EP0988453A1 - Screw spindle vacuum pump and operating method - Google Patents

Screw spindle vacuum pump and operating method

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Publication number
EP0988453A1
EP0988453A1 EP98934953A EP98934953A EP0988453A1 EP 0988453 A1 EP0988453 A1 EP 0988453A1 EP 98934953 A EP98934953 A EP 98934953A EP 98934953 A EP98934953 A EP 98934953A EP 0988453 A1 EP0988453 A1 EP 0988453A1
Authority
EP
European Patent Office
Prior art keywords
screw
vacuum pump
chamber
inlet
inlet opening
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP98934953A
Other languages
German (de)
French (fr)
Other versions
EP0988453B1 (en
Inventor
Heiner KÖSTERS
Christian Dahmlos
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sterling Fluid Systems Germany GmbH
Sterling Fluid Systems GmbH
Original Assignee
Sterling Fluid Systems Germany GmbH
Sterling Fluid Systems GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sterling Fluid Systems Germany GmbH, Sterling Fluid Systems GmbH filed Critical Sterling Fluid Systems Germany GmbH
Publication of EP0988453A1 publication Critical patent/EP0988453A1/en
Application granted granted Critical
Publication of EP0988453B1 publication Critical patent/EP0988453B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
    • F04C29/04—Heating; Cooling; Heat insulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C2240/00—Components
    • F04C2240/40—Electric motor
    • F04C2240/402—Plurality of electronically synchronised motors

Definitions

  • the temperature of the gas delivered by a compressor increases according to the compression pressure ratio.
  • screw compressors that rely on the least possible play both between the two rotors and between the rotors and the housing, the thermal expansion caused on the parts of the compressor can lead to problems.
  • the pre-inlet quantity supplied to the chambers is small in view of the efficiency of the machine. For example, when operating a screw machine as a compressor (US Pat. No. 4,812,110; US Pat. No.
  • the solution according to the invention consists in the features of claims 1 to 3. Accordingly, a screw pump vacuum pump is assumed which has at least three delivery chambers located one behind the other along each rotor. These are completed if you do not play the game that is unavoidable with dry extraction.
  • the last chamber on the pressure side shortly before it opens to the pressure side, is brought almost or completely to the final compression pressure through the pre-inlet by introducing a pre-inlet flow of cool gas which is at least five times larger than that Intake mass flow.
  • An operating point is assumed in which the ratio of the outer to the inner compression is at least five. On the one hand, this achieves effective cooling in the most critical area of the rotors with regard to temperature control.
  • this cooling also affects the penultimate chamber, because part of the cooler gas, which is under much higher pressure, flows back to the penultimate chamber in the last chamber.
  • this arrangement has the advantage that the development of noise is considerably reduced, because when the last chamber opens towards the pressure side, the pressure equalization is essentially complete. This means that at least 75% of the final pressure is reached by the pre-inlet before the last chamber is opened on the pressure side, preferably 90%.
  • Internal compression is the ratio of the volumes of the chamber closest to the suction side when this chamber is closed and the chamber closest to the pressure side when this chamber is opened. If the cross-sectional shape of the screw spindles is constant over the length, the internal compression is equal to 1.
  • a further possibility for defining the pre-entry according to the invention is contained in claim 2. Then the last chamber on the pressure side, before opening to the pressure side, should be supplied with a pre-inlet volume flow that is greater than 75% of the theoretical suction capacity of this chamber at the time of pre-inlet divided by the internal compression ratio. If the pre-admission extends over a period of considerable length, the point in time at which the pre-admission ends must be taken as a basis. Instead, the mean time between opening and closing the pre-admission can also be used. The volume flow is related to the outlet pressure and the temperature of the gas to be admitted. The theoretical pumping speed is the volume of the chamber at the decisive time multiplied by the speed.
  • the cross section of the pre-inlet opening in mm 2 should be at least as large as the theoretical suction capacity of the assigned chamber in m 3 / h, but preferably twice, more preferably three times as large.
  • the pre-inlet opening that is to say the wall opening which the gas enters the chamber introduces, no narrower cross-sections are upstream that affect the effect of the opening width again.
  • the theoretical pumping speed of the chamber is the product of the volume of this delivery chamber, the number of screw turns and the speed, based on the maximum speed that can be expected in continuous operation.
  • the powerful pre-inlet according to the invention is particularly effective in the last stage when the helical pitch of the rotors is constant, that is to say the compression is theoretically isochoric. But the invention also proves itself with a decreasing gradient, because the gradient is generally never reduced so much that the final pressure is reached in the normal operating point of the pump even without pre-admission in the last stage. Moreover, the invention does not rule out that, in addition to the strong pre-inlet in the last stage, a small pre-inlet is also provided in earlier stages, although in most applications this is unnecessary or even undesirable.
  • the deterioration in the suction capacity of the vacuum pump is negligible if the speed is not too low.
  • the pre-inlet opening is designed as a slot, in which at least the pressure-side boundary edge is formed parallel to the associated displacement screw thread.
