An electroplated paint car is actually a process in which an electroplated coating is used instead of a metallic paint or a magnetic paint. The scientific name is vacuum plating, which belongs to physical plating and is environmentally friendly. First, the appearance part of the car to be painted is placed in a vacuum plating furnace as a target, and the metal is evaporated into a gas state to bombard the target. The coating thickness is on the nanometer scale. The coating can be a precious metal or other colored metal. It can also be chrome.
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Process: loading drum→electrochemical degreasing→hot water washing→cold water washing→acid etching→water washing→activation→rolling galvanized iron alloy→empty tank to bring out liquid→cleaning→cleaning→rolling barrel people passivation barrel →Cleaning→lighting→cleaning→passivation→heat sealing→drying→drying
1, pre-plating treatment
(1) Electrochemical degreasing
(2) Acid etching
HCL500 mL/L, additive 40-50MLL/L, water 450-460 mL/L, room temperature min2-5
Features: low acidity, no acid mist, no pollution to the environment, good effect, both rust and light degreasing, the cost is still lower than pickling.
(3) Activation
HCI (A ·K) 10-20ml/L, the rest is water, room temperature 2 to 3 min
Features: It can remove the floating rust before the groove of the barrel plating, ensure the bonding strength between the substrate and the coating, and stabilize the pH value of the solution.
2, barrel plating
(1) Formula composition
Zncl2 40-70 g/L, kci or NaCI (refined salt) 180-230 g/L, FPSO4- 7 H2O5-12g/L, ZF-A cylinder opening agent 15-20 mL/L, ZF brightener 6-12 mL/L, ZF-B modifier 5-10 mL/L, pH 3.5-5.5-60 °C, 100-300 A/æ…, Zn, Fe anode ratio (10-12): 1. Barrel plating is not pure Iron anode, drum speed 8-10 r / nvn, coating iron content 0.2% -0.8%.
(2) Solution preparation
First dissolve ZnCL2 and KCI with 1/2 volume of water, add 1g/L of zinc powder and powdered activated carbon, respectively, and filter the human trough; adjust the pH to 4 with reagent hydrochloric acid; dissolve the miso with water, add people to 10 times water dissolved FeSO4 solution container, the solution immediately turbid, left to clear and transparent colorless when added, 1 to 2 times water (summer and cold water, winter and spring hot water) diluted ZF-A open cylinder and ZF bright #}n, dilute ZF-B adjuster with 3 times water to add people; add water to the required volume, stir evenly, electrolyze for 4h.
3, post processing
The galvanized layer emits light by nitric acid to increase the brightness of the coating, and the nitric acid of the zinc-iron alloy emits light. The purpose is to remove the extremely thin impurity film on the surface of the coating to make the bright coating clearer and ensure good adhesion between the coating and the passivation film. The passivation process can obtain the appearance of passivation film such as silver white, blue white, color, military green to black. The chromium salt content is very low, the chromium salt is 0.5-5g/L, and no cleaning is required after passivation. No environmental pollution.
Factors affecting automotive plating
1, the main salt
ZnCl2 is the main salt, the content can be changed in a wide range. The liquid temperature affects the normal dissolution of the anode with the change of temperature, and the dissolution is faster in summer and autumn. The lower limit is taken (40-50g/L), and the anode dissolution is slow in winter and spring. 70g/L) low main salt content, large concentration polarization, can improve the cathode polarization, make the coating crystal fine, disperse ability and deep plating ability; too low will also affect the dispersion and deep plating ability ZnCL2 content, deposition The speed is fast, the brightness is good, but the dispersion ability is poor, and the low current density area (such as the standard rib) is fogged and extinguished.
2, conductive salt
The automatic wire conductive salt is KCl. High content, good conductivity, improved dispersing ability, stable plating solution; high content, easy to turbid plating solution, affecting plating quality. This situation occurs, adding fresh water in an appropriate amount, the solution recovers clear: below the lower limit, poor conductivity, Dispersion ability, deep plating ability decreased, low area such as screw ribs fog, gray.
3, stabilizer
C6H8O6 is a stabilizer for iron. The effect is small. Since C6H8O6 contains trace amounts of furfural impurities, the content is higher than the upper limit. When it accumulates to a certain value, the adhesion between the coating and the substrate is poor. Below the lower limit, the stability is poor. Affect the quality of plating.
