DK3012075T3

DK3012075T3 - Method for operating a facility for waterjet cutting and facility for water jet cutting

Info

Publication number: DK3012075T3
Application number: DK15190372.1T
Authority: DK
Inventors: Andreas Perndorfer; Ewald Perndorfer; Daniel Paster
Original assignee: Andreas Perndorfer; Ewald Perndorfer
Priority date: 2014-10-20
Filing date: 2015-10-19
Publication date: 2018-03-19
Also published as: EP3012075B1; RS57018B1; PL3012075T3; AT515943B1; HUE036924T2; AT515943A4; SI3012075T1; HRP20180419T1; NO3012075T3; ES2662858T3; EP3012075A1

Description

[0001] The invention relates to a process for operating a system for water jet cutting with a high pressure pump exhibiting several plungers, connected to a water tank and with a high pressure line connected to the high pressure pump, which is connected to a cutting head through a cutting head valve, wherein the high pressure pump is driven and the cutting head valve is opened for the cutting process, and to a duly suitable system for water jet cutting.

[0002] Based on the high pressures required for water jet cutting and comparable high flow rates, for water jet cutting systems, high pressure pumps with plungers are frequently used, wherein with the arrangement of three plungers, the pressure fluctuations can be reduced to a level permissible for water jet cutting, so that pressure accumulators to compensate for such pressure fluctuations can be dispensed with. The plunger pumps are normally driven by rotary current motors that are controlled by a frequency converter that provides the required rotary speed for the relevant desired flow rate. The water sucked in by the high pressure pump from a water tank is then directed with the set pressure, depending on the cutting conditions, for example, between 500 and 4000 bar, through a high pressure line to the cutting head, where it leaves through a clean water nozzle with a speed of up to 800 m/s (at a flow pressure of 4000 bar), before any abrasive is directed with the water jet. To finish the cutting process, a cutting head valve upstream of the clean water nozzle is closed and the rotary current motor is reduced to a lower speed, so as not to have to run up the high pressure pump for a new cutting process from a stopped state. The amount of water conveyed after blocking the cutting head valve from the high pressure pump is conveyed back via a return line into the water tank that is released through a return valve when the cutting head valve is closed. Consequently, the cutting head valve is to be opened for a new cutting process, the return valve is to be closed and the high pressure pump accelerated to the required operating rotational speed, so that inside the high pressure line connected to the cutting head, the required operating pressure only gradually builds up, with the result that, during the start of cutting, due to the increase of the water exit speed from the clean water nozzle over time, the cutting pattern changes, which has a disadvantageous effect particularly when broaching, therefore during cutting processes that do not start from one edge of the workpiece but start within a workpiece surface.

[0003] The invention is therefore based on the task of being able to operate systems for water jet cutting with plunger pumps in such a way that, with an further cutting process, a sufficient water pressure is available to ensure a uniform cutting pattern from the start, without having to use a pressure accumulator.

[0004] Starting from a process illustrated in the preamble, the invention solves the task in that, at the end of the cutting process, the high pressure pump is stopped while the cutting head valve is closed, while maintaining the pressure in the high pressure line and at the start of the cutting process, it is put back into operation while the cutting head valve is opened.

[0005] As the pressure in the high pressure line does not drop as a result of these measures when blocking the cutting head valve for terminating the cutting process, the pressure for restarting a cutting process is available so that, immediately after opening the cutting head valve, cutting can be done at operating pressure. The prerequisite is that, within the opening time for the cutting head valve, the high pressure pump is accelerated at the required rotary speed for the relevant operating pressure in the high pressure line and/or is stopped within the closing time of this valve. Therefore, no return line is required, to direct the water otherwise conveyed during the cutting break back into the water tank.

[0006] If, for a subsequent cutting process, a lower operating pressure is needed in the high pressure line, as this is normally the case if broaching is to be done, then before opening the cutting head valve, the pressure in the high pressure line is lowered accordingly, so that the cutting process can be undertaken when opening the cutting head valve with the reduced operating pressure.

[0007] Conventional drives for plunger pumps using rotary current motors, activated via frequency converters corresponding to the required rotary speed, are generally not in a position to accelerate the plunger pump within the short opening and closing times of the cutting head valves to the rated rotary speed and/or to brake from the rated rotary speed to a stop. For this reason, in systems for water jet cutting that are suitable for the process according to the invention, it is proposed that drive of the high pressure pump comprises a servo-motor that can be switched on depending on the operation of a cutting head valve, with a servo-inverter, and that for activating the servo-inverter a controller connected both to a setpoint generator and to an actual value transmitter is provided for the pressure in the high pressure line. Using such servo-drives, the required accelerations can be achieved within milliseconds, so that the relevant specified water pressure is available immediately when opening the cutting head valve. As the activation of the servo-inverter is undertaken depending on the difference between the setpoint and actual value of the pressure in the high pressure line, the changes affecting flow resistance in the area of the clean water nozzle do not have any significance because, due to this activation of the servo-inverter, for example, wear phenomena on the clean water nozzle are to be considered automatically.

[0008] To be able to lower the pressure in the high pressure line during a cutting process with respect to the pressure requirements of a subsequent cutting process, as required, the high pressure line can be connected via an adjustable pressure-reducing valve to a return line that is preferably used also to shut off the return line, if the pressure-reducing valve is not needed.

