings. Therefore, Portland Bolt will roll threads whenever possible.
When manufacturing bolts, other than mild steel or high strength low allow bolts such as F1554 Grade 36 or F1554 Grade 55, the bolts must be quenched and tempered after heading. Heat treating is a process where the bolts are heated, submerged in liquid (quenched), and then tempered in order to obtain the required mechanical properties of the specification. The headed anchor bolts are then tested according to the specification after heat treating to confirm the mechanical requirements have been met.
Headed anchor bolts are wheelebrated before they are hot-dip galvanized in order to remove excess forging scale. Stainless steel headed anchor bolts will be wheelabrated to remove the forging scale prior to the heat treat process known as solution annealing.
If required, hot-dip galvanizing is the final manufacturing process when producing a run of headed anchor bolts. Galvanizing is a process in which a zinc coating is applied to headed anchor bolts that will be exposed to the elements, and provides corrosion resistance.
Watch the hot-dip galvanizing process at Portland Bolt
- The bolts will be dunked in caustic soda to remove any organic material, such as cutting oil and then quickly rinsed with water.
- The bolts will be submerged in sulfuric acid. This process removes mill scale and helps the zinc bond to the headed anchor bolts by etching the steel.
- After the acid bath, the bolts will be rinsed and then dipped in a flux solution which helps the zinc bond to the steel.
- The bolts will be dipped in a tank of 840-degree molten zinc until the zinc has bonded to the steel.
- After removing the bolts from the molten zinc, a high-speed spinner removes the excess zinc from the threads to allow for a quality nut-fit.