1. Sulfate galvanizing process
1) Common process flow:

Hydrochloric acid pickling → water washing → water washing → sulfuric acid activation (electrolytic pickling) → water washing → Water washing → Galvanizing → water washing → soaping or passivation → water washing → hot water drying

Detailed concentration of each process

(1) Pickling rust removal HCl50%,H2O50%, appropriate amount of pickling additives, temperature; Room temperature, until the rust is gone.

(2) Sulfuric acid activation H2SO4 10%, (anode electrolysis) temperature 15-35℃, time: 5-10 seconds, DA 5-10A/dm2. (3) Sulfate galvanized: zinc sulfate 300-450g/L, boric acid 25-35g/L,S-30 brightener, 16-20ml/L,pH 3.5-4.5, temperature 10-35℃,Dk10-60A/dm2.
2) Plating solution preparation:

(1) Add about 1/2 tap water to the plating tank, and then add the calculated amount of zinc sulfate heptahydrate.

(2) Boric acid should be dissolved with 10 times the amount of hot water. Boric acid can be put into a container, add hot water above 90 ° C, and pour it into the plating tank after continuous stirring to dissolve it completely.

(3) Add 1-2G /L zinc powder and stir for 1 hour before filtering.

(4) After adding brightener, the electrolysis can be done for several hours.
3) The role of each component:

(1) Zinc sulfate is the main salt, providing zinc ions in the plating solution. Zinc sulfate concentration mainly affects the current density and deposition rate used. Taking wire plating as an example, the plating time is very short, only tens of seconds, which requires as much current density as possible. In order to increase the current density, and in the case of taking a large current density does not cause the coating to burn, the zinc ion concentration in the plating solution must be high, the zinc sulfate concentration of 300g/L, coupled with the cathode wire is rapidly moving, practice shows that this concentration is sufficient for the plating wire (plate) material.

(2) Boric acid 25-35g/L, excellent pH buffer.
4) The effect of operating conditions:

(1)pH value: The pH value is roughly between 3.0-5.0. In addition to the different composition of the solution, the pH value is related to the plating method used and the current density. Electroplating wire and horizontal continuous plating strip steel, current density in 10-30A/dm2, pH value can be selected between 4.0-5.0. As for the transformation of continuous strip plating, the current density used is larger, Dk reaches 20-60A/dm2, and the pH value should be appropriately low, which can be selected between 3.4-4.5. In short, the pH value should be treated differently according to different circumstances.

(2) Temperature: generally about 25 ° C, generally used for continuous plating of wire and steel strip, the concentration of the bath is relatively high, and some are almost close to saturation, the concentration should not crystallize at 10 ° C, and can meet the needs of the coating thickness, the bath concentration is too high is not necessary. When the temperature of the bath is reduced, the current density will be reduced, and the linear speed of the bath will be slowed down accordingly.

(3) cathode current density: sulfate galvanizing is usually used to electroplate wire and strip steel, and the cathode of the plating part is moving at high speed. When the concentration of zinc ions is increased, a high current density can be used. The maximum cathode current density of sulfate galvanizing process can reach 100A/dm2. The principle of current density selection is that when the bath concentration is high, the temperature is high and the line speed is high, the allowed current density is large, and the reverse is to be reduced. In short, under the premise of not letting the zinc coating burn, the current density is as large as possible, which is both economical and can ensure the quality of the coating.

Current reference value for continuous plating of wire

2. Maintenance and troubleshooting of plating solution
The use of a Baume meter for rapid determination, although this rapid determination method has errors, but for the control of the concentration of the bath can be.

Relationship between zinc sulfate content and Baume degree

1) Daily maintenance:

(1)Brightener consumption is generally 1 kg per 1 ton of wire production, and some Brightener should be added in batches or according to the appropriate amount per hour, and the general principle is that the brightener used for each 1 ton of wire should be added several times. This can reduce brightener consumption and ensure product quality. The zinc sulfate content can be controlled according to the relationship between the zinc sulfate pommel degree in the front, that is, 300g/L pommel degree 18, 400g/L Pommel degree 24, that is, as long as the bath pommel degree is controlled between 18-24. Boric acid supplement can be added weekly 5-15g/L, boric acid is basically not consumed by electrolysis, mainly high-speed production of a large number of losses, it is best to laboratory analysis prevail. Each additional Baume degree requires approximately 16.5g/L zinc sulfate, and the amount of zinc is generally 7.12g/m2 for a 1um thick zinc layer.

(2) When the water of each washing tank is dirty, it must be updated, such as chaos or conductivity > 2000US/CM or pH < 5, the water needs to be changed again.

(3) Plating tank, zinc sulfate 300-450g/L, boric acid 30-35g/L, control the concentration of the plating solution between 18-24 Baume, boric acid is better, control about 30g/L, use the concentration meter to measure the Baume every day, at least 2 times a week for laboratory analysis. The bath must be kept clean, and the filter is opened every day to filter the plating solution, which is very conducive to improving the quality of the coating. When iron impurities are high, potassium permanganate needs to be treated, potassium permanganate 0.05-0.1g/L, after being fully dissolved with water, it is added to the plating solution under strong agitation. The pH value must be measured frequently every day, and the pH control is between 4-4.5. The temperature is generally controlled at about 25 degrees, too high product fog brightener consumption is too large.

(4) Post-processing. After washing 1-2 times after purification, finally hot water: hot water must be above 70 degrees, and finally dry. Post-treatment commonly used saponification, is to use Shanghai saponification tablet, into soapy water, the concentration is about 50g/L.

3. Large treatment scheme of sulfate galvanizing solution
(1) If the low current is black, first play about 1g/L of zinc powder, stir while adding, stir for half an hour after finishing.

(2) Potassium permanganate 0.3-0.5 g /L, fully dissolved in water, added to the plating solution under agitation, stir for half an hour to an hour after adding.

(3) When organic impurities are large, add 1-3 g /L of activated carbon, stir fully for one hour and filter.

(4) It is best to electrolysis with small current for one night after processing.

(5) Add the appropriate amount of brightener according to the situation, and first confirm the effect of treatment with Hall tank test and determine the amount of additive added after treatment. The lead in sulfate galvanizing can be removed by sodium sulfide, and the amount of sodium sulfide required is determined by Hall tank test first, taking care not to overdo it too much, and then the colloidal residual sodium sulfide is removed by activated carbon.