How to guarantee the coating quality of the drum surface (1)

The quality of steel drum surface coating depends not only on the surface quality of the coating and the steel drum itself, but also has a great relationship with the whole process of coating formation (including coating process, machine equipment and working environment). Correct selection of reasonable coating technology is a necessary condition for improving the surface coating quality of steel drums.

First, the main purpose of steel drum surface coating

Coating refers to the process of spraying paint on the surface of a steel drum that has been surface-treated and dried to form a film. The coating process is generally composed of three basic steps of surface treatment (including surface cleaning and chemical treatment), spraying and drying of the steel drum before painting.

The paint is a flowing or powdered organic material that can be dried and solidified on the surface of the drum to form a thin film that is evenly covered and adheres well to the surface of the drum.

First of all, the surface of the steel drum is painted to protect the steel drum from external corrosion. Because the steel drum is in use, due to external rain, sunlight, weathering and various media, the surface of the steel drum is eroded. So that the surface of the drum rust, or even rust. According to statistics, about 2% to 5% of steel barrels are scrapped each year due to corrosion. The coating is to cover the surface of the drum with a layer of a certain resistance to moisture, water resistance, weather resistance, oil resistance and chemical resistance, so as to achieve the effect of protecting the steel drum and prolonging its service life. .

Second, the surface coating of the drum is to package the steel drum (decorative effect). Using the diversity of paint colors and spraying construction techniques, steel drums can be coated according to user requirements, habits, hobbies, and market requirements to obtain decorative coatings of different colors, gloss, patterns, etc., thereby increasing the number of steel drums. Values ​​to expand the scope of application of steel drums.

Second, the steel drum surface coating process requirements

In order to ensure the quality of the coating of the steel drum, not only the surface quality of the steel drum, but also the application, performance and construction process of the coating itself must be considered, because the performance and role of the coating are reflected in the coating. Therefore, the selection of paint types and reasonable painting processes and painting equipment and operating environment are mutually reinforcing and mutually restrictive. So must do the following:

1. The requirements for paint performance of steel drum surface coating

The purpose of the drum surface coating is to protect it and decorate it. Its specific requirements for paints are bright color, strong adhesion, and a smooth surface. In order to meet these conditions, it is necessary to carefully analyze the properties and uses of the coating. Because each coating has its own special properties and advantages and disadvantages, it is necessary to avoid weaknesses and choose the coating type and coating system. At present, the coating methods used by the steel industry in the country are different, and some use electrostatic spraying ( Spraying and painting, and some use high-pressure airless spraying. In the past two years, as more and more two-color buckets and three-color buckets have been requested by users, manufacturers using high-pressure airless painting will also increase.

2. Develop a reasonable steel drum coating process

According to the use of steel barrels and the quality requirements for coating, as well as the actual situation of the barrel companies, to develop a set of scientific, advanced and reasonable coating process, which should include: coating species, a detailed coating process and Technical conditions, equipment and tools used, quality standards and testing, acceptance standards and methods, etc., in order to facilitate the operator to select the type of paint according to process requirements, and fine operation according to process requirements to ensure the appearance quality of steel drums.

3、Strictly pre-treat the surface before steel drum coating

Drum raw materials are exposed to air during production and transportation. Due to the effects of oxygen and water contained in the air and possibly contained SO2, CO2, H2S, etc., corrosion may easily occur; foreign matter, such as oxide scale, may be easily adhered during transportation. Oil, processing debris, dust and so on. In addition, during the production process of steel drums, it is easy to cause dirt or damage on the surface of steel drums, and it is also easy to cause corrosion of metal on the surface of steel drums, which results in a reduction in the quality of steel drums. Therefore, it is necessary to perform surface treatment before coating the steel drum to eliminate the unfavorable factors that affect the coating quality of the steel drum, thereby improving the coating quality of the steel drum, which is very important for the steel drum.

