Galvanized

Galvanized
7.1 Properties of zinc and zinc coating

(1) Color: light gray metal

(2) Proportion: 7.14

(3) Atomic weight: 65.37

(4) Atomic value: 2

(5) Standard potential: -0.7628v

(6) Melting point: 419℃

(7) Atomic number: 30

(8) Boiling point: 907℃

(9) Density: 7.13

(10) Characteristics: brittle. Relatively hard. It has better plasticity when heated to 100~150℃. It can be rolled and forged, but it becomes brittle at 250.

Zinc is relatively stable in dry air, and the white mold layer that easily forms carbonate or oxide on the surface in water and humid air is protective

, Zinc is an amphoteric metal, which corrodes in acid, sulphide and sulphide. The standard potential of zinc is relatively negative, so its coating is an anodic protection.

Low cost, easy to process, good effect, many steel parts are galvanized, but it is not easy to make frictional coating

7.2 Zinc Plating

(1) Acid zinc plating

(2) Alkaline non-cyanide zinc plating (alkaline plating)

(3) Cyanide zinc plating

7.3 Acid zinc plating

The simple shape of plating parts and the base paint are used more, and the advantages and disadvantages are as follows

advantage

(1) Available gloss, smooth, galvanized coating similar

(2) Can be directly plated on carbonized and nitrided steel and cast iron

(3) Higher current efficiency

(4) The waste liquid is easy to handle, just use high pH to precipitate zinc

(5) Good conductivity, saving electricity

(6) Low hydrogen embrittlement

(7) Glossy coating can be obtained at higher temperature

(8) The plating bath is stable, with low toxicity and low cost

Disadvantage

(1) The plating bath is highly corrosive, and the plating tank and auxiliary equipment need to be lined

(2) Welding and assembly plating parts are not suitable, there will be bleadout

(3) Poor ductility of thick coating

(4) Rough crystals

(5) Poor uniformity

(6) Filtering, cooling pipes and refrigeration equipment need to have

7.4 Alkaline Non-Cyanide Zinc Plating

advantage

1. Low toxicity

2. The waste liquid is easy to handle, only the zinc is precipitated

3. Low cost

4. Good uniformity

5. Available just plating tank

Disadvantage

1. The composition of the plating bath needs to be strictly controlled and analyzed every day

2. The pre-treatment requires high-quality springs

3. When the zinc content is small, the current efficiency is reduced

4. Sensitive to metal impurities and hard water impurities

5. The coating is cyanide galvanized and brittle

6. Additives are needed, otherwise the dark coating will appear

7. Special additives, non-general raw materials, need to be provided by the manufacturer

7.4.1 Alkaline-non-cyanide bath

Can be formulated in two ways

1. Anode zinc is soluble in caustic solution

2. Dissolve zinc oxide and caustic

The preparation procedure is as follows

1. Use a small amount of water to mix with zinc oxide in the plating tank to form a slurry, or it is best to use another matching bath to do it

2. Slowly stir caustic soda and water into one-third of the amount of water

3. Stir fully until the zinc oxide is completely dissolved

4. Add 6 lbs/100 gallons of zinc powder and stir for 30 to 60 minutes

5. Precipitate and filter or pour into the plating tank

6. Put in the anode zinc plate and use low current density electrolysis to remove impurities for one night

7. Analyze the content of zinc and caustic soda and adjust the ingredients to add additives

The formula is as follows

Zinc oxide 1.5 oz/gal

Caustic soda 10 oz/gal

Addition agents as indicated

Bath temperature 70 ~115 F

7.5 Gloss cyanide galvanized spring

Advantages

1. Long history of use and rich experience

2. The pre-processing requirements are not strict

3. Excellent coverage

4. The analysis and control of bath ingredients are relatively easy

5. Good coating ductility

6. The plating bath is less corrosive

Lack

1. The plating bath is highly toxic and must be treated with cyanide waste

2. Heat treatment and cast iron parts cannot be plated

3. Higher temperature operation is required, otherwise the gloss coating cannot be obtained, and the temperature must be above 105F

4. Poor conductivity of the plating bath

5. Under high current density, current efficiency drops sharply