EP0456632B1 - Method of manufacturing for impeller of centrifugal pump and this impeller - Google Patents

Method of manufacturing for impeller of centrifugal pump and this impeller Download PDF

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Publication number
EP0456632B1
EP0456632B1 EP91890094A EP91890094A EP0456632B1 EP 0456632 B1 EP0456632 B1 EP 0456632B1 EP 91890094 A EP91890094 A EP 91890094A EP 91890094 A EP91890094 A EP 91890094A EP 0456632 B1 EP0456632 B1 EP 0456632B1
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EP
European Patent Office
Prior art keywords
impeller
drawing die
centrifugal pump
individual beads
deep drawing
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.)
Expired - Lifetime
Application number
EP91890094A
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German (de)
French (fr)
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EP0456632A1 (en
Inventor
Leopold Ing. Nigischer
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.)
Xylem Water Solutions Austria GmbH
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Pumpenfabrik Ernst Vogel 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
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Publication of EP0456632A1 publication Critical patent/EP0456632A1/en
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04DNON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00Details, component parts, or accessories
    • F04D29/18Rotors
    • F04D29/22Rotors specially for centrifugal pumps
    • F04D29/2205Conventional flow pattern
    • F04D29/2222Construction and assembly

Definitions

  • the invention relates to a method for producing a centrifugal pump impeller, preferably a radial or radially inclined centrifugal pump impeller, in sheet metal construction.
  • the aim of the invention is to reduce the number of individual pieces from which such an impeller is constructed and to simplify or make the manufacturing process considerably simpler.
  • any curved, in particular continuous, curved tracks or impeller blades can be produced: this method is therefore very particularly suitable for small quantities or for custom-made products.
  • the tool costs in this process are very low, since all the required impellers or impeller blade shapes can be produced with a few simple, essentially point-shaped or cutting-shaped deep-drawing tools, whereas, in the case of the previous, compression-molded impellers (see, for example, US Pat. No. 3,340 813 and 3 059 582) each have to produce their own, very expensive press rams for each impeller shape.
  • the impeller produced according to the method according to the invention is essentially assembled from two impeller side walls and fastened to a pump shaft. Despite the smaller wall thickness and therefore lighter weight, the beaded wheel side wall has a higher strength than known wheel side walls due to this machining process.
  • a further improvement and, in particular, rationalization of the method according to the invention is achieved according to a further embodiment of the invention in that the deep-drawing tool is guided either with a fixed sheet metal blank or the sheet metal blank is guided along the curved tracks in the case of a fixed deep-drawing tool, and that the deep-drawing tool is preferably also used at the same time as a connecting tool for the two impeller side walls is used, an electrical voltage being applied to the deep-drawing tool when the bead depth is reached, and spot welding is thus achieved.
  • the invention also relates to a centrifugal pump impeller produced by the method according to the invention in a radial or radially inclined sheet-metal construction, which is characterized in that the impeller blades produced by individual beads along in particular continuous curved tracks have a more or less clearly visible one according to the number or spacing of the individual beads Show ripple in the course of the continuous cam tracks and that the hydraulic characteristics of the impeller can be changed in addition to the influence of the cam track by the choice of the spacing of the individual beads, especially with free spaces remaining in between. This makes it possible to cause a deliberate disturbance of the flow at the impeller blade, as is sometimes desired in pump deliveries, in order to limit the delivery rate or to maintain a defined maximum power consumption.
  • FIG. 1 shows a radial section through an impeller
  • FIG. 2 shows a partial section along the line II-II in FIG. 1
  • FIG. 3 shows a plan view in the axial direction of a part of the impeller
  • FIG. 4 schematically shows the manufacture of different impeller blades in an axial view similar to FIGS. 3 and 5, a sectional view along the line VV and the line V'-V 'in FIG. 4.
  • the reference numeral 1 denotes an impeller blade, which is arranged in a conventional manner between the pressure-side wheel side or end wall 3 and the suction-side wheel side or end wall 4.
  • the impeller is also fastened in a conventional manner by means of the hub 5 to a pump shaft, not shown, and the sealing strip fastening 6.5 is also designed in accordance with the prior art.
  • the impeller blades 1 are formed by beading or deep-drawing the pressure-side wheel side wall 3 and accordingly in one piece with this wall 3.
  • the suction-side wheel side wall 4 is made somewhat thicker.
  • the impeller blades 1 can also be formed by beading the wall 4 or by beading both walls 3 and 4.
  • Fig. 3 shows an impeller blade 1 formed by beads in an axial view, the suction side wheel side wall 4 being removed.
  • This impeller blade 1 has been produced by beading with an essentially punctiform or cutting-shaped deep-drawing tool along the continuous cam track 2.
  • FIG. 4 which shows a view analogous to FIG. 3, shows how the deep-drawing tool, the so-called shuttle 7, seated on a stamp 8, is moved along the double arrow and along the continuous curved path 2 over the wheel side wall 3 and / or 4 (with the sheet disk 3, 4 being fixed) in order to stamp the impeller blade 1 out of this side wall 3 and / or 4.
  • the boat 7 is guided between two side supports 9 during its up and down movement (see the double arrow in FIG. 5) or these are moved together with the boat 7.
  • the shuttle 7 and the two side supports 9 can also be arranged in a stationary or fixed manner and the sheet round blanks 3, 4 can be moved or guided along the curved path 2.
  • the impeller blade 1 with a uniform width is shown as an example, another impeller blade with changing width, which is formed from the individual beads 1 ', 1 ⁇ , 1 ⁇ ', 1 IV , 1 V , etc. More or less large free spaces 10 can be provided between these individual beads.
  • the impeller blade 1 with a uniform width is produced in that the individual beads are set so close to one another in the course of the manufacturing process that practically a uniformly wide groove is formed
  • NC control numerically controlled
  • PC control computer
  • template or hand-controlled You could also call this process "curve beading”.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)

