Method and design for a quiet abrasive jet nozzle for high productivity

Abstract

A noise-reduced abrasive blasting assembly and system are described. The new assembly and system include a standard blasting tube, an accelerator tube, a coupling, and a nozzle. The improved abrasive blasting system maintains abrasive particle velocity while reducing exit gas velocity and, therefore, reducing sound generation. This is accomplished by an acceleration section having a reduced inner diameter and sufficient length to provide the necessary abrasive particle velocity. The new system maintains the productivity and efficiency of a conventional abrasive blasting system, but greatly reduces noise generation and reduces operator fatigue due to the lower weight of the load-bearing portion of the system.

Description

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was supported in part by the United States Government ("Government") under Contract FA8222-14-M-0006 with the Department of the Air Force. This invention was also supported in part by the Government under Contract N68335-17-C-0581 with the Office of Naval Research. Accordingly, the Government has certain rights in this invention. Technical Field

[0003] The present invention relates to apparatus and methods for abrasive blasting. More particularly, the present invention describes a noise reducing abrasive blasting assembly and system and methods of constructing the same. Background Art

[0004] Blasting operations for removing paint and surface coatings are essential to the U.S. Armed Forces' ships, aircraft, and land vehicles, as well as to industrial vehicles and machinery. But these operations frequently expose maintenance personnel to sound pressure levels (SPLs) of 119 dB and greater, which presents serious health, productivity, and compliance issues for blasting operators. Many blasting operators suffer hearing loss as a direct result of long-term exposure to blasting noise. Personal protective equipment (PPE) such as earplugs and earmuffs can reduce direct risks, but can result in loss of situational awareness and still not meet OSHA level requirements for noise exposure limits. The OSHA noise standard (29 CFR 1910.95) limits workers' permissible noise exposure limits (PELs) to an 8-hour time-weighted average of 90 dBA, and does not assume that better hearing protection will reduce workers' noise exposure. Only by reducing sound at its source can workers experience noise as harmless.

[0005] Figure 1 Shown in FIG. 1 is a conventional, prior art supersonic abrasive blasting system 10 that includes a compressor 12, a compressor tube 14, and an abrasive tank 16 that contains abrasive media 18. An abrasive metering valve 20 controls the rate at which the abrasive media 18 is released into a standard blasting tube 22. The released media 18 travels through the blasting tube 22 to a claw coupling 24, where the media 18 then passes through a supersonic converging-diverging nozzle 26 where the media 18 is released into the environment at supersonic speeds and with considerable noise.

[0006] Figure 2Detail of a prior art convergent-divergent nozzle 26 is shown in cross section in FIG. The nozzle 26 includes a barrel 28 having a bore 30 having a converging bore portion 32, a throat 34, and a diverging bore portion 36. Gas mixed with abrasive media 18 is compressed as it travels through the converging portion 32 and then dispersed through the diverging portion 36, causing particles of the media 18 to accelerate within and flow out of the diverging portion 36 of the nozzle 26.

[0007] Conventional abrasive blasting system setups use a single 1 inch ID blast tube 22 and a convergent-divergent supersonic nozzle attachment 26. The abrasive blasting media in these setups undergoes the majority of its acceleration over the short distance between entering the nozzle 26 and subsequently exiting the nozzle 26.

[0008] As demonstrated in Settles' paper (Settles G., A scientific view of the productivity of abrasive blasting nozzle, 1996), the particles are accelerated from a relatively low velocity before the nozzle to a higher velocity as they flow through the diffuser and outlet of the nozzle. This minimizes wear in the tube, especially for highly abrasive media. Figure 3 This behavior is shown in a graph reproduced from Settles' paper in which the predicted and measured velocities through a Laval nozzle are shown. As shown, throughout the nozzle, the particle velocity is consistently well below 50% of the gas velocity.

[0009] like Figure 1 and Figure 2 Currently available abrasive blasting systems, such as the abrasive blasting system shown in , generate excessive noise that exceeds the levels set by occupational safety organizations for workplace noise, and therefore require the use of personal protective equipment to protect hearing and limit the operator's exposure to such noise. Therefore, there is a need for an abrasive blasting system that generates less noise, thereby reducing noise-induced hearing loss and / or tinnitus and improving situational awareness in noisy operating environments, while the system also exhibits equivalent productivity and efficiency.

[0010] like Figure 1 and Figure 2 The currently available abrasive blasting systems of the abrasive blasting system shown in are large and heavy, causing stress and fatigue to the user. Therefore, there is a need for a smaller and lighter abrasive blasting system for ease of use and extended use time. Summary of the invention

[0011] These and other objects are achieved in the noise-reducing abrasive blasting assembly and system of the present invention. The new assembly and system provide effective abrasive blasting with significantly less noise than the prior art while reducing ergonomic stress from the size and weight of the load-bearing portion of the system.

[0012] New assemblies and systems provide greater length in the tube, nozzle, or both over which particles are accelerated prior to exit, thereby bringing the velocity of the particles closer to that of the gas at the exit, and enabling the use of lower gas exit velocities to reduce the noise of the system while maintaining or even increasing particle velocity and, therefore, productivity. While the amount of blasting time a blast operator is allowed is related to noise exposure (due to, for example, regulatory compliance issues), nozzle productivity, which is related to the velocity of the abrasive leaving the nozzle, is equally of concern in abrasive blasting. Higher velocities mean that a blast operator can spend less time blasting per square meter. Less time translates into higher worker productivity and lower operating costs.

[0013] In some embodiments, the new assembly and system include a standard jet tube, a novel accelerator tube section, a coupling including a transition coupling, and a nozzle. The improved jet system maintains the desired abrasive particle velocity while reducing the outlet gas velocity and thus reducing sound generation. This is achieved by incorporating a straight acceleration section that is not present in the prior art jet systems, which has a sufficient length to provide the necessary abrasive particle velocity. The new system maintains the productivity and efficiency of conventional abrasive jet systems, but greatly reduces noise generation and reduces operator fatigue due to the lower weight of the load-bearing portion of the system.

[0014] One aspect of the present invention is an abrasive blasting apparatus that generates significantly less noise than conventional supersonic abrasive blasting systems while exhibiting equal or greater efficiency and blasting results when compared to prior art supersonic abrasive blasting apparatus.

[0015]

[0013] Another aspect of the present invention is an abrasive blasting apparatus having a smaller and lighter load-bearing portion than conventional supersonic abrasive blasting systems while exhibiting equal or greater efficiency and results.

[0016] Another aspect of the present invention is an abrasive blasting system that utilizes a section of accelerator tube having a smaller inner diameter than a conventional standard blasting tube, the additional length of accelerator tube being used to accelerate the media particles to a desired velocity before the particles enter the blasting nozzle.

[0017] Another aspect of the present invention is the use of a transition piece to provide a step-down in the inner diameter of the media path from the standard injection tube to the accelerator tube.

[0018] Another aspect of the present invention is an abrasive blasting system that utilizes a nozzle having a straight section following a diverging section to accelerate media particles to a desired velocity before the particles exit the blasting nozzle.

[0019] Another aspect of the invention is that as energy is transferred to the particles, the velocity of the air exiting the straight section after the diverging section decreases, thereby causing the nozzle to produce less sound.

[0020] In some embodiments, the new assembly and system include a tube and nozzle assembly having: a first portion having a first inner diameter; a contracting portion having an inner diameter smaller than the first inner diameter; a converging portion connecting the first portion to the contracting portion and having a converging inner diameter; and a straight portion located downstream of the contracting portion, the straight portion having a constant inner diameter smaller than the inner diameter of the first portion. The straight portion has a length such that when the sandblasting nozzle assembly is operated with a predetermined gas / particle mixture and a predetermined pressure, the velocity of the gas leaving the jet nozzle assembly is reduced by at least 30% relative to the jet nozzle assembly without the straight portion. Any noise reduction that does not affect the productivity of the system or make the nozzle bulky or difficult to control is desirable. A reduction of only 7% in the outlet gas velocity results in a 3dB reduction in noise, which is a significant improvement. In various embodiments, the length of the straight portion is effective to reduce the outlet gas velocity by 7% to 43%, in some embodiments by 30% to 40%, and in some embodiments by 35% when operating with a predetermined gas / particle mixture and a predetermined pressure. In operation, fluid flows sequentially through the first portion, the converging portion, the contracting portion, and the straight portion.

[0021] In some embodiments, the contraction, convergence and straight portions are all parts of the nozzle, which may also have a diffusion portion connecting the contraction to the straight portion. The convergence, contraction, diffusion and straight portions may together form a nozzle, and the contraction may be the throat of the nozzle. The length of the straight portion may be at least 2 / 10 of the inner diameter of the straight portion and less than 10 times the inner diameter of the straight portion. The straight portion has a constant inner diameter in some embodiments, and has a slightly diffuse profile or a slightly convergent profile (the inner diameter changes by 5% or less over the length of the straight portion) in other embodiments. When calculating the appropriate length for the straight portion, a slightly diffuse or convergent profile may be considered to achieve the desired flow in the straight portion (i.e., a Mach number of 1 at or near the outlet of the straight portion). In some embodiments, the straight portion has at least a portion with an alternating diameter change, such as a change of 1 / 8 inch, thereby producing a ridge, which increases the surface friction on the inside of the portion and affects the required length (which can be incorporated into the friction calculation when determining the length of the straight portion), but may reduce the particle velocity somewhat. For a straight section with a variable inner diameter, references herein to the diameter of the straight section may be considered references to the average inner diameter of the straight section or to the inner diameter of the straight section at its outlet. The nozzle may be a No. 6 nozzle. In other embodiments, the nozzle may be a nozzle of any diameter, including but not limited to a No. 4 nozzle, a No. 5 nozzle, a No. 7 nozzle, a No. 9 nozzle, and a No. 10 nozzle.

[0022] In some embodiments, the inner diameter of the straight portion is selected to produce a predetermined "hot spot" diameter for abrasive action.

[0023] In other embodiments, the inner diameter of the straight portion is selected to match the outlet of the diverging portion.

[0024] In some embodiments, the noise reduction abrasive jet nozzle assembly further includes a media tank, an abrasive media, and a compressed gas carrying the abrasive media, and the tube and nozzle assembly includes one or more tube sections.

[0025] The present invention achieves sufficient abrasive particle velocity in a gas stream with a lower exit velocity through a greater acceleration distance, thereby reducing the nozzle generated noise experienced from the supersonic jet nozzle. The jetting production rate can be adjusted by adjusting the abrasive mass flow rate.

[0026] At least one embodiment of the present invention is a high-productivity quiet abrasive nozzle, the nozzle comprising: a converging portion having a converging inner diameter; a throat connected to the converging portion; a diverging portion connected to the throat; and a straight portion connected to the diverging portion and immediately after the diverging portion. The straight portion has a length such that, assuming that both jet nozzles are operated with the same predetermined gas-particle mixture and predetermined pressure, the velocity at which the gas leaves the jet nozzle is reduced by at least 30% relative to the same jet nozzle with the straight portion removed. In addition, in operation of the high-productivity quiet abrasive nozzle, the fluid flows sequentially through the converging portion, the throat, the diverging portion, and the straight portion. In a preferred embodiment, the fluid flows directly from the converging portion to the throat, to the diverging portion, to the straight portion, and to the exterior of the nozzle (atmosphere / environment) without any other intermediate portions.

[0027] In some embodiments, the inner diameter of the straight portion is less than the maximum inner diameter of the converging portion. In some embodiments, the straight portion has a constant inner diameter, and in other embodiments, the inner diameter of the straight portion may vary by up to 5% over the length of the straight portion.

