DE2154479A1 - Method and device for the simultaneous production of several compacted silicon nitride molded bodies by means of hot pressing - Google Patents

Description

Dip !, ing. G. Koch _{? niiT 1071}

Dr.T.Kaibach ** ^{uniia / 1} KKieehen 2
K »Snjersir.8, Tel. 240275 2154479

The Secretary of State for Defense, London, Great Britain

Method and device for the simultaneous production of several deserved silicon nitride molded bodies by means of hot pressing

The invention relates generally to hot pressing of silicon nitride and, more particularly, to a method and apparatus for the production of several silicon nitride moldings in a pressing process.

According to the method according to the invention for the simultaneous production of several silicon nitride molded bodies in The hot-pressing process is carried out in such a way that a hollow shape is successively formed with several batches consisting of silicon nitride powder and a flux charged, which are separated from each other by mold separators are, the coming with the powder batches in contact surfaces of the mold and the mold separators with a Release agents were coated, and that the batches were then removed by the simultaneous application of heat and pressure converted into a molded silicon nitride body compacted by hot pressing

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Al "release agent can" in an aqueous suspension of magnesium oxide powder be used ο

The filling of the hollow mold with the individual batches can be carried out to the extent that the one of the molds formed by the farm dividing parts are subdivided into a number of smaller spaces for filling by means of the fora space lower part devices flux be · Wk standing batch loaded and then the mold space-TJnterteilvorrichtung removed.

The invention also relates to a device for Implementation of the method according to the invention. The according to the invention The device is characterized by a hollow shape, several mold separating parts and devices for applying heat to the powder batches Pressure.

According to preferred embodiments it can be provided that a heat supply device surrounding the hollow shape insulated induction heating coil is provided; and that sur pressurization a press with a water-cooled Press head is provided

The cavity mold and the mold separators can be made of graphite, and the mold can be made on a block a hit-resistant oxide such as cast aluminum oxide also stabilized zirconium oxide and cellular silicon nitride can be used.

The following are exemplary embodiments of the invention

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application described with reference to the drawing; in this show:

Pig 1 shows an embodiment in a schematic side view form of a device for hot pressing τοη silicon nitride according to the inventive method;

FIG. 2 shows a plan view of part of the device from FIG. 1 cur an illustration of the device for the mold;

FIG. 3 shows another embodiment which is varied compared to FIG. 2 the filling device for the press molds

FIG. K is a detailed partial view of the filling device according to FIG.

As can be seen from FIG. 1, the device rips open a hollow cylindrical foretell 10 made of graphite, which is uneven from an induction heat winding 12 in an insulating layer Ik and stands on a block 16 made of cast aluminum oxide. The induction heating coil is connected to an alternating current source 18; the circuit has a switch 20.

The interior of the molded part 10 is divided into a number of fora spaces by means of dividing parts in the form of graphite disks 22 divided. The play between the dividing parts dividing the mold and the molded part is between

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0.015 "and 0.020" In the drawing, the fora spaces formed are shown filled with charges 2k of silicon nitride powder and metal oxide in a ratio of 1 part magnesium oxide to 20 parts silicon nitride.

To mix the batches 2k , the silicon nitride powder is spread over a large area made of a flexible material such as a sheet of drawing paper and the magnesium oxide powder is sprinkled onto the silicon nitride by hand brushed with the Maachenzahi 150 · This process causes a thorough mixing of the silicon nitride and magnesium oxide while avoiding contamination, as would occur if the two powders were mixed in a ball mill.

The grain size of the magnesium oxide powder is smaller as 300 mesh; the grain size of the silicon nitride powder Is also smaller than wire mesh 300, although the silicon nitride powder is completely or partially also Can have grain sizes of less than 100 mesh without this having a significant loss in the quality of the End products would have ο

The following densities were achieved with different proportions of grain sizes smaller than 100 mesh:

- with powder that is 100 # grain size smaller than Mesh number 100 has - 86 ^ the theoretical density ι

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BATH ORIGINAL

- ait powder of 95 % grain size smaller than 100 mesh and 5 $> grain sizes smaller than 300 - 91 ^ of the theoretical density;

- with powder of 90 # grain size smaller than 100 mesh and 10 ^ grain size smaller than 300 mesh - 96 f> the theoretical dich fco;

The lowermost batch rests on a graphite disk 26, and the uppermost batch is correspondingly closed with a graphite disk 28. The head piece 30 of a, for example, hydraulically operated press rests against the disk 28 on the press head - it is cooled with water which enters the press head via a line 32 and exits it via a line 3k.

