JP2000051926A - Ceramic hot working tool and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a hot rolling time and to extend a tool life. SOLUTION: A ceramic plug for hot working, of which the contact face with a stock material is made of a ceramic, has a glass coated layer formed on the contact face. The glass having the softening point of 500-1500 deg.C is coated in thickness of 10-5000 μm. In piercing, the glass coated layer is softened by the heat of a heated stock material so as to exhibit a lubrication function. As compared to the plug not having the coated layer, the friction resistance to the stock material to be brought into contact is reduced, thus the piercing is smoothly done.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot working tool used for hot rolling and hot plastic working, and more particularly, to a seamless pipe manufacturing method using an inclined roll drilling method and a hole punching method. The present invention relates to a hot working tool (also referred to as a hot rolling tool) such as a die used for drawing or extruding a plug (hereinafter, also simply referred to as a plug) or a pipe, a wire, a shape, or the like.

[0002]

2. Description of the Related Art Hot working tools such as plugs and dies (hereinafter also referred to as working tools or simply tools) are exposed to high temperatures due to constant contact with a heated material and have extremely high stress. Such as receiving
Under severe conditions of high temperature and high pressure. For this reason,
The contact surface with the material, such as the tip portion or outer peripheral surface of the plug, the squeezed portion of the die, and the shaping portion, is liable to cause abrasion, melting, seizure, etc., and has a short life. Therefore, as a countermeasure, for example, in the case of a plug made of steel-based metal, an oxide scale (coating) is formed on the surface (contact surface) of the plug to extend the life of the plug (Japanese Patent Publication No. 52-822
No. 30). There is also known a method in which a lubricant is applied to the surface of a plug in advance and then piercing-rolling is performed to extend the life (JP-A-5-138213). However, in the processing of difficult-to-machine materials such as stainless steel, the effects are not sufficient.

Under these circumstances, as disclosed in Japanese Patent Application Laid-Open Nos. 60-137511 and 2-182330,
Technology of ceramicizing plugs with silicon nitride,
There is also known a technique in which ceramic is coated on the surface of a steel plug body as disclosed in JP-A-62-170479. These are intended to extend the service life by forming the contact surface with ceramic.

[0004]

However, when ceramic is used as a hot working tool, there are the following problems. For example, in a plug used in the Mannesmann pipe manufacturing method, when a difficult-to-machine material such as stainless steel is rolled and drilled as a material (a billet), frictional resistance is relatively high due to a problem of wettability with a metal component forming the material. However, there is a problem that it takes a long time to pierce. That is, the ceramic plug has a problem that the drilling efficiency is relatively poor and the productivity is low.

[0005] Moreover, the longer the perforation time, the longer the contact time with the heated material, so that the temperature of the ceramic tool tends to rise, which causes the shortening of its life. That is, ceramic has a smoother surface than conventional steel tools and has a good heat transfer coefficient, so that the temperature of the tool is likely to rise. Further, since the specific gravity of the ceramic tool is small, the heat capacity of the tool is smaller than that of the conventional steel tool, and the temperature tends to increase. As a result, the ceramic plugs become hot during the rolling and drilling process, and they come into contact with water (cooling water) in the operating environment, causing thermal shock,
They may break during use. For this reason, it was pointed out that ceramic tools are shorter-lived than steel tools.

SUMMARY OF THE INVENTION An object of the present invention is to improve the problems of such ceramic hot working tools such as ceramic plugs when hot-rolling (working) a difficult-to-work material such as stainless steel. However, an object of the present invention is to improve the working efficiency of such rolling and the like, and to extend the life of a ceramic hot working tool.

[0007]

According to the present invention, there is provided a ceramic hot working (rolling) tool in which a contact surface with a material is made of ceramic, wherein a glass coating layer is formed on the contact surface. It is characterized by becoming.

