EP2151300B1 - Device and method for cleaning objects using dry snow - Google Patents

Abstract

The device has an expansion channel for producing carbon dioxide crystals from liquid carbon dioxide, and a venturi nozzle (7) for discharging the crystals, where the nozzle mixes the crystals with abrasive additives. The crystals and the additives are fed into a section (25) of small cross section of the nozzle, and the channel is partially spiral shaped around a compression part (23) of the nozzle. The additives are selected from a group consisting of lava granules, oil emulsive core e.g. cherry stone, glass beads and plastic granules e.g. polyethylene, polyamide and polycarbonate. An independent claim is also included for a method for cleaning surfaces of an object using dry snow.

Description

The present invention relates to an apparatus and method for cleaning articles by dry snow.

For cleaning the surfaces of objects in the industrial sector a variety of chemical and physical cleaning methods and possibilities are known.

Chemical cleaning methods require a high expenditure on safety and disposal facilities due to the often aggressive means used there and due to legal regulations. Therefore, in the physical cleaning processes in which the impurities are usually removed by bombardment or irradiation of the surface to be cleaned with sand, metal or glass particles, it is required that the cleaning be carried out even in separate cabins. For this purpose, the component to be cleaned must first be removed from the corresponding machine and inserted into such a cabin.

Another alternative is to clean components by bombardment with dry ice. Dry ice is carbon dioxide converted to the solid state and cooled to at least -78.5 ° C. Dry ice passes under atmospheric pressure directly from the solid state in the gaseous, whereby no molten liquid is formed. This can be particularly easy Way, namely with normal compressed air, both the bombardment with dry ice and the suction and removal of dirt particles done.

Dry ice is present during production in the form of snow. The generation of CO ₂ snow locally by means of a nozzle of liquid CO ₂ and the direct irradiation of a surface with this snow, possibly with the assistance of compressed air, is procedurally comparatively easy to handle and easy to automate.

However, the cleaning effect of CO ₂ snow is limited. To remove more stubborn soils, it is compressed into granules or pellets or the like by pressing them through dies. The mass density of the pellets is about 1000 kg / m ³ . They have the form of pins with a length of about 5 mm to 30 mm and a diameter of about 3 mm.

To further increase the cleaning effect of CO ₂ particles suggests the FR-A-2 837 122 to provide the cryogenic CO ₂ with an additive of synthetic or mineral particles. The CO ₂ particles are preferably around 150-250 microns, the synthetic or mineral particles by 50 microns in size. The synthetic additives may be formed, for example, from tallow or resin-coated recycling waste. With this method, coatings, such as paint, anti-corrosion paint, dust or grinding dust and natural impurities, such as fats are to be removed.

Cryotechnics, NL offers a similar process called CryoAdd, which uses dry ice (CO ₂ ) in the form of pellets, nuggets or blocks to clean objects, this dry ice material being blown onto the surface to be cleaned in a stream of compressed air. To increase the cleaning effect, abrasive or non-abrasive material can be added to this compressed air / dry ice mixture. Non-abrasive particles penetrate into the soil layer and allow for increased effect of explosive sublimation of the dry ice particles, while abrasive particles are used to mechanically remove hard surface layers.

However, the use of CO ₂ pellets also has disadvantages. For CO ₂ pellets, a special silo must be provided. If the pellets are stored too long in the silo, they clump together. The cleaning function of the pellets depends strongly on the storage time.

There are various devices (eg Cold Jet, Micro Clean) are known in which provided CO ₂ pellets or block ice in a separate device such as a rasp or the like. again to be crushed and then fed to a nozzle of the device. This comminution requires a lot of energy and thus leads to higher cleaning costs.

In the DE 2005 005 638 B3 A method and apparatus for cleaning, activating or pretreating workpieces by means of carbon dioxide snow blasting is described. By means of the device carbon dioxide snow is produced from pressurized CO ₂ fluids and at least one carrier pressure gas. An outlet nozzle is provided which accelerates the mixture, producing a two-phase carbon dioxide gas and carbon dioxide particles in an agglomeration chamber by agglomeration and densification of carbon dioxide snow crystals and radially admixing the carrier gas into a multi-stage mixing chamber. The mixing chamber is arranged in front of the outlet nozzle. In this way, a turbulent gas flow of high energy is provided for machining the workpiece. The apparatus may include a feed system which supplies solid abrasive particles in a first region or second region of the mixing chamber in order to improve the blasting performance.