[0009] Using the drawing, that shows a system for water jet cutting in a schematic flow diagram, the process according to the invention is explained in more detail.

[0010] The system for water jet cutting exhibits one high pressure pump 1 with three plungers 2 that are driven via a crankshaft 3 by a servo-motor 4. The water needed for cutting a workpiece is taken from water tank 5 via an intake line 6 connected to a high pressure pump 1 and directed through a high pressure line 7 on the discharge side connected to the high pressure pump 1 to a cutting head 8. This cutting head 8 comprises a clean water nozzle 9 for generating a water jet for cutting the workpiece. The water jet coming out of the clean water nozzle 9 may, as required, be mixed in with abrasives to increase cutting performance, that is indicated by the arrow 10. A cutting head valve 11 is connected upstream of the clean water nozzle 9, through the actuator 12 of which the cutting head 8 can be switched on and off.

[0011] To regulate the rotary speed of the servo-motor 4, the servo-inverter 13 belonging to the servo-motor 4 is biased by a speed sensor 14. The servo-inverter 13 is activated by a controller 15 with a setpoint generator 16 for the pressure in the high pressure line 7. Furthermore, the actual value of the pressure in the high pressure line 7 is recorded by an actual value transmitter 17 connected to the high pressure line 7 and forwarded to the controller 15, so that the servo-inverter 13 can be activated depending on the difference between the setpoint and actual value of the pressure in the high pressure line 7.

[0012] If the cutting head valve 11 is closed by the actuator at the end of a cutting process, the pressure in the high pressure line 7 increases immediately, which leads to the servo-motor 4 being switched off by the controller 15, wherein the pressure in the high pressure line 7 is maintained and is consequently available again for the following cutting process.

[0013] To initiate the next cutting process, the cutting head valve 11 is to be opened again by the actuator 12 and at the same time, the servo-motor 4 is to be accelerated to the pump rotary speed relating to the setpoint of the pressure in the high pressure line 7, and indeed within the opening time for the cutting head valve 11, which is possible without further ado via an activation of the servo-inverter 13 together with the activation of the actuator 12 for the cutting head valve 11. This means that the new cutting process can be started with a flow pressure of the water in the high pressure line 7, which at least approaches the setpoint, so that no changes can be produced in the cutting pattern during the cutting process.

[0014] On the basis of the cutting conditions of a following cutting process, if the setpoints for the pressure in high pressure line 7 are to be decreased, then with a corresponding setpoint specification in the preceding cutting break, the pressure in the high pressure line 7 can to be lowered using a pressure-reducing valve 18 in a return line 19 connected to the high pressure line 7. If the pressure-reducing valve 18 is not needed, the return line 19 can be blocked by the pressure-reducing valve 18 if its actuator 20 is activated accordingly.

Claims

A method for operating a water jet cutting system with a high-pressure pump (1), which is provided with a plurality of pistons (2) and is connected to a water tank (5) and with a high-pressure line (7) which is connected to the high-pressure pump ( 1) and connected via a cutting head valve (11) to a cutting head (8), the pistons (2) of the high-pressure pump (1) for the cutting process being driven by a crankshaft (3) by a drive for generating pressure in the high-pressure line (7) ) and the cutting head valve (11) is opened, characterized in that the high-pressure pump (1) at the end of the cutting process, while the cutting head valve (11) closes, while maintaining the pressure in the high-pressure line (8) is stopped by a servomotor (4) in the drive via the crankshaft (3). ) and at the beginning of the cutting process, while the cutting head valve (11) opens, is again operated by the servomotor (4) in the drive via the crankshaft (3).

Method according to claim 1, characterized in that the pressure in the high pressure line (7) can be reduced to a value which can be preset before the cutting head valve (11) opens.

Method according to claim 1 or 2, characterized in that the high pressure line (7) is connected to a return line (19) via an adjustable pressure reduction valve (18).

Method according to claims 2 and 3, characterized in that the pressure in the high pressure line (7) can be reduced via the pressure reduction valve (18) which can be adjusted according to the preset value.

5. Water jet cutting system with a crankshaft (3), with a drive, with a high-pressure pump (1), which is provided with a plurality of pistons (2) and is connected to a water tank (5) and can be operated where the pistons (2) is driven by the drive via the crankshaft (3) and with a high-pressure line (7) connected to the high-pressure pump (1) and connected via a cutting head valve (11) to a cutting head (8), characterized in that the high-pressure pump (1) ) drive comprises a servo motor (4) which can be coupled depending on the operation of the cutting head valve (11) and drives the crankshaft (3), with a servo converter (13) and that a regulator (15) is provided for activating the servo converter (13). ) connected, on the one hand, to a nominal value encoder (16) and, on the other hand, to an actual value encoder (17) for the pressure in the high-pressure line (7), so that the high-pressure pump (1) at the end of the cutting process, while the cutter head valve (11) closes while maintaining the pressure in the high pressure line (8) Ace of the servomotor (4) in the drive via the crankshaft (3) and at the beginning of the cutting process, while the cutting head valve (11) opens, is again operated by the servomotor (4) in the drive via the crankshaft (3).

System according to claim 5, characterized in that the high pressure line (7) is connected to a return line (19) via an adjustable pressure reduction valve (18).