Hunter Galvanizing FAQ's
What is Hot Dip Galvanizing?
Hot dip galvanizing is the best protective coating solution available. It is a method of protecting steel from corrosion by steel. Layers of zinc form on top, providing a tough, abrasion resistant coating that will be maintenance free for many years to come.
Why does the hot dip galvanized finish look different on the same piece of steel?
Patterns, colour and finish will be determined by the metallurgy and the rate of reactivity between each piece of steel and the molten zinc which bonds to the surface. Coatings may have a spangled effect; others may display lacework or reptilian like patterns as elements within the steel chemistry react differently to zinc.
What is Wet storage stain or White rust?
The markings are wet storage stain, a bulky white deposit commonly referred to as “white rust” Wet storage stain forms when moisture such as rainwater or dew attacks the pure zinc layer of the galvanized coating. This phenomenon occurs on newly galvanized items predominantly when they are in a poorly ventilated environment. This environment is typified where items remain closely stacked or nested restricting adequate ventilation between galvanized items. Items where surfaces remain in close contact whilst bundled will generate white rust if moisture is present. It is recommended that bundles of product such as angles, purlins, plates, flat bar RHS and SHS be broken apart after transportation to permit adequate ventilation please refer to our “Hot Dip Galvanizing Fundamentals and Guidelines” for further information.
Can I repair wet storage stains / White Rust?
The wet storage stain / white rust can easily be repaired if caught early enough. This is usually done with a mild diluted acid solution such as CLR or a metal wash. White rust deposits should be washed down using a hard bristle nylon brush and then rinsed off with running water. please refer to our “Hot Dip Galvanizing Fundamentals and Guidelines” for further information
Do you galvanize to an architectural finish?
An architectural finish is a loose term within the galvanizing industry, one which in the main does not generally refer to a specific colour or element of shine; rather providing a good galvanizing job, subject to design, welding practice, size and shape and steel metallurgy. As explained in the Australian Standards, coatings on fabricated articles should not be judged by the same standards as those applied to continuously galvanized products such as sheet steel and wire, since these are produced by processes which permit a high degree of control over coating thickness and appearance. Nor should hot dip galvanized coatings be judged by the same manner as painted coatings as the process is not a controlled nor an aesthetic based process. The hot dip galvanizing process is one based on the reaction of perfectly clean steel emerged in a bath of temperature-controlled molten zinc. The metallurgical reaction takes place as a result of this combination. please refer to our “Hot Dip Galvanizing Fundamentals and Guidelines” for further information
What sizes are the baths at Hunter Galvanizing?
Hunter Galvanizing Tomago facility has two hot dip galvanizing baths capable of accommodating a wide range of manufactured or fabricated structures.Bath sizes: 7m(l) x 3m(d) x 1.8m(w) and 10m(l) x 2.4m(d) x 1.5m(w)
Why would my steel distort when it is hot dip galvanized?
The percentage of items which are affected by distortion issues is relatively low given the volume of items which are hot dip galvanized. An item's dimensional stability can be compromised by a number of factors. By understanding the causes of distortion and adopting simple design principles the effects can be minimised. lnherent internal stress is present in every steel section. Stresses may be a result of the steel mill rolling, handling and transport methods or incurred during subsequent manufacturing processes; cutting, welding, hole punching or other cold working. At galvanizing temperatures (approx. 450"C) steel sections can experience a reduction of up to 50% in their yield strength. Whilst normal strength is returned upon cooling; this effect combined with release of internal stresses can result in distortion in some items. Distortion can also be the result of different thermal expansion and contraction rates occurring when thin items such as sheet, plate and mesh are used in conjunction with items of thicker sections. Thin sections or weaker areas within a fabrication may lose their shape as heat is transferred through the item. Thermal and contraction rates also differ during the process of double dipping, increasing the propensity of some sections to lose their shape or distort. Refer to Double (End or Side) Dipping. Non symmetrical sections or fabrications with cleats or plates welded to one side may bow. This potential is prevalent in channels and large welded beams.
What is "Double Dipping?
Subject to the overall size and degree of difficulty; items with dimensions greater than our baths may be double dipped. The term double dipping has no bearing on coating thickness; it relates to dipping a large item into the galvanizing bath one end or one side at a time. To achieve a hot dip galvanized coating over the entire surface one end is pre-treated and dipped in the molten zinc; the item is withdrawn, and turned end to end. The second end or side is then cleaned in pre-treatment chemicals and dipped.
Can I weld the item after hot dip galvanizing process has been completed?
Satisfactory high quality welds can be made on hot dip galvanized steel with tensile, bend and fatigue properties identical to those of welds made on uncoated steel. However, welding speeds will be slower and there will be increased spatter. General Guidelines: All welding and oxy cutting processes can readily be used on galvanized steel with minimal variations required. Zinc coatings should be ground 25mm-100mm either side of the intended weld zone and on the surface and underside. All welds made in galvanized articles should be protected against rust as soon as welding is finished. Care should be taken to ensure adequate ventilation is provided to minimise the possibility of adverse fume reaction. Residue from welding electrodes will prevent zinc bonding with the weld surface if not removed prior to hot dip galvanizing. Affected joints in service can be cleaned and coated with a suitable zinc enriched paint. Weld spatter should be removed prior to delivery. Extraction equipment should be utilised when welding galvanized steel in confined areas
Why do I need holes in my job?
For Hanging - The shape and dimensions of an item will determine how it is suspended during the hot dip galvanizing process. Where possible holes located in cleats, flanges or base plates will be utilised to suspend general fabricated items. Should holes not be available they will be required to be added to enable the item to be hung in the correct plane and allow processing liquids to drain and to minimize distortion. Subject to weight; items less than 2m require one hole or lifting lug placed at one end. Longer and heavy items will require holes or lifting lugs at both ends. Holes should be a minimum of 12mm diameter, large enough for jigging wire to be passed through. Larger fabrications will require numerous wire strands to be used and hole sizes should be adjusted accordingly. For Drainage and Entrapment - When an item is suspended on a headframe it remains in the same hanging position throughout the hot dip galvanizing process. Holes are required to be in the appropriate location to ensure pre-treatment acids, molten zinc and zinc ash can flow freely from all item surfaces as it is submerged and withdrawn from each processing bath. General Guidelines: A hole, gap or mitre in the corners of gussets or stiffeners will assist processing products to drain. Holes through end plates or web plates will also provide suitable access for zinc and zinc ash to drain and means of air to escape. By adopting a hole in every corner principle the majority of issues relating to draining can be eliminated and the best possible hot dip galvanized finish can be achieved. We recommend holes should not be less than 'l2mm in diameter, (larger if the design permits) to enable zinc and zinc ash to escape freely as items are withdrawn from the galvanizing bath.