Accordingly, when a ceramic hot working tool is used, for example, in a plug for producing a seamless pipe, when a material is pierced (during hot rolling), a glass coating layer (hereinafter referred to as a coating layer) is heated by the heat of the heated material. Also called)
Is softened and a lubricating action is exhibited. Thereby, the frictional resistance with the contacting material is smaller than that of the plug without the coating layer. Therefore, the drilling is performed smoothly, and the drilling time is reduced or the drilling efficiency is improved. That is, since the glass softens under the environmental temperature during hot working and acts as a lubricant between the material (for example, the inner surface of the raw tube) and the contact surface (ceramic surface) of the tool, the glass in rolling (perforation) Resistance is reduced, and processing is facilitated.

The glass may be one having a softening point at which the glass softens at a processing temperature and has an appropriate viscosity, and the coating may be formed by welding or bonding glass powder. In this case, when welding
As will be described later in detail, the ratio of the coefficient of linear thermal expansion between the ceramic and the glass needs to be in an appropriate range. If the difference is large, the adhesion strength of the glass to the ceramic is not maintained and the glass is peeled off.

Also, as described above, a ceramic tool is different from a conventional tool made of cast steel or the like, and thus receives a large thermal shock because the temperature tends to rise. However, in the present invention, since a coating layer is formed, it does not form a protective film. In addition to exerting a heat shielding (insulating) effect, it creates a situation in which thermal shock is not directly applied to the ceramic. Therefore, the ceramic is less likely to be damaged by thermal shock, and a longer tool life is expected. Further, since the ceramic has high abrasion resistance, it is difficult to form irregularities on the contact surface. Therefore, generation of scratches on the processed surface such as the inner surface of the tube is reduced, and improvement in quality is expected.

The hot working tool according to the present invention broadly includes a hot rolling tool such as a plug used in the Mannesmann tube method and a die used in drawing or extruding a pipe or bar. The plugs include piercer plugs that are used for hot extrusion pipe making tools, press roll piercer plugs, plugs used for drawing pipes, and floating plugs.Dice include hot drawing dies and hot forging dies. Applicable. The coating layer may be a single layer or a plurality of layers. Further, a carbon coating layer may be formed on a ceramic, and a glass coating layer may be formed thereon.

The coating layer is preferably formed on the entire contact surface from the viewpoint of lubricating action, but may be formed on a portion. For example, in the case of a plug, it is preferable to form a coating layer on the entire tip and side surfaces of the bullet (cannonball) shape from the viewpoint of lubrication, but only the tip has the effect. In the case where only the bullet-shaped tip portion of the plug is ceramicized, a coating layer may be formed on the tip portion of the ceramic member or on the entire contact surface of the ceramic member with the material.

The glass constituting the coating layer is
Generally, the softening point is 500 ℃, depending on the heating temperature of the material
It is preferable that the temperature is in the range of ~ 1500C. The glass is heated in the process of contacting the material, and the viscosity is reduced according to the degree of the softening point, and the lubricating action is reduced. When the softening point is lower than 500 ° C., the viscosity becomes too low at the time of processing such as drilling,
This is because the lubricating action is reduced and the heat shielding effect is also reduced. On the other hand, if the softening point exceeds 1500 ° C., the lubricating effect is low because the viscosity of the glass is too high, and the coating layer itself is peeled off due to brittleness, so that the rolling efficiency may be reduced. The glass forming the coating layer has a softening point of 500 to 900 ° C., although it depends on the heating temperature of the material.

The thickness of the glass coating layer may be appropriately set so that a lubricating effect is expected. However, if it is too thin, it has no effect, and if it is too thick, it breaks or peels off at the beginning of rolling (perforation). 10 μm (0.01 mm) to 500
A range of 0 μm (5 mm) is a preferable thickness range.

The ceramic is not particularly limited, but preferably has silicon nitride as a main component. Ceramics themselves need to have heat resistance in order to adapt to the usage environment, but silicon nitride has a small coefficient of thermal expansion and excellent thermal shock resistance,
This is because the fracture toughness is superior to other ceramics. Those having a strength at 1000 ° C. of 300 MPa or more are preferred. In order to increase the adhesion strength between the glass coating layer and the ceramic, it is preferable that the surface of the ceramic has moderate unevenness rather than smoothness. However, if the surface is too rough, the work surface of the work becomes rough, which is not preferable. In consideration of these, the surface roughness of the ceramic is 2 at the maximum height (Rmax) regardless of the coating method.
The burnt skin surface may be treated by blasting or the like so that the thickness becomes from μm to 60 μm.

