Treatment And Effects Of Impurities

1.The effect of iron impurities

There are two kinds of iron impurities in the bath: one is iron bivalent, the other is iron trivalent. The plating solution can still produce normally when the content of ferric iron reaches 10g/L, which may be related to the fact that ferric iron cannot produce electrochemical co-deposition with zinc on the cathode. The bivalent iron in the bath is more sensitive, so that the range of current density is significantly reduced, especially affecting the quality of the coating at the high current density. In the hull cell experiment, it was found that at 0.2g/L iron, nearly 20mm of the high current end appeared scorched and rough area, and at 0.3g/L, almost half of the sample appeared scorched and rough area, while the coating in the low current area was gray. This plating solution for rolling plating, will appear close to the wall of the rolling plating coating serious scorch, this is the common black spot potassium chloride rolling plating, that is, the barrel eye mark.

Generally in production, when the iron content is greater than 5g/L, the coating in the low current density area will appear yellow. The treatment method of this fault is to add 30% hydrogen peroxide in the plating solution, the ratio is 0.5-1ml/L per liter of the plating solution, and then stir fully, adjust the PH value of the plating solution to 6, and then filter the plating solution to remove the iron in the plating solution.

A .major source of iron impurities

a.10-20 minutes before electroplating (rolling plating), plating parts are not completely on the plating before the basic chemical reaction with the plating solution, the generation of bivalent iron;

b.Plating before treatment is not good, cleaning is not clean, the surface of iron and iron or adsorption on the surface of iron filings into the plating solution.

c.Parts falling into the cylinder are not salvaged in time.

d.Iron impurities introduced by raw materials.

2.The effect of copper impurities

The copper ions in the plating solution mainly come from the copper rod, copper hanger, copper hook, zinc anode and so on falling into the aqueduct and self-dissolving. Raw materials into, especially zinc chloride content is higher, when the plating solution Cu2+ concentration is more than 10mg/L, the coating is gray black, copper impurities will cause low current area dark, high content in the plating solution, after nitric acid light plating brown, plating passivation is not bright, hair and black. The treatment method is generally better with replacement method, that is, 1-2g/L zinc powder is added into the aqueduct, fully stirred, standing for 1 hour and then filtered. Small current electrolysis, the PH value adjusted to 3-4, control the cathode current in 0.1-0.2a /dm2, so that Cu2+ reduction on the cathode to remove, such as the roller electrolysis to use parts with plating electrolysis, to avoid the generation of bivalent iron impurities.

Copper impurities mainly lie in the prevention of ordinary times, galvanized anode is best to use No. 0 zinc ingot, followed by the prevention of copper rod, copper hook and hanging device falling into the aqueduct, but also to prevent the patina falling into the aqueduct.

3.The influence of lead impurities

The impurity of lead in plating solution mainly comes from zinc anode and zinc chloride. Lead impurities can cause fog in the high current area, black or light black in the low current area, high content of the outcrop layer, when the lead content is more than 5mg/L, passivation film luster becomes worse, when the lead content is more than 10mg/L, the plating bath coverage ability is reduced, serious no coating. Removal method is the same as copper impurity.

4.The influence of hexavalent chromium

Hexavalent chromium is an oxidant, which has a great effect on potassium chloride galvanized solution, especially in the area of low current density. The chromium trivalent has little effect on potassium chloride galvanized solution, but too much chromium trivalent can also lead to pitting of galvanized layer. General trivalent chromium ion content should be less than 0.1g/L, and hexavalent chromium ion content generally do not exceed 3ppm.

Once the potassium chloride galvanized solution is contaminated by hexavalent chromium, the source of the pollution should be found out first, and the source should be blocked first. The treatment method of hexavalent chromium is to use insurance powder, first reduce hexavalent chromium to trivalent chromium, and then adjust the PH value of the solution to about 6.0, precipitation and filtration.

5.The effect of nitrate

Nitrate is also a strong oxidizer, the brightener has a certain damage, generally nitrate ion should be less than 0.5g/L, a small amount of nitrate ion can be used for a long time electrolytic treatment of small current density, if the content is too high, can only replace the solution.

6.The effect of organic impurities

The decomposition of additives and the accumulation of grease will produce organic impurities. If the content of organic impurities is too high, the coating will become dark or produce stripes, and the brittleness will increase. The coating will mist and not shine after passivation, and the covering ability will be reduced and the coating will be rough.

The treatment method is to increase the bath temperature to about 45℃, add 3g-5g/L activated carbon, stir for 30 minutes, stand filtration. After activated carbon treatment, the additive will also lose a part, must be appropriate to add, add the amount of hull slot to determine.