JP3007488B2 - Mold for cold isostatic pressing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for cold isostatic pressing, which is preferably used for forming hollow products.

[0002]

2. Description of the Related Art As a method of forming ceramics and metal powder by cold isostatic pressing, particularly a method of forming a hollow product,
There is known a method in which a powder is placed in a rubber mold in which a metal core is set, hermetically sealed, cold isostatically pressed, and the obtained molded product is processed into a required shape. FIG. 5 is a view showing a configuration of an example of a mold for cold isostatic pressing used in the above-mentioned conventional molding method.

In FIG. 5, a conventional cold isostatic press molding die 21 has a mounting portion 22a for attaching a rubber stopper provided at the tip end.
, Top 22b, bottom 22c, top 22b and bottom 2
2c, a conical core 22 having an upper portion 22b lightly chamfered, and the core 22 provided inside the lower portion 23a and a bottom 22c of the core 22 engaged. For example, a disk having a thickness of, for example, 18 mm and having a rubber outer cylinder 23 having a thickness of 5 mm and a mounting hole 24 a for a mounting portion 22 a at a center portion, and closing an upper portion 22 b of the core bar 22 and an upper portion 23 b of the rubber outer cylinder 23. And a rubber stopper 24 in a shape of a circle.

[0004] In order to perform cold isostatic press molding using the molding die 21 having the above-described configuration, first, the rubber stopper 24 of the molding die 21 is removed, and then the core metal 22 and the rubber outer cylinder 23 are connected to each other. The space is filled with a molding powder by a vibrator until a constant weight reaches a baseline, and the space is closed with a rubber stopper 24 and sealed. Next, the molding die 21 filled with the molding powder is charged under hydrostatic pressure, press-molded at a predetermined hydrostatic pressure, and after removing the hydrostatic pressure, a molded product is taken out of the molding die 21 to obtain a molded body. Was getting.

[0005]

Means for Solving the Problems The conventional molding die 2 described above.
In the molded article obtained by using No. 1, a shear layer 31 causing firing breakage was sometimes generated at the upper part of the molded article during cold isostatic press molding. Therefore, when the formed body is finished and fired, there is a problem that cracks are generated in the upper part of the formed body as shown in FIG. For this reason, as shown in FIG. 6, a molded product larger than a product in which a portion where a sintering crack occurs due to the shear layer 31 is formed, and the portion is cut and removed in advance during the finishing process and baked. There was also a problem that the amount of powder used increased.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a mold for a cold isostatic press capable of obtaining a compact with a minimum cutting allowance even if the compact is obtained by a cold isostatic press.

[0007]

According to the present invention, a mold for cold isostatic pressing is provided with a core having a bottom portion, an upper portion, and a tapered portion therebetween, in a rubber outer cylinder. A mold for cold isostatic pressing having a structure in which a bottom portion and a lower portion of the rubber outer cylinder are engaged, and an upper portion of the core metal and an upper portion of the rubber outer cylinder are covered with a rubber stopper. The portion in contact with the molding powder at the boundary between the upper portion and the tapered portion has an R shape.

[0008]

In the above-described structure, the portion in contact with the molding powder at the boundary between the upper portion of the metal core and the tapered portion, that is, the portion serving as the starting point where a shear layer is generated, is formed into an R shape. The tightening of time can be homogenized,
The generation of the shear layer can be dispersed. As a result, it is possible to prevent the occurrence of cracks due to the presence of the shear layer after firing, to reduce the number of cut portions in the finishing process, and to eliminate waste of expensive raw materials to be used.

When the thickness of the rubber plug is tapered so as to gradually decrease from the center to the outer periphery, the deformation of the rubber plug during cold isostatic pressing at a high pressure is reduced by the powder. The larger the outer peripheral portion, the easier it is to bend, and the upper surface of the pressed body after pressing can be made substantially flat, so that the cutting allowance can be further reduced, which is preferable. The “tapered shape” in the present invention refers to a so-called tapered shape in which the thickness of the rubber plug always decreases by a constant amount from the central portion to the outer peripheral portion. The concept includes a shape that does not change and gradually becomes thinner from the center toward the outer periphery.

[0010] Further, in the case where a gradient is provided at the bottom of the cored bar, that is, a so-called sloping gradient, the slip of the raw material at the time of pressurization is improved, and chipping due to springback from the mold of the molded body when the pressurized pressure is released is eliminated. It is preferable because it can be performed.
Further, when a rib is provided on the outer peripheral portion of the rubber plug and the upper portion of the rubber outer cylinder is engaged with the rib, the rubber outer cylinder does not come off from the rubber plug even during cold isostatic pressing at high pressure. At the same time, the thickness of the entire rubber stopper can be reduced, which is preferable.

