Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C5/00—Devices or accessories for generating abrasive blasts
  • B24C5/02—Blast guns, e.g. for generating high velocity abrasive fluid jets for cutting materials
  • B24C5/04—Nozzles therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
  • B24C1/003—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods using material which dissolves or changes phase after the treatment, e.g. ice, CO2
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C7/00—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts
  • B24C7/0046—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts the abrasive material being fed in a gaseous carrier

Definitions

• the invention relates to a blasting method for cleaning surfaces, in which a carrier gas is fed under pressure through a blasting line to a blasting nozzle and liquid CO2 is fed in via a feed line, converted into dry snow by expansion and fed into the blasting line, and a device for carrying it out this procedure.
• a blasting method of this type is described in US Pat. No. 5,616,067.
• the CO2 is introduced in liquid form into an annular chamber which surrounds the jet line through which compressed air flows, and is fed from there via a ring of converging capillaries into the jet line, so that the relaxation only takes place when it enters the jet line.
• the dry snow created in this way is carried along by the compressed air and accelerated and discharged onto the workpiece to be cleaned via the jet nozzle.
• This method is used in particular for the gentle cleaning of pressure-sensitive surfaces, for example electronic circuit boards.
• US Pat. No. 5,679,062 discloses a blasting method in which gaseous or liquid CO2 or a gas-liquid mixture is expanded at the outlet of a nozzle and introduced into an expanded swirl chamber in which part of the gaseous and / or liquid CO2 is converted into dry snow becomes.
• the outlet of the swirl chamber is directly connected to a jet nozzle.
• the carrier gas used here is only the gaseous CO 2 gas which is supplied or is formed by evaporation.
• US Pat. No. 5,725,154 A describes a blasting method in which dry snow is produced by releasing liquid CO 2 with the aid of an expansion valve.
• the dry snow is fed through a thin hose, which is coaxially surrounded by a hose for supplying the carrier gas, to a jet gun, which then releases a mixture of carrier gas and dry snow.
• a blasting device in which liquid CO 2 is supplied via a capillary which opens into a conically widening nozzle, the diameter of which increases towards the outlet to approximately 3 times the diameter of the capillary.
• This nozzle is of an annular Laval Surround nozzle in which the carrier gas supplied under pressure is accelerated to supersonic speed.
• the mouths of the CO 2 nozzle and the Laval nozzle are at the same height, so that two concentric jets are emitted, namely an inner jet, which mainly consists of dry snow, and a jacket jet, through which the dry snow outside the nozzle is to be accelerated.
• the blasting methods described at the outset are not suitable for these applications because the achievable volume outputs and jet speeds are insufficient and / or because the dry snow does not form in sufficient quantity or does not have the correct consistency, so that the kinetic energy of the dry snow particles is too low ,
• blasting systems have previously been used for cleaning larger, heavily contaminated surfaces, in which dry ice or dry snow is provided in solid form in suitable cooling containers and metered into a compressed air flow.
• the compressed air and the dry snow serving as blasting agent are then released together via a pressure hose that connects the blasting system to the blasting nozzle.
• Blasting devices and methods of this type require a high installation effort and correspondingly high installation costs as well as a high effort for the storage of the dry snow.
• the object of the invention is therefore to provide blasting methods and blasting devices with which high blasting powers and a high cleaning effect can be achieved with little effort.
• the CO 2 is introduced from the supply line into the beam line via an expanded relaxation space.
• the formation of highly abrasive dry snow or dry ice is achieved simply by the fact that the relaxation space has a sufficiently large volume.
• the cleaning effect could be multiplied by enlarging the relaxation area under otherwise identical conditions.
• This surprising phenomenon is presumably due to the fact that in the larger relaxation space between the mouth of the feed line and the feed point into the jet line there is a temporary decrease in the flow velocity and thus an increase in the particle density, so that it initially becomes fine during the expansion atomize dry snow particles to larger particles or condense before they are carried away by the flow of the carrier gas. In this way, dry snow particles with a larger mass are created, which then have a high cleaning effect due to their higher kinetic energy.
