RU2246391C2 - Method for abrasive-gas treatment and nozzle apparatus for performing the same - Google Patents

Abstract

FIELD: cleaning of large-size metallic constructions such as ships, tanks for oil products, sheets and so on due to removing from them different coatings, deposits, stains in different media including sea water, aggressive media, gas atmosphere and at condition under pressure.

SUBSTANCE: method comprises steps of supplying compressed gas; speeding up flow up to supersonic velocity values, expanding it, mixing abrasive with compressed gas and ejection of abrasive-gas mixture onto treated surface. Gas flow is mixed with abrasive before speeding-up for preparing abrasive-gas mixture whose expansion is realized until pressure value lower than that of environment. Addition of gas from environment is controlled. Speeding up of abrasive-gas mixture is stopped after achieving velocity of mean-mass particles of abrasive consisting 0.7 - 0.95 of gas velocity. At speeding up and expanding in each cross section of gas flow abrasive concentration in mixture is sustained in range 0.01 -1 vol.%; total pressure P* of gas flow is sustained by value no less than limit pressure Pl and reduced gas velocity λ is sustained by value no more than limit reduced velocity λr determined according to given relation.

EFFECT: enhanced efficiency due to elimination of sudden changes of pressure, uniform mixing of abrasive and gas, complete usage of energy of compressed-gas pressure, increased surface area of treated surfaces.

11 cl, 6 dwg, 2 ex

Description

The invention relates to the field of gas abrasive treatment of surfaces from various coatings, deposits, rust, in particular large-sized metal structures, for example, ships, containers for oil products, sheets, etc. in various environments, including sea water, in aggressive environments, in a gas atmosphere and under pressure.

A known method of abrasive gas surface treatment, comprising dividing the air flow from a source of compressed gas into two parts, with a smaller part of the air falling into a sealed tank with abrasive, which is supplied with air from the tank to a large part of the air, mix them, the resulting mixture is transported by a hose to a supersonic nozzle apparatus, in which the abrasive material is dispersed in a supersonic air stream and thrown onto the surface to be treated [1, p. 293, Fig. 12]. However, in the known method, the abrasive is poorly accelerated in a supersonic air flow and has a low kinetic energy, which leads to low productivity of the processing process.

A known design of the gun for abrasive-air surface treatment, consisting of a housing with nozzles for supplying materials and a chamber in which a nozzle for feeding the abrasive is installed, is also a critical section, passing into the output nozzle. The inner surface of the outlet nozzle has a conical-cylindrical shape, and the nozzle for feeding the abrasive is made in the form of a nozzle mounted coaxially at the beginning of the conical part and the outlet nozzle with an annular gap relative to the critical section of the chamber, while the plane of its outlet coincides with the critical section [2] .

However, the nozzle design does not provide high-quality mixing of the abrasive in the conical-cylindrical part of the nozzle with a supersonic air flow, and, accordingly, has a low productivity.

Closest to the claimed is a method of abrasive gas surface treatment, including the initial expansion of compressed air and its acceleration to supersonic speed, the simultaneous supply of an accelerated air stream under the pressure of the working substance in a dense layer with a low speed of translational motion, the creation of an abrasive-air mixture, its supply into the nozzle for acceleration and ejection onto the surface to be treated. In this case, compressed air is expanded to a level below atmospheric, and the mixture is accelerated to a fixed value of total pressure above atmospheric level, while the flow rate of the working substance is controlled by its supply pressure [2].

The disadvantage of the prototype method is poor-quality mixing of the abrasive with a supersonic air stream, low acceleration in a supersonic air flow due to the occurrence of direct pressure surges, which sharply reduce the air flow rate due to the high volume concentration of the abrasive when it is mixed with a supersonic stream. These shortcomings reduce productivity and processing quality.

Closest to the claimed is a nozzle device made in the form of a supersonic nozzle for abrasive gas surface treatment, including a tapering subsonic inlet part, a critical section and an outlet part [1, p. 290, Fig. 10a].

However, the design of the device does not provide high performance due to the incomplete use of pressure energy of compressed air and the impossibility of high costs of abrasives to obtain high-quality treatment of contaminated surfaces.

