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China’s Rising Industry—Metal Thermal Spraying Coating Technology
Release time:
2020-08-11 22:12
Source:
Metal Thermal Spraying Coating Technology
Due to its wide range of coating materials, rapid deposition rate, high flexibility, ease of automated processing, and strong adaptability, thermal spraying technology has already gained widespread application. Statistical data indicate that... An advanced aircraft engine manufactured abroad requires more than 5,000 components that have undergone thermal spraying. Thermal barrier coatings have become one of the key technologies in the manufacturing of high-performance aircraft engines. Additionally, according to statistical reports from abroad on the application of high-performance ceramic coatings, Thermal-sprayed ceramic coatings account for two-thirds of the high-performance ceramic materials market in North America. This figure is broadly consistent with domestic reports indicating that the output value generated by thermal spraying represents roughly one-third of the total output value of all surface technologies, suggesting that thermal-spraying technology has become one of the key surface engineering technologies. 。
The development history of thermal spraying technology and the origin of the term “thermal spraying” are as follows:
Thermal spraying technology was first invented in 1910 by Dr. Schop of Switzerland, at the time being named “metal spraying.” In 1943, METCO in the United States published the first “Metal Spraying” handbook. Then, in 1959, METCO in the U.S. published its seventh edition, renaming it “Flame Spraying.” Due to technological advancements, the 7th International Thermal Spraying Conference was held in London from September 10 to 14, 1973, and the name was changed again to “Metal Spraying.” However, at the 8th International Thermal Spraying Conference, held from September 27 to October 1, 1979, in Miami—a renowned resort town in Florida, U.S.—it was decided to adopt the term “thermal spraying.” This is how the term “thermal spraying” came into being.
Thermal spraying has given rise to different techniques and applications across various eras:
1910: Wire Flame Spraying Technology; Wire flame spraying is widely used to prepare corrosion- and wear-resistant coatings on the surfaces of mechanical components, chemical containers, and rollers. With appropriate modifications to the nozzle section of the spray gun, it can also be used for spraying plastic powders.
1920s: Arc wire spraying technology has the following characteristics:
1) Apply special and aluminum coatings to steel components for long-term protection.
2) Spraying aluminum onto steel parts can prevent high-temperature oxidation.
3) Spray stainless steel or other wear-resistant metals onto steel parts for wear and corrosion protection.
4) Apply coatings of materials such as carbon steel and bronze onto mechanical parts for component repair.
5) Apply shielding coatings, etc., to plastic products.
6) Produce composite copper plates by arc-spraying or casting aluminum.
1950s: Explosive Spraying and Plasma Spraying Technologies
Plasma arc flame jets have high temperatures, making them ideal for spraying high-melting-point materials. The coating density can reach 85–98%, and the bonding strength can be as high as 35–70 MPa. The quality of plasma-sprayed coatings is significantly superior to that of flame-sprayed coatings. Primarily used for:
1) Wear-resistant and friction-reducing coatings;
2) Corrosion-resistant coating;
3) High-temperature oxidation resistance, resistance to high-temperature gas flow erosion, and thermal barrier coatings;
4) Manufacturing high-melting-point composite materials based on metals and ceramics.
Explosive spraying:
The powder is injected into the spray gun, while an oxy-acetylene gas mixture is simultaneously introduced. The ignited gas mixture generates a high temperature of 3,300°C, heating the powder and propelling it onto the workpiece surface at a velocity exceeding twice the speed of sound. This process forms a coating with a diameter of approximately 20 mm and a thickness of about 8 μm, characterized by high bonding strength and high density. The entire coating consists of overlapping, small, circular flakes.
1) On the damping platform for aviation engine ferroalloy fan blades, 0.25 mm-thick WC was applied using thermal spray; this increased the blade’s service life by a factor of 10.
2) A 0.12 mm-thick layer of Cr3C2 is sprayed onto the positioning retaining ring of the combustion chamber, increasing its service life by a factor of seven.
3) Currently, explosive spraying is mainly used to prepare high-quality wear-resistant coatings.
60 Era: Self-fluxing alloy powder flame, plasma spraying, and spray welding technologies
1980s: Supersonic Flame Spraying Technology
Supersonic Flame Spraying
The fuel gases (hydrogen, propane, propylene, or MAPP) and the oxidizer (O2) are introduced into the combustion chamber in specific proportions for mixing. This mixture undergoes an explosive combustion, generating high-temperature combustion gases that flow through four inclined nozzles located in the upper part of the combustion head and enter the copper nozzle. The powder is fed into the high-temperature combustion gases at a controlled rate via a powder-supply gas (Ar or N2), which flows along the central carbide sleeve inside the combustion head. The high-temperature, high-speed combustion gases carry the powder out of the nozzle, and the high-speed jet impacts the workpiece to form a coating. The entire torch is cooled by circulating water.
1990s: Laser Cladding Technology
China’s thermal spraying technology began in the 1950s, when Wu Jianchun and Zhang Guanbao established the country’s first specialized spraying plant in Shanghai. At that time, they developed oxy-acetylene flame wire-spray and electric-spray equipment and started offering metal-spraying services to external clients. China’s thermal spraying technology got off to an early start—wire-electric-arc spraying was already being developed in the 1950s. In the 1960s, certain military-industrial departments began researching plasma spraying. By the 1970s, a relatively complete range of spraying equipment and materials had emerged. However, overall progress remained slow, and it wasn’t until recent years that the technology began to develop more rapidly.