The preferred method of forming the coating layer is as follows. A slurry containing glass powder as a component is applied to a contact surface with a material in a ceramic hot working tool, heated to a temperature equal to or higher than the annealing point of the glass, and the glass powder is melted to some extent to form the contact. A glass coating layer is formed on the surface.
Here, "some melting" means that the entire glass powder is not melted. Unless the ratio of the coefficient of thermal expansion between the ceramic and the glass is 1, the glass is broken due to the difference in the coefficient of thermal expansion between the two when they are all melted and solidified. The method of coating while maintaining the bonding strength between particles by melting somewhat like this (hereinafter, referred to as
Melting method) is appropriate.

The relationship between the linear thermal expansion coefficients of the two is that when the linear thermal expansion coefficient of the glass forming the glass coating layer is Lc and the linear thermal expansion coefficient of the ceramic forming the ceramic hot working tool is Ls, Lc and Ls are Lc /
It is appropriate that Ls = 0.5 to 1.8. In this specification, the linear thermal expansion coefficient indicates a one-dimensional thermal expansion coefficient, and means an average thermal expansion coefficient between room temperature and 30 ° C. for glass and between room temperature and 800 ° C. for ceramic. And in a mixture of multiple types of glass powder,
This is the average coefficient of thermal expansion of a plurality of glasses obtained by mixing them.

In this case, it is important that the linear thermal expansion coefficients of the ceramic and glass match (approximately). If the linear thermal expansion coefficients of the glass powder and the ceramic are largely different, the coating layer can be in close contact. Therefore, coating by a melting method is not suitable. In this case,
A glass coating layer may be formed on the contact surface of the ceramic hot working tool by applying a liquid or paste-like organic binder or adhesive mixed with glass powder to the contact surface with the material. . However, it is necessary to have an appropriate adhesive strength up to the heating temperature at the time of processing (when using a tool), and for example, an epoxy-based adhesive is used. The glass coating layer can be formed by a drying method, a thermal spraying method, a plating method, or the like in addition to the above.

Here, the drying method means that a glass that can be hydrated with water is applied in a solution state to a contact surface of a ceramic hot working tool with a material and dried by heating. It is to form a layer. That is, like water glass (Na ₂ SiO ₂ ), glass that hydrates with water is applied to the ceramic in a solution state by spraying or the like, and the water is dried by applying heat.
This is a method in which glass is applied to the ceramic surface by removing it. Water glass has a property that it contains a large amount of water and can be dissolved in water. Such water glass can be strongly adhered to the surface of the ceramic by the anchor effect or the adhesion or bonding by chemical bonding, and therefore, a coating layer having high adhesive strength can be formed easily and inexpensively. The bonding (joining) by the anchor effect is as follows. Glass melted in water is dispersed at the molecular level, not the particle level. Therefore, in the step of drying water, the glass can enter small gaps (irregularities) on the surface of the ceramic. In this way, the unevenness of the surface exerts an anchor effect and is firmly adhered to the surface. Further, when the water dries, the bonding portions of the glass that have been bonded to the water molecules are chemically bonded to each other, and the glasses are bonded to each other. Strong bonding is also achieved by such bonding (bonding) by chemical bonding.

It is to be noted that a preferable glass for the coating layer is
Borosilicate glass (SiO _Two= 81%, B_TwoO
_Two= 12.7%, Al_TwoO_Three= 2.3%, Na_TwoO = 4
%), Aluminosilicate glass (SiO_Two= 56%, B_Two
O_Three= 8%, Al_TwoO_Three= 16%, CaO = 18%)
As an example, the type and composition of glass are limited to this
Never. The viscosity of glass varies greatly with its composition.
Therefore, an appropriate softening point in relation to the temperature during hot working
(500 to 1500 ° C)
Select and use.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hot working tool according to the present invention will be described below with reference to FIG. FIG. 1 is a partially broken sectional view of a plug according to the present invention used in the Mannesmann pipe manufacturing method and an enlarged view of a main part thereof. In FIG. 1, reference numeral 1 denotes a ceramic plug, which is made of silicon nitride, sialon,
Alternatively, it is formed by firing a powder press-formed product containing alumina as a main component. In this example, a plug main body (hereinafter, also simply referred to as a main body) 2 forming a bullet-shaped portion and a rear end portion are integrally formed in a concentric cylindrical shape. Fitting part 3 to mandrel
Excluding the rear end face 4 including the fitting portion 3, that is, the glass coating layer 11 is formed to have a predetermined thickness by a melting method or the like.