  • the slot length should expediently be greater than 1/10 of the rotor diameter, preferably also greater than 1/5. It is expediently on the order of a third of the rotor diameter.
  • the width of the pre-inlet opening in the axial direction is expediently between half and the entire head width (measured in the same direction) of the displacement screw thread. It can even exceed the head width a little, as long as the pre-inlet filling of the last chamber on the pressure side is not endangered by the connection of the pre-inlet opening with the following chamber which is already occurring.
  • the suction edge of the pre-inlet opening can also run parallel to the associated displacement screw. However, it may be more expedient to at least partially incline the boundary on the suction side to the associated one
  • Form displacement screw thread in order to avoid a sudden opening of the pre-inlet opening, which could be associated with undesirable sound generation, in favor of a gradual opening.
  • the aim is for the pre-inlet opening to be closed before the chamber opens on the pressure side.
  • the pre-inlet opening at that rotor position in which the chamber is just opening on the pressure side is just covered by the associated screw thread. This avoids, for example, that a pressure surge entering the chamber from the pressure side penetrates to the pre-inlet opening and drives back heated gas which would reduce the cooling effect during the next pre-inlet process. This also avoids acoustic inconveniences.
  • the pre-inlet opening is already closed when the chamber is opened on the pressure side, provided that it is ensured that the pre-inlet opening is closed in the period of time that the pressure pulse coming from the pressure-side opening of the chamber at the speed of sound would need to reach the pre-inlet opening.
  • the free, axial projection of the pre-inlet opening over the cover edge of the associated screw thread should be smaller than its distance from the end of the screw thread forming the pressure-side opening of the chamber, multiplied by the number of revolutions and divided by the speed of sound.
  • Avoidance of undesirable interaction are provided between pre-admission and pressure side chamber opening (for example, min "1 above 6,000) are present at a high operating speed because at lower velocity these disadvantages speeds less consequence.
  • the pre-inlet is controlled by the interaction of the pre-inlet opening with the top surface of a screw thread. Although this is the preferred embodiment, it should not be ruled out that the pre-inlet opening is preceded by valves which are responsible for the timing of the pre-inlet or, in addition to the screw thread head surface, are jointly responsible.
  • pre-inlet opening or slot does not require the opening to be undivided.
  • an opening can be composed, for example, of a large number of individual bores which are separated from one another by webs.
  • the pre-inlet can take place by appropriately stretching the pre-inlet opening over a larger part of the chamber length.
  • An embodiment is preferred in which the pre-inlet opening, which is composed of a plurality of separate partial openings, extends over at least half the chamber length. It can be up to 270 °.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Applications Or Details Of Rotary Compressors (AREA)
  • Diaphragms For Electromechanical Transducers (AREA)
  • Manufacturing Of Printed Circuit Boards (AREA)
  • Coating With Molten Metal (AREA)
  • Non-Positive Displacement Air Blowers (AREA)
  • Electromagnetic Pumps, Or The Like (AREA)
  • Compressors, Vaccum Pumps And Other Relevant Systems (AREA)
  • Press Drives And Press Lines (AREA)
  • Forklifts And Lifting Vehicles (AREA)
  • Glass Compositions (AREA)
  • Valves And Accessory Devices For Braking Systems (AREA)

Abstract

The invention relates to a screw spindle vacuum pump with at least three sealed-off pumping chambers fitted one behind the other along each rotor. The invention also relates to a method for operating this compressor. Shortly before it opens onto delivery side of the pump, the last chamber on delivery side is brought almost to final compression pressure by preadmission. This is achieved by supplying a preadmission current at least five times greater than the suction mass flow rate. For this, the minimum ratio of outer compression to inner compression must be five.

