23.02.2008Method for abrasive high-pressure water jet cutting with a high-pressure water jet containing ice crystals

Abstract

A method for abrasive high-pressure water jet cutting with a high-pressure water jet containing ice crystals, wherein the ice crystals are generated before the high-pressure water jet emerges from the nozzle, characterized in that the high-pressure line (2) is designed so as to branch in the direction of the nozzle (3) into at least two parallel line strands (4, 5) which are operatively connected to a cooling section (6, 7), wherein the line strands (4, 5) in connection with the cooling sections (6, 7) are operated alternately in an ice crystal generation phase and an ice crystal supply phase in such a way that the one line strand (4) which is initially blocked off from the high-pressure line (2) and the nozzle (3) is in a low-pressure phase for ice crystal generation, while the other line strand (5) which is initially open towards the high-pressure line (2) and nozzle (3) for supplying the ice crystals (13) to the nozzle (3) is in its high-pressure phase (ice crystal supply phase,cutting phase).

Description

[0001] The invention relates to a method for abrasive high-pressure waterjet cutting using a high-pressure waterjet containing ice crystals. The ice crystals are generated before the high-pressure waterjet exits the nozzle and are used to cut workpieces, particularly fiber composite materials. Since the abrasive particles are only present for a limited time, soiling or contamination of the workpiece by abrasive residues is avoided.

[0002] DD 298 618 A5 describes a process for abrasive high-pressure waterjet cutting. Water under high pressure is cooled to -10°C to -20°C before exiting the nozzle and remains in a liquid state under the given pressure conditions. Upon exiting the nozzle, the high pressure dissipates to ambient pressure, and a portion of the water crystallizes into ice. These ice crystals can be used as an abrasive for cutting workpieces.

[0003] A similarly based process for cutting the edge strips of a paper web is described in DE 10 2004 046 030 A1. Here, too, the cooled, highly pressurized water exits a nozzle as a free jet into the atmospheric pressure, with ice crystals forming at the latest when it hits the surface of the web to be cut.

[0004] The disadvantages of these two solutions are that a sufficient flow of abrasive agent cannot be ensured because the time available for the water jet emerging from the nozzle until it hits the workpiece to be cut is too short to form the necessary ice crystals, which act as an abrasive agent, in sufficient number and size to carry out the cutting process.

[0005] DE 197 56 506 C2 discloses a method for abrasive high-pressure water jet cutting in which crushed particles of dry ice are added to the water in front of the nozzle as an abrasive agent.

[0006] The process known from DE 196 32 883 A1 also works on the principle that a substance is added to the water before it exits a nozzle. This process creates an abrasive substance in the water through a change in state. To form ice crystals, liquid nitrogen is introduced into the water, causing at least a portion of the water to undergo a physical change of state and crystallize into ice. These ice crystals, carried by the water jet, exert an abrasive effect on the workpiece after exiting the nozzle.

[0007] DE 101 25 280 A1 describes a method for removing, cleaning, and cutting with a pressurized liquid mixture. This method exploits the different pressure-temperature behavior of liquids to generate a powerful pressure jet. Ice crystals are created as an abrasive at the nozzle outlet by depressurization. In one embodiment, a liquid phase is converted to a gaseous state under pressure.

[0008] While the latter process eliminates the need for additional water cooling, their disadvantages include the high level of equipment required for mixing and safely handling the respective additive (dry ice or liquid nitrogen). If the proportion of ice crystals in the water is too low, there is a risk that the number of ice crystals will decrease so much after exiting the nozzle by the time the abrasive jet hits the workpiece that the abrasive cutting effect is no longer sufficiently guaranteed.

[0009] The object of the invention is to propose a method for abrasive high-pressure water jet cutting in which the ice crystals are continuously available and in sufficient numbers for the realization of the cutting process on the workpiece, whereby a stable cutting process on the workpiece is to be realized.

[0010] According to the invention, this object is achieved in a generic method by the features of patent claim 1.

[0011] The advantages of the invention are that, for high-pressure waterjet cutting with ice crystals, a continuous abrasive flow is provided with minimal equipment complexity, providing sufficient cutting performance for the workpiece separation process. Cyclical switching between the line sections with the cooling sections allows the required ice crystals to be maintained in reserve for continuous implementation of the cutting process. Furthermore, separate and metered additives do not need to be stored, and safety-related handling is eliminated.