The technical problem solved by the inventions is to increase productivity by eliminating direct pressure surges and ensuring uniform mixing of the abrasive with gas, as well as the full use of the pressure energy of the compressed gas and increasing the surface area to be treated.

The technical problem is solved with the help of a set of features specified in independent claims 1 and 7 of the claims.

In the method of abrasive-gas surface treatment according to the first claim, including gas supply, its subsequent acceleration to supersonic speeds, its expansion, mixing the abrasive with gas and the ejection of the abrasive-gas mixture onto the surface to be treated, according to the invention, the gas is mixed before accelerating with the abrasive with obtaining 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 upon reaching the velocity of the average mass particles of the abrasive equal to 0.7-0.95 gas velocity, while in the process of dispersal 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 * flow not lower than the limiting R _CR , and the reduced gas velocity λ is not higher than the limiting reduced velocity λ _CR , and λ _CR and P _{CR are} determined from the relations:

и

and

where R _n - environmental pressure, MPa;

k is the gas adiabatic exponent (dimensionless quantity).

Pre-mixing the gas with the abrasive allows you to get a homogeneous abrasive-gas mixture before it is dispersed, and not to combine both the mixing and dispersal processes according to the prototype method, which helps to prevent direct pressure surges that sharply reduce the flow rate due to the high volume concentration of the abrasive. The expansion of the abrasive gas mixture is carried out to a pressure below ambient pressure, while regulating the flow of gas from the environment, which allows the use of the inventive method under water at an ambient pressure of 0.1-1.0 MPa or more and to provide a different degree of vacuum during acceleration abrasive gas mixture. At the same time, this ensures an increase in pressure in the flow to a value at which gas inflow from the environment to the zone of minimum pressure of the over-expansion nozzle is excluded, which helps to prevent direct pressure surges in the mixture flow.

When the speed of the average mass particles of the abrasive is equal to 0.7-0.95 of the gas velocity, the acceleration of the abrasive-gas mixture is stopped, which allows you to limit the length of the over-expansion nozzle, without significantly reducing the kinetic energy of the abrasive stream. If the claimed ratio is less than 0.7, then the kinetic energy of the abrasive stream will be significantly reduced, and if it is more than 0.95, then the over-expansion nozzle will have an unreasonably long length.

In the process of acceleration and overexpansion in each section, it is necessary to maintain the concentration of abrasive in the mixture in the range of 0.01-1 volume%. This is necessary in order to ensure high performance abrasive gas surface treatment by eliminating the occurrence of direct jumps in the abrasive gas stream. The same goal is also pursued by maintaining the total pressure of the flow P * not lower than the limiting value of P _ol , and the reduced gas velocity λ - not higher than the limiting λ _pr determined from the claimed relationships.

If the concentration of abrasive in the mixture is less than 0.01 vol.%, It will not be possible to ensure a sufficiently large consumption of abrasive and, accordingly, high performance sandblasting equipment. When the abrasive concentration in the mixture is more than 1 vol.% In the flow of the abrasive-gas mixture, intense direct and oblique shock waves occur due to the large difference in the velocities of the particles of the abrasive and gas [3]. As a result of large losses of the total gas pressure, it is impossible to disperse the abrasive particles to high speeds and to provide high surface treatment performance.

When processing “light” surfaces, the abrasive-gas mixture is re-expanded to a pressure below 0.6 of the ambient pressure (claim 2), the flow of the mixture is inhibited and compressed, while ensuring constant acceleration of the mass-average abrasive particles in the mixture. This allows to exclude the influx of gas from the environment into the zone of minimum pressure in the overexpansion nozzle [4].

When performing claims 1, 2 and 3 of the claims, when it is necessary to maintain the maximum acceleration of the mass-average abrasive particles, the difference in gas velocities and the mass-average abrasive particles (Δ V) is maintained in the range of 300-400 m / s, which ensures increased acceleration of the abrasive with a short length of the over-expansion nozzle. In the case of Δ V <300 m / s, it is practically impossible to disperse the abrasive particles to speeds of more than 250 m / s with a length of the over-expansion nozzle of less than 200 mm. This is especially true for large particles of abrasive larger than 500 microns.

