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Application of painting layers – hydro-dynamic painting

The choice of application method depends mostly on the type of the construction, manner of surface preparation, type of used paint and working conditions for painting.

Optimal paint application methods ensuring the best protection and decoration properties are specified in technical charts of every product. They also contain recommended hydro-dynamic spraying parameters. It is recommended that anti-corrosion products should be applied with hydro-dynamic spraying or brushes, while surface and base paints can be applied with hydro-dynamic spraying, brushes or shafts and, some of them, after diluting with appropriate solvent, can be applied with pneumatic spraying as well.

Hydro-dynamic spraying

An appliance for hydro-dynamic spraying works by sucking the painting product in through a pump, forcing it through a high-pressure pipe to the nozzle embedded in a special spray-gun. The nozzle has a 0.1-2 mm hole and the paint, due to exceeding the critical speed, gets dispersed while leaving the nozzle. Hydro-dynamic spraying is applied in steel construction production facilities and at construction of elements measuring over 10 cm. Painting smaller objects with more complex shapes is uneconomical.  

The advantages of painting with hydro-dynamic spraying are: high efficiency of painting (even up to 800m2/hour), saving on painting material (30% in juxtaposition to pneumatic spraying), obtaining correct surfaces from painting materials (also thyrothropic), much thicker layer as opposed to pneumatic spraying and smaller dusting and concentration of solvent steam.

Conditions for conducting painting works

Temperature and humidity are very important factors influencing the quality of painting layers.

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Optimal temperature of air during painting works ranges from +5O C to +25O C, for surface temperature to +40O C. The temperature of steel surface during painting should be at least 3O C higher than the temperature of dew point of the surrounding air in order to avoid condensation of humidity on the surface.

The best results of painting works are obtained during painting at relative humidity up to 85%. An increase of the relative humidity over 85% creates favourable conditions for formation of a film of absorbed water on the surface which reduces the drying rate of the paint layer.

Dew point is the temperature at which air with specified content of steam reaches the state of saturation at an invariable value of atmospheric pressure. At the temperature of dew point (TDP) in the air, or on the objects contacting the air, condensation of steam takes place. If humidity of air is lower than 100%, TDP is always lower than the temperature of air, whereas the lower the humidity, the higher the difference.