EP2032309B1 - Device and method for machining a solid material using a water jet - Google Patents

Abstract

A method of machining a solid material using a water jet discharging from a nozzle is specified, wherein the water jet contains ice crystals and impacts on the solid material. In this case, a medium which is gaseous under standard conditions is dissolved in water at a mixing stage under pressure (1-150 bar) and is then compressed to 1000-4500 bar and pressed through a nozzle, under conditions which allow the dissolved gaseous medium to bubble out after leaving the nozzle, whereupon the heat of solution is withdrawn from the water and the ice crystals are formed.

Description

The invention relates to a device and a method for processing a solid material with a water jet emerging from a nozzle, which contains ice crystals and impinges on the solid material.

Water or air jets, especially under high pressure, are used in a variety of ways to process various materials. The jet is usually expanded through a narrow die to normal pressure and used for surface removal such as e.g. Rough cleaning, polishing, burring / deburring, removal of coatings / decoating, paint cleaning etc. or used for cutting or drilling materials or workpieces. Also artistic activities such as "negative graffiti", ie drawing by deliberate detachment of color through the thin stream of water or air, are possible.

Examples of known devices for material processing go, for example, from DE 198 49 814 A1 as well as from the DE 198 49 813 A1 under supply of an abrasive material. From the DE 10 2004 046 030 A1 a method and an apparatus according to the preamble of claims 1 and 5 for cutting a web is known, wherein ice crystals are formed in the water jet. The formation of the ice crystals can be assisted by adding carbon dioxide to the water in the high-pressure area in front of the nozzle, which evaporates after it leaves, whereby the heat of vaporization of the carbon dioxide extracts energy from the water.

However, the known methods and devices for cutting or drilling material processing are only suitable for the processing of soft materials. Hard materials such as steel can only be abraded, that is, the jet of water must contain solid particles such as sand, corundum or similar abrasives. It is particularly disadvantageous that the workpieces can be contaminated by the abrasive material when, for example, sand remains on the surface or in cracks and laboriously needs to be removed again.

Furthermore, the production of ice crystals in an air or in a water jet is known, wherein the ice crystals replace the sand or other abrasive materials in the air jet or in the water jet. A pre-cooling of the water by a cryogenic liquid for the production of ice crystals in the water jet is, for example, from the US 5,341,608 out.

A disadvantage of this method, however, is that the ice crystals are already formed in front of the nozzle and it often comes about that the nozzle is eroded or clogged or overheated by the increased friction and thereby melt the ice crystals again.

The object of the invention is thus to provide a method and an apparatus for processing a solid material with a water jet, which offers a simple and cost-effective way to form ice crystals in the water jet after the exit of the water jet from the nozzle.

According to the invention it is provided that in the method for processing a solid material with a water jet emerging from a nozzle containing ice crystals and impinging on the solid material, a gaseous medium under standard conditions at a pressure of 1-150 bar, preferably in a mixing stage , dissolved in water. Thereafter, the solution in a high pressure stage, e.g. a commercial water jet cutting machine, compressed to 1000-4500 bar and pressed through a nozzle under conditions that cause segregation of the water and the dissolved medium after leaving the nozzle, the heat of the solution is removed from the water and ice crystals are formed.

This is advantageous because thereby the ice crystals are formed on the one hand with little effort and on the other hand after flowing through the nozzle and thus wear of the nozzle, the clogging of the nozzle by the ice crystals formed and a heating of the nozzle by the high friction and subsequent melting of the Ice crystals can be prevented.

Further advantageous developments of the invention will become apparent from the dependent claims.

Advantageously, the dissolution of the gaseous medium in the water in a simple and cost-effective manner in the mixing stage by passing the gaseous medium from gas cylinders or pressure cartridges under pressure through the water.

A further advantage is that a tuning of the solution concentration of the gaseous medium and a pre-cooling of the water controls the particle fraction and the particle size of the ice crystals formed in the water jet, as this allows a simple adaptation of the physical properties of the water jet to the material to be processed.