In the case of Δ V> 400 m / s, particles of abrasive material are also almost impossible to accelerate to speeds of more than 250 m / s without additional gas heating.

Clause 4 of the formula indicates the need to ensure that the total gas pressure in the stream is not less than P _n / π _cr immediately before the abrasive-gas mixture is released, which ensures stable operation of the over-expansion nozzle and, accordingly, constant high productivity of the abrasive treatment.

According to paragraph 5 of the claims, in the boundary layer of the flow of the abrasive gas mixture before it is discharged, a liquid is supplied to the surface to be treated, sprayed around the circumference of the stream of abrasive gas stream and an abrasive gas stream surrounded by sprayed liquid is thrown onto the surface to be treated, which ensures dust removal during surface cleaning.

According to claim 6, when processing “light” and “medium” in severity of surface treatment, the overexpanded 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. Such mixing allows you to control the flow of air from the environment and significantly increase the area of the treated surface in one pass (more than 3 times), which leads to a significant increase in productivity.

The specified technical problem is also solved using a nozzle device for implementing the proposed method.

In the nozzle device according to claim 7 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, the outlet part is additionally equipped with a re-expansion nozzle coaxially with the critical section, the length of which L _per is determined according to the formula:

where d $\genfrac{}{}{0ex}{}{\text{out}}{\text{per}}$ and D $\genfrac{}{}{0ex}{}{\text{in}}{\text{per}}$ - the diameters of the outlet and inlet sections of the re-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 °, the diameter of the inlet section of the over-expansion nozzle D $\genfrac{}{}{0ex}{}{\text{in}}{\text{per}}$ determined by the formulas:

and the diameter of the outlet section of the over-expansion nozzle D $\genfrac{}{}{0ex}{}{\text{out}}{\text{per}}$ is 0.5-0.95 of the diameter of its maximum cross section D $\genfrac{}{}{0ex}{}{\text{max}}{\text{per}}$ , which is determined by the formulas:

where δ $\genfrac{}{}{0ex}{}{\text{in}}{\text{per}}$ - the thickness of the displacement layer at the entrance to the re-expansion nozzle, m;

f _cr - the area of the critical section, m ² ;

P _to - the total pressure at the inlet to the nozzle, MPa;

T _to - full temperature at the entrance to the nozzle, K;

P * _vkhper - total pressure at the entrance to the re-expansion nozzle, MPa;

T * _vkhper - full temperature at the entrance to the re-expansion nozzle, MPa;

q (λ) is the gas-dynamic function of the reduced flux density of the abrasive-gas mixture, dimensionless quantity;

δ $\genfrac{}{}{0ex}{}{\text{min}}{\text{IN}}$ - the minimum thickness of the displacement layer, m;

P * _{a min} is the total minimum pressure at the outlet of the over-expansion nozzle, MPa;

δ $\genfrac{}{}{0ex}{}{\text{min}}{\text{o}}$ , F $\genfrac{}{}{0ex}{}{\text{o}}{\text{cr}}$ , P _he are the coefficients;

δ $\genfrac{}{}{0ex}{}{\text{in}}{\text{per}}$ = 0.2 · 10 ^-3 m, δ $\genfrac{}{}{0ex}{}{\text{min}}{\text{o}}$ = 0.5 · 10 ^-3 m, F $\genfrac{}{}{0ex}{}{\text{about}}{\text{cr}}$ = 0.71 · 10 ^-4 m ² , P _he = 0.1 MPa.

The specified design of the over-expansion nozzle ensures acceleration of the abrasive-gas mixture to supersonic speeds, allows you to fully use the energy of compressed gas, significantly increase the productivity of sandblasting equipment and the surface area to be treated in one pass. In this case, the calculation of the length of the re-expansion nozzle is carried out depending on the diameters of its inlet and outlet sections, the opening angle and the diameters of the mass-average particles of the abrasive material, which eliminates the occurrence of direct pressure surges in the flow of the abrasive-gas mixture and ensures reliable high-performance operation of the device.