• the relationship should then apply to the volume V of the relaxation space based on the cross-sectional area A of the feed line for the liquid CO 2: v l / 3 / A l / 2> 3 or preferably V 1 3 ⁇ 1 2 > 10.
• the volume V of the relaxation space can also be related to the throughput ⁇ of liquid CO 2.
• the following should apply: V / ⁇ > 0.2 m 3 s / kg, preferably V / ⁇ > 0.6 ⁇ ) X s / kg.
• the method can also be carried out in the case of a smaller volume of the relaxation space if the smaller volume is compensated for by a higher pressure and correspondingly a higher throughput of the carrier gas and / or if the relaxation space has a sufficient length, for example a length of at least 15 or 30 mm.
• the temperature prevailing in the relaxation room is regarded as an essential factor for the formation of highly abrasive dry ice particles. This temperature should be as low as possible, preferably below -40 ° C. If the process according to the invention is carried out with a sufficiently high carrier gas throughput (for example 0.75 m 3 / min) and if the throughput of liquid CO2 is in an optimal ratio to the air throughput, for example in the order of 0.1 to 0. 4 kg CO2 per cubic meter of carrier gas (volume under atmospheric pressure), the cooling effect resulting from the evaporation of CO2 is apparently so great that the relaxation room is kept at a sufficiently low temperature.
• a sufficiently high carrier gas throughput for example 0.75 m 3 / min
• the throughput of liquid CO2 is in an optimal ratio to the air throughput, for example in the order of 0.1 to 0. 4 kg CO2 per cubic meter of carrier gas (volume under atmospheric pressure)
• the cooling effect resulting from the evaporation of CO2 is apparently so great that the relaxation room is kept at a
• the relaxation room is therefore thermally insulated from the surroundings, so that the desired high cleaning effect can be achieved even with a small relaxation room volume and small throughputs. It proves to be advantageous if the supply line for the liquid CO 2 is also thermally insulated from the environment and is in good thermal contact with the walls of the relaxation room (e.g. through a heat exchanger), so that already in a certain pre-cooling of the liquid CO 2 takes place in the supply line.
• the blasting device therefore has at least one interfering edge in the flow path between the junction point of the feed line for the liquid CO2 and the blasting nozzle.
• This interfering edge can, for. B. be formed at the transition point between the relaxation space and the beam line when the relaxation space opens laterally into the beam line.
• interfering edges can also be formed by an internal thread in a pipe socket forming the relaxation space or by fixed or movable internals such as an impeller, a worm or the like in the relaxation space.
• a blasting device with a source of liquid CO2, a relaxation nozzle connected to the source for producing dry snow and a pressure source connected to a constriction and converging from the constriction are also suitable for carrying out the method.
• the relaxation space opens into the straight-line flow line at an angle of approximately 10 to 90 °, preferably 20 to 45 °, in the direction of flow.
• a certain suction effect is achieved by the flow of the carrier gas, and the dry snow is gently diverted into the flow direction prevailing in the jet line.
• the flow of the carrier gas in the jet line has a component transversely to the longitudinal direction of the relaxation space, it is to be expected that a vortex will form at least in the downstream area of the relaxation space, which will extend the dwell time of the dry snow in the relaxation space and thus the agglomeration or that Particle or dry ice crust growth encouraged.
• the entry angle is preferably more acute so that the dry ice does not hit the opposite wall of the jet line.
• the junction of the relaxation space in the jet line is a short distance upstream of the jet nozzle.
• the blasting nozzle preferably has a constriction, so that the carrier gas and the blasting medium are accelerated to high speed. It is particularly preferred to design the jet nozzle as a Laval nozzle, in which an acceleration of approximately the speed of sound or supersonic speed is achieved.
• the distance between the mouth of the relaxation space in the jet line and the narrow point of the jet nozzle (14) should preferably be greater than the diameter of the jet line.
• the supply of dry ice immediately upstream of the nozzle reduces the temperature of the medium and increases its density, which shifts the operating point of the Laval nozzle.
• the cross section of the narrow place the Laval nozzle larger than in the event that the medium is supplied with the same pressure and throughput exclusively via the jet line.
