SU1745364A1 - Method of painting surfaces - Google Patents

Abstract

Usage: in paint technology with pneumatic and kinetic spraying of paint. SUMMARY OF THE INVENTION: Surface painting is carried out by finely spraying paint to form a spray cone and supplying a gas stream from the cooled (-20) to (-30) ° C carbon dioxide concentric to the spray cone, in which powdered refrigerant — dry is introduced. carbon dioxide. 1 il.

Description

The invention relates to the field of paint coating technology with pneumatic and kinetic spray paint.

There is a known method of painting surfaces, which contains a fine dispersion of paint with the formation of a spray plume and the flow of an expanding annular gas flow concentric with the spray tip with the formation of a protective gas bell.

The gas bell reliably prevents fine particles of paint from entering the atmospheric air, reduces the aerodynamic resistance of the paint spray and increases its range.

A disadvantage of the known method is that the annular gas flow forming the gas bell itself experiences a significant aerodynamic resistance due to turbulent friction against stationary atmospheric air, which reduces the effectiveness of paint spray protection, which has a large

density than the gas flow in the gas bell due to the presence of paint particles.

The closest in technical essence and the achieved effect is the method of painting surfaces, containing finely dispersed paint to form a spray cone and feeding a pre-cooled gas with a density exceeding air density concentric to the spray paint in order to form an expanding annular gas flow in the form of a protective gas bell . Carbon dioxide with a high density and high heat capacity is used as a gas. Cooling the gas further increases its density. In general, the denser gas of a gas bell, spreading like a submerged jet in less dense atmospheric air, forms substantially less turbulent eddies on the boundary surface of the gas bell-atmosphere, which increases the range of the gas bell, at the same time increasing the range

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paint spray and reduce the loss of paint particles to the atmosphere.

The disadvantage of this method is that due to the intense heat and mass exchange between the gas bell and atmospheric air, this bell rapidly accumulates thermal energy, which leads to a decrease in the density of the gas bell and the kinetic energy of this bell. At the same time, excessive precooling of carbon dioxide, forming a gas bell is impossible due to the rapid transition of carbon dioxide to the solid state at -78.5 ° C. This may cause the paint to freeze in the spray pattern. A solution to this technical contradiction may be, first, to continue cooling the gas directly in the gas bell, and, second, to increase the density of the gas bell by saturating it with solid particles. An integral solution to the problem is to saturate the gas hardening bell with particles that simultaneously cool it.

The aim of the invention is to increase the gas bell range and productivity by additionally cooling the gas directly in the expanding ring stream and saturating this stream with solid particles. To do this, a powdered coolant, such as dry carbon dioxide, is introduced into the pre-cooled gas when it is supplied concentrically to the spray paint.

The drawing shows a diagram of the implementation of the method of painting surfaces.

The method of painting surfaces is carried out as follows:

fine spray paint is produced by a pneumatic or kinetic method to form a spray cone;

cool the gas with a density greater than the density of air, for example, carbon dioxide, below the temperature of atmospheric air;

injected into pre-cooled carbon dioxide - powdered refrigerant, for example, dry carbon dioxide:

forming from the cooled two-phase mixture of gaseous carbon dioxide and powdered dry carbon dioxide an annular expanding gas flow concentric to the paint spray with the formation of a protective gas bell; ...

direct the spray paint to the surface to be painted.

From the working chamber 1, through a nozzle 2, finely dispersed paint or varnish is produced in the usual manner with the formation of an expanding spray 3 according to arrows A. At the same time, from source 4, for example, a cylinder or a gas generating station, via screen 5, carbon dioxide is fed through pipe 6 along arrow B into chamber 7 with an annular gas nozzle 8. Before being supplied to the inlet 6, carbon dioxide is cooled in the refrigerator 9 to a temperature below

5 ambient air temperatures, for example, up to -20 ...- 30 ° C, and using a dispenser 10, powdered refrigerant 12, for example, dry carbon dioxide, is introduced into the gas stream from an isothermal bunker 11. After exiting

From the annular nozzle 8, a biphasic mixture of carbon dioxide and dry carbon dioxide forms a gas bell 13, which separates the spray pattern of paint 3 from atmospheric air. The specified two-phase mixture

5 moves in the gas bell 13 in passing the paint spray 3 with a speed equal to or greater than the speed of the latter, as a result of which the paint particles in the flame 3 do not practically experience aerodynamic resistance and do not enter the atmospheric air until they come in contact with the painted surface 14. In gas bell 13 heat exchange occurs between fine particles

5 dry carbon dioxide and carbon dioxide, which compensates for the heat exchange between the gas bell and the environment, thereby ensuring the isothermality of the gas bell. Sublimation (sublimation) dry

0 carbon dioxide provides compensation for mass transfer between the gas bell 13 and the environment. At the same time the saturation of the gas bell with dry particles of carbon dioxide at the initial

5, its propagation area allows increasing its kinetic energy reserve. At the boundary of the gas bell 13 with atmospheric air, shown by the dotted line in the drawing, the gas bell experiences aero friction due to the formation of boundary turbulent eddies, however, the nnoTHOcfb of the gas bell is higher than atmospheric air, which significantly reduces its aerodynamic drag.

The advantage of this method is that the compensation of heat and mass transfer of the gas bell with the environment and an increase in its kinetic energy by the introduction of powder; The refrigerant is more profitable compared to, for example, an increase in the gas outflow rate, since an increase in gas velocity causes a quadratic increase in aerodynamic drag, and an increase in gas flow density (including two-phase flow) with an equivalent amount of movement, conversely, reduces aerodynamic drag. In general, this increases the range of the gas bell, reduces the likelihood of paint particles from the spray torch in the atmospheric air, and improves sanitary and hygienic working conditions.

Claims (1)

Invention Formula 0 The method of painting surfaces, which includes finely dispersed paint to form a spray cone and supply a gas stream from carbon dioxide cooled to -20 to -30 ° C concentric with the spray torch, characterized in that, in order to increase the gas bell’s long range and performance, to a cooled one. A stream of carbon dioxide is injected with powdered coolant — dry carbon dioxide.