JP2007032802A - Ceramic screw body and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic screw body provided with a screw part capable of reducing manufacturing cost and having excellent electric insulation property, chemical resistance, protection against corrosion, and strength. <P>SOLUTION: A ceramic bolt 1 being the ceramic screw body is formed by heating and baking a powder-like raw material containing zirconia being a main component and yttria being a by-component after molding by pressurization to realize such a shape that a male screw part 11 is provided on at least one end side of a stem part 10. Outside diameter (d) of the stem part 10 is smaller than outside diameter D<SB>1</SB>of the male screw part 11, and pitch dimension P of the male screw part 11 is set to be larger than pitch dimension of a coarse thread. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ceramic screw body provided with a screw body on at least one end side of a shaft rod portion, particularly a ceramic having high corrosion resistance (electric corrosion, chemical corrosion) and high strength characteristics mainly composed of zirconia. It relates to a screw body.

Conventionally known screw bodies made of ceramics, for example, bolts having small diameters such as M6, M8, and M10, are also formed by injection molding. Patent documents disclosing these bolts include, for example, Patent Document 1 (Japanese Patent Laid-Open No. 6-170893), Patent Document 2 (Japanese Utility Model Laid-Open No. 5-1010), Patent Document 3 (Japanese Patent Laid-Open No. 6-081826), and Patent Document 4 (Japanese Patent Laid-Open No. 7-190032) and Japanese Patent Laid-Open No. 8-004738. In particular, Patent Document 1 discloses a technique related to ceramic bolt injection molding. Examples of the bolt material include alumina, zirconia, alumina-zirconia composite material, mullite, silicon nitride, silicon carbide, and the like. Patent Document 3 discloses a ceramic bolt reinforced with a fiber. A bolt in which the outer diameter of the male screw portion is larger than the outer diameter of the non-screw portion is disclosed in Patent Document 6 (Japanese Patent Laid-Open No. 2002-122114). Furthermore, Patent Document 7 (Japanese Patent Laid-Open No. 9-229037) discloses a bolt in which the outer diameter of the male thread portion is larger than the outer diameter of the non-thread portion and a curved surface is formed between the two.
JP-A-6-170893 5-1010 JP-A-6-081826 JP 7-190032 A JP-A-8-004738 JP 2002-122114 A Japanese Patent Laid-Open No. 9-229037

  Although there are many market demands for ceramic screw bodies such as ceramic bolts, the current situation is that the provision of screw bodies is not sufficient. The reason is that ceramics have weakness in strength. Moreover, the provision of screw bodies that can meet various market demands such as price, strength, and types of screw bodies has not been sufficient.

  The present invention has been made in view of such circumstances, and its purpose is to reduce the manufacturing cost, and in addition to the inherent electrical insulation, chemical resistance, and corrosion resistance of ceramics, a ceramic screw having a screw portion with improved strength. The body is on offer.

  Therefore, the ceramic screw body according to claim 1 is provided with a male screw portion on at least one end side of a shaft rod portion which is a non-male screw portion, and a powdery raw material containing zirconia as a main component and yttria as a subcomponent. The outer diameter of the shaft bar is smaller than the outer diameter of the male thread, and the pitch dimension of the male thread is larger than the pitch of the coarse thread. It is a feature.

  According to a second aspect of the present invention, in the ceramic screw body according to the first aspect, the male screw portion is provided on both ends of the shaft bar portion.

  The ceramic screw body according to claim 3 is characterized in that, in the ceramic screw body according to claim 1 or 2, the pitch dimension of the male thread portion is 1.3 to 3 times larger than the pitch dimension of the coarse thread.

  A ceramic screw body according to a fourth aspect of the present invention is the ceramic screw body according to any one of the first to third aspects, wherein a top and a valley of a thread of the male screw portion are processed into a curved surface.

  The ceramic screw body according to claim 5 is the ceramic screw body according to any one of claims 1 to 4, wherein at least the male thread portion after the heating and firing has a surface roughness lower than a roughness before the surface processing. It is processed so that it becomes.

  The method for manufacturing a ceramic screw body according to claim 6 includes: a male screw portion provided on at least one end side of a shaft rod portion that is a non-male screw portion, with a powdery raw material containing zirconia as a main component and yttria as a subcomponent. A method for manufacturing a ceramic screw body in which a molded body is formed by pressure molding so as to have a formed shape, and then heated and fired to form a ceramic screw body, the mold for forming the molded body Is characterized in that the outer diameter of the shaft rod portion is smaller than the outer diameter of the male screw portion and the pitch dimension of the male screw portion is larger than the pitch dimension of the coarse screw.