• the sublimation of dry snow increases the gas volume and accelerates the flow in front of, in or behind the constriction of the nozzle.
• drops of liquid CO2 can get into the jet line or the jet nozzle and only evaporate there.
• the position at which this evaporation and / or sublimation takes place can be adjusted by regulating the carrier gas flow so that an optimal jet speed is achieved.
• the throughput of the carrier gas is too high, so that a high dynamic pressure builds up in front of the jet nozzle, the amount and the cleaning efficiency of the dry snow produced decrease. It is therefore expedient to provide a throttle valve in the jet line upstream of the opening parts of the expansion space, with which the throughput of the carrier gas can be optimally adjusted.
• a metering valve is preferably also provided in the feed line for the liquid CO2 directly at the inlet into the blasting device, so that the throughput ratio of carrier gas and CO2 can be set directly on the blasting device.
• a small amount of water or another solid or liquid blasting agent (for example solid dry ice pellets) is metered into the carrier gas flow and / or into the expansion space in order to further increase the cleaning effect.
• FIG. 1 shows a section through a blasting device for performing the method according to the invention
• Figure 2 shows a section through a blasting device according to a modified embodiment
• Figure 3 shows an enlarged detail of Figure 2
• Figure 4 is a schematic section through a gradually tapering beam line
• Figures 5 to 7 sections and a front view of a nozzle of the blasting device.
• a beam line 10 is formed by a straight cylindrical tube which has an inside diameter DL of 39 mm.
• An inlet 12 of the jet line is connected to a compressor, not shown, via which compressed air is supplied at a pressure of, for example, 1.1 MPa.
• a jet nozzle 14 designed as a Laval nozzle is coupled to the mouth of the jet line 10.
• This jet nozzle has a converging section 16, the inside diameter of which decreases from 32 mm at the upstream end to 12.5 mm at a constriction 18, and a divergent section 20, whose inside diameter increases from the constriction 18 to 19 mm at the downstream end.
• the total length LL of the jet nozzle is 224 mm.
• the length LC of the converging section 16 is 83 mm.
• a connecting sleeve 22 between the jet line 10 and the Laval nozzle 14 has an inner diameter of approximately 32 mm, corresponding to the inlet diameter of the jet nozzle.
• the tube forming the jet line 10 has a branch 24 which opens into the jet line 10 at an angle of 45 ° in the direction of flow.
• the distance D between the branch 24 and the inlet opening of the jet nozzle 14 is approximately 66 mm.
• a throttle valve 26, for example a ball valve, is arranged upstream of the branch 24 in the jet line 10.
• a tubular transition piece 28 is screwed into the branch 24, the free end of which is connected via a reducing piece 30 to a flexible feed line 32 for liquid CO 2.
• the supply line 32 is connected to a pressure bottle, not shown, which holds a supply of CO 2 under such a pressure that the CO2 remains liquid at ambient temperature. This pressure is, for example, about 5.5 MPa at an ambient temperature of 20 ° C.
• the feed line 32 has an inner diameter of 3 mm.
• the liquid CO 2 flows out via the feed line 32 due to the pressure drop, without any conveying devices being required.
• the throughput is limited by the small cross section of the feed line 32.
• the transition piece 28 forms a relaxation space 34 which has two cylindrical sections 36, 38 with different diameters.
• the upstream section 36 which directly adjoins the feed line 32, has an inner diameter DC1 of 20 mm and a length L1 of 85 mm.
• the downstream section 38 with an inner diameter DC2 of 32 mm and a length L2 of 105 mm is connected via a short conical section.
• the total length LE of the relaxation room 34 is thus 190 mm.
• the branch 24 has an inside diameter DC3 of 39 mm, corresponding to the inside diameter DL of the beam line 10.
• the liquid CO2 can suddenly relax. Part of the CO2 is evaporated. Evaporation and pressure relief result in cooling, so that another part of the liquid CO2, which is finely atomized when entering the relaxation room, condenses into fine dry snow particles. Since the cross-sectional area of the upstream section 36 of the expansion space 34 is approximately 44 times the cross-sectional area of the feed line 32, the mixture of gaseous CO2 and dry snow flows through the upstream portion 36 of the expansion space at a moderate speed. Upon entering downstream section 38, the speed is further reduced. On their way through the relatively long relaxation space 34, the fine dry ice particles can clump together to form larger particles (agglomeration).