[0011]

FIG. 1 is a view showing the structure of an example of a mold for cold isostatic pressing according to the present invention. In this example, a molding die for molding a hollow cylindrical product made of, for example, zirconia, for example, a sleeve used for an NC lathe or the like is shown. In FIG. 1, a mold 1 for cold isostatic pressing according to the present invention includes a mounting portion 2a for attaching a rubber stopper provided at a tip portion, an upper portion 2b, a bottom portion 2c, and a taper between the upper portion 2b and the bottom portion 2c. 2d, a rubber outer cylinder 3 in which the core 2 is provided, and a lower portion 3a of the core 2 is engaged with a bottom 2c of the core 2, and a mounting portion 2a for the core 2 in the center. Mounting hole 4a
And a disc-shaped rubber stopper 4 for closing the upper part 2b of the cored bar 2 and the upper part 3b of the rubber outer cylinder 3, and these configurations are not different from the conventional mold.

A feature of the mold 1 for cold isostatic pressing of the present invention is that a portion of the boundary between the upper part 2b of the cored bar 2 and the tapered portion 2d which comes into contact with the molding powder has an R shape. The curvature of the R shape is 3 to 8 as is clear from the examples described later.
mm is preferable. In this way, by forming the boundary portion between the upper portion 2b of the cored bar 2 and the tapered portion 2d into an R shape, the generation of the shear layer generated at this portion is eliminated by dispersing the concentration of the shear stress. Therefore, a portion to be cut by the finishing process can be eliminated. Note that the R shape here is not necessarily limited to a shape having a complete curvature, but refers to a concept showing a general curvature of an R portion.

In the embodiment shown in FIG. 1, the thickness of the rubber plug 4 is tapered so that the thickness gradually decreases from the center toward the outer periphery. Has a tapered shape whose thickness hardly changes. As a result, the deformation of the rubber plug 4 can be more easily deflected toward the outer peripheral portion with more powder, the upper surface of the molded body after pressing can be made substantially flat, and the cutting allowance at the time of finishing processing can be further reduced. Is preferred because Further, it is more preferable that the R shape of the central portion of the rubber plug 4 is larger than the R shape of the cored bar 2 in that cracks due to a shear layer are prevented in this portion at the time of hydrostatic pressure pressurization.

Further, in the embodiment shown in FIG. 1, the surface of the bottom 2c of the metal core 2, which is in contact with the raw material powder, is provided with a gradient in which the height is reduced toward the outer peripheral portion, that is, a so-called sloping gradient. Chipping due to springback when removing from the mold can be eliminated. Further, since the rib 4b is provided on the outer peripheral portion of the rubber stopper 4 and the upper part 3a of the rubber outer cylinder 3 is engaged with the rib 4b, the rubber outer cylinder 3 is separated from the rubber stopper 4 during molding by cold isostatic pressing. As a result, the rubber stopper 4 can be made thinner.

FIG. 2 is a diagram showing the configuration of another example of a mold for cold isostatic pressing according to the present invention. In this example, a molding sleeve for molding a cylindrical sleeve having a uniform inner diameter and a two-step outer shape, or a shape that requires cutting the outer diameter of the cylindrical sleeve is shown. In the example shown in FIG. 2, the same members as those of the molding die shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The difference between the example shown in FIG. 2 and the example shown in FIG.
This is the shape of the rubber outer cylinder 3 for obtaining a product with a tapered shape of the rubber stopper 4 and a two-step outer diameter. That is, unlike the example shown in FIG. 1, the tapered shape of the rubber plug 4 shown in FIG. 2 has a so-called tapered shape in which the thickness of the rubber plug 4 always decreases by a constant amount from the center to the outer periphery. Is a point. When producing a two-stage sleeve, it is preferable to use such a tapered rubber stopper 4.

Hereinafter, an actual example will be described. Example 1 In order to examine the influence of the R shape of the boundary between the upper portion 2b and the tapered portion 2d in the present invention, the presence or absence of a firing crack was examined by changing the curvature R variously. First, 150 parts by weight of water and 1 part by weight of an organic binder were added to 100 parts by weight of partially stabilized zirconia powder having an average particle size of 0.4 μm,
The mixture obtained was mixed and crushed with an attritor for about 1 hour, and passed through a 20 μm comb.
A partially stabilized zirconia powder granulated to μm was prepared as a molding powder.

Next, FIG. 3 shows the detailed dimensions of the rubber plug 4 and the tip shown in FIG. 1 with an R as shown in Table 1 below at the boundary between the upper portion 2b and the tapered portion 2d. A conical core 2 having a diameter of 54 mm including the upper part 2b and a diameter D
1, the maximum thickness is t1, the minimum thickness is t2, and the ratio of D1 / t1 to t1 / t2 as shown in Table 1 is given. Using a molding die 1 composed of a rubber stopper 4 and a rubber outer cylinder 3 having a thickness of a rib 4b in contact with an upper portion 3b of 3mm and a rubber outer cylinder 3, the molding powder made of zirconia prepared is cold-statically cooled. It was press-molded under water pressure and fired, and the presence or absence of cracks during firing was examined. Table 1 shows the results.

