EP0072909B1 - Method for manufacturing a metal intermediate layer - Google Patents

Description

The invention relates to a method for producing an oxidation-resistant covering between inclined pressing surfaces of two supports, at least one of which is made of ceramic. A preferred application of the invention is the attachment of rotor blades between wings in the rotor (disk) of an axial turbine.

The connection of rotor blades to the rotor disk, if at least one of these components consisted of ceramic material, has previously led to problems, in particular if the blade root made of hot-pressed Si ₃ N _{4 has been} inserted into a metallic blade ring with dovetail grooves or into a grooved rotor disk made of other ceramics.

The types of said groove are known, i.e. the groove generally runs in its longitudinal direction either as a unit for a foot parallel to the rotor axis or obliquely as in the case of a helical gear or coaxially as an annular groove for all blades or feet of the blade ring. Because of the ceramic material, the foot is usually dovetail-shaped like a pine cone in a cut perpendicular to the longitudinal and insertion direction of the groove, in such a way that the generally flat supporting surfaces (bearing surfaces) of the foot and the groove, which in this cut have the same shape has like the foot and into which it is inserted, at an acute angle to the rotor radial foot median plane running in that direction. This flank angle is generally 30 ° to 75 °. As a result, the wings are pressed obliquely when the centrifugal forces of the rotor blade act.

In the foot area, the highest mechanical loads on the rotor blade occur during operation due to the centrifugal force of the rotor blade which causes the pressure on the wings, so that the load-bearing capacity of even high-strength ceramics, such as hot-pressed silicon nitride (Si ₃ N ₄ ), is largely exploited or not partially is sufficient.

A major difficulty is that the brittle, non-plastically deformable ceramic blade, i.e. her foot or its wings, does not lie or lie uniformly along the groove on their wings, which is due to inevitable manufacturing inaccuracies. This often leads to local stress increases, which reduces the breaking speed or permissible centrifugal load on the blade.

One way to reduce or eliminate this disadvantage is to insert a metal foil between the wings. This film compensates, by being plastically deformed, the production inaccuracies mentioned at least for the most part and ensures an at least reasonably uniform application of force, so that a higher breaking strength or the like and a longer service life can be achieved for the blade.

In addition, the film reduces the friction between the foot and the groove, so that the risk is reduced that the blade or its foot is jammed in the groove by temperature changes and experiences additional stress. To explain this, the following: The rotor disc becomes hot during operation, which causes the groove to widen and the blade to move radially outward, and when cooling, the blade, if the film is not provided, does not go back due to the friction and the groove width decreases and exerts additional tension on the shovel or its foot.

The following is a disadvantage of the film: although the film adapts due to plastic deformation, stress peaks in the ceramic base or additionally in the ceramic armature disc caused by manufacturing inaccuracies are only partially reduced. Furthermore, the assembly of the blade or its foot and the film is difficult if these parts are small. There is also a risk that the film will slip before or during operation of the turbomachine.

According to DE-A-2 834 222, a method for producing turbo rotors, in particular gas turbine wheels, is known, for which the blade attachment is carried out by sintering the blade feet into the wheel disk. Nickel-based alloys can serve as sintered materials. It is also proposed there that the blade feet are coated with a ductile material before being sintered into the wheel disk. The purpose of such a coating is to compensate for the very different thermal expansions between the blade / sintered material, so that there are no impermissibly large tensions at the interface between the blade and the sintered layer. Metal powder such as e.g. Niobium mentioned, which can be applied to the blade feet by metal spraying or in the form of aqueous solutions using a binder. An aqueous solution promotes oxidation.

A metal spraying process must inevitably be carried out before the parts are assembled with the press surfaces, because after the assembly these surfaces can no longer be reached from the outside with a spray gun.

A turbine rotor is known from DE-A-2 250 563, in which a gap between the rotor and the base of a guide vane is filled by soft solder material. A soldering material must be brought to a much higher soldering or brazing temperature than is necessary for the chemical application of a layer. As a result, the gap between the press surfaces, which is small and uniform, widens locally should.