• the particles can also grow in part through recondensation of gaseous CO2.
• branch 24 which has been expanded again, relatively large dry snow particles have therefore formed, which are now caused by the suction Effect of the compressed air flowing through the jet line 10 are sucked away and taken to the jet nozzle 14.
• the jet nozzle 14 the compressed air and the dry snow are accelerated to high speed, possibly supersonic speed, so that a jet with a high cleaning effect emerges from the jet nozzle.
• this jet is directed at a surface to be cleaned, the dry snow acts as a blasting agent with which the surface can be cleaned efficiently.
• a longer hose section can be provided between the point at which the relaxation space opens into the jet line and the jet nozzle 14.
• feed lines 32 open into the jet line 10 via respective relaxation spaces.
• the openings of the relaxation spaces in the beam line can be distributed over the circumference of the beam line and / or offset in the axial direction.
• several supply lines 32 open into a common relaxation space.
• Another carrier gas can also be supplied via the jet line 10 instead of compressed air.
• Another blasting agent can also be added to this carrier gas or the compressed air. It is also conceivable to allow additional solid or liquid blasting media to discharge into the blasting line upstream or downstream of the branch 24 or, if appropriate, also into the relaxation space 34 via lateral feeds.
• Figure 2 shows a blasting device according to a modified embodiment.
• the relaxation space 34 is formed only by the interior of the branch 24.
• This branch has an internal thread 40 into which the reducer 30 is screwed.
• a metering valve 42 is arranged at a short distance upstream of the reducer 30, with which the throughput of liquid CO 2 can be adjusted.
• a setting has proven to be favorable in which the throughput of liquid CO 2 is approximately 0.1 to 0.3 kg per cubic meter of carrier gas (air) (the carrier gas throughput relates to the carrier gas volume under atmospheric pressure).
• the part of the beam line 10, which contains the branch 24, and the section of the feed line 32 directly adjoining the reducer 30 are embedded in a sheath 44 made of heat-insulating material, which is indicated by dash-dotted lines in the drawing.
• This on the one hand facilitates the handling of the blasting device designed as a steel gun and on the other hand improves the thermal insulation of the expansion space 34 and the adjoining section of the feed line, so that a lower temperature is achieved in the expansion space.
• the branch 24 is shown enlarged in FIG. It can be seen that the internal thread 40 extends beyond the reducer 30 and forms part of the inner wall of the relaxation space 34.
• the flow path for the dry snow from the mouth of the feed line 32 to the jet line 10 is limited by a number of interfering edges.
• a first interference edge is formed directly by the abrupt cross-sectional widening from the feed line 32 to the inner cross section of the relaxation space 34 on the inner surface of the reducer 30. Further interfering edges are located at the junction parts of the branch 24 in the beam line 10.
• the threads of the internal thread 40 also act as interfering edges.
• the relaxation space 34 has the same inside diameter as the beam line 10, but can optionally also have a smaller inside diameter.
• the angle at which the branch 24 opens into the beam line 10 can also be varied, preferably in the range between 20 and 45 °.
• the length LE of the relaxation space (measured on the central axis) is approximately 49 mm, and the diameter DC3 of the relaxation space is 32 mm.
• the relaxation space 34 then has a volume V of approximately 39 cm 3 .
• the lead 32 has an inner cross section of about 7 mm 2, corresponding to a diameter of 3 mm, the ratio V ⁇ / A 1 - 72 is about 12.8.
• the air throughput through the jet line 10 is preferably about 3 to 10 m 3 / min, with an optimum at about 4.5 m / min.
• the corresponding throughputs ⁇ of CO2 are approximately 0.0015 kg / s to 0.05 kg / s or 0.023 kg / s for the optimum.
• the corresponding values for the ratio V / ⁇ are then 0.0026 - 0.0008 m 3 s / kg or 0.0018 m 3 s / kg for the optimum.