From the EP 1 501 655 B1 goes forth a blasting method and a blasting device. In this device, liquid CO _{2 is} supplied via a feed line to a relaxation space expanded in cross-section. By relaxing the liquid CO _{2 is converted} into dry snow and fed together with a carrier gas under pressure to a jet nozzle. In this device may be provided, solid or liquid blasting agent via lateral feeds in the beam line upstream or downstream of a branch, which is arranged in front of the jet nozzle, is, or if necessary, in an even further downstream relaxation room open.

The WO 03/022525 A2 discloses a blasting method and apparatus. Here, a stream of a blasting medium, which carries an abrasive blasting agent provided. With the help of an adapter, an additional jet medium is supplied from a pressure source. The supply of the additional radiation medium takes place immediately before a jet nozzle, which has a bottleneck. It can be provided via the second blasting system to perform a radiation agent with higher abrasiveness, for example, granules.

From the US 4,924,643 A is a method and apparatus for irradiating workpieces by means of CO ₂ - pellets and additives. As additives particles are provided which are solid under ambient temperature, such as metal or plastic particles. The device has a sealed housing. In the housing, a nozzle for discharging the CO ₂ - pellets and the additives is arranged. The nozzle is connected via a line section and a valve with a funnel-shaped container. The funnel-shaped container is filled with the solid particles. Furthermore, the nozzle is connected via a line section to a device for producing CO ₂ pellets, wherein the pellets are brought by a crusher to the desired size. Via a line section, the nozzle is connected to a Trägergaszuführquelle formed, for example, for supplying compressed air at a pressure between 4 and 7 bar. The nozzle has a kind of mixing chamber, into which the line sections open to feed the particles, to supply the compressed air and to feed the CO ₂ pellets. In this mixing chamber thus the CO ₂ pellets and the additives are mixed together and then brought by the compressed air in the direction of a nozzle formed in the cross-sectional constriction and widening. Due to the cross-sectional constriction and widening the CO ₂ pellets and the additives accelerated and emitted to the object to be cleaned.

In the US 200410147204 A1 is an apparatus for processing thin-film structures, such as printed circuit boards, described with dry ice particles and abrasive particles, wherein a surface layer to be selectively removed. The abrasive particles may be formed, for example, of diamond particles, silicates, carbon nanotubes (CNTs), fullerene and alumina. By means of a nozzle, the dry ice particles and the abrasive particles adhering to them are to be blasted onto a component to be processed. The embodiment depicted in FIG. 10 of this publication is a device according to the preamble of claim 1.

The object of the present invention is to provide an apparatus and a method with which the efficiency of cleaning with dry snow can be further increased.

In particular, the object of the invention is to provide a method and a device suitable for carrying out the method for cryogenic cleaning of objects by means of dry snow with simultaneously high cleaning action and good handling and automation.

The object is achieved by a device according to claim 1 and a method according to claim 8.

According to the invention, a mixture of CO ₂ snow and abrasive additive is produced and directed to the object to be cleaned, wherein the mixture is preferably applied with compressed air.

According to the invention, a device for cleaning objects by means of dry snow is provided. The apparatus comprises an expansion channel for generating CO ₂ snow from liquid CO ₂ , a nozzle for discharging the CO ₂ snow, and means for mixing the CO ₂ snow with an abrasive additive, wherein the means for mixing the additive is the nozzle is.

The combination of CO ₂ snow and abrasive additive can clean surfaces considerably more than CO ₂ snow alone and therefore compensates well for the energetic weaknesses of the snow blasting process. On the other hand, the disadvantages of pellets do not occur. In particular, it is possible to accurately meter the cleaning effect and provide consistent. In contrast to the handling of CO ₂ pellets, this method of production is easy to control in terms of process technology and can be easily automated.

By applying compressed air, the resulting material flow can be ideally conditioned and the consumption of CO ₂ or additive can be limited.