Description

Schraubenspindelvakuumpumpe und Verfahren zum Betrieb derselben Screw vacuum pump and method of operating the same
Die Temperatur des von einem Verdichter geförderten Gases erhöht sich gemäß dem Verdichtungsdruckverhältnis. Bei Schraubenverdichtern, die auf möglichst geringes Spiel sowohl zwischen den beiden Rotoren als auch zwischen den Rotoren und dem Gehäuse angewiesen sind, kann die an den Teilen des Verdichters verursachte Wärmedehnung zu Problemen führen. Es ist bekannt (DE-A 195 22 559), die Temperatur des in den Förderzellen der Maschine enthaltenen Gases durch Voreinlaß herabzusetzen. Darunter versteht man den Einlaß kühleren Förderme- diums in die Förderzellen von einer Stelle höheren Drucks her. Die jeweils den Kammern zugeführte Voreinlaßmenge ist dabei mit Rücksicht auf den Wirkungsgrad der Maschine gering. So genügt es beispielsweise beim Betrieb einer Schraubenspin- delmaschine als Verdichter (US-A 4,812,110; US-A 5,082,427), lediglich einen Teil des geförderten Gases zum Voreinlaß zurückzuführen. Auch sind beim Betrieb einer Schraubenspindel- maschine als Vakuumpumpe andere Voraussetzungen als im Verdichterbetrieb zu beachten. Erstens ist das Druckverhältnis im Vakuumbetrieb ungleich höher als im Verdichterbetrieb, nämlich typischerweise weit über 100. Zweitens ist - entsprechend diesem Druckverhältnis - die im geförderten Gas erreichte Temperatur wesentlich höher. Schließlich muß darauf geachtet werden, daß das erreichbare Vakuum nicht durch Rückströmung des Voreinlasses beeinträchtigt wird. Der Erfindung liegt die Aufgabe zugrunde, eine SchraubenspindelVakuumpumpe und ein Verfahren zum Betrieb derselben zu schaffen, die durch Voreinlaß eine effektive Kühlung bei geringer Beeinträchtigung des Wirkungsgrads und des erreichba- ren Vakuums erlauben.The temperature of the gas delivered by a compressor increases according to the compression pressure ratio. With screw compressors that rely on the least possible play both between the two rotors and between the rotors and the housing, the thermal expansion caused on the parts of the compressor can lead to problems. It is known (DE-A 195 22 559) to reduce the temperature of the gas contained in the feed cells of the machine by pre-inlet. This means the inlet of cooler pumping medium into the pumping cells from a point of higher pressure. The pre-inlet quantity supplied to the chambers is small in view of the efficiency of the machine. For example, when operating a screw machine as a compressor (US Pat. No. 4,812,110; US Pat. No. 5,082,427), it is sufficient to return only part of the gas conveyed to the pre-inlet. When operating a screw spindle machine as a vacuum pump, other requirements than in compressor operation must also be observed. First, the pressure ratio in vacuum mode is much higher than in compressor mode, namely typically well over 100. Secondly, according to this pressure ratio, the temperature reached in the gas being pumped is much higher. Finally, care must be taken that the achievable vacuum is not impaired by backflow of the pre-inlet. The invention has for its object to provide a screw spindle vacuum pump and a method for operating the same, which, by pre-inlet, allow effective cooling with little impairment of the efficiency and the achievable vacuum.
Die erfindungsgemäße Lösung besteht in den Merkmalen der Ansprüche 1 bis 3. Demnach wird eine Schraubenspindelvakuumpum- pe vorausgesetzt, die längs jedes Rotors mindestens drei hin- tereinander liegende Förderkammern aufweist. Diese sind jeweils abgeschlossen, wenn man von dem bei trockener Förderung unvermeidlichen Spiel absieht. Bei einer solchen Maschine ist erfindungsgemäß vorgesehen, daß die druckseitig letzte Kammer, kurz bevor sie sich zur Druckseite hin öffnet, durch den Voreinlaß nahezu oder völlig auf den Verdichtungsenddruck gebracht wird, indem ein Voreinlaßstrom kühlen Gases eingelassen wird, der mindestens fünfmal größer ist als der Ansaug- massenstrom. Dabei wird ein Betriebspunkt vorausgesetzt, in welchem das Verhältnis der äußeren zur inneren Verdichtung mindestens fünf ist. Zum einen wird dadurch eine effektive Kühlung in dem bezüglich der Temperaturführung kritischsten Bereich der Rotoren erreicht. Zum anderen wirkt sich diese Kühlung auch auf die vorletzte Kammer aus, weil ein Teil des unter wesentlich höherem Druck stehenden, kühleren Gases in der letzten Kammer zur vorletzten zurückströmt. Schließlich hat diese Anordnung den Vorteil, daß die Geräuschentwicklung beträchtlich vermindert wird, weil dann, wenn die letzte Kammer sich zur Druckseite hin öffnet, der Druckausgleich schon im wesentlichen vollendet ist. Damit ist gemeint, daß wenig- stens 75% des Enddrucks durch den Voreinlaß vor dem druckseitigen Öffnen der letzten Kammer erreicht sind, vorzugsweise 90%.The solution according to the invention consists in the features of claims 1 to 3. Accordingly, a screw pump vacuum pump is assumed which has at least three delivery chambers located one behind the other along each rotor. These are completed if you do not play the game that is unavoidable with dry extraction. In such a machine it is provided according to the invention that the last chamber on the pressure side, shortly before it opens to the pressure side, is brought almost or completely to the final compression pressure through the pre-inlet by introducing a pre-inlet flow of cool gas which is at least five times larger than that Intake mass flow. An operating point is assumed in which the ratio of the outer to the inner compression is at least five. On the one hand, this achieves effective cooling in the most critical area of the rotors with regard to temperature control. On the other hand, this cooling also affects the penultimate chamber, because part of the cooler gas, which is under much higher pressure, flows back to the penultimate chamber in the last chamber. Finally, this arrangement has the advantage that the development of noise is considerably reduced, because when the last chamber opens towards the pressure side, the pressure equalization is essentially complete. This means that at least 75% of the final pressure is reached by the pre-inlet before the last chamber is opened on the pressure side, preferably 90%.