According to claim 8, the area of the inlet section of the over-expansion nozzle is not less than the area of the outlet section of the expanding part of the nozzle, which is necessary to exclude the formation of direct jumps and intense oblique shock waves of the seal, which lead to significant losses in the total gas pressure and, consequently, a significant decrease in productivity devices.

In addition, according to claim 9, the re-expansion nozzle is additionally provided with a cylindrical part, the diameter of which is chosen from the conditions:

F $\genfrac{}{}{0ex}{}{\text{min}}{\text{c}}$ and F $\genfrac{}{}{0ex}{}{\text{max}}{\text{c}}$ - the minimum and maximum cross-sectional areas of the cylindrical part, m ² ,

δ $\genfrac{}{}{0ex}{}{\text{max}}{\text{B}}$ - the maximum thickness of the displacement layer, m,

in the case if P * _ac <P _n / π _cr ,

and if P * _ac ≥ P _n / π _cr ,

where P * _AC is the total pressure at the outlet of the cylindrical part of the nozzle, MPa,

P _{ac min} $\genfrac{}{}{0ex}{}{\text{*}}{}$ - the minimum total pressure at the exit of the cylindrical part of the nozzle, MPa,

and the length of the cylindrical part L _C is determined from the conditions:

L $\genfrac{}{}{0ex}{}{\text{min}}{\text{c}}$ <L _c <L $\genfrac{}{}{0ex}{}{\text{max}}{\text{c}}$ ,

where l $\genfrac{}{}{0ex}{}{\text{min}}{\text{c}}$ D _n = 5,

- средний размер частиц,

- average particle size,

L $\genfrac{}{}{0ex}{}{\text{max}}{\text{c}}$ (P * _{ac min} ) is the length of the cylindrical part of the nozzle at which P * _ac = P * _{ac min} .

The nozzle device according to claim 9 is used in cases of cleaning operations on difficult to clean surfaces (firmly bonded rust, mill scale, epoxy and bitumen coatings), it provides a high degree of cleaning with high performance.

For dedusting during sandblasting according to claim 10 of the claims, a removable water collector with nozzles for supplying water is sealed on the outer surface of the re-expansion nozzle, the inner cavity of the re-expansion nozzle communicated through radial holes in the wall with the internal cavity of the collector. This allows you to enclose the flowing abrasive gas mixture in a finely divided water bell and to prevent the ingress of abrasive and dust as a result of cleaning into the surrounding atmosphere.

The nozzle device according to claim 11 is equipped with a removable ejector mounted coaxially with the ejection nozzle, 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 operating conditions of the ejector, which ensures the regulation of gas flow from the environment, increase in the area of the treated surface in one pass and, accordingly, a very high productivity on the “light” and “medium” on the complexity of processing surfaces.

The design features of the nozzle device make it possible to carry out all the necessary operations provided by the claimed method and solve the indicated technical problem - increasing productivity by eliminating direct pressure surges of the abrasive-gas mixture flow and uniformity of mixing of the abrasive with gas, as well as more complete use of the pressure energy of compressed gas and a significant increase in the area of the treated surfaces in one pass of the nozzle device.

The inventive method can only be carried out using the inventive nozzle device, which allows us to conclude that both inventions are interconnected by a single inventive concept.

The invention is illustrated as follows.

The implementation scheme of the proposed method is shown in figure 1, figure 2 presents the design of a supersonic nozzle of the inventive nozzle device according to claim 7.

Figure 3 - design of a supersonic nozzle according to claim 9 of the claims.

Figure 4 - design of a supersonic nozzle according to claim 10 of the claims.

5 is a design of a supersonic nozzle according to claim 11 of the claims.

6 is a graph for determining the operational parameters, providing a supersonic gas flow in the nozzle.

The nozzle injection device for implementing the method of abrasive gas surface treatment includes sources of compressed gas 1, a sealed tank 2, pipelines 3, 4, valve 5, a mixing chamber 6, a hose 7 with an abrasive gas mixture and a supersonic nozzle 8. Supersonic nozzle 8 includes the inlet tapering part 9, the critical section 10 with an area of F _cr , the output part 11, as well as a re-expansion nozzle 12.

The nozzle 8 may be provided with a cylindrical part 13 with a diameter D _c and made coaxially with the nozzle 8.