Description

Die Erfindung bezieht sich auf ein Verfahren zum Herstellen eines Kreiselpumpenlaufrades, vorzugsweise eines radialen oder radial schräggesteilten Kreiselpumpenlaufrades, in Blechbauweise.The invention relates to a method for producing a centrifugal pump impeller, preferably a radial or radially inclined centrifugal pump impeller, in sheet metal construction.

Bisher wurden solche Laufräder aus mehreren Einzelteilen zusammengebaut. Ziel der Erfindung ist es, die Zahl der Einzelstücke, aus denen ein solches Laufrad aufgebaut ist, zu verringern und das Herstellungsverfahren wesentlich zu vereinfachen bzw. zu verbilligen. Dies wird erfindungsgemaß dadurch erreicht, daß die Laufradschaufeln durch Sicken mit einem im wesentlichen punkt- oder schneidenförmigen Tiefziehwerkzeug entlang insbesondere stetiger Kurvenbahnen in der druckseitigen und/oder saugseitigen Radseitenwand erzeugt werden, wobei die einzelnen Sicken (schrittweise) aufeinanderfolgend längs der Kurvenbahn gesetzt werden.So far, such wheels have been assembled from several individual parts. The aim of the invention is to reduce the number of individual pieces from which such an impeller is constructed and to simplify or make the manufacturing process considerably simpler. This is achieved according to the invention in that the impeller blades are produced by beading with an essentially punctiform or cutting-shaped deep-drawing tool along, in particular, continuous cam tracks in the pressure-side and / or suction-side wheel side wall, the individual beads being set (step by step) in succession along the cam track.