  The method of manufacturing a ceramic screw body according to claim 7 is the method of manufacturing a ceramic screw body according to claim 6, wherein at least a surface roughness of a male screw portion of the fired body formed by heating and firing the formed body is a surface processing. The surface is processed so as to be lower than the previous roughness.

  According to the ceramic screw body according to claim 1 and the ceramic screw body manufacturing method according to claim 6, zirconia is the main component, and the outer diameter of the shaft rod portion is smaller than the outer diameter of the male screw portion. Further, it is possible to provide a ceramic screw body capable of reducing the production cost without causing a decrease in strength. And since the pitch dimension of a thread is larger than the pitch dimension of a coarse thread, the intensity | strength of a thread part improves and the ceramic screw body which improved strength can be provided. The male screw portion may be provided on both end sides of the shaft rod portion as in the ceramic screw body according to claim 2. Examples of the screw body include hexagon head bolts and hexagon socket head bolts. The pitch dimension of the male thread is preferably 1.3 to 3 times larger than the pitch dimension of the coarse thread as in the ceramic screw body according to claim 3.

  According to the ceramic screw body of claim 4, by processing the top and valley of the thread of the male screw into a curved surface, in addition to the action of the ceramic screw body according to claims 1-3, Even if foreign matter is mixed into the valley of the female screw that is screwed with the male screw part, the tightening action of the ceramic screw body can be maintained.

  Furthermore, according to the ceramic screw body according to claim 5 and the ceramic screw body manufacturing method according to claim 7, at least the roughness of the surface of the male screw portion is reduced, so that the ceramic according to claim 1. It has been confirmed that the strength of the screw body and the ceramic screw body manufactured by the manufacturing method according to claim 6 is further enhanced. Thereby, the application range of a ceramic screw body expands.

  Therefore, according to the ceramic screw body according to claims 1 to 5 and the method for manufacturing the ceramic screw body according to claims 6 and 7 according to the present invention, the manufacturing cost can be reduced, and electrical insulation, chemical resistance, A ceramic screw body with improved strength in addition to corrosion resistance can be provided. In particular, it is possible to provide a screw body (bolt or the like) suitable for use as a civil engineering member, for example, a screw body suitable for use in an adverse environment including an atmosphere containing sulfide or chloride.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Fig.1 (a) is the schematic which showed the side surface of the ceramic volt | bolt which concerns on one Embodiment of this invention. FIG.1 (b) is sectional drawing of the screw thread formed in the external thread part of the said ceramic bolt. 2 (a) and 2 (b) are schematic views showing a side surface of a ceramic bolt according to another embodiment of the present invention. FIG. 2C is an enlarged cross-sectional view showing a state of a connecting portion between a screw portion and a shaft rod portion formed on the ceramic bolt.

  The ceramic bolt 1 includes a shaft rod portion 10 and a male screw portion 11 as shown in FIG. The male screw portion 11 may be formed on one end side or both end sides of the shaft rod portion 10. Examples of the ceramic screw body according to another embodiment of the present invention include a hexagon head bolt and a hexagon socket head bolt.

  Examples of the hexagon head bolt and the hexagon socket head bolt include the ceramic bolt 4 shown in FIG. 2 (a) and the ceramic bolt 5 shown in FIG. 2 (b). In the ceramic bolt 4, the outer diameter of the shaft rod portion 40 is smaller than the outer diameter and valley diameter of the male screw portion 41. A neck lower round portion 42 is formed at a connecting portion between the shaft rod portion 40 and the male screw portion 41. In the ceramic bolt 5, the outer diameter of the shaft rod portion 50 is smaller than the outer diameter and valley diameter of the male screw portion 51. The shaft bar portion 50 and the male screw portion 51 are connected via a connecting portion 53. The connecting portion 53 has a tapered side surface formed so that the outer diameter gradually decreases. In addition, as shown in FIG.2 (c), the neck lower round part 52 is formed in the external thread part 51, the connection part 53, and the connection part.

  The pitch dimension of the male thread portion 11 is set larger than the pitch dimension of the coarse thread. According to this configuration, the strength of the male screw portion 11 is improved, and a ceramic bolt with improved strength can be provided. Specifically, the pitch dimension P of the male thread portion 11 may be set 1.3 to 3 times larger than the pitch dimension of the coarse thread.

