GB1562089A - Process for the production of silicon nitride mouldings - Google Patents
Process for the production of silicon nitride mouldings Download PDFInfo
- Publication number
- GB1562089A GB1562089A GB3395976A GB3395976A GB1562089A GB 1562089 A GB1562089 A GB 1562089A GB 3395976 A GB3395976 A GB 3395976A GB 3395976 A GB3395976 A GB 3395976A GB 1562089 A GB1562089 A GB 1562089A
- Authority
- GB
- United Kingdom
- Prior art keywords
- hot
- silicon nitride
- pressing
- hot pressing
- mould
- 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
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
- C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
- C04B35/593—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by pressure sintering
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Ceramic Products (AREA)
- Turbine Rotor Nozzle Sealing (AREA)
Description
(54) A PROCESS FOR THE PRODUCTION OF SILICON NITRIDE MOULDINGS
(71) We, ANNAWERK
KERAMISCHE BETRIEBE GmbH, a body corporate organised under the laws of
Germany of D-8633 Rd dental, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:
This invention relates to a process for the production of silicon nitride mouldings, optionally having a density gradient within the moulding, more especially for the production of turbine rotors, by means of a special compression-moulding process and a special mould cavity.
It is known that mouldings of silicon nitride and/or silicon oxynitride are distinguished by particularly high strength, hardness, wear resistance, impact strength and also by particularly high resistance to changes in temperature. One particular advantage of mouldings such as these is that these properties remain substantially intact at temperatures of up to 14000C.
Whereas the so-called reaction sintering process gives mouldings with a porosity of no less than about 20%, substantially pore-free and hence mechanically stronger mouldings can be produced by the so-called hot pressing technique, in which silicon nitride powder is compression-moulded in corresponding mould cavities in the presence of an oxidic pressing aid at temperatures of around 17500C.
It is also known (cf. German Offenlegungsschrift No. 2,134,072) that mould
ings of reaction-sintered silicon nitride can
be completely consolidated by hot pressing
at 1700"C in the presence of a suitable pres
sing aid. The mouldings obtained in this way
have, over their entire cross-section, a
uniform structure, density, hardness and
strength in uniform distribution comparable
with those of silicon nitride hot-pressed in known manner.
Mouldings produced by conventional processes can be used for a variety of different applications, for example as rotors in hot gas turbines. However, in cases where it is desired to produce for example rotors for hot gas turbines in the form of mouldings by conventional processes, difficulties arise insofar as rotors such as these, which rotate at extremely high speeds in the gas turbines, are subjected to considerable centrifugal forces in their structure. It is known that, in a rotor of the type in question, tensile stresses increase considerably towards the centre, whereas the thermal stressing and hence the requirements imposed on the creep strength of rotors of the type in question increase towards their periphery.
Accordingly, it was obvious to design rotors of this kind in such a way that the rotor vanes consist of reaction-sintered silicon nitride and the rotor wheel of hot-pressed silicon nitride in order in this way to combine the properties of favourable creep strength of reaction-sintered porous silicon nitride with the properties of extreme hardness, strength and resistance to oxidation of hotpressed Si3N4.
To this end, a wheel which has already been hot-pressed and a reaction-sintered vane assembly are fitted together, which can be done in different ways (German Offenlegungsschrift Nos. 2,353,551 and 2,154,480). Unfortunately, these known processes are attended by the disadvantage that they start from two different components which have to be fitted firmly together by way of a joint. As a sudden transition from one material to the other, this joint gives rise to such heavy internal stressing both during the manufacture of the rotors and when they are in service that the useful life of the rotors is unsatisfactory.
Accordingly, an object of the present invention is to provide a process for the pro duction of silicon nitride mouldings of which part is hot-pressed and part is reactionsintered, in which process, it is possible to obtain, where necessary, a continuous density transition between the reactionsintered and hot-pressed silicon nitride components.
Thus, the present invention provides a process for the production of a silicon nitride moulding of which part is hot-pressed and part is reaction-sintered, which comprises subjecting a reaction-sintered preliminary pressing, provided in a part to be hot-pressed with a hot pressing aid and the said part having dimensions greater than the desired final dimensions to allow for compaction, to hot-pressing in a mould of reaction-sintered silicon nitride which contains a hot-pressing aid and which is of complementary shape to the pressing and separated from it by an intermediate layer to prevent sintering together, the mould and the preliminary pressing being pressed between opposed plungers shaped to vary the compression path between the plungers, so that only the part of the preliminary pressing to be hot pressed is compacted.
