Talking about the Application of Nitrogen Spraying Technology in Commercial Vehicle Coating Line

The traditional spraying process uses the filtered compressed air as the paint carrier, and the paint overspray and droplet rebound are serious, resulting in increased paint and solvent consumption and high cost

1 Overview of Nitrogen Spraying

1.

The compressed air first passes through the filter, and then the filtered compressed air passes through the nitrogen generator to generate nitrogen with a purity of more than 95%.

1.

When the traditional compressed air passes through the nitrogen spray equipment to polymerize the fiber membrane, the differences in the solubility and diffusion coefficient of various gas molecules in the membrane lead to different relative permeation rates of different gas molecules in the membrane

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The separated high-purity nitrogen gas is heated to a certain temperature to ensure that the coating temperature is constant during the nitrogen spraying process, and it is not easily affected by the spraying environment temperature

1.

Nitrogen ionization devices are generally used for spraying non-metallic workpieces, because the electrostatic charge generated on the surface of metal parts can be eliminated by grounding, while for non-metallic workpieces, the surface is not only prone to electrostatic charge, but also difficult to pass through.
Grounding is eliminated, and in severe cases, electrostatic discharge will occur with surrounding metal conductors (support or human body)
.
The electrostatic charge generated on the surface of the workpiece will attract suspended particles or dander due to electrostatic adsorption, resulting in paint quality defects.
The ionization device can ionize nitrogen molecules, and through the principle of the same charge and the repulsion of the opposite, the surface of the workpiece can adsorb the corresponding particles.
The electric charge is neutralized.
The neutralized workpiece reduces the adsorption of particles and dander in the environment, improves the spraying quality, and effectively reduces overspray
.

2 Advantages of nitrogen spraying

2.
1 Stable single paint carrier

Compressed air contains a variety of molecules, and the particle size and speed of each molecule are different, and turbulence will occur during the spraying process, resulting in waste of paint overspray
.
However, in nitrogen spraying, the purity of nitrogen is as high as 95% or more, and the molecules of the coating carrier are single and stable, and no turbulence will occur, which not only saves the coating, but also ensures the stability of the spraying and improves the spraying quality of the coating
.

2.
2 The paint atomization is more uniform

The moving speed of nitrogen molecules is 1 times faster than that of air molecules (0.
1 MPa), and the volume is smaller than that of air molecules.
Under the same spraying quality, nitrogen spraying uses lower paint atomization pressure, and the reduction of pressure not only saves the consumption of compressed air, but also In addition, the overspray and rebound of paint droplets are reduced, the paint mist in the spray booth is reduced, and the spraying environment is improved, thereby prolonging the service life of the filter element in the spray booth
.

2.
3 Better paint leveling effect

The nitrogen equipment has an integrated heating function, which can indirectly reduce the viscosity of the paint, and nitrogen is almost insoluble in organic solvents and does not react with the paint
.
Therefore, compared with air spraying, nitrogen is more helpful for the leveling of the coating after spraying and improves the visual effect of the coating appearance
.

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4 Improve yield rate

Nitrogen is generated by the principle of gas selective infiltration.
The compressed air needs to pass through three filtration systems before infiltration, which ensures that the generated nitrogen is cleaner, and the ionized nitrogen molecules are neutralized by the opposite charges, which can eliminate the static electricity on the surface of the workpiece and reduce the Adsorption of particles and dander, thereby reducing defects such as fiber hair and particles, and improving yield
.

3 Application of nitrogen equipment in FAW Jiefang

The FAW Jiefang cab coating line mainly produces J6, J7 and related military cabs.
The current coating process adopts solvent-based 3C2B process
.
In order to further improve the paint quality of the cab, improve the efficiency of manual spraying, and reduce the consumption of paint, in early 2018, the nitrogen technology was applied in the painting workshop of FAW Jiefang, and it was installed in 4 manual spraying stations of the topcoat line for overcoating.
Nitrogen is a "one-to-one" type, and the equipment model is Nitro master.
The nitrogen equipment of this model is small in size and easy to move
.

