Specification for the hottest electroplating proce

2022-09-19
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Specification of electroplating process

II specification of nickel plating process

(I) roller installation

roller clamping should be stable, conductive, shaft end sealing should be good, and no liquid should flow. Use 1 ~ 2m iron wire to wrap around both sides of the clamped drum, so that the chamfer on both sides of the drum is free of burrs

(II) cleaning treatment

before electroplating, the drum should be cleaned first. If there is oil stain on the surface of the drum, what will be the impact of the non stick nickel plating layer and the uneven installation of the peeling force measuring part before and after on the indicated value?. The steps are as follows

(1) special metal cleaning agents were used. Last year, China's production capacity exceeded 65million tons to remove oil and other debris. At present, most companies use the "Silver Lake metal detergent" produced by Yuncheng Silver Lake chemical plant, which is configured from high-efficiency washing raw materials such as surfactants. It has good degreasing effect, strong cleaning power, and good corrosion and rust resistance. When in use, the detergent is prepared into 2% - 5% aqueous solution, soaked and brushed at room temperature, and the heating effect is better. Generally, use 600 × water sandpaper to put on the detergent and polish the drum evenly and forcefully

(2) wash the plate roller and protective sleeve with clean water, and clean the joint when plating the small plate, and then use 3% ~ 5% dilute sulfuric acid (H2SO4) to activate the surface

(3) carefully wash the plate roller and protective sleeve with distilled water. The standard of cleaning is not to hang water drops on the layout and to be completely soaked by water. Unclean cleaning will cause blistering and peeling of nickel coating. After cleaning, it can be put into the nickel plating bath for electroplating

(III) nickel plating

nickel is one of the iron group metals. Its plating solution has greater cathodic polarization and anodic polarization in the electroplating process. Without complexing agent, a fine and dense nickel coating can be obtained

the purpose of nickel plating is mainly to prevent iron from replacing copper (the solution is nickel sulfate), so that the copper layer can be firmly combined with the roll core. Because in the case of no current, when the iron roller core of the plate cylinder contacts the acidic copper plating solution, a replacement reaction will occur, and this layer of copper belongs to chemical reaction replacement copper, which is not firmly combined with the iron core. Therefore, the cleaned drum cannot be directly put into acidic copper plating solution for electroplating, but must be nickel plated before copper plating

1. The main component of nickel plating solution

(1) the content of nickel sulfate (NiSO4 · 7H2O) in the plating solution is specified by some companies as 180 ~ 220g/l, and set higher by some companies as 250 ~ 320G/L. If the nickel sulfate content is about 300g/l, the coating color is uniform, and a higher current density is allowed, and the deposition speed is fast

(2) the content of nickel chloride (NiCl2 · 6H2O) in the plating solution is specified by some companies as 30 ~ 50g/l, some as 55 ~ 60g/l, and others as 40 ~ 50g/L

nickel chloride is an anode activator. On the one hand, chloride ion can activate the anode, on the other hand, nickel ion can supplement the concentration of nickel ion in the solution. Both are effective components

(3) boric acid (H3BO3) is a buffer, which can free hydrogen ions (h+) and borates (h2bo32-). Its content in the plating solution is specified by some companies as 40 ~ 55g/l, 35 ~ 50g/l and 30 ~ 45g/L. Boric acid can stabilize pH value in nickel plating solution. In the process of nickel plating, the pH value of the plating solution must be kept within a certain range. In actual production, the general specification is 4.0 ~ 4.6, usually 4.2. If the pH value is too low, h+ is easy to discharge, which reduces the current efficiency of nickel plating, and the coating is easy to produce pinholes; If the pH value is too high, the plating solution is turbid, and the metal ions around the cathode will be clamped into the coating in the form of metal hydroxide, which will degrade the mechanical properties and rough the appearance of the coating. Therefore, the pH value must be strictly controlled in production

boric acid can not only stabilize the pH value, but also make the coating crystal fine and not easy to scorch. When using high current density, the plating solution with high boric acid content (40g/l) should be used

2. Preparation method of plating solution

calculate the required amount of chemicals according to the volume, dissolve them in hot water, mix them in a container, add distilled water to dilute to the required volume, let them stand for clarification, introduce the plating solution into the plating tank by filtration method, and then add the dissolved sodium dodecyl sulfate solution, stir it evenly, take samples for analysis, and use it for production after adjusting and passing the trial plating

3. Process conditions

(1) temperature of nickel plating solution

the temperature of nickel plating solution is generally controlled at 40 ℃ ± 1 ℃. Raising the temperature of the plating solution can improve the solubility and conductivity of salts in the plating solution, accelerate the diffusion rate of nickel ions to the cathode, reduce the internal stress of the coating, make the coating flexible and malleable, and at the same time, accelerate the deposition and increase the current efficiency of the cathode and anode with the help of higher cathode current density. However, with the increase of temperature, the evaporation of the plating solution increases, and the nickel salt is also easy to be hydrolyzed to generate nickel hydroxide precipitation. Especially, after the hydrolysis of iron impurities in the plating solution, iron hydroxide precipitation will be generated, which will increase the pinholes and burrs of the coating. Therefore, when using high temperature and high current density plating solution, the amount of boric acid should be increased

(2) cathode current density

in the process of nickel plating, the cathode current density is closely related to temperature, nickel ion concentration, pH value and stirring degree. Generally speaking, when the concentration of plating solution is high, the value of P and H is low, and accompanied by heating and stirring, it is allowed to use a higher cathode current density. When the temperature and concentration of the plating solution are low, only a small cathode current density can be used. In actual production, the current density of plating is 3 ~ 4A/DM2

(3) Baume degree (be °)

for Baume degree, some companies' specifications are 17 ~ 20, and some are 20 ~ 22. Note that Baume degree is high and prone to pitting, so it should be strictly controlled in the best range in actual production

(4) plating time

the plating time is generally 15 ~ 20 minutes

(5) anode in Nickel Plating Bath

the anode in nickel plating bath is electrolytic nickel plate

4. Process maintenance

(1) make the solution ratio accurate, and make appropriate adjustments to the solution according to different equipment. If the active component content of the solution is low, the current will be too low. Therefore, check the pH value and be ° value every day, and make up for what is missing. When changing shifts, strict records of relevant health standards should be made for each plastic material often used. The liquid level should be sufficient and the pH value should meet the standard (no less than 3.8). Nickel plating solution should be tested twice a week

(2) filter pump shall be added to the nickel cylinder to filter the nickel solution to ensure its cleanness

(3) nickel sulfate and other components in some companies are relatively high, so the newly prepared bath liquid is easy to cause the coating to bulge, so the bath liquid should be a little thinner. After nickel plating, use 1000 × fine sandpaper to smooth it, and never touch fingerprints

(4) after nickel plating, it must be washed with pure water. If washed with clean water, the binding force of nickel and copper will be affected due to poor water quality

(5) zinc and iron are the biggest hazards of nickel plating, so molten copper is not allowed to enter the nickel plating tank during hoisting

(6) after nickel plating, it is forbidden to place it for a long time (no more than 40 minutes). Soak it with water to prevent nickel passivation in the air

(7) when it is found that there are many pinholes in the nickel coating, the anti pinhole agent hydrogen peroxide can be used. Dilute 30% hydrogen peroxide to 1 ~ 3ml/l, slowly pour it into the plating solution, and constantly stir it to remove impurities in the plating solution. Then filter the plating solution

5. The quality standard of nickel coating

(1) the thickness of one side of nickel coating is 8 ~ 10 μ m。

(2) the nickel layer is a slightly yellow fully covered coating, and burrs and other defects are not allowed

(to be continued)

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