EP0686229B1 - Procede de production d'une pointe abrasive sur une aube de turbine - Google Patents

Procede de production d'une pointe abrasive sur une aube de turbine Download PDF

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Publication number
EP0686229B1
EP0686229B1 EP94907629A EP94907629A EP0686229B1 EP 0686229 B1 EP0686229 B1 EP 0686229B1 EP 94907629 A EP94907629 A EP 94907629A EP 94907629 A EP94907629 A EP 94907629A EP 0686229 B1 EP0686229 B1 EP 0686229B1
Authority
EP
European Patent Office
Prior art keywords
coat
assembly
blades
deposition
infill
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
EP94907629A
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German (de)
English (en)
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EP0686229A1 (fr
Inventor
John Foster
Alan Taylor
Martin Patrick Chatterley
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.)
Praxair ST Technology Inc
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Praxair ST Technology Inc
Praxair Technology Inc
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Publication of EP0686229A1 publication Critical patent/EP0686229A1/fr
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
    • F01D11/08—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator
    • F01D11/12—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator using a rubstrip, e.g. erodible. deformable or resiliently-biased part

Definitions

  • This invention relates to blades for turbines and compressors and in particular relates to the production of blade tip seals.
  • the matrix comprises a major part of cobalt and minor parts of chromium, tantalum and alumina while the lining material of the shroud comprises a major part of cobalt with minor parts of nickel, chromium and aluminium and a small quantity of yttrium.
  • Various methods for producing such tips have been proposed.
  • detonation spray coating of the matrix is used.
  • the abrasive portion of the tip is then formed on the inner tip portion by electrodeposition of alternating layers of chromium and nickel about the abrasive particles.
  • the outer tip portion can then be aluminided to produce a matrix alloy of NiCrAl.
  • GB-A-2241506 a method of producing a gas turbine blade having an abrasive tip which comprises producing a binding coat on the tip of the blade body by electrodeposition, the binding coat comprising MCrAlY where M is one or more of iron, nickel and cobalt, anchoring to the binding coat coarse particles of an abrasive material by composite electrodeposition from a bath of plating solution having the abrasive particles suspended therein, and then plating an infill around the abrasive particles. It has been found that this method, all stages of which are of a metal plating nature and are therefore relatively inexpensive and readily controllable, produces a very effective abrasive blade tip.
  • compressor or turbine rotor blades are assembled on a compressor or rotor disc and abrasive tips are produced on the tips of the assembled blades by electrodeposition or by electroless deposition.
  • the present practise is for the blades to be assembled on the disc and for the blade tips to be machined to produce a properly balanced disc. The blades are then marked, disassembled from the disc, mounted on a jig, tipped, removed from the jig and then reassembled on the disc in the same order and positions that they previously occupied.
  • the process according to the invention is particularly suited to blade tipping using the methods described in GB-A-2241506 in which a binding coat is produced on the tip of each blade by electrodeposition, coarse particles of an abrasive material are anchored to be binding coat by composite electrodeposition of the particles and an anchoring coat and then plating an infill around the particles.
  • the binding coat may comprise MCrAlY where M is one or more of iron, nickel and cobalt.
  • the anchoring coat may be of cobalt or nickel or MCrAlY as defined above and the infill may also be MCrAlY and defined above.
  • the blades are tipped while assembled on a compressor or rotor disc, which term is intended to cover bosses, rings and similar blade mounting elements which terms are used for substantially the same structures.
