JPS6112962B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the structure of a mold for hot-pressing ceramics such as alumina, and more particularly to an improved hot-pressing mold mainly made of graphite or the like for obtaining a sintered body having a polygonal cross section. A conventionally known hot press die for pressing a columnar molded body with a polygonal cross section is an integrated hot press die (die) having a cylindrical outer shape and a center hole for hot press having a polygonal cross section in the center of the cylinder. is used. Graphite is mainly used as the material. Graphite has a low resistance to tensile stress, and with conventional molds, when pressure is applied from above and below, stress is concentrated at the corners of the graphite die through the pressurized sintered material, resulting in easy breakage. There is. In order to prevent this damage, it may be possible to increase the outer diameter, but graphite is expensive and costly, and in any case, the corners are likely to be damaged, and the inner surface of the mold may be rubbed when taking out the sintered product. It also tends to wear out, so it may need to be replaced. Therefore, the thicker the wall, the higher the cost as a whole, and the cost of processing the inner surface of the polygon is also higher. In addition, as another conventional example, there is one that has a double structure of an inner mold and an outer mold, and the inner mold is divisible. However, this type of hot press mold is simply used to prevent damage to the sintered product during mold release, and no consideration is given to the aforementioned stress concentration at the corners. It was hot. In other words, in this type of conventional mold, even if there is a corner in the inner mold, the dividing portion is determined regardless of the location of the corner, since the purpose is only to prevent the above-mentioned damage. I can do it.
Therefore, during pressing, stress concentration occurs at the corners of the inner mold, which also has an adverse effect on the durability of the mold and the formability of the sintered product. The object of the present invention is to eliminate the drawbacks of the known hot press molds as described above. That is, this purpose consists of a cylindrical die arranged on the outer periphery and a sleeve forming the peripheral wall surface of the center hole, the sleeve having its outer surface in contact with the inner surface of the cylindrical die and its inner surface forming the polygonal center hole. This is solved by a hot press type, which is characterized in that it is a plane including one side of the polygon, and is divided into a number equal to the number of sides of the polygon at a position including the vertex of the polygon. The present invention will be explained in detail below. First, in the present invention, instead of the conventional integrated press mold, one hot press mold is formed by combining the cylindrical die 1 forming the outer periphery and the sleeves 3 and 3' forming the press mold surface, that is, the inner periphery. do. This sleeve is divided by partial sleeves 5 whose surfaces include each side of the central hole 4, which has a polygonal cross section. Most preferably, this method of division is such that each plane of the partial sleeve including one side of the polygonal center hole 4 is extended, and the inner surface of the cylindrical die 1 at the outer periphery is
It is divided by intersecting with (Figure 1). In addition, the sleeve can also be divided into partial sleeves by a plane including the center axis of the die cylinder and each vertex of the polygonal cross section (FIG. 3). A hot press die consisting of a combination of a sleeve divided into partial sleeves and an outer cylindrical die is
It has become clear that it is possible to prevent stress from concentrating on the polygonal center hole, that is, the portion corresponding to the corner of the sintered body to be formed. The sleeve is already divided at the corners, so stress cannot be concentrated on the sleeve itself at the corners, and the radial pressing force on the sleeve is due to the force of the cylindrical die that comes into contact with the outer periphery of the sleeve. Since the stress is received in a distributed manner over a large portion of the cylindrical die by the inner circumferential surface, stress concentration does not naturally occur in the cylindrical die. As a result, the pressure resistance and number of service life of the cylindrical die are increased, and the number of service life of the punch is also increased. During hot pressing, the graphite mold is heated to approximately 1800°C in a high frequency induction furnace, which increases the risk of breakage due to stress concentration, but according to the present invention, the durability of the hot press mold is greater than that of conventional methods. is greatly improved. Furthermore, when taking out the sintered body to be molded after hot pressing, in the present invention, after taking out the sintered body together with the sleeve, the sleeve can be separated and removed, and the sliding area between the sleeve mold surface and the sintered body can be removed. This has the advantage of reducing wear and damage caused by motion. In contrast, in the conventional method, it is necessary to directly pull out the sintered body from the die, and at this time, damage to the mold surface of the die, especially at the corners, is unavoidable. In the present invention, the sleeve needs to be replaced to the same extent as the die in the conventional method, but since the sleeve is simple and compact, the cost can be reduced considerably compared to replacing the entire die. . In use, it is preferable to apply a heat-resistant lubricant, such as hexagonal boron nitride, between the cylindrical die and the sleeve. Although the present invention is primarily directed to graphite hot press molds, it is also applicable to cases where known hot press mold materials such as silicon carbide, silicon nitride, alumina, aluminum nitride, etc. are used based on the same principle. Further, the cross-sectional shape of the center hole of the hot press mold of the present invention is not limited to the square of the embodiment, but may be any other polygon or polygon. Examples of the present invention will be described below. Example A cylindrical die with an outer diameter of 80 mmφ x inner diameter of 156 mmφ x height of 300 mm was manufactured using commercially available graphite OT5200 (extrusion molded product) as shown in Figure 1, and a center hole (100 mm x 100 mm) with a square cross section was made. The sleeve shown in FIGS. 1 and 2, which is formed within a cylindrical die, was fabricated from the same material. These were combined to form a hot press mold, and an integrated hot press mold (conventional method) having the same outer mold as the combined mold was manufactured from the same material as a control example. Using these two types of hot press molds, a room temperature pressure test was conducted using Al ₂ O ₃ powder as a pressurized sample.
Pressure was applied from both the top and bottom using a 100 mm x 100 mm punch, and the bursting pressure was measured. The results are shown in Table 1.

[Table] Further, using the two types of molds described above, hot press sintering was performed by heating and holding the molds at 1800° C. in a high frequency induction furnace and applying a pressure of 100 Kg/cm ² . On this occasion,
The Al ₂ O ₃ powder had a height of 200 mm when pressed before sintering, and a sintered body with a height of 70 mm after sintering was obtained. After sintering,
After cooling, the sample was taken out by extruding from the bottom to the top. However, for the product of the present invention, the sample was taken out together with the sleeve, and for the control example, only the sample was extruded and taken out. This operation was repeated and the durability of the die, sleeve and punch was investigated, and the results are shown in Table 2.

[Table] Note that hexagonal boron nitride was applied as a lubricant to the contact areas between the sleeve and die, the die and punch, and the sleeve and punch of the present invention.

[Brief explanation of drawings]

FIG. 1 is a plan view of one embodiment of the invention, FIG. 2 is an enlarged perspective view of a partial sleeve, and FIG. 3 is a plan view of another embodiment of the invention. 1... Cylindrical die, 3, 3'... Sleeve, 4
...Central hole.

Claims (1)

[Scope of Claims] 1. In a hot press mold having a cylindrical outer shape and a center hole for hot pressing with a polygonal cross section in the center of the cylinder, a cylindrical die 1 and a center hole 4 arranged on the outer periphery are used.
The sleeves 3 and 3' form a peripheral wall surface of the cylindrical die 1, and the outer surfaces of the sleeves 3 and 3' are in contact with the inner surface of the cylindrical die 1, and the inner surface thereof is a plane including one surface of the polygonal center hole 4, A hot press type characterized in that the polygon is divided into a number equal to the number of sides of the polygon at a position including the apex of the polygon. 2. The hot press mold according to claim 1, wherein each plane including one surface of the polygonal center hole of the sleeve 3 is extended to divide the sleeve. 3. The hot press mold according to claim 1, wherein the sleeve 3' is divided by a plane including a line connecting each vertex of the cross section of the polygonal center hole 4 and the cylindrical central axis. .