Zn the mold part 10, three thermocouples 36 ₁ 38 and k0 are at the bottom, in the middle and at the upper end and provided with corresponding Temperaturanzelgevorrichtungen 42, kh and 46. Another thermocouple 41 is provided in the middle of the graphite disk 26 and connected to a temperature display device k7 «

Fig. 2 illustrates a mold forming apparatus 48 for charging the individual mold spaces with the powder batches so that the powder is uniform and coherently distributed over each of the mold spaces. This mold cavity lower part device has a central one circular sheet metal strip 60, on which eight radially extending flat plates 52 are attached. That from the molded part 10 and between awei graphite disks 22

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The volume defined by the lower part device k8 arranged in the lower part is equal to the volume of powder charge required to achieve the desired thickness of an essentially completely compressed silicon nitride disc.

To introduce the powder batches, the lower part device is placed on the disc 26 ; then the spaces between adjacent plates 52 and the central space are filled with the powder; as soon as all of the powder has been filled in »the bottom device is pulled out and a graphite echo is placed on the batch. This process is repeated until the mold is filled with all of the batches leveled by placing a four-armed plate on the disc and an alcohol leveling scale on top of it. If the disk is not horizontal _9, it can be aligned until the leveling scale indicates that the disk is at right angles to the vertical axis of the molded part 10. By dividing each mold space into a number of smaller spaces, the powder batches can be loaded in such a way that the powder is evenly distributed without the formation of voids

In the figures 3 and k an Alfc © rna tiv & wt a guide of the mold space lower part device for loading an annular mold space is shown. As can be seen from FIG. 3, the annular shape is defined in an outer graphite ring 5k and a central graphite inducer 56. This mold space is created by a number of containers 58,,,, which are open at their end faces. 02, 64 and 66

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Divides into a number of trees; a 1st these containers at 58 in Fig. k shown in side view. In this special design, a highly compressed silicon nitride ring is to be produced, one surface of which is bevelled, so that the containers are all bevelled on their underside *

In operation, all containers are filled with powder, namely the middle containers 60, 62 and 6k are filled with powder and containers 62, 6k and 68 are removed. This process is repeated until the container 60 or one of the containers 58, 60, 6Z or 6k is adjacent to the container 66 , which can then be removed, whereupon the mold space is completely filled.

The essence of this process is that the loose powder is always held between two containers that are either filled with powder or empty may be, with one of the containers, for example the container 60, remains stationary, such that the loose Powder is always confined between two containers »

All in contact with the charging material coming surfaces of the disks 22, 28 and 26 are prior to contact with the charge powder with a Suspension of magnesium oxide in water coated in order to prevent the compacted silicon nitride from adhering to these components. The inner wall of the molded part 10 is coated with a suspension of boron in Wcsaer. These Suspension appears as a relatively thick coating

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BAD OftKSJNAL

applied from about 0.010 "thick · on the mold part 10, because" buyor was heated to "in · temperature in the range between 100 ⁰ C to 150 ⁰ C · The transfer, therefore, is dried, and dae boron nitride remains on the inner wall of the molding × 10 This coating is then rubbed off with a fine emery cloth in such a way that only a thin powder layer remains, which fills the pores in the graphite of the molded part 10 and at the same time acts as a high-temperature lubricant.

When all batches 2k are loaded , the press is lowered onto the stack of loading batches with only a very slight contact force, which is just sufficient to absorb any play and exclude excess air. f1 a temperature of 1350 ⁰ C indicating 1 in this tent point of the pressing pressure is increased to a half (British) ton per square inch · in proportion as the feed »batches are compressed, the press at a constant pressure of the decreasing height of the decks of must from follow the loading "batches and cutting discs, and the temperature must be carefully controlled, since d & c powder is a V-crumb insulator before compaction, but becomes a heat conductor as it approaches maximum compaction"

At about 1800 ⁰ C, the oxygen reacts in the magnesium oxide-releasing agent with the graphite to form Kohlenetoffdioxyd wherein dae magnesium evaporated, and adhesion of the compacted Siliziumni; ridi is prevented at the moldings.

