Exploring the surface treatment before painting the steel drum (1)

For steel drums, its production materials are hot-rolled and cold-rolled steel sheets, and most of them are ordinary metal materials. During steel manufacturing, preservation and transportation processes, the surface often contains oil stains or rust stains due to process and corrosion resistance requirements. . In the production process of steel drums, exposure to air, water, etc., due to the oxygen and water in the air and may contain the role of sulfur dioxide, carbon dioxide, hydrogen sulfide and other gases, it is easy to corrosion; Second, when the steel drum repair welding, most The barrel makers use soldering for repairs. Since the hydrochloric acid is used to corrode and weld the contact surface before the soldering, the chlorinated hydrogen in the hydrochloric acid diffuses in the surrounding air, which can easily cause the corrosion of the metal on the surface of the steel drum, resulting in the performance of the steel drum being reduced or even damaged; The surface of the steel drum is often susceptible to adhesion or foreign material formation during processing and handling. Such as oxide scales, oil, processing debris (flashing, flying iron, etc.), dust, etc.; these will affect the drum surface coating adhesion and protection properties. Therefore, it is not appropriate to directly paint steel drums that have just been finished, but to perform proper surface treatment in order to remove the unfavorable factors that affect the quality of the coating on the surface of the steel drums; the quality of the surface treatment of the steel drums prior to painting is good or bad. Surface coating is very important.

First, the purpose of pretreatment of steel drum surface

The purpose of the surface treatment before drum coating is:

1. Reinforce the adhesion of steel drum surface coating;

2. Improve the protective performance of the coating on the steel drum;

3, to create a good condition for the flatness of the steel drum coating, improve the decorative coating steel drum.

II. Types, composition of major dirt on the surface of steel drums and their effects on coating performance

Dirt on the surface of the drum can be divided into:

1, oil pollution

Oil on the surface of the drum can usually be divided into four categories.

(1) Rolling oil used for steel plate rolling.

In the processing of metal materials, rolling oil is used. According to different rolling methods, rolling oil is divided into direct rolling oil, circulating rolling oil and water-insoluble rolling oil.

The direct rolling oil is mainly animal and vegetable oils such as butter oil and brown thorn oil. It is added with emulsifying dispersant and anti-high pressure agent. It is used after emulsification with water. It is generally used after it is discarded. Therefore, the degree of oil aging is minimal, and there is very little mixed with solid dirt. And motor oil.

The fundamental difference between the cyclic rolling oil and the direct rolling oil is the use of repeated cycles, the oil aging is severe, and a large amount of solid dirt is mixed.

Non-water-soluble rolling oils are used directly in the oil state because they do not contain water and do not decompose and age due to the addition of water.

(2) The surface of the steel plate is coated with anti-rust oil

In order to prevent the corrosion of the processed steel plate during storage and transportation, the general steel plate must be coated with anti-rust oil on the surface to prevent corrosion.

(3) The oil on the surface of the drum

The oil is generally the internal lubricant used in the production process of steel drums during processing. Oils do not generally adhere to the surface of steel drums alone, and are usually present in a form that is mixed with rolling oil.

(4) Other oil pollution

Other oil pollution includes drawing oil, grease, and graphite castor oil on the top material of the bottom of the bucket in order to ensure the quality of deep drawing. These oils mainly originate from the processing process and transportation and storage of steel drums and their raw materials; their main components are mineral or animal and vegetable oils, paraffins, resins, graphite and various organic and inorganic fillers;

These oils mainly affect the drying performance of the coating on the drum surface, reduce the adhesion and hardness of the coating on the drum surface, and the brightness of the surface coating film.

2, oxides

It includes oxide scale and yellow rust. Its main sources are the following:

(1) Oxide scale mainly originates from the rolling process of hot-rolled steel sheet and the moisture during storage and transportation;

(2) Yellow rust mainly comes from the storage process of the steel plate. When the steel plate storehouse exposes to rain or reacts with water, oxygen, sulfur dioxide, and carbon dioxide in the air to generate triiron tetroxide, ferric oxide, and iron oxide, etc. Rust

(3) Corrosion caused by direct contact with water and atmosphere during production;

(4) The air in the production workshop is not clean and even contains hydrogen chloride gas, which causes the outer surface of the steel drum to rust.

Oxide makes the surface coating of the drum poor adhesion. The iron hydroxide is formed under the action of oxygen and water to cause the coating to peel off and fall off.

3, solid attachments

Solid attachments mainly include iron filings, latex, solder fluxes, and dust and acid and acid salts. Iron scrap, welding slag and dust mainly come from the manufacturing process, welding process and storage and transportation process of steel drums. The flux, part of the welding slag, acid and acid salts are mainly derived from the soldering and pickling processes during the repair of steel drums. These iron filings, welding slag, dust and their salts will degrade the appearance and coating adhesion of the drum. When the solid attachments fall off, the coating on the surface of the steel drum will be destroyed; and the acid and its acid salt will accelerate the corrosion of the metal coating on the surface of the drum, thereby causing the surface coating of the drum to peel off and fall off.