Due to the fact that the additive is added only in the nozzle, the additive with the dry snow only comes into contact immediately before blasting.

The solid additives have a high heat capacity and a high temperature compared to dry snow. By adding the additive in the nozzle, the residence time of the additive in dry snow is short. This ensures that there is no appreciable heat transfer from the additive to the dry snow. As a result, the dry snow is delivered in almost unchanged quality together with the additive to the object to be cleaned.

Another significant advantage is that the abrasive additive only comes in contact with the nozzle. As a result, no increased wear caused by the additive takes place on the components upstream of the nozzle.

According to one embodiment, liquid CO _{2 is} supplied to an expansion channel and relaxed in it in such a way that CO ₂ snow and preferably additionally CO ₂ gas are produced therefrom. The CO ₂ snow is then fed to a Venturi nozzle. In such a construction, the dry snow produced is used without intermediate steps as it is produced. The handling and storage of liquid carbon dioxide is well and safely manageable.

The CO ₂ snow is preferably supplied in the section of the narrowest cross section of the Venturi nozzle or on the negative pressure side of the Venturi nozzle.

The abrasive additive will also be added in the section of the narrowest section of the venturi or on the vacuum side of the venturi.

The feed to the Venturi nozzle may be at least partially helically guided around the compression part of the Venturi nozzle. The addition at the narrowest point or the point of the smallest cross-section is advantageous because of the prevailing high flow velocity and the well-defined and stable flow conditions. Due to the helical arrangement, the supply for the CO ₂ snow, which requires a specific line length, can be realized in a space-saving manner.

Alternatively, the abrasive additive may be added at the mouth of the venturi, with the abrasive additive preferably being introduced by suction into the mass flow of CO ₂ snow and air.

• Sande (z.B. Quarz-, Muschel-,Lava-, Granitsand)
• Lavagranulat oder dergleichen,
• Calciumcarbonat,
• Calciumbicarbonat,
• Natriumhydrogencarbonat,
• Glasperlen oder dergleichen,
• Glasbruch, vorzugsweise aus Glasperlen oder dergleichen
• Metallpulver und/oder Metallstaub, vorzugsweise aus Eisen, einer Eisenlegierung, Aluminium, Kupfer oder Messing oder dergleichen,
• Korund oder dergleichen,
• Nuss-Schalen und/oder Bruchstücke davon,
• ölhaltige Kerne wie etwa Kirschkerne und/oder Bruchstücke davon,
• Kunststoffgranulat, vorzugsweise aus PE, PA, oder PC oder dergleichen.

The abrasive additive preferably comprises at least one of the following substances:

• Sands (eg quartz, shell, lava, granite sand)
• Lava granules or the like,
• calcium carbonate,
• calcium bicarbonate,
• sodium bicarbonate,
• Glass beads or the like,
• Glass breakage, preferably from glass beads or the like
• Metal powder and / or metal dust, preferably of iron, an iron alloy, aluminum, copper or brass or the like,
• Corundum or the like,
• Nut shells and / or fragments thereof,
• oily kernels such as cherry pits and / or fragments thereof,
• Plastic granules, preferably made of PE, PA, or PC or the like.

Fig. 1

zeigt eine prinzipielle Funktionsweise der Erfindung.

Fig. 2

zeigt ein erstes Ausführungsbeispiel der Erfindung.

Fig. 3

zeigt ein zweites Ausführungsbeispiel der Erfindung.

Fig. 4

zeigt ein drittes Ausführungsbeispiel der Erfindung.

Fig. 5

zeigt eine Abwandlung des dritten Ausführungsbeispiels.

Other objects, features and advantages of the present invention will become apparent from the description of the exemplary embodiments illustrated in the accompanying drawings.

Fig. 1

shows a basic operation of the invention.

Fig. 2

shows a first embodiment of the invention.

Fig. 3

shows a second embodiment of the invention.

Fig. 4

shows a third embodiment of the invention.

Fig. 5

shows a modification of the third embodiment.

First, the principle of operation of the present invention will be described with reference to a schematic representation in FIG Fig. 1 explained.

