JPH07247172A - Material for electrically conductive punch and spacer for pressure compacting - Google Patents

Abstract

PURPOSE:To obtain an electrically conductive punch and spacer material for the pressure compacting and sintering of ceramic or metallic powder, with high mechanical strength, durable to high compacting pressure, capable of reducing electric power consumption when sintered by current injection, thus enabling rapid heating thereof. CONSTITUTION:This material comprises 5-40wt.% of carbon and the rest of one or more kinds selected from carbides and borides of groups 4A, 5A and 6A elements, respectively, and inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for putting ceramics or metal powder into a die and press-molding and firing it.
The present invention relates to materials for punches and spacers that are pressure jigs.

[0002]

2. Description of the Related Art First, a method of pressure molding and firing of ceramics or metal powders which is generally used at present will be described. When the ceramics or metal powder is pressure-molded and fired, the powder 2 is loaded in the die 1 having the shape shown in FIG. Since the surface of the punch 3 in contact with the powder 2 is severely damaged by high temperature or chemical reaction with the powder, a spacer 5 is used as a consumable part between the punch and the powder.
Is often inserted. In addition, a plurality of fired bodies can be obtained by firing once by further adding spacers and loading powder between the spacers. In addition, after the powder is molded into the required shape in advance, it is embedded in another highly fluid powder (graphite, etc.) in the die and pressed and heated to apply pseudo isotropic firing. There is also a way to do.

The dies, punches and spacers are required to withstand high heat and are therefore made of high strength carbon. In many cases, the inside of the die and the surfaces of the punch and the spacer are coated with h-BN or the like to prevent the seizure and chemical reaction with the fired body and the seizure between the die and the punch.

Although it is necessary to apply heat to raise the temperature of the powder for firing, there are several methods for applying the heat as described below. : Method of applying radiant heat from various heaters installed outside the die,
: A method of heating a die or powder by high frequency induction heating to obtain a high temperature .: A method of energizing part or all of a punch / die / spacer and powder to obtain a high temperature by Joule heat. In the above method, firing by electric discharge between powders can also be expected. In the case of firing by the other method, it is usual not to apply h-BN or the like, which is an insulative substance, to the surface to be energized such as a punch.

Next, problems of the currently used methods for pressure molding and firing of ceramics or metal powders will be described. When the heat required for firing is obtained by energization, carbon generally has low conductivity, so the electrical resistance of punches and spacers increases, and the power consumed as Joule heat in these parts is large, and therefore the temperature rise is high. There are problems such as taking time.

As a material having heat resistance equivalent to that of carbon and lower electric resistance, 4A and 5 in the periodic table of elements are used.
Ceramics such as carbides, borides, nitrides, and silicides of Group A and 6A elements are known, but these materials have high rigidity and are fragile, so they are said to be destroyed when the temperature gradient is steep. It is weak against thermal shock and cannot be used as a punch or spacer for pressure molding and firing.

[0007]

SUMMARY OF THE INVENTION The present invention provides a ceramic or metal powder which has high strength, withstands a high molding pressure, and has high electric conductivity, thereby reducing power consumption during electric firing and enabling rapid heating. It is an object to provide a punch or spacer material for pressure forming and firing.

[0008]

The present invention has the following constitution in order to achieve the above object. That is, 5 to 40% by weight of C and the balance of 4A, 5A, 6
A material for a high-strength conductive punch and a spacer for pressure molding, which comprises one kind or a mixture of two or more kinds selected from carbides or borides of Group A elements and inevitable impurities.

[0009]

The punching and spacer material proposed by the present invention is mainly composed of conductive ceramics, so that high strength and high conductivity are achieved, and addition of C reduces the rigidity and improves the toughness. Since it has been achieved, it is highly resistant to thermal shock and can be put to practical use. As a result, by reducing the power consumption in the punch and the spacer, the power cost was reduced and the power supply device was downsized, and the electric power was effectively supplied to the object to be fired, which enabled high-speed heating.

First, the reason why C is added is that since C has a lower rigidity than ceramics, the rigidity of the whole can be reduced by adding C to ceramics to form a composite. Also, the brittleness of ceramics (low toughness)
Is improved by the addition of C, such as deflection of cracks at the time of fracture and stress relaxation in the C portion. Due to the synergistic effect of reducing rigidity and improving toughness, the thermal shock resistance of the material of the present invention is significantly improved.

The amount of C is preferably 5 to 40% by weight, and if it is less than 5%, the effects of reducing rigidity and improving toughness are not sufficient. Again 40
%, The strength of the whole composite decreases due to the low strength of C, and the conductivity of the whole composite decreases due to the low conductivity of C, so that reduction of power consumption and high-speed heating cannot be realized. .

The carbides or borides of the elements of the 4A, 5A, and 6A group, which form the balance, may be used alone because they show high conductivity, but they are expected to improve the toughness due to the combined effect, and therefore two or more kinds thereof can be used. It is also possible to mix and use.

Since nitrides and silicides of 4A, 5A, and 6A group elements also have heat resistance and high conductivity, a small amount can be added to the material of the present invention, but at high temperatures, they can chemically react with C. It is difficult to add a large amount because it causes deterioration and is not meaningful to add.

When an extreme temperature gradient is generated in the punch and the spacer due to the firing conditions, only the spacer can be made of high strength carbon which is a conventional material to prevent the material from breaking according to the present invention.