4, pH
The pH value is optimal at 4-5, at which time the solution is stable, the iron content of the coating is 0.2%-0.8%, the fine pH of the coating is higher than 5.5, the hydrogen consumption is large, the solution tends to alkalinize, and the hydroxide is sucked on the electrode. Forming a film on the surface, inhibiting zinc deposition, accelerating iron deposition, increasing iron content of the coating, lightly coating rough, heavy solution volatilization, slow deposition rate and dark pH of the coating below 3.5, high acidity of solution, fast dissolution of anode, leading to main salt The ratio is out of balance, the decomposition of the additive, the turbidity of the solution, the quality of the barrel plating are affected, and the production shows that the color of the coating obtained by different pH values ​​is different: the upper and lower limits of the pH are close, the brown is deeper, and the color is lighter; pH 4-5 The rainbow color is the best: so the pH is controlled at 4-5.
5, cathode current density
Calculating the current density in barrels is the traditional method of barrel plating. It is more general. In fact, the total area of ​​the barrel-plated parts is larger than the conductive area. Therefore, the conductive area should be calculated according to the shape and load of the barrel. If you observe that there is no roller eye, the brightness of the high and low areas of the coating is uniform, indicating that the set current is just right, there is no need to correct the plating, the plating solution is stable, and the performance is normal.
Electroplating technology in modern automotive applications
Piston, piston ring, connecting rod
The piston, piston ring and connecting rod are three-sport moving parts of the automobile engine, and the friction loss accounts for 40-50% of the total loss of the engine. Reducing the weight of the piston, piston ring and connecting rod and improving the friction environment have great significance for reducing engine vibration, noise and fuel consumption. In the past, the piston did not perform any surface treatment or only chemical immersion tin (formation of the initial wear-in layer): the piston ring was chrome-plated and phosphatized: the connecting rod was only oxidized by the splicing of the phase; the bearing bush on the connecting rod was plated with Pb- Sn binary alloy and electroplating Sn treatment. These electroplated layers have not been able to meet the needs of modern engine speed, high power, compactness and ECR technology development.
bush
In order to prevent the Sn in the coating from forming a brittle phase by thermal diffusion from the body, on the bearing bush of the high-power engine, it is necessary to apply a nickel grid on the body, and replace the Pb-Sn binary with the electroplated Pb-Sn-Cu alloy. Alloy plating.
Inlet and exhaust valve
The friction loss of the intake and exhaust valves is about 2% of the energy loss of the station engine. Measures to reduce losses: reduce the structural size of the inlet and outlet valves, and use a lightweight material port such as Zinc Alloy Heat-resistant steel. Working at 750 ° C high temperature, there is a smog in the engine exhaust gas, the Qin gas exhaust valve will undergo intense oxidation, potassium must be carried out on the surface, usually by spraying molybdenum, salt bath furnace nitriding treatment. Recently, the treatment method that attracts people's attention is to treat the carburizing treatment. The process has little impact on the environment. The TiC hard layer formed on the surface is 50μm deeper than the permeation layer treated by the heat-resistant steel salt bath furnace, and the hardness reaches HV700. Oxidation, wear resistance, heat resistant steel gas valve, processing cost is more expensive than salt bath furnace treatment
Exhaust cylinder, silencer
The exhaust system installed in the chassis part of the vehicle is corroded by environmental impacts such as the impact of mud and sand, and is subjected to scouring and oxidative corrosion of high-temperature exhaust gas above 400 °C. The working environment is very harsh. The materials of the exhaust system are mostly made of stainless steel and hot-dip aluminum. In the process of use, the aluminum plate often occurs blackening and rusting of the coating. The corrosion test of the whole car has a grade 5 corrosion in 40 cycles, and the corrosion resistance is not as good as stainless steel. The addition of a silicon element cable to the hot-dip aluminum l can suppress the growth of the iron-aluminum alloy layer and improve the processing performance. The service life of the hot-dip aluminum plate is related to the thickness of the coating, the molding process, and the operating temperature.
Shock absorber connecting rod
In the past, the damper connecting rod was electroplated with an Eth hard hard chrome process, and the corrosion resistance could not meet the requirements. Recently used HEEF25 microcrack chrome plating process, the thickness of the coating is 20±5μ; and the specification of 10l±3μ, the general requirement is 400-600 strips/cm, which is positive for ensuring the corrosion resistance and lubricity of the damper connecting rod. effect. The current density in this process has a significant relationship with the number of microcracks, crack morphology and amount of osmosis. The general control is at 58A/dm2. The design of the cylindrical anode and the polishing after plating have an impact on the quality.
Car decoration
Modern car decoration parts are mostly made of plastic parts. Corrosion resistance, thermal shock resistance and decorative properties required for high-grade automotive plastic decorative plating parts are extremely high.
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