Water-based paint construction requirements for coating line equipment!

sequence

In compliance with increasingly stringent environmental regulations, water-based paint coating technology that can reduce VOC emissions has been rapidly developed.
With the continuous in-depth research on water-based paint technology, the construction window of water-based paint has been continuously widened, and the construction difficulty has been reduced.
At the same time, the film quality of water-based paint can be comparable to that of solvent-based paint.
These factors all promote the performance of water-based paint in painting.
The application is more and more extensive.
Then combined with the characteristics of water-based paint and the design concept of the coating line, then a brief analysis of the equipment of the water-based paint coating line will be conducted on com" href="http://">Coating Online Coatingol.
com .

1.

Water-based paint characteristics

Figure 1 shows the comparison between water-based paint and solvent-based paint.

It can be seen that most of the composition in the water-based paint is pure water (only a small amount of alcohol and ether organics), and the characteristics of water affect the construction characteristics of the water-based paint.

Some physical properties of toluene in water and solvent paints are shown in Table 1.

Table 1 Some physical properties of water and toluene

2.

Water-based paint requirements for coating equipment

In view of the characteristics of water-based paint, corresponding measures have been taken in the design and equipment of the water-based paint coating line.

When the water-based paint line is newly planned or the existing coating line is modified, some equipment needs to be adjusted as necessary.

2.

1 Spray booth

The spray booth is the main space for spraying operations.
The large amount of pure water and a small amount of additives contained in the water-based paint mist will directly corrode the internal structural parts of the spray booth.
Therefore, the wall panels of the spray booth are required to be made of stainless steel, and the paint mist trapping devices (such as venturi structure, waste paint treatment circulating water pipelines, etc.
) in the lower part of the spray booth are also required to be made of stainless steel.

2.

2 Exhaust system

The Comprehensive Emission Standard of Air Pollutants (GB 16297-1996) stipulates the emission rate and volume of VOC.
The discharge rate of xylene in the solvent paint spraying system directly determines the height of the exhaust cylinder.
After using water-based paint, the content of toluene and xylene in the organic waste gas is almost zero, but the content of non-methane total hydrocarbons increases, and the height of the exhaust cylinder only needs to meet the emission rate requirements of non-methane total hydrocarbons.
In this way, the height of the exhaust cylinder can be reduced, the civil construction cost is reduced, and the air pressure of the exhaust fan is reduced, and the operating cost is also reduced.

2.

3 Air conditioning system

The construction window of water-based paint is narrower than that of solvent-based paint, so water-based paint has stricter requirements on the temperature and humidity of the spray booth (see Figure 2).

Figure 2 Comparison of construction windows between water-based paint and solvent-based paint

The harsh requirements of water-based paint on the construction environment require the air-conditioning system to have cooling and humidity control functions.

At present, the summer air supply of solvent-based paint spray booths in my country rarely uses constant cooling.
Water-based paint coating air conditioning systems generally first reduce the air temperature through the surface cooling section (to make the air reach the dew point to precipitate moisture), and then heat the air with the precipitated moisture to the working temperature.

In terms of air delivery and exhaust, when the solvent paint is sprayed, the exhaust air is not suitable for reuse due to the high solvent content in the exhaust air.

After changing to water-based paint, the solvent content in the exhaust air is greatly reduced, and the exhaust air can basically be used for air circulation after treatment.

2.

4 Paint delivery system

Water-based paint should be stored at 5~30℃, and the paint mixing room needs to have constant temperature and humidity conditions to prevent the paint from freezing or overheating and to ensure the stability of the paint.
The application viscosity of water-based paint is higher than that of solvent-based paint, and the required paint supply pressure is also higher.
The diaphragm regulator suitable for water-based paint systems adopts a high-pressure, high-flow straight-through design.
The diaphragm regulator should be easy to clean, but its price is about 2 times higher than the diaphragm regulator for solvent-based paint.
The traditional water-jacketed temperature control system is difficult to meet the requirements of water-based paint for temperature control accuracy, and the pipe-in-pipe temperature control system should be used instead.
Since water-based paints are only stable within a certain pH range, water-based paints increase the requirements for pH control, and pH monitoring equipment needs to be added.
The alkaline characteristics of the water-based paint make the pipes and other parts that directly contact the paint to be made of 304L or 316 stainless steel, and the surface passivation treatment is required.

 

Unlike the solvent paint cleaning system, the water-based paint cleaning system can be cleaned with a single solvent.
The cleaning fluid of the water-based paint cleaning system is composed of pure water and a hydrophilic solvent.
The pure water and the hydrophilic solvent are cleaned by a pneumatic diaphragm pump each.
In the solvent mixing tank, after stirring, the mixed solvent is pumped to each point of use by the hydraulic pump.
Therefore, compared with the solvent paint cleaning system, the water-based paint cleaning system adds 1 set of pure water pump (water tank), 1 set of solvent pump (containing solvent tank) and 1 set of solvent hydraulic pump (containing solvent tank and stirrer, etc.
).
Since water-based paint is more sensitive to shearing force, the heat exchanger and back pressure valve of the water-based paint delivery system need to use low-shear equipment.

 

The water-based paint transfer system uses a double-blade agitator (see Figure 3).
Both the return pipe and the paint supply pipe are set at the bottom of the paint tank, and the agitator and paint tank are made of stainless steel.
The paint tank should have high airtightness to prevent skin formation in the tank.
When not in production, the pump frequency of the water-based paint agitator can be reduced by half, and then adjusted to the normal operating frequency when you go to work, which can reduce energy consumption and reduce the shearing effect on the paint.

Figure 3 Double-blade agitator for paint tank

to sum up

With the full use of water-based paint and the continuous progress of its research and development technology, the construction window of water-based paint will be expanded and the construction process will become more mature.

The utilization rate and qualification rate of paint will continue to increase, operating costs, and "three wastes" emissions.
The amount, processing cost, and energy consumption will continue to decrease, and the application of water-based paint will be more extensive in the future.