Hot Dip Galvanizing

Hot-dip galvanising provides the ideal corrosion protection for steel. In suitable applications, no other protective coating matches the unique combination of low initial cost, durability, predictable performance, low maintenance and resistance to impact and mechanical damage offered by galvanising.

In order to be galvanised, steel goes through a series of cleaning tanks and is finally immersed in molten zinc at 450°C. Provided there is suitable venting, hot-dip galvanising provides both internal and external protection on hollow structures. The Phoenix Galvanizing plant is the largest in KwaZulu Natal and one of the largest in the South Africa. Our Zinc Kettle’s considerable dimensions are 14m x 1.4m x 2.5m. Steel articles, weighing up to 5 tons can be galvanised in a single dip.

Goods Receiving

Receiving - weighing

Our friendly Goods Receiving staff members will check the design of the steel work to assure compliance with Hot Dip Galvanizing requirements. The steelwork is allocated a job number and weighed.

Please Note: Epoxies, vinyl’s, asphalt, or welding slag must be removed before galvanizing by grit-blasting, sand-blasting or other mechanical means. Phoenix Galvanizing does not provide blasting services.


Pre-Treatment:

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.

Jigging

Jigging - Attach to crane

Steel items are secured to fly beams, which carry the steel through the galvanizing system. Steel is secured by means of multiple strands of highly durable steel wire.


Surface Preparation and Hot Dip Galvanizing:

Surface preparation is the most important step in the application of a zinc coating. In most instances where a coating fails before the end of its expected service life, it is because of incorrect or inadequate surface preparation.

The galvanizing process has its own built-in means of quality control because zinc will not react with an unclean steel surface. Any failures or inadequacies in surface preparation will be immediately apparent when the steel is withdrawn from the zinc bath because the unclean areas will remain uncoated, and immediate corrective action can be taken.

Degreasing

Degrease tank - some chemical

A hot alkali solution removes organic contaminants such as dirt, paint markings, grease, and oil from the metal surface.


Water Rinse

Water Rinse - One

The degreasing solution is rinsed off in water.


Acid Wash

Acid Wash - HCL Acid Pickling

A dilute solution of ambient hydrochloric acid removes mill scale and iron oxides (rust) from the steel surface.


Water Rinse

Water Rinse - Two

The acid is rinsed off in water.


Flux

Flux

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 prior to immersion in the molten zinc.


Hot Dip Galvanizing

Molten zinc tank

During the Hot Dip Galvanizing step of the process, the material is completely immersed in a bath of molten zinc. The bath requires at least 98% pure zinc maintained at 435-455 Celsius.

While immersed in the kettle, the zinc reacts with the iron in the steel to form a series of metallurgically bonded zinc-iron intermetallic alloy layers, commonly topped by a layer of impact-resistant pure zinc. Once the fabricated items’ coating growth is complete, it is withdrawn slowly from the galvanizing bath, and the excess zinc is removed by draining, vibrating, and/or centrifuging.

Hot Dip Galvanizing Process Time Lapse Video

Passivation

Passivation Wash

Galvanized articles are cooled either by immersion in a passivation solution or by being left in open air.


Weighing

Weighing

The items are then weighed and the total cost is worked out.


Quality Control

Galvanized items are inspected and rectified

The inspection of hot-dip galvanized steel is simple and quick.

The two properties of the hot-dip galvanized coating most closely scrutinized are coating thickness and appearance/surface condition. A variety of simple physical tests can be performed to determine thickness, uniformity, adherence, and appearance.

Materials are galvanized according to long established, accepted, and approved standards of SABS SANS 121. These standards cover everything from the minimum coating thicknesses required for various categories of galvanized items to the composition of the zinc metal used in the process.


Dispatch

Dispatch - Items are stacked ready for dispatch.

The galvanised items are placed in the dispatch lot ready for collection.