[0028] In certain embodiments, the length of the straight portion is at least two tenths of the inner diameter of the straight portion. In other embodiments, the length of the straight portion is less than ten times the inner diameter of the straight portion. In other embodiments, the length of the straight portion is between 1 inch and 10 inches. In yet another embodiment, the length of the straight portion is 2.5 inches.

[0029] In some embodiments, the nozzle is configured such that, for a predetermined gas to particle mixture and a predetermined pressure, a supersonic flow of gas is isolated to the interior of the nozzle and the supersonic gas flow accelerates the abrasive particles in the straight portion.

[0030] In some embodiments, the nozzle is further configured such that, for a predetermined gas and particle mixture and a predetermined pressure, the gas Mach number at the straight section exit is lower than the gas Mach number at the diverging section exit, thereby reducing operating noise.

[0031] In some embodiments, the nozzle is further configured such that, for a predetermined gas and particle mixture and a predetermined pressure, the gas Mach number decreases from a gas Mach number greater than 1 at the exit of the diverging section to a gas Mach number of 1 at the exit of the straight section.

[0032] In at least one embodiment of the present invention, the straight portion is configured to be attached to and removed from the diffusion portion. Some embodiments also include one or more additional straight portions, which are configured to be attached to and removed from the diffusion portion. The straight portion and the one or more additional straight portions can each have different lengths and / or different inner diameters. In some embodiments, each of the one or more additional straight portions has the following length: the length of the one or more additional straight portions is such that when the jet nozzle is operated with different predetermined gas and particle mixtures and predetermined pressures, the speed at which the gas leaves the jet nozzle is reduced by at least 30% relative to the jet nozzle in the case where the straight portion is removed. In some embodiments, one or more of the straight portions can be configured to be attached to each other so that the total length of the straight portion can be quickly modified by attaching or removing such a straight portion.

[0033] In some embodiments, the straight portion is cylindrical in shape.

[0034] In some embodiments, the nozzle is a No. 4 nozzle, a No. 5 nozzle, a No. 6 nozzle, a No. 7 nozzle, or a No. 8 nozzle. In some embodiments, the nozzle is made of a material selected from the group consisting of tungsten carbide, silicon carbide, boron carbide, acrylic, ceramic, stainless steel, hardened steel, aluminum, or a combination thereof. In yet another embodiment, the nozzle further comprises at least one protective grip.

[0035] Some embodiments of the present invention also include a fluid flowing through the diverging section with a Mach number greater than 1 at an exit from the diverging section to the straight section.

[0036] Some embodiments of the present invention further include a fluid flowing through the straight portion and having a Mach number of 1 at an exit of the straight portion.

[0037] Some embodiments of the present invention include a plurality of abrasive particles in a supersonic fluid flow inside a nozzle, the supersonic fluid flow experiencing a normal shock wave in a straight portion.

[0038] In some embodiments, the length of the straight portion is such that the jet nozzle has a noise level of 90 dbA or less when operating with a predetermined gas and particle mixture and a predetermined pressure. In other embodiments, the length of the straight portion is such that when the jet nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the jet nozzle has a noise level reduced by 3 dBA or more compared to a jet nozzle without the straight portion. In other embodiments, the length of the straight portion is such that when the jet nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the jet nozzle has a noise level reduced by 6 dBA or more compared to a sandblasting nozzle without the straight portion.

[0039] In some embodiments, the length L of the straight portion is at least L * , the L * As given by the following equation:

[0040]

[0041] where, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight portion, M is the Mach number of the fluid at the inlet of the straight portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

[0042] In some embodiments, the length L of the straight portion is adjusted according to the ratio of the back pressure to the outlet pressure. * , where L * Given by the following equation:

[0043]

[0044] where, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight portion, M is the Mach number of the fluid at the inlet of the straight portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow. In other words, L * It can be calculated according to the above equation, and then L can be calculated according to L * Adjustments are made to account for situations where the ratio of back pressure to outlet pressure is not 1.

[0045] The present invention, in its various embodiments, also includes a method for manufacturing a high-productivity quiet abrasive jet nozzle, such as, for example, the high-productivity quiet jet nozzle described above in this article, which includes: a converging portion having a converging inner diameter; a throat connected to the converging portion; a diverging portion connected to the throat; and a straight portion connected to the diverging portion, wherein the straight portion has the following length: the length of the straight portion is such that, assuming that both jet nozzles are operated with the same predetermined gas and particle mixture and predetermined pressure, the velocity at which the gas leaves the jet nozzle is reduced by at least 30% relative to the same jet nozzle with the straight portion removed; and wherein, in operation of the nozzle, the fluid flows through the converging portion, throat, diverging portion and straight portion in sequence. The method includes: determining, for a predetermined mixture of gas and abrasive particles and a predetermined pressure, a minimum length of the straight section required, the minimum length being the length that produces a Mach number of 1 for the gas at or within an inner diameter of the straight section prior to exiting the straight section; and manufacturing a nozzle having a straight section having a length equal to or greater than the minimum length.

[0046] In some embodiments, the method further includes: determining an optimal length of the straight portion so that the gas Mach number decreases from a peak at a first point, i.e., at the end of the diverging portion, before the exit of the straight portion to a Mach number of 1 at a second point at a length equal to or within a length equal to the inner diameter of the straight portion without entering subsonic speed between the first point and the second point; and manufacturing a nozzle having a straight portion with the optimal length.

[0047] In some embodiments, determining the optimal length includes analyzing the effect of friction from the walls of the straight portion and / or analyzing the effect of the plurality of abrasive particles on reducing the air flow velocity in the straight portion.

[0048] In some embodiments, the method further comprises: adjusting the length of the straight portion according to a particular operating condition to determine a length that produces a desired combination of sound reduction and productivity; and manufacturing a nozzle having the length.

[0049] In some embodiments, the method further comprises: repeatedly computer simulating the high productivity quiet abrasive jet nozzle described herein above over a range of straight portion lengths to find a length having a desired combination of sound reduction and productivity; and manufacturing a nozzle having that length.

[0050] The present invention, in its various embodiments, further includes a nozzle attachment for high-productivity quiet abrasive jetting, the nozzle attachment comprising a straight tubular portion adapted to be connected to the outlet of a sandblasting nozzle. The straight tubular portion has a length such that when the abrasive jet nozzle is operated with a predetermined mixture of gas and particles and a predetermined pressure, the velocity of the gas leaving the abrasive jet nozzle to which the straight tubular portion is attached is reduced by at least 30% relative to the abrasive jet nozzle to which the straight tubular portion is not connected. In a preferred embodiment, the straight tubular portion has a constant inner diameter along its entire length. In some embodiments, the inner diameter of the straight tubular portion may vary by up to 5% over its length. In a preferred embodiment, the inner diameter of the straight tubular portion (particularly at the inlet) is arranged to match the inner diameter at the outlet of a given abrasive jet nozzle or a group of abrasive jet nozzles with which the straight tubular portion is to be used. In a preferred embodiment, the straight tubular portion has no diverging or converging portions or attachments, and when the nozzle attachment is mounted on the abrasive jet nozzle, the fluid flow goes directly from the diverging portion of the nozzle into the straight tubular portion nozzle attachment and from the straight tubular portion directly into the atmosphere / environment (e.g., toward the target surface for abrasive jetting). Similarly, for embodiments in which the straight portion is embedded in the end of the abrasive jet nozzle, such as the embodiments described above, the fluid can flow directly from the diverging portion into the straight portion and from the straight portion into the atmosphere / environment without any intermediate portions.

[0051] In at least one aspect of the nozzle attachment, the abrasive jet nozzle is a No. 4, No. 5, No. 6, No. 7, or No. 8. The numerical rating of the nozzle (No. 6, No. 8, etc.) is a well-known rating measurement based on the orifice size (inner diameter at the exit).

[0052] In some embodiments, the nozzle attachment further comprises a fixture for connecting the straight tubular portion to the abrasive jet nozzle.

[0053] In some embodiments, the nozzle attachment further includes a fixture embedded in the straight tubular portion to help connect the straight tubular portion to the abrasive jet nozzle.

[0054] In further aspects of the nozzle attachment, the inner diameter of the straight tubular portion is less than the maximum inner diameter of the converging portion of the abrasive jet nozzle.

[0055] In other aspects of the nozzle attachment, the straight tubular portion is configured such that: for a predetermined gas and particle mixture and a predetermined pressure, when the straight tubular portion is connected to the abrasive jet nozzle, the supersonic flow of gas does not continue beyond the outlet of the straight tubular portion, and the supersonic gas flow accelerates the abrasive particles in the straight tubular portion.

[0056] In other aspects of the nozzle attachment, the straight tubular portion is configured such that: when the straight tubular portion is connected to the abrasive jet nozzle, for a predetermined gas and particle mixture and pressure, the gas Mach number at the straight tubular portion outlet is lower than at the divergent portion outlet of the sandblasting nozzle, thereby reducing operating noise.

[0057] In another aspect of the nozzle attachment, the straight tubular portion is configured such that: when the straight tubular portion is connected to the sandblasting nozzle, for a predetermined gas and particle mixture and a predetermined pressure, the gas Mach number is reduced from a gas Mach number greater than 1 at the outlet of the diverging portion of the sandblasting nozzle to a gas Mach number of 1 at the outlet of the straight portion.

[0058] In other aspects of the nozzle attachment, the length of the straight tubular portion is at least two tenths of the diameter of the straight tubular portion. In some embodiments, the length of the straight tubular portion is less than 10 times the diameter of the straight tubular portion. In other embodiments, the length of the straight tubular portion is between 1 inch and 10 inches. In other embodiments, the length of the straight tubular portion is 2.5 inches.

[0059] In other aspects of the nozzle attachment, the straight tubular portion is cylindrical in shape. In some embodiments, the straight tubular portion is made of a material selected from the group consisting of tungsten carbide, silicon carbide, boron carbide, acrylic, ceramic, stainless steel, hardened steel, aluminum, or combinations thereof.

[0060] In another aspect of the nozzle attachment, the length of the straight tubular portion is such that: when the straight tubular portion is connected to the abrasive jet nozzle, the jet nozzle has a noise level of 90 dBA or less when operating with a predetermined gas and particle mixture and a predetermined pressure. In another aspect of the nozzle embodiment, the length of the straight tubular portion is such that: when the straight tubular portion is connected to the abrasive jet nozzle, when the jet nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the noise level of the sandblasting nozzle is reduced by 3 dBA or more compared to a jet nozzle without the straight tubular portion. In another aspect of the nozzle embodiment, the length of the straight tubular portion is such that: when the straight tubular portion is connected to the abrasive jet nozzle, when the jet nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the noise level of the sandblasting nozzle is reduced by 6 dBA or more compared to a sandblasting nozzle without the straight tubular portion.

[0061] Other aspects of the nozzle attachment have a straight tubular portion of length L, wherein L is at least L * , L * As given by the following equation:

[0062]

[0063] Wherein, in the case where the straight tubular section is connected to the sandblasting nozzle, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight tubular section, M is the Mach number of the fluid at the inlet of the straight section, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

[0064] Some aspects of the nozzle attachment have a straight tubular portion having a length L, wherein L is adjusted based on at least a ratio of back pressure to outlet pressure. * , where L * Given by the following equation:

[0065]

[0066] Wherein, D is the diameter of the straight tubular section when it is connected to the sandblasting nozzle, for a predetermined mixture of gas and abrasive particles, M is the Mach number of the fluid at the inlet of the straight section, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

[0067] The present invention, in its various embodiments, also includes a method for manufacturing a nozzle attachment as described herein above to reduce the noise of an attached abrasive jet nozzle without reducing nozzle productivity. The method includes: determining the minimum length required for the nozzle attachment as described herein above for a predetermined mixture of gas and abrasive particles and a predetermined pressure, the minimum length producing a Mach number of 1 for the gas at or within a straight tubular portion inner diameter prior to the outlet of the straight portion; and manufacturing a straight tubular portion having a length equal to or greater than the minimum length.