• the constriction 18 of the jet nozzle 14 has a diameter of 13.1.
• the beam line 10 has a smaller inner diameter of 12.7 mm
• the diameter DC3 of the relaxation space 34 is also 12.7 mm
• the length LE of the relaxation space is approximately 37 mm.
• the relaxation space has a volume V of approximately 4.7 cm 3 .
• the air throughput is then preferably between 1.5 and 2.5 m 3 / min. If the ratio of CO 2 to air is again 0.3 kg / m 3 , the ratio V / ⁇ is between 0.00062 and 0.00037 m 3 s / kg. The value V l / 3 / A 1/2 in this case about 6.3.
• the constriction 18 of the jet nozzle 14 preferably has a diameter of 8 mm.
• the internal cross section of the beam line 10 remains essentially constant in the exemplary embodiments described above, embodiments are also possible in which this internal cross section varies.
• the inner cross section of the beam line can narrow in the manner shown in FIG. 4 in two stages, but with flowing transitions. Possible positions for the branch 24 are also shown in FIG. 4.
• the relaxation room should not be too small in volume and in particular should not be too small in length.
• the length of the relaxation space is 100 mm or more.
• the feed line 32 has an inner diameter of 3 mm
• embodiments are also conceivable in which the feed line 32 upstream or preferably at the confluence with the expansion space 34 has a constriction with a diameter of only 1.0 or 1.3 mm.
• a cold tank can optionally be provided for the supply of the liquid CO 2 via the feed line 32, in which the CO 2 at a temperature of approximately - 20 ° C under a pressure of less than 2.2 MPa, for example about 1.8 MPa, is kept liquid.
• FIGS. 5 to 7 show a modified embodiment of the jet nozzle 14, which 5 has the function of a Laval nozzle, but is designed as a flat nozzle and allows a fan-shaped expanded jet to be produced which has a relatively uniform density and speed profile over its width .
• This jet nozzle has upstream a cylindrical section 14a with the length La and the inner diameter Da, which is followed by a transition piece j 0 14b with the length Lb.
• Downstream is a flattened section 14c with the length Lc, which has a rectangular inner cross section.
• the transition piece 14b is used to adapt the cylindrical inner cross section of the section 14a to the rectangular inner cross section of the section 14c.
• This rectangular inner cross section has a substantially constant width W ig and a height which increases from a value H1 at the narrow point, at the end of the transition piece 14b, to a somewhat larger value H2 at the mouth.
• W ig the width W ig
• the jet nozzle 14 according to FIGS. 7 to 7 has the following dimensions:
• the inner surface has unevenness, which in the example shown is formed by longitudinal ribs 14d.
• Such bumps lead to a significant reduction in noise pollution, especially in supersonic operation.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Cleaning In General (AREA)
• Nozzles (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Cleaning By Liquid Or Steam (AREA)
• Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
• Recrystallisation Techniques (AREA)
• Carbon And Carbon Compounds (AREA)
• Cleaning Or Drying Semiconductors (AREA)

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• 2003
  • 2003-07-01 DK DK03807743T patent/DK1501655T3/da active
  • 2003-07-01 WO PCT/EP2003/007011 patent/WO2004033154A1/fr not_active Application Discontinuation
  • 2003-07-01 ES ES03807743T patent/ES2260691T3/es not_active Expired - Lifetime
  • 2003-07-01 BR BR0306448-4A patent/BR0306448A/pt not_active IP Right Cessation
  • 2003-07-01 AU AU2003249922A patent/AU2003249922A1/en not_active Abandoned
  • 2003-07-01 DE DE50302893T patent/DE50302893D1/de not_active Expired - Lifetime
  • 2003-07-01 US US10/528,390 patent/US7484670B2/en not_active Expired - Fee Related
  • 2003-07-01 MX MXPA05003096A patent/MXPA05003096A/es active IP Right Grant
  • 2003-07-01 EP EP03807743A patent/EP1501655B1/fr not_active Revoked
  • 2003-07-01 AT AT03807743T patent/ATE322357T1/de active
  • 2003-07-01 CN CNB038223317A patent/CN100500380C/zh not_active Expired - Fee Related

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