The outer diameter d of the shaft rod portion 10 is set smaller than the outer diameter D ₁ and the valley diameter D ₂ of the male screw portion 11 as shown in FIG. The shaft rod portion 10 and the male screw portion 11 are connected via a connecting portion 12. The connecting portion 12 has a tapered side surface formed so that the outer diameter gradually decreases. According to such a configuration, it is possible to provide a ceramic bolt that can reduce the production cost without causing a decrease in strength.

  The top 111 and the trough 112 of the thread 110 of the male thread 11 may be processed into a curved surface as shown in FIG. This is because the tightening action of the ceramic bolt can be maintained even if foreign matter enters a valley of a female screw (not shown) that is screwed into the valley 112 or the male screw portion 11.

The ceramic bolt 1 is formed by pressing a powdery raw material containing zirconia as a main component and yttria as a subcomponent to form a molded body having a predetermined form (for example, the form of the ceramic bolt shown in FIGS. 1 and 2). After forming, it is produced by heating and baking. Incidentally, the mold for forming the molded body, the pitch dimension P of the external thread portion 11 with an outer diameter d is smaller than the outer diameter D ₁ and root diameter D ₂ of the male thread portion 10 of the axial rod portion 10 is parallel It is formed to be larger than the pitch dimension of the internal thread.

  The zirconia powder may have a particle size of 50 nm or less. The pressure at the time of pressure molding is set to 50 MPa or more. A known method such as CIP (Cold Isostatic Pressing) or HIP (Hot Isostatic Pressing) may be used as the pressure forming means. . The temperature at the time of baking is set to 1400 ° C. or higher.

  It is preferable that at least a portion of the male screw portion 11 of the fired body produced by heating and firing is subjected to surface processing so that the roughness is lower than the roughness before the surface processing. The sintered body has a surface roughness of about 150 μm, but if the surface is modified so that the surface roughness is less than 30 μm, the strength of the screw body can be increased and the application range of the screw body is expanded. To do. Of course, it can be used in the required strength range without modifying the surface. A known processing method may be employed as the surface treatment method. For example, a friction processing method disclosed in Japanese Patent Application Laid-Open No. 2001-19537 and Japanese Patent Application Laid-Open No. 3-279286, and further a processing method using blasting and ultrasonic waves can be given. Incidentally, the surface processing of at least the male screw portion 11 means that when there is a rod shaft portion 10 connected to the male screw portion 11 as shown in FIG. It means that the whole surface is processed.

  Next, Table 1 shows the results of examining the strength of ceramic bolts manufactured under various pressure forming conditions and firing conditions.

Sample S1 is composed of zirconia as a main component (zirconium oxide, average crystallite diameter of 38 nm), yttria as a subsidiary component (yttrium oxide, 4.95 to 5.35 wt%), and inevitable components (SiO ₂ ≦ 0.02 wt%, A raw material containing Al ₂ O ₃ ≦ 0.15 to 0.35 wt% (model TZ-3YSB-C, non-surface area 7 m ² / g, average granule diameter 82 μm, manufactured by Tosoh Corporation) and a predetermined shape A ceramic bolt obtained by press-molding at a molding pressure of 50 MPa so as to form a molded body and then firing the molded body by raising and lowering the temperature at a predetermined firing temperature shown in Table 1 It is. This ceramic bolt has the shape of a double screw bolt as shown in FIG. 1A. The overall length L is 160 mm, the length L ₁ of the shaft rod portion 10 is 80 mm, and the length L of the male screw portion 11. ₂ is 40 mm, the outer diameter D ₁ of the male screw portion 11 is 24 mm, the valley diameter D ₂ of the male screw portion 11 is 21 mm, the outer diameter d of the shaft rod portion 10 is 19 mm, the curved surface radius R of the inclined portion is 30 mm, and the male screw portion 11 The pitch P was set to 6 mm, and the curved surface radius r of the thread 111 and the valley 112 of the male screw portion 11 was set to 1.5 mm. The pressure molding was performed by a method based on the CIP method. A molding rubber mold made of urethane rubber having a hardness of 50 was used as a mold for the pressure molding method. Moreover, the external appearance was evaluated by confirming the presence or absence of a crack visually before using a molded object for baking. The green body was fired in an electric furnace capable of performing a degreasing step and a firing step of the green body (molded body before firing) and arbitrarily changing the firing temperature. The appearance of the fired body obtained by this firing was also evaluated by visually confirming the presence or absence of cracks.