[0068] In some embodiments, the method for manufacturing the nozzle attachment described above also includes: determining the optimal length of the straight tubular portion of the nozzle attachment described above so that the gas Mach number decreases from a peak at a first point, i.e., at the end of the diverging portion of the connected sandblasting nozzle, before the outlet of the straight tubular portion to a Mach number of 1 at a length equal to the inner diameter of the straight tubular portion or at a second point within a length equal to the inner diameter of the straight tubular portion, without entering subsonic speed between the first point and the second point; and manufacturing the straight tubular portion having the optimal length.

[0069] In some embodiments, determining the optimal length includes analyzing the effect of friction from the wall of the straight tubular portion and / or analyzing the effect of the plurality of abrasive particles on reducing the velocity of the gas flow in the straight tubular portion.

[0070] In some embodiments, the method for manufacturing the nozzle attachment described herein further includes: adjusting the length of the straight tubular portion according to a specific operating state to determine a length that produces a desired combination of sound reduction and productivity; and manufacturing the straight tubular portion having this length.

[0071] In some embodiments, the method for manufacturing the nozzle attachment described above also includes: repeatedly performing computer simulations on the straight tubular portion of the nozzle attachment described above within a range of straight tubular portion lengths to find a length that has a desired combination of sound reduction and productivity; and manufacturing the straight tubular portion having this length.

[0072] Generally, any known abrasive jet nozzle can be adjusted to a nozzle according to an embodiment of the present invention. For example, an existing nozzle No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8, No. 9, No. 10, No. 11 or No. 12 can be adjusted to have a straight portion at the end of the diffuser portion of the nozzle, as described herein, to implement an embodiment of the present invention. Similarly, a nozzle attachment according to an embodiment of the present invention can be adapted to be attached to any known abrasive jet nozzle. When the nozzle attachment is mounted on an existing nozzle, the assembly as a whole (i.e., the existing nozzle combined with the attached nozzle attachment) can be regarded as a high-productivity quiet abrasive jet nozzle. In addition, abrasive jet nozzles and nozzle attachments according to embodiments of the present invention can be suitable for a variety of applications and a variety of operating conditions, including pressure, particle load, type of abrasive particles and fluid, nozzle material, etc. In particular, any given nozzle or nozzle attachment according to an embodiment of the present invention can be adapted to: for a predetermined mixture of gas and particles and a predetermined pressure or for a predetermined range of mixtures of gas and particles and a predetermined pressure, a certain result or a result within a certain range is achieved. Nozzles or nozzle attachments according to embodiments of the present invention may, for example, be adapted to achieve a noise reduction of at least 3 dB relative to prior art abrasive jet nozzles for a predetermined mixture of gas and particles and a predetermined pressure, including a nozzle pressure between 20 psi and 200 psi and a particle load of an abrasive consumption rate of 50 pounds to 10,000 pounds per hour, or any range of pressures and particle loads within these ranges. For example, such conditions are suitable for nozzles No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8, No. 9, No. 10, No. 11, and No. 12. The particle load may be determined in part by what type of roughness profile the jetter wants to have and the jet pressure used. The predetermined mixture of gas and particles may, for example, be compressed air with sand and / or any other abrasive particles. The phrase "predetermined mixture of gas and particles and predetermined pressure" may include gas type, particle type, nozzle pressure, back pressure, and particle load. Back pressure is typically atmospheric pressure, and may be assumed to be atmospheric pressure if not specifically mentioned. For example, compressed air with sand particles, a nozzle pressure of 100 psi, and a particle loading of 1,000 lbs / hr is an exemplary predetermined gas to particle mixture and predetermined pressure.

[0073] Additional embodiments of the present invention include a high productivity quiet abrasive jet nozzle assembly including a high productivity quiet abrasive jet nozzle as described herein above.

[0074] The principles described in the present invention can be applied to applications other than abrasive jetting where the sound level of the fluid flow is problematic, even in applications where a nozzle is not used. In particular, in applications where supersonic fluid flow results in high noise levels, passing the fluid flow through a straight tubular portion before entering the atmosphere / environment can reduce the velocity of the fluid. In the case where the straight tubular portion is sized to induce shock waves when the fluid is discharged into the environment or just before it is discharged into the environment, the noise level is particularly reduced. Even in non-supersonic flows, the straight tubular portion reduces the velocity and noise level. The use of a straight tubular portion is particularly useful in applications where the fluid is used to accelerate particles or other objects in the fluid flow that are at a speed lower than the fluid, because the straight portion can reduce the fluid velocity while increasing the velocity of the entrained object, thereby reducing the noise level without sacrificing productivity.

[0075] Therefore, based on the above and continuing description, the present invention in its various embodiments may include one or more of the following features in any non-mutually exclusive combination:

[0076] A high production rate quiet abrasive jet nozzle having a converging portion with a converging inner diameter;

[0077] A high production rate quiet abrasive jet nozzle having a throat connected to a converging section;

[0078] A high production rate quiet sandblasting nozzle having a diffuser connected to a throat;

[0079] A high production rate, quiet abrasive jet nozzle having a straight section connected to and immediately after a diffuser;

[0080] A high production rate quiet abrasive blasting nozzle having a straight section having a length such that when the blasting nozzle is operated with a predetermined gas to particle mixture and a predetermined pressure, the velocity of the gas exiting the blasting nozzle is reduced by at least 30% relative to a blasting nozzle with the straight section removed;

[0081] A high production rate quiet abrasive jet nozzle wherein, in operation, the fluid flows sequentially through a converging section, a throat, a diverging section and a straight section;

[0082] A high production rate quiet abrasive jet nozzle wherein the diameter of the straight section is smaller than the maximum inner diameter of the diverging section;

[0083] A high production rate quiet abrasive jet nozzle wherein the nozzle is configured such that: for a predetermined gas to particle mixture and a predetermined pressure, a supersonic flow of gas is isolated to the interior of the nozzle and the supersonic gas flow accelerates the abrasive particles in the straight section;

[0084] A high production rate quiet abrasive jet nozzle wherein the nozzle is configured such that: for a predetermined gas to particle mixture and a predetermined pressure, the gas Mach number at the straight section exit is lower than the gas Mach number at the diverging section exit, thereby reducing operating noise;

[0085] A high production rate quiet abrasive jet nozzle wherein the nozzle is configured such that: for a predetermined gas to particle mixture and a predetermined pressure, the gas Mach number decreases from a gas Mach number greater than 1 at the diverging section exit to a gas Mach number of 1 at the straight section exit;

[0086] A high production rate quiet abrasive jet nozzle wherein the length of the straight portion is at least two tenths of the inner diameter of the straight portion;

[0087] A high production rate quiet abrasive jet nozzle wherein the length of the straight portion is less than ten times the inner diameter of the straight portion;

[0088] A high production quiet abrasive jet nozzle wherein the length of the straight portion is between 1 inch and 10 inches;

[0089] A high production quiet abrasive jet nozzle where the straight section length is 2.5 inches;

[0090] A high production quiet abrasive jet nozzle wherein the straight section is configured to be attached to and detached from the diffuser section;

[0091] A high productivity quiet abrasive jet nozzle further comprising one or more additional straight sections configured to be attached to and detached from a diffuser section, wherein the straight section and the one or more additional straight sections have different lengths and / or different inner diameters;

[0092] A high production rate quiet abrasive jet nozzle, wherein each of the one or more additional straight sections has a length such that when the jet nozzle is operated with a predetermined gas to particle mixture and pressure, the velocity of the gas exiting the jet nozzle is reduced by at least 30% relative to the jet nozzle with the straight sections removed;

[0093] A high production rate quiet abrasive jet nozzle, wherein the straight portion is cylindrical in shape;

[0094] A high production rate quiet abrasive jet nozzle, wherein the nozzle is a No. 4 nozzle, a No. 5 nozzle, a No. 6 nozzle, a No. 7 nozzle or a No. 8 nozzle;

[0095] A high production rate quiet abrasive jet nozzle, wherein the nozzle is made of a material selected from the group consisting of tungsten carbide, silicon carbide, boron carbide, acrylic, ceramic, stainless steel, hardened steel, aluminum, or a combination thereof;

[0096] A high production rate quiet abrasive jet nozzle, wherein the nozzle further comprises at least one protective grip;

[0097] A high production rate quiet abrasive jet nozzle further comprising a fluid flowing through a diverging section and having a Mach number greater than 1 at an exit from the diverging section to a straight section;

[0098] A high production rate quiet abrasive jet nozzle further comprising a fluid flowing through a diverging section and having a Mach number of 1 at the exit of the straight section;

[0099] A high production rate quiet abrasive jet nozzle further comprising a plurality of abrasive particles in a supersonic fluid stream inside the nozzle, the supersonic fluid stream being subjected to a normal shock wave in a straight portion;

[0100] A high production rate quiet abrasive jet nozzle wherein the length of the straight portion is such that: the jet nozzle has a noise level of 90 dBA or less when operated with a predetermined gas and particle mixture and a predetermined pressure;

[0101] A high productivity quiet abrasive jet nozzle, wherein the length of the straight portion is such that: when the jet nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the jet nozzle has a noise level reduced by 3 dBA or more compared to a jet nozzle without the straight portion;

[0102] A high production quiet abrasive blasting nozzle wherein the length of the straight portion is such that when the blasting nozzle is operated with a predetermined gas and particle mixture and pressure, the blasting nozzle has a noise level reduced by 6 dBA or more compared to a blasting nozzle without the straight portion;

[0103] A high productivity quiet abrasive jet nozzle wherein the length L of the straight portion is at least L * , L * As given by the following equation:

[0104]

[0105] Wherein, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight portion, M is the Mach number of the fluid at the inlet of the straight portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and, γ is the specific heat ratio of the fluid flow;

[0106] A high productivity quiet abrasive jet nozzle wherein the length L of the straight portion is adjusted to at least L according to the ratio of back pressure to outlet pressure * , where L * Given by the following equation:

[0107]

[0108] where, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight portion, M is the Mach number of the fluid at the inlet of the straight portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and, γ is the specific heat ratio of the fluid flow;

[0109] A method for manufacturing a high productivity quiet abrasive jet nozzle as described herein above to reduce nozzle noise without reducing nozzle efficiency. The method comprises: determining a minimum length of a straight section of a high productivity quiet abrasive jet nozzle as described herein above for a predetermined mixture of gas and abrasive particles and a predetermined pressure, the minimum length being the length required to produce a Mach number of 1 for the gas at or within a straight section inner diameter prior to the outlet of the straight section; and manufacturing a nozzle having a straight section having a length equal to or greater than the minimum length;

[0110] A method for manufacturing a high productivity quiet abrasive jet nozzle as described herein, the method further comprising: determining an optimum length of a straight section of the high productivity quiet abrasive jet nozzle as described herein so that the gas Mach number decreases from a peak at a first point, i.e., at the end of a diverging section, before the exit of the straight section to a Mach number of 1 at a second point at or within a length equal to the inner diameter of the straight section without entering subsonic speed between the first and second points; and manufacturing a nozzle having a straight section of the optimum length;

[0111] A method for manufacturing a high productivity quiet abrasive jet nozzle as herein described, wherein the step of determining the optimum length comprises: analyzing the effect of friction from the walls of the straight portion; and / or analyzing the effect of abrasive particles reducing the air flow velocity in the straight portion;

