Exploring the surface treatment before steel drum coating (1)

Exploring the surface treatment before steel drum coating (1)

Xin Qiaojuan

For steel drums, the materials are hot-rolled and cold-rolled steel sheets, most of which are ordinary metal materials. In the process of steel manufacturing, storage and transportation, due to the needs of process and anti-corrosion, the surface often has oil or rust stains. . In the process of steel drum production, contact with air, water, etc., due to the action of oxygen and water in the air and possibly sulfur dioxide, carbon dioxide, hydrogen sulfide and other gases, corrosion is likely to occur; secondly, most of the steel barrel repair welding The barrel manufacturers use tin soldering for repair. Because hydrochloric acid corrodes the welding contact surface before soldering, and the hydrogen chloride in hydrochloric acid diffuses in the surrounding air, it is easy to cause corrosion of the metal surface of the steel drum, which leads to the performance of the steel drum is reduced or even damaged; The surface of the steel drum is often easy to adhere or generate foreign matter during processing and handling. Such as oxide scale, oil stains, processing debris (such as burrs from the curling edge, iron cutting, etc.), dust, etc.; these will affect the adhesion and protection properties of the surface coating of the steel drum. Therefore, the steel drum that has just been finished should not be directly coated, but appropriate surface treatment is needed to remove the unfavorable factors affecting the surface coating quality of the steel drum; the quality of the surface treatment of the steel drum before painting, the steel drum Surface coating is very important.

First, the purpose of pre-coating treatment on the surface of the steel drum

The purpose of surface treatment before steel drum coating is to:

1. Enhance the adhesion of the surface coating of the steel drum;

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

3. Create good conditions for the flatness of the steel drum coating and improve the decorativeness of the steel drum coating.

Second, the type and composition of the main dirt on the surface of the steel drum and its effect on the coating properties

The dirt on the surface of the steel drum can be divided into:

1, oil pollution

The oil on the surface of steel drums can usually be divided into four categories.

(1) Rolling oil used in rolling of steel sheets.

Rolling oil is required during the processing of metal materials. Rolling oils are classified into direct rolling oils, cyclic rolling oils, and water-insoluble rolling oils depending on the rolling method.

The direct rolling oil is mainly animal and vegetable oil such as butter-type palm tung oil. It is added with emulsified dispersing agent and high-pressure resistant agent. It is used after emulsification with water. It is usually discarded after use. Therefore, the oil aging degree is extremely small, and there is little mixed solid dirt. And motor oil.

The fundamental difference between cyclic rolling oil and direct rolling oil is the repeated use of the oil, which is severely aged and mixed with a large amount of solid dirt.

The water-insoluble rolling oil is directly used in an oil state because it does not contain water and does 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 corrosion of the processed steel plate during storage and transportation, the steel plate is usually coated with anti-rust oil on the surface to prevent corrosion.

(3), the oil on the surface of the steel barrel

The oil is generally the lubricating oil used in the production equipment during the processing of the steel drum. The oil generally does not adhere to the surface of the steel drum alone, and is usually present in a form mixed with rolling oil.

(4), other oil stains

Other oil stains include pressed oil, grease and graphite castor oil applied to the top of the barrel to ensure the deep drawing quality when drawing the bottom of the barrel. These oils are mainly derived from the processing and transportation of steel drums and raw materials; their main components are mineral or animal and vegetable oils, paraffin, resin, graphite and various organic additives and inorganic fillers;

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

2, oxide

It includes scale and yellow rust. Its main sources are as follows:

(1) The scale is mainly derived from the rolling process of hot rolled steel sheets and the moisture during storage and transportation;

(2) Yellow rust is mainly derived from the storage process of steel plates. When the warehouses in which the steel plates are stored are exposed to rain or contact with water, oxygen, sulfur dioxide, carbon dioxide, etc., they react to form triiron tetroxide, ferric oxide and iron oxide. Corrosion

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

(4) The air in the production workshop is not clean and even contains hydrogen chloride gas, so that the outer surface of the steel drum is rusted.

Oxide makes the coating on the surface of the steel drum poorly attached. Iron hydroxide is formed under the action of oxygen and water to cause the coating to peel and fall off.

3, solid attachments

Solid deposits mainly include iron filings, latex, welding flux and dust, and acid and acid salts. Among them, iron filings, welding slag and dust are mainly derived from the manufacturing process, welding process and storage and transportation process of steel drums. The flux, part of the welding slag, acid and acid salt are mainly derived from the soldering and pickling process during the repair of the steel drum. These iron filings, welding slag, dust and their salts will deteriorate the appearance quality of the steel drum and the adhesion of the coating. When the solid deposits fall off, the coating on the surface of the steel drum is destroyed; and the acid and its acid salt accelerate the corrosion of the metal under the coating on the surface of the steel drum, so that the surface coating of the steel drum is peeled off and peeled off.