Ein so starker Voreinlaß ist bei bekannten Maschinen, deren Kammerzahl geringer ist, nicht möglich, weil infolge größerer Leckverluste der Druck in der Kammer beim Öffnen des Auslasses schon stärker angewachsen ist und demzufolge eine geringere Druckdifferenz für den Voreinlaß zur Verfügung steht. Auch spielt in diesem Zusammenhang wieder der erhebliche Unterschied im Druckverhältnis zwischen Verdichtern und Vakuumpumpen eine Rolle; infolge des geringeren Druckverhältnisses herrscht bei Verdichtern in der sich zum Auslaß hin öffnenden Kammer ein verhältnismäßig höherer Druck als bei Vakuumpumpen.Such a strong pre-inlet is not possible in known machines, the number of chambers of which is smaller, because the pressure in the chamber has already increased more as a result of greater leakage losses when the outlet is opened, and consequently a lower pressure difference is available for the pre-inlet. The considerable difference in the pressure ratio between the compressors and vacuum pumps also plays a role in this context; due to the lower pressure ratio, compressors in the chamber opening towards the outlet have a relatively higher pressure than vacuum pumps.
Unter der inneren Verdichtung ist das Verhältnis der Volumina der der Saugseite nächsten Kammer beim Schließen dieser Kam- mer und der der Druckseite nächsten Kammer beim Öffnen dieser Kammer zu verstehen. Wenn die Querschnittsform der Schraubenspindeln über die Länge konstant ist, ist die innere Verdichtung gleich 1.Internal compression is the ratio of the volumes of the chamber closest to the suction side when this chamber is closed and the chamber closest to the pressure side when this chamber is opened. If the cross-sectional shape of the screw spindles is constant over the length, the internal compression is equal to 1.
Eine weitere Möglichkeit zur Definition des erfindungsgemäßen Voreinlasses ist in Anspruch 2 enthalten. Danach soll der druckseitig letzten Kammer, bevor sie sich zur Druckseite hin öffnet, ein Voreinlaßvolumenstrom zugeführt werden, der größer ist als 75% des theoretischen Saugvermögens dieser Kammer im Zeitpunkt des Voreinlasses geteilt durch das innere Verdichtungsverhältnis. Wenn sich der Voreinlaß über eine Zeitspanne nicht unerheblicher Länge erstreckt, ist der Zeitpunkt zugrunde zu legen, in welchem der Voreinlaß endet. Statt dessen kann auch der mittlere Zeitpunkt zwischen dem Öffnen und dem Schließen des Voreinlasses zugrunde gelegt werden. Der Volumenstrom ist auf den Auslaßdruck und die Temperatur des einzulassenden Gases zu beziehen. Das theoretische Saugvermögen ist das Volumen der Kammer im maßgebenden Zeitpunkt multipliziert mit der Drehzahl.A further possibility for defining the pre-entry according to the invention is contained in claim 2. Then the last chamber on the pressure side, before opening to the pressure side, should be supplied with a pre-inlet volume flow that is greater than 75% of the theoretical suction capacity of this chamber at the time of pre-inlet divided by the internal compression ratio. If the pre-admission extends over a period of considerable length, the point in time at which the pre-admission ends must be taken as a basis. Instead, the mean time between opening and closing the pre-admission can also be used. The volume flow is related to the outlet pressure and the temperature of the gas to be admitted. The theoretical pumping speed is the volume of the chamber at the decisive time multiplied by the speed.
Die bisher üblichen, kleinen Voreinlaßöffnungen, denen eine beträchtliche Drosselwirkung innewohnt, reichen dafür nicht aus. Nach einer Faustregel soll der Querschnitt der Voreinlaßöffnung in mm2 mindestens so groß sein wie das theoreti- sehe Saugvermögen der zugeordneten Kammer in m3/h, vorzugsweise jedoch doppelt, weiter vorzugsweise dreifach so groß. Dies setzt selbstverständlich voraus, daß der Voreinlaßöffnung, also derjenigen Wandöffnung, die das Gas in die Kammer einführt, keine engeren Querschnitte vorgeschaltet sind, die die Wirkung der Öffnungsweite wieder beeinträchtigen. Das theoretische Saugvermögen der Kammer ist in diesem Zusammenhang das Produkt aus dem Volumen dieser Förderkammer, der Zahl der Schraubengänge und der Drehzahl, wobei die maximale Drehzahl zugrunde gelegt wird, mit der im Dauerbetrieb zu rechnen ist.The previously common, small pre-inlet openings, which have a considerable throttling effect, are not sufficient for this. According to a rule of thumb, the cross section of the pre-inlet opening in mm 2 should be at least as large as the theoretical suction capacity of the assigned chamber in m 3 / h, but preferably twice, more preferably three times as large. Of course, this presupposes that the pre-inlet opening, that is to say the wall opening which the gas enters the chamber introduces, no narrower cross-sections are upstream that affect the effect of the opening width again. In this context, the theoretical pumping speed of the chamber is the product of the volume of this delivery chamber, the number of screw turns and the speed, based on the maximum speed that can be expected in continuous operation.