[0112] A method for manufacturing a high productivity quiet abrasive jet nozzle as described herein, the method further comprising: adjusting the length of the straight portion to determine the length of the straight portion that produces a desired combination of sound reduction and productivity according to a particular operating condition; and manufacturing a nozzle having that length;

[0113] A method for manufacturing a high productivity quiet abrasive jet nozzle as described herein, the method further comprising: iteratively computer simulating a high productivity quiet abrasive jet nozzle as described herein over a range of straight section lengths to find a length having a desired combination of sound reduction and productivity; and manufacturing a nozzle having that length;

[0114] A nozzle attachment for high production rate quiet abrasive blasting, the nozzle comprising a straight tubular section for connection to an outlet of a blasting nozzle, wherein the length of the straight tubular section is such that: when the blasting nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the velocity of the gas leaving the blasting nozzle is reduced by at least 30%;

[0115] A nozzle attachment for high production quiet abrasive blasting, wherein the abrasive blasting nozzle is a No. 4 nozzle, No. 5 nozzle, No. 6 nozzle, No. 7 nozzle or No. 8 nozzle;

[0116] A nozzle attachment for high production rate quiet abrasive jetting, the nozzle also comprising a fixture for connecting the straight tubular portion to the abrasive jet nozzle;

[0117] A nozzle attachment for high production rate quiet abrasive jetting, the nozzle also including a fixture embedded in the straight tubular portion to help connect the straight tubular portion to the abrasive jet nozzle;

[0118] A nozzle attachment for high production rate quiet abrasive jetting, wherein the inner diameter of the straight tubular portion is less than the maximum inner diameter of the converging portion of the abrasive jet nozzle;

[0119] A nozzle attachment for high productivity quiet abrasive jetting, wherein the straight tubular section is configured such that: for a predetermined gas and particle mixture and a predetermined pressure, when the straight tubular section is connected to the abrasive jet nozzle, the supersonic flow of gas does not exceed the outlet of the straight tubular section and the supersonic gas flow accelerates the abrasive particles in the straight tubular section;

[0120] A nozzle attachment for high productivity quiet abrasive blasting, wherein the straight tubular section is configured such that: when the straight tubular section is connected to a blasting nozzle, for a predetermined gas and particle mixture and a predetermined pressure, the gas Mach number at the straight tubular section outlet is lower than the gas Mach number at the outlet of the diverging portion of the blasting nozzle, thereby reducing operating noise;

[0121] A nozzle attachment for high productivity quiet abrasive blasting, wherein the straight tubular section is configured such that: when the straight tubular section is connected to a blasting nozzle, for a predetermined gas and particle mixture and a predetermined pressure, the gas Mach number is reduced from a gas Mach number greater than 1 at the outlet of the diverging section of the blasting nozzle to a gas Mach number of 1 at the outlet of the straight section;

[0122] A nozzle attachment for high production rate quiet abrasive blasting, wherein the length of the straight tubular portion is at least two tenths of the diameter of the straight tubular portion;

[0123] A nozzle attachment for high production rate quiet abrasive jetting wherein the length of the straight tubular portion is less than ten times the diameter of the straight tubular portion;

[0124] A nozzle attachment for high production rate quiet abrasive blasting wherein the length of the straight tubular portion is between 1 inch and 10 inches;

[0125] A nozzle attachment for high production rate quiet abrasive blasting wherein the length of the straight tubular portion is 2.5 inches;

[0126] A nozzle attachment for high production rate quiet abrasive blasting, wherein the straight tubular portion is cylindrical in shape;

[0127] A nozzle attachment for high production rate quiet abrasive blasting, wherein the straight tubular portion is made of a material selected from the group consisting of tungsten carbide, silicon carbide, boron carbide, acrylic, ceramic, stainless steel, hardened steel, aluminum, or a combination thereof;

[0128] A nozzle attachment for high productivity quiet abrasive blasting, wherein the length of the straight tubular portion is such that when the straight tubular portion is connected to the abrasive blasting nozzle, the blasting nozzle has a noise level of 90 dBA or less when operating with a predetermined gas and particle mixture and a predetermined pressure;

[0129] A nozzle attachment for high productivity quiet abrasive blasting, wherein the length of the straight tubular portion is such that: when the straight tubular portion is connected to the abrasive blasting nozzle, the blasting nozzle has a noise level reduced by 3 dBA or more compared to a blasting nozzle without the straight tubular portion when the blasting nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure;

[0130] A nozzle attachment for high productivity quiet abrasive blasting, wherein the length of the straight tubular portion is such that when the straight tubular portion is connected to a blasting nozzle, the blasting nozzle has a noise level reduced by 6 dBA or more compared to a blasting nozzle without the straight tubular portion when the blasting nozzle is operated at a predetermined gas and particle mixture and pressure;

[0131] - A nozzle attachment that achieves a predetermined noise level reduction for a nozzle pressure between 20 psi and 200 psi and a particle loading of an abrasive consumption rate of 50 pounds to 10,000 pounds per hour, or any value or any range of values ​​within these ranges.

[0132] A nozzle attachment for high productivity quiet abrasive blasting, wherein the length L of the straight tubular portion is at least L * , L * As given by the following equation:

[0133]

[0134] Wherein, in the case where a straight tubular section is connected to an abrasive jet nozzle, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight tubular section, M is the Mach number of the fluid at the inlet of the straight section, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and, γ is the specific heat ratio of the fluid flow;

[0135] A nozzle attachment for high production rate quiet abrasive jetting, wherein L is adjustable based on the ratio of back pressure to outlet pressure to at least L * , where L * Given by the following equation:

[0136]

[0137] Wherein, in the case where a straight tubular section is connected to an abrasive jet nozzle, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight tubular section, M is the Mach number of the fluid at the inlet of the straight section, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and, γ is the specific heat ratio of the fluid flow;

[0138] A plurality of nozzle attachments are configured to be connected to each other to combine the lengths of the plurality of nozzle attachments;

[0139] A method for manufacturing a nozzle attachment as herein described above to reduce the noise of an attached abrasive jet nozzle without reducing nozzle productivity, the method comprising: determining, for a predetermined mixture of gas and abrasive particles and a predetermined pressure, a minimum length of a straight tubular portion of the nozzle attachment as herein described above, the minimum length being the length required to produce a Mach number of 1 for the gas at or within an inner diameter of the straight tubular portion prior to the outlet of the straight portion; and manufacturing a straight tubular portion having a length equal to or greater than the minimum length;

[0140] A method for manufacturing a nozzle attachment as described herein above to reduce the noise of an attached abrasive jet nozzle without reducing nozzle productivity, the method further comprising: determining an optimal length of the straight tubular portion of the nozzle attachment as described herein above so that the gas Mach number decreases from a peak at a first point, i.e., the end of the diverging portion of the attached sandblasting nozzle, before the outlet of the straight tubular portion to a Mach number of 1 at a second point at or within a length equal to the inner diameter of the straight tubular portion without entering subsonic speed between the first and second points; and manufacturing the straight tubular portion having the optimal length;

[0141] A method for manufacturing a nozzle attachment as herein described to reduce the noise of an attached abrasive jet nozzle without reducing nozzle productivity, wherein the step of determining the optimum length comprises: analyzing the effect of friction from the wall of the straight tubular portion; and / or analyzing the effect of a plurality of abrasive particles on reducing the velocity of the gas flow in the straight tubular portion;

[0142] A method for manufacturing a nozzle attachment as described herein above to reduce the noise of an attached abrasive jet nozzle without reducing nozzle productivity, the method further comprising: adjusting the length of the straight tubular portion to determine the length of the straight portion for a desired combination of sound reduction and productivity according to specific operating conditions; and manufacturing the straight tubular portion having this length;

[0143] A method for manufacturing a nozzle attachment as described herein to reduce the noise of an attached abrasive jet nozzle without reducing nozzle productivity, the method further comprising: iteratively computer simulating a straight tubular portion of the nozzle attachment as described herein over a range of straight tubular portion lengths to find a length having a desired combination of sound reduction and productivity; and manufacturing the straight tubular portion having that length; and

[0144] A high productivity quiet abrasive jet nozzle assembly, the assembly comprising a high productivity quiet abrasive jet nozzle as described herein;

[0145] - A nozzle or nozzle attachment having a distal straight portion, the straight portion having an inner diameter that varies by 5% or less over the length of the straight portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0146] Figure 1 A conventional prior art supersonic abrasive jet system is shown.

[0147] Figure 2 The cross-sectional view shows Figure 1 A conventional prior art supersonic converging-diverging nozzle is used in the abrasive blasting system shown in FIG.

[0148] Figure 3 The graph is reproduced from Settles' paper (Settles G., A scientific view of the productivity of abrasive blasting nozzles, 1996) and shows the large difference between the predicted and measured velocities through a conventional Laval nozzle and the abrasive velocity and the exit air velocity.

[0149] Figure 4 is a graph showing the drag coefficient of a sphere as a function of Mach number for two Reynolds numbers.

[0150] Figure 5 is a graph showing the required jet exit velocity reduction to achieve a desired sound pressure level (SPL) reduction based on the relationship between the jet exit velocity and the generated jet noise;

[0151] Figure 6 is a graph showing simulated particle velocity versus distance for a 20 / 30 mesh V-type acrylic media in a 345 m / s accelerator section.

[0152] Figure 7 It is a Moody Diagram used to estimate the friction coefficient based on the Reynolds number and pipe roughness.

[0153] Figure 8 An improved noise reduction abrasive jet system according to an embodiment of the present invention is shown.

[0154] Fig. 9 The cross section shows the Figure 8 Detail of a gradually decreasing inner diameter transition piece of the abrasive media path employed in a noise reduction abrasive blasting system as shown in FIG.

[0155] Fig.10 is a photograph of a prototype noise reducing abrasive jet accelerator tube and nozzle in accordance with an embodiment of the present invention.

[0156] Fig.11 is a photograph showing in comparison the productivity of a noise-reduced abrasive jet nozzle according to an embodiment of the present invention (left) and conventional jetting using a No. 8 nozzle (right) by jetting V-shaped media on a half exposed coated bakeware for 30 seconds, both using 4 turns of the abrasive metering valve knob.

[0157] Fig.12 is a photograph comparing the results of using a noise reducing abrasive blasting system according to an embodiment of the present invention operated with additional abrasives to a conventional system operated with a standard No. 8 nozzle.

[0158] Fig.13 The self-spectra of a prior art supersonic abrasive jetting apparatus with a standard No. 8 nozzle and a prototype of the present invention using V-type media and 40 psi operating pressure, as well as the background noise level from the jet compressor unit.

[0159] FIG. 14A to FIG. 14B They are the side view and three-dimensional perspective view of the standard No. 6 nozzle.

[0160] Fig.15 This is a cross-sectional view of the XL6 nozzle.

[0161] FIG. 16A to FIG. 16B is a side perspective view of an improved spray nozzle according to an embodiment of the present invention ( Fig.16A ) and cross-sectional view ( Fig. 16B ).

[0162] FIG. 17A to FIG. 17B is a side perspective view of an improved spray nozzle having an extended length according to an embodiment of the present invention ( Fig.17A ) and cross-sectional view ( Fig. 17B ).

[0163] Fig.18 is a schematic diagram showing the expansion of a converging-diverging nozzle.

[0164] FIG. 19A to FIG. 19Bis shown by the standard No. 6 nozzle ( Fig.19A ) and an improved nozzle according to an embodiment of the present invention ( Fig.19B ) CFD results of Mach number distribution at 67 psig nozzle pressure using ANSYS Fluent.