It is particularly advantageous that the gaseous medium is carbon dioxide, since this is easy and inexpensive to produce and especially useful in the food industry.

Advantageously, a preferred embodiment of a device for processing a solid material with a water jet emerging from a nozzle, which contains ice crystals and impinges on the solid material, a supply line with an inlet valve and a pump for water in a mixing area, in which a pressure of 1 -150 bar prevails, connected to the mixing area via a high-pressure pump high-pressure tank and a nozzle connected to the container, wherein in the fed via the supply line in the mixing area water in the mixing area, a gaseous medium under pressure can be supplied and dissolved in the water, since this embodiment is a simple and inexpensive way to dissolve a gas in water.

It is furthermore advantageous that the gaseous medium can be introduced into the water via a shower device arranged in the mixing area, wherein the shower device is designed in particular in the form of a shower head with a plurality of outlet openings, since this enables a uniform distribution of the gaseous medium over a large volume ,

An advantageous embodiment variant provides that the water is supplied by atomization, as this allows a very homogeneous mixing.

A likewise very advantageous embodiment possibility provides that the gaseous medium can be introduced into the water via dry ice pellets containing the gaseous medium and the gaseous medium can be released under pressure in the water, as this avoids tank devices and feed lines for the gaseous medium can.

It is also advantageous that the gaseous medium is fed to a mixing stage for mixing with the water in a medium pressure range (1-150 bar). This is what it is in easy way possible to use commercially available storage containers for gaseous media, in particular in the form of a gas cylinder or gas cartridge.

In addition, it is advantageous that the mixing area is connected to a return line, via which excess gaseous medium can be fed back into the supply line, as this allows excess gaseous medium to be recycled.

Since the water is forced through the nozzle under a pressure of 1000-4500 bar, this allows a large jump in temperature upon expansion of the water jet to normal pressure and thus the reliable formation of ice crystals.

Fig. 1

eine stark schematisierte Ansicht eines bevorzugten Ausführungsbeispiels einer erfindungsgemäß ausgeführten Vorrichtung zur Bearbeitung eines festen Werkstoffs mit einem Wasserstrahl, und

Fig. 2A-D

vier Ausführungsbeispiele für Mischbereiche der erfindungsgemäßen Vorrichtung gemäß Fig. 1.

Hereinafter, a preferred embodiment of a device suitable for carrying out the method according to the invention for processing a solid material with a water jet apparatus will be described with reference to the figures. In the drawing show:

Fig. 1

a highly schematic view of a preferred embodiment of an inventive device for processing a solid material with a water jet, and

Fig. 2A-D

four embodiments for mixing areas of the device according to the invention according to Fig. 1 ,

As already mentioned above, the admixture of abrasive material to the jet of water is necessary for working solid materials, if harder materials or surfaces are to be processed, whereby preferably sand is used, which, however, has a number of disadvantages. Sand and other solid abrasive materials remain on the treated material and must be removed. A major advantage of using ice crystals instead of sand as abrasive material is the prevention of contamination. The ice crystals melt after processing, and the remaining water can be removed, for example, by simple drying, whereby the treated material remains clean throughout the process. In addition, the use represents an environmental advantage, since there is no sand waste, which must be eliminated or recycled. A staggered with ice crystals as Abrasivmaterial water jet can therefore be used without hesitation in the industries of electronics, (bio) medicine, food, car paints, space, etc. Also, the costs are lower, because ice unlike others Abrasive materials such as sand need not be delivered and stored, but can be made, for example, from the tap water by using electricity.

Known measures for adding ice into the water jet, however, have a number of disadvantages. In particular, the formation of the ice crystals in the flow direction in front of the nozzle causes the nozzle to be eroded or clogged or so hot due to the increased friction that the ice crystals melt again. Due to this so-called ex-situ mixing procedure, a minimum diameter of the water jet is required, which ultimately leads to limited maximum pressure and energy efficiency. The high costs for the production of ice crystals or the technical complexity and space requirements are further disadvantages of this method.

