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Suitable Surface Conditions Large Items or Thick Steels Adhesive residue contaminates steel surface. Very thick coatings may form on items which are large and consist of heavy steel sections. Longer immersion and handling times required to process these sections may result in the metallurgical properties of the steel having high reactivity with the zinc whilst in the galvanizing bath. Further information relating to zinc reactivity is available in Effects of Steel Chemistry. Rusted Items Light mill scale and surface rust on items can be removed within our pre-treatment process. Heavily rusted steel will require abrasive blasting prior to delivery to remove the rust layers. If the steel surface is pitted after blasting, this effect will be evident after the hot dip galvanized coating is applied. Surface rust is easily removed in our process. •Cutting Oil Some cutting lubricants can become baked onto the steel surface during fabrication. Oil based fluids are not visible during pre-treatment processing and may contaminate the surface preventing the coating from forming. Cutting oils should be cleaned from the surface prior to delivery. Pitted surfaces will be evident after galvanizing. Steel Coatings The bond between the steel and zinc is unable to be achieved if any form of substance remains on the steel surface after chemical treatment. Resistant substances which can prevent the coating from forming include (however are not limited to) pre-existing zinc coatings, paint, lacquer and adhesive residue from identification labels and stickers. •Adhesive Residue Manufacturer’s steel identification stickers will deteriorate during pre-treatment processing; however non visible adhesive residue may remain and prevent successful formation of the zinc coating. Stickers should be removed and the immediate area prepared by suitable means to remove the adhesive substance prior to despatch. •Marking Pens Paint pigmentation from marking pens may be resistant to chemical cleaning. During pre-treatment processing paint layers are removed, however, non-visible pigments may remain. The zinc coating will form around the residue pigmentation and remnants of workshop markings may remain evident after galvanizing. Oil based paint markings should be removed by suitable means from steel surfaces prior to delivery for galvanizing. Drilling lubricant can contaminate the steel surface preventing successful coating. Oil based paint markings should be ground from the steel surface prior to hot dip galvanizing. •Masking In some applications, small mating or threaded areas may be required to be uncoated. This can be achieved by applying a small amount of a suitable adhesive or sealing product on the area creating a barrier to pre-treatment acids and zinc. The following products will have varying success in preventing zinc coatings from forming and some clean up of the surrounding surfaces will be required by the fabricator after galvanizing. –Tapes high temperature tape / duct tape –Sealants silicone adhesive sealant / petroleum gel / household caulk –Paints Maskote / Stop Galv Application of a high temperature tape or sealants will prevent zinc from forming in small areas. •Penetrant Dye for Welds Dyes utilised for weld checks can create issues if unable to be removed by pre-treatment chemicals. Dyes should be removed from steel surfaces with a suitable paint removing solution or by light sanding prior to despatch for galvanizing. •Painted Sections Most pipe and tube sections manufactured in Australia are painted with water based coatings which generally can be removed within our process. Some local manufacturers of pipe and tube products and most offshore producers coat their product range with clear varnish or black bituminous paint. These coatings are resistant to chemical removal within our galvanizing plant and are required to be abrasive blasted prior to delivery. To avoid additional costs and extended processing times, hollow sections should be stipulated that they be suitable for hot dip galvanizing when ordering from your steel supplier. All steel sections with powder coated, brush or spray paint coatings must be abrasive blasted prior to despatch to Hunter Galvanizing. Dyes utilised to check for weld penetration can contaminate the steel surface and should be removed prior to delivery. Primer paint coatings can be removed from most domestically produced pipe and tube sections during our process. •Pre Existing Zinc Coatings Pre existing zinc coatings must be stripped from all items including in-line produced lengths of hollow section, purlins, wire and mesh prior to hot dip galvanizing. Additional charges are necessary for this procedure and lead times may be increased. Some pipe and tube products have an external light coating of zinc and a painted internal surface. These items will require internal abrasive blasting prior to delivery to our facility in addition to acid stripping. Thermal Cut Edges Flame, laser and plasma cutting will change the structure of the steel composition in the immediate area of the heat source. These areas may present thinner coating thicknesses and a lack of adhesion, reducing the ability of the zinc alloy layers to bond with the base metal. The high temperatures utilised to cut material depletes the alloying elements in surface of the steel. As discussed in Hot Dip Galvanized Coatings the formation of the coating structure relies on the alloying of iron and zinc in the galvanizing bath. Should insufficient alloying elements be present, the minimum coating thickness may not be able to be achieved; and cohesion of the galvanized coating will also be limited. To eliminate such issues, grind the heat affected surface and bevel the cut edge. Pre existing zinc coatings must be removed prior to hot dip galvanizing. Flame cut edges should be ground prior to delivery for galvanizing.