By virtue of the process according to the invention, it is also possible in a single operation to produce turbine rotors of silicon nitride which have a continuous density transition between the hot-pressed rotor wheel and the reaction-sintered rotor vanes.
To this end, preforms are produced from a reaction-sintered nitride which represent, on the one hand, a preform for the rotor and, on the other hand, bodies with an exactly matching contour which serve as moulds and which, provided with a separation layer, are compressed in the hot press in such a way that the turbine blades are excluded from this compression and a continuous density transition between the reaction-sintered and hotpressed silicon nitride is formed between the vanes and the turbine rotor wheel. In order to be able to compress the reaction-sintered material in the hot press, the necessary hot pressing aids are either already present before nitriding or are introduced into the preliminary pressing by infiltration. The vanes do not contain any hot pressing aids and are therefore not hot pressed.
By using moulds of the same reactionsintered material which, during the hot pressing operation, is compressed in the same way as the pressing, it is possible to produce the most exact contours in order to keep the extremely high finishing costs as low as possible.
When, in conventional processes, the rotor wheel is pressed into a presintered vane assembly, it is extremely difficult and only possible by means of a second annular die assembly to keep the vane assembly so firm that it is not forced apart in the radial direction. In another embodiment of the process according to the invention, this is avoided by designing the mould in such a way that it projects beyond the pressing and externally surrounds it. During the pressing operation, this mould is uniformly compressed throughout with the result that its outer section is always able to absorb the lateral compressive forces which would otherwise interfere with the vane assembly.
In addition, it is possible, by suitably shaping the graphite plungers and the reactionsintered moulds, to ensure that the vane assembly is not co-compressed (i.e. the vane assembly is not compressed during the hot pressing process which compresses the rotor wheel).
It is also possible to ensure that a continuous, gradually increasing compression is obtained at the base by correspondingly adjusting the compression path in the reaction-sintered mould.
An embodiment of the process according to the invention is shown by way of example in the accompanying drawing.
The drawing shows the arrangement for the hot pressing of a gas turbine rotor in accordance with the invention, consisting of a hot-pressed rotor 1, a reaction-sintered vane assembly 6 and a transition zone 7 which connects the rotor and vane assembly.
The density of the silicon nitride in the transition zone decreases continuously from the dense, hot-pressed rotor to the porous, reaction-sintered vane assembly. The shape of the workpiece ultimately obtained is shown in chain lines, whilst the solid lines represent the condition of the workpiece before hot pressing.
The rotor 1 consists of reaction-sintered silicon nitride. In the axial direction of the hot pressing operation, it is oversize by an amount which can be calculated by the difference in porosity between the reactionsintered material and the hot-pressed material. The vane assembly 6 is already in its final form. The transition zone 7 linearly or even non-linearly connects the rotor wheel 1 and the vane assembly 6. The rotor 1 contains a hot pressing aid, whereas the vane assembly 6 has no such addition.
Two symmetrical annular moulds 2, which have exactly the profile of the pressing 1, are separated from this workpiece by a nonreacting separation layer, for example of boron nitride or graphite. These moulds 2 are also made of the same reaction-sintered material, provided with the hot pressing aid, and accordingly have the same oversize as the pressing 1. The two moulds 2 are larger in diameter than the pressing 1 and as a result are in contact with one another outside the pressing 1. In the vicinity of the vane assembly 6, the moulds 2 are flat, in other words they do not follow the complicated contour of the vanes, but instead corresponding nonsintering spacer members or a non-sintering powder are introduced between the vanes.
Since this zone 6 cannot be hot-pressed and cannot even be deformed by the hot pressing operation, the two moulds 2 are oversize in this zone arising out of the compression path of the mould material. In the transition zone 7, the configuration of the moulds corresponds to the required continuous transition of compression from the vane assembly 6 to the rotor wheel 1.
Two graphite plungers 3 are designed in accordance with the shape of the moulds 2.
The whole is surrounded by a graphite ring 4.