[0018]

[Table 1]

From the results shown in Table 1, the core metal 2 of R6 and D1 are 1
A molded article obtained by using a molding die 1 using a rubber stopper 4 having a diameter of 46 mm and D1 / t1 = 7 and t1 / t2 = 2.1 does not generate a sintering crack, whereas a rubber cracked under the condition of R2. Even if the shape of the plug 4 was changed, it was not possible to eliminate the occurrence of the firing crack, and it was found that R3 or more was preferable. In this example, the maximum value of the t1 dimension is D1 / t1 = 6.
As mentioned above, it turned out that it is preferable that it is preferably 7 or more. However, the amount of the molding powder used increased. further,
In this example, the value of t1 / t2 is 1.6 to 2.1, but it has been found that the value t / t2 can be sufficiently used up to 2.6. However, when it was set to 2.6, the rubber stopper 4 sometimes came off during cold isostatic pressing.

Example 2 A partially stabilized zirconia powder was prepared as a molding powder in the same manner as in Example 1, and the upper portion 2b, the tapered portion 2d, and the shape shown in FIG. Upper part 2 including a tip part with an R as shown in Table 2 below at the boundary of
b, a conical core 2 having a diameter of 26 mm, a diameter D2,
The maximum thickness is t3, the minimum thickness is t4, and the ratio of D2 / t3 to t3 / t4 as shown in Table 2 is a tapered shape that gradually becomes thinner from the core metal mounting portion to the outer peripheral portion. Rib 4
Using a molding die 1 comprising a rubber stopper 4 having a thickness b of 3 mm and a rubber outer cylinder 3 having a two-step outer diameter, the presence or absence of cracks during firing was examined in the same manner as in Example 1. Table 2 shows the results.

[0021]

[Table 2]

From the results shown in Table 2, the core metal 2 and D2 of R6 are 9
0 mm, D2 / t3 = 5, t3 / t4 = 1.5-2.
The molded article obtained by using the molding die 1 using the rubber plug 4 of No. 3 does not generate a fired crack, whereas the R2 condition eliminates the occurrence of a fired crack even if the shape of the rubber plug 4 is changed. It was found that R3 or more was preferable. In this example, the maximum value of the dimension of t3 is D2 /
It turned out that it is preferable that t3 = 4 or more. However, the amount of the molding powder used increased. Furthermore, in this example, it turned out that the optimal value of t3 / t4 is preferably 1.5 to 2.3. However, when it was set to 2.3, the rubber stopper 4 sometimes came off during cold isostatic pressing.

[0023]

As is apparent from the above description, according to the present invention, the portion of the boundary between the upper portion of the cored bar and the tapered portion that comes into contact with the molding powder, that is, the portion that becomes the starting point of the generation of the shear layer. Has an R-shape, so that the tightening during cold isostatic press molding can be homogenized and the generation of a shear layer can be dispersed. As a result, it is possible to prevent the occurrence of cracks due to the presence of the shear layer after firing, to reduce the number of cut portions in the finishing process, and to eliminate waste of expensive raw materials to be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of a mold for cold isostatic pressing according to the present invention.

FIG. 2 is a view showing the configuration of another example of a mold for cold isostatic pressing according to the present invention.

FIG. 3 is a view for explaining dimensions in Example 1 of the molding die shown in FIG. 1;

FIG. 4 is a view for explaining dimensions in Example 2 of the molding die shown in FIG. 2;

FIG. 5 is a view showing a configuration of an example of a conventional mold for cold isostatic pressing.

FIG. 6 is a view for explaining a drawback of a conventional mold for cold isostatic pressing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold for cold isostatic pressing 2 Core metal 3 Rubber outer cylinder 4 Rubber stopper

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-126505 (JP, A) JP-A-3-293101 (JP, A) JP-A-63-319108 (JP, A) 101358 (JP, U) JP 46-1397 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28B 3/00 102 B28B 7/18

Claims (4)

(57) [Claims] 1. A rubber core having a bottom portion, an upper portion, and a tapered portion between them is provided in a rubber outer cylinder, and a bottom portion of the core metal and a lower portion of the rubber outer cylinder are engaged with each other, and In a mold for cold isostatic pressing having a structure in which the upper part of the gold and the upper part of the rubber outer cylinder are covered with a rubber stopper, a portion that comes into contact with the molding powder at the boundary between the upper part of the core metal and the tapered part is described. A mold for cold isostatic pressing characterized by having an R shape. 2. The mold for cold isostatic pressing according to claim 1, wherein the thickness of the rubber stopper is tapered so that the thickness gradually decreases from the center to the outer periphery. 3. The method according to claim 1, wherein the bottom of the metal core is sloped.
The mold for cold isostatic pressing as described. 4. The mold for cold isostatic pressing according to claim 1, wherein a rib is provided on an outer peripheral portion of said rubber stopper, and an upper portion of said rubber outer cylinder is engaged with said rib.