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After the mold has cooled down, the graphite discs 22 and 28 removed and the dense silicon nitride disks be extracted from the molded part 10.

For optimal execution of the procedure you should preferably the following conditions are observed}

a) Xn the molded part 10 should koln or only a very small amount vertical temperature gradient exist} allows this can be achieved by reducing the thermal conduction paths leading away from the molded part 10 to a minimum, d. h «the surface area in contact with the molded part 10 of the alumina block 16 should be as small as possible.

b) The temperature gradient along the molded part 10 should be as small as possible; this can be achieved by that one carries out the separating parts 22 with the greatest possible thickness, such that they have a good heat conduction path Form · Experience has shown that aiii diameter / Dikke ratios of about 5 t 1 for the door parts 22 on the one hand sufficient strength and sufficient thermal conductivity properties guaranteed.

c) The molded part 10 should be constructed in such a way that, when the temperature in the center dex * graphite ^{disk 26 is 1350 °} C., the edge of the disk has a temperature of no more than 1700 ^° C. This is intended a safety margin between the actual temperature of the batch and the Sissoziationotesperatur dee Slliziuinnitridpulvers, to ensure the bie in the range of 1900 ⁰ C 2050 ° C.

P- Si .tantariapa ru ohe ι

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BATH

Claims (1)

Claims /1.J method for simultaneous production Hehrerer compressed Siliziumnitrld-Forsitfcarpör -alttöls ¥ anBpx eyeletting * ■ s, characterized in that _p isan a hollow form successively riding aaUreriiu s * i> s silicon nitride powder and a flux charged batches OEA ^ ahendenden , which are separated from each other dareh mold separating parts «ind, where the with de». The surfaces of the mold and the mold that came into contact were separated by a separating agent, and then the batches were transferred into a silicon nitride mold body compacted by hot molds by the same application of heat and pressure. 2. Process according to claim 1, characterized in that the individual batches each contain SiLisRiismnitrid-Powder and Magneaiumoxid in a ratio of 1 IaIl Magnosiumoxid to 20 parts of silicon nitride, i / o with ay.ts grain sizes of the two Beatandtaile smaller than Kaj ^ Iien number 300 are _e and that κ by SusaBnoK-iBJ. see the batches from the two components the 13ea i and ta lie on a leaf or a B'oli © from bisgfiaaieai t-isa-feerial and once through a Biob Jar Masehemssahl 50 and then through a sieve of the Mascheaaahl 150 3 · Method according to claim 1 or J: _p ßadnjfch gökönris! «Rejects that as a separating agent © ine -5» -. Ep-raai :: ii of oxide is denied in water » 209822/0857 BAD ORIÖHM. 4 »The method according to claim 1, characterized in that dafi the one formed by the mold separating parts spaces for filling using mold space lower part devices be subdivided into a number of smaller spaces that “At these smaller spaces pit the atus silicon nitride powder and the flux is charged with the existing batch and then removing the die subdivision assembly. 5. The method according to claim k, characterized in that the mold space lower plate device has a central part (50) which forms a closed figure, from which a plurality of radial arms (52, Fig. 2) arranged at equal intervals extend outwards. 6 · The method according to claim h using a mold space lowering device in the form of three or more containers open at their front strings »characterized in that each of the containers is filled with a powder charge, that the container at the end is left filled with the powder while the remaining container or containers taken out and arranged next to each other on one side of the end container, that the removed container is again charged with powder and again taken out together with the other dor Bnd container and with the exception of the last end of the converted container, and that this process up to repeated to completely fill the mold. 7. Apparatus for performing the method according to claim 1, characterized by ο a hollow ο shape (1O), 209822/0857 BATH by several mold parting parts (22) and by devices for applying heat (12) and pressure (30) to the powder batches (2k). 8. Apparatus according to claim 7 »characterized in that a Wttrmezufuhrvorrichtung the hollow shape (lO) surrounding insulated Induktionsheizvicklung (12) provided is" 9. Device according to claim 7 or 8, characterized in that that a press with a water-cooled press head is provided for pressurization. 10, device according to one or more of claims 7 to 9t daduroh characterized that the hollow shape (lO) and the mold parting parts (22, 26, 28) are made of graphite and the hollow form (10) stands on a block (16) made of cast aluminum oxide. 209822/0857 Blank page