As shown in Fig. 1 a device for cleaning 1 via a supply line 2 carbon dioxide (CO ₂ ), via an abrasive line 3, an abrasive additive (A) and a compressed air line 4 compressed air (DL) is supplied.

Within the device 1, a mixture of dry snow, abrasive and compressed air is generated from these components and discharged as a cleaning jet 5. The cleaning jet 5 is directed to an object 6 to be cleaned. Any devices for shutting off and regulating the mass flows of carbon dioxide, the compressed air and the additive and for keeping or generating the respective substances are not shown in detail in the figure; their execution will be adapted by the skilled person to the conditions and properties of the substances.

According to the invention, the device comprises a device for mixing CO ₂ snow with an abrasive additive, which is designed as a nozzle, preferably under pressure with compressed air, wherein the resulting mixture is dispensed onto the object to be cleaned.

The addition of abrasive material or of abrasive substances produces a mixture whose cleaning effect is superior to that of CO ₂ snow alone. The cleaning effect must be precisely metered and consistently provided. The combination of CO ₂ snow and the abrasive additive is easy to automate and is easy to control in terms of process engineering, eliminating the annoying handling of dry ice pellets.

Fig. 2 shows an embodiment of an apparatus according to the present invention. A venturi 7 is preceded by a connecting piece 8 and an ejection funnel 9 connected downstream. The venturi 7, the connecting piece 8 and the discharge funnel 9 can be integrated in a pistol grip (not shown in detail) or in a tool holder of a machine (not shown in more detail).

Via the supply line 2, the connecting piece 8 is connected to a container 10. The container 10 contains liquid carbon dioxide (LCO ₂ ). A pump 11 and a solenoid valve 12 are provided for regulating the mass flow. The solenoid valve 12 is shown in the figure as open / close valve (shut-off valve), but may also be designed as a control valve. The solenoid valve 12 can be controlled by a control device (not shown in detail) with a predetermined duty cycle to control the opening and closing times. A pressure tank 13 is provided to pressurize the container 10 with a predetermined pressure. The container 10 is cold-insulated.

About the only indicated compressed air line 4 the connecting piece 8 is also supplied compressed air. The connecting piece 8 is designed as an expansion channel. Of the Power is released in the expansion channel 8. In this way, a dry snow stream is generated which is mixed with the compressed air as the connecting piece continues to move.

In the section of the smallest cross-section of the Venturi nozzle 7, an abrasive material is supplied via the abrasive material line 3. This is entrained by the high flow velocity in the section of the smallest cross section and is distributed in the compressed air / dry snow stream to a mixture which is discharged via the discharge funnel 9 as a cleaning jet 5.

For the purposes of the invention, the venturi serves as a means for mixing the CO ₂ snow with an abrasive additive, preferably under pressurized air. The discharge hopper 9 serves as a means for directing the resulting mixture on the object to be cleaned, while the connecting piece serves as a means for supplying dry snow.

In Fig. 3 a second embodiment of the present invention is shown. A venturi nozzle 14 is supplied with compressed air / dry snow stream generated in an expansion channel and discharged at the outlet cross section 15 of the venturi nozzle.

The Venturi nozzle 14 is arranged coaxially within a tube wall 16, where it is flowed around by a stream of abrasive material as a sheath flow 17. At the outlet cross section 15 of the venturi 14, the abrasive stream is sucked by the compressed air / dry snow stream and entrained and mixed into a mixture 20, which is guided in a discharge pipe 19 for further use as a cleaning jet. In a region 18, the cross section of the tube wall 16 tapers to that of the discharge tube 19, whereby an additional acceleration effect is achieved.

By means of a bore 21 in the region of the smallest cross-section of the Venturi nozzle on the one hand a balance of pressure fluctuations can be achieved, on the other hand For example, the bore 21 may be formed such that a partial flow of the abrasive stream is already supplied here to the premix.

Fig. 4 shows the third, preferred embodiment of the invention. The device for cleaning comprises a nozzle 7, in which all essential parts are incorporated in a housing 22. The nozzle is designed, for example, as a Venturi nozzle 7. In the housing 22, a tapered compression portion 23 upstream and an expanding expander portion 24 is introduced upstream. The compression member 23 and the expansion member 24 meet within the housing 22 and together form the venturi nozzle with a small diameter portion (narrowest nozzle portion) 25.

