Fourth, to improve the coating pollution
Currently, the performance of the steel barrel industry is not very good, but most of the barrel plants will spend their energy on management, steel, paint, energy, and other aspects of reducing consumption. If we reduce the coating pollution, we can find ways to reduce consumption and increase efficiency. This is not a good thing to benefit the country and the people.
1, pre-treatment flush water exchange
As mentioned before, most of the fluids currently used in the steel barrel industry in China are chemical degreasing agents containing surfactants, sodium hydroxide, trisodium phosphate, sodium carbonate, sodium silicate, and various additives. It is alkaline, so after the oil has been recycled for a long time, it will turn into alkaline waste water. At this time, it is necessary to change the shower water.
Most of the phosphating solutions are partially acidic liquids containing phosphoric acid, phosphates, nitrates, molybdates, and various types of additives. After phosphating, the circulating showering water becomes acidic for a long time. Waste water, and then do not change the water, then it will affect the paint coating.
At this time, unexpected results will occur if the two showers are changed.
After deoiling, the surface of the steel drum is alkaline because of the relationship between the oil and the oil. If a certain acidic phosphating solution containing a small amount of phosphating solution is used after the rinsing, it will not only partially neutralize the steel. The surface of the barrel is alkaline, and it is also beneficial to the subsequent phosphating process.
The surface of the phosphatized steel drum is partially acidic due to the phosphating solution. If the alkaline rinsing solution is used to elute the shower, the surface of the phosphating layer of the partially acidic drum is neutralized. However, there is a problem to be noticed here. In addition to being alkaline, the oil washing wastewater contains oil from the surface of the steel drum, so if the oil content is high, it will cause pollution of the surface of the steel drum. It is to reduce the oil content in the oil flushing wastewater. It is also necessary to repeatedly clean the water and make sure that the surface of the phosphating layer of the steel drum is clean.
The reuse of such exchange shower wastewater reduces the discharge of sewage and saves water.
2, change the paint species and spraying method
In addition to the pre-treatment, there are two main ways to improve the coating contamination of steel drums, that is, to change the type of paint and construction methods, and to eliminate or reduce the production of harmful substances from steel drums from root wood. For example, solvent-based paints that cause serious pollution can be changed to water-based paints, powder paints, or high-solid-state paints to eliminate or reduce atmospheric pollution of organic volatiles in the paints. Efficient coating methods are used to increase paint utilization and reduce Scatter of paint, etc.
The main source of coating contamination of steel barrels is the coating itself, and the most important pollution of coatings to the environment is organic volatiles. However, organic volatiles are an important component of solvent-based coatings. Therefore, water-based paints and powder coatings are worthy of promotion in terms of environmental protection and development. In fact, some barrel factories have already used water-based paints and powder paints in part, and some even have used powder paints. Of course, judging from the current production needs of the steel barrel industry, it is impossible to completely remove the solvent-based paint. What we can do is to use high-solid-solvent paints as much as possible, which is to reduce the air pollution. The direct, most economical, most effective, and most immediate way. And this is not only conducive to environmental protection, but also an effective means of reducing consumption and increasing efficiency.
Changing the coating method and improving the spraying device are also effective means to improve the coating efficiency and reduce the scattering of paint mist. We can analyze the comparison of the three most commonly used spraying methods in our steel barrel industry:
The air-spraying is carried out by means of the negative pressure caused by the air flow of the compressed air and the paint is taken out and dispersed into a mist by the spray gun and sprayed on the surface of the steel drum. The air spray paint mist is carried by the air flow. There is a lot of air in the paint mist, which causes the paint to spread with the air flow. Moreover, the organic volatiles in the paint accelerate the evaporation speed due to the air flow diffusion. . Therefore, air spray is one of the methods used for paint spraying that has the largest environmental pollution and waste of paint.
High-pressure airless spraying is a high-pressure piston inside a closed container that applies high pressure to the paint. High-pressure paint is passed through a high-pressure hose and a spray gun. The olive-shaped nozzle hole converts pressure energy into velocity energy and atomizes the paint into particles. Drum surface. Compared with air spray, because the paint mist does not contain a lot of air, it will not form the phenomenon that the paint splashes with the air flow, the utilization of the paint is significantly improved, and the pollution to the environment is also greatly reduced. In addition, since the high-pressure airless spray coating can spray relatively high-viscosity paints with relatively high air spray viscosities, the amount of diluent used in spraying can be reduced, which also reduces the environmental pollution and, of course, reduces the coating cost.
Compared to the above two spraying methods, electrostatic spraying has the least environmental pollution. Electrostatic spraying is to apply the negative high-voltage electrical connection generated by the high-voltage electrostatic generator to the spray gun electrode of the metal sharp edge or tip discharge, while the steel drum is grounded through the hanging chain or other transmission device, so that a negative electrode and a steel drum form a Uneven electrostatic field. *Corona phenomenon. Firstly, a large amount of electrons are excited near the negative electrode (spray cup). After the paint mist enters the electric field, it combines with the electrons to form negative particles. Under the action of the electric field force, it flies toward the positively charged steel drum. surface. Electrostatic spraying will not or very little fly away in the air, which is the main reason for the least environmental pollution in several spraying methods. If a negative DC high-voltage power grid with enameled wire is installed behind and on both sides of the steel drum in the spray booth, the spray booth will not be contaminated by paint spray due to the repulsion of negatively charged paint mist. .
There are many ways to reduce the environmental pollution of steel drum coating. For example, the coatings currently used in our steel drum industry, except for nitrocellulose paints and X-891 paints that are room temperature and quick drying, can be reduced in viscosity by heating ( Such as X-622 epoxy drum coating, the temperature from 25 °C to 40 °C, the viscosity can be reduced by about 20%), which can reduce or even do not use thinner to spray paint; in the spraying, especially The use of nozzles with small linear spray angles in air spraying can reduce the splash of paint mist; the use of high-quality spray equipment can also make the paint fog more refined, with less scattering and better coating effect.
As long as we think seriously, the contamination of steel drums to the environment will surely be reduced to a minimum, the paint consumption of painting will surely be minimized, and the coating quality of steel drums will be better.
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