However, when a seamless pipe is formed by such a plug 1 by the Mannesmann tube method, a heated material (billet) 101 is pressed against the tip of the plug 1 to start piercing. During this perforation process, the glass coating layer 11 (hereinafter, also referred to as glass) is heated and softened. The softened glass 11 is the surface 2a of the plug 1
At the same time, it exists between the material 101 and performs a lubricating action.
Therefore, since the frictional resistance is reduced as compared with such a ceramic plug having no glass, the perforation time is reduced. In the perforation process, the temperature of the ceramic forming the plug 1 is reduced by the heat shielding effect of the softened glass, so that the life of the plug 1 is extended. As described above, in the plug 1 of the present embodiment, a raw tube can be efficiently formed even when a difficult-to-machine material such as stainless steel or chrome steel is pierced or rolled, and the life thereof can be extended. And
If the glass 11 comes off after its use, a glass coating layer may be formed again and used repeatedly.

It is preferable that a coating layer is formed on the entire surface of the plug, except for the rear end surface, since substantially the entire surface (outer peripheral surface) of the plug makes contact with the material.
A considerable effect can be expected even if the coating is applied only to the rolled portion at the leading end and the arc-shaped portion following the rolled portion without coating the entirety. In the plug,
As described above, the entirety is not made of ceramic, but is made of ceramic only at the tip end portion 22 and is combined with a tool body 23 made of metal other than the ceramic, like a ceramic combination plug 21 shown in FIG. Can be similarly embodied. In this case, it is preferable to form the coating layer 11 on the entire surface (contact surface with the material) of the ceramic member forming the tip portion 22.

Next, the melting method, which is a preferred method of forming a coating layer in the plug of FIG. 1, will be described in detail. First, a glass powder is mixed with water, and an organic binder is further added to prepare a coating liquid (slurry). Next, the main body 2 of the surface of the ceramic plug 1
The coating liquid is applied to the entire surface 2a of the tip portion and the outer peripheral surface by a brush or the like, or dipping is performed while the axis is horizontal and rotated about the axis, to apply a predetermined thickness. After drying, the glass is heated to a predetermined temperature (in the range from the annealing point to the softening point) to remove the organic binder, soften the glass, and melt the glass to some extent. By doing so, the particles of the glass powder are appropriately bonded, and the coating layer 11 is formed by fusion.

In the bonding method using an epoxy resin, a glass powder is mixed with an epoxy adhesive or binder having a low viscosity at room temperature, and a softener is added to form a paste or liquid, which is applied and cured. Good. That is, a paste containing the glass powder is applied to a required portion on the surface of the plug, and then heated to cure the adhesive, thereby forming a glass coating layer.

Next, the ceramic plug 1 shown in FIG. 1 is manufactured from silicon nitride or the like, and glass coating layers having different materials and thicknesses are formed to form various kinds of samples (outer diameter φ41 m).
m), and a rolling (piercing) experiment was performed on each of the samples (one each) by the Mannesmann tube method, and the piercing time and the temperature of the plug tip portion 20 seconds after the completion of piercing were compared with those of a comparative example. . The results are as shown in Tables 1 to 3. The comparative example (sample) is a ceramic plug without a glass coating layer. The material used for the roll piercing test was SUS304, having a diameter of 55 mm and a length of 300 m.
m, which is heated to 1250 ° C.
A 0 mm, 6 mm thick shell was produced. The rolling roll used had a diameter of 350 mm, a body length of 800 mm, and a rotation speed of 60 rpm.

