APPARATUS AND METHOD FOR PRODUCING A HIGH-PRESSURE FLUID USED FOR FLUID-JET CUTTING

Abstract: The invention relates to an apparatus for producing a high-pressure fluid jet used in fluid-jet cutting. As main components, the apparatus comprises a body (3), a shaft (10) journalled (5a, 5b, 6a, 6b) therein, a power unit (1, 2) for driving shaft (10), a nozzle assembly (11) in connection with body (3), at least two pump units (7) mounted successively on shaft (2) and operating on kinetic principle, and a set of conduits (8, 9) for carrying the fluid inside body (3) and through pump units (7) to nozzle assembly (11). In each pump unit (7), the fluid pressure is adapted to be stepwise increased by means of the rotation energy of shaft (10) in a manner that along said set of conduits (8, 9) the fluid is carried from the outlet side or the like of the preceding pump unit to the inlet side or the like of the following pump unit.

Description: Apparatus and method for producing a high-pressure fluid used for fluid-jet cutting The present invention relates to an apparatus for producing a high-pressure fluid used for fluid-jet cutting. The prior art fluid-jet creating apparatus construct¬ ions for use in fluid-jet cutting have been generally based on the applications of a so-called Intensifier principle. This involves creating a hydraulic pressure on a displacement pump principle by using a piston assembly controlled by means of valves. In most cases, the piston assembly acguires its energy from an electric motor through hydraulic transmission. The hydraulic pressure created by means of a piston assembly is pulsating in nature and, thus, the ap¬ paratus requires a pressure accumulator for equalizing the fluid pressure prior to using such fluid in the actual fluid-jet cutting. It is obvious from the above that, as a whole, the construction is rather complicated with several moving parts and assemblies. On the other hand, perhaps the most significant drawback in the prior art mechanisms is that, par- ticularly in terms of the contacting seal surfaces of a piston assembly, the maintenance interval is rela¬ tively short, i.e. even the operation of appr. 200 hours requires overhaul of the apparatus. The ap¬ paratus also has a short overall operating life, less than 10.000 hours. It is also obvious that, since the apparatus is subject to regulations on pressure vessels due to its large highpressurized volume, such apparatus will be expensive, capacious and requires a significant observance of the labour safety code in its design. Since the above-entities invention intimately involves the production of a high-pressure (appr. 3000-3500 bar) fluid at high speeds of rotation, reference can be made in this context first of all to the publication K. Kamijo, K. Hirata: Performance of small high speed cryogenic pumps, Journal of fluids engineering, June 1985, vol. 107, pp. 197-204. This publication dis- closes a rocket engine fuel pump which is capable of developing considerably high pressures. The liquid oxygen pumps in rocket engines are generally single- stage centrifugal pumps with a typical pressure increase of 120-250 bar. Instead, the increase level of liquid hydrogen pumps can be elevated to values which on water correspond to a pressure increase of 1830 bar. On the other hand, in terms of high speeds of rotation reference can be made to the publication J. E. Boretz et al: Turbine organic rankine engine system for artificial heat application, 749120, pp. 813-823, which discloses a centrifugal pump whose speed of rotation is 200.000 rpm. It is generally known that the speeds of rotation of e.g. rocket engine fuel pumps seldom exceed 80.000 rpm. In practice, the object of an apparatus and a method of the invention is to produce a pressure increase in the order of 3000 bar in liquid. On the other hand, in view of the overall dimensions of the apparatus and particularly in view of a positive function for the apparatus, the operation is carried out at speeds of rotation which exceed 5 x lO ^ An object of the present invention is to substantially eliminate the above drawbacks associated with the prior art fluid-jet cutting technique and, thus, to elevate the available standard of technology. The invention offers a possibility of designing an ap¬ paratus which has a long operating life and requires substantially less maintenance than the prior art equipment. In addition, the apparatus can be con¬ structed to be extremely compact in size, whereby it is possible to expand the range of technical applicat¬ ions of fluid-jet cutting. In order to achieve the above objects, an apparatus of the invention is primarily characterized in that said apparatus comprises: - a body, a shaft journalled inside the body, - a power unit for driving the shaft, - a nozzle assembly which is connected with the body, at least two pump units mounted successively on the shaft and operating on kinetic principle, and a set of