Upstream of the compression part 23 is supplied from a source not shown compressed air DL. In the section of the smallest cross-section 25 26 CO ₂ snow is supplied from Vorentspannung via a CO ₂ supply. Likewise, an abrasive A is fed there via an abrasive feed 27. The CO ₂ supply 26 may be formed as an expansion channel 8, in which the CO ₂ snow is generated from liquid CO ₂ . Due to the high flow velocity in the section of the smallest cross-section 25 CO ₂ snow and abrasive are entrained and discharged together with the compressed air as a cleaning jet 5 downstream of the expansion part 24.

Fig. 5 shows a modification of the third embodiment. While in the latter both feeds 26 and 27 are formed as straight holes along the compression part 23, in the modification, the CO ₂ supply 26 'and the expansion channel 8 is helically guided around the compression part 24 around. In this way, the CO ₂ supply 26 ', which may have a considerable run length (eg 500 mm - 800 mm), compared to a straight design in a space-saving manner in the housing 22' are housed.

In all embodiments, the abrasive additive may be any solid that has an abrasive action and can be conveyed in the desired shape. It is based on the conditions, in particular the desired intensity of the abrasive Effect, but also the procurement options, the price, the storage and promotion properties and other properties and effects selected.

• Sande (z.B. Quarz-, Muschel-,Lava-, Granitsand)
• Lavagranulat oder dergleichen,
• Calciumcarbonat,
• Calciumbicarbonat,
• Natriumhydrogencarbonat (Backpulver),
• Glasperlen oder dergleichen,
• Glasbruch, vorzugsweise aus Glasperlen oder dergleichen
• Metallpulver und/oder Metallstaub, vorzugsweise aus Eisen, einer Eisenlegierung, Aluminium, Kupfer oder Messing oder dergleichen,
• Korund oder dergleichen,
• Nuss-Schalen und/oder Bruchstücke davon,
• ölhaltige Kerne wie etwa Kirschkerne und/oder Bruchstücke davon,
• Kunststoffgranulat, vorzugsweise aus PE, PA, oder PC oder dergleichen.

The following substances are available as abrasive additives:

• Sands (eg quartz, shell, lava, granite sand)
• Lava granules or the like,
• calcium carbonate,
• calcium bicarbonate,
• Sodium bicarbonate (baking powder),
• Glass beads or the like,
• Glass breakage, preferably from glass beads or the like
• Metal powder and / or metal dust, preferably of iron, an iron alloy, aluminum, copper or brass or the like,
• Corundum or the like,
• Nut shells and / or fragments thereof,
• oily kernels such as cherry pits and / or fragments thereof,
• Plastic granules, preferably made of PE, PA, or PC or the like.

It is also possible to use several additive substances in a selected mass or volume ratio. In this case, separate lines and feed points can be provided for different additives. For example, one additive may be added in the section of least cross-section 25, another in the exit section of the Venturi nozzle. It is also possible to provide a plurality of feed points in the region of the smallest cross section 25.

In addition to abrasive additives, it is also possible to add binders, antimicrobial, disinfectant, surfactants or odorizing substances as further additives. In this case, further feeding points come into consideration. For example, a liquid additive can be added directly into the cleaning jet or it can already be added to a liquid carbon dioxide before it is released.

Instead of the Venturi nozzle, a Laval nozzle may also be provided.

The inventive method and apparatus for cleaning objects by means of dry ice are characterized by the use of a mixture of CO ₂ snow, compressed air and an abrasive additive for cleaning articles.

