Metallisation Smooth Galvanizing – Zinc Thermal Spray System. in Malta
Definition of: Galvanizing / Galvanize is a coating process with a protective layer of zinc on(iron or steel).
Definition of: Smooth Galvanizing , adjective
Smooth: having an even and regular surface; free from impurities or unwanted elements from a substance, perceptible projections, lumps, or indentations.
Also known as Metallizing – Metallisation “Cold Galvanizing” Rust Prevention System
Thermal Spraying Application (Zinc Coating)
Metallizing is the general name for the technique of coating metal on the surface of non-metallic objects.
Techniques for metallization started as early as mirror making. In 1835, Justus von Liebig discovered the process of coating a glass surface with metallic silver, making the glass mirror one of the earliest items being metallized. Plating other non-metallic objects grew rapidly with introduction of ABS plastic. Because a non-metallic object tends to be a poor electrical conductor, the object’s surface must be made conductive before plating can be performed. The plastic part is first etched chemically by a suitable process, such as dipping in a hot chromic acid–sulfuric acid mixture. The etched surface is sensitised and activated by first dipping in tin(II) chloride solution, then palladium chloride solution. The processed surface is then coated with electroless copper or nickel before further plating. This process gives useful (about 1 to 6 kgf/cm or 10 to 60 N/cm or 5 to 35 lbf/in) adhesion force, but is much weaker than actual metal-to-metal adhesion strength.
Vacuum metallizing involves heating the coating metal to its boiling point in a vacuum chamber, then letting condensation deposit the metal on the substrate’s surface. Resistance heating, electron beam, or plasma heating is used to vaporize the coating metal. Vacuum metallizing was used to deposit aluminum on the large glass mirrors of reflecting telescopes, such as with the Hale telescope.
Cold sprayable metal – VeroMetal® is a metallizing process that seamlessly applies cold sprayable or puttyable metal to almost any surface. The composite metal consists of two (waterbased binder) or three different ingredients: metal powder, binder and hardener. The mixture of the ingredients is casted or sprayed on the substrate at room temperature. The desired effect and the necessary final treatment define the thickness of the layer, which normally varies between 80 and 150 micron. After the spraying process the work piece should rest for approximately 60 minutes. Then the work piece is dried for 6 – 12 hours at a temperature of 20-60°C. Afterwards the surface is ready for the next treatment steps.
Vacuum metallizing is a process where a metallic coating material is placed in a vacuum chamber with the workpiece to be coated. The material that is being applied is then heated until it starts to evaporate; this vaporized metal condenses on the product or workpiece as a thin metallic film. As this is happening, the part is being rotated for uniformity of the coat. Thin layers of paint can then be applied to produce other colors. Once complete, a clear sealer is usually added to prevent flaking.
The metalizing process always begins with proper surface preparation. Next, aluminum wire or zinc wire is continuously melted in an electric arc spray or gas flame spray gun. Clean, compressed air strips droplets of molten metal from the wire depositing these particles onto the steel forming the protective coating. This sprayed metal coating acts both a barrier coating and a galvanic coating in one.Owners should consider metalizing rather than painting, re-blasting and re-painting.The metalizing or thermal spray process consists of surface preparation by abrasive blasting, metal spraying and sealing or topcoating the sprayed metal. The twin spray wires used for atmospheric or immersion service are pure zinc.
Metallizing is considered a cold process in that the aluminum or zinc is deposited onto steel by spraying rather than by dipping the steel into a bath of molten zinc as with galvanizing. The steel remains relatively cool at about 250º-300ºF. There is virtually no risk of heat distortion or weld damage by metalizing. Any steel structure that can be blast cleaned may be metalized. Applications include:
Advantages of Galvanizing:
Prevention against corrosion
Can be painted over, without having the paint peeling off
No damage will be done to the metal itself – there will be no distortion or wrapping of metal
Cleaning of the surface from oil and other contaminants
Surface preparation that usually consists of abrasive grit blasting to roughen the surface
Thermal spraying: The sprayed metal impacts and attaches to the roughened steel and solidifies. Subsequent layers of spray should build up the coating thickness to as thick as 300 microns (1600 g/m2 or 5 oz/ft2), although coatings 80 microns thick (425 g/m2 or 1.3 oz/ft12) are more typical.
Sealing of the coating unless it is to be painted to provide additional protection to the steel
To guarantee good bond strength between the steel target and the sprayed metal coating, a specified roughness must be applied to the steel surface. Grit blasting is mainly used, based on impact of an abrasive, rather than shot blasting, which uses steel shot because the abrasive gives a rougher surface that allows for better coating bond strength. The purpose of the preparation is to remove surface imperfections such as oxides of iron, and to provide a surface profile on the steel target that has angular peaks and valleys, caused by the impact of the abrasive. The norm for surface preparation is EN 8501-1 Grade SA3. The blast profile should not exceed 100-125 μm, or excessive roughness of the sprayed surface, even after applying 100 μm of metallic sprayed coating, will persist.