  Sample S2 was prepared by the same raw material, molding method, and firing method as Sample 1 except that the molding pressure was 70 MPa, and the appearance evaluation of the compact and the fired body was performed in the same manner as the evaluation of Sample 1.

  Sample S3 was prepared by the same raw material, molding method, and firing method as Sample 1 except that the molding pressure was 80 MPa, and the appearance evaluation of the compact and the fired body was performed in the same manner as the evaluation of Sample 1.

  Sample S4 was prepared by the same raw material, molding method, and firing method as Sample 1 except that the molding pressure was 90 MPa, and the appearance evaluation of the compact and the fired body was performed in the same manner as the evaluation of Sample 1.

  Sample S5 was prepared by the same raw material, molding method, and firing method as Sample 1 except that the molding pressure was 98 MPa, and the appearance evaluation of the compact and the fired body was performed in the same manner as the evaluation of Sample 1.

  Sample S6 was prepared by the same raw material, molding method and firing method as Sample 1, except that the molding pressure was 70 MPa and the firing temperature and the temperature rise and fall patterns were the conditions shown in Table 1. The appearance of the fired body was evaluated in the same manner as the evaluation of Sample 1.

  Sample S7 was prepared by the same raw material, molding method, and firing method as Sample 6 except that the molding pressure was 80 MPa, and the appearance evaluation of the compact and the fired body was performed in the same manner as the evaluation of Sample 1.

  Sample S8 was prepared by the same raw material, molding method, and firing method as Sample 6, except that the molding pressure was 90 MPa, and the appearance evaluation of the compact and the fired body was performed in the same manner as the evaluation of Sample 1.

  As apparent from the appearance evaluation results of the molded body and the fired body shown in Table 1, it was confirmed that no cracks occurred in the samples S1 to S5 at the stage of the molded body and the fired body. On the other hand, in Samples S6 to S8, cracks did not occur at the stage of the molded body, but it was confirmed that cracks occurred at the stage of the fired body. This crack is considered to have occurred because the temperature drop in the firing process was too rapid and the degassing inside the molded body was insufficient.

  Table 1 shows the results of evaluating the strength of samples S1 to S5 where no cracks occurred. The strength evaluation was performed by measuring the tensile breaking stress. As shown in FIG. 3, the tensile test for evaluating the tensile breaking stress is performed by placing a ceramic bolt 63 as a sample on a ceramic insert 62 made of alumina ceramics embedded in concrete 61 placed in a mold 60. After screwing, a tensile member 65 was connected to the ceramic bolt 63 by a coupler 64, and the tensile member 65 was pulled through a load cell 66, and a tensile stress at break was measured by applying a load. About the measurement result of the said tensile breaking stress, the measurement result when not carrying out surface treatment of a sintered body and when carrying out surface treatment is shown. In the surface treatment, the surface of the sample was roughened (the roughness was less than 30 μm and the roughness was less than 10 μm) by grinding the entire surface of the male thread portion and the shaft rod portion of the sample with a diamond grindstone.

As is clear from the measurement results of the tensile breaking stress shown in Table 1, it was confirmed that a ceramic bolt having a strength of tensile breaking stress of 308 N / mm ² or more can be obtained when the surface treatment is not performed. It was. In addition, the fracture | rupture was recognized by generation | occurrence | production in the incomplete thread part (shaft bar part near a male thread part).

The tensile rupture stress of the ceramic bolt of the nominal name M6 which is a commercially available zirconia ceramic bolt according to the conventional example is 33.8 N / mm ² , and the tensile rupture stress of the ceramic bolt of the nominal name M8 is 77.0 N / mm ² . Therefore, according to the samples S1 to S5, even if the surface treatment is not performed at the stage of the fired body (even if the surface roughness is less than 150 μm), a ceramic bolt with higher strength than the conventional product is obtained. It was shown that it can be provided.

Further, as apparent from the measurement results of the tensile breaking stress shown in Table 1, it is confirmed that a ceramic bolt having a strength of tensile breaking stress of 319 N / mm ² or more can be obtained when the surface treatment is applied. It was done. In particular, it was confirmed that when the surface roughness was set to less than 30 μm, a ceramic bolt having a strength of 319 N / mm ² or more was obtained. Furthermore, it was confirmed that when the surface roughness was set to less than 10 μm, a ceramic bolt having a strength of 324 N / mm ² or more was obtained.

