Flame spraying technology
Flame spraying is a surface modification technique that uses the thermal energy of a combustion flame to heat the spray material to a molten or semi-molten state, then sprays it onto the substrate via a high-speed airflow to form a coating. Since its introduction in the early 20th century, this technique has been widely adopted in industry due to its advantages, including simple equipment, flexible operation, and low cost, becoming a key component of surface engineering. It can be applied to virtually any solid material, including metals, ceramics, plastics, and wood, imparting various properties such as wear resistance, corrosion resistance, high temperature resistance, thermal insulation, and electrical conductivity to the substrate, effectively extending the service life of the workpiece and reducing production costs.
Flame spraying technology can be categorized in various ways. Based on the form of the sprayed material, it can be divided into powder flame spraying, wire flame spraying, and rod flame spraying. Powder flame spraying is suitable for a variety of metal, alloy, ceramic, and cermet powders, and can produce a variety of functional coatings, making it the most widely used. Wire flame spraying uses metal or alloy wire as the spraying material, and features simple equipment and stable feed, making it suitable for large-scale production. Rod flame spraying, primarily used for ceramics, produces denser coatings but has a relatively narrower application range. Based on the type of flame, it can be further divided into acetylene-oxygen flame spraying, propane-oxygen flame spraying, and hydrogen-oxygen flame spraying. Acetylene-oxygen flame spraying has the highest temperature (reaching 3100°C) and is the most widely used.
The core advantages of flame spraying technology lie in its broad material adaptability and process flexibility. Nearly all metals and their alloys (such as zinc, aluminum, copper, nickel-based alloys, and iron-based alloys), ceramics (such as alumina, zirconium oxide, and tungsten carbide), cermets, and plastics can be used as spray materials. By selecting different materials, coatings that meet various performance requirements can be produced. For example, nickel-based alloy powders can be used to produce corrosion-resistant coatings for chemical equipment; alumina ceramic powders can be used to create wear-resistant coatings for the surface reinforcement of machine tool guides; and zirconium oxide powders can be used to create thermal insulation coatings for protecting high-temperature furnace linings. Furthermore, this technology can handle workpieces of various shapes and sizes, from small precision parts to large components (such as bridge steel structures and the inner walls of storage tanks). The thermal impact on the substrate is minimal, and the substrate temperature can typically be controlled below 200°C, preventing deformation and performance degradation.
The coating performance of flame spraying technology depends on the spraying material, process parameters and substrate pretreatment quality. The bonding between the coating and the substrate mainly relies on mechanical bonding, and the bonding strength is usually 10-30MPa, which is lower than plasma spraying and detonation spraying, but sufficient to meet the requirements of general working conditions. The coating has a high porosity (generally 5%-15%), which reduces the density and corrosion resistance of the coating, but also provides space for sealing treatment, which can significantly improve the coating performance by filling the pores. The hardness, wear resistance and other properties of the coating are mainly determined by the spraying material. For example, the hardness of the tungsten carbide coating can reach 80-90HRC, which has excellent wear resistance and is suitable for occasions with severe wear.
With the advancement of industrial technology, flame spraying technology is constantly innovating and improving. The emergence of high-velocity flame spraying (HVOF) technology, by increasing flame speed and temperature, significantly improves the bonding strength and density of coatings, approaching the level of plasma spraying. The application of automated flame spraying production lines has improved coating quality stability and production efficiency. The development of new environmentally friendly spraying materials has reduced the use of toxic and hazardous substances and reduced environmental pollution. In the future, flame spraying technology will continue to develop towards higher efficiency, intelligentization, and environmental protection, playing a greater role in equipment manufacturing, energy and environmental protection, aerospace, and other fields. Furthermore, combined with other surface treatment technologies (such as laser cladding and electrophoretic coating) will further expand its application scope and provide more comprehensive surface solutions for industrial production.