conduits for delivering the fluid into the body and by way of the pump units to the nozzle assembly, whereby in each pump units the fluid pressure is adapted to be stepwise increased by means of the shaft rotation energy in a manner that along the set of conduits the fluid is further carried from the outlet side of the preceding pump to the inlet side of the following pump. Thus, in this solution, a shaft is driven by means of a power unit for translating the shaft rotation energy at a certain efficiency into a fluid pressure increase by increasing the pressure stepwise in each successive pump unit all the way to a final pressure. In the apparatus, over each pump unit there only prevails a pressure difference which is equal to the pressure increase resulting from said pressure boosting stage. It is obvious that the shaft is required to have a relatively high speed of rotation, e.g. appr. 2 x 105 rpm, in order to design constructionally a rela¬ tively compact-size apparatus. Other preferred embodiments of the invention are set forth in the annexed non-independent claims. The invention relates also to a method for producing a high-pressure fluid used for fluid-jet cutting. The characterizing features of this method are set forth in the characterizing clause of the annexed independent claim directed to a method. The invention is also defined by the annexed claim directed to application. The invention will now be described in more detail in the following specification with reference made to the accompanying, schematic example illustrating one embodiment of the invention in a longitudinal cross- section in the longitudinal direction of the shaft. In the drawing, reference numeral 2 designates a body of the apparatus, which is preferably made of a metal by using suitable working techniques. The body 3 is constructed to be erectable in a manner that the other apparatus components to be fitted therein can be installed during the course of erecting the body. This type of constructional details are quite obvious to a skilled person and need not be described further in this context. Inside said body 3 is journalled a shaft 10. A first end of the shaft is provided with a power unit 1, 2 for driving the shaft. In the present embodiment, the power unit 1, 2 comprises an air turbine having its rotor 1 mounted on the first end of shaft 10. The turbine stator is indicated by reference numeral 2 and letter A indicates the supply of compressed air into the stator, the flow of air from stator to rotor being shown by the flow-direction arrows. The air- turbine technique as well as alternative construct¬ ions for a power unit are also in such a way obvious to a skilled person that there is no need to describe them further in this context. A second end of shaft 10, which is the opposite end relative to the location of power unit 1, 2, is fitted with a nozzle assembly 11, which in the present embodiment is fastened to body 3. In the illustrated embodiment, said shaft 10 is successively provided with four pump units 7. The pump units are mounted at fixed intervals on the shaft, whereby between each successive pair of pump units if fitted a packing, particularly a labyrinth packing 4, between body 3 and shaft 10. A cor¬ responding packing, particularly a labyrinth packing, is also fitted between the first pump unit and a first journalling assembly 5a, 5b, 6a as well as between the final pump unit and a second journalling assembly 6b as well as on body 3 adjacent to the first end of the shaft. The apparatus further includes a set of conduits 8, 9 for delivering the fluid into the body (shown by letter B in the drawing) and through all pump units 7 to nozzle assembly 11. The set of conduits is adapted to extend through first journalling assembly 5a, 5b, 6a as well as through second journalling assembly 6b, both journalling assemblies being adapted to operate on a liquid lubrication principle. In each pump unit, the fluid pressure is adapted to be raised stepwise with the rotation energy of shaft 10 in a manner that the fluid is always carried along the set of conduits to the inlet side of a preceding pump unit, whereby the preceding pump unit is always located closer to the second end of shaft 10 than the following pump unit. Each pump unit is mounted on shaft 10 in a manner that the inlet side of the unit is closer to the second end of the shaft than the outlet side of the pump unit. Between the inlet side and the outlet side is fitted a packing, such as a labyrinth packing, acting between this particular pump unit and body 3. Thus, a higher pressure prevailing at a pressure chamber 11a or a like included in nozzle assembly 11, which pressure produces an axial force on shaft 10 urging it towards power unit 1, 2, can be at least partially compensated for since a pressure difference created in the pump unit produces in each pump unit an axial force which is oppositely directed relative to the above-mentioned