Diese Definition des theoretischen Saugvermögens enthält im Unterschied zu der oben unter Bezugnahme auf Anspruch 2 gegebenen Definition die Zahl der Schraubengänge als Faktor. Dies erklärt sich daraus, daß hier die Gesamtheit der Einlaßöffnungen angesprochen ist, die im Falle einer mehrgängigen Schraubenspindel gleichzeitig mehreren Kammern zugeordnet sein können, während in Anspruch 2 lediglich eine einzelne Kammer betrachtet wird.In contrast to the definition given above with reference to claim 2, this definition of the theoretical pumping speed contains the number of screw turns as a factor. This is explained by the fact that the entirety of the inlet openings is addressed here, which in the case of a multi-start screw spindle can be assigned to several chambers at the same time, while claim 2 only considers a single chamber.
Besonders wirksam ist der erfindungsgemäße, kräftige Voreinlaß in der letzten Stufe dann, wenn die Schraubengangsteigung der Rotoren konstant ist, die Verdichtung also theoretisch isochor stattfindet. Aber auch bei abnehmender Steigung bewährt sich die Erfindung, weil die Steigung in der Regel niemals so stark vermindert wird, daß auch ohne Voreinlaß in der letzten Stufe im normalen Betriebspunkt der Pumpe der End- druck erreicht wird. Im übrigen schließt die Erfindung nicht aus, daß zusätzlich zu dem kräftigen Voreinlaß in der letzten Stufe auch noch ein geringer Voreinlaß in früheren Stufen vorgesehen ist, obgleich dies in den meisten Anwendungsfällen unnötig oder gar unerwünscht ist.The powerful pre-inlet according to the invention is particularly effective in the last stage when the helical pitch of the rotors is constant, that is to say the compression is theoretically isochoric. But the invention also proves itself with a decreasing gradient, because the gradient is generally never reduced so much that the final pressure is reached in the normal operating point of the pump even without pre-admission in the last stage. Moreover, the invention does not rule out that, in addition to the strong pre-inlet in the last stage, a small pre-inlet is also provided in earlier stages, although in most applications this is unnecessary or even undesirable.
Da der erfindungsgemäße Voreinlaß erst in der letzten Stufe stattfindet und mindestens drei aufeinanderfolgende Förderkammern vorgesehen sind, ist die Verschlechterung des Saugvermögens der Vakuumpumpe vernachlässigbar, sofern die Dreh- zahl nicht zu gering ist.Since the pre-inlet according to the invention only takes place in the last stage and at least three successive delivery chambers are provided, the deterioration in the suction capacity of the vacuum pump is negligible if the speed is not too low.
Bei einer vorteilhaften Ausführungsform der erfindungsgemäßen Vakuumpumpe ist die Voreinlaßöffnung als Schlitz ausgebildet, bei dem wenigstens die druckseitige Begrenzungskante parallel zu dem zugehörigen Verdrängerschraubengang ausgebildet ist. Dies ergibt den Vorteil, daß der Schlitz bis zum letztmöglichen Zeitpunkt mit größtmöglichem Querschnitt offen ist. Die Schlitzlänge soll zweckmäßigerweise größer als 1/10 des Rotordurchmessers sein, vorzugsweise auch größer als 1/5. Sie liegt zweckmäßigerweise in der Größenordnung eines Drittels des Rotordurchmessers. Die Breite der Voreinlaßöffnung in Axialrichtung liegt zweckmäßigerweise zwischen der halben und der ganzen Kopfbreite (in derselben Richtung gemessen) des Verdrängerschraubengangs. Sie kann die Kopfbreite sogar ein wenig übersteigen, solange die Voreinlaßfüllung der druckseitig letzten Kammer nicht durch die bereits eintretende Verbindung der Voreinlaßöffnung mit der folgenden Kammer gefähr- det wird.In an advantageous embodiment of the vacuum pump according to the invention, the pre-inlet opening is designed as a slot, in which at least the pressure-side boundary edge is formed parallel to the associated displacement screw thread. This has the advantage that the slot is open with the largest possible cross section until the last possible time. The slot length should expediently be greater than 1/10 of the rotor diameter, preferably also greater than 1/5. It is expediently on the order of a third of the rotor diameter. The width of the pre-inlet opening in the axial direction is expediently between half and the entire head width (measured in the same direction) of the displacement screw thread. It can even exceed the head width a little, as long as the pre-inlet filling of the last chamber on the pressure side is not endangered by the connection of the pre-inlet opening with the following chamber which is already occurring.
