Dacromet is a surface treatment technology widely used in the anti-corrosion field of metal fasteners. Its core is to provide long-term rust protection for the metal through a composite coating of zinc, aluminum sheet and inorganic chromate. In recent years, the use of Dacromet screws in the automotive, construction, power and other industries has increased significantly, which is inseparable from its unique performance advantages, but at the same time there are certain limitations.
The core advantages of Dacromet technology
The anti-rust ability of Dacromet coating is far superior to that of traditional electroplating. Experimental data show that its salt spray resistance test time can reach more than 1000 hours (ordinary galvanized only 24 hours), which benefits from the layered structure of zinc and aluminum sheets in the coating and the passivation of inorganic chrodate. Zinc serves as the sacrificial anode protection substrate, and aluminum forms a physical barrier. The dual protection mechanism makes it perform well in harsh environments such as wet, acid rain and Marine climate. For example, the service life of transmission tower bolts in coastal areas can be extended by 3-5 times after Dacro treatment.
Traditional electroplating requires pickling to remove rust, which may lead to brittle fracture of steel caused by hydrogen absorption, and Dacrobar treatment without pickling and electrolysis, especially suitable for high-strength fasteners (such as automobile engine bolts). This feature makes it a rigid requirement in aerospace and automotive manufacturing.
Environmental protection Dacromet does not contain hexavalent chromium, and the coating can withstand 300℃ high temperature, suitable for brake system, exhaust pipe and other high temperature components. In contrast, galvanized coatings begin to fail above 100 0°C. In addition, its closed coating process reduces wastewater discharge and is more in line with modern environmental regulations.
The limitations of Dacromet
Dacro treatment requires special equipment, and the price of coating raw materials (such as high purity zinc aluminum powder) is expensive, and its cost is 30%-50% higher than that of ordinary galvanization. For low added value fasteners, the economy is insufficient.
The coating is matte silver gray, the aesthetic degree is not as good as galvanized bright zinc; And because of the high proportion of non-metallic components, poor conductivity, not suitable for conductive electromechanical occasions (such as grounding bolts).
Dacromet coating and substrate for mechanical bonding (non-metallurgical bonding), by strong friction easy to flake. Once damaged, it needs to be reworked as a whole and cannot be repaired locally, which increases the maintenance cost.
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