axial force. The first journalling assembly 5a, 5b, 6a comprises both a central radial 6a bearing assembly and an axial 5a, 5b bearing assembly fitted in axial direction on either side of said radial bearing assembly 6a. For the axial bearing assembly, a bearing housing 13, included in the first journalling assembly and forming a part of the set of conduits (initial part) , is fitted with radial flanges mounted on shaft 10 for both axial forces possibly acting in the axial direct¬ ion of shaft 10. The second journalling assembly 6b, which is mounted on the second end of shaft 10, only comprises a radial liquid lubricated bearing. The set of conduits comprises on the one hand borings 9 made inside the body and on the other hand pump units control means, which are connected with each other. Pump units 7 can be designed e.g. for operation either on centrifugal or Pitot principle. The drawing illustrates schematically the impeller of a pump unit operating on centrifugal principle. It is obvious that an apparatus of the invention can be considerably varied and modified within the scope of the basic inventive concept. For example, the journalling can be designed as a so-called magnet bearing application, whereby the construction of the set of conduits is independent of the lubrication of bearings. Naturally, it should be appreciated that the liquid lubricated bearing constructions can be designed in a manner that the liquid lubrication is effected with separate liquid or fluid. EXAMPLE The following example specifies one embodiment of the invention by means of an exemplary calculation. The following initial values are selected to dimensioning a fluid-jet cutting apparatus: flow rate 2 1/min, number of pump units 10, and rotating speed of shaft 200.000 rpm. Thus, the specific speed of rotation of the shaft will be 0.05 rad. Furthermore, in order to minimize disc losses, the selected blades are curved forward in the direction of flow. Calculated on the basis of the above data, the diameter D (see drawing) of the impellers will be 20 mm. The shaft diameter d is selected to be 10 mm, whereby a water lubricated bearing, capable of withstanding 200.000 rpm, is simple to provide in terms of manufacturing technique. Bladed leading wheels are used for a maximum efficien- cy, whereby said body 3 will have a diameter D 2 appr. 60 mm. The length of body 3 in the longitudinal direction of the shaft will be appr. 190 mm. In order to avoid cavitation, the pressure of a fluid supplied into the apparatus must be at least 40 bar (the fluid being water) . The most significant single dissipation or loss is the disc friction of impellers which is in the order of 26 k . Thus, the apparatus requires a total output of appr. 40 kW and efficiency of 30 %. The required output can be produced e.g. by means of a simple impulse turbine (hole diameter 31 mm) as shown in the drawing, supplied with compressed air having a pressure of three bar. The efficiency of an apparatus as described above can be raised to appr. 50 % if it is designed for a speed of rotation of 400.000 rpm in a manner that the flow rate is 2 1/min, or by raising the flow rate to 8 1/min with the speed of rotation of the shaft remaining at 200.000 rpm. Accordingly, the speeds of rotation of the shaft can be lowered, e.g. to what is stated as a lower limit in the method claim, provided that the requirements e.g. in terms of liquid volume flow rate and/or the size of an apparatus make it possible to apply this basis for dimensioning. The above exemplary calculation is only used to demonstrate by way of an example that construction of the apparatus is technically plausible. It is obvious that the employed pump unit can be a centrifugal pump (Partial Emission or Full Emission) . At the stated specific speed of rotation 0.05 rad, a Pitot pump would provide a higher efficiency but it is probably difficult to design its rotating chamber to withstand a combined stress resulting from centri¬ fugal force and compression force. It is obvious that the above-mentioned Pitot pump can be designed to withstand at speeds of rotation which are lower than the above specific speed of rotation. In an apparatus shown in the drawing, the compensation of axial forces is effected by using the inner rim of the rear sections of the impellers of the pump units as counter pistons to compensate for the major com¬ pression force applied to the end of the shaft. The packings employed are non-contact labyrinth packings which are manufactured with a small clearing. Such labyrinth packings have undergone practical tests and have proved well capable of withstanding speeds of rotation of appr. 300.000 rpm. If the efficiency of the exemplified apparatus is 30%, the final fluid temperature will be appr. 200°C. It is clear that a high pressure prevents vaporization of water and in most practical applications this temperature does not affect the actual fluid-jet cutting operation.