Incidentally, the main components (composition) of the glass used for the coating are as follows (1) to (10). (1) Borosilicate glass A (SiO ₂ = 81%, B ₂ O ₃ = 12.
7%, Al ₂ O ₃ = 2.3%, Na ₂ O = 4%), (2)
Borosilicate glass B (SiO ₂ = 79%, B ₂ O ₃ = 1
2.7%, Al ₂ O ₃ = 2.3%, Na ₂ O = 5%),
(3) Aluminosilicate glass (SiO ₂ = 56%, B ₂ O
₃ = 8%, Al ₂ O ₃ = 16%, CaO = 18%), (4)
Lead borate glass (SiO ₂ = 61%, B ₂ O ₃ = 7
%, PbO = 32%), (5) Potassium borosilicate (S
iO ₂ = 68%, B ₂ O ₃ = 24%, K ₂ O = 8%),
(6) Lead potash glass (SiO ₂ = 56%, B ₂ O ₃ = 8)
%, Al ₂ O ₃ = 16%, CaO = 18%), (7) zinc borosilicate glass (SiO ₂ = 71%, ZnO = 1%,
(B ₂ O ₃ = 13%), (8) high silicate glass (SiO ₂ =
96.5%, B ₂ O ₃ = 3%, Al ₂ O ₃ = 0.5
%), (9) lead zinc borate glass (PbO = 30%, B ₂
O ₃ = 12%, ZnO = 20%), (10) zinc borate glass (ZnO = 30%, SiO ₂ = 58%, B ₂ O ₃ = 1)
2%)

[0028]

[Table 1]

Table 1 shows that the ceramic was silicon nitride, the glass was (1) borosilicate glass A, which was used as a glass coating layer by a melting method (Nos. 1 to 7), and the comparative sample (No. 1). 8, 9). This glass has a softening point of 821 ° C., an annealing point of 560 ° C., and a linear thermal expansion coefficient of 32.5 × 10 ⁻⁷ . Then, the ratio of the linear thermal expansion coefficient Lc of glass to the linear thermal expansion coefficient Ls of ceramic (Lc /
Ls) is 1.12. The fusion of the glass is performed by applying a slurry so that the coating layer has a predetermined thickness, heating the slurry to 720 ° C., and then naturally drying it in the air for 30 minutes.

As shown in Table 1, the sample of the present invention (No.
In 1) to 7), the perforation time was 5.6 to 7.0 seconds regardless of the thickness of the coating layer. On the other hand, the comparative sample without the coating layer (No. 8, 9)
It took 7.8 seconds or more for the ceramic plug of No. That is, in the sample of the present invention, the perforation time was reduced by about 10 to 30%, and the productivity was able to be remarkably improved. The temperature at the tip of the plug was determined using the comparative sample (No. 8,
9) was 980 ° C. or higher, whereas the sample of the present invention (N
o. 1-7) was 800-940 ° C. This demonstrates that the coating layer has the effect of reliably reducing the temperature of the tool tip during drilling. The effect of reducing the temperature is useful for preventing cracking of the ceramic due to thermal shock or extending its life.

Further, according to the results of the present invention samples Nos. 1 and 2, the coating layer was 0.01 mm or 0.1 mm
Is effective even when it is thin.
Even when the thickness is as thick as mm, the effect is obtained, and from the results of Sample No. 6, it can be seen that the effect is obtained even when the coating surface is formed on a ceramic having a rough surface of Rmax 50 μm.

Incidentally, a plug using silicon nitride as a base material was manufactured as follows. First, an average particle size of 0.5 μm,
Specific surface area (BET) of 10 m ² / g, α rate of 95%, oxygen content of 1.2 wt%, 90 wt% of silicon nitride powder, average particle diameter of 0.8 μm, and MgO of specific surface area (BET) of 10 m ² / g
5 wt% powder, average particle size 0.5 μm, specific surface area (BE
T) Each raw material powder was blended with 10 m ² / g of Yb ₂ O ₃ powder at 5 wt%, and mixed with ethanol in a ball mill for 50 hours. The mixture (slurry) was granulated by spray drying, molded into a plug shape by CIP molding, and fired to obtain a plug for perforation. After firing, the surface was polished with a diamond grindstone to finish the surface roughness according to JIS to Rmax: 2.1 μm by a 10-point method. However, the sample No. 6 had a thickness of 50 μm (baked surface) by sandblasting without polishing after firing.

