All the subtleties of painting a car with oxygen

Painting a car with oxygen

Most often, when painting a car, pneumatic spray guns are used. The traditional sources of air for such devices are compressors. However, it is possible to connect oxygen cylinders to them. The following are the features of such equipment and oxygen painting is considered.

Pneumatic spray guns

The main structural elements of pneumatic spray guns are represented by a body in the form of a gun, a spray can, also called a tank, a start button, a nozzle, an air supply regulator, an air hose. The paint container can be mounted on the top or bottom of the tool, or be mobile, that is, have various installation options.

The following is the principle of operation of pneumatic spray guns. When the start button is activated, compressed air enters the tool. The paint is transferred under air pressure or as a result of vacuum into the nozzle, where it mixes with air and exits the tool in the form of a mist. The air supply regulator allows you to control the flow of the sprayed material by changing the intensity of air flow from the blower to the paint sprayer. Spray guns are equipped with several nozzles to change the shape of the spray jet.

The main parameter of spray guns is the working pressure. For most of these instruments, it is 2 - 6 atm. When choosing an airbrush, it must be borne in mind that it must be designed for a higher pressure than that which a compressor or other injection element can create. A performance margin of 20% is considered sufficient. Therefore, an airbrush is first purchased, and the injection device is selected according to its performance.

Another important parameter of spray guns is spray technology. It determines the features of the application of the material, its consumption, as well as the air consumption and the required pressure, that is, the main characteristics. According to this parameter, pneumatic spray guns are divided into three main types.

Types of spray guns

HP

This class of spray guns includes high pressure devices. They require a pressure of 5 - 6 bar. These tools are characterized by fast application of material at high consumption. This is due to the low degree of its transfer, which is understood as the ratio of the volume of the sprayed material to its amount that has fallen on the working surface. For pneumatic spray guns of the system under consideration, the values ​​of this parameter are no more than 45 - 50%. That is, if such tools are used for painting for their intended purpose, at best, half of the purchased paint will be used. The rest of it will be lost in the form of fog, which will settle on the surrounding objects, polluting them. Moreover, the fumes of some paints and varnishes have a negative impact on health.

For the reasons mentioned above, the HP system pneumatic spray guns are considered inefficient and obsolete, as a result of which they are being phased out. In some countries, painting them is prohibited.

HVLP

Devices of this type develop high pressure at the inlet and low pressure at the outlet of the nozzle (up to 0.7 - 1 atm). They provide a degree of material transfer to the work surface up to 75%. Moreover, in comparison with the instruments HP the considered spray guns provide a significantly higher quality coating.

LVLP

Tools of this type work with low pressure both at the inlet and outlet. They are characterized by the highest degree of material transfer to the working surface (up to 90%). In addition, such spray guns consume a small amount of air (180 - 200 l / min), so there is no need to equip them with high-performance injection equipment.

Painting

Car wash

You must first prepare the car. First of all, wash it. Then you need to remove attachments from the car, such as bumpers, lighting fixtures, sidelights, and a radiator grille. These parts are also washed and stored separately from the car. Then the car is inspected for defects in the body and paintwork in good lighting conditions. Dents, cracks, scratches, chips and other damage found are noted with acrylic paint or chalk. The next step is to eliminate them. It is first necessary to clean the damaged areas to the metal by removing the paintwork by sanding with 60, 80, 100 grit. In this case, it is necessary to ensure a smooth transition between the main surface of the car body and the damaged fragment. Ideally, the height difference should be imperceptible and can only be determined by touch. To do this, in the process of work, you need to constantly check the transition. Upon completion of grinding, the surface is degreased by wiping with cotton rags moistened with white spirit or some other solvent.

After that, you need to remove the dents by puttying. For this, synthetic polyester auto-filler is used. It is mixed in small quantities with a hardener and applied to the work surface with rubber spatulas in cross movements. It should be borne in mind that the hardening of the putty occurs within half an hour, so you need to apply it to the car quickly enough. Complete drying of the material at a temperature of 20ºС takes 30 - 45 minutes. After that, the surface is brought to the body geometry, grinding with sandpaper with a grit of 120 - 600. In this case, it is necessary to periodically check the result of the work by touch. It may be necessary to repeat the putty and sanding. The final check is carried out by applying a thin layer of primer, preferably from an aerosol can. In this case, defects will appear that will need to be eliminated.

