RU2002133252A - METHOD OF ABRASIVE-GAS SURFACE TREATMENT AND NOZZLE DEVICE FOR ITS IMPLEMENTATION - Google Patents

Claims (11)

1. The method of abrasive gas surface treatment, including the supply of compressed gas, the subsequent acceleration of the flow to supersonic speeds, its expansion, mixing the abrasive with compressed gas and the discharge of the abrasive gas mixture onto the surface to be treated, characterized in that the gas stream is mixed with the abrasive before acceleration to obtain an abrasive gas mixture, the expansion of which is carried out to a pressure below the ambient pressure, regulate the flow of gas from the environment and stop the acceleration of the abrasive gas mixture when achieved and the velocity of the average mass particles of abrasive, equal to 0.7-0.95 gas velocity, while in the process of acceleration and expansion of the mixture in each section of the stream maintain the concentration of abrasive in the mixture of 0.01-1 vol.%, the total pressure P ^{* of the} stream not lower than the limiting R _CR , and the reduced gas velocity λ not higher than the limiting reduced velocity λ _CR , and R _CR and λ _CR determined from the relations

and

where R _n - environmental pressure, MPa; k is the gas adiabatic exponent (dimensionless quantity). 2. The method of abrasive gas surface treatment according to claim 1, characterized in that when the pressure of the flow of the abrasive gas mixture is lower than 0.6 from the ambient pressure, the flow of the mixture is inhibited and compressed, providing a constant acceleration of the middle particles of the abrasive in the mixture. 3. The method of abrasive gas surface treatment according to claims 1 and 2, characterized in that when the gas expands in the mixture stream, the difference between the gas velocities and the mass average abrasive particles in the range of 300-400 m / s is maintained. 4. The method of abrasive gas surface treatment according to claims 1 to 3, characterized in that immediately before the ejection of the abrasive gas mixture, the total gas pressure in the stream is not lower than the value of P _n / π _cr , and the gas-dynamic function π _cr is determined by the formula

5. The method of abrasive gas surface treatment according to claims 1 and 4, characterized in that a liquid is supplied to the boundary layer of the flow of the abrasive gas mixture before its discharge. 6. The method of abrasive gas surface treatment according to claims 1 to 4, characterized in that the expanded flow of the abrasive gas mixture is mixed with a limited amount of air from the environment and provide a gas and air velocity not lower than sound velocity in each section of their mixing zone. 7. A nozzle device for abrasive gas surface treatment, including a mixing chamber and a supersonic nozzle with an inlet tapering part, a critical section and an outlet part, characterized in that the nozzle exit section is additionally provided with a re-expansion nozzle coaxially with the critical section, the length of which L _per is determined according to the formula

Where

and

- diameters of the outlet and inlet sections of the over-expansion nozzle; α is the opening angle of the re-expansion nozzle, while the length of the nozzle part from the critical section to the inlet of the re-expansion nozzle is 80-120 diameters of the abrasive particles average in weight, the opening angle α is 3-30 °, and the diameter of the exit section of the re-expansion nozzle

is 0.5-0.95 in diameter of its maximum section

which is determined by the formulas

Where

- the minimum thickness of the displacement layer, m; F _cr - the area of the critical section, m ² ;

- total minimum pressure at the outlet of the over-expansion nozzle, MPa; q (λ) is the gas-dynamic function of the reduced flux density of the abrasive-gas mixture, dimensionless quantity;

8. The nozzle device according to claim 7, characterized in that the area of the input section of the over-expansion nozzle is not less than the area of the output section of the expanding part of the nozzle. 9. The nozzle device according to claims 7 and 8, characterized in that the re-expansion nozzle is additionally provided with a cylindrical part, the diameter of which is selected from the conditions

Where

and

- the minimum and maximum diameters of the cylindrical part of the nozzle, m;

and

- the minimum and maximum cross-sectional areas of the cylindrical part, m ² ;

- the maximum thickness of the displacement layer, m, in this case, if

,

and in case

where P $\genfrac{}{}{0ex}{}{\text{*}}{\text{ace}}$ - total pressure at the exit of the cylindrical part of the nozzle, MPa; P _{ac max} * is the minimum total pressure at the outlet of the cylindrical part of the nozzle, MPa; and the length of the cylindrical part L _C is determined from the conditions

- average particle size;

- the length of the cylindrical part of the nozzle at which

10. The nozzle device according to claims 7 to 9, characterized in that a removable water collector with nozzles for supplying water is sealed to the outer surface of the re-expansion nozzle, the inner cavity of the re-expansion nozzle communicating via radial holes in the wall with the inner cavity of the collector. 11. The nozzle device according to claims 7 to 9, characterized in that it is equipped with a removable ejector mounted on the re-expansion nozzle coaxially with it, and the inlet area of the ejected air and the cross-sectional area of the ejector mixing chamber are determined depending on the conditions for ensuring critical operation of the ejector .