Mit dem erfindungsgemaßen Verfahren können beliebig gekrümmte, insbesondere stetige kurvenbahnen bzw. Laufradschaufeln erzeugt werden: dieses Verfahren ist somit vor allem für geringe Stückzahlen bzw. für Sonderanfertigungen sehr gut geeignet. Die Werkzeugkosten bei diesem Verfahren sind sehr gering, da mit wenigen einfachen, im wesentlichen punkt- oder schneidenförmigen Tiefziehwerkzeugen alle benötigten Laufräder bzw. Laufradschaufelformen erzeugt werden können, wogegen, bei den bisherigen, formgepreßten Laufrädern (vgl. z.B. die US-A-3 340 813 und 3 059 582) jeweils eigene, sehr teure Preßstempel für jede Laufradform angefertigt werden müssen. Dies gilt auch für das durch die DE-C-800 238 Bekannte, wodurch die Schaufeln eines aus zwei miteinander verbundenen Radscheiben bestehenden Gebläserades offenbar in einem einzigen Ziehvorgang mit einem jeweils nur für eine einzige Laufradform geeigneten Preßstempel aus den Radscheiben gebildet werden. Für verschiedene Schaufelformen bzw. Radgrößen benötigt man beim Bekannten daher jeweils verschiedene Preßstempel. Auch die für den Herstellungs- bzw. Bearbeitungsvorgang erforderlichen Drücke sind beim erfindungsgemäßen Verfahren um Größenordnungen geringer.With the method according to the invention, any curved, in particular continuous, curved tracks or impeller blades can be produced: this method is therefore very particularly suitable for small quantities or for custom-made products. The tool costs in this process are very low, since all the required impellers or impeller blade shapes can be produced with a few simple, essentially point-shaped or cutting-shaped deep-drawing tools, whereas, in the case of the previous, compression-molded impellers (see, for example, US Pat. No. 3,340 813 and 3 059 582) each have to produce their own, very expensive press rams for each impeller shape. This also applies to what is known from DE-C-800 238, as a result of which the blades of an impeller consisting of two interconnected wheel disks are apparently formed from the wheel disks in a single drawing operation with a press ram suitable only for a single impeller shape. You need for different blade shapes and wheel sizes in the known, therefore, different press stamps. The pressures required for the manufacturing or machining process are also orders of magnitude lower in the method according to the invention.

Das gemaß dem erfindungsgemaßen Verfahren hergestellte Laufrad wird im wesentlichen aus zwei Laufradseitenwanden zusammengebaut und auf einer Pumpenweile befestigt. Trotz der geringeren Wandstärke und somit geringeren Gewichtes hat die gesickte Radseitenwand durch diesen Bearbeitungsvorgang eine höhere Festigkeit als bekannte Radseitenwände.The impeller produced according to the method according to the invention is essentially assembled from two impeller side walls and fastened to a pump shaft. Despite the smaller wall thickness and therefore lighter weight, the beaded wheel side wall has a higher strength than known wheel side walls due to this machining process.

Eine weitere Verbesserung und insbesondere Rationalisierung des erfindungsgemäßen Verfahrens wird gemäß einer weiteren Ausgestaltung der Erfindung dadurch erreicht, daß entweder bei feststehender Blechronde das Tiefziehwerkzeug oder bei feststehendem Tiefziehwerkzeug die Blechronde entlang der Kurvenbahnen geführt wird und daß vorzugsweise das Tiefziehwerkzeug gleichzeitig auch als Verbindungswerkzeug für die beiden Laufradseitenwände verwendet wird, wobei an das Tiefziehwerkzeug bei Erreichen der Sickentiefe eine elektrische Spannung angelegt und damit eine Punktschweißung erzielt wird.A further improvement and, in particular, rationalization of the method according to the invention is achieved according to a further embodiment of the invention in that the deep-drawing tool is guided either with a fixed sheet metal blank or the sheet metal blank is guided along the curved tracks in the case of a fixed deep-drawing tool, and that the deep-drawing tool is preferably also used at the same time as a connecting tool for the two impeller side walls is used, an electrical voltage being applied to the deep-drawing tool when the bead depth is reached, and spot welding is thus achieved.