Next, the ceramic is made of silicon nitride, sialon or the like, and the surface roughness of each is set to Rmax 2.1 μm.
m, and Table 2 shows the results of perforation on samples (Nos. 10 to 17) in which various glasses were coated to a thickness of 1 mm. The ratio (Lc / Ls) of the linear thermal expansion coefficient Lc of glass to the linear thermal expansion coefficient Ls of ceramic is 0.93 to 1.
6. However, in sample Nos. 16 and 17, this ratio was 1.
The glass was slightly larger than 62 or as small as 0.25. In the melting method, the glass was cracked or peeled off during the cooling process, and a coating layer could not be formed.

[0034]

[Table 2]

As shown in Table 2, Sample Nos. 16, 1
In all of the samples except for the sample No. 7, the comparative example (sample
Nos. 8 and 9), the effect of shortening the perforation time and reducing the temperature at the tip of the plug was observed. From this result, while the melting method is effective as a method of forming the coating layer,
In this case, it is important that the linear thermal expansion coefficients of the glass and the ceramic should match as much as possible.

The plugs having sialon as a base material in Table 2 were prepared by the same method as described above, using the following powders. Average particle size 0.5 μm, specific surface area (BET) 1
0 m ² / g, 92% by weight of silicon nitride powder having an α ratio of 95% and an oxygen content of 1.2% by weight, an average particle diameter of 0.8 μm, and a specific surface area (B
ET) 10 m ² / g of Y ₂ O ₃ powder of 10 wt%, average particle size of 0.8 μm, and specific surface area (BET) of 10 m ² / g of A
It was manufactured using ₃ wt% of 1N powder, 5 wt% of Al ₂ O ₃ powder having an average particle diameter of 0.9 μm and a specific surface area (BET) of 9 m ² / g. Further, when alumina is used as a base material, the purity is 99.99%, the average particle size is 0.2 μm, and the specific surface area (BE
T) Production was performed using 100 m% of Al ₂ O ₃ powder of 12 m ² /.

Next, a sample in which various types of glass were formed to a thickness of 1 mm by a bonding method instead of a melting method to a silicon nitride ceramic having a surface roughness of 2.1 μm (No. 18 to 18)
Table 3 shows the results of the perforation in 22). The coating layer was prepared by mixing each glass powder with an epoxy resin to form a paste, applying the paste to a predetermined coating layer thickness, and curing at 120 ° C. for 24 hours. Also,
Ratio of linear thermal expansion coefficient between glass and ceramic (Lc / Ls)
Is 1.12 to 3.14. Sample No. 22 is a comparative example using glass having a high softening point of 1530 ° C.

[0038]

[Table 3]

As shown in Table 3, all the samples except for Sample No. 22 exhibited a comparative example (Sample No.
8, 9), the effect of shortening the perforation time and reducing the temperature at the tip of the plug was observed. In addition, in the case where the coating layer is formed by mixing and applying the glass without melting the resin, it can be seen that there is no problem even if the ratio of the linear thermal expansion coefficient between the glass and the ceramic is large. That is, when the ratio of the coefficient of linear thermal expansion between the glass and the ceramic is large, it can be seen that such a bonding method is effective as a coating method. The sample No. In Comparative Example 22, because of the high silicate glass, the softening point of the glass was as high as 1510 ° C.,
Therefore, at a heating temperature of 1250 ° C., there is no lubricating effect,
The perforation time was conversely longer. In addition, the sample No. As shown in FIG. 21, lead borate glass has a glass softening point of 44.
The viscosity was low at a heating temperature of 1250 ° C., which was low at 5 ° C., and in FIG.

In the above-described embodiment, the case where the present invention is embodied in a plug for producing a seamless pipe is exemplified. However, the present invention can be applied to other hot working tools. FIG. 3 is a cross-sectional view of a die 51 used for drawing a bar.
The narrowed portion 52 and the shaping portion 53 of the die forming the contact surface with the material 111 may be ceramicized, and a glass coating layer may be formed on the surface.

