- Use good quality materials. The quality of the materials you use play a key role in the quality of the galvanized goods.
- Avoid high reactive steels and weld material. These have elevated levels of phosphorous or silicon.
- Avoid pipe that has lacquer or varnish finishes from the manufacturer these will require shot blasting.
- Remove all welding flux prior to delivery to our facility. These residues will result in bare spots.
- Avoid mixing old rusty material with new; this may result in over-
pickling and pitting of the new material.
- Fully shot blast all cast or malleable iron and painted steelwork.
- Drill adequate drainage and ventilation holes (12 mm) to allow free flow of air and zinc.
- Be cautious of tight moving assemblies such as hinges or sliding assemblies. These may freeze together during processing.
Galvanising Guidelines and FAQS
Powder coating gives consumers, businesses, and industry one of the most economical, longest-lasting, and most color-durable quality finishes available. Powder coated surfaces are more resistant to chipping, scratching, fading, and wearing than other finishes. Color selection is virtually unlimited with high and low gloss, metallic, and clear finishes available. And colors stay bright and vibrant longer. Texture selections range from smooth surfaces to a wrinkled or matte finish, and rough textures designed for hiding surface imperfections.
Protects the Environment
Powder coating is also highly protective of our environment. While liquid finishes contain solvents which have pollutants known as volatile organic compounds (VOCs), powder coating contains no solvents and releases negligible amounts, if any, of VOCs into the atmosphere. Thus, there is no longer a need for finishers to buy costly pollution control equipment. In addition, most powder coating overspray that does not adhere to the part can be retrieved and reused, virtually eliminating the waste commonly found in liquid finishing processes.
Elimination of VOCs and reduction of wastes saves money and helps companies comply more easily with Government environmental legislation. In fact, one of the major elements in expanding the market for powder coating has been the implementation over the past 30 years of stringent air pollution control legislation.
The appliance industry benefits from powder coating on front and side panels of ranges and refrigerators, washer tops and lids, dryer drums, air-conditioner cabinets, water heaters, dishwasher racks, and cavities of microwave ovens. Powder coating has also replaced porcelain enamel on many washer and dryer parts.
The automotive industry uses powder coating on wheels, bumpers, hubcaps, door handles, decorative trim and accent parts, truck beds, radiators, filters, and numerous engine parts. A clean powder topcoat has been developed to protect auto bodies. BMW and Volvo are using it on their new model cars, and GM, Ford, and Chrysler have formed a consortium to test this technique on their production lines.
The architectural and building market powder coats aluminium extrusions used on frames for windows and doors and modular furniture. Many highway and building projects use powder coating on light poles, guard rails, signs, posts, and fencing.
There are also innumerable everyday uses for powder coated products such as lighting fixtures, antennas, and electrical components. Farmers have powder coated tractors and farm equipment. Fitness buffs use golf clubs and golf carts, ski poles and bindings, snowmobiles, bicycles, and exercise equipment that are powder coated. Shop owners have powder coated display racks, shelves, store fixtures, and vending machines. Office workers use metal furniture, computer cabinets, mechanical pencils and pens, thumbtacks, and other desk accessories that are powder coated. Parents have powder coated baby strollers, cribs, metal toys, and wagons. And home owners have lawn mowers, barbecue grills, patio furniture, garden tools, electronic components, bathroom scales, tool boxes, and fire extinguishers which benefit from a powder coated finish.
A) Poor Adhesion. A powder coat will give good initial adhesion to a metal surface, provided it is degreased and free from loose dust or other contamination. However, once in surface, the paint film will allow permeation of moisture and gases such as oxygen and sulphur dioxide. This can result in a complete breakdown of adhesion and the film can detach from the surface often in a dramatic way. Furthermore, such permeation will promote corrosion of the metal accelerating the process.
B) Pin Holing. The predominant reason for pin holing lies within the substrate itself. During the hot dip galvanising process gasses can get trapped within the metal skin and then during the curing of the powder coating the trapped gasses start to escape through the paint film. It is for this reason that pin holing occurs. However, this should not be a catalyst for rejection. It is recognized within BS6497 that this can be a problem and is regarded as being acceptable if not excessive.
