What is Galvanizing...

In 1742, a chemist named Melouin presented a paper to the French Royal Academy in which he described how a zinc coating could be obtained on iron by dipping it in molten zinc.

However, it was not until the 1830's that patents were taken out in England and France covering this process for protecting iron from rust. More than 150 years on, applications for hot dip galvanizing continue to grow and it has become part of every day life.

It is environmentally friendly, aesthetically pleasing and helps save our natural resources by protecting steel from the damaging effects of corrosion.

Galvanizing is a term often used to describe zinc coatings in general. However, different types of zinc coating vary in thickness and effectiveness. It is therefore important to understand that all zinc coatings are not the same and the life of a zinc coating is directly proportional to its thickness.

Hot dip galvanizing after fabrication provides the best long term corrosion protection for steel products achieved through a continuous and extremely tough metallurgically bonded coating which offers both barrier and sacrificial protection. The zinc coating reacts with the atmosphere to form a thin, passive zinc oxide layer which then protects the surface from further corrosion. Even if the zinc layer is damaged, the zinc corrodes in preference to the underlying steel and heals itself around the point of damage.

This is in stark contrast to paint coatings or other metal coatings such as nickel or chrome. Here accelerated corrosion of the underlying steel takes place around the damaged area.

Centrifuge (Spin) Galvanizing

From time to time you may have a requirement for galvanizing items which may be unsuitable for conventional dipping. Perhaps they have no hanging holes, are very small or have threads or small holes which must be kept clean and clear during galvanizing.

We offer a centrifuge galvanizing service which is particularly suitable for larger quanities of small components and threaded fasteners.

CENTRIFUGE GALVANIZING MAXIMUM LENGTH - 600mm

For further advice on centrifuge galvanizing please contact our technical department.

Surface Preparation

Before we galvanize your work, it is dipped in hydrochloric acid and pickled. This process chemically cleans the work to enable the galvanizing to take place. Pickling will remove mill scale, light rust and dirt but certain types of surface contamination will not be removed and if present will result in processing delays and /or a poor quality coating. The following surface contaminations will cause problems and should be removed before work is sent to us for galvanizing.

  • Old zinc coatings- it is not possible to galvanize over an existing galvanized coating. In this case the old coating must be removed. Stripping and re-galvanizing can be an expensive and time consuming process and is best avoided if possible.

  • Oil based paints - including over-spray, colour coding marks, stockholders identification marks.

  • Oil and Grease- including grease on box sections and lubricants used for punching and drilling.

  • Anti-splatter sprays- avoid using oil and silicon based products. Use only water soluble solution and use them sparingly.

  • Lacquer - often found on pipe work and fittings.

  • Weld slag and Sticky labels
KETTLE CAPACITY

Barn Street Plant
  4m x 1.7m x 1.8m deep

SPECIALIST GALVANIZING CAPACITY

Spin Galvanizing
  Max 600mm long

Please phone for advice if you have a fabrication which requires hot dip galvanizing and cannot be easily accommodated in a single dip.

HOLLOW WORK

To ensure total corrosion protection it is important that both the inside and outside of each section of the fabrication are galvanized. The galvanizing kettle operates at a temperature of 450C, During the dipping process the pressure within a sealed compartment will increase rapidly. Therefore, vent and drainage holes are vitally important in hollow work. Inadequate venting can result in an explosion thus creating a dangerous environment within the vicinity of the galvanizing kettle.

HEAT DISTORTION

Hot dip galvanizing is carried out at approximately 450C and often, in highly stressed materials, distortion can be a problem. This can be particularly problematic if sheet or mesh is used in a fabrication.

Heat distortion is unpredictable and generally occurs as a result of circumstances outside our control. We cannot eliminate it completely, however, careful design and selection of materials can significantly reduce the risk.

Venting and Drainage

As work is immersed in the molten zinc air needs to be able to escape. When the work is withdrawn from the kettle the excess zinc needs to drain freely. Any parts of the fabrication which create a 'trap' require holes. The vent or drain holes must be of adequate size (never less than 10 mm dia) and correctly positioned. Holes which are incorrectly positioned or too small may result in a poor quality coating and will involve remedial work which will incur additional costs and extended turnaround time.

Diameter/width of hollow section Minimum diameter of hole
<25mm 10mm
25-50mm 12mm
50-100mm 16mm
100-150mm 20mm
>150mm 25mm

TECHNICAL HELP

For quotations, technical advice or assistance please contact


Angela Clarke

 

©Copyright Arkinstall Galvanizing Limited

about us technical quality location transport gallery contact