Steel drum painting and environmental protection (3)

Fourth, ways to improve coating pollution

Now the benefits of the steel drum industry are not very good, but most of the barrel factories spend their energy on management, steel, paint, energy and other aspects of reducing consumption, if we can reduce the pollution of coatings, we can also find ways to reduce consumption and increase efficiency. This is not a good thing for the benefit of the country and for the benefit of the people.

1, pre-treatment shower water exchange

As mentioned above, most of the degreasing liquids currently used in China's steel drum industry are chemical degreasers containing surfactants, sodium hydroxide, trisodium phosphate, sodium carbonate, sodium silicate and various additives. It is alkaline, so the time of rinsing after de-oiling is long, and it becomes alkaline wastewater. At this time, it is necessary to replace the shower water.

Most phosphating solutions are acidic liquids containing phosphoric acid, phosphate, nitrate, molybdate and various additives. The leaching water after phosphating has become acidic for a long time. Waste water, then do not change the water, it will affect the paint coating.

At this time, if the two showers are replaced with each other, unexpected results will occur.

The surface of the steel drum after degreasing is also alkaline due to the relationship between the oil and the oil. If it is washed with phosphating wastewater containing a small amount of phosphating solution, it is not only partially neutralized. The surface of the barrel is alkaline, and it is also advantageous for the subsequent phosphating process.

On the surface of the phosphating steel barrel, the surface of the steel barrel is acidic due to the phosphating solution. If the alkaline water is used to remove the oil, the surface of the phosphating layer of the acidic steel barrel is partially neutralized. However, there is a problem to be paid attention to here. In addition to being alkaline, the draining wastewater of the oil also contains grease that is cleaned from the surface of the steel drum. Therefore, if the oil content is high, the phosphating surface of the steel drum will be contaminated. That is, the amount of oil in the oil-washing wastewater is very low, and it is necessary to re-evaluate the clear water to make sure that the surface of the phosphating layer of the steel drum is clean.

The reuse of such interchangeable shower water wastewater not only reduces sewage discharge but also saves water.

2, change the paint variety and spraying method

In addition to pre-treatment, there are two main ways to improve the pollution of steel drum coating, which is to change the coating variety and construction method, and to eliminate or reduce the production of harmful objects in the steel drum from the root wood. If the solvent-based paint that causes serious pollution is changed into water-based paint, powder paint or high-solids paint to eliminate or reduce the pollution of the organic volatiles of the paint to the atmosphere, adopt high-efficiency coating method to improve the utilization rate of the paint and reduce The scattering of paint, etc.

The main source of pollution in steel drum coating is the coating itself, and the most important pollution of the coating to the environment is organic volatiles. However, organic volatiles are an important component of solvent-based coatings, so water-based paints and powder coatings are worthy of advocacy from an environmental point of view and development direction. In fact, some barrel mills have already used water-based paints and powder coatings in part, and even some barrel mills have used powder coatings. Of course, from the current production needs of the steel drum industry, it is impossible to completely dispose of solvent-based coatings. What we can do is to use high-solids solvent-based coatings as much as possible. Direct, most economical, most effective, and the most immediate way. Moreover, 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 coating coating efficiency and reduce paint mist scattering. We can analyze the comparison of the three most commonly used spray methods in our steel drum industry:

The air spray takes the paint out by means of the negative pressure caused by the compressed air flow and is dispersed into a mist by the spray gun to be sprayed on the surface of the steel drum. The air sprayed paint mist is carried by the airflow. The paint mist is mixed with a large amount of air, which causes the paint to spread with the airflow. Moreover, the organic volatiles in the paint accelerate the volatilization rate due to the diffusion of the airflow. . Therefore, air spraying is the most environmentally harmful method in several methods of coating, and the waste of coating is also the largest.

High-pressure airless spraying is to apply high pressure to the paint by the high-pressure piston in the closed container, and the high-pressure paint is passed through the high-pressure hose and the spray gun, and the pressure energy is converted into the velocity energy through the olive-shaped nozzle hole, so that the paint is atomized into the particles to be sprayed. Steel drum surface. Compared with air spraying, since the paint mist does not contain a large amount of air, the coating does not splash with the airflow, the utilization rate of the paint is remarkably improved, and environmental pollution is greatly reduced. And because high-pressure airless spray can spray a coating with a much higher viscosity than air spray, the thinner used in the spray can be reduced, which also reduces environmental pollution, and of course reduces the coating cost.

Compared to the above two spraying methods, electrostatic spraying has minimal environmental pollution. Electrostatic spraying is the application of a negative high-voltage electrical connection generated by a high-voltage electrostatic generator to a metal sharp-edged or tip-discharged spray gun electrode, while the steel drum is grounded through a suspension chain or other transfer device to form a gap between the negative electrode and the steel drum. Uneven electrostatic field. By corona phenomenon, firstly, a large amount of electrons are excited and emitted near the negative electrode (the spray cup). After the paint mist enters the electric field, it combines with the electrons to form negatively charged particles. Under the action of the electric field force, it is directed to fly to the positively charged steel drum. surface. Electrostatic spraying does not or rarely scatters the paint mist into the air, which is the main cause of minimal environmental pollution in several spray methods. If a negative-voltage DC high-voltage power grid with an enameled wire is installed behind and on both sides of the steel drum in the spray booth, the inner wall of the spray booth will not be contaminated with paint mist due to the repelling effect of the paint mist which is also negatively charged. .

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 lacquer and X-891 coating at room temperature and fast drying, can reduce the viscosity by heating ( For example, X-622 epoxy steel barrel special inner coating, the temperature is increased from 25 ° C to 40 ° C, the viscosity can be reduced by about 20%), so that the paint can be reduced or even not used to spray the paint; in spraying, especially The use of a linear nozzle with a small spray angle in air spray can reduce the splash of paint mist; the use of high-quality spray equipment can also make the paint mist more refined, less scattered, and better coating effect.

As long as we pay attention to it, the pollution of the steel barrel coating will definitely be minimized, the coating material consumption of the coating will be reduced to a minimum, and the coating quality of the steel drum will be better.

General Manager Xu Guoxing

Shanghai Xugong Coating Technology Co., Ltd. (formerly Shanghai Steel Barrel Technology Equipment Research Institute)

Address: 1362 Yangshupu Road

Zip code: 200090

Telephone; 65192374; 13818681834

Fax; 65192374