An ejector 14 can be installed on the output part of the over-expansion nozzle 12, which is fixed with screws 15 and is removable. On the outer surface of the re-expansion nozzle 12, a water collector 16 is sealed, equipped with nozzles 17 for supplying water. The inner cavity of the nozzle 12 by means of radial holes 18 in the wall of the nozzle 12 communicates with the inner cavity of the manifold 16. The collector 16 is removable.

The inventive method is as follows.

From the source of compressed gas 1, a smaller part (<3%) of the gas enters through the gas pipe 3 into the tank 2 with an abrasive, for example metal filings, and the main part of the gas through the gas pipe 4 enters the mixing chamber 6. The abrasive is loaded into the tank 2 through valve 5. the gas supply to the tank 2, the valve 5 is automatically closed, and when the gas pressure in the tank 2 is equal to the pressure of the gas source, the abrasive material is fed into the mixing chamber 6, where it is mixed with compressed air (gas) to obtain an abrasive gas mixture. The mixture is fed through a hose 7 to a supersonic nozzle 8.

In the nozzle 8 is acceleration of the abrasive gas mixture. In the tapering part 9 of the nozzle 8, the abrasive material is accelerated to a speed of ≈ 50 m / s. The mixture is then fed through a critical section 10c with an area of F _cr , the outlet part 11, where the abrasive gas flow expands to ambient pressure, and the abrasive accelerates. The speed of the abrasive at the outlet of the output part 11 is 100-200 m / s, depending on the particle size of the abrasive and the length of the output part.

In the case of an air atmosphere, the abrasive-gas mixture is expanded in the outlet part 11 of the nozzle 8 to a pressure of 0.1 MPa, and in the case of surface treatment under water at a depth of 10 m, the mixture is expanded to a pressure of 0.2 MPa. Moreover, the greater the depth of water, the higher pressure values (> 0.2 MPa) the expansion of the abrasive-gas mixture.

In the over-expansion nozzle 12 (if necessary 13), the abrasive-gas mixture is also expanded depending on the type of environment. In an air atmosphere, the mixture is expanded to pressures below ambient pressure (up to 0.005-0.06 MPa). In the case of using a nozzle under water at a depth of 10 m, the mixture is re-expanded to a pressure of 0.01-0.1 MPa, and the greater the depth (> 10 m), the re-expansion is carried out to higher pressure values (> 0.1 MPa).

EXAMPLE OF IMPLEMENTATION OF A METHOD IN A WATER ENVIRONMENT

As accelerating abrasive gas, air is used (k = 1.4).

The total air pressure at the inlet to the nozzle P _k was 1.3 MPa, and the total temperature T _k = 300 K. The volumetric air flow through the nozzle Q _B was 6 m ³ / min at T = 288 K and P = 0.1 MPa.

Sandblasting was carried out under water at a depth of 10 m, the ambient pressure (outside the nozzle) P _n was 0.2 MPa.

As the abrasive material used quartz sand with an average particle size d _h = 250 μm and the density of the abrasive material ρ _A = 2.7 · 10 ³ kg / m ³ .

The total pressure in the nozzle is not lower than the limiting P _ol , and the reduced flow rate λ is not higher than the reduced limiting λ _ol :

The range of change in the total pressure in the nozzle P * was 0.57-1.3 (P * / P _n = 2.85-6.5), and the range of change in the reduced velocity was λ = 1-1.7. In accordance with the schedule (Fig.6 g) the conditions were met (P *> P _CR , λ <λ _CR ) and a supersonic air flow was provided along the entire length of the nozzle.

Abrasive flow rate G _A = 0.5 G _in , where G _in - mass air flow.

G _in = Q _B · ρ _B (T _{holes, holes} P)) / 60 where ρ (T _nor P _nor) - air density under normal atmospheric conditions: ρ _a = 1.225 kg / m ^3.

Mass air flow rate G _B ≈ 0.1225 kg / s, respectively, the flow rate of abrasive material G _A ≈ 0.066 kg / s.