That is, according to the present invention, in a ceramic hot working tool whose contact surface with a material is made of ceramic, a glass is formed on a portion of the contact surface with the material which is liable to cause abrasion, melting, seizure or the like. The tool consists of forming a coating layer, and the tools are hot working tools such as plugs used for processing the inner surface of seamless pipes and dies used for drawing rods. Widely applicable to.

[0042]

As is apparent from the above description, the ceramic hot working tool according to the present invention has a glass coating layer formed on the surface in contact with the material, and thus is heated during working. Since the glass is softened by the heat of the material and performs a lubricating action, even if the material is difficult to process, the frictional resistance with the contacting material is smaller than that of a tool having no coating layer. Therefore, the processing is performed smoothly by that much, and the processing time is shortened or the processing efficiency is improved. Then, since the coating layer is formed, it forms a protective film and acts as a heat shield (heat insulation), so that the ceramic is less likely to be damaged by thermal shock, and a longer tool life is expected.

[Brief description of the drawings]

FIG. 1 is a partially broken cross-sectional view of a plug according to the present invention used in the Mannesmann pipe manufacturing method and an enlarged view of a main part thereof.

FIG. 2 is a partially broken sectional view of another plug and an enlarged view of a main part thereof.

FIG. 3 is a sectional view of a die and an enlarged view of a main part thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic plug 2 Plug main body 2a Full surface (contact surface) of the front end portion and outer peripheral surface of main body 11 Glass coating layer 22 Front end portion 51 Dice 52 Restricted portion (contact surface) 53 Shaping portion (contact surface) 101, 111 Material

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Katsura Matsubara 14-18, Takatsuji-cho, Mizuho-ku, Nagoya Japan Special Ceramics Co., Ltd. (72) Takaaki Toyooka 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Chita Works Co., Ltd. (72) Inventor Akira Ito 1-1 1-1 Kawasaki-cho, Handa City, Aichi Prefecture Kawasaki Steel Co., Ltd. Chita Works F-term (reference) 4E096 EA09 FA08 FA09 FA16 FA21 GA01 HA11 4G062 AA08 AA09 AA15 BB04 BB05 BB06 BB08 CC01 DA06 DA07 DA08 DB02 DB03 DB04 DC03 DC04 DD01 DE03 DE04 DF05 EA01 EB03 EC03 ED01 EE04 EF01 EG01 FA01 FA10 FB01 FC01 FD01 FE01 FF01 FG01 FH01 FJ01 FK01 FL01 GA01 GA10 GB01 H01 H01 H01 H01 H01 H05 JJ03 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM05 MM40 NN29 NN32 PP13 PP14

Claims (9)

[Claims] 1. A hot working tool made of ceramic, wherein a contact surface with a material is made of ceramic, wherein a glass coating layer is formed on the contact surface. 2. The ceramic hot working tool according to claim 1, wherein the softening point of the glass forming the glass coating layer is in the range of 500 ° C. to 1500 ° C. 3. The glass coating layer having a thickness of 1
The ceramic hot working tool according to claim 1 or 2, wherein the diameter is in a range of 0 µm to 5000 µm. 4. The ceramic hot working tool according to claim 1, wherein the ceramic is mainly composed of silicon nitride. 5. A ceramic hot working tool according to claim 1, wherein the ceramic hot working tool is a plug for producing a seamless pipe. 6. A slurry containing glass powder as a component is applied to a contact surface of a ceramic hot working tool with a material, and heated to a temperature equal to or higher than the annealing point of the glass to melt the glass powder to some extent. Forming a glass coating layer on the contact surface by heating. 7. When the linear thermal expansion coefficient of glass forming a glass coating layer is Lc, and the linear thermal expansion coefficient of ceramic forming a ceramic hot working tool is Ls.
7. The method for manufacturing a ceramic hot working tool according to claim 6, wherein Lc and Ls are in a relationship of Lc / Ls = 0.5 to 1.8. 8. A glass coating on the contact surface of a ceramic hot working tool by applying a liquid or pasty organic binder or adhesive mixed with glass powder to the contact surface with the material. A method for producing a ceramic hot working tool, comprising forming a layer. 9. A glass coating layer is formed on a contact surface of a ceramic hot working tool with a material which is hydrated with water in a solution state, and heated and dried by heating. A method for producing a ceramic hot working tool.