Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
  • B05B1/005—Nozzles or other outlets specially adapted for discharging one or more gases

Definitions

• a blowing device having a low noise level.
• Blowing tools are used within the industry in many connec ⁇ tions.
• An example is cleaning by means of air blowing, e.g. at turning and milling operations.
• Other examples are coo ⁇ ling, heating and drying, and transport of various details, e.g., at automatic machine tools.
• It may also be the ques ⁇ tion of blowing by means of other gases than air, e.g., pro ⁇ tective gas at welding operations .
• the noise generated by such blowing tools is frequently so high that levels of impaired hearing are reached.
• Fig. 1 is a longitudinal cross-sectional view.
• the gas is supplied to the tool via a high pressure hose or pipe 2, which is coupled to a source of gas having a pres- sure above the atmospheric pressure .
• a hand grip 3 is depressed which causes a valve slide 4 to be displaced so that gas can pass via a groove 5 in the slide and an extension tube 6 out through the mouth 7 of the extension tube .
• the mouth is not shaped as a so-called Laval nozzle, a maximum exhaust velocity is obtained at the so-called criti ⁇ cal pressure ratio.
• the pressure before the mouth at which the critical pressure ratio is reached is determined by the counterpressure after the mouth, which is in turn influenced by the degree of co-ejection or entraining ejection, i.e., to what extent the air jet leaving the mouth in its movement will entrain surrounding air.
• OMPI will be required in order to attain the critical pressure ratio.
• the interior of the blowing tool is designed so as to achieve low losses, i.e., if all passages for the gas befor the nozzle have a substantially greater cross sectional are than that of the nozzle 7, the pressure of the gas immedia ⁇ tely before the nozzle would be substantially the same as the pressure, for instance 6 to 8 bars, of the gas supplied by the pipe 2.
• the pressure of the gas after its expansion after the nozzl is never lower than the critical pressure, p , i.e. not low than 0.528 times the pressure immediately before the exit o the gas.
• the pressure of the gas after the expansion is normally at least 3 bars.
• the nozzle has such pro ⁇ perties that it provides a co-ejection sufficient for the counterpressure after the nozzle 7 to deviate only slightly from the pressure immediately after the expansion zone, i.e. in the contraction zone.
• the gas having the pressure p would otherwise meet a subpressure and expand in an explosi manner and the gas particles would be accelerated laterally so that a subpressure would be created in the jet core whic would have a retarding effect on the gas particles. This would be repeated periodically so that a standing pressure wave would be obtained consuming the energy of the gas belo the critical pressure while generating a strong noise. Also the effective blowing power of the jet would be considerabl reduced.
• the flow area at the valve In order to provide, at a predetermined supply pressure, a restriction of a mass flow obtained at a fully open valve, the flow area at the valve must be reduced. If the degree of restriction is such that the flow area at the valve is less than 0.52 times the flow area of the mouth, indepen ⁇ dently of the supply pressure and the counter pressure, the flow velocity at the valve is at least 1.2 times higher than the flow velocity at the mouth given by the pressure ratio. At such a restriction that the flow velocity at the valve is higher than the flow velocity obtained from the pressure ratio at the outlet, the noise generation at the valve is higher than the noise generation at the mouth.
• valve assembly is located at a smaller distance than a few meters from the mouth, the acoustic resistance is so small that the sound power is propagated out into the environment:around the mouth proper, so that the sound power obtained at the valve will totally or partly determine the sound level around a blowing tool in operation. To what extent this condition will occur is determined by the flow velocity actually present at the mouth. For if the velocity losses within the extension tube 6 are small the flow velocity ob ⁇ tained in practice at the mouth will be determined by the flow velocity at the valve.
• the flow velocity at the valve can give rise to two sound sources, which, besides that they may be added each one cause a higher sound level as compared with the case in which a reduced mass flow had been obtained by a reduced supply pressure, e.g., at a com- pressor equipment.
• the noise level increasing effect may be 3 to 10 dB(A) .
• the difference depends on the degree of reduction. Even in the cases where the flow area at the valve or at the connection of the tool is larger that the through-flow area at the mout the flow velocity at the valve or the connection may indirect ly cause an increased exhaust velocity and thus a more power ful noise generation as compared to the case, in which the valve or connection area is considerably larger than the out let area. For in a flow at subsonic velocity through a tube with losses, the pressure drop will cause a reduction of. the density of the flowing medium and, consequently, a correspon ding increase of the flow velocity.
• the object of the- present invention is to provide a blowing tool having a low noise level, a great blowing power and a high mechanical efficiency.
• the tool provides a flow, which is continuously controllable within a large range.
• a blowing device or a blowing tool, respectively, according to the present invention has the characteristic features stated in the claims.
• the device according to the invention may be considered as two series connected nozzles, which are separated by a chamber.
• the valve is a first restriction of the gas passage and the end nozzle is a second restriction.
• the flow channel connected to these restrictions is so wide that the velocity energy there can be disregarded, whereby the chamber, after the first restriction, will cause the kinetic energy at the first restriction to be lost.
• a state is obtained, which will be equivalent with the flow therethrough only but from a reservoar having a lower pres ⁇ sure.
• connection 8 the valve 11, 13 and the nozzle 17 of the blowing device have been provided with such through-flow areas that when the tool is in operation and the valve is fully open the pressure within the chamber 16 is at least equal to 0.9 times the gas pressure fed to the blowing de ⁇ vice.
• the chamber will also opera te as a pressure equalizing zone, thus reducing turbulences occurring at the first restriction.
• the end nozzle is desig ⁇ ned so that it will provide a high co-ejection of external 5 gas.