Gegenstand der Erfindung ist auch ein nach dem erfindungsgemäßen Verfahren hergestelltes Kreiselpumpenlaufrad in radialer oder radial schräggestellter Blechbauweise, das dadurch gekennzeichnet ist, daß die durch einzelne Sickungen entlang insbesondere stetiger Kurvenbahnen hergestellten Laufradschaufeln entsprechend der Anzahl bzw. dem Abstand der Einzelsicken eine mehr oder weniger deutlich sichtbare Welligkeit im Verlauf der stetigen Kurvenbahnen aufweisen und daß durch die Wahl der Abstände der Einzelsicken, insbesondere bei dazwischenliegend verbleibenden Freiräumen, die hydraulische Charakteristik des Laufrades zusätzlich zum Einfluß durch die Kurvenbahn veränderbar ist. Dies ermöglicht es, eine gewollte Störung der Strömung an der Laufradschaufel herbeizuführen, wie es manchmal bei Pumpenförderungen erwünscht ist, um die Fördermenge zu begrenzen oder eine definierte maximale Leistungsaufnahme einzuhalten.The invention also relates to a centrifugal pump impeller produced by the method according to the invention in a radial or radially inclined sheet-metal construction, which is characterized in that the impeller blades produced by individual beads along in particular continuous curved tracks have a more or less clearly visible one according to the number or spacing of the individual beads Show ripple in the course of the continuous cam tracks and that the hydraulic characteristics of the impeller can be changed in addition to the influence of the cam track by the choice of the spacing of the individual beads, especially with free spaces remaining in between. This makes it possible to cause a deliberate disturbance of the flow at the impeller blade, as is sometimes desired in pump deliveries, in order to limit the delivery rate or to maintain a defined maximum power consumption.

Die Erfindung wird nun an Hand von in den Zeichnungen dargestellten Ausführungsbeispielen näher erläutert. Es zeigen: Fig. 1 einen radialen Schnitt durch ein Laufrad, Fig. 2 einen Teilschnitt längs der Linie II-II in Fig. 1, Fig. 3 eine Draufsicht in axialer Richtung auf einen Teil des Laufrades, Fig. 4 schematisch die Herstellung von verschiedenen Laufradschaufeln in axialer Ansicht ähnlich der Fig. 3 und Fig. 5 eine Schnittansicht längs der Linie V-V bzw. der Linie V'-V' in Fig. 4.The invention will now be explained in more detail with reference to exemplary embodiments shown in the drawings. 1 shows a radial section through an impeller, FIG. 2 shows a partial section along the line II-II in FIG. 1, FIG. 3 shows a plan view in the axial direction of a part of the impeller, FIG. 4 schematically shows the manufacture of different impeller blades in an axial view similar to FIGS. 3 and 5, a sectional view along the line VV and the line V'-V 'in FIG. 4.

In Fig. 1 ist mit dem Bezugszeichen 1 eine Laufradschaufel bezeichnet, die in üblicher Weise zwischen der druckseitigen Radseiten- bzw. -stirnwand 3 und der saugseitigen Radseiten- bzw. -stirnwand 4 angeordnet ist. Das Laufrad ist in ebenfalls üblicher Weise mittels der Nabe 5 auf einer nicht dargestellten Pumpenwelle befestigt und auch die Dichtleistenbefestigung 6,5 ist gemäß dem Stand der Technik ausgebildet.In Fig. 1, the reference numeral 1 denotes an impeller blade, which is arranged in a conventional manner between the pressure-side wheel side or end wall 3 and the suction-side wheel side or end wall 4. The impeller is also fastened in a conventional manner by means of the hub 5 to a pump shaft, not shown, and the sealing strip fastening 6.5 is also designed in accordance with the prior art.

Wie aus Fig. 2 ersichtlich ist, sind die Laufradschaufeln 1 durch Sicken bzw. Tiefziehen der druckseitigen Radseitenwand 3 ausgebildet und demgemäß mit dieser Wand 3 einstückig. Die saugseitige Radseitenwand 4 ist in diesem Ausführungsbeispiel etwas dicker ausgebildet. Selbstverständlich können die Laufradschaufeln 1 auch durch Sicken der Wand 4 oder aber durch Sicken beider Wände 3 und 4 gebildet werden.As can be seen from FIG. 2, the impeller blades 1 are formed by beading or deep-drawing the pressure-side wheel side wall 3 and accordingly in one piece with this wall 3. In this exemplary embodiment, the suction-side wheel side wall 4 is made somewhat thicker. Of course, the impeller blades 1 can also be formed by beading the wall 4 or by beading both walls 3 and 4.