[0012] An advantageous procedural development of the invention emerges from patent claim 2.

[0013] They show: Fig. 1 a schematic diagram of the arrangement for carrying out the method according to the invention, in which the upper line string is operated in the high-pressure phase (= ice crystal supply phase, cutting phase) and the lower line string in the low-pressure phase (= ice crystal generation phase) Fig. 2 a schematic diagram of the arrangement for carrying out the method according to the invention, after the reciprocal switching between the line strings has taken place in such a way that the lower line string is now operated in the high-pressure phase (= ice crystal supply phase, cutting phase) and the upper line string in the low-pressure phase (= ice crystal generation phase)

[0014] In the Fig. Figure 1 is a schematic representation of the arrangement for carrying out the method according to the invention for abrasive high-pressure waterjet cutting using a high-pressure waterjet containing ice crystals. The water, pressurized to a pressure of 2000 to 3000 bar by the high-pressure pump 1, is pumped through a high-pressure line 2 toward the nozzle 3. This high-pressure line branches into two parallel lines 4, 5, each of which is operatively connected to a cooling section 6, 7, through which the pumped water 8 is cooled to at least -10°C. Each cooling section is also assigned two high-pressure shut-off valves 9 and 10, respectively, and a pressure limiting valve 11 and 12, respectively.

[0015] While the line string 4, which is initially open with the pressure limiter valve 11 closed and the high-pressure shut-off valves 9 open towards the high-pressure line 2 and nozzle 3, is operated in an ice crystal feed phase (high-pressure phase, cutting phase), in which the ice crystals 13 previously generated in a low-pressure phase (preferably normal pressure) of this line string 4 emerge from the nozzle 3 together with the water jet 14 to process the workpiece, the line string 5 is sealed off from the high-pressure line 2 and nozzle 3 by the closed high-pressure shut-off valves 10, but the pressure limiter valve 12 assigned to the line string 5 is open, as a result of which a low pressure is established in the line string 5 which is shut off from the high-pressure line 2, as a result of which low pressure then occurs in the physical change of state in the water 8 to the phase transition from solid to liquid and thus to the formation of ice crystals 13 (ice crystal generation phase).If the ice crystal formation in the line section 4 is coming to an end, according to . Fig. 2 in line section 5 the pressure limiting valve 12 is closed and the high pressure valves 10 are opened, while in line section 4 the pressure limiting valve 11 is opened and the high pressure valves 9 are closed, so that the abrasive stream originating from line section 5 and consisting of the water jet 14 with ice crystals 13 is now fed to the nozzle 3 without interruption, while in line section 4 the ice crystal generation phase now begins due to the renewed creation of a low pressure.

[0016] The operation described above takes place by regulating the time regime between the high-pressure and low-pressure phases in the line strings 4, 5 alternately, so that the ice crystals 13 required for workpiece processing can be provided continuously and in sufficient numbers.

[0017] Depending on the specific working conditions and the associated time regime control, it is possible to operate more than two parallel line strings that are operatively connected to a cooling section. List of reference symbols 1 high-pressure pump 2 high-pressure line 3 nozzles 4 cable harness 5 Cable harness 6 Cooling section 7 Cooling section 8 Water 9 High-pressure shut-off valve 10 High-pressure shut-off valve 11 Pressure relief valve 12 Pressure relief valve 13 ice crystals 14 Water jet

Claims

[1] Method for abrasive high-pressure water jet cutting with a high-pressure water jet containing ice crystals, wherein the ice crystals are generated before the high-pressure water jet exits the nozzle, characterized byin that the high-pressure line (2) is branched in the direction of the nozzle (3) into at least two parallel line strands (4, 5) which are operatively connected to a cooling section (6, 7), the line strands (4, 5) in connection with the cooling sections (6, 7) being operated alternately in an ice crystal production phase and an ice crystal supply phase in such a way that the one line strand (4) which is initially blocked off from the high-pressure line (2) and the nozzle (3) is in a low-pressure phase for ice crystal production, while the other line strand (5) which is initially open towards the high-pressure line (2) and nozzle (3) for supplying the ice crystals (13) to the nozzle (3) is in its high-pressure phase (ice crystal supply phase, cutting phase). [2] Method for abrasive high-pressure water jet cutting according to claim 1 characterized bythat the mutual operation of the pipe strings (4, 5) in the high-pressure and low-pressure phases is achieved by regulating the time regime.

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