Research & Application of Thermal Spray Technology at the Institute for Tropical Technology
The thermal spraying technology has some advantages that it saves precious materials, create material layers of desired thicknesses, and it is suitable to make new parts or restore used ones. Moreover, this technology can also be used to make in-situ, local treatments for large or complicated objects.
In thermal spraying, the temperature of sprayed surface can be kept at about 100°C; therefore, we can spray different materials onto the surface of flammable materials such as wood, cloth, paper, polymer... Thermal spray technology is especially suitable for treating objects easily deformed by heat.
At the Institute for Tropical Technology, researches and applications of thermal spraying have been done since 1995, focusing on three main objects: anti-corrosion coatings in atmospheric and aqueous environments; functional coatings, and coatings for protection against wear.
Anti-corrosion coatings in atmospheric and aqueous environments
Protective coating materials are divided into two groups, group of materials acting as a sacrificial anode to protect steel (Zn, Al, Mg and their alloys), and group of materials acting as barriers to prevent the approach of corrosive agents to steel surfaces (stainless steel, Ti alloys, Mo, Pb, Sn,...). In many cases, metallic coatings, used alone or combined with paint coatings, have been noticed in researches and applications due to their low prices and diversely protective capabilities. Typical research, application and transfer here include an over-6-year-durability coating system "zinc - paint" for protection against corrosion in seawater of valves of Tra Linh II irrigation - Thai Binh province, a coating system "tint - paint" for protection against corrosion of valves operating in brackish sour water, and a 5-year-durability zinc coating for protection against atmospheric corrosion of outdoor exhibits at the Vietnam Military History Museum.
Application of zinc coating for protection against atmospheric corrosion of outdoor exhibits at the Vietnam Military History Museum
Functional coatings
In practice, there are various demands for materials that are heat resistant, chemically resistant, wear resistant, electrically conductive, resistant to electromagnetic interference, decorative,... In many cases, materials have to work under simultaneous influence of several factors such as chemicals, suspended particles, and high temperature that lead to high temperature wear-corrosion. The interactions between the environment and the material occur normally on the surface layer; therefore, to deal with parts not produced in our country, the solution is to create functional coatings on the surface of common cast iron and steel materials. Some common functional coatings are NiCr, NiAl, FeCrB alloys, SUS 316L stainless steel, Cu and Cu alloys. We have applied this technology successfully in many works with different companies such as Dai Hung Petroleum Operating Company Limited - PetroVietnam Exploration Production Corporation, Honda Vietnam, VIFA Coating Joint Stock Company, Lao Cai Copper Factory,...
Restoration of worn turbine blade ROFS-690M-2 at Na Loi Hydropower Plant (Dien Bien province)
Wear - resistant coatings
The wear - resistant coatings are a special kind in the group of the functional coatings due to the demands for protection of objects operating in aggressive environments, such as dry wear, lubricated wear, wear under high load impingement, high-speed sliding wear. Based on the working conditions of the objects, we can use materials such as high carbon steel, Cr alloy steel, FeCrB alloy or NiCr alloy to restore the worn objects to their initial dimensions. In fact, we have applied successfully this technology to different industrial fields such as cement production (Hai Phong, But Son, La Hien, Tuyen Quang, Yen Binh, Cuong Thinh,...), energy production (Cao Ngan and Na Yang thermal electricity plants, Na Loi hydropower plant), engineering, automobile and motorcycle manufacturing,…
Restoration of worn bearing parts of a cylinder of a 12m air exhausted ventilator (Hai Phong Cement Company)
In recent years, along with the development of the scientific and technical equipments, quality improvement and lifetime extension of the objects are essential. Thermal spray technology has been concerned and applied by many industries and companies in Vietnam. Based on our obtained results, the thermal spraying research team at the Institute for Tropical Technology has performed well our motto "Focusing on highly applicable researches for urgent needs in the industrial production in Vietnam."