Numerical modeling (Program based on the PC) the flow polyfractional gas suspension of abrasive particles with the above parameters (p _k, T _c, d _h, ρ _A, G _A, g _b) showed that disperse abrasive mixture to the superficial gas velocity λ _max = 1.7, the total pressure P * decreased to a value of 1.0 MPa. Then the minimum gas pressure in the flow P _min = P * · π (λ _max ) was 0.1 MPa, where π (λ) is the gas-dynamic function.

Then, the volume concentration of abrasive material in the stream was determined during acceleration and over-expansion of the abrasive-gas mixture:

- средний объем частиц абразива,Where

- the average particle size of the abrasive,

n _h - the number of particles of abrasive per unit volume of the mixture.

The number of particles of abrasive per unit volume of the mixture was determined from the ratios:

G _A = ℵ G _B

where V _h - the average particle velocity of the abrasive (m / s),

V _In - air speed (m / s),

ρ _In - the density of air in the stream (kg / m ³ ),

F is the cross-sectional area of the stream (m ² ),

ℵ - the ratio of the mass flow of abrasive and air.

From the above ratios received:

The volume concentration of the abrasive С _{А was} calculated at the beginning of overexpansion, with maximum overexpansion of the flow and at the nozzle exit.

Numerical simulation of the flow of a multifractional gas suspension of particles made it possible to determine the values of the flow parameters P *, P, λ, V _cr , V _h , ρ _B ) in these sections and, accordingly, to determine the volume concentration of the abrasive.

1. The concentration of abrasive at the beginning of overexploitation:

With P * = 1.18 MPa, T * = 295 K, P = P _n = 0.2 MPa, λ = 1.55, V _cr = 315 m / s, V _h = 150 m / s, ρ _in ( P = P _n ) = 4.0 kg / m ³ , the value of C _A = 0.24%.

2. The concentration of the abrasive with a maximum overexpansion of the flow:

With P * = 1.0 MPa, T * = 292 K, P = P _min = 0.10 MPa, λ _max = 1.7, T = 151 K, V _cr = 313 m / s, V _h = 210 m / s, ρ _в (Р = Р _н ) ≈ 2.32 kg / m ³ , the value С _A ≈ 0.11%.

3. The concentration of abrasive at the nozzle exit:

With P * = 0.57 MPa, T * = 287 K, P = P _a = 0.22 MPa, λ = λ _a = 1.2, T = 218 K, V _cr = 310 m / s, V _h = 320 m / s, ρ _в (Р = Р _а ) = 3.6 kg / m ³ , С _A ≈ 0.078%.

Thus, in the process of acceleration and expansion of the mixture in each flow section, the concentration of abrasive in the mixture was maintained in the range of 0.01-1% (0.078% ≤ C _A ≤ 0.24%).

Acceleration abrasive gas mixture was quenched at a rate of weight average abrasive particle V = _ca 320 m / s and the gas velocity V _n = V _cr, λ _a = 310 · 1,2≈ 370 m / s.

When the pressure of the over-expansion flow was lower than 0.6 from the ambient pressure (P _min = 0.10 MPa, P _min / P _n = 0.10 / 0.2 <0.6), the mixture flow was inhibited (V _ha = 370 m / s and V _{g max} = V _cr λ _max = 530 m / s, V _ha <V _{g max)} and compressed (P _min = 0,10 MPa, P = 0.22 MPa, _and, P _min <P _a).

During gas expansion, the difference between the gas velocities and the mass average abrasive particles was maintained in the range of 300-400 m / s (V _g = V _cr λ _o = 490 m / s, V _cho = 160 m / s, Δ V = V _{g max} -V _{h max} = 330 m / s).

Immediately before the ejection of the abrasive gas mixture, the total gas pressure in the stream was not lower than the value of P _n / π _cr :

Р_н/π _кр=0,38 МПа, Р_н/π _кр<Р* _а.When P * _a = 0.57 MPa,

P _n / π _cr = 0.38 MPa, P _n / π _cr <P * _a .

EXAMPLE OF PERFORMANCE OF THE DEVICE FOR IMPLEMENTATION OF THE APPLIED DEVICE

The initial values of the parameters are the same as in the example implementation of the method.