[0165] FIG. 20A to FIG. 20B is shown by the standard No. 6 nozzle ( Fig. 20A ) and an improved nozzle according to an embodiment of the present invention ( Fig. 20B ) CFD results of Mach number distribution at 100 psig nozzle pressure using ANSYS Fluent.

[0166] FIG. 21A to FIG. 21B The figure shows the effect of increasing the wall resistance by changing the standard No. 6 nozzle ( Fig.21A ) and an improved nozzle according to an embodiment of the present invention ( Fig. 21B ) CFD results of Mach number distribution at 67 psig nozzle pressure using ANSYS Fluent.

[0167] Fig. 22 is a graph showing the average 1 / 3 octave band acoustic spectrum for various nozzles.

[0168] FIG. 23 is a cross-sectional view of a standard converging-diverging abrasive jet nozzle.

[0169] Fig.24 Shown is a cross section of an abrasive jet nozzle according to an embodiment of the present invention.

[0170] Fig.25 A cross section of an abrasive jet nozzle is shown with abrasive particles in a stream according to an embodiment of the present invention.

[0171] Fig.26 A cross section of an abrasive jet nozzle according to an embodiment of the present invention is shown, wherein the length is equal to L * Or the length ratio L * Slightly longer.

[0172] Fig. 27 The effect of increasing or decreasing the nozzle pressure on the exit state of the straight portion of the nozzle is shown. DETAILED DESCRIPTION

[0173] As explained below, a solution to the problem of excessive noise from prior art supersonic abrasive jet systems has been discovered.

[0174] The acceleration of a particle in a flow can be simulated using the drag coefficient empirically determined based on data from Bailey and Hialt as proposed previously (Settles & Geppert, 1997). The acceleration of a particle of mass m can be calculated from the drag force D as

[0175]

[0176] Where A is the cross-sectional area of ​​the sphere, and U rel is the relative velocity between gas and particles. Figure 4 Shown in FIG. 1 are the drag coefficients of a sphere as a function of the Mach number for two Reynolds numbers.

[0177] Previous studies have shown that the noise power P of a jet is proportional to the eighth power of the velocity and the square of the jet diameter (Powell, 1959):

[0178] P∝U 8 D 2

[0179] In addition, the sound pressure level SPL is proportional to the sound power level SWL, where

[0180]

[0181] Therefore, it can be deduced that SPL, velocity, and diameter are proportional to:

[0182]

[0183] exist Figure 5 This relationship is shown graphically in . Thus, if the nozzle exit velocity is reduced by, for example, 30%, the SPL is expected to drop by 12.5 dB, while a 43% reduction in exit velocity results in an expected 20 dB drop in SPL.

[0184] In order to have the same throughput as prior art nozzle abrasive jetting systems, the particle velocity must be maintained. Figure 2 The conventional nozzles shown in have gas velocities much higher than the particle velocities, and these high gas velocities are responsible for the higher sound levels. The present invention maintains the particle velocity while reducing the nozzle exit gas velocity and thus reducing the generation of sound. This requires a longer acceleration length relative to prior art nozzle abrasive jet systems.

[0185] The mass of the sphere is the density of the particle ρ particle Multiply by volume So the acceleration becomes:

[0186]

[0187] The solution can be found in a step-by-step manner and Figure 6 The solution for a 20 / 30 mesh V-type acrylic media in a gas stream with a velocity of 345 m / s is shown in . This shows that a 4 meter accelerator section is required in the tube to achieve a particle velocity of 275 m / s.

[0188] Based on the expected exit velocity of 483 m / s from the previous model for a standard No. 8 nozzle operating at 40 psi, the exit velocity was reduced by 30% to 345 m / s (roughly the speed of sound), and an exit velocity of 345 m / s reduced the SPL by 12.5 dB. Therefore, the length of the tube needs to be long enough to match the particle velocity of the No. 8 nozzle at 40 psi.

[0189] The current invention achieves sufficient abrasive particle velocity in a gas stream with a lower exit velocity through a greater acceleration distance, thereby using a supersonic jet nozzle to reduce the noise perception generated by the nozzle. The jetting productivity can be adjusted by adjusting the abrasive mass flow rate.

[0190] Pressure loss or head loss is unavoidable and must be taken into account. As the length of the pipe increases, the pressure will drop and eventually reduce the flow rate. However, this loss can be calculated. The head loss or pressure loss due to friction along the pipe is given by the Darcy-Weisbach equation as:

[0191]

[0192] Where L is the length of the pipe section, D is the pipe diameter, ρ is the density of the fluid, V is the average fluid velocity, and f D is the Darcy friction coefficient based on the Reynolds number Re and the relative pipe roughness ∈ / d and is equal to about 0.02 for plastic / rubber. Figure 7 A Moody Diagram for estimating the friction coefficient from the Reynolds number and the pipe roughness is shown.

[0193] A 3 / 4 inch ID jet pipe operating near "choked" conditions has a velocity of 230 to 340 m / s and a Reynolds number of 300,000 to 436,000. The resistance over the length of the pipe causes a pressure loss which reduces the average velocity in the pipe.

[0194] If choked flow conditions exist where the downstream pressure drops below a critical value, the velocity in the tube will be sonic,

[0195]

[0196] Among them, the heat capacity ratio K for air is 1.4, that is,

[0197] p * =0.528p0

[0198] For 40 psig or 54.7 absolute, p* is 28.9 psia or 14.2 psig.

[0199] Based on the results of the analytical model discussed above, the preferred embodiment of the present invention is designed to take the airborne particles out of the exemplary 1 inch tube and accelerate them through the smaller diameter tube a sufficient distance so that a high production rate particle velocity is obtained. The transition piece that gradually reduces the inner diameter of the tube provides a smooth transition between the different tube section diameters and minimizes pressure losses.

[0200] according to Figure 8 In the preferred embodiment of the noise reduction abrasive blasting system of the present invention shown in , the compressor 112 pressurizes the gas to nearly 120 psi. The compressed gas is pumped through the starting pipe section 114 to the abrasive medium tank 116 that contains the abrasive medium 118. The abrasive metering valve 120 controls the release rate of the abrasive medium 118. A standard 1 inch inner diameter jet pipe 124 is attached to the metering valve 120 at one end and to the transition coupling 122 at the other end. A section of accelerator pipe 130 with a reduced inner diameter, such as 3 / 4 inch, connects the transition coupling 122 to the nozzle 134 through a claw coupling 132. The transition coupling 122 is used to gradually reduce the inner diameter of the path taken by the abrasive medium 118 from the 1 inch diameter sandblasting pipe 124 to the smaller diameter accelerator pipe 130.

[0201] Fig. 9 1 shows the details of the transition coupling 122 and the nozzle 134 in cross-section. The coupling 122 includes a housing 128 enclosing a hole (not shown). The jet tube side 125 of the transition coupling 122 has a 1 inch inner diameter hole, while the accelerator side 130 of the transition coupling 122 has a 3 / 4 inch diameter hole. Each side of the transition coupling 122 is connected to a corresponding tube using conventional claw coupling 132 technology.

[0202] The exit diameter 136 of the nozzle 134 is sized to control the desired abrasive "hot spot" diameter so that the effective blasting area of ​​the noise reduction abrasive blasting system can be matched to the effective blasting area of ​​a conventional supersonic nozzle.

[0203] Other preferred embodiments of the noise reduction abrasive jetting system of the present invention are systems that include more than one accelerating tube section and employ more than one transition coupling, each section in the accelerating tube having a reduced inner diameter. Other types of couplings, nozzles, metering valves, and abrasive media may be employed in the system of the present invention without departing from the scope of the present invention.

[0204] More details are given below on how to design the nozzle according to the present invention in various embodiments of the present invention into a configuration that uses, in sequence, a convergent section, a throat section, a divergent section, and a straight section. One-dimensional supersonic flow in a pipe with friction can be represented by the following equation, where x1 and x2 are the locations of interest, and M1 and M2 correspond to the local Mach numbers at these locations. D is the diameter of the pipe, f is the friction coefficient, and γ is the specific heat ratio:

[0205]

[0206] Among them, the wall shear stress τ is related to the friction coefficient as follows:

[0207]

[0208] If L * Defined as the length where the Mach number in the duct is reduced to 1 by friction, the following well-known relationship is obtained:

[0209]

[0210] Among them, the average friction coefficient is defined as:

[0211]

[0212] The local temperature, static pressure, density, and total pressure at the throat of the sound are related to each other by the following equations:

[0213]

[0214]

[0215]

[0216]

[0217] To create a noise-reduced version of a conventional nozzle, the conventional outlet area to throat area ratio can be examined, which is the square of the ratio of the outlet diameter to the throat diameter, A. e / A*=(D e / D*) 2This area ratio then determines the Mach number at the end of the diverging section according to the known area-Mach number relationship:

[0218]

[0219] Then the exit Mach number of the convergent part M e Used together with the friction coefficient of the duct wall and the equation for determining the length of duct required to reduce the Mach number inside the duct to 1. Then this length L * is the length of the straight section required for the nozzle to produce a Mach number of 1 at the outlet without any abrasive media. Any length above this length will produce a positive shock wave at the outlet. Since a positive shock wave has subsonic flow downstream of the shock wave, the flow velocity is significantly reduced and therefore the sound produced by the flow is significantly reduced.

[0220] Rearranging the previous equation to solve for L * The following results were produced:

[0221]

[0222] Abrasive jet nozzles use some type of abrasive that is accelerated in the nozzle as it moves toward the outlet. As the abrasive particles are accelerated, energy is transferred from the stream to the particles. The effect of adding abrasive to the stream is similar to increasing the coefficient of friction of the straight section and therefore reducing the length required to achieve a positive shock wave at or just before the outlet. In general, the more abrasive added to the stream, the shorter the length of the straight section of pipe required to achieve a positive shock wave at or just before the outlet. A more detailed estimate of the effect of abrasive can be calculated starting with the drag from one abrasive particle,

[0223]

[0224] Among them, U rel is the relative velocity of the air / gas flow to the particle velocity, and, d particle is the diameter of the abrasive particle. The number of particles in a specific volume n p can be used to calculate the total force on the flow within this volume according to the following equation:

[0225] F volume =n p F particle drag

[0226] Although a more accurate calculation would include changes in the entire volume, the average value can be used for approximation. p The value can be approximated using the following equation:

[0227]

[0228] Among them, Q abs is the mass rate of abrasive consumption, Q air is the volume velocity of the gas flow, D is the diameter of the straight portion, L is the length of the straight portion, and m p is the mass of the abrasive particles. The mass of the particles can be calculated according to the following equation:

[0229]

[0230] but

[0231]

[0232] Based on this value of resistance to a volume, such as the volume of the straight part of a quiet nozzle, the equivalent additional force from the abrasive on the fluid as a function of the wall area can be calculated by the following equation:

[0233]

[0234] Although this is not a shear force, because the force on the fluid volume is divided by the wall area rather than the flow cross-sectional area, the same sign as the shear force is used so that this force can ultimately be incorporated into L * in the equation.

[0235]

[0236] Then, the approximate length at which the Mach number becomes 1 can be calculated based on the following equation, where M refers to the Mach number at the beginning of the straight section:

[0237]

[0238] Therefore, this length is considered to be the minimum length of the straight section after the diverging section, which is after the throat, which is after the converging section. This length assumes that the exit pressure is equal to the back pressure or the pressure after the exit. Deviation from this assumption will result in the shock wave moving outward when the exit pressure of the straight section is greater than the back pressure or moving inward when the exit pressure of the straight section is less than the back pressure. These deviations can be quantified using known methods based on the pressure at the nozzle inlet, the ratio of the nozzle throat area to the nozzle outlet area, and the back pressure (usually the local atmospheric pressure). Generally, when the flow is sonic, that is, the Mach number is 1, the exit pressure is a function of the pressure upstream of the throat and the ratio of the exit area of ​​the diverging section to the throat area. Therefore, control of the upstream pressure at the entrance of the converging section controls the exit pressure.