In order to generate the ice crystals in situ, however, it is necessary to operate at temperatures of 243 K or lower, since water, e.g. at a pressure of 200 MPa freezes only at 253 K (ie 20 K lower than at atmospheric pressure) and additionally shows the tendency to overcool. Furthermore, the sintering of the ice particles is effectively prevented only below 243 K, because above 243 K, a thin liquid film (of the order of nanometers) on the ice surface leads to sintering. In order to suppress the supercooling, nucleators can be added in principle. These are solid organic or inorganic substances that are nuclei for ice crystal growth. However, the use of nucleators, which must be continuously fed through an intake manifold, again brings the problem of poor environmental compatibility with it, whereby a use in the food industry is no longer possible.

According to the invention, to avoid the disadvantages mentioned, the cooling of the water and thus the production of ice particles in the water jet can be achieved by dissolving a gaseous medium, for example carbon dioxide, at a pressure of 1-150 bar in a mixing device in the water and then Mixture is fed by means of a high-pressure pump to a nozzle. Due to the pressure drop after the nozzle segregation occurs. The release of the gaseous medium extracts from the water, in addition to the cooling by expansion, the heat of solution of the gaseous medium, so that it comes after the nozzle to spontaneous cooling and the formation of ice crystals in the water jet. The cooling thus achieved is in the range of several degrees Celsius, so that a much lower cost must be invested in the cooling system of the device. Also, the problems of wear of the nozzle and its constipation can be bypassed. The described approach is possible in principle with a variety of gaseous media, since many gases are very soluble in water. by virtue of the possibility of using carbon dioxide (CO ₂ ) in the drinking water industry or because of the comprehensive knowledge of the physical and chemical properties such as solubility in water and heat of dissolution, the invention is described in more detail below using the example of CO ₂ .

Fig. 1 shows in a highly schematic view of an embodiment of an apparatus 1 for processing solid materials by means of a water jet 2, preferably a high pressure water jet, which contains a gas admixture. The device 1 essentially comprises a mixing region 3 in which the water and a gaseous medium, in the exemplary embodiment carbon dioxide, are mixed with one another. The water is introduced under low pressure (ie, for example, operating pressure of the water supply network) via a supply line 4 with an inlet valve 5 and a pump 6 in the mixing region 3. The carbon dioxide is introduced, for example, via a shower device 7 from a tank 8, for example a gas cylinder, via a feed line 9 into the mixing area 3. The shower device 7 is formed, for example, in the form of a shower head with a plurality of outflow openings, through which the gaseous medium flows into the water located in the mixing region 3. A return line 10 with a further pump 6 allows the return of excess gaseous medium in the supply line 9. The pressure in the mixing region 3 is approximately 200 bar, which is referred to below as the medium pressure.

After dissolving the gaseous medium in the water this is brought by a pump 11 to a pressure of about 4000 bar, which is referred to below as high pressure, and forwarded to a container 12 to flow from there to a nozzle 13. With the water jet 2 emerging there, which is pressed under high pressure through the nozzle 13, the material 14 is processed. The control of the pressure and the flow rate of the water takes place with suitable measuring devices 15, which can be arranged at various suitable locations of the device 1.

According to the invention, the formation of the ice crystals takes place only after the nozzle 13. The crystallization is excited by the expansion or by the atomization of the water jet 2, which leads to a sudden bubbling to release the dissolved carbon dioxide from the now supersaturated water-gas solution. A solution heat amount of -20.54 kJ / mol is thereby removed from the water. This results in an instantaneous, very strong cooling and the spontaneous formation of ice crystals in the expanded water jet 2, depending on the output pressure of the water. Thus, problems such as clogging, wear or overheating of the nozzle 13 can be prevented. An appropriate vote of CO ₂ solution concentration and precooling allows control of the particle fraction and the particle size in the water jet 2, so that it can be adapted to the particular requirements of the material to be processed 14, for example, with many large ice crystals for fast, rather coarse cleaning large areas or with many small ice crystals for polishing a surface. Even hard materials 14 can be processed cleanly.

