Electro galvanizing

Electro galvanizing, also known as cold galvanizing in the industry, is the process of forming a uniform, dense and well bonded metal or alloy deposition layer on the surface of the workpiece by electrolysis.

Compared with other metals, zinc is relatively cheap and easy to be plated. It is a low value anti-corrosion electroplated coating. It is widely used to protect iron and steel parts, especially to prevent atmospheric corrosion, and for decoration. Plating technology includes bath plating (or hanging plating), barrel plating (suitable for small parts), blue plating, automatic plating and continuous plating (suitable for wire and strip).

According to the classification of electroplating solution in China, it can be divided into four categories:

1. Cyanide galvanizing

Because (CN) is highly toxic, environmental protection puts forward strict restrictions on the use of cyanide in electro galvanizing, continuously promotes the development of electroplating solution system to reduce cyanide and replace cyanide, and requires the use of low cyanide (micro cyanide) electroplating solution.

After electroplating by this process, the product quality is good, especially color plating, and the color remains good after passivation.

2. Zincate galvanizing

This process evolved from cyanide zinc plating. There are two factions in China, namely: a) the "DPE" series of Wuhan Material Protection Institute; b) "De" series of radio and television stations. Both belong to zincate zinc plating with alkaline additives, and the pH value is 12.5 ~ 13.

With this process, the lattice structure of the coating is columnar and has good corrosion resistance, which is suitable for color galvanizing.

Note: after the product is out of the slot - >; Washing - >; Light emitting (nitric acid + hydrochloric acid) - >; water washing - >; passivation - >; water washing - >; water washing - >; scalding - >; drying - >; aging treatment (80 ~ 90 ℃ in the oven).

3. Chloride galvanizing

This process is widely used in electroplating industry, accounting for up to 40%.

After passivation (blue white), zinc can replace chromium (comparable to chromium plating), especially after adding water-soluble varnish, it is difficult for laymen to distinguish whether it is zinc plating or chromium plating.

This process is suitable for white passivation (blue white, silver white).

4. Sulfate galvanizing

This process is suitable for continuous plating (wire, strip, simple, thick and large parts and components) with low cost.

Ttechnological process

Taking galvanized ferroalloy as an example, the process flow is as follows:

Chemical degreasing → hot water washing → water washing → electrolytic degreasing → hot water washing → water washing → strong corrosion → water washing → electro galvanized ferroalloy → water washing → water washing → light out → passivation → water washing → drying.

Bath preparation

Preparation of plating solution (taking ll as an example):

(1) first add 1 / 3 volume of purified water into the plating bath;

(2) dissolve sodium hydroxide with 1 / 3 pure water (it will generate heat during dissolution, so care must be taken);

⑶ mix zinc oxide into paste with a small amount of water, then add more pure water and fully stir. Slowly add the stirred zinc oxide into the dissolved sodium hydroxide solution, stir while adding, and add it into the plating tank after full complexation;

(4) when the bath temperature drops below 30 ~ C, add 85g of baser and stir fully;

(5) dissolve 15ml basef in 15g baser, and then add the mixture to the plating bath;

(6) add 4ml of h-o624 and stir fully; Add water to the prepared volume;

(7) add brighteners zf-105a and zf-105b; Stir well.

Black passivation process flow: water washing → light out → water washing → black passivation → water washing → post-treatment → drying.

influence factor

(1) effect of zinc content

The zinc content is too high, the bright range is narrow, it is easy to obtain a thick coating, and the iron content in the coating is reduced; The zinc content is too low and the bright range is wide. It takes a long time to reach the required thickness, and the iron content of the coating is high.

⑵ effect of sodium hydroxide

When the content of sodium hydroxide is too high, it is easy to burn at high temperature; When the content of sodium hydroxide is too low, the dispersion ability is poor.

(3) influence of iron content

The iron content is too high, the iron content in the coating is high, and the passivation film is not bright; If the iron content is too low, the iron content of the coating is low, the corrosion resistance is reduced, and the color is olive.

(4) influence of brightener

Zf-iooa is too high and the coating is brittle; Too low, no coating in low current area, uneven passivation color; Zf-100b is too high and the coating is brittle; Too low, the whole coating is not bright.

(5) influence of temperature

If the temperature is too high, the dispersion ability decreases, the iron content of the coating is high, the corrosion resistance decreases, the color of the passivation film is uneven and the passivation film is hairy; The temperature is too low, the high current density area is charred, the coating is brittle and the deposition speed is slow.

(6) influence of cathode movement

Cathode movement must be used. Moving too fast, the coating in the high current density area is rough; If it is too slow, air flow may occur and there is no coating locally.