[0239] The noise reduction abrasive jet nozzle can also take the form of a standard nozzle with an attachment that is connected to the end via threads or clamps or other known fixing methods or devices. Therefore, any of the characteristics of the straight portion of the noise reduction abrasive jet nozzle described herein can be applied to the straight portion of such an attachment, and vice versa. For standard nozzles that lack threads at the outlet of the diffusion portion, threads can be machined into the diffusion portion to cooperate with threads on the attachment (or fixture), or clamps or other fixtures can be used. Many different types of clamps for connecting adjacent tubular objects are known. This attachment in the embodiment is the same as the "straight portion" of the nozzle described herein, except that it can be separated from the other parts of the nozzle. In this way, the standard nozzle can be reconfigured into a quiet noise reduction abrasive jet nozzle. These accessories and the method for determining the size of these accessories follow the same design principles and steps as those already outlined herein. The attachment can be provided separately and / or provided together with the fixture to facilitate application in the modification of an existing standard nozzle, or the attachment can be provided together with the rest of the nozzle and an optional fixture. The remainder of the nozzle may be a standard nozzle, or may be a custom nozzle or a standard nozzle that has been specifically adapted to removably secure the attachment to the diffuser portion of the nozzle, such as by providing threads on the end of the diffuser portion. The attachment and diffuser portion of the nozzle may have various known securing structures built in to help removably secure the attachment to the diffuser portion. In embodiments, a variety of attachments may be provided (with or without the remainder of the nozzle) for use with various corresponding gas / abrasive particle mixtures and / or pressures.

[0240] Example

[0241] Fabrication and testing of initial prototypes

[0242] include Figure 8 and Fig. 9 Prototypes of the components shown in the figure were manufactured as Fig.10 As shown in , the prototype has the following features for testing:

[0243] Four-meter accelerator section with 3 / 4-inch inner diameter to achieve sonic conditions (345 m / s)

[0244] A straight bore nozzle with a 0.79 bore to match the output diameter of a No. 8 nozzle to achieve the same “hot spot” as the current standard No. 8 setup

[0245] Connectors, etc.

[0246] The sound pressure level was measured using both a handheld integrated sound pressure meter and a separate microphone data acquisition system. The nozzle pressure measured near the end of the 1-inch pipe before the coupling was 40 psi. The V-type media was introduced by opening the media valve 4 full turns. The sound pressure level test results in dB are as follows:

[0247] nozzle Overall sound pressure level (dB) Standard No. 8 108 QB-1 Prototype 94.5

[0248] The productivity was qualitatively evaluated by using both the No. 8 nozzle and the subject prototype on a half-exposed coated baking tray for 30 seconds, as Fig.11 The effect of adjusting the knob of the abrasive metering valve was examined by adjusting the knob to six turns for the prototype and comparing the output of this setting to a standard No. 8 nozzle using a four-turn setting.

[0249] Fig.12 It is shown that the prototype operated at the six-turn setting is significantly more efficient than the standard No. 8 operated at the four-turn setting. These results indicate that the present invention can be operated with equal or better productivity than the standard No. 8 nozzle while producing 16 dB lower noise as measured at the operator.

[0250] Tests were also performed to examine the total sound pressure level and sound spectrum of the prototype compared to a standard No. 8 nozzle, both of which were operated at 40 psi. The test results demonstrated that the noise reduction was broad spectrum, such as Fig.13 shown.

[0251] Other preferred embodiments of the noise reduction abrasive jetting system of the present invention are systems that employ a new nozzle having a straight section after the diverging section to accelerate the media particles to a desired velocity before the particles leave the jetting nozzle. This low noise abrasive jetting nozzle is suitable for replacing nozzles such as a standard No. 6 nozzle, and improves jetting productivity and reduces noise generation. The outlet shock wave condition of the new nozzle is designed to significantly reduce the jet noise from the flow leaving the nozzle. Comparative testing between the new nozzle and existing commercial nozzles achieved a noise reduction of 17dB(A), while demonstrating improved productivity in tests using garnet. CFD modeling shows an improved particle acceleration zone. In addition, evaluations of using the new nozzle with steel shot compared to using a standard No. 6 nozzle showed: improved productivity; reduced noise; and improved productivity; reduced acoustic noise; and reduced operator fatigue.

[0252] FIG. 14A to FIG. 14B6 inch, and the throat 1420 is 0.5 inch in length, and the divergent portion 1430 is 3.13 inches in length, the inner diameter of the opening is 1.25 inches, the throat diameter is 0.38 inches, and the outlet diameter is 0.55 inches. The length of the outlet portion 1440 is 0.10 inches and is also diffuse. The nozzle is the standard for abrasive jet operations. Conventional nozzles are convergent / divergent nozzles such as standard No. 6. The particular version shown has a wider inlet, which means that the uniformity of particle distribution is enhanced. This particular version has a convergent portion at the inlet, a straight throat portion with a diameter of 6 / 16 inches (hence the name No. 6), and then a diffuser portion that continues to the outlet. The peak velocity of this design occurs at the outlet (and thereafter). Fig.15 is a cross-sectional view of a nozzle 1500 of size XL6, which, as shown, has an overall length of 11.71 inches and a FIG. 14A to FIG. 14B The standard No. 6 nozzle shown in FIG. 1 has a longer diverging section 1530 (8.31 inches instead of 3.13 inches). The converging section 1510, throat 1520, and outlet 1540 are identical.

[0253] FIG. 16A to FIG. 16B 16 and 17 are side perspective and cross-sectional views of an improved jet nozzle 1600 according to an embodiment of the present invention, respectively. The total length of the nozzle shown is 9.07 inches, wherein the length of the throat 1620 is 0.50 inches, the length of the divergent portion 1630 is 3.13 inches, and the length of the straight portion 1650 is 2.56 inches, wherein the converging portion 1610 constitutes the remaining length. The inner diameter of the opening is 1.25 inches, the diameter of the throat is 0.375 inches, and the diameter of the straight portion is 0.55 inches. The convergence angle is 8.88 degrees, and the angle of the divergent outlet portion 1640 is 50 degrees. FIG. 17A to FIG. 17B 17 and 17 are side perspective and cross-sectional views of an improved spray nozzle 1700 having a convergent portion 1710, a throat 1720, a divergent portion 1730, a straight portion 1750, and an outlet portion 1740, respectively, with the length being extended according to an embodiment of the present invention. FIG. 16A to FIG. 16B Compared to the nozzle 1600 shown in FIG. 1 , the nozzle 1700 has a longer straight portion 1750 and the overall length of the nozzle 1700 is similar to Fig.15 The overall length of the nozzle 1700 is 11.71 inches, except that the length of the straight portion 1750 is 5.20 inches. FIG. 16A to FIG. 16B The nozzles 1600 shown in FIG. 1 are of the same dimensions.

[0254] Since the sound produced from the air leaving the nozzle depends largely on the air velocity, a design with a lower air outlet velocity without reducing the abrasive particle velocity allows equal or higher productivity while greatly reducing the volume. The new nozzle applying this method adds a straight section (neither convergent nor diffuse) to the end of the divergent section of the conventional nozzle design. This extends the particle acceleration section while reducing the outlet Mach number as energy is transferred from the air to the particles. The extension of the acceleration section is based on the maximum Mach number reached at the end of the divergent section. In various embodiments, the length of the straight section ranges from 1 / 5 of the nozzle throat diameter to ten times the nozzle throat diameter, but can also extend to 10 times the straight section diameter. The increased interaction distance between the slower abrasive and the air in the flow decelerates the air in a manner similar to wall friction, thereby more effectively accelerating the abrasive particles while reducing the nozzle outlet velocity.

[0255] Fig.18 is a schematic diagram showing the expansion of a convergent-divergent nozzle in an overexpanded 1810 state, a fully expanded 1820 state, and an underexpanded 1830 state. Conventional jet nozzles are typically operated in what is considered an overexpanded state, meaning that as the flow exits and contracts 1840 after the nozzle exit, the flow passes through an oblique shock wave 1870. The flow is supersonic throughout the diverging portion of the nozzle and at the exit, and the jet pressure is adjusted to atmospheric pressure by means of an oblique shock wave 1840 outside the exit plane. In contrast, the fully expanded flow 1850 does not expand or contract after the exit, while the underexpanded flow 1860 expands in an expansion fan 1880 after the exit.

[0256] Considering the No. 6 nozzle, a fully expanded nozzle with an outlet to throat area ratio of A / A*=2.15 will be driven by a 183psi pressure reservoir and achieve an outlet Mach number of 2.3. Under appropriate circumstances, reducing the reservoir pressure can induce a positive shock wave at the outlet plane of the nozzle, thereby significantly reducing the speed of the gas when leaving the nozzle. However, reducing the reservoir pressure of a conventional abrasive jet nozzle reduces the particle velocity and makes this setting impractical. However, when the supersonic section is uniformly extended, the effect of the jet medium on the supersonic flow structure causes a positive shock wave to form at a pressure higher than the expected reservoir. The longer high Mach number nozzle section followed by a positive shock wave at the nozzle outlet reduces the outlet velocity of the air and therefore reduces the generation of noise. This has the same effect as running a non-abrasive nozzle at a sufficiently low pressure to produce a positive shock wave at the outlet. Having a positive shock wave at the outlet significantly reduces the air outlet velocity, while having little effect on the net abrasive velocity.

[0257] The straight barrel section also causes some friction losses simply due to wall surface roughness, which results in a slightly lower Mach number toward the nozzle end. For example, for a nominal friction coefficient of 0.005 over the length of the straight section of 2.56 inches, this results in a drop in Mach number from M=2.3 to M=1.8. This case is even more over-expanded and is more likely to result in a positive shock wave if the output is subsonic and quiet.

[0258] FIG. 19A to FIG. 19B are CFD results 1900 and 1901, which show the CFD results 1900 and 1901 for the standard No. 6 nozzle ( Fig.19A ) and an improved nozzle according to an embodiment of the present invention ( Fig.19B ) Mach number distribution for a single-phase compressible gas flow without a medium at a nozzle pressure of 67 psig using ANSYS Fluent. FIG. 20A to FIG. 20B are CFD results 2000 and 2001, which show the CFD results 2000 and 2001 for the standard No. 6 nozzle ( Fig. 20A ) and an improved nozzle according to an embodiment of the present invention ( Fig. 20B ) Mach number distribution at 100 psig nozzle pressure using ANSYS Fluent. The results clearly show that the modified nozzle has an extended acceleration section under various conditions compared to the standard No. 6 nozzle. In this model, at 67 psig, the modified nozzle has a slightly lower maximum Mach number than the standard No. 6 nozzle (2.21 vs. 2.26), but has a longer cross section over which supersonic flow exists to accelerate the particles. Similar results were found at a nozzle pressure of 100 psig.

[0259] FIG. 21A to FIG. 21B are CFD results 2100 and 2101 showing the effect of increasing the wall resistance on the standard No. 6 nozzle ( Fig.21A ) and an improved nozzle according to an embodiment of the present invention ( Fig. 21B ) Mach number distribution at 67 psig nozzle pressure using ANSYS Fluent. Increased wall drag uses an increased wall friction coefficient to simulate the drag of the particles on the flow. The main lesson from this result is that the longer straight nozzle section of the modified nozzle has a greater impact on the flow structure.