The admixture of the carbon dioxide in the mixing zone 3 can, as in the Fig. 2A to 2D shown schematically in part, take place directly in the mixing area 3, as already in Fig. 1 represented and in Fig. 2A shown enlarged.

Also by presenting in the mixing zone 3 a compressed to about 200 bar gaseous medium and then atomized water droplets introduced into this system, as in Fig. 2C As shown, it is possible to achieve effective mixing and solution of the gas.

Furthermore, it is possible, as in Fig. 2D shown schematically to submit water in the mixing zone 3, dry ice pellets 16 or frozen carbon dioxide pellets 16 at a temperature of about -78 ° C in the mixing area 3 introduces and then applies pressure. In the relatively warm compared to the pellets 16 water, the pellets 16 melt immediately with strong bubbling, the carbon dioxide goes into solution by the pressure. Incidentally, the water also cools down, which is advantageous in view of the formation of ice crystals in the further course.

In all cases, a saturated mixture of water and carbon dioxide leaves the mixing zone 3 in the direction of the container 12.

In the mixing zone 3, the water is first mixed with carbon dioxide by dissolving the CO ₂ in the water, for example by passing CO ₂ from the tank 8, which is in the in Fig. 1 illustrated embodiment is designed as a gas cylinder. The use of print cartridges, as they are known for mineral water, is possible. The process of dissolving carbon dioxide in water can be controlled by monitoring the pH via a suitable sensor, since due to the reaction equilibrium of CO ₂ / H ₂ O with HCO ₃ ^- / H ⁺ saturated solutions with CO _{2 are} acidic; For example, at 298 K, a pH of 3.9 is present. The temperature of the device 1 rises slightly by the heat of dissolution of the carbon dioxide, so that a heat dissipation in the mixing region 3 is indicated for example by a water cooling.

The water jet 2 is produced by the water-carbon dioxide mixture pumped by the pump 11, which must be designed high pressure suitable, in the container 12 and then forwarded to the nozzle 13 and is pressed through it. For existing pumps 11 and nozzles 13 can be used without further technical modifications. There must be no additional materials supplied from the outside, so it is no additional intake manifold necessary.

As an indication of how large the achievable cooling is, the following estimate can serve. The achievable temperature difference is calculated by the amount of dissolved carbon dioxide (n _cO2 ), the amount of water (n _H2O ), the isobaric heat capacity of liquid water (cp _H2O = 75.3 J / (K mol)) and the enthalpy of solution of carbon dioxide in water (ΔH = -20.54 kJ / mol). Up to a pressure of approx. 300 bar CO ₂ , the mole fraction of carbon dioxide n _CO2 / n _total , ie the proportion of CO ₂ molecules dissolved in the water, can be expressed linearly with the CO ₂ partial pressure via the Henry law. The proportionality constant of Henry's Law is CO ₂ k _CO2 = 1650 bar. As long as the CO ₂ partial pressure p _{CO2 is} much smaller than k _CO2 , the cooling results in a linear relationship in p _CO2 with a proportionality constant of ΔH / (cp _H2O k _CO2 ), which yields a proportionality constant of 0.165 K / s when known values are used. bar results. Thus, per bar of dissolved CO ₂ , the temperature drops by 0.165 K, at 100 bar, therefore, by 16.5 K.