Regarding the materials used for the punches and spacers of the present invention, the inventors of the present invention have previously invented that by adding C to TiC, a material excellent in thermal shock resistance and wear resistance can be obtained ( Japanese Patent Application No. 3-31436).
The present inventors have accomplished the present invention as a result of various experiments as a material for a high-strength conductive punch for pressure molding.

Next, the manufacturing method will be described. C, carbide and boride powders are blended and kneaded so as to fall within the range of the components of the present invention. The kneading is preferably performed by a ball mill or the like so that the added powders are uniformly mixed, and more preferably wet by using water or an organic solvent. Further, it is preferable that the kneading is performed for 12 hours or more so that the kneading is sufficiently performed. The raw material that has been made into a slurry by kneading is dried, crushed into a powder using a mortar or the like, and then molded and fired. The slurry may be dried using a spray dryer or the like, and may be directly made into powder or granules.

The molding and firing may be performed by molding with a mold or a cold isostatic method and then firing at normal pressure, but in order to obtain a dense and high-strength fired product, it is preferable to use the hot pressing method.
Firing is performed in nitrogen or argon or in vacuum, but it is desirable to perform firing in argon in order to avoid decomposition and chemical reaction of the added compound. The firing temperature must be 1700 ° C or higher, and 2000 ° C to obtain a dense sintered body.
The above is desirable. Appropriate processing such as grinding is applied to the obtained fired body to obtain a desired punch or spacer shape.

[0018]

【Example】

(Example 1) Table 1 shows the characteristics of materials for punches and spacers according to the present invention, which were made by trial using TiC and C.
As comparative examples, the case where the amount of C is less than 5%, the case where it exceeds 40%, and the value of commercially available high-strength carbon (C) are also shown.

Each material excluding commercially available carbon was kneaded by mixing each raw material at a weight ratio shown in Table 1 in a planetary ball mill using acetone as a solvent for 12 hours, followed by drying and crushing and firing by a hot pressing method. The firing temperature is 2000 ° C., the press pressure is 40 MPa, and the time is 2 hours.

The punch and spacer material according to the present invention has higher strength and higher conductivity than the conventional high-strength carbon, so that it can withstand high molding pressure and suppress power consumption in the punch and spacer portions. It turns out that is possible. Further, when the amount of C is less than 5% by weight, it has high strength and high conductivity, but the thermal shock resistance ΔT is as bad as 200 ° C. or less, and it is not practical when it is used as a punch and a spacer. On the other hand, when the amount of C is 40% or more, the conductivity is low and the strength is low.
Not particularly superior to high strength carbon.

[0021]

[Table 1]

(Embodiment 2) A punch and a spacer are made of TiC ceramics containing 10% by weight of C, which is a material according to the present invention, as a comparative example, ceramics made of only TiC, TiC ceramics containing 3% by weight of C, and We will introduce an example of using high-strength carbon, which is a conventional material, and used for firing powder. The shapes of the punch and the spacer are as shown in FIG. 1, and the diameter of the punch and the spacer was 30 mm. The powder to be fired was carbon steel, and 25 g of each was fired in two layers. The heating was performed by applying a constant-current controlled direct current to 3V. The inner surface of the die shown in FIG. 1 is insulated by coating 6 with h-BN so that no current flows in the die portion.

Among the comparative examples, the TiC ceramics and the TiC ceramics containing 3% by weight of C were
Immediately, it was broken due to thermal shock and was not practical. FIG. 2 is a comparison of the temperature rises of the objects to be fired during the electrical pressure firing. A conventional material, high-strength carbon, requires about 700 seconds to raise the temperature from room temperature to 800 ° C., whereas the material according to the present invention requires only about 50 seconds, and high-speed heating is possible. Recognize. Also, the power consumption during this period required 1.5 kw · h for the high-strength carbon material, whereas it decreased to 1.2 kw · h for the material of the present invention. It is considered that this is because the electric power consumption in these parts was suppressed because the conductivity of the punch and the spacer was improved. It is expected that the effect of reducing the power consumption will be remarkable when firing the ceramic powder having lower conductivity.

Example 3 Table 2 shows the properties of various materials according to the present invention. All materials were produced by the same firing method as in Example 1, but the firing temperature was changed because the optimum value differs depending on the material. All materials are superior in strength and conductivity to the high-strength carbon of the comparative example, and have a thermal shock resistance of ΔT350 ° C. or higher, and are suitable as materials for high-strength conductive punches for pressure molding and spacers. I know there is.

[0025]

[Table 2]

[0026]

As described above, according to the present invention, it is possible to provide a high-strength conductive punch and a spacer for pressure molding which have high strength and excellent conductivity.

[Brief description of drawings]

FIG. 1 is a diagram showing a method of pressure molding and firing of ceramic or metal powder, which is generally used at present.

FIG. 2 is a diagram showing a comparison of a temperature rising rate between a material according to the present invention and carbon which is a conventional material.

[Explanation of symbols]

 1 Die 2 Powder 3 Punch 4 Electrode 5 Spacer 6 Coating

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B30B 11/02 A 8824-4E C04B 35/52 35/56 35/58 105 K C04B 35/52 B 35/56 G (72) Inventor Yutaka Sato 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Corporation Advanced Technology Research Laboratories (72) Hidehiro Endo 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Shinichi (72) Inventor Masanori Ueki 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. A C content of 5-40% by weight and a balance of 4%.
High-strength conductive punches and spacers for pressure forming, characterized by being composed of one or more mixtures selected from carbides or borides of elements A, 5A and 6A, and unavoidable impurities. Materials.