  • a compressor or rotor disc which term is intended to cover bosses, rings and similar blade mounting elements which terms are used for substantially the same structures.
  • Various particles may be employed. Examples include zirconia, alumina and various nitrides, silicides and borides known from the abrasive art.
  • the preferred abrasive is cubic boron nitride, preferably having a particle size between 125 and 150 ⁇ m. It is possible for the infill, or at least the upper or outer portion thereof, to include abrasive particles of a size substantially smaller than the main abrasive particles, for example approximately 20 ⁇ m.
  • the MCrAlY of the binding coat, the anchoring layer where this is MCrAlY, and the infill where this is MCrAlY may have various compositions of which suitable examples are described in British Patent Specification GB-2167446B.
  • the electrodeposition may be effected by various forms of apparatus. However, suitable forms of apparatus are described in British Patent Specification Nos. GB-2182055A and European Patent Specification No. EP-0355051A. These describe apparatus which comprises an electroplating tank which is divided into two zones by a vertical wall extending from close to the bottom of the tank up to just beneath the surface of the solution in the bath.
  • the deposition of the infill is preferably accompanied by vibration of the assembly, preferably in a vertical direction. It is believed that such vibration ensures an even distribution of CrAlY particles, particularly in those regions which are shaded by the overhang of the abrasive particles and which regions might otherwise be depleted of particles.
  • the frequency of the vibration is preferably between 10 Hz and 1 kHz, the particularly preferred figure being about 50 Hz. A peak acceleration of up to 10 g is preferred.
  • each lower level phase is longer than each higher level phase; thus the lower level phases may be for between 30 seconds and 2 minutes duration with a peak acceleration of about 2 g and the higher level phases may be for about 5 seconds duration with a peak acceleration of about 10 g.
  • the process to be described is intended to form abasive tips on the blades of a as turbine rotor assembly 52 which is shown in Figure 5.
  • the assembly comprises five turbine discs 53 mounted on a hollow shaft assembly 54 forming part of the complete turbine.
  • the shaft assembly is mounted on a shaft 26 for the tipping process which will be described below.
  • Each of the discs 53 has mountings, for example fir-tree slots, in which the roots of the blades are mounted. It should be emphasised that in the preferred procedure the blades are mounted in the discs in their final positions and will not subsequently be disassembled from the discs.
  • the tipping process is carried out in the apparatus shown in Figures 1 to 3 of the drawings.
  • This comprises a vessel or container 1 having a parallelepiped shaped upper portion 2 and a downwardly tapering lower portion 3 in the form of an inverted pyramid which is skewed so that one side face 4 forms a continuation of one side face 5 of the upper portion.
  • the vessel 1 contains a partition 6 which lies in a vertical plane parallel to the side faces 4 and 5 of the vessel and makes contact at its side edges 7 and 8 with the adjacent vertical and sloping faces of the vessel.
  • the partition thus divides the vessel into a larger working zone 9 and a smaller return zone 11.
  • the partition 6 terminates at a horizontal edge 12 above the bottom of the vessel to afford an interconnection 13 between the working zone 9 and the return zone 11.
  • the partition 6 terminates at a horizontal edge 14 below the top edges of the vessel 1.
  • an air inlet 15 which is connected to an air pump (not shown).
  • a fixture 21 mounted in the working zone 9 is a fixture 21 to which the assembly to be coated is mounted, the fixture 21 being arranged to position the assembly within the vessel in a manner to be described in greater detail below.
  • Conductors are provided to apply a voltage to the assembly mounted on the fixture 21 relative to an anode which is suspended in the working zone.
  • the assembly is mounted on the fixture 21 which is positioned in the vessel as shown.