Fig. 3 zeigt eine durch Sicken gebildete Laufradschaufel 1 in axialer Ansicht, wobei die saugseitige Radseitenwand 4 abgenommen ist. Diese Laufradschaufel 1 ist durch Sicken mit einem im wesentlichen punkt- oder schneidenförmigen Tiefziehwerkzeug entlang der stetigen Kurvenbahn 2 erzeugt worden.Fig. 3 shows an impeller blade 1 formed by beads in an axial view, the suction side wheel side wall 4 being removed. This impeller blade 1 has been produced by beading with an essentially punctiform or cutting-shaped deep-drawing tool along the continuous cam track 2.

Dieser Vorgang bzw. das erfindungsgemäße Verfahren zur Herstellung eines solchen Kreiselpumpenlaufrades wird an Hand der Fig. 4 und 5 besser verständlich. In Fig. 4, die eine zur Fig. 3 analoge Ansicht zeigt, ist dargestellt, wie das auf einem Stempel 8 sitzende Tiefziehwerkzeug, das sogenannte Schiffchen 7 längs des Doppelpfeils und längs der stetigen Kurvenbahn 2 über die Radseitenwand 3 und/oder 4 bewegt wird (wobei die Blechronde 3,4 feststeht), um die Laufradschaufel 1 aus dieser Seitenwand 3 und/oder 4 auszuprägen. Wie aus Fig. 5 ersichtlich ist, wird das Schiffchen 7 bei seiner Auf- und Abbewegung (siehe den Doppelpfeil in Fig. 5) zwischen zwei Seitenstützen 9 geführt bzw. werden diese mit dem Schiffchen 7 mitbewegt. Es können aber auch das Schiffchen 7 und die beiden Seitenstützen 9 ortsfest bzw. feststehend angeordnet und die Blechronde 3,4 entlang der Kurvenbahn 2 bewegt bzw. geführt werden.This process and the method according to the invention for producing such a centrifugal pump impeller can be better understood with reference to FIGS. 4 and 5. FIG. 4, which shows a view analogous to FIG. 3, shows how the deep-drawing tool, the so-called shuttle 7, seated on a stamp 8, is moved along the double arrow and along the continuous curved path 2 over the wheel side wall 3 and / or 4 (with the sheet disk 3, 4 being fixed) in order to stamp the impeller blade 1 out of this side wall 3 and / or 4. As can be seen from FIG. 5, the boat 7 is guided between two side supports 9 during its up and down movement (see the double arrow in FIG. 5) or these are moved together with the boat 7. However, the shuttle 7 and the two side supports 9 can also be arranged in a stationary or fixed manner and the sheet round blanks 3, 4 can be moved or guided along the curved path 2.

In Fig. 4 ist außer der mit gleichmäßiger Breite ausgeführten Laufradschaufel 1 als Beispiel auch eine andere Laufradschaufel mit wechselnder Breite dargestellt, die aus den Einzelsicken 1′,1˝,1˝′,1IV,1V usw. gebildet ist. Zwischen diesen Einzelsicken können mehr oder weniger große Freiräume 10 vorgesehen sein.In Fig. 4, the impeller blade 1 with a uniform width is shown as an example, another impeller blade with changing width, which is formed from the individual beads 1 ', 1˝, 1˝', 1 IV , 1 V , etc. More or less large free spaces 10 can be provided between these individual beads.

Während somit die Laufradschaufel 1 mit gleichmäßiger Breite dadurch erzeugt wird, daß die einzelnen Sicken im Zuge des Herstellungsvorganges so eng aneinander gesetzt werden, daß praktisch eine gleichmäßig breite Rinne entsteht, wird beim anderen Beispiel einer Laufradschaufel bewußt ein Abstand zwischen den Einzelsicken 1′,1˝, ... gelassen, um ein gewolltes bzw. gesteuertes Abreißen der Strömung an der Laufradschaufel herbeizuführen, wie es für manche Anwendungsfälle von Vorteil sein kann.Thus, while the impeller blade 1 with a uniform width is produced in that the individual beads are set so close to one another in the course of the manufacturing process that practically a uniformly wide groove is formed, in the other example of an impeller blade there is deliberately a distance between the individual beads 1 ', 1 Gelassen, ... left to bring about a deliberate or controlled breaking of the flow at the impeller blade, which can be advantageous for some applications.