The area of the critical part of the nozzle was determined from the ratio:

- постоянный для данного газа коэффициент, для воздуха

,Where

- constant coefficient for a given gas, for air

,

P *, T * - total pressure and total temperature of the air at the inlet to the nozzle (P * = P _to , T * = T _to ),

The nozzle device was additionally equipped with a cylindrical part (p. 7, 8, 9 of the claims). The length of the nozzle part from the critical section to the entrance to the re-expansion nozzle was equal to: L _o = 100 · d = 0.025 (m).

The maximum diameter of the expanding part of the re-expansion nozzle D $\genfrac{}{}{0ex}{}{\text{max}}{\text{per}}$ were chosen equal to the diameter of the cylindrical part of the nozzle D _c . The diameter of the cylindrical part was calculated in accordance with paragraph 9 of the claims. The value of the minimum total pressure at the exit of the cylindrical part of the nozzle P * _{ac min was} chosen equal to 0.57 MPa. Then the minimum possible area of the cylindrical part of the nozzle was (P _as > P _n / π _cr ):

Maximum possible area:

In accordance with Fig.6 λ _CR (P * _{ac min} / P _n ) = 1.85.

.According to the tables of gas-dynamic functions q (λ = 1.85) = 0.353, in this case

.

The smallest possible diameter of the cylindrical part of the nozzle:

then D $\genfrac{}{}{0ex}{}{\text{min}}{\text{c}}$ = 11.9 · 10 ^-3 (m).

The maximum possible diameter of the cylindrical part of the nozzle:

then D $\genfrac{}{}{0ex}{}{\text{max}}{\text{c}}$ = 18.6 · 10 ^-3 (m).

Due to erosion, the nozzle diameter may increase by 4-6 mm over a long time. Therefore, of the possible diameters of the cylindrical part of the nozzle, a diameter close to the minimum was chosen, namely, D _c = 12 · 10 ^-3 (m). Accordingly, the maximum diameter of the expanding part of the over-expansion nozzle was 12 · 10 ^-3 m.

In accordance with an example implementation of the method (P * = 1.18 MPa, T * = 295 K, λ = 1.55), the input section area of the over-expansion nozzle was:

.Diameter of the inlet section of the over-expansion nozzle D $\genfrac{}{}{0ex}{}{\text{in}}{\text{per}}$ determined by the formula:

.

(м), тогда D $\genfrac{}{}{0ex}{}{\text{вх}}{\text{пер}}$ =9,5· 10^-3 (м).Numerical simulation of the flow of a polyfractional gas suspension of abrasive particles made it possible to determine the value of the thickness of the displacement layer in each flow section:

(m), then D $\genfrac{}{}{0ex}{}{\text{in}}{\text{per}}$ = 9.5 · 10 ^-3 (m).

.In accordance with paragraph 7 of the claims, the length of the conical part of the re-expansion nozzle was:

.

The angle α was chosen equal to 5 °. Then: L _per = 29 · 10 ^-3 (m).

The length of the cylindrical part L _C selected from the conditions:

L $\genfrac{}{}{0ex}{}{\text{min}}{\text{c}}$ <L _c <L $\genfrac{}{}{0ex}{}{\text{max}}{\text{c}}$ , L $\genfrac{}{}{0ex}{}{\text{min}}{\text{c}}$ = 5D _C = 60 · 10-3 (m),

Numerical simulation of the flow of a multifractional gas suspension of abrasive particles made it possible to determine the length of the cylindrical part of the nozzle at which P * _ac = P * _{ac min} = 0.57 MPa. This length was equal to 187 · 10 ^-3 m, and

L _max = min {300 · 10 ^-3 , 187 · 10 ^-3 } = 187 · 10 ^-3 (m).

The length L of the cylindrical part of the nozzle chosen equal to 180 _q · 10 ^-3 m, as 60 · 10 ^-3 <180 · 10 ^-3 <187 · 10 ^-3 .

Sources of information

1. Reference. Paintwork in mechanical engineering. M .: "Engineering", 1974.

2. RF patent No. 2137593, 24 C 1/00, 5/04, 1999.

3. V. M. Boyko, V. P. Kiselev, S. P. Kiselev and others. On the interaction of a shock wave with a cloud of particles, FGV, 1996, v. 32, No. 1.