  • the vessel is filled to a level 17 above the top edge 14 of the partition 6 with a plating solution containing particles to be co-deposited. Air is admitted to the inlet 15 and this rises up and the return zone 11, raising solution and entrained particles. At the top of the return zone. The air escapes and the solution and particles flow over the broad crested weir formed by the top edge 14 of the partition and flow down past the assembly on the fixture 21. At the bottom of the working zone 9, the particles tend to settle and slide down the inclined sides of the vessel towards the interconnection 13 where they are again entrained in the solution and carried round again.
  • the fixture 21 on which the workpieces to be coated are mounted is shown in detail in Figures 4 and 5, in simplified form in Figures 2 and 3 and is omitted from Figure 1 for reasons of clarity.
  • the fixture 21 comprises a deck 22 which fits over the top of the vessel 1, a depending pillar 23 towards one end and a depending pillar 24 at the other end, the pillars having journals 25 in which the ends of the shaft 26 of the assembly are mounted.
  • the deck 22 supports an electric motor 31 which rotates the shaft 26 through a vertical shaft 32, a first bevel gear 33 and a second bevel gear 34 mounted on a spindle 35.
  • a vibrator 42 mounted on the deck 22 and is connected by lines 45 to the motor 31.
  • the controller 43 is designed so that the motor 31 is driven in one direction only so as to rotate the shaft 26 about a horizontal axis.
  • the assembly 52 is degreased in a vapour degreaser or a proprietary degreasing agent such as GENKLENE (Registered Trade Mark).
  • the assembly is then grit blasted as necessary to provide a key for the masking wax and the assembly is then inserted into a wax bath to mask all the surfaces of the discs and blades.
  • the assembly is then mounted in journals and rotated so that the tips of the blades move past a wiper which removes the masking wax from the tips of the blades.
  • the assembly is then given an anodic clean for five minutes at 6 to 8 volts in a cleaning solution consisting of sodium hydroxide/gluconate/thiocyanate and is then rinsed thoroughly in cold running water.
  • the exposed tips of the blades are then etched by submerging the assembly in a solution comprising approximately 300 gms/1 ferric chloride, 58 gms/1 hydrochloric acid and 1% hydrofluoric acid (60% w/w) for five minutes at room temperature and again rinsed thoroughly in cold running water.
  • the assembly is then placed in a nickel chloride bath to provide a strike which is given at 3.87 amps per square decimeter (36 amps per quare foot) for four minutes.
  • the strike bath comprises approximately 350 gms/1 nickel chloride and 33 gms/1 hydrochloric acid.
  • the assembly is then placed in the fixture shown in Figure 4 and the fixture is placed in the apparatus shown in Figures 1 to 3.
  • the bath contains a cobalt plating solution with 20 to 30 weight percent particles of CrAlY containing 67-68 parts by weight Cr, 29-31 parts by weight Al and 1.5 to 2.4 parts by weight Y with a size distribution both in the bath and in the as-deposited coating as given in the following table, the columns relating to the size band being the upper and lower limits of the cut measured in micrometers.
  • Plating is continued for a period of 4 hours at a current density of 0.075 amps per decimeter (10 amps per square foot) with the controller set to rotate the motor at such a speed as to rotate the assembly at 0.33 revolutions per minute. Air is admitted continuously to maintain circulation of the solution and suspended CrAlY particles.
  • This plating provides a binding coat of CoCrAlY on the tips of the blades to a thickness of between 25 and 50 ⁇ m. Deposition of CoCrAlY from the bath described will produce a layer having a composition which is approximately in weight percent: Al 10, Cr32, Y 0.5 and the balance Co.
  • the assembly is then rinsed over the tank with demineralised water and then removed from the region of the tank and rinsed in running water.
