Testing Galvanized coatings.

Galvanizing quality is regulated under ISO 1461, the international standard for hot dip galvanizing.

Depending on the batch size of the items in the order, various sampling regimes are in place to determine which items are tested. Highland oprate a system that tests in excess of the standard.

Common tests include:

Coating thickness: Using a magnetic measuring device the thickness of the galvanizing can be measured to within a micron or two without destroying the coating. Steel that is at least 6mm thick should get 85 microns average coating thickness. Many points on the surface are measured.

Visual: No flux residues should be present after processing, nor should there be any significant irregularities in the surface finish.

Completeness: The coating should be complete, without bare patches. The standard allows for minimal repair where a coating is incomplete.

Testing the Process

In order to acheive a coating that meets the specification, the process chemistry and parameters must also be tested, and the following are some of those tests.

Zinc chemistry: The molten zinc must conform to the purity requirements of ISO1461. Contaminants such as tin, aluminium, nickel and others can quickly become out of spec if not measured frequently. Chemistry has impact on coating thickness, shine, colour and physical properties of the coating.

Zinc temperature: One of the many influencing factors on coating thickness, the temperature must be kept to within about +/- 5 degrees.

Acid Chemistry: The hydrochloric acid which is used to clean the steel must be of suitable chemistry. It need not only acid strength sufficient for the job, but also enough iron chloride strength to adequately clean the steel. An inhibitor is added to ensure the steel is cleaned, not dissolved!