Typical thermal spray system
Demonstration of the Basic Thermal Spraying Process
Coating structure
Characteristics of thermal spraying technology:
In terms of application, thermal spraying technology has evolved from preparing decorative coatings to producing a wide variety of functional coatings, such as wear-resistant, corrosion-resistant, oxidation-resistant, heat-insulating, conductive, insulating, friction-reducing, lubricating, and radiation-shielding coatings.
Thermal spraying can be used both for repair and for manufacturing. Since the properties of the coating material are superior to those of the substrate, coating the surface of parts with such materials can significantly enhance product quality.
Advantages:
(1) The substrate and coating materials are widely available.
(2) Low substrate temperature.
(3) Flexible operation.
(4) Wide coating thickness range.
Disadvantages:
(1) Low thermal efficiency.
(2) Low material utilization rate and significant waste.
(3) Low adhesion strength between the coating and the substrate
Selection of coating materials:
(1) Thermal spray materials ideally should have a relatively wide liquid-phase region, as a wider liquid-phase region allows the molten droplets of the coating material to remain in the liquid phase for a longer duration.
(2) It exhibits excellent thermal stability and does not sublime or decompose in high-temperature flame flows. If a material readily decomposes at thermal spraying temperatures, it is unsuitable for thermal spraying.
(3) The spraying material, in its molten state, should exhibit good wettability with the substrate to ensure strong bonding between the coating and the substrate.
(4) Have a thermal expansion coefficient similar to that of the substrate to prevent significant thermal stress caused by a large difference in expansion coefficients.
Coating formation process:
(1) The spray material is heated to a molten state.
(2) The spray material is atomized into tiny molten droplets that impact the substrate surface at high velocity. The greater the kinetic energy of the particles impacting the substrate and the larger the degree of impact-induced deformation, the better the bond strength of the resulting coating.
(3) The molten high-speed particles deform upon impact with the substrate surface and, after cooling and solidifying, form a coating.
The process flow of thermal spraying includes:
(1) Surface Pre-treatment
(2) Thermal Spraying
(3) Post-processing
(4) Machining, etc.
Surface pretreatment of the substrate:
(1) Purification treatment: Remove surface dirt.
(2) Roughening treatment: Enhances the adhesion between the coating and the substrate.
The reason why roughening treatment can enhance the adhesion strength of coatings is:
1) Provide surface compressive stress:
2) Provide opportunities for interlocking with coating particles;
3) Increase the bonding area;
4) Clean the surface.
Thermal spraying has become an important method for preparing wear-resistant coatings and is widely used in various sectors of the national economy. The porous layered structure of the coating gives it wear-resistant performance that differs significantly from that of similar bulk materials, with the most important distinguishing feature being the influence of applied load. Under low-stress service conditions, thermal spray coatings exhibit excellent wear resistance. However, when the stress exceeds a certain level, wear accelerates due to the rapid propagation of cracks along the interfaces between deposited particles. Especially under conditions of erosion, cavitation, fretting, fatigue, and abrasive wear, the potential of coating materials can be realized only at 10% to 30%. Therefore, conducting fundamental research to establish a systematic relationship among the microstructure of coatings, their performance, service conditions, and service effectiveness—and by building a database to guide the design and application of wear-resistant coatings—will be an important approach for fully harnessing material potential, enhancing the service performance of thermal-sprayed coatings, and achieving resource and energy conservation.
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Relevant Information
The complete set of plasma-sprayed equipment has been shipped to the customer’s site in Thailand.
Core spraying equipment: SX-80 plasma spray main unit, with a 15,000℃ flame suitable for multiple materials including zirconia and silicon carbide; powder feeding accuracy of ±1%, and coating thickness tolerance ≤ ±5 μm. Environmental protection support system: Customized soundproof booth + pulse dust collector—effectively addressing spray noise pollution while achieving highly efficient dust recovery, compliant with Thai environmental standards. Automated equipment: 6-axis industrial robot + intelligent spray cart, enabling precise spraying of complex workpieces and automated loading/unloading, boosting production efficiency by 40%.
On-site engineers provide hands-on training, focusing on the core operations of plasma spraying equipment such as the SX-80. Sanxin has customized a complete solution for its customers, including an automated spraying robotic arm, a soundproof booth, and a dust removal system—ensuring both high spraying efficiency and compliance with environmental standards.
Guangzhou Sanxin Thermal Spraying Turntable Shipment
Guangzhou Sanxin Company manufactures single-station and multi-station thermal spray turntables, which can be paired with plasma equipment, supersonic equipment, and arc equipment. We offer rapid, customized production tailored to customer requirements and product dimensions. A thermal spray turntable is a high-precision rotary worktable specifically designed for thermal spraying processes—including flame spraying, plasma spraying, and arc spraying. By providing controllable rotational speed and exceptional stability, it ensures uniform coating thickness on the workpiece surface, thereby enhancing spraying efficiency and quality.
SX-80 plasma equipment is being used at a customer site in Russia.
SX-80 plasma equipment is being used at a customer site in Russia.
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