[0260] Fig. 22 is a graph showing the average 1 / 3 octave band sound spectra for various nozzles and is discussed in more detail below.

[0261] 23 is a cross-sectional view of a prior art standard converging-diverging abrasive jet nozzle 2300 showing a Mach number of 1 at the throat 2304 and a Mach number greater than 1 at the outlet 2310. The converging portion 2303 extends from the inlet of the nozzle to the beginning 2303 of the throat, and the diverging portion 2306 extends from the end 2305 of the throat to the end 2307 of the nozzle.

[0262] Fig.24 A cross section of a nozzle 2400 according to an embodiment of the invention is shown, wherein a converging portion 2402 extends from an inlet 2401 of the nozzle to the beginning 2403 of a throat 2404, which ends at 2405, and after the throat 2404 is a diverging portion 2406, which transitions at point 2407 to a straight barrel portion 2408, which extends to the end 2409 of the nozzle. The Mach number at the outlet 2407 of the diverging portion is M1, which is greater than 1. L * represents the length of the straight cylindrical portion 2408 over which the flow will become sonic (M=1) due to wall friction. At the outlet 2410, the flow has a Mach number M less than 1. e .

[0263] Fig.25 25 shows a cross section of a nozzle 2500 according to an embodiment of the present invention, wherein a converging portion 2502 extends from an inlet 2501 to the beginning 2503 of a throat 2504, followed by a diverging portion 2506, which extends from the end 2505 of the throat to the beginning 2507 of a straight cylindrical portion 2508, which continues to the end 2509 of the nozzle. Abrasive particles 2512 are in the flow through the nozzle 2500, ΔL represents L * Due to the introduction of abrasive particles 2512 relative to Fig.24 The reduced length of the nozzle shown in FIG. 2 introduces abrasive particles 2512 to reduce the energy in the flow.

[0264] Fig.26A cross section of a nozzle 2600 according to an embodiment of the present invention is shown, wherein a converging portion 2602 is followed by a throat 2604 extending from a throat inlet 2603 to a throat outlet 2605, the throat 2604 is followed by a diverging portion 2606 extending from the throat outlet 2605 to an inlet 2607 of a straight cylindrical portion 2608 terminating at an end 2609 of the nozzle, wherein abrasive particles 2612 are in the flow, and a Mach number graph 2620 represents the Mach number (M) along the axial dimension (x) of the nozzle. For an optimized nozzle designed according to the present invention, the Mach number remains above 1 until the outlet, which is indicated by the label "L=L * " is shown by the profile 2622. For a nozzle designed according to the present invention with a slightly lower degree of optimization, the length of the straight portion 2608 is about L * Being slightly longer, the Mach number will drop to below 1 in the straight portion 2608 and then rise to 1 at the exit 2610 as shown by profile 2624.

[0265] Fig. 27 A cross section of a nozzle 2700 is shown according to an embodiment of the invention, wherein a converging portion 2702 is followed by a throat 2704 extending from a throat inlet 2703 to a throat outlet 2705, the throat 2704 is followed by a diverging portion 2706 extending from the throat outlet 2705 to an inlet 2707 of a straight cylindrical portion 2708 terminating at an end 2709 of the nozzle, wherein abrasive particles 2712 are in the flow, and a Mach number graph 2720 showing the Mach number (M) along the axial dimension (x) of the nozzle. Contours 2722, 2724, 2726 show the effect of increasing or decreasing the nozzle pressure on the outlet conditions of the straight portion of the nozzle. When the outlet pressure p e Equal to back pressure p b and the length L of the straight portion 2708 is equal to L * When the nozzle pressure p0 increases, a shock wave is formed in the flow at the outlet, as shown in profile 2722, resulting in a subsonic flow after the outlet. Increasing the nozzle pressure p0 results in a higher outlet pressure p e , and when p e Exceeding back pressure p b When the nozzle pressure is 2708, a supersonic exit flow with higher noise is generated, as shown in profile 2726. In order to avoid supersonic exit flow at this nozzle pressure, the length L of the straight portion 2708 can be increased to more than L * , and / or the friction of the nozzle inner wall and / or the abrasive particles can be increased so that the gas flow velocity in the straight section decreases more rapidly. Reducing the nozzle pressure results in a lower outlet pressure p e, and the shock wave moves upstream from the exit, where the particle acceleration decreases slightly due to the lower Mach number profile, as shown in profile 2724.

[0266] The productivity and noise performance of the new nozzles described above were compared with standard commercially available No. 6 nozzles, including the standard No. 6 nozzle and the extra long (XL) nozzle. Prior to testing, 20 18" x 18" panels of 14-gauge steel were uniformly powder coated (coating thickness of 10 mils to 12 mils) to be used to evaluate the nozzle's productivity (the time required to clean the panels to a set level). All tests were conducted with the new 30 / 40 garnet media at 67 psi nozzle pressure.

[0267] For each nozzle tested, the sound level was measured with a sound level meter at the operator's left shoulder while the nozzle was operated in the open air (to avoid the sound produced by sand hitting metal during actual spraying). The sound level in the 1 / 3 octave band was measured for a period of 10 seconds, and the MIN sound level, MAX sound level, and AVG sound level were automatically calculated and stored. The background sound level was also recorded to confirm that the background noise did not affect the measured nozzle noise level.

[0268] Next, a video was recorded of each nozzle as it was used to spray one side of a powder coated test panel. The video was used to quantify the productivity of each nozzle (determining the time required to clean the test panel to the desired finish). Feedback from the sprayer after using each nozzle, including impressions of sound levels and productivity, was also recorded.

[0269] Table 1 summarizes the main results of the tests, along with some operator comments. Based on the first round of testing, the quietest and most productive nozzle was a modified nozzle known as the Oceanit BN6V1 or Oceanit Short SS, which was developed in FIG. 17A to FIG. 17B The nozzle is shown schematically in Figure 1. This nozzle was 16 dB quieter and cleaned the test panel in 51 seconds, compared to 69 seconds for the standard long nozzle. The XL nozzle (XL No. 6) showed some improvement in sound performance, but no increase in productivity and was considered too large and heavy for daily use.

[0270]

[0271] Table 1, Summary of test results (30 / 40 garnet, at 70 psi nozzle pressure)

[0272] Based on the results of the first round, a second test was conducted with the standard No. 6 nozzle and two Oceanit nozzles with straight sections (also shown in Table 1). Again, the Oceanit Short SS was the operator's favorite nozzle and was 15.2 dB quieter than the standard No. 6 nozzle and cleaned the test panel in 39 seconds (compared to 41 seconds for the standard No. 6 nozzle). The Oceanit BN6-V1 was significantly quieter than the standard No. 6 nozzle, so much so that the operator felt that ear protection was not necessary, and the Oceanit BN6-V1 was more productive, had less recoil, and caused less thermal warping of the test panel.

[0273] Fig. 22 The average sound levels 2200 measured for the 1 / 3 octave bands are shown in . These confirm that the sound levels of the two new nozzles with straight sections 2230 (BNG-V1), 2240 (BNG-V2) are lower across the entire spectrum compared to the standard nozzle 2210 and also significantly lower than the XL nozzle 2220 across most of the spectrum. It is also worth noting that the peak 2250 of the standard nozzle (Standard No. 6) is centered at 4000 Hz, which may be associated with the greater turbulence generated by the high-speed jet and / or jet screeching, which is avoided by the subsonic exit velocity after the positive shock wave at the nozzle exit.

[0274] Additional testing was conducted on a new nozzle (Oceanit BN6V1) with a shorter straight section versus a standard No. 6 nozzle using steel shot media at about 90 psi nozzle pressure. The same coated panels described for the above tests were used to measure the productivity of the nozzles (time for the spray to clean the panel). Two tests were conducted on each nozzle. The results are shown in Table 2 below. In the first test, the new nozzle performed the same as the standard nozzle (about 53 seconds per nozzle to clean the panel). In the second test, the new nozzle outperformed the standard nozzle (30 seconds versus 47 seconds). Generally, the second test is more reliable because the user has time to adapt to the particular nozzle.

[0275]

[0276] Table 2: Steel shot, 90 psi.

[0277] Thus, the new noise reduction abrasive jet nozzle is proven to be superior in commercial abrasive jet environments. High particle velocity produces a high productivity nozzle. Low outlet air velocity produces a low noise nozzle. The new nozzle maintains or increases the abrasive particle velocity leaving the nozzle while reducing the outlet air velocity. The new nozzle (based on the No. 6 nozzle) uses an extended outlet section that extends the high Mach number acceleration region of the nozzle while producing a much lower outlet velocity in part (in some embodiments) by forming a positive shock wave at the end of the nozzle. In tests using garnet and steel shot, the productivity of the new nozzle was shown to be superior to the standard No. 6 nozzle while achieving a 17dB noise reduction over commercial nozzles, reducing recoil and resulting user fatigue, and improving operating characteristics. CFD modeling shows an improved particle acceleration region.

[0278] Reducing employee exposure to hazardous noise to below the OSHA 8-hour time-weighted average alleviates the need for employers to modify employee current practices, reduces the need for personal protective equipment (PPE), reduces the potential for injury in the event of a PPE failure, and ensures that personnel in adjacent "safe areas" are protected from exposure. Most importantly, reducing noise in a spraying facility to 90 dBA or less allows workers to operate for up to an 8-hour standard workday in compliance with OSHA. It should also be understood that reducing noise by a minimum of 3 dBA will benefit workers using such quieter nozzles. In fact, reducing noise by, for example, 6 dBA will be very important in reducing the risk of worker injury.

[0279] Although the test of the embodiment of No. 6 nozzle is described above, other embodiments can be any size including No. 8 nozzle, No. 7 nozzle and No. 5 nozzle or No. 6 90 degree nozzle or other 90 degree nozzle. The same design can be applied to any convergent-divergent nozzle using any type of abrasive media / material including cinder, garnet, acrylic acid, etc. Usually, compressed air is used. In some embodiments, water vapor can be used. The new nozzle can be made of, for example, tungsten carbide, silicon carbide, boron carbide, acrylic acid, ceramic, stainless steel, hardened steel, aluminum, any other known nozzle material or a combination of the above (with or without wear-resistant ceramic liner). The nozzle can have a protective handle to improve operation and eliminate concerns about static electricity of the stainless steel version. The nozzle can be designed to be used for various pipe pressures and spray modes and used with various pipe pressures and spray modes.

[0280] As will be understood from the description, drawings, and examples described above and cited herein, the noise-reduced abrasive blasting system of the present invention allows abrasive blasting to be performed with a significant reduction in the resulting noise while providing equivalent or improved productivity and efficiency compared to conventional abrasive blasting systems. This improved noise-reduced abrasive blasting system promotes worker health and safety and provides a quieter environment for nearby personnel.

[0281] Embodiments of the improved abrasive jetting system utilize an extended accelerator section in the tube and / or nozzle to maintain particle velocity while reducing gas exit velocity. A straight bore nozzle can be used to create the desired effective abrasive area. The maintained particle velocity provides equivalent abrasive production rate, while the reduced gas velocity provides reduced resulting noise.

[0282] Although the specific preferred embodiments and examples of the manufacture and testing of the present invention have been shown and described, it is obvious that the present invention is not limited thereto. Without departing from the spirit and scope of the present invention, those skilled in the art will think of many modifications or changes, variations, modifications, substitutions and equivalents, and these are all considered as part of the present invention disclosed herein.

