Image: EGGA.
The galvanizing process.
FOCUS ON SURFACE FINISHING The benefits of galvanizing
The purpose of hot dip galvanizing is to protect steel against corrosion. Reducing corrosion rates on steel fabrications means:
A sustainable process
According to EGGA, the galvanized coating can follow the steel structure through multiple cycles of reuse.
■ A galvanized coating is inherently climate resilient as its protective ability is largely unaffected by changes in temperature and other climatic factors.
■ Galvanized coatings are bonded to the steel, which allows the steel product to be reused along with the original coating without need for recoating.
■ Galvanized steel components that have reached the end of their design life, or are uninstalled for any other reason, can be regalvanized and returned to the original use.
■ If the reuse cycles come to an end, both steel and zinc are recycled together in well-established steel recycling processes— with the zinc being returned, without loss of properties, to zinc production plants and eventually back into the galvanizing process.
“ Spin galvanizing is a process used to coat small metal parts with zinc. It is particularly useful for coating small, complex parts that may be difficult to dip into a galvanizing bath. The process involves placing the pieces in a basket, which is then submerged in molten zinc, withdrawn and spun at high speeds. Spin galvanizing is used to increase the lifespan of steel by making it more robust, durable and rust-resistant,” explained Joseph Ash Galvanizing.
The steel due to be spin galvanized will need to be cleaned so that it is ready to be dipped in the galvanizing bath. There are multiple pre-treatment steps before the spin galvanizing stage( including de-greaser, acid and flux).
“ Spin galvanizing makes the metal more durable, reducing the frequency of maintenance needed and the associated labour costs such as transportation. It is also a fast process with a short turnaround time, so the parts are returned quicker,” outlined Joseph Ash Galvanizing in the UK.
Surface preparation
Surface preparation for galvanizing, says the American Galvanizers Association, consists of three steps:
1. Degreasing / caustic cleaning: A hot alkali solution, mild acidic bath or biological cleaning bath removes organic contaminants such as dirt, paint markings, grease and oil from the metal surface. Epoxies, vinyls, asphalt or welding slag, which cannot be removed by degreasing, must be removed before galvanizing by grit-blasting, sand-blasting or other mechanical means.
2. Chemical cleaning: A dilute solution of heated sulfuric acid or ambient hydrochloric acid removes mill scale and iron oxides( rust) from the steel surface. As an alternative to( or in conjunction with) chemical cleaning, this step can also be accomplished using abrasive cleaning or air blasting sand, metallic shot or grit onto the steel.
3. Fluxing: The final surface preparation step in the galvanizing process, a zinc ammonium chloride solution, serves two purposes. It removes any remaining oxides and deposits a protective layer on the steel to prevent any further oxides from forming on the surface before immersion in the molten zinc.
A sheet metal dragon sculpture galvanized by Wedge Group in the UK.
■ Less time spent on regularly maintaining steel, saving time that can be spent doing other tasks.
■ Less need to create replacement fabrications, saving money on material costs. Galvanizing has a cheap lifetime cost compared to alternatives.
■ Corrosion-resistance means that fabrications remain safe to use particularly for structural steel, load-bearing fabrications or other fabrications that rely on structural integrity.
■ Both the process and the byproduct of galvanizing( the galvanized steel) fit into a circular economy.
Growing applications
Corrosion is caused by the inherent tendency of metals, when subjected to air and moisture, to revert to their original earthly forms of ore through a chemical or electrochemical reaction.
“ For years, protecting steel from corrosion typically involved either the use of hot-dip galvanizing or some type of paint or powder coating system. However, more corrosion specialists are utilising both methods of corrosion protection in what is commonly referred to as a duplex system— simply painting or powder coating steel that has been hot-dip galvanized after fabrication,” explained
“ The synergistic effect of using two coatings extends the service life for unparalleled corrosion protection, while the metallurgicallybonded galvanized coating serves as an ideal primer to provide an impervious barrier for the base steel. When paint and galvanized steel are used together, the corrosion protection is superior to either protection system used alone,” it added.
The galvanizing process itself is constantly evolving with companies investing in the latest equipment and introducing new procedures in response to the ever-changing world. This is especially true for harsh chemicals and substances.
Applications for hot dip galvanized steel continue to evolve, and new markets are emerging all the time. Increasing numbers of specifiers now select hot dip galvanized steel for additional reasons such as low initial cost; durability; longevity; availability; versatility; sustainability and aesthetics. n
ISMR May 2026 | ismr. net | 45