Auch die saugseitige Begrenzungskante der Voreinlaßöffnung kann parallel zum zugehörigen Verdrängerschraubengang verlaufen. Jedoch kann es zweckmäßiger sein, die saugseitige Be- grenzungskante zumindest teilweise geneigt zum zugehörigenThe suction edge of the pre-inlet opening can also run parallel to the associated displacement screw. However, it may be more expedient to at least partially incline the boundary on the suction side to the associated one
Verdrängerschraubengang auszubilden, um dadurch ein schlagartiges Öffnen der Voreinlaßöffnung, das mit unerwünschter Schallerzeugung verbunden sein könnte, zugunsten eines allmählichen Öffnens zu vermeiden. Im allgemeinen wird ange- strebt, daß die Voreinlaßöffnung geschlossen ist, bevor die Kammer sich druckseitig öffnet. Mit anderen Worten ist die Voreinlaßöffnung bei derjenigen Rotorstellung, in der sich die Kammer soeben druckseitig öffnet, von dem zugehörigen Schraubengang gerade abgedeckt. Dadurch wird beispielsweise vermieden, daß ein beim Öffnen von der Druckseite her in die Kammer eindringender Druckstoß bis zur Voreinlaßöffnung vordringt und erhitztes Gas in diese zurücktreibt, das die Kühlwirkung beim nächsten Voreinlaßvorgang vermindern würde. Auch schalltechnische Unannehmlichkeiten können dadurch vermieden werden. In vielen Fällen ist es aber nicht erforderlich, daß die Voreinlaßöffnung beim druckseitigen Öffnen der Kammer bereits geschlossen ist, sofern dafür gesorgt ist, daß die Voreinlaßöffnung in derjenigen Zeitspanne geschlossen wird, die der von der druckseitigen Öffnung der Kammer mit Schallgeschwindigkeit ausgehende Druckimpuls bis zum Erreichen der Voreinlaßöffnung benötigen würde. Mit anderen Worten soll der freie, axiale Überstand der Voreinlaßöffnung über die Abdeck- kante des zugehörigen Schraubengangs kleiner sein als ihr Abstand von dem die druckseitige Öffnung der Kammer bildenden Ende des Schraubengangs, multipliziert mit der Umdrehungszahl und dividiert durch die Schallgeschwindigkeit.Form displacement screw thread, in order to avoid a sudden opening of the pre-inlet opening, which could be associated with undesirable sound generation, in favor of a gradual opening. In general, the aim is for the pre-inlet opening to be closed before the chamber opens on the pressure side. In other words, the pre-inlet opening at that rotor position in which the chamber is just opening on the pressure side is just covered by the associated screw thread. This avoids, for example, that a pressure surge entering the chamber from the pressure side penetrates to the pre-inlet opening and drives back heated gas which would reduce the cooling effect during the next pre-inlet process. This also avoids acoustic inconveniences. In many cases, however, it is not necessary that the pre-inlet opening is already closed when the chamber is opened on the pressure side, provided that it is ensured that the pre-inlet opening is closed in the period of time that the pressure pulse coming from the pressure-side opening of the chamber at the speed of sound would need to reach the pre-inlet opening. In other words, the free, axial projection of the pre-inlet opening over the cover edge of the associated screw thread should be smaller than its distance from the end of the screw thread forming the pressure-side opening of the chamber, multiplied by the number of revolutions and divided by the speed of sound.
Es reicht im allgemeinen, wenn diese Bedingungen, die zurIt is generally sufficient if these conditions are used for
Vermeidung eines unerwünschten Zusammenwirkens zwischen Voreinlaßöffnung und druckseitiger Kammeröffnung vorgesehen sind, bei hoher Betriebsgeschwindigkeit (beispielsweise oberhalb 6.000 min"1) vorliegen, weil bei niedrigeren Geschwindig- keiten diese Nachteile weniger ins Gewicht fallen.Avoidance of undesirable interaction are provided between pre-admission and pressure side chamber opening (for example, min "1 above 6,000) are present at a high operating speed because at lower velocity these disadvantages speeds less consequence.
Bei den obigen Ausführungen wurde vorausgesetzt, daß der Voreinlaß durch das Zusammenwirken der Voreinlaßöffnung mit der Kopffläche eines Schraubengangs gesteuert wird. Obwohl dies die bevorzugte Ausführung ist, soll nicht ausgeschlossen sein, daß der Voreinlaßöffnung Ventile vorgeschaltet sind, die für die zeitliche Steuerung des Voreinlasses verantwortlich oder, neben der Schraubengang-Kopffläche, mitverantwortlich sind.In the above, it has been assumed that the pre-inlet is controlled by the interaction of the pre-inlet opening with the top surface of a screw thread. Although this is the preferred embodiment, it should not be ruled out that the pre-inlet opening is preceded by valves which are responsible for the timing of the pre-inlet or, in addition to the screw thread head surface, are jointly responsible.
Es sei darauf hingewiesen, daß der Begriff Voreinlaßöffnung oder Schlitz nicht verlangt, daß die Öffnung ungeteilt ist. Aus herstellungswirtschaftlichen Gründen kann man eine solche Öffnung beispielsweise aus einer Vielzahl einzelner Bohrungen zusammensetzen, die durch Stege voneinander getrennt sind.It should be noted that the term pre-inlet opening or slot does not require the opening to be undivided. For reasons of manufacturing economy, such an opening can be composed, for example, of a large number of individual bores which are separated from one another by webs.
