Application of air-blown sprayer

1 Introduction

Transformer coating generally uses dip coating, shower coating, air spray, high pressure airless spray and other methods; for difficult to dip, spray coating of large components, usually using air spray, a few airless spray, but the air spray coating coating is low utilization At 50% or even only 30%, the compressed air consumption is large, and a large amount of paint mist is generated, which seriously pollutes the environment. The utilization rate of high-pressure airless spray paint is about 60%, and the coating film is prone to sagging, and the paint mist is also high. . Mixed-air spraying not only overcomes the disadvantages of both, but also has obvious advantages.

2, mixed gas spraying principle

The air-blown spraying was invented by combining the advantages of air spraying and airless spraying. Its main points include: (1) Using a special sprayer with a certain pressure ratio to pressurize the paint to 4 to 5 MPa and then eject it through the nozzle. (2) The filtered, compressed air is sent to the air cap and is ejected through specially designed holes. A part of the compressed air is involved in the atomization process of the paint, that is, the atomized paint is further atomized to make it finer and more evenly distributed, and the other part of the compressed air forms a wind curtain around the paint spray flow of the paint. Paint mist flows around and restricts its application to the workpiece. In short, the mixed gas spray atomization force comes from two aspects, one is from the liquid, the paint is suddenly decompressed and expanded and then atomized after being pressed; the other is from the flow of gas, ie compressed air, to promote further atomization of the paint. Together these two elements are called twin atomization. This spraying method is called mixed gas spraying.

3, mixed gas spraying process parameters

The air-blown sprayer is used for transformer coating and has good use effect. After production verification, the process parameters are determined as follows:

Supply pressure: 0.4 ~ 0.6Mpa

Pump pressure: 0.3～0.4Mpa

Auxiliary pressure: 0.15～0.2Mpa

Spraying amount: 1.2L/min

Spray width: 400mm

Spraying distance: 250～300mm

4, operation precautions

In order to improve the quality of the coating and ensure the use of the coating, according to production experience and experience, the following operational precautions are proposed:

a) Dust control in the operating environment must not affect the appearance of the coating. The temperature must not fall below 0°C.

b) The paint should be filtered before use, stirring evenly, and the viscosity should be controlled within 25-30S.

c) Spray gun paint The gun filter should be removed to prevent the gun from becoming clogged.

d) When the pump is started and cleaned, the pump speed must not exceed 40 strokes/minute, and the pump pressure should be 0.05 to 0.07 Mpa.

e) The supply pressure must not exceed 0.6Mpa.

f) It is not advisable to apply mixed-air coating to workpieces such as tube radiators.

g) The thickness of a spray is 20-50un, and the number of sprayed layers should be controlled as required.

h) To prevent sagging, control paint viscosity and spray distance.

5, the application of mixed gas spraying

Through production applications over a period of time, it has been proven that mixed-air spraying has the following significant advantages:

a) Improve coating quality

The mixed-air spraying method can obtain a high-quality decorative coating surface, and the key to obtaining such a surface is the spray atomization effect. A good atomization effect depends on two aspects of the spray mist flow. One is the fineness of each paint droplet after the paint is atomized, ie, the size of each droplet diameter; the other is the paint droplets. The degree of uniform distribution of the paint mist formed throughout the paint mist flow width. Due to the dual atomization principle, the mixed-air spray method has achieved satisfactory results in both areas.

Due to the good atomization effect of the mixed-air spraying, the paint atomized droplets are fine and distributed uniformly; the obtained coating film is more uniform, smooth and detailed than the air spraying method, and can effectively overcome the film defects such as sagging and “virtual smoke”. Therefore, it has been widely used in various industrial sectors since the 1990s.

b) Saving paint

It has been verified by production practice that mixed-air spray coating can save 20 to 40% of paint compared with air spray, and can save 10 to 15% of paint compared to high-pressure airless spray method. The reason is that the coating pressure used for air-blown spraying is less than that for high pressure and airless, and the pressure of the compressed air used is much smaller (0.1-0.2 Mpa) than air spraying. Under such working conditions, the initial velocity of the paint sprayed by the nozzle is much lower than that of the high-pressure airless spray, the initial velocity of the compressed air is greatly reduced, so that the exterior of the mist flow is further constrained by a circular air curtain, limiting the flow of paint mist to the surroundings. Escape. These two factors determine that the air-blown spray method greatly reduces the flying of spray paint, which is more than 20 times lower than air spray.

c) Improve production efficiency

Because the air-mixed spray gun has a large amount of paint sprayed, it is 10 times that of the air spray gun; the paint mist flow width is up to 400mm, while the air spray rate is only 70~100mm; the mixed gas spray one film thickness up to 20~50um, air spray gun Only 10 ~ 15um, which can reduce the number of construction; so mixed-air spray with high production efficiency.

d) Improve the working environment

Because the mixed gas spraying paint has a higher pressure and less airless spray, the initial velocity of the paint sprayed by the nozzle is much lower than that of the high pressure airless spray, and the spraying paint mist flow has almost no rebound; at the same time, the paint curtain is caused by the effect of the air curtain. Dissipation is limited; these two factors determine the dramatic reduction in paint mist during operation. After on-site testing, the air-blown sprayer produced paint mist more than 20 times lower than the air spray gun. The concentration of toluene and xylene is 5 times lower, which effectively improves the working environment.

e) It has good process performance. It is widely adaptable to viscosity, suitable for many kinds of coatings, it can reduce the amount of thinner material and is easy to operate, so it is easy to popularize and apply.
Although the mixed-air spray method has many advantages, there are also deficiencies, such as one-time investment close to high-pressure airless spray, and the need for equipment and pipeline cleaning before work every day.

6. Summary

Production practice proves that the mixed-air sprayer has the advantages of good coating film quality, saving coating, high production efficiency, less paint fog, and good processability. It is particularly suitable for the coating of large-scale components, and is currently a relatively advanced coating equipment. The promotion of transformer coating has a good prospect.