C) Aesthetics. Different physical and chemical characteristics of the same paint may have varied reactions with a galvanized surface. Some types of powder coatings containing polyesters may not be suitable for use over galvanized steel. It is for this reason that specially formulated powders containing anti gassing agents are made by powder manufacturers for standard fencing colours. These anti gassing agents do not eliminate the problem of pin holing but minimize it. Even a difference in gloss level will give a different finish. A matt finish is considered more appropriate than a full gloss finish, because the latter will reflect all metal imperfections through the finish. When specifying colours please consult us to see if the requested powder is available in the appropriate grade.
D) White Rust. A white film (sometimes called white rust) may appear on zinc surfaces during storage or shipment. The film is found on material with newly galvanized, bright surfaces and especially in such areas as crevices between closely packed sheets and angle bars. This white rust can form if the surfaces come into contact with condensate or rainwater, and the moisture does not dry quickly. Zinc surfaces that have developed a normal protective layer of Zinc Carbonate are seldom attacked.
When zinc coatings corrode openly in air, zinc oxide and zinc hydroxide are normally formed. In the presence of atmospheric carbon dioxide, these compounds are transformed into basic zinc carbonate. If the supply of air to the surface of a zinc coating is restricted, as in a narrow crevice, then sufficient carbon dioxide is not supplied for the later, normal formation of zinc carbonate.
The layer of zinc oxide and zinc hydroxide is voluminous and porous and adheres loosely to the zinc surface. Consequently, it does not protect the zinc surface against oxygen in the water. Corrosion can therefore proceed as long as there is moisture left on the surface. When white rust occurs the objects should be arranged so their surfaces dry rapidly. The attack ceases and with a free supply of air to the surfaces the normal protective layer of zinc carbonate forms.
A) White rust is best avoided by preventing newly galvanized surfaces from coming into contact with rain or condensate water during storage and transport.
B) Materials stored outside should be arranged in such a way that the water can easily run off the surfaces – i.e. always stack your items on an incline plane.
C) Please allow ventilation by putting wooden planks in between items where possible. The more atmospheric carbon dioxide that reaches the metal, the less will be the problem. Do not over stock without adequate ventilation.
D) Temporary protection against white rust can be obtained by applying a passivation seal after hot dip galvanising. The seal can be either cromate or phosphate in nature.
E) Acrylic films containing corrosion inhibitors can be applied to prevent the formation of wet storage film.
Unfortunately for powder coaters the alkaline cleaners will not remove the zinc oxide scale. This poses the problem that paint on zinc surfaces is more sensitive than many other substrates, because even small quantities of impurity on the surfaces can effect the adhesion of the paint film. The solution to this problem lies in using a combination of alkaline and acidic cleaning.
Alkaline pre-cleaning is beneficial for removing substances that do not readily react with acid cleaners such as grease, oil, soaps, lubricants and carriers coating. A build up of such materials in the acid bath can interfere with the cleaning action, especially when the cleaning time is limited.
Acidic cleaning refers to the chemical removal of zinc oxide scale by spraying in an aqueous acidic solution. Wide variations are possible in type, strength and temperature of the acidic solutions used, depending upon time constraints as well as thickness, composition and the physical nature of the scale.
At LGPC we only undertake to powder coat materials that have been galvanised immediately by us, therefore we are in complete control and have the unique opportunity to ensure no white rust is generated whatsoever upon freshly galvanised materials. This give your products increased protection and adhesion against any galvanised materials that have been subject to white rust issues.
3. Alkaline or Acid clean
5. Zinc Phosphate
7. De-Ironised rinse or Chrome Seal
The LGPC processes are designed to produce coatings which are chemically and physically bonded to the metal. The zinc phosphate coating underneath the paint is there to prolong the useful life of the paint film by protecting the metal from corrosion, particularly at damaged sites, and to assist the adhesion of the paint. The whole purpose of EN13438 is to achieve durability and corrosion protection. The aesthetics will vary with the type of powder used and the gloss level specified. As stated before a matt finish gives the best results on a galvanized substrate.