  • the holder is then placed in a Woods nickel bath or 1 volume percent sulphuric acid bath to reactivate the surfaces and the assembly is then placed in a second bath similar to the first bath except that in place of the CrAlY particles it contains particles of cubic boron nitride of 100/220 mesh i.e. approximately 125-150 ⁇ m.
  • no air is admitted through the inlet and plating is commenced at 2.7 amps per decimeter (25 amps per square foot) and then air is switched on for a period of 5 seconds.
  • the boron nitride particles go into circulation and cascade over the assembly.
  • Plating is then continued without the admissions of air for a period of approximately 40 minutes to secure the particles resting on the blade tips to the tips. It may be found that in some cases it is beneficial to have a further burst of 5 seconds of air after 20 minutes to ensure a uniform and maximum distribution of CBN particles over the blade tip surfaces.
  • the assembly is now removed from the CBN bath, is rinsed over the tank and is then rinsed in a static bath and finally rinsed thoroughly in running water.
  • the surfaces being coated are then reactivated in a Woods nickel or 1% sulphuric acid bath and the fixture is replaced in the CoCrAlY bath.
  • the motor is activated to rotate the assembly at 0.33 rpm and plating is continued for 7 hours at 1.075 amps per decimeter (10 amps per square foot) with continuous admission of air to maintain circulation of the solution and suspended CrAlY particles. This fills the spaces under and around the CBN particles with CoCrAly to a depth which, as can be seen in Figure 6, leaves the tips of the abrasive particles slightly proud of the surrounding CoCrAly.
  • the assembly may be rotated with a start-stop action.
  • the motor is controlled to produce a rotation of the assembly unidirectionally and at a speed of one rotation in 3 minutes with the rotation being intermittent with 10 second stop periods being interspersed with three second go periods.
  • the vibrator may be used.
  • the vibrator is arranged to give a vibration at a frequency of 50 Hz with alternating periods of high intensity and low intensity vibration, the high intensity periods having a duration of 5 seconds and a peak acceleration of 10 g and the low intensity periods having a duration of 75 seconds with a peak acceleration of 2 g.
  • the vibration and the rotation produce homogeneous infill and ensure that the CrAlY particles reach the areas shadowed by the CBN particles.
  • the fixture is removed and the assembly is rinsed over the tank with demineralised water and then rinsed thoroughly in running water.
  • the masking material is then removed and the assembly is taken out of the jig and degreased.
  • the assembly is then heat treated from between 1/2 and 1 hour at 1090 plus or minus 10°C in vacuum or in 50-100 millibar partial pressure argon and fast gas quenched.
  • the blades may then be aluminized by one of the well-known processes such as pack aluminizing.
  • One of the tips produced in the manner described is shown in section in Figure 6 and can be seen to comprise the body 80 of the blade, a binding coat 81 of MCrAlY of a thickness, in this example, of 25-50 ⁇ m, an anchoring coat 82 of MCrAlY of a thickness of 10-20 ⁇ m in which is anchored the bottom portions of the abrasive particles 83 of cubic boron nitride with a particle size of 125-150 ⁇ m, and an infill 84 of MCrAly with a thickness of 70-110 ⁇ m.
  • the anchoring coat in the specific process described is Co, not CoCrALY.
  • the anchoring coat may be of Co, Ni or MCrALY as defined above.
  • particles of pure cubic boron nitride it would be possible to use particles of this or another abrasive which are coated with a material which will protect them, for a time at least, from severe oxidation.
  • particles of this or another abrasive which are coated with a material which will protect them, for a time at least, from severe oxidation.
  • cubic boron nitride particles which had been given a substantially air-impermeable coating of aluminium oxide or an intermetallic such as nickel aluminide.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Grinding And Polishing Of Tertiary Curved Surfaces And Surfaces With Complex Shapes (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
  • Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)

