Thermal spray coating technology has been widely used throughout Europe and gradually proves its superiority in many projects. In addition to providing corrosion protection and performance enhancement, the metal coating is also used to repair and restore corroded or misc-machined parts. So how exactly is this method done? What makes this coating so outstanding? We will answer all in the article below.
Classification and application of metal coating technology in industries
Thermal Spray Coating technology is increasingly interesting based on the benefits and efficiency. With the development of techniques and technology, metal coating methods have also been improved in many aspects to bring better efficiency. So let’s learn about coating characteristics, practical applications, and the advantages/disadvantages of this advanced technology through the sections presented below.
Metal coating technology definition and characteristics
The metal coating is a technological method used to restore and regenerate layers of metal/non-metallic materials, the surface of material parts. The mechanism of this method is to partially or wholly heat solid materials in the form of powders, wires, bars, or drug cores utilizing a high-energy matter stream (gas or plasma flow). The material is dispersed into particles in a fine mist and accelerated to push the particles to the prepared surface to be coated.
All thermal spray methods involve the release of treated material particles onto the cleaned part to be coated. The coating material adheres to the surface and forms a continuous coating. With such forming characteristics, the coating will have a layered structure. In it, the material elements are deformed and stacked on top of each other. There are stable bonding processes that create the coating structure at the contact surface between the details and the part and the contact surface of the elements.
Thermal spray coating materials can be metal, steel, alloy, ceramic, plastic, and composite materials. Metal coating technology provides coatings with thicknesses ranging from approximately 20 micrometers to several millimeters, depending on the process and materials. And can be applied in a variety of thicknesses, typically 100 – 750 microns. Coating quality is usually assessed by measuring porosity, oxide content, macro and micro-hardness, bond strength, and surface roughness.
Thermal spraying has the versatility application, creating coatings for various materials and components to resist abrasion, corrosion, and cavitation. In addition, the coating spray process is also used to provide conductivity or electrical insulation, lubrication, high or low friction, sacrificial wear, chemical resistance, and other desirable surface properties.
Classification of Metal coating technology – The most popular processes nowadays
Metal coating is used in many different industries with valuable applications. These coatings are solid materials consisting of metals or alloys (in the form of wires, rods, or powders) that are heated and melted in contact with fuel combustion in the injector. The flame from the atomizer will power the heated mixture. As a result, the mixture is sprayed onto the metal surface and creates a solid coating with good adhesion. Here are the four most popular methods today to create a thermal spray coating:
- Flame Spray method
Flammable gas flame spraying is considered an effective method of metal coating spraying and has been widely applied in various industries for the past 100 years. Flame spraying is also divided into two popular types: wire spraying and powder spraying. The flame injection process uses an oxy-acetylene flame. The heat from the flame melts the coating material, and the compressed air pushes it onto the material’s surface to be coated. This process is also another form of “cold process” due to the relatively low operating temperatures throughout the process.
- Arc Spray method
The electric arc spray method is widely used due to its cost-effectiveness and time-saving construction. This method forms an arc by contracting two oppositely charged metal wires, usually of the same composition. This leads to melting at the tip of the wire material. The air atomizes the molten spray material and accelerates to the surface. We can adjust the injection speed by changing the wire feed when heating it. The arc spray coating provides high bond strength, low surface temperature, and high coverage rate, making it suitable for large areas of coating material. Typical applications for this method include anti-wear, anti-corrosion, component repair, and anti-fraying. This system has high mobility, so it is very suitable for large structures or intricate details on-site and local processing applications.
- HVOF (High-Speed Oxygen Injection) method
HVOF (High-velocity oxygen fuel) is a metal coating process applied to material surfaces that need thick and high adhesion. The mechanism of the HVOF process is to push the material powder in a semi-molten form at supersonic speed to the surface of the material to be coated. Fuel (hydrogen/kerosene) is mixed with oxygen and ignited in the combustion chamber, and the combustion gas is accelerated in the injection chamber through the nozzle. This creates a significant acceleration which increases the speed of the particles in the mixture. The result is a fragile coating evenly distributed over the surface with a high mechanical bond to the surface components, with good adhesion.