Claims: Claims : 1. An apparatus for producing a high-pressure fluid used for fluid-jet cutting, characterized in that said apparatus comprises: - a body (3) , - a shaft (10) journalled (5a, 5b, 6a, 6b) inside body (3), - a power unit (1, 2) for driving shaft (10) , a nozzle assembly (11) which is connected with body (3), at least two pump units (7) mounted successively on shaft (10) and operating on kinetic principle, and a set of conduits (8, 9) for delivering the fluid into body (3) and by way of pump units (7) to nozzle assembly (11) , whereby in each pump unit (7) the fluid pressure is adapted to be stepwise increased by means of the rotation energy of shaft (10) in a manner that along said set of conduits (8, 9) the fluid is further carried from the outlet side or the like of the preceding pump unit to the inlet side or the like of the following pump unit. 2. An apparatus as set forth in claim, characterized in that said power unit (1, 2) is connected to the first end of shaft (10) and that said nozzle assembly (11) is connected to a pressure chamber or a like adjacent to the second end of the shaft, the fluid being carried therein along set of conduits (8, 9) from the outlet side of the final pump unit. 3. An apparatus as set forth in either of claims 1 or 2, characterized in that shaft (10) is journalled to body (3) by means of liquid lubricated bearings. 4. An apparatus as set forth in claim 3, characterized in that the lubricating liquid comprises water having its pressure increased by means of the apparatus. 5. An apparatus as set forth in any of claims 1-4, characterized in that a bearing housing (13) included in at least a first journalling assembly (5a, 5b, 6a) adjacent to the first end of shaft (10) is designed as a part of set of conduits (8, 9) . 6. An apparatus as set forth in any of claims 1-5, characterized in that said bearing housing (13) adjacent to the first end of shaft (10) , which is designed as a part of the set of conduits, comprises at least one both axial (5a, 5b) and radial (6a) liquid lubricated bearing assembly. 7. An apparatus as set forth in claim 1, characterized in that between pump units (7) is fitted a sealing, especially a labyrinth packing (4) , acting between shaft (10) and body (13) . 8. An apparatus as set forth in claim 1, characterized in that the pump unit and/or the body includes a sealing or packing, especially a labyrinth packing, between inlet and outlet side, said packing acting between the pump unit in question and the body. 9. An apparatus as set forth in claim 1, characterized in that in each pump unit the fluid inlet side is arranged relative to the fluid outlet side in a manner that an axial component force, caused by a pressure difference created in said pump unit and applied to shaft (10) , is directed towards the second end of the shaft which is closer to nozzle assembly (11) . 10. An apparatus as set forth in claim 1, charac¬ terized in that the pump units are operating on centrifugal and/or Pitot principle. 11. An apparatus as set forth in claims 1-4, charac¬ terized in that a bearing housing (14) included in at least said second journalling assembly (6a) adjacent to the second end of shaft (10) is designed as a part of the set of conduits, and that the journalling assembly comprises a radial bearing assembly. 12. A method for producing a high-pressure fluid used for fluid-jet cutting, characterized in that - at least two pump units (7) operating on kinetic principle are successively mounted in connection with a shaft (10) , journalled inside a body (3) and driven by a power unit (1, 2) , the fluid used for fluid-jet cutting is carried through said pump units to a nozzle assembly included in said apparatus, whereby in each pump unit the fluid pressure is adapted to be stepwise increased by means of the rotation energy of shaft (10) in a manner that the fluid is further carried from the outlet side or the like of the preceding pump unit to the inletside or the like of following pump unit. 13. A method as set forth in claim 12, characterized in that the speed of rotation of shaft (10) is selected to be at least 5 x 10 4 rpm. 14. A method as set forth in claim 12, characterized in that the fluid pressure is increased by means of the apparatus to at least 3 x 10 3 bar. 15. The application of at least two successive pump units mounted on a shaft journalled inside a body for producing a high-pressure fluid used for fluid-jet cutting.

Inventors: HELEVIRTA KAUKO, LARJOLA JAAKKO, HELEVIRTA, KAUKO, LARJOLA, JAAKKO
Applicants: HIGH SPEED TECH LTD OY, OY HIGH SPEED TECH LTD.
Application year: 1991
Main classification: F04D1
IPC codes: B26F3, F04D1, F04D13, F04D29