4, strict steel drum surface coating film coating process

When the paint is evenly sprayed on the surface of the clean steel drum, after drying, a layer of protective film with good performance, namely the paint film, can be obtained. The entire film formation process can be divided into two stages, namely the coating process and the dry film formation process.

1 coating process

The coating process is a simple physical process and refers to the process of uniformly coating the coating on the surface of the drum with the required thickness. This process is generally done by an automatic sprayer. Although the coating process is simple, it must meet the two major requirements it requires, namely a certain thickness and uniform coating, can not appear missing coating, sagging and coarse grain defects. The coating thickness is a very important process parameter in the coating process. The cured coating formed by any coating has a certain gas permeability, which is related to the structural pores of the coating. The structural pore size of the coating is 10-6 to 10-7 mm on average, which is larger than the molecular diameter of the gas and the liquid, so not only the gas can pass, but generally the ions and the low molecular liquid can also pass. In order to improve the water resistance and gas permeability resistance of the coating as much as possible, the coating must have a certain thickness so as to cover the structural pores overlapping each other. The minimum thickness that a coating can reach for protection is usually referred to as the critical thickness. For example, the critical thickness of the coating process of the steel drum is 0.02mm, that is, the thickness of the paint film formed by coating the steel drum must not be less than this critical thickness. Only such a film thickness can achieve the purpose of protecting the steel drum from external corrosion. Different coatings have different critical thicknesses, but the coating thickness must be met during the coating process. In addition, the uniformity of the coating is also very important. If it is not uniform, the anti-corrosion property will be reduced if it is too thin, and defects such as sagging, wrinkling, etc. will easily occur at excessive thicknesses.

2Drum coating drying process

Most paints are coated on steel drums. The process of changing from a liquid to a solid film (except for dusting) is called the drying process of the paint. The dry film formation process is a comprehensive physical-chemical process including solvent evaporation, condensation, and oxidative polymerization. The entire process has both physical and chemical effects. It can be broadly divided into two stages:

a. Solvent evaporation phase

The solvent evaporation stage on the drum surface generally occurs during the pre-drying period. Immediately after painting, a large amount of solvent evaporates, and the volatilization process is almost performed on the free surface of the liquid. Due to the volatilization of the solvent, the film concentration on the surface of the drum changes, and the paint loses its fluidity from the surface.

b. Chemical reaction stage

The paint on the drum surface loses its fluidity after volatilization of the solvent. Under the effect of heat energy, there are some * condensation reactions to form the network structure of the polymer compound. Other paint bases are oxidized in the air and the polymerization reaction forms a network structure. The polymer compound, this process is a more complex chemical reaction process, but the final result is a polymer compound with a network structure with unequal degree of polymerization. This polymer compound has good properties and almost all protective properties of the paint film are provided by it.

Therefore, heat and time are necessary during the drying of the film coating on the surface of the drum. Without sufficient heat and sufficient time, the coating cannot obtain sufficient chemical reaction energy or the reaction cannot be fully performed. The so-called selection of the proper drying specification is to set a proper configuration of the drying temperature and the drying time in order to obtain sufficient heat, so that the paint film reaches the optimum structure for protecting the steel drum and the decorative steel drum.

5, strictly monitor the coating quality of steel drums

In order to guarantee the coating quality of the steel drum surface, it is necessary to have accurate inspection equipment and inspection methods to monitor every important part of the steel drum coating operation to control the quality of the steel drum coating to meet the specified high standards. The inspection of the coating quality of steel drums includes the inspection of the pre-painting quality, the quality inspection of the coating products, the quality monitoring of each process during the coating construction, and the quality of the coating after the coating is completed.

6, timely treatment of drum surface coating defects

The defects found during the inspection of the coating process and the final coating performance shall be promptly dealt with and corresponding measures shall be taken to remedy the defects to ensure the coating quality on the surface of the steel drum so as to achieve the purpose of paint coating.