LIST OF REFERENCE NUMBERS

1

Device for cleaning

2

Supply line for CO ₂

3

Conduction for abrasive

4

Line for compressed air

5

mass flow

6

object to be cleaned

7

venturi

8th

Union joint

9

discharge hoppers

10

Container for liquid CO ₂

11

pump

12

magnetic valve

13

pressure tank

14

venturi

15

exit plane

16

pipe wall

17

bowl channel

18

mixing area

19

drain pipe

20

mixture

21

drilling

22.22 '

casing

23

compression part

24

expansion part

25

Section of the smallest cross section

26.26 '

CO ₂ feed

27

Abrasive supply

A

abrasive

DL

compressed air

LCO ₂

liquid CO ₂

Claims (14)

1. Device (1) for the cleaning of articles by means of dry snow, with an expansion duct (8) for generating CO₂ snow from liquid CO₂, with a nozzle (7, 14) for dispensing the CO₂ snow, and with an arrangement (7, 14) for mixing the CO₂ snow with an abrasive additive, the expansion duct (8) preceding the nozzle, and the arrangement for mixing the additive (A) being the nozzle, characterized in that the device (1) has a compressed-air line in order to act with compressed air (DL) upon the CO₂ snow and the abrasive additive (A).
2. Device according to Claim 1, characterized in that the CO₂ snow is supplied in the portion of the smallest cross section (25) of the Venturi tube nozzle.
3. Device according to Claim 2, characterized in that the arrangement for supplying the CO₂ snow to the Venturi tube nozzle leads at least partially helically around the compression part of the Venturi tube nozzle.
4. Device according to one of Claims 1 to 3, characterized in that the abrasive additive is added in the region of the smallest cross section (25) of the Venturi tube nozzle.
5. Device according to one of Claims 1 to 4, characterized in that the abrasive additive is added at the mouth of the Venturi tube nozzle, the abrasive additive preferably being introduced by suction action into the mass flow of CO₂ snow and air.
6. Device according to Claim 5, characterized in that the Venturi tube nozzle is arranged within a tube wall and the abrasive additive flows around the Venturi tube nozzle within the tube wall in the manner of a jacket.
7. Device according to one of Claims 1 to 6, characterized in that the abrasive additive has at least one of the following substances:

   - lava granulate or the like,

   - calcium carbonate,

   - calcium bicarbonate,

   - sodium hydrogen carbonate,

   - glass beads or the like,

   - broken glass, preferably composed of glass beads or the like,

   - metal powder and/or metal dust, preferably composed of iron, an iron alloy, aluminium, copper or brass or the like,

   - corundum or the like,

   - nutshells and/or fragments thereof,

   - oleaginous stones, such as, for example, cherry stones and/or fragments thereof,

   - plastic granulate, preferably composed of PE, PA, or PC or the like.
8. Method for the cleaning of articles by means of dry ice, liquid CO₂ being expanded to form CO₂ snow, and subsequently a mixture of CO₂ snow and of abrasive additive being generated in a nozzle and being directed onto the article to be cleaned, characterized in that the mixture is acted upon with compressed air.
9. Method according to Claim 8, characterized in that the CO₂ snow is supplied in the region of the smallest cross section of the Venturi tube nozzle.
10. Method according to Claim 9, characterized in that the CO₂ snow, before being supplied to the Venturi tube nozzle, is led at least partially helically around the compression part of the Venturi tube nozzle.
11. Method according to either one of Claims 9 and 10, characterized in that the abrasive additive is added in the region of the smallest cross section of the Venturi tube nozzle.
12. Method according to either one of Claims 10 and 11, characterized in that the abrasive additive is added at the mouth of the Venturi tube nozzle, the abrasive additive preferably being introduced by suction action into the mass flow of CO₂ snow and air.
13. Method according to Claim 12, characterized in that the abrasive additive flows around the Venturi tube nozzle in the manner of a jacket.
14. Method according to one of Claims 8 to 13, characterized in that the abrasive additive has at least one of the following substances:

    - sands (for example, quartz, mussel shell, lava or granite sand)

    - lava granulate or the like,

    - calcium carbonate,

    - calcium bicarbonate,

    - sodium hydrogen carbonate,

    - glass beads or the like,

    - broken glass, preferably composed of glass beads or the like,

    - metal powder and/or metal dust, preferably composed of iron, an iron alloy, aluminium, copper or brass or the like,

    - corundum or the like,

    - nutshells and/or fragments thereof,

    - oleaginous stones, such as, for example, cherry stones and/or fragments thereof,

    - plastic granulate, preferably composed of PE, PA or PC or the like.

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