4. L.E. Sternin. The basics of gas dynamics. M .: Publishing House of the Moscow Aviation Institute, 1995, p.105, Fig. 2.5.

5. G.N. Abramovich. Applied gas dynamics. M .: Nauka, 1976.

Claims (11)

1. The method of abrasive gas surface treatment, including the supply of compressed gas, its subsequent acceleration to supersonic speeds, expanding, mixing the abrasive with gas and ejecting the abrasive gas mixture onto the surface to be treated, characterized in that the gas 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 the average speed reaches ce abrasive particles equal 0,7-0,95 gas velocity, wherein during acceleration and expansion of the mixture in each section of the flow is maintained concentration of the abrasive in admixture about 0.01-1. % total pressure

flow not lower than the limit

, and the reduced gas velocity

- not higher than the maximum reduced speed

, and

, and

determined from the relations

, Where

- environmental pressure, MPa;

- gas adiabat index (dimensionless quantity). 2. The method according to claim 1, characterized in that when the flow pressure of the abrasive-gas mixture is reduced below 0.6 from the ambient pressure, the mixture flow is inhibited and compressed, providing constant acceleration of the middle particles of the abrasive in the mixture. 3. The method according to claim 1 or 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 according to any one of claims 1 to 3, characterized in that immediately before the release of the abrasive gas mixture, the total gas pressure in the stream is not lower than the value

, and the gas-dynamic function

determined by the formula

. 5. The method according to claim 1 or 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 according to any one of 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 in each section of their mixing zone. 7. A nozzle device for abrasive gas surface treatment, comprising a mixing chamber and a supersonic nozzle with an inlet tapering part, a critical section and an outlet part, characterized in that the outlet part of the nozzle is additionally provided with a re-expansion nozzle coaxially made with a critical section, the length of which

determined by the formula

, Where

and

- diameters of the outlet and inlet sections of the over-expansion nozzle;

- the opening angle of the over-expansion nozzle; the length of the nozzle part from the critical section to the inlet of the re-expansion nozzle is 80-120 diameters of the mass-average abrasive particles, the opening angle

is 3-30 °, the diameter of the inlet section of the over-expansion nozzle

determined by the formulas

,

, and the diameter of the outlet section of the over-expansion nozzle

is 0.5-0.95 in diameter of its maximum section

which is determined by the formulas

,

, Where

- the thickness of the displacement layer at the entrance to the re-expansion nozzle, m;

- critical section area, m ² ;

- total pressure at the inlet to the nozzle, MPa;

- full temperature at the entrance to the nozzle, K;

- total pressure at the inlet to the oversize nozzle, MPa;

- full temperature at the entrance to the oversize nozzle, MPa;

- gas-dynamic function of the reduced flux density of the abrasive-gas mixture, dimensionless quantity;

- the minimum thickness of the displacement layer, m;

- total minimum pressure at the outlet of the over-expansion nozzle, MPa;

- coefficients;

= 0.2 · 10 ^-3 m,

= 0.5 · 10 ^-3 m,

= 0.71 · 10 ^-4 m ² ,

= 0.1 MPa. 8. The 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 device according to claim 7 or 8, characterized in that the re-expansion nozzle is additionally provided with a cylindrical part, the diameter of which is chosen from the conditions:

,

,

,

,

Where

= 1.5 · 10 ^-3 , m;

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 ;

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

,

,

, and in case

,

,

where

- total pressure at the exit of the cylindrical part of the nozzle, MPa;

- minimum total pressure at the exit of the cylindrical part of the nozzle, MPa; moreover, the length of the cylindrical part

determined from the conditions:

,

= 5

,

Where

- average particle size, m;

- the length of the cylindrical part of the nozzle (m) at which

. 10. A device according to any one of claims 7 to 9, characterized in that a removable water collector with water supply nozzles is sealed to the outer surface of the oversizing nozzle, the inner cavity of the oversizing nozzle communicated through radial holes in the wall with the inner cavity of the manifold. 11. The device according to any one of 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 operating conditions ejector.

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