When, as in this case, the turbine wheel is intended to have a bore at its centre, a corresponding round graphite core 5 is introduced.
The hot pressing conditions correspond to those normally used for the production of compact mouldings of silicon nitride and are governed by the type and quantity of hot pressing aid. In general, the hot pressing operation is carried out at temperatures of from 1600 to 1800"C and at pressures of from 150 to 500 kp/cm2.
WHAT WE CLAIM IS:
1. A process for the production of a silicon nitride moulding of which part is hotpressed and part is reaction-sintered, which comprises subjecting a reaction-sintered preliminary pressing, provided in a part to be hot-pressed with a hot pressing aid and the said part having dimensions greater than the desired final dimensions to allow for compaction, to hot pressing in a mould of reactionsintered silicon nitride which contains a hot pressing aid and which is of complementary shape to the pressing and separated from it by an intermediate layer to prevent sintering together, the mould and the preliminary pressing being pressed between opposed plungers shaped to vary the compression path between the plungers, so that only the part of the preliminary pressing to be hot pressed is compacted.
2. A process as claimed in Claim 1, wherein the mould projects beyond the pressing and externally surrounds it.
3. A process as claimed in Claim 1 or 2, wherein a silicon nitride moulding having a density gradient within the moulding is obtained by appropriate configuration of the mould and by the predetermination of the compression path.
4. A process for the production of a silicon nitride moulding of which part is hotpressed and part is reaction-sintered substantially as described with particular reference to the accompanying drawing.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (4)
1. A process for the production of a silicon nitride moulding of which part is hotpressed and part is reaction-sintered, which comprises subjecting a reaction-sintered preliminary pressing, provided in a part to be hot-pressed with a hot pressing aid and the said part having dimensions greater than the desired final dimensions to allow for compaction, to hot pressing in a mould of reactionsintered silicon nitride which contains a hot pressing aid and which is of complementary shape to the pressing and separated from it by an intermediate layer to prevent sintering together, the mould and the preliminary pressing being pressed between opposed plungers shaped to vary the compression path between the plungers, so that only the part of the preliminary pressing to be hot pressed is compacted.
2. A process as claimed in Claim 1, wherein the mould projects beyond the pressing and externally surrounds it.
3. A process as claimed in Claim 1 or 2, wherein a silicon nitride moulding having a density gradient within the moulding is obtained by appropriate configuration of the mould and by the predetermination of the compression path.
4. A process for the production of a silicon nitride moulding of which part is hotpressed and part is reaction-sintered substantially as described with particular reference to the accompanying drawing.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE19752536676 DE2536676C3 (en) | 1975-08-18 | 1975-08-18 | Process for the production of silicon nitride molded bodies with a density gradient within the molded body |
Publications (1)
Publication Number | Publication Date |
---|---|
GB1562089A true GB1562089A (en) | 1980-03-05 |
Family
ID=5954212
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB3395976A Expired GB1562089A (en) | 1975-08-18 | 1976-08-16 | Process for the production of silicon nitride mouldings |
Country Status (4)
Country | Link |
---|---|
DE (1) | DE2536676C3 (en) |
FR (1) | FR2321458A1 (en) |
GB (1) | GB1562089A (en) |
IT (1) | IT1070228B (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2812019C2 (en) * | 1978-03-18 | 1982-06-03 | Kernforschungszentrum Karlsruhe Gmbh, 7500 Karlsruhe | Device for producing a preform from silicon nitride |
-
1975
- 1975-08-18 DE DE19752536676 patent/DE2536676C3/en not_active Expired
-
1976
- 1976-08-16 GB GB3395976A patent/GB1562089A/en not_active Expired
- 1976-08-16 FR FR7624923A patent/FR2321458A1/en active Granted
- 1976-08-17 IT IT6903076A patent/IT1070228B/en active
Also Published As
Publication number | Publication date |
---|---|
IT1070228B (en) | 1985-03-29 |
DE2536676A1 (en) | 1977-02-24 |
DE2536676B2 (en) | 1978-08-10 |
DE2536676C3 (en) | 1979-10-25 |
FR2321458B1 (en) | 1980-06-13 |
FR2321458A1 (en) | 1977-03-18 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PS | Patent sealed | ||
732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
PCNP | Patent ceased through non-payment of renewal fee |