Recently, Dacromet technology has once again received attention from the industry. Dacromet was first born in the late 1950s, and its development process is full of innovation and breakthroughs.
In the cold winter of North America and northern Europe, in order to alleviate the ice on the road, people commonly use salt to sprinkle the ground, but it is followed by the erosion of the steel matrix by chloride ions, resulting in serious damage to the vehicle. American scientist Mike Martin developed a highly dispersed water-soluble coating based on metal zinc sheet, adding aluminum sheet, chromic acid, deionized water as a solvent, and formed a thin coating after coating and baking, successfully resisting chloride ion erosion, so that anti-corrosion technology to a new level. This technology was later adopted by the US military as an anti-corrosion military technology (US Army standard McL-c-87115).
In the 1970s, Japan's NDS company introduced dacromet technology from the United States, and bought out the right to use it in the Asia-Pacific region, and developed rapidly in Japan after improvement, and many coating plants and pharmaceutical units have adopted it. China officially introduced the technology from Japan in 1994, initially applied to the defense industry and domestic auto parts, and now has expanded to power, construction, Marine engineering, household appliances, hardware and standard parts, railways, Bridges, tunnels, highway guardrail, petrochemical, biological engineering, medical equipment powder metallurgy and other industries.
The basic composition of Dacromet coating solution includes metal (mainly ultrafine scaly zinc, aluminum), solvent (such as ethylene glycol and other inert organic solvent), inorganic acid components (such as chromic acid, etc.) and special organic compounds (viscosifying dispersion components of the coating solution, the main component is cellulose white powder).
There are three main anti-corrosion mechanisms: first, the barrier effect, the overlapping of sheet zinc and aluminum layers, preventing the corrosive medium from reaching the matrix; Second, passivation, the passivation film generated during the treatment process has good corrosion resistance; The third is the cathodic protection effect, which is similar to the galvanized layer and provides cathodic protection to the substrate.
Compared with the traditional electroplating process, Dacromet has many advantages as a "green electroplating" technology. For example, its corrosion resistance, the thickness of the film layer is only 4-8μm, the anti-rust effect is more than 7-10 times that of the traditional electric galvanizing, hot dip galvanizing or coating method, and the salt spray test of the standard parts and pipe joints treated by the dallol process does not appear red rust for more than 1200h; No hydrogen brittleness, suitable for coating stressed parts; High heat resistance, high temperature corrosion resistance, heat resistance of more than 300℃; Good bonding force and recoating performance, good bonding with metal matrix, strong adhesion with other additional coatings, easy to spray and color parts after treatment; Good permeability, can enter the workpiece deep hole, slit, pipe inner wall and other parts to form coating; No pollution and public hazards, production and processing and workpiece coating process does not produce pollution waste gas, reduce the treatment cost.
However, Dacromet technology also has some shortcomings, such as some products contain chromium ions harmful to the environment and human body (now improved under the environmental protection policy), high sintering temperature and long time leading to large energy consumption, poor surface hardness and wear resistance, single coating color, electrical conductivity is not good.
Nevertheless, dacromet technology is still widely used. In the field of heavy-duty vehicles, it is used for the anti-corrosion of small and medium-sized supports, connectors, exposed parts and fasteners of various high-strength chassis to avoid hydrogen embrittlement; Excellent anti-corrosion properties are shown in the metal parts made in high thermal environment such as around the engine. For various elastic parts, it can meet the requirements of high corrosion resistance and high weather resistance; In the treatment of tube and cavity parts with complex shapes, there is no uneven plating or missing plating, and it is not corroded by various oils, antifreeze, cleaning agents, etc., and it has good chemical resistance and weather resistance.
With the continuous advancement of technology, the performance of Dacromet technology is also continuously optimized and improved. For example, [specific time] Wanfeng Aowei Company's Dacromet coating products have completed the delivery of core components of Shenzhou spacecraft return capsule for many times, and the technical characteristics of its supporting products, such as superior corrosion resistance and air tightness, have been fully recognized by customers. At the same time, relevant companies are also constantly exploring the shortcomings of Dacromet technology to meet the needs of more areas.
In addition, in the context of increasingly strict environmental requirements, the environmental assessment of dacromet production projects is also becoming more and more important. For example, the new project with an annual output of 1000 tons of Dacromet metal products of Zhongshan Huixiang Dacromet Metal Products Co., Ltd. has passed strict environmental impact assessment approval. Changshu Dacromet Metal Products Co., Ltd. was fined 235,000 yuan because the construction project did not prepare an environmental impact assessment, began construction without authorization and put environmental protection facilities into production without acceptance.
In the future, Dacromet technology is expected to play an important role in more fields, but also need to continue to improve and perfect in environmental protection, energy saving and other aspects to achieve sustainable development.