Research on guarantee measures for steel drum coating quality (1)

Research on guarantee measures for steel drum coating quality (1)

Xin Qiaojuan

The quality of the surface of the steel drum depends not only on the quality of the coating and the steel drum itself, but also on the overall process of the coating (including the coating process, machinery and working environment). Proper selection of reasonable coating techniques and processes is a necessary condition to improve the quality of the surface coating of steel drums.

First, the purpose of the surface coating of steel drum

The surface of the steel drum is first coated to protect the steel drum from external corrosion. Because the users of ordinary steel drums pile up the manufactured steel drums on the outdoor work site. Due to the action of rain, sun, weathering and various media, the steel drum is eroded, the metal is rusted, and even rusted. According to statistics, about 2% of steel drums are scrapped every year due to corrosion, and the coating is covered with a layer of moisture resistance, water resistance, weather resistance, oil resistance and chemical resistance. The performance of the coating, in order to achieve the effect of protecting the steel drum and extending its service life; secondly, it is decorative and advertised for the steel drum. Using the color diversity of the paint and the technology of spraying construction, the steel drum can be painted according to the user's requirements, habits, hobbies and market demand to obtain different color, gloss, pattern and other decorative coatings, so that the appearance of the steel drum Bright, bright and dazzling, giving people a pleasing feeling. Thereby increasing the added value of the steel drum and expanding the application range of the steel drum.

Second, steel drum coating requirements for coatings

In the national standard of steel drums, the outer surface coating of the steel drum is not specified, but the requirements are put forward in principle, and the specific measurement requirements of the adhesion of the coating film are made. Therefore, suitable coatings must be selected as required in the barrel coating process. At present, most domestic barrel manufacturers use high-pressure airless spraying production lines or electrostatic spraying production lines to carry out surface coating and drying lines of steel drums for drying the coating film. Most of the coatings used are baking type amino resin coatings. This is because the amino resin type coating has the following characteristics:

1, light color, bright colors;

2, the coating film is bright and full;

3, the coating film is tough, good adhesion, high mechanical strength; paint weather resistance, anti-powdering, anti-cracking performance is good, and does not stick back;

4, water resistance, wear resistance, oil resistance, insulation are better.

5, a wide range of uses. Amino resin coatings are currently the most widely used industrial coatings.

The purpose of the steel drum coating is to improve the corrosion resistance of the steel drum and prolong its service life. It is protective and decorative. Therefore, it requires coating paint not only to have good corrosion resistance, but also to have good physical and mechanical properties.

1. Good corrosion resistance

Corrosion resistance of a coating means that the cured coating is physically and chemically stable to the corrosive medium it contacts. These corrosive media include water, acid, alkali, salt and various chemicals as well as waste liquid, air, water gas, chemical gas, etc. It is required that the steel drum coating film is neither swollen by the corrosive medium, dissolved, or destroyed by corrosive media. Decomposes, does not cause harmful chemical reactions with corrosive media.

The stability of the cured coating film to various corrosive media depends on its chemical structure and the chemical genes it contains. Water is the most common corrosive medium, which can hydrolyze chemical bonds in coatings into small molecules, so that the entire coating loses its polymer network structure and reduces its corrosion resistance. Therefore, the hydrolysis resistance of the coating film is an important indicator for determining the corrosion resistance of the coating film. The water has a high osmotic pressure and can dissolve certain impurities through the coating film, so that the osmotic pressure inside and outside the liquid is different. In the process of balancing the internal and external pressures, the coating film is often foamed or fine cracks are generated, and various corrosive media are taken in. Causes serious rust.

Various chemical media have different effects on the coating film, but whether it is pure solvent corrosion or environmental stress corrosion, it is related to the dissolution ability of the medium to the coating film.

The above are one of the factors to consider when selecting and formulating anti-corrosion coatings (paints). However, it must be noted that the corrosion resistance cannot be over-emphasized regardless of its physical and mechanical properties. Otherwise, the coating can not withstand the mechanical action under working conditions, causing premature cracking and spalling, and thus losing the anti-corrosion effect.

2, less gas permeability and water permeability

In neutral or weakly alkaline media, atmospheric corrosion of steel drums requires the action of moisture and oxygen. If there is no water and oxygen, the corrosion rate is almost zero. The corrosion of the steel drum after painting is essentially due to the penetration of water and oxygen into the coating and metal interface at a considerable rate. Obviously, the breathability and water permeability of an excellent corrosion-resistant coating should be as small as possible. For this purpose, it is necessary to select a film-forming substance having a small gas permeability and a filler having a large shielding effect, and to achieve a desired thickness of the coating layer.

The gas permeability of the cured coating film is related to its structural pores and the coating pinholes produced during the curing process. The diameter of the pores of the coating structure is about 10-5 to 10-7 cm, and the pore diameter of the pinhole is about 10-2 to 10-4 cm, which is larger than the molecular diameter of the gas and the low molecular liquid. The pinholes of the cured coating are closely related to the coating, solvent and construction conditions, and the necessary coating thickness is also an important condition for reducing the gas permeability of the coating.

3, good adhesion and sufficient mechanical strength

Whether the cured coating film can be firmly attached to the metal substrate is one of the key factors for protecting the metal from the corrosion of the medium. In addition, the cured film should have sufficient physical and mechanical strength to withstand the stress under operating conditions.

The adhesion of the coating refers to the ability of the coating to adhere firmly to the surface of the steel drum without peeling off. It is related to the polarity and molecular transformation of the film-forming resin, and is also closely related to the surface state of the steel drum.

Under the premise of ensuring the adhesion of the cured coating film, the coating is also required to have suitable hardness, good flexibility, flexibility, impact resistance and wear resistance. These properties are also determined by the chemical structure of the film-forming resin and the surface condition of the steel drum.

In addition to the performance requirements of the above three aspects, the steel drum coating should have good electrical insulation, temperature resistance, weather resistance and necessary decorative properties. At the same time, economic considerations should also be considered to minimize costs, and production must take into account construction performance.