3.
1 Equipment installation and debugging

The improved nitrogen equipment is installed in the manual spraying station of the topcoat line in the painting workshop.
The original compressed air inlet pipe and outlet joint are retained through the three-way valve, and the inlet pipe of the nitrogen spraying equipment is connected to separate a constant temperature and The high-purity nitrogen outlet joint ensures that the station can switch between compressed air and nitrogen spraying
.
Since the nitrogen equipment is installed in the clean room, the nitrogen equipment is required to be a Class II explosion-proof product, and the equipment has good grounding performance.
The installation meets the requirements of relevant national standards and regulations to ensure safe use
.
The installation of nitrogen equipment is relatively simple, mainly the transformation of the compressed air pipeline and the installation of the nitrogen joint at the station.
It is recommended to use a three-way valve to retain the compressed air joint, which can ensure that the nitrogen equipment can be switched to the compressed air state at any time when there is a problem.
Guaranteed production
.

The debugging of nitrogen equipment is mainly to adjust the pressure and temperature of nitrogen.
According to different production site conditions, seek the optimal pressure and temperature to achieve the best use effect.
At present, the pressure of the equipment is 0.
5 MPa and the temperature is 50 ℃.
The effect is best
.

3.
2 Nitrogen spraying effect tracking

After the equipment debugging is completed, the orange peel of the paint surface after nitrogen spraying, the saving of paint and the increase of film thickness are tracked and counted, and the quality effect of the paint surface after nitrogen is used as the paint carrier is analyzed
.

3.
2.
1 Lacquer orange peel

Track and count the orange peel (LW and SW) of the cab paint surface after air spraying and nitrogen spraying respectively

Conclusion: The orange peel degree of the paint surface of nitrogen spraying is better than that of air spraying, the LW value is reduced by 3 to 5 points, and the SW value is reduced by 4 to 7 points, and the visual effect of the cab paint surface of nitrogen spraying is obviously better than that of air spraying
.

3.
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2 Saving paint

Under the same spraying conditions, a small batch spraying test was carried out on the production line, and the paint consumption of air and nitrogen spraying was compared, and the single-unit paint consumption of the corresponding carrier was obtained
.

Conclusion: Compared with air spraying, nitrogen spraying paint has higher utilization rate and can save 8.
6% of paint
.

After the nitrogen equipment was put into operation and the batch was stably produced, the on-site paint consumption was continuously tracked for 3 months to verify the paint consumption of air and nitrogen spraying, and the corresponding carrier paint consumption data was obtained
.

Conclusion: It has been verified by production line spraying that compared with air spraying, nitrogen spraying technology can save 10.
4% of paint, which has the prospect of production line promotion and application
.

3.
2.
3 Film Thickness Improvement

Under the same spraying conditions, spraying tests were carried out on air and nitrogen carriers, and the film thickness data at the same point of the corresponding carriers were obtained
.

Conclusion: Under the same spraying conditions, the film thickness of nitrogen spraying has an upward trend, which is about 7% higher than that of air spraying.
It can be seen that on the premise of ensuring a certain film thickness, the nitrogen spraying technology can appropriately reduce the spraying pressure.
So as to achieve the goal of saving paint and reducing VOC emissions
.

4 Conclusion

The improvement of the appearance quality of the paint surface of the cab has always been an important topic in the study of the painting process.
From the application of nitrogen spraying technology in the production line, nitrogen spraying can not only improve the appearance quality of the paint surface, but also save the paint and achieve the improvement of quality and cost reduction.
As a result, nitrogen spraying is worthy of promotion and application, and nitrogen technology can be applied not only to manual or automatic spray guns, but also to solvent-based paints or water-based paints.
It can continue to be used after adding robots or transforming water-based paints in the future, which is forward-looking
.