Die Steuerung längs der Kurvenbahn 2 erfolgt am besten durch eine numerisch gesteuerte (NC-Steuerung) Vorrichtung, kann aber auch computer-(PC-Steuerung), schablonen- oder handgesteuert erfolgen. Man könnte diesen Vorgang auch als "Kurvensicken" bezeichnen.The control along the cam track 2 is best carried out by a numerically controlled (NC control) device, but can also be computer (PC control), template or hand-controlled. You could also call this process "curve beading".

Mit einigen wenigen schiffchen 7 (ca. 5 bis 10 Stück) können auf diese Weise die unterschiedlichsten Konturen (Kanalkonturen) der Laufradschaufeln 1 erzeugt werden.With a few boats 7 (approx. 5 to 10 pieces), the most varied contours (channel contours) of the impeller blades 1 can be produced in this way.

Claims (3)

  1. A method of manufacturing an impeller of a centrifugal pump, preferably a radial or radially inclined impeller of a centrifugal pump, constructed as sheet metal, characterized in that the impeller blades are produced by beading by means of an essentially punctual or knife-shaped deep-drawing die particularly along continuous curved paths in the pressure side and/or suction side impeller side wall, with the individual beads being set (gradually) successively along the curved path.
  2. A method according to claim 1, characterized in that either the deep drawing die (with the metal sheet round being stationary) or the metal sheet round (with the deep drawing die being stationary) is guided along the curved paths and that preferably the deep drawing die is simultaneously used as a linkage tool for the two impeller side walls, an electrical voltage being applied to the deep drawing die when the beading depth is attained, thereby achieving point welding.
  3. An impeller of a centrifugal pump manufactured by a radial or radially inclined sheet metal construction method by means of the process according to claim 1 or 2, characterized in that the impellers produced by individual beads (1', 1'', 1''', 1IV, 1V, ...) particularly along continuous curved paths (2) have a more or less clearly visible waviness corresponding to the number or the spacing of individual beads (1', 1'', 1''', 1IV, 1V, ...) in the course of the continuous curved paths (2), and that by selecting the spacing of individual beads (1', 1'', 1''' , 1IV, 1V, ...), particularly with clearances (10) remaining therebetween, the hydraulic characteristics of the impeller can be changed in addition to the influence exerted by the curved path (2).
EP91890094A 1990-05-09 1991-05-06 Method of manufacturing for impeller of centrifugal pump and this impeller Expired - Lifetime EP0456632B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT1040/90 1990-05-09
AT104090 1990-05-09

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EP0456632A1 EP0456632A1 (en) 1991-11-13
EP0456632B1 true EP0456632B1 (en) 1995-01-04

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2123409B1 (en) * 1996-01-23 1999-08-16 Bombas Electricas Sa CLOSED IMPELLER FOR CENTRIFUGAL PUMPS.

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4314284A (en) * 1978-11-07 1982-02-02 Nippon Electric Co., Ltd. Video head deflection apparatus for special motion reproduction by helical scan VTR

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DD40849A (en) *
DE800238C (en) * 1948-10-02 1950-10-17 Maschf Augsburg Nuernberg Ag Blower wheel
GB789674A (en) * 1954-12-03 1958-01-29 Plessey Co Ltd Improvements in or relating to impellers
US4134284A (en) * 1977-06-01 1979-01-16 Achim Nitschke Method and apparatus for the manufacture of hollow bodies
JPS5933035A (en) * 1982-08-16 1984-02-22 Hitachi Ltd Bead forming method

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4314284A (en) * 1978-11-07 1982-02-02 Nippon Electric Co., Ltd. Video head deflection apparatus for special motion reproduction by helical scan VTR

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EP0456632A1 (en) 1991-11-13

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