Fifth, the steel drum coating process requirements
In order to ensure the quality of the coating of the steel drum, not only the quality of the surface 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 choice of coating types, suitable coating processes, and coating equipment and operating environment are mutually reinforcing and mutually restrictive. To do this, the following points must be understood when painting steel drums:
(I) Formulate a reasonable steel drum coating process
According to the specific use of steel drums and the quality requirements for coating, as well as the actual conditions of the steel drum production enterprises, a set of scientific, advanced and reasonable painting processes are formulated. The contents shall include: coating types, detailed coating procedures and technical conditions, quality standards for equipment and tools used, and testing and acceptance criteria and methods, so as to facilitate the operator to select coating types according to process requirements, and perform fine operations according to the process requirements. To ensure the surface coating quality of steel drums.
(II) Strictly performing the treatment before the surface coating of steel drums
Steel drums are exposed to air during the production, storage, transportation and production of raw materials. Due to the effects of oxygen and water in the air and possibly contained sulphur dioxide, carbon dioxide, hydrogen sulfide, etc., corrosion of the steel drums is easy; secondly, raw materials and steel drums are transported. In the process, it is easy to adhere to foreign materials such as oxide scale, oil stains, processing debris, dust, etc. Thirdly, most of the manufacturers use soldering to repair the leakage of steel drums, because hydrochloric acid is used before soldering. Corrosion of the welding surface, and hydrogen chloride in the hydrochloric acid diffused in the surrounding air, it is also likely to cause corrosion of the metal surface of the drum. As a result, the performance of the drum is reduced or even damaged. 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.
(3) To ensure the drying of the coating on the surface of the drum
The paint is applied to the surface of the drum, most of which is a process of changing from a liquid to a solid film (except for powder coating), which is called a dry film-forming process. The dry film formation process is a comprehensive physical-chemical process including solvent evaporation, condensation, and oxidative polymerization. The entire process is physical and chemical. It can be roughly divided into two stages:
1, solvent evaporation stage
The solvent volatilization stage on the drum typically occurs during the pre-drying period. Immediately after the coating, a large amount of solvent evaporates, and the volatilization process takes place almost on the free surface of the liquid. Due to the volatilization of the solvent, the concentration of the coating film is changed and the coating loses its fluidity.
2, chemical reaction stage
The solvent that volatilizes on steel drums loses its fluidity. Under the action of thermal energy, there are some * condensation reactions that form macromolecular compounds in a network structure; others are oxidized in the air, and polymerized to form a high degree of network structure. Molecular 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. Divine polymer compounds have good properties and almost all protective properties of the coating are provided by it.
In summary, it is known that heat and time are indispensable in the dry film formation process. Without sufficient heat and sufficient time, the coating will not receive enough chemical reaction energy or the reaction will not proceed completely. The so-called selection of an appropriate drying specification is to provide sufficient heat to set a proper matching of the drying temperature and the drying time so that the coating film can reach the optimum structure for protecting the steel drum and the decorative steel drum.
(D), strictly monitor the coating quality of steel drums
In order to ensure the coating quality of steel drums and to prevent the rework of large numbers of steel drums, it is necessary to have accurate inspection equipment and inspection methods to monitor every important part of steel drum coating operations to control the coating quality of steel drums. Meet the prescribed high standards. The inspection of the coating quality of steel drums includes the inspection of the quality of the pre-painting treatment, the inspection of the quality of the coating product itself, the quality monitoring of each process during the coating construction process, and the quality of the coating film after the coating is completed.
The quality inspection of steel drum coating can be divided into surface quality inspection, middle inspection and final inspection before spraying.
The surface quality of the steel drum before painting is the basis of the coating and directly affects the coating quality of the steel drum. The main contents of the inspection are as follows:
1. Detect the concentration of the surface treatment agent of the drum before painting, the temperature of the liquid, the degree of cleanness of the water for washing, and the spray amount of the nozzle.
2. Detect the surface condition of the steel drum after treatment. The surface of the steel drum should be free from grease, dirt, etc. If chemical treatment is used, the resulting film should be uniform, dense, and rust-free.
The intermediate inspection includes quality inspection of moisture and spraying processes. The main contents are as follows:
1. Check whether the water is completely removed before spraying, including whether there is moisture in the steel drum.
2. Check the quality of the coating used for spraying, including whether the viscosity and other indicators meet the requirements.
3, testing the quality of spray, spray leveling should not have sags, exposed bottom and other serious defects.
The final inspection refers to the quality inspection of finished steel drums after drying. The main contents are as follows:
1. Check the quality of the coating film. The coating film should not have defects such as granules, bites, and pinholes.
2. Detect the degree of dryness, hardness, thickness and adhesion of the coating. The coating film should be completely dried, the coating film thickness should be uniform and meet the technical requirements, and the coating film hardness and adhesion should also meet the required standards.
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