If you start with cold tap water of about 10 ° C, then an escape of dissolved at 100 bar CO _{2 would be} sufficient to reach temperatures below freezing. The cooling by the expansion of the water jet 2 from the container 12 at 4000 bar to 1 bar after the nozzle 13 is not considered. At atmospheric pressure, 3.4g at 273K or 1.5g CO ₂ at 298K are soluble in one liter of water. This corresponds to 1.93 or 0.85 liters of CO ₂ (0.077 mol or 0.034 mol) per liter of water. At elevated pressure, for example in carbonated mineral water, significantly larger amounts are soluble.

The released carbon dioxide can be recycled or extracted if necessary. However, it must be ensured that the addition of carbon dioxide to the ambient air is not too high, otherwise there is danger of suffocation, such as through ventilation or correspondingly large spaces.

The invention is not limited to the illustrated embodiment, but for example, with other gaseous media feasible.

Claims (12)

1. Method for machining a solid material using a water jet discharging from a nozzle, said water jet containing ice crystals and impacting on the solid material, wherein a medium which is gaseous under standard conditions is introduced and pressed through a nozzle under conditions which allow the dissolved gaseous medium to bubble out after leaving the nozzle, whereupon the heat of solution is withdrawn from the water and ice crystals are formed, characterized in that the medium which is gaseous under standard conditions is dissolved in the water at a pressure of 1-150 bar and subsequently compressed to 1000-4500 bar.
2. Method according to claim 1, characterized in that the dissolving of the gaseous medium in the water is carried out at a mixing stage by passing the gaseous medium from gas cylinders or pressure cartridges through the water at a pressure of 1-150 bar or by inserting dry ice pellets into the water, said pellets containing the gaseous medium.
3. Method according to claim 1 or 2, characterized in that a modulation of the concentration of the gaseous medium in solution and of the temperature of the water governs the particle fraction and the particle size of the ice crystals formed in the water jet.
4. Method according to any of claims 1 to 3, characterized in that the gaseous medium is carbon dioxide.
5. Device for machining a solid material (14) using a water jet (2) discharging from a nozzle (13), said water jet (2) containing ice crystals and impacting on the solid material (14), comprising a feed pipe (4) with an inlet valve (5) and a first pump (6) for pumping water into a mixing section (3), a vessel (12) connected with the mixing section (3) via a second pump (11) and a nozzle (13) connected with the vessel (12), wherein in operation a gaseous medium is fed under pressure into the water which is introduced into the mixing section (3) via the feed pipe (4) before or in the mixing section (3) and wherein it is dissolved in the water, characterized in that the device is designed so that in operation the water used as an operating fluid is compressed in two steps, namely in a first step with a pressure of 1-150 bar, at which pressure the medium which is gaseous under standard conditions is dissolved in water, and subsequently, in a second step, at 1000-4500 bar, so that by pressing through the nozzle (13) a bubbling-out of the dissolved gaseous medium occurs, whereupon the heat of solution is withdrawn from the water and the ice crystals are formed.
6. Device according to claim 5, characterized in that the gaseous medium is introducible into the water via a douche gadget (7) arranged in the mixing section (3), said douche gadget (7) in particular being designed in the form of a shower head with a multiplicity of outlets.
7. Device according to claim 5, characterized in that in operation the gaseous medium is introduced into the water upstream with respect to the mixing section (3).
8. Device according to claim 5, characterized in that in operation the water is fed in by means of nebulization.
9. Device according to claim 5, characterized in that the gaseous medium is introducible into the water via dry ice pellets (16), which contain said gaseous medium, and that the gaseous medium is soluble in the water under pressure.
10. Device according to any of claims 5 to 8, characterized in that the gaseous medium is provided in a tank (8) which in particular is designed in the form of a gas cylinder or a gas cartridge and from which said gaseous medium can be supplied to the device (1) via a feed pipe (9).
11. Device according to claim 10, characterized in that the mixing section (3) is connected with a return pipe (10), through which excessive gaseous medium can be fed back into the feed pipe (9).
12. Device according to any of claims 5 to 11, characterized in that the gaseous medium is carbon dioxide.

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