You also need to set up the spray gun, which involves the regulation of several parameters. First of all, a nozzle is selected based on the material used. For primers, varnishes, enamels, a variant with a diameter of 1.8 - 2 mm is used, for stains - 1.2 - 1.4 mm, for water-based paints - 2.2 - 2.5 mm. Next, you need to adjust the air inlet pressure depending on the spray system. For devices like HP it should be 2.5 - 3.5 atm, for HVLP- 1.5 - 2.5 atm. In addition, the length of the hose is taken into account, adding 0.5 atm for every 6 m. The viscosity of the sprayed material is also important. For most options, average pressure values ​​\u200b\u200bare optimal, however, for low-viscosity substances, it is lowered, and for viscous materials, it is increased. Finally, adjust the shape of the torch. It should be oval and have a height of 12 - 15 cm.

Oxygen cylinder with reducer

Oxygen painting requires a second pressure regulator upstream of the spray gun. When the tool button is pressed, it is adjusted depending on the type of sprayed material. Provided that a nozzle of 1.5 - 1.8 mm is used for metallic, a value of 2.5 - 3.5 atm is set, for acrylic paints and varnish - 1.8 - 2.2 atm. In addition to the spray gun, you will need an oxygen cylinder, an oxygen hose 10 m long, and an oxygen reducer. And the balloon can be rented. A reducer is screwed to the cylinder, a hose is attached to it, which is connected to the spray gun. An outlet pressure of 7 kg is set on the reducer. Instead of a spray gun, you can use a spray gun with a 1/3 or 1/4 nozzle. It is much cheaper, but it is more difficult for them to regulate the supply of material.

The final stage of preparation for painting a car is to prepare the enamel. Painting a car involves the use of options that dry in natural conditions without baking. The material is diluted with solvent 650 to the desired consistency. The viscosity of the paint is checked by measuring the rate of runoff from a metal rod dipped in it with a diameter of 1-2 mm. If it is 3 - 4 drops per second, the viscosity is considered normal for painting. Also, before use, the paint should be filtered through a nylon stocking. As you can see, the preparatory stage includes many operations, so it can take up to 90% of the time of the entire painting process. If the car is not damaged, the amount of work will be significantly reduced.

In the process of painting a car, the paint sprayer is moved with smooth reciprocating movements 15–25 cm from the working surface perpendicular to it. The paint is applied starting from the roof of the car in 2 - 3 layers with breaks of 15 - 20 minutes between them. Complete drying of the car occurs in 24 - 36 hours at 20ºС.

Work should be carried out in a ventilated, clean, well-lit area, wearing protective equipment. Spraying starts and ends outside the work surface to avoid accumulation of paint along its edges. The application of paint should be started from the far side so that the mist is deposited on the painted surface. Flat surfaces are cross-coated in two passes. Stripes of paint overlap each other half the width. Spraying should start from the ends, holding the spray gun at an angle. Since it is impossible to apply the entire layer on them at once in order to avoid smudges, the ends are painted in two passes. The second half of the material is applied after painting the main surface. Corner painting should be carried out under reduced pressure to limit the formation of vortex flows, parallel to the long side. During breaks, the spray gun should be washed with a solvent, pouring it into the tank, and lowering the nozzle into a container with it.

In the event that oxygen painting is carried out with a spray gun instead of an airbrush, it is also necessary to adjust the paint supply, oxygen pressure and the shape of the torch on it.

To do this, use the regulators from the end, at the bottom and on the left side, respectively. Since the pressure should already be set on the reducer, the spray gun is opened completely and a test application of paint is carried out. To apply the first layer, set the minimum paint supply and the maximum torch. This is necessary so that the paint is only sprayed. Spraying is applied in two doses with an interval of 10 minutes. Then the ink supply is increased. The third layer is applied to wet, that is, from a distance of no more than 20 cm, so that there is a complete overlap. If after that the ground shines through, you will have to apply a fourth coat of paint.


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