Abstract

L'invention se rapporte à un procédé de production de pointes abrasives sur des aubes de rotor de turbine ou de compresseur par dépôt élctrolytique ou autocatalytique. Au moins une partie du processus de dépôt est effectuée sur les aubes assemblées sur un disque de rotor de turbine ou de compresseur. Les pointes sont par conséquent formées sur les aubes après avoir pris leurs positions de fonctionnement finales sur le disque, de sorte qu'un démontage ultérieur, qui aurait été nécessaire auparavant, est évité. L'ensemble est de préférence monté avec son axe rotatif horizontal, et le dépôt peut être accompagné de vibrations de l'ensemble dans le sens vertical.

Claims (10)

  1. Procédé de production d'extrémités abrasives sur des ailettes de rotor de turbine ou de compresseur par dépôt électrolytique ou sans courant, caractérisé en ce qu'au moins une partie du processus de dépôt est effectuée sur les ailettes lorsqu'elles sont assemblées en un montage d'ailettes sur un rotor (53) de compresseur ou de turbine.
  2. Procédé suivant la revendication 1, dans lequel le processus de dépôt comprend la production d'une couche liante (81) sur des extrémités de corps des ailettes par dépôt électrolytique ou sans courant, la couche liante comportant du MCrAlY, où M est un ou plusieurs des éléments suivants : fer, nickel et cobalt, l'ancrage à la couche liante au moyen d'une couche d'ancrage (82) de particules grossières (83) d'une matière abrasive par dépôt sans courant ou électrolytique mixte à partir d'un bain d'une solution de plaquage contenant en suspension les particules abrasives, et ensuite le plaquage d'une matière de remplissage (84) autour des particules abrasives.
  3. Procédé suivant la revendication 2, dans lequel la couche d'ancrage (82) est du cobalt ou du nickel.
  4. Procédé suivant la revendication 2, dans lequel la couche d'ancrage (82) est du MCrAlY, où M est du Ni ou du Co ou du Fe ou deux de ces métaux ou tous ceux-ci.
  5. Procédé suivant la revendication 3 ou 4, dans lequel l'épaisseur de la couche d'ancrage (82) est inférieure à 30 µm.
  6. Procédé suivant l'une quelconque des revendications 2 à 5, dans lequel la matière de remplissage (84) comporte du MCrAlY où M est du Ni ou du Co ou du Fe ou deux de ces métaux ou tous ceux-ci.
  7. Procédé suivant l'une quelconque des revendications 2 à 6, dans lequel le dépôt de la matière de remplissage (84) est suivi d'une étape de traitement thermique appliquée au montage pour homogénéiser la couche liante (81), la couche d'ancrage (82) et la matière de remplissage (84).
  8. Procédé suivant l'une quelconque des revendications 2 à 6, dans lequel le dépôt de la matière de remplissage (84) est suivi d'un traitement thermique d'une durée comprise entre ½ et 1 heure à 1090°C plus ou moins 10°C sous vide ou sous une pression partielle d'argon de 50-100 millibars et d'une trempe rapide par du gaz.
  9. Procédé suivant la revendication 7 ou 8, dans lequel le traitement thermique est suivi d'une étape d'aluminisation pour recouvrir d'aluminium les extrémités des ailettes.
  10. Procédé suivant l'une quelconque des revendications précédentes, dans lequel au moins une partie du dépôt est accompagnée par la mise en vibration du montage, de préférence dans une direction verticale.
EP94907629A 1993-02-25 1994-02-25 Procede de production d'une pointe abrasive sur une aube de turbine Expired - Lifetime EP0686229B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB939303853A GB9303853D0 (en) 1993-02-25 1993-02-25 Rotor blades
GB9303853 1993-02-25
PCT/GB1994/000374 WO1994019583A1 (fr) 1993-02-25 1994-02-25 Procede de production d'une pointe abrasive sur une aube de turbine

Publications (2)

Publication Number Publication Date
EP0686229A1 EP0686229A1 (fr) 1995-12-13
EP0686229B1 true EP0686229B1 (fr) 1997-03-26

Family

ID=10731055

Family Applications (1)

Application Number Title Priority Date Filing Date
EP94907629A Expired - Lifetime EP0686229B1 (fr) 1993-02-25 1994-02-25 Procede de production d'une pointe abrasive sur une aube de turbine

Country Status (10)

Country Link
EP (1) EP0686229B1 (fr)
JP (1) JPH08506872A (fr)
AU (1) AU684263B2 (fr)
CA (1) CA2153899A1 (fr)
DE (1) DE69402305T2 (fr)
ES (1) ES2099596T3 (fr)
GB (1) GB9303853D0 (fr)
RU (1) RU2118717C1 (fr)
SG (1) SG47413A1 (fr)
WO (1) WO1994019583A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102009007666A1 (de) 2009-02-05 2010-08-12 Mtu Aero Engines Gmbh Verfahren zur Herstellung einer verschleißfesten Beschichtung auf einem Bauteil
EP3121307A1 (fr) 2015-07-20 2017-01-25 MTU Aero Engines GmbH Blindage et procédé de réalisation d'un blindage