[0283] By way of example and not limitation, the size of the nozzle and the type of couplings and the specific configuration and size of the tubes, couplings, nozzles and accelerator sections can be varied according to the general principles of the invention as described herein to accommodate different operating conditions, target materials, project specifications, budgetary considerations and user preferences. The nozzle can have any throat diameters such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc., which are included in the embodiment characterized by the new nozzle with a straight section. In addition, more than one transition coupling and accelerator tube section and inner diameter can be used in the system of the present invention. The invention described herein includes all these modifications and variations.

[0284] Furthermore, the present invention should be considered to include all possible combinations of each and every feature described in the present description, the appended claims and / or the drawings which may be considered to be new, inventive and industrially applicable.

[0285] In the embodiment of the present invention described here, there can be multiple variations and modifications. Although some illustrative embodiments of the present invention have been shown and described here, extensive modifications, changes and substitutions are considered in the above disclosure. Although the above description contains many details, these should not be interpreted as limitations on the scope of the invention, but should be interpreted as examples of one or another preferred embodiment of the present invention. In some cases, some features of the present invention can be adopted without correspondingly using other features.

[0286] Therefore, the foregoing description should be construed broadly and understood as being given by way of illustration and example only, with the spirit and scope of the present invention being limited only by the claims that will finally issue.

Claims

1. A high productivity quiet abrasive jet nozzle comprising: a converging portion having a converging inner diameter; a throat connected to the converging portion; a diffuser portion connected to the throat; as well as a straight portion connected to the diffuser portion and immediately behind the diffuser portion; wherein the straight portion has a length such that when the injection nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the velocity of gas leaving the injection nozzle is reduced by at least 30% relative to the injection nozzle with the straight portion removed; and wherein, in operation, the fluid flows sequentially through the convergent portion, the throat, the divergent portion and the straight portion, wherein the fluid flows through the diverging section and the Mach number at the exit from the diverging section to the straight section is greater than 1, wherein the length L of the straight portion is at least L * , the L * Given by the following equation: Wherein, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight portion, M is the Mach number of the fluid at the inlet of the straight portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

2. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The inner diameter of the straight portion is smaller than the maximum inner diameter of the converging portion.

3. A high productivity, quiet abrasive jet nozzle assembly comprising the abrasive jet nozzle according to claim 1.

4. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The nozzle is configured such that, for the predetermined gas-particle mixture and predetermined pressure, a supersonic flow of the gas is isolated to the interior of the nozzle and the supersonic gas flow accelerates the abrasive particles in the straight portion.

5. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The nozzle is configured such that: for the predetermined gas and particle mixture and the predetermined pressure, the gas Mach number is: The outlet of the straight portion is smaller than the outlet of the divergent portion, thereby reducing the operating noise; as well as The gas Mach number decreases from greater than 1 at the outlet of the diverging section to a gas Mach number of 1 at the outlet of the straight section.

6. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The length of the straight portion is between at least two tenths of the inner diameter of the straight portion and The straight portion is between ten times the inner diameter.

7. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The length of the straight portion is between 1 inch and 10 inches.

8. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The straight portion is configured to be attached to and detached from the diffuser portion.

9. The high productivity quiet abrasive jet nozzle of claim 8, further comprising one or more additional straight sections configured to be attached to and detached from the diffuser section, wherein: The straight portion and the one or more additional straight portions each have at least one of a different length and a different inner diameter.

10. The high productivity quiet abrasive jet nozzle of claim 9, wherein: Each of the one or more additional straight sections has a length such that, when the injection nozzle is operated with a different predetermined gas-to-particle mixture and a predetermined pressure, the velocity at which the gas leaves the injection nozzle is reduced by at least 30% relative to the injection nozzle with the straight sections removed.

11. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The straight portion is cylindrical in shape.

12. The high productivity quiet abrasive jet nozzle of claim 1 further comprising a fluid flowing through the straight portion and having a Mach number of 1 at an exit of the straight portion.

13. The high productivity quiet abrasive jet nozzle of claim 1 further comprising a plurality of abrasive particles in a supersonic fluid flow within an interior of said nozzle, said supersonic fluid flow being subjected to a shock wave in said straight portion.

14. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The nozzle is made of a material selected from the group consisting of tungsten carbide, silicon carbide, boron carbide, acrylic, ceramic, stainless steel, hardened steel, aluminum, or combinations thereof.

15. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The nozzle also includes at least one protective grip.

16. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The length of the straight portion is such that the spray nozzle has a noise level of 90 dBA or less when operated with the predetermined gas and particle mixture and predetermined pressure.

17. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The length L of the straight portion is at least L * , the L * It is adjusted according to the ratio of back pressure to outlet pressure, where L * Given by the following equation: Wherein, for a predetermined mixture of gas and abrasive particles, D is the diameter of the straight portion, M is the Mach number of the fluid at the inlet of the straight portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

18. A method for manufacturing the nozzle according to claim 1 to reduce the noise of the nozzle without reducing the productivity of the nozzle, the method comprising: determining, for the predetermined mixture of gas and abrasive particles and predetermined pressure, a minimum length of the straight section according to claim 1, the minimum length of the straight section being the length required for the gas to produce a Mach number of 1 at or within a straight section inner diameter prior to exit from the straight section; as well as The nozzle is manufactured to have a straight portion having a length equal to or greater than the minimum length.

19. The method according to claim 18, further comprising: The optimum length of the straight portion according to claim 1 is determined so that the Mach number of the gas decreases from a peak value at a first point as the end of the divergent portion before the outlet of the straight portion to a Mach number of 1 at a second point at or within a length equal to the inner diameter of the straight portion without entering subsonic speed between the first point and the second point; as well as The nozzle is manufactured with a straight portion having the optimum length.

20. The method according to claim 19, wherein: The step of determining the optimal length includes at least one of the following: An analysis is made of the effect of friction from the walls of the straight section, and The effect of the plurality of abrasive particles on reducing the air flow velocity in the straight portion was analyzed.

21. The method of claim 18, further comprising: Repeatedly computer-simulating the nozzle of claim 1 over a range of straight section lengths to find a length that provides a desired combination of sound reduction and productivity; And manufacturing the nozzle having the length.

22. A nozzle attachment for high productivity quiet abrasive blasting comprising: a straight tubular portion for connecting to an outlet of an abrasive jet nozzle; wherein the straight tubular portion has a length such that when the abrasive jet nozzle is operated with a predetermined gas and particle mixture and a predetermined pressure, the velocity of the gas leaving the abrasive jet nozzle connected to the straight tubular portion is reduced by at least 30%, wherein, when the straight tubular portion is connected to the outlet of the abrasive jet nozzle, the straight tubular portion is immediately behind the outlet of the abrasive jet nozzle, wherein the straight tubular portion is configured such that: for the predetermined gas-particle mixture and the predetermined pressure, when the straight tubular portion is connected to the abrasive jet nozzle, the supersonic flow of gas does not continue beyond the outlet of the straight tubular portion, and the supersonic gas flow accelerates the abrasive particles in the straight tubular portion, Wherein, the length L of the straight tubular portion is at least L * , the L * Given by the following equation: wherein, in the case where the straight tubular portion is connected to the abrasive jet nozzle, for the predetermined mixture of gas and abrasive particles, D is the diameter of the straight tubular portion, M is the Mach number of the fluid at the inlet of the straight tubular portion, is the average friction coefficient of the straight section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

23. The nozzle attachment of claim 22, further comprising a fastener embedded in the straight tubular portion to assist in connecting the straight tubular portion to the abrasive jet nozzle.

24. The nozzle attachment of claim 22, wherein: The inner diameter of the straight tubular portion is smaller than the maximum inner diameter of the converging portion of the abrasive jet nozzle.

25. The nozzle attachment of claim 22, wherein: The straight tubular portion is configured such that: when the straight tubular portion is connected to the abrasive jet nozzle, for the predetermined gas and particle mixture and the predetermined pressure, the gas Mach number is: The outlet of the straight tubular portion is smaller than the outlet of the diverging portion of the abrasive jet nozzle, thereby reducing operating noise; and The gas Mach number is reduced from greater than 1 at the outlet of the diverging portion of the abrasive jet nozzle to a gas Mach number of 1 at the outlet of the straight tubular portion.

26. The nozzle attachment of claim 22, wherein: The length of the straight tubular portion is between at least two tenths of the diameter of the straight tubular portion and ten times the diameter of the straight tubular portion.

27. The nozzle attachment of claim 22, wherein: The straight tubular portion has a length between 1 inch and 10 inches.

28. The nozzle attachment of claim 22, wherein: The straight tubular portion is cylindrical in shape.

29. The nozzle attachment of claim 22, wherein: The straight tubular portion is made of a material selected from the group consisting of tungsten carbide, silicon carbide, boron carbide, acrylic, ceramic, stainless steel, hardened steel, aluminum, or combinations thereof.

30. The nozzle attachment of claim 22, wherein: The length of the straight tubular portion is such that, when the straight tubular portion is connected to the abrasive jet nozzle, the abrasive jet nozzle has a noise level of 90 dBA or less when operating with the predetermined gas and particle mixture and the predetermined pressure.

31. The nozzle attachment of claim 22, wherein: The length L of the straight tubular portion is at least L * , the L * It is adjusted according to the ratio of back pressure to outlet pressure, where L * Given by the following equation: wherein, in the case where the straight tubular portion is connected to the abrasive jet nozzle, for the predetermined mixture of gas and abrasive particles, D is the diameter of the straight tubular portion, M is the Mach number of the fluid at the inlet of the straight tubular portion, is the average friction coefficient of the straight tubular section, f abrasives is the friction coefficient of the particles in the fluid flow, and γ is the specific heat ratio of the fluid flow.

32. A method for manufacturing a nozzle attachment according to claim 22 to reduce the noise of an attached abrasive jet nozzle without reducing the productivity of the nozzle, the method comprising: determining, for the predetermined mixture of gas and abrasive particles and predetermined pressure, a minimum length of the straight tubular section according to claim 22, the minimum length of the straight tubular section being the length required for the gas to produce a Mach number of 1 at or within a straight tubular section inner diameter prior to exit from the straight tubular section; as well as The straight tubular portion is manufactured to have a length equal to or greater than the minimum length.

33. The method of claim 32, further comprising: The optimum length of the straight tubular portion according to claim 22 is determined so that the Mach number of the gas decreases from a peak value at a first point as an end of a diverging portion before the outlet of the straight tubular portion to a Mach number of 1 at a second point at or within a length equal to the inner diameter of the straight tubular portion without entering subsonic speed between the first point and the second point; as well as The straight tubular portion having the optimal length is manufactured.

34. The method of claim 33, wherein: The step of determining the optimal length includes at least one of the following: Analyzing the effect of friction from the wall of the straight tubular portion, and The effect of the plurality of abrasive particles on reducing the air flow velocity in the straight tubular portion was analyzed.

35. The method of claim 32, further comprising: iterative computer simulations of the straight tubular section of claim 22 over a range of straight tubular section lengths to find a length that provides a desired combination of sound reduction and productivity; and manufacturing the straight tubular portion having the length.

36. The high productivity quiet abrasive jet nozzle of claim 1, wherein: The length of the straight portion is such that, when the spray nozzle is operated with the predetermined gas and particle mixture and predetermined pressure, the spray nozzle has a noise level reduced by 3 dBA or more compared to a spray nozzle without the straight portion.

37. The nozzle attachment of claim 22, wherein: The length of the straight tubular portion is such that, when the straight tubular portion is connected to the abrasive jet nozzle, when the jet nozzle is operated with the predetermined gas and particle mixture and the predetermined pressure, the jet nozzle has a noise level reduced by 3dBA or more compared to the abrasive jet nozzle without the straight tubular portion.

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