• the media jet will obtain a higher total mass flow but the noise generation will also be reduced.
• the nozzle comprises a plurali 10 ty of elongated gas exit channels the through-flow areas an also the added or total through-flow areas thereof being substantially less than the through-flow area of said chambe
• the higher counter pressure after the end nozzle, caused by the increased co-ejection, will allow a higher supply pres ⁇ sure to be utilized before a critical flow velocity will occur in the end nozzle.
• the dimensions of the valve are 25 such that at fully open valve the critical pressure ratio thereacross cannot be obtained, until after the critical overpressure has been obtained across the end nozzle.
• Figs. 2 to 10 show embodiments of a device according to the invention.
• Fig. 2 shows a longi
• Fig. 3 and 4 show the nozzle in longitudinal section and in end view respectively.
• Fig. 5 and 6 correspond to Fig. 2 but with the tool valve in half open and fully open position
• Figs. 7 and 8 shows a longitudinal section and an end view respectively of a second embodiment
• Figs. 9 and 10 show correspondig views of a third embodi ⁇ ment of the invention.
• a nipple 8 for the connection of a supply conduit for pressurized gas to the tool has a centre channel 9 hav ⁇ ing a cross sectional area A.
• a circular valve body 13 is secured to a control arm 12, said valve body being pressed towards the valve seat by means of a spring 14.
• the valve seat has a larqe diameter, whereby the flow velocity through a wholly open valve will be low, thus reducing the turbulences after the valve. As stated above the noise after the end nozzle will increase with increased turbulence of the gas reaching said nozzle.
• a conical or tapering extension sleeve wholly or partly formed of rubber or other elastic material, enclosing a cylindrical chamber 16.
• a pressure stabilized zone is obtai ⁇ ned.
• the chamber 16 ought to be greater than, suitably at least 2 times and preferably at least 3 times the sum of the thr ⁇ ugh- flow areas of the outlet channels 30.
• control arm 12 Owing to the fact that the control arm 12 is coupled to th end nozzle 17 the control arm maintains its concentric or coaxial position within the chamber even when the extensio sleeve 15 is displaced obliquely. This is essential in ord to avoid turbulences around the control arm.
• control arm 12 is, in the manner desci bed, coupled to the end nozzle acoustical resonances in th form of standing sound waves between the wall surfaces of the chamber 16 are also eliminated.
• differe ces in dynamic pressure at the movable valve member slight offset at the through-flow of the gas will not come into resonances with strong acoustical pressure maxima and in this manner so called “shriek” sounds often occurring in water-taps are avoided.
• the end nozzle 17 is circularly cylindrical and near its periphery it has a series of annularly located, cylindrical channels 30 having a small diameter d in relation to the mouth diameter D of the nozzle.
• the combined or total ⁇ i cross-sectional area of the channels must be smaller than all through-flow areas within the tool, i.e. smaller than the flow area A at the channel 9 but also smaller than the flow area of the valve as wholly opened. This is important in order that a critical flow shall notbe obtained at these restrictions before a critical flow occurs in the end nozzle.
• the channels should have a lengt L, which is at least 10 times the diameter d.
• L the contraction zone, i.e. the cross-section 0 where the gas is contracted in order thereafter to expand adiabatically, will come to exist shortly before the exit, i.e. within the respective outlet channel, so that the de ⁇ gree of expansion of the respective air jet is more uniform than in the case when the contraction occurs somewhat out-
• Half of the cone angle, 0t according to Fig. 3, of the exter ⁇ nal mantle of the nozzle should be less than 20°, preferably less than 15°, e.g. 4 to 10°.
• the mantle surface 32 should be smooth along all or at least a substantial portion of the
• the tool is also provided with means for a fixed adjustment of a predetermined gas flow. Such an adjustment is illustrated in Fig. 6.
• a stud 19 connected to the valve body 13 wings 23 are provided, which, when the extension sleeve 15 is screwed in a direc-
• the diameter d of the bores 30 may be about 0.3 to 1.5 mm and the bores may 35 have a mutual distance between centres of at least twice the bore diameter d.
• the centre axes of the bores are loca- ted on a circle with the diameter r Dy, wherein Dy may be la ger thanlD-6d.
• An inner series of bores may also be provid in a circle with the diameter Di, which is preferably larg than 2d. In the centre of the nozzle no bore corresponding to the bores 30 should be present.
• the maximum opening section of the valve 11, 13 shall be greater than, suitably at least 1.2 times and preferably at least 1.5 times the total cross sectional area of the outlet of the nozzle, i.e. the sum of the cross sectional areas of the outlet channels of the nozzle. At a smaller than maximum opening section of the valve this section can represent the narrowest section and cause noise.
• valve 11, 13 of the blowing tool is therefore suitably designed in such a manner that, when the valve opening has a through-flow area of about 0.5 times the total through- flow area of the outlet openings 30 of the nozzle, the dis tance between the movable valve member and the valve seat does not at any point exceed 0.2 millimeters and preferabl does not exceed 0.1 millimeter.
• the nozzl 17 is provided with one or more projections 40.
• Figs. 7, 8 and 41 Figs. 9 and 10, extending from the end surface or plane 33 of the nozzle.
• the lengts M of said projections is substantial and at least 1.2 times, preferably at least 2 times the diameter of the respective outlet channels 30, and the projections can be placed between the channels 30 as shown in Figs. 7 and 8.
• a single projec ⁇ tion 41 can be provided centrally of said surface 33, and surrounded by the outlet openings 30.
• Said projections are designed so that the co-ejection referred to above will no be materially disturbed and so that the noise level at the nozzle outlet is substantially increased.
• a prototype of the device according to the present invention in accordance with the embodiment illustrated in Fig. 2 has been subjected to practical testing and has been compared on one hand with many commercially available so-called silent blowing nozzles having a body of porous, sintered metal in ⁇ serted into the exhaust tube and has also been compared with many other conventional blowing tools.
• the con ⁇ ventional tools gave rise to higher air consumption and con ⁇ siderably higher noise levels and blowing power than the blo- wing tool according to the invention.

