Dacromet is the transliteration and abbreviation of DACROMET, abbreviated as Dacromet, Dakrust, and Dickron. It is named zinc-chromium coating in China. It is a new type of anti-corrosion coating with zinc powder, aluminum powder, chromic acid and deionized water as the main components.

The protective effect of Dacromet film on steel substrate can be summarized as follows

● Barrier effect: Due to the overlapping of flaky zinc and aluminum layers, the process of corrosive media such as water and oxygen reaching the substrate is hindered, which can play an isolated shielding role.
● Passivation effect: During the Dacromet treatment process, chromic acid reacts chemically with zinc, aluminum powder and substrate metal to form a dense passivation film, which has good corrosion resistance.
● Cathodic protection effect: The main protective effect of zinc-aluminum-chromium coating is the same as that of galvanized layer, which is to provide cathodic protection for the substrate.

Dacromet is a new type of surface treatment technology. Compared with traditional electroplating process, Dacromet is a "green electroplating". Its advantages are as follows

● Super corrosion resistance: The thickness of the Dacromet film layer is only 4-8μm, but its anti-rust effect is more than 7-10 times that of traditional electrogalvanizing, hot-dip galvanizing or paint coating. Standard parts and pipes treated with the Dacromet process have no red rust in the salt spray test for more than 1200h.
● No hydrogen embrittlement: Dacromet's treatment process determines that Dacromet has no hydrogen embrittlement, so Dacromet is very suitable for the coating of stress-bearing parts.
● High heat resistance: Dacromet can resist high temperature corrosion, and the heat resistance temperature can reach more than 300℃. The traditional electrogalvanizing process will peel and be scrapped when the temperature reaches 100℃.
● Good bonding and re-coating performance: Dacromet coating has good bonding with the metal substrate, and has strong adhesion with other additional coatings. The treated parts are easy to spray and color, and the bonding with organic coatings even exceeds that of phosphating films.
● Good permeability: Due to the electrostatic shielding effect, it is difficult to electroplate zinc on deep holes, slits, inner walls of pipes and other parts of the workpiece, so the above parts of the workpiece cannot be protected by electroplating. Dacromet can enter these parts of the workpiece to form a Dacromet coating.
● No pollution and public hazards: Dacromet will not produce wastewater and waste gas that pollute the environment during the entire process of production, processing and workpiece coating, and does not require three wastes treatment, which reduces the processing cost

Dacromet equipment, process, Dacromet coating liquid and supporting pre- and post-processing equipment composition

● Main equipment: pre-processing equipment [carbonization degreasing, ultrasonic spray degreasing cleaning machine; shot blasting (sand blasting) rust removal], coating equipment: water curtain spray room, semi-automatic coating machine, fully automatic coating machine; sintering equipment: Dacromet mesh belt sintering furnace; box sintering furnace, trolley sintering furnace.
● Dacromet liquid preparation equipment, Dacromet testing equipment
● Central automation, informationization, and intelligent control system (composed of host computer (HMI), PLC, field instruments, etc. Among them, the automation system PLC mainly completes communication, data collection, important logic control, etc. The host computer plays a role in centralized monitoring and management.)

Suggestions for production line equipment selection

● The heating furnace can use electricity, natural gas, and liquefied petroleum gas as energy.
● According to the investment and capital, the coating equipment can be selected: water curtain spray room, semi-automatic coating machine, and fully automatic coating machine.
● According to the production capacity requirements, the mesh belt sintering furnace can select 12 meters, 16 meters, 18 meters, 24 meters heating furnace, reciprocating multi-layer heating furnace, small batch can select box sintering furnace, trolley sintering furnace.
● The coating machine material frame can be selected from 500, 650mm, 800, and 900mm.

Performance and application of Dacromet

The Dacromet process has no hydrogen embrittlement, good weather resistance and corrosion resistance, so it is widely used. The biggest advantage of Dacromet coating is its excellent corrosion resistance, which can be improved by 7-10 times compared with the traditional electrogalvanizing surface treatment process. It is widely used in metal surface corrosion protection in the fields of automotive parts, national defense and military products, subways, electronic and electrical products, chemicals, oceans, electricity, communications, construction, railways, highways, bridges, tunnels, marine engineering, ships and moorings, petrochemicals, bioengineering, medical equipment, cable trays, natural gas pipelines, wind power generation, solar power generation, steel structure engineering, small hardware and standard parts.

Special application scenarios

● Anti-corrosion of various high-strength chassis small and medium brackets, connectors, exposed parts and fasteners on trucks, such as various special-shaped steel brackets, bolts (including riding bolts, wheel bolts, etc.), nuts, etc. Fasteners with grade ≥10.9 on automobiles, because Dacromet coating not only has high corrosion resistance, but also can ensure no hydrogen embrittlement. High-strength steel is at risk of hydrogen embrittlement during pickling and electroplating. Although it can be dehydrogenated by heat treatment, it is difficult to completely remove it. The Dacromet coating process does not require pickling and activation, and there is no electrochemical reaction that causes hydrogen evolution, which avoids the occurrence of hydrogen embrittlement.
● Anti-corrosion of metal parts in high-temperature environments such as around the engine, such as heat shields, exhaust pipes, radiators, engine cylinder heads and other parts. The passivation film on the surface of the traditional galvanized layer will be destroyed at around 70°C, and the corrosion resistance will drop sharply. The curing temperature of the Dacromet coating is about 300°C. The chromate polymer in the coating does not contain crystal water. The coating is not easily destroyed at high temperatures and exhibits excellent corrosion resistance. The parts treated with the Dacromet process are used for a long time at 250°C, and their appearance remains almost unchanged, and the corrosion resistance is very strong.
● Anti-corrosion of various elastic parts on trucks, such as hoops, semicircular clamps, various springs, leaf springs, etc. These parts have high requirements for strength and hardness. Electroplating will produce hydrogen embrittlement. If the dehydrogenation is not thorough, it is easy to tear or corrode fatigue under dynamic load for a long time, which will bring safety hazards to the driving of the car. Especially for heavy-duty trucks, the working environment is relatively harsh, so the surface treatment requirements for these parts are also relatively high. Dacromet coating has high corrosion resistance and high weather resistance, which is very suitable for the surface treatment of such automotive parts.
● Anti-corrosion of various complex-shaped pipes and cavity parts on heavy-duty trucks, such as engine exhaust pipes and mufflers. If such parts are electroplated, due to the complex shape of such parts and the limitations of the electroplating process, the formed coating is uneven, and even leakage plating may occur, which will sharply reduce the corrosion resistance of the parts and directly affect the performance and service life of automotive parts. The Dacromet process uses dipping and other methods, so there is no problem of poor uniform coating and depth during the electroplating process. In addition, the Dacromet treatment liquid has excellent penetration ability and can form a good protective film in the gaps of close contact. It is particularly suitable for the corrosion protection of pipes and automobile parts with complex cavities. Some assembly parts are also suitable for Dacromet treatment after assembly. In addition, the Dacromet coating is not corroded by various oils, antifreeze, cleaning agents and other chemicals, and has good chemical resistance and weather resistance. Therefore, Dacromet is very suitable for the corrosion protection of truck chassis and automobile external parts.