After thermal spraying the metallic coating is sealed if it is not to be painted. Sealing is very different from painting. Sealers are of low viscosity and penetrate into the pores of the sprayed coating. The overall thickness of the coating is not increased by sealing. The sealer reduces the surface that is exposed to the corrosive environment and therefore reduces the corrosion rate.The sealer gives a smoother surface, reducing the pickup of dirt and other contaminants, preserving surface appearance and reducing maintenance costs. Colored sealants are available to change the appearance of the sprayed structure. A sealed sprayed metallic coating is a complete protective system, suitable for many outdoor exposures, without the need for added paint coatings. Many types of sealers have been examined, including polyurethane, phenolic, epoxy, wash primers and silicates and have all reported improvement over the uncoated sprayed coatings.
Thermal sprayed Zn-based coatings are either zinc and aluminium coatings or their alloys (mostly Zn and Zn-15%Al coatings). Moreover special alloys such as cored wire ZnMgAl are becoming available.
Thermal spraying is mainly performed with flame spray or electric arc guns fed with zinc or zinc alloy wire, or to a less extent, zinc powder. Cold spraying is an emerging technique for applying this metal coating.
Zinc thermal spraying is very versatile and the perfect corrosion protection solution for the large steel structures typically used for wind energy. It can be applied either in a factory or on-site. It requires dry conditions for application, with a temperature always above 5°C higher than the local dewpoint of air.
Thermal Spray Processes
Thermal spraying methods are classified according to DIN EN 657, according to the type of metal being fed to the spray, the source of thermal energy for melting and the source of energy for spraying the metal at the target to be coated.
The most widely used processes for Zn, Zn-15%Al and Al are the 2-wire electric arc spray process and the flame spray process.
Twin wire arc sprayingSchematic diagram of twin wire arc spraying
Heat Source: Electric arc
Transfer: Compressed air
Process: Two wires (hence a common term for the process is Twin Wire Arc Spray), are fed into the pistol and electrically charged, one positive and one negative. The wires are forced together and form an electric arc, melting the wire. Compressed air, passing through a nozzle, atomises the molten metal and sprays it onto the work piece. There are three methods of wire feeding, push, pull and push/pull. The higher the current rating of the system, e.g. 350A, 700A etc., the higher the spray rate.
Schematic diagram of flame spraying
Heat Source: Gas fuel* and oxygen flame (*commonly propane or acetylene)
Material: Wire or powder or ceramic rods
Transfer: Compressed air (wire flame)
Process : The gas fuel and oxygen are mixed and ignited to produce a flame. The material, either a wire or powder is fed into the flame. For wire flame spray, the material is melted and the compressed air, passing through a spray nozzle atomises the molten metal and sprays it onto the work piece. The larger the wire diameter, the higher the spray rate. For powder flame spray, the powder particles (metal or ceramic ) are softened in the flame and the speed of the flame gases through the nozzle sprays the softened powder onto the work piece.
For both processes spray distances between 15 and 30 cm between the spray gun tip and the steel receiving the sprayed coating are common. The character of the sprayed metal droplets is given by the rate of thermal energy input to the combustion chamber, the mass feed rate of the wire and the character of the spray given by the flame, together with the distance between the gun and the target.
After the metal spray droplets are ejected from the gun in liquid form, they can become coated with a small amount of oxide, depending upon the spray gas, and may partially solidify before impacting the substrate. Usually the droplets are mainly liquid when they impact the target and flatten upon impact, so that the coating builds up from layers of these flatten droplets that become immediately solid upon impact.
Because of this rapid solidification there is no opportunity for diffusion bonding and therefore the main bond strength between the coating and target is developed by mechanical interlocking.
A major advantage of zinc thermal spray processes is that the coatings can be applied without significant heat input, therefore the properties of the base steel and welded zones will not be changed by any heat from the application on the thermal sprayed coatings.
Another new process that is just beginning to be used is the cold spraying process. However it is still in developmental stages for the coating of Zn.
Applications of zinc thermal spraying for corrosion protection
Thermally sprayed zinc and zinc alloy coatings are used for corrosion protection by numerous industries.
IZA has a particular focus on the following industries, with special emphasis on the wind turbine and the cruise ship industry where zinc thermal spraying can provide excellent corrosion protection.
electric utilities (u.a. windmills)
mining, construction and dredging
oil and gas exploration
pulp and paper
ship and boat manufacture/repair
A typical steel surface profile produced by abrasive grit is can be found in below figure, showing the favorable angular profile produced by abrasive grit.
For a smooth protraction of galvanizing and paint for wrought iron – metal – steel – works
Home improvement & remodeling service in Malta
Soft blasting can save your old or new work and coat it with a smooth galvanizing – metallisation – zinc thermal spray coat.
Services we offer:
smooth galvanizing – metallisation – zinc thermal spray coat as your work required
than we paint it with 2 coats of epoxy primer as an undercoat protraction.
and finally with 2 coats of hardener spray painting finishing, that can and will be applied imminently on your galvanized work.
This service is ideal for exterior balcony – balconies – railing – railings – fancies – stairs – staircase – handrails – banisters – gate – gates – doors – windows – security grills – security guards – garage doors – garden and indoor furniture and much much more.
MALTA EUROPE EUROPEAN QUALITY SUPERB SYSTEM
For info call Tel: +356 21237820 Mob: 79604517
Services – we provide – on the following below subjects
other services relating to our our online display of wrought iron and art metal works.