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB9326082D0 (en) * 1993-12-21 1994-02-23 Baj Coatings Ltd Rotor blades
US5935407A (en) * 1997-11-06 1999-08-10 Chromalloy Gas Turbine Corporation Method for producing abrasive tips for gas turbine blades
JP2002256808A (ja) * 2001-02-28 2002-09-11 Mitsubishi Heavy Ind Ltd 燃焼エンジン、ガスタービン及び研磨層
JP3801452B2 (ja) 2001-02-28 2006-07-26 三菱重工業株式会社 耐摩耗性コーティング及びその施工方法
US7063250B2 (en) 2001-05-31 2006-06-20 Mitsubishi Heavy Industries, Ltd. Coating forming method and coating forming material, and abrasive coating forming sheet
JP2002371803A (ja) * 2001-06-13 2002-12-26 Mitsubishi Heavy Ind Ltd 動翼用耐摩耗層の形成方法、耐摩耗層及びその再生方法
JP2003148103A (ja) * 2001-11-09 2003-05-21 Mitsubishi Heavy Ind Ltd タービンおよびその製造方法
DE10251902B4 (de) * 2002-11-07 2009-05-07 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Verfahren zum Beschichten eines Substrats und beschichteter Gegenstand
FR2915495B1 (fr) * 2007-04-30 2010-09-03 Snecma Procede de reparation d'une aube mobile de turbomachine
US9957629B2 (en) 2014-08-27 2018-05-01 Praxair S.T. Technology, Inc. Electroplated coatings

Family Cites Families (9)

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Publication number Priority date Publication date Assignee Title
US4279706A (en) * 1980-03-27 1981-07-21 Alsthom-Atlantique Method and assembly for depositing a metal on a cylindrical bore which passes through a central portion of a large part
FR2563540B1 (fr) * 1984-04-26 1989-05-05 Alsthom Atlantique Dispositif pour effectuer un depot metallique sur les parties frottantes d'un rotor de turbine
US4608128A (en) * 1984-07-23 1986-08-26 General Electric Company Method for applying abrasive particles to a surface
GB2167446B (en) * 1984-10-05 1988-05-05 Baj Ltd Electrode deposited composite coating
GB2182055B (en) * 1985-10-28 1989-10-18 Baj Ltd Improvements relating to electrodeposited coatings
GB8818069D0 (en) * 1988-07-29 1988-09-28 Baj Ltd Improvements relating to electrodeposited coatings
GB8914156D0 (en) * 1989-06-20 1989-08-09 Refurbished Turbine Components Apparatus for use in the repair of machines
US5074970A (en) * 1989-07-03 1991-12-24 Kostas Routsis Method for applying an abrasive layer to titanium alloy compressor airfoils
GB2241506A (en) * 1990-02-23 1991-09-04 Baj Ltd Method of producing a gas turbine blade having an abrasive tip by electrodepo- sition.

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102009007666A1 (de) 2009-02-05 2010-08-12 Mtu Aero Engines Gmbh Verfahren zur Herstellung einer verschleißfesten Beschichtung auf einem Bauteil
EP3121307A1 (fr) 2015-07-20 2017-01-25 MTU Aero Engines GmbH Blindage et procédé de réalisation d'un blindage
DE102015213555A1 (de) 2015-07-20 2017-03-09 MTU Aero Engines AG Dichtrippenpanzerung und Verfahren zur Herstellung derselben

Also Published As

Publication number Publication date
CA2153899A1 (fr) 1994-09-01
JPH08506872A (ja) 1996-07-23
EP0686229A1 (fr) 1995-12-13
RU2118717C1 (ru) 1998-09-10
SG47413A1 (en) 1998-04-17
ES2099596T3 (es) 1997-05-16
AU6112694A (en) 1994-09-14
GB9303853D0 (en) 1993-04-21
DE69402305D1 (de) 1997-04-30
AU684263B2 (en) 1997-12-11
WO1994019583A1 (fr) 1994-09-01
DE69402305T2 (de) 1997-10-16

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