Landscapes

• Jet Pumps And Other Pumps (AREA)
• Details Of Valves (AREA)
• Percussion Or Vibration Massage (AREA)
• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
• Pipe Accessories (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20335204

Family Applications (1)

Country Status (13)

Families Citing this family (5)

Family Cites Families (9)

• 1978
  • 1978-06-14 SE SE7806883A patent/SE7806883L/xx not_active Application Discontinuation
• 1979
  • 1979-06-08 DE DE792952876A patent/DE2952876A1/de not_active Withdrawn
  • 1979-06-08 GB GB8022680A patent/GB2047574A/en not_active Withdrawn
  • 1979-06-08 JP JP50094679A patent/JPS55500443A/ja active Pending
  • 1979-06-08 WO PCT/SE1979/000131 patent/WO1980000064A1/en unknown
  • 1979-06-12 NO NO791957A patent/NO791957L/no unknown
  • 1979-06-12 GR GR59320A patent/GR68502B/el unknown
  • 1979-06-13 FI FI791890A patent/FI791890A/fi not_active Application Discontinuation
  • 1979-06-13 IT IT23541/79A patent/IT1121094B/it active
  • 1979-06-13 BE BE0/195721A patent/BE876956A/fr unknown
  • 1979-06-13 NL NL7904639A patent/NL7904639A/xx not_active Application Discontinuation
• 1980
  • 1980-01-29 EP EP79900651A patent/EP0016042A1/de not_active Withdrawn
  • 1980-02-13 DK DK61980A patent/DK61980A/da unknown
  • 1980-07-07 SE SE8004994A patent/SE8004994L/xx unknown
• 1983
  • 1983-10-03 SE SE8305416A patent/SE451236B/sv not_active IP Right Cessation

Non-Patent Citations (1)

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