A compressor wheel arrangement is known from US-A-3,910,719, in which the gaps between the walls of the wheel disk slots and the feet of rotor blades are filled with an adhesive composition. This adhesive has a hardener, after hardening of which the blades should be firmly anchored in the impeller at low temperatures. Such an adhesive remaining in the gap between the pressing surfaces can only be used to a limited extent at compressive strengths and operating temperatures which are substantially below those of turbines and in which case metal oxidation need not be feared. A hardener or binder is necessary there. Sintered connections, soldered and adhesive connections are fixed connections. Fixed connections are not applicable everywhere.

The object of the invention is to provide a method for producing an oxidation-resistant covering between inclined pressing surfaces on two supports to be connected, of which at least one consists of a ceramic material, which can be carried out easily and safely even after assembly and where the metal powder is applied in a suspension that does not have an oxidizing effect.

• a) die Träger der Preßflächen zusammengebaut werden;
• b) ein Metallpulver in Suspension-in einer organischen Flüssigkeit auf den Preßflächen durch Kapilarkräfte im schmalen Zwischenraum zwischen den Preßflächen aufgetragen wird;
• c) die Suspension zwischen den Preßflächen getrocknet und das organische Mittel ausgetrieben wird.

The solution to this problem is characterized in that

• a) the supports of the pressing surfaces are assembled;
• b) a metal powder in suspension - in an organic liquid - is applied to the pressing surfaces by capillary forces in the narrow space between the pressing surfaces;
• c) the suspension between the pressing surfaces is dried and the organic agent is driven off.

The connection made according to the invention is flexible. As a result, stress peaks are reduced better because such a covering or these coverings can be easily deformed by pressing on the pressing surfaces, or are better deformable than a film. Furthermore, the covering or the coverings can be produced with little effort and the covering adheres firmly to the press surface, or the coverings adhere firmly to both press surfaces.

To produce the covering, the metal powder suspension mentioned in the invention is applied to the pressing surface or surfaces, where it dries up. When the dried suspension is subsequently heated, the non-metallic constituents of the suspension can escape, and the coating then remains. It consists of the metal of the metal powder. The metal powder granules have an average grain size of in particular 0.1 J.Lm to 50 J.Lm.

The invention is generally applied when the pressing or joining point is exposed to high thermal stress in addition to the pressing surface pressure. The invention can also be advantageously used when the press or joint is under pressure of a fluid; the press or joint is generally better sealed with the covering or coverings according to the invention than with the film.

The covering produced according to the invention is particularly hooked on pressing surfaces, engaging behind or the like, such as e.g. in the case of the aforementioned blade attachments, where the pressing by pulling then occurs, in the case of these blade attachments by the centrifugal force. But it can also e.g. can be used against each other without snagging.

For suspension of the metal powder in an organic liquid, a lacquer, a lacquer-like or similar liquid, preferably zapon or nitro lacquer or a resin dissolved in alcohol, such as e.g. Colophomium. According to a further feature of the invention, the metal powder is selected from the group consisting of platinum, nickel, chromium, titanium, tantalum, copper, magnesium, zinc or a mixture of at least two of these metals. Which metal or which metal mixture is chosen depends on the operating temperature of the press or joint to be provided with the covering. Furthermore, the suspension used is usually thin. Furthermore, the suspension can be applied easily. It dries e.g. in the manner of a lacquer in air. The non-metallic component of the suspension must not have an oxidizing effect on the metal powder when heated. A reducing effect, e.g. at the rosin. The non-metallic components can be driven off completely by heating.

The production according to the invention of an oxidation-resistant covering with the aid of an easily applicable metal powder suspension has the advantage that it is still possible to apply it to the pressing surfaces after the parts have been assembled. This is due to the good flow properties of the suspension, which also dries easily and is easy to burn out. Furthermore, it is not oxidizing, which is particularly useful for metal powders oxidizing in air.

Complete filling of the narrow space between the pressing surfaces is made easier with the help of capillary forces. The surface is deposited evenly and adheres well to the press surfaces. Manufacturing accuracy is largely compensated for even without plastic deformation of the covering. When using metal powders in air oxidizing metals such as Nickel or titanium can be applied in a reducing atmosphere.

• Fig. 1 zeigt dies in einem zur Nutlängs- und Fußeinschiebrichtung senkrechten Schnitt 1-1, und
• Fig. 2 zeigt dies in einem zum Schnitt I-I und zur läuferradialen Fuß-Mittelebene senkrechten Ebene 11-11.