Dies ergibt den Vorteil, daß der Voreinlaß durch entsprechende Streckung der Voreinlaßöffnung über einen größeren Teil der Kammerlänge stattfinden kann. Bevorzugt wird eine Ausführung, bei welcher sich die aus mehreren getrennten Teilöff- nungen zusammensetzende Voreinlaßöffnung über mindestens die Hälfte der Kammerlänge erstreckt. Sie kann bis zu 270° betragen. This gives the advantage that the pre-inlet can take place by appropriately stretching the pre-inlet opening over a larger part of the chamber length. An embodiment is preferred in which the pre-inlet opening, which is composed of a plurality of separate partial openings, extends over at least half the chamber length. It can be up to 270 °.

Claims

Patentansprüche claims
1. Verfahren zum Betrieb einer Schraubenspindelvakuumpumpe mit mindestens drei längs jedes Rotors hintereinander liegenden abgeschlossenen Förderkammern und mit Voreinlaß zum Zuführen kühlen Gases, dadurch gekennzeichnet, daß die druckseitig letzte Kammer, kurz bevor sie sich zur Druckseite öffnet, durch den Voreinlaß nahezu auf den Verdichtungsenddruck gebracht wird und daß bei einem Verhältnis der äußeren zur inneren Verdichtung von mindestens 5 der Voreinlaß-Massenstrom mindestens 5-mal größer ist als der Ansaug-Massenstrom.1. A method of operating a screw-type vacuum pump with at least three closed delivery chambers lying one behind the other along each rotor and with a pre-inlet for supplying cool gas, characterized in that the last chamber on the pressure side, just before it opens to the pressure side, is brought almost to the final compression pressure through the pre-inlet and that with a ratio of the outer to the inner compression of at least 5, the pre-inlet mass flow is at least 5 times greater than the intake mass flow.
2. Verfahren zum Betrieb einer Schraubenspindelvakuumpumpe mit mindestens drei längs jedes Rotors hintereinander- liegenden abgeschlossenen Förderkammern und mit Voreinlaß zum Zuführen kühlen Gases, dadurch gekennzeichnet, daß der druckseitig letzten Kammer, bevor sie sich zur Druckseite öffnet, ein Voreinlaßvolumenstrom zugeführt wird, der (bezogen auf den Auslaßdruck) größer ist als 75% des theoretischen Saugvermögens dieser zugeordneten Kammer geteilt durch das innere Verdichtungsverhältnis.2. A method of operating a screw-type vacuum pump with at least three closed delivery chambers lying one behind the other along each rotor and with a pre-inlet for supplying cool gas, characterized in that a pre-inlet volume flow is supplied to the last chamber on the pressure side before it opens to the pressure side, which (referred to to the outlet pressure) is greater than 75% of the theoretical pumping speed of this assigned chamber divided by the internal compression ratio.
3. Schraubenspindelvakuumpumpe mit einem Paar innerhalb ei- nes Schöpfraums umlaufender Verdrängerrotoren, deren3. Screw-type vacuum pump with a pair of positive-displacement rotors rotating within a pumping chamber, their
Schraubengänge unter Bildung von mindestens drei hintereinander angeordneten, voneinander abgeschlossenen Kammern ineinander greifen, und mit wenigstens einer der druckseitig letzten Kammer zugeordneten Voreinlaßöff- nung, dadurch gekennzeichnet, daß der Querschnitt der Voreinlaßöffnung in mm2 mindestens so groß ist wie das theoretische Saugvermögen der zugeordneten Kammer in m3/h.Screw threads interlock to form at least three chambers which are arranged one behind the other and with at least one pre-inlet opening assigned to the last pressure-side chamber, characterized in that the cross-section of the pre-inlet opening in mm 2 is at least as large as the theoretical pumping speed of the assigned chamber in m 3 / h.
4. Schraubenspindelvakuumpumpe nach Anspruch 3, dadurch gekennzeichnet, daß die Voreinlaßöffnung als Schlitz und wenigstens ihre druckseitige Begrenzungskante parallel zu dem zugehörigen Verdrängerschraubengang ausgebildet ist.4. Screw-type vacuum pump according to claim 3, characterized in that the pre-inlet opening as a slot and at least its pressure-side boundary edge in parallel is formed to the associated displacement screw.
5. Schraubenspindelvakuumpumpe nach Anspruch 4 , dadurch ge- kennzeichnet, daß die Schlitzlänge größer als 1/10 des5. Screw-type vacuum pump according to claim 4, characterized in that the slot length is greater than 1/10 of
Rotordurchmessers ist.Rotor diameter is.
6. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 5, dadurch gekennzeichnet, daß die Breite der Vor- einlaßöffnung in Axialrichtung zwischen der halben und der ganzen Kopfbreite des Verdrängerschraubengangs liegt.6. Screw-type vacuum pump according to one of claims 3 to 5, characterized in that the width of the pre-inlet opening lies in the axial direction between half and the entire head width of the positive displacement.
7. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 5, dadurch gekennzeichnet, daß die Breite der Voreinlaßöffnung in Axialrichtung größer als die Kopfbreite des Verdrängerschraubengangs ist.7. Screw spindle vacuum pump according to one of claims 3 to 5, characterized in that the width of the pre-inlet opening in the axial direction is greater than the head width of the displacement screw.
8. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 7, dadurch gekennzeichnet, daß auch die saugseitige8. Screw-type vacuum pump according to one of claims 3 to 7, characterized in that the suction side
Begrenzungskante parallel zum zugehörigen Verdrängerschraubengang verläuft.Boundary edge runs parallel to the associated displacement screw.
9. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 7, dadurch gekennzeichnet, daß die saugseitige Begrenzungskante zumindest teilweise geneigt zum zugehörigen Verdrängerschraubengang verläuft.9. Screw spindle vacuum pump according to one of claims 3 to 7, characterized in that the suction-side boundary edge extends at least partially inclined to the associated displacement screw.
10. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 9, dadurch gekennzeichnet, daß die Voreinlaßöffnung bei derjenigen Rotorstellung, in der sich die Kammer soeben druckseitig öffnet, von dem zugehörigen Schraubengang gerade abgedeckt ist.10. Screw spindle vacuum pump according to one of claims 3 to 9, characterized in that the pre-inlet opening at that rotor position in which the chamber just opens on the pressure side is just covered by the associated screw thread.
11. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 9, dadurch gekennzeichnet, daß die Voreinlaßöffnung bei derjenigen Rotorstellung, in der sich die Kammer soeben druckseitig öffnet, von dem zugehörigen Schrauben- gang noch nicht gänzlich abgedeckt ist, aber- ihr freier, axialer Überstand über die Abdeckkante dieses Schraubengangs kleiner ist als ihr Abstand vom Ende des der druckseitigen Kammeröffnung zugeordneten Endes des Schraubengangs mal Umdrehungszahl durch Schallgeschwindigkeit.11. Screw spindle vacuum pump according to one of claims 3 to 9, characterized in that the pre-inlet opening at that rotor position in which the chamber just opens on the pressure side, from the associated screw gear is not yet completely covered, but its free, axial overhang over the cover edge of this screw thread is smaller than its distance from the end of the screw thread speed associated with the pressure chamber opening by the speed of sound.
12. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 11, dadurch gekennzeichnet, daß die Voreinlaßöffnung aus einer Mehrzahl von Bohrungen zusammengesetzt ist.12. Screw-type vacuum pump according to one of claims 3 to 11, characterized in that the pre-inlet opening is composed of a plurality of bores.
13. Schraubenspindelvakuumpumpe nach einem der Ansprüche 3 bis 12, dadurch gekennzeichnet, daß die sich ggf. aus mehreren Teilöffnungen zusammensetzende Voreinlaßöffnung über mindestens die Hälfte der Kammerlänge erstreckt. 13. Screw-type vacuum pump according to one of claims 3 to 12, characterized in that the pre-inlet opening, which may be composed of several partial openings, extends over at least half the chamber length.
EP98934953A 1997-06-11 1998-06-09 Screw spindle vacuum pump and operating method Expired - Lifetime EP0988453B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE19724643 1997-06-11
DE19724643A DE19724643A1 (en) 1997-06-11 1997-06-11 Screw compressor and method of operating the same
PCT/EP1998/003544 WO1998057067A1 (en) 1997-06-11 1998-06-09 Screw spindle vacuum pump and operating method

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EP0988453A1 true EP0988453A1 (en) 2000-03-29
EP0988453B1 EP0988453B1 (en) 2003-08-20

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US (1) US6273696B1 (en)
EP (1) EP0988453B1 (en)
JP (1) JP4002304B2 (en)
KR (2) KR20010013692A (en)
AT (1) ATE247780T1 (en)
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DE (2) DE19724643A1 (en)
DK (1) DK0988453T3 (en)
ES (1) ES2206958T3 (en)
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PT (1) PT988453E (en)
WO (1) WO1998057067A1 (en)
ZA (1) ZA984959B (en)

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ES2206958T3 (en) 2004-05-16
NO327604B1 (en) 2009-08-31
DK0988453T3 (en) 2003-12-15
JP4002304B2 (en) 2007-10-31
DE19724643A1 (en) 1998-12-17
NO996129L (en) 1999-12-10
EP0988453B1 (en) 2003-08-20
ATE247780T1 (en) 2003-09-15
NO996129D0 (en) 1999-12-10
JP2002504205A (en) 2002-02-05
CA2293618A1 (en) 1998-12-17
CA2293618C (en) 2007-09-18
KR20010013692A (en) 2001-02-26
PT988453E (en) 2004-01-30
KR20010013629A (en) 2001-02-26
KR100340166B1 (en) 2002-06-10
WO1998057067A1 (en) 1998-12-17
US6273696B1 (en) 2001-08-14
ZA984959B (en) 1999-04-12
DE59809350D1 (en) 2003-09-25

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