- Plasma spray method
The plasma coating process involves spraying a molten or semi-molten powder onto the surface of a material to create a coating. The coating material is injected in powder form into a high-temperature plasma flame. Under the heating agent and carrier gas, the material is rapidly pushed onto the surface of the device to be coated. The coatings produced by plasma spraying can be a few micrometers to several millimeters thick. Plasma sprayed coatings typically use higher temperatures and lower velocities (compared to HVOF), allowing them to be applied to a wide variety of coated surfaces, including ceramics.
Application of metal coating technology and advantages/disadvantages
Application of thermal spray
Metal coating can be used in many practical applications, including protecting aircraft, buildings, and other structures from extreme temperatures, chemicals, or environmental conditions such as high humidity and rain. Some popular applications include:
- Thermal spray coatings are widely used in preventing corrosion of many materials, especially with high wear resistance. Thermal spray coatings are used for detailed surfaces operating in harsh environments such as the sea, environments with high levels of salt fog and high humidity, etc., with the effect of enhancing resistance to abrasion and corrosion chemicals or the environment. Thereby greatly extending the life of components. Pure aluminum and zinc-aluminum alloys used in thermal spray coating provide effective protection for marine coatings. Thermal spray coatings are commonly applied to bridges, boats and dams, piers, and other onshore and offshore structures.
- Thermal spraying is an industrial method used to restore, renovate and re-surface the surface of metal parts, especially the rotating and moving parts of various machines. They include road and rail vehicles, ships, aircraft, pumps, valves, printers, electric motors, paper machines, chemical plants, food machines, resource mining machinery, earth excavator, generator, aerospace, turbine insulation. As can be seen, metal coatings are applied to virtually any piece of equipment that is subject to wear, erosion or corrosion and needs to be restored. This is done by using arc, flame, or HVOF injection systems to spray steel, nickel alloys, carbides, stainless alloys, copper, and many other materials.
- In addition, the thermal coating is also used to increase the hardness and heat resistance of frequently worn equipment, such as boiler tubes, boiler walls of coal-fired power plants, furnaces in paper mills, etc. chemistry. Used for anti-wear coating of screws and shafts and can be sprayed onto steam turbine nozzles, blades and housings to restore worn parts.
Insulation coatings are also known to be a perfect solution to corrosion problems under insulation. Learn more about metal coatings to reduce insulation corrosion effectively in this article Application of metal coating method to reduce corrosion in insulation.
However, as a highly appreciated and widely applied technology solution, thermal spraying is not always the best solution for projects. So, let’s look at the pros and cons of metal coating to determine its suitability for your plan in terms of efficiency and implementation costs.
Advantages of the thermal spray method
- Broad applicability: creating thermal spray coating is used in many large and small-scale projects.
- Long service life: Some applications have been rated to last more than 50 years.
- Higher life-cycle costs: metal coating extends equipment life and effectively reduces temporary maintenance.
- High mobility and easy automatic control are suitable for the on-site and local processing of large structures or intricate details.
- Ease of application in cold weather: Unlike most coating systems, thermal spray can be applied to metal surfaces at any temperature.
- Easily controlled coating thickness: We can precisely control coating thickness with optimal coating selection and modern engineering application to achieve optimum deposition.
- Even complex-shaped surfaces can be effectively coated using the robotic application of thermal spray coatings.
Disadvantages of the thermal spray coating method
Besides the above advantages, the thermal spray method still has some disadvantages that need to be overcome:
- Higher initial costs due to technical and technological requirements
- Requires a more elevated surface preparation level and involves removing other surface defects to achieve a good effect.
- The thermal spray process requires highly skilled and experienced technical workers and heavy and hazardous working conditions.
- Much spray material loss
Despite some limitations, metal coating technology is still considered a corrosion protection method that shows great promise in the future. Not only does it provide a long-lasting solution, but it has also proven effective in protecting surfaces over the years. Advances in thermal spray equipment have dramatically increased injection rates since the technique has become widely used, significantly cutting down on the time it takes to complete projects.
If you want to find an effective, economical, and limited solution to the above disadvantages, VIVABLAST’s professional technicians will directly evaluate and apply the appropriate metal coating method for your projects. Surface preparation and coating processes are carried out according to standard procedures, using advanced spray-painting technologies to provide the ultimate anti-corrosion solution for your property.
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