In the drawing is an embodiment of the invention with an axial blade attachment to one Rotor disc of an axial gas turbine shown.

• Fig. 1 shows this in a section perpendicular to the groove longitudinal and foot insertion direction 1-1, and
• FIG. 2 shows this in a plane 11-11 perpendicular to section II and to the rotor radial center plane of the foot.

The direction mentioned is designated by 10, the middle plane mentioned by 11. The direction 10 runs - see FIG. 2 - obliquely to the circumferential direction - arrow 17 - of the rotor disk 13. Essentially, the ceramic base 15 of the ceramic axial vane and the associated groove 18 of the metallic rotor disk 13 together with two exaggeratedly thick for better visibility, metallic intermediate linings 14 said axial blade attachment. At the foot 15 there is a broken-off, waist-like transition part 16 and, which is not shown, a blade platform and the blade blade adjoining this; the bucket is made in one piece from all these parts. The base 15 and the groove 18 on each side of the central plane 11 and in mirror image to it have two mutually corresponding, plane, mutually parallel wings 19 and 20, which run to the central plane 11 at a flank angle a of approximately 40 ° (see FIG. 1) and between which the intermediate covering 14 is located. Each of the two wing pairs 19, 20 is pressed obliquely because of the flank angle a by the radially acting centrifugal force - arrow 24. The wings 19 and 20 extend (see FIG. 2) from one end face 21 to the other end face 22 of the rotor disk 13. The intermediate layer 14 extends over this entire length of the wing faces 19 and 20 (FIG. 2) and the entire width of the wing 19 and practically the entire width of the wing 20 (Fig. 1). The wing 19 is somewhat narrower than the wing 20 and is located at full load of the axial gas turbine as shown in Fig. 1 on both sides at a small distance from the longitudinal edges of the wings 20. - To produce the metallic intermediate covering 14, a metal powder suspension with a paint as non-metallic constituent is brushed on the outside of the space between the wings 19 and 20 on the long side 23 thereof, and the capillary forces completely fill this space with this suspension. The fill is air dried, i.e. the solvent of the paint evaporates. The dried fill is then heated by the fluid flowing into the bladed flow space, so that the solid portion of the lacquer escapes. The intermediate covering 14 adheres firmly to the wings 19 and 20.

Claims (6)

1. Method of producing an oxidation-resistant coating in the region of oblique pressing surfaces (19, 20) on two carriers (13, 15) which are to be connected and of which at least one consists of ceramic material, characterised in that

a) the carriers (13, 15) of the pressing surfaces (19, 20) are assembled together;

b) a powdered metal in suspension in an organic fluid is applied to the pressing surfaces (19,20) by capillary forces in the narrow intermediate space between the pressing surfaces;

c) the suspension between the pressing surfaces (19, 20) is dried and the organic medium is forced out.

2. Method according to Claim 1, characterised in that the non-metallic constituent of the suspension is a lacquer or a lacquer-like or similar fluid, preferably zapon or cellulos nitrate lacquer, or is a resin such as colophony or pine resin dissolved in alcohol.

3. Method according to one of Claims 1 or 2, characterised in that in the case of metals used in the powdered metal and which do not oxidise on contact with air, drying and additional heating takes place in air, while in the case of metals which are used in the powdered metal and which do oxidise on contact with air, crying is carried out in air or in a barrier gas, an additional heating being carried out in a barrier gas.

4. Method according to one of the preceding Claims, characterised in that in the case of the metals of the powdered metal oxidising on contact with air, production of an oxidation-resistant coating (14) involves heating the applied suspension in a reducing barrier gas atmosphere to about 60 up to about 95% of the fusion temperature of the metal in the coating (14).

5. Method according to Claim 1, characterised in that the powdered metal of one or a plurality of metals of the group platinum, nickel, chromium, titanium, tantalum, copper, magnesium, zinc is contained in the lacquer or lacquer-like fluid in a medium granulation of about 0. 1 µ m up to 50 µm.

6. Method according to one of the preceding Claims, characterised by the combination of two carriers (13, 15) with their pressing surfaces (19, 20), of which one surface (20) forms the oblique face on a recess in the rotor disc of a fluid-flow or turbo engine and the other surface (19) forms the oblique surface on a root (15) of a blade which is fixed in the recess.

Images