  Therefore, it can be seen that a ceramic bolt with sufficient strength can be obtained without subjecting the fired body to surface treatment, and if the surface treatment is performed, the strength can be further improved by 10% or more. It can be seen that ceramic bolts can be provided.

Further, the total length L manufactured by the same manufacturing method as the samples S1 to S5 is 160 mm, the length L ₁ of the shaft rod portion is 80 mm, the length L ₂ of the male screw portion is 40 mm, and the outer diameter D _{1 of the} male screw portion is 24 mm. , root diameter D ₂ of the male screw portion is 21 mm, the pitch P of the external thread portion is 6 mm, radius of curvature r of the thread peaks and valleys of the external thread portion examines tensile stress for the ceramic bolt shape of both screw bolts is 1.5mm It was confirmed that the tensile breaking stress of the ceramic bolt that was not surface-treated at the stage of the fired body was 208 to 237 N / mm ² . Moreover, it was confirmed that the tensile fracture stress of the ceramic bolt subjected to the surface treatment at the stage of the fired body is 235 to 269 N / mm ² .

  Therefore, in ceramic bolts, the outer diameter of the shaft rod part should be smaller than the outer diameter of the male thread part, and the pitch dimension of the thread and valley of the male thread part should be larger than the pitch dimension of the thread and valley of the coarse male thread. It was confirmed that the strength of the ceramic bolt was improved. In addition, when the pitch dimension of the thread and valley of the male thread portion was 1.3 times or less than the pitch dimension of the thread and valley of the coarse male thread, no improvement in strength was observed. Furthermore, the improvement in strength was not observed at 3 times or more compared to the case of 3 times. From this, it is appropriate that the pitch dimension of the thread and valley of the male thread part is 1.3 to 3 times the pitch dimension of the thread and valley of the coarse male thread. It was confirmed that 5 times is preferable. Moreover, it was confirmed that about 2 times is preferable from the viewpoint of bolt tightening.

(A) is the schematic which showed the side surface of the ceramic bolt which concerns on one Embodiment of this invention, (b) is sectional drawing of the screw thread formed in the external thread part of the said ceramic bolt. (A) And (b) is the schematic which showed the side surface of the ceramic bolt which concerns on other one Embodiment of this invention, (c) is the state of the connection part of the screw part formed in the said ceramic bolt, and a shaft bar part. FIG. Explanatory drawing of the performance test of a ceramic bolt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 4, 5 ... Ceramic bolt 10, 40, 50 ... Shaft rod part 11, 41, 51 ... Male thread part 42, 52 ... Neck round part 12, 53 ... Connection part 110 ... Screw thread, 111 ... Top, 112 ... valley

Claims (7)

  A powdery raw material containing zirconia as a main component and yttria as a subcomponent is heated after pressure molding so that a male screw part is provided on at least one end side of a shaft bar part which is a non-male screw part. A ceramic screw body formed by firing, wherein the outer diameter of the shaft rod portion is smaller than the outer diameter of the male screw portion, and the pitch dimension of the male screw portion is larger than the pitch dimension of the coarse screw.   The ceramic screw body according to claim 1, wherein the male screw portion is provided on both ends of the shaft rod portion.   The ceramic screw body according to claim 1 or 2, wherein a pitch dimension of the male thread portion is 1.3 to 3 times larger than a pitch dimension of the coarse thread.   The ceramic screw body according to any one of claims 1 to 3, wherein a top and a valley of a thread of the male screw part are processed into a curved surface.   5. The ceramic screw body according to claim 1, wherein at least the male screw portion after the heating and firing is processed so that a surface roughness thereof is lower than a roughness before the surface processing.   A powdery raw material containing zirconia as a main component and yttria as a subcomponent is pressure-molded so that a male screw part is provided on at least one end side of a shaft bar part which is a non-male screw part. A method of manufacturing a ceramic screw body in which a molded body is formed by heating and firing to form a ceramic screw body, wherein a mold for forming the molded body has an outer diameter of the shaft rod portion of the male screw portion. A method for manufacturing a ceramic screw body, wherein the ceramic screw body is formed so as to be smaller than an outer diameter and to have a pitch dimension of the male screw portion larger than that of a coarse thread. The ceramic screw according to claim 6, wherein the surface of the fired body formed by heating and firing the molded body is processed so that the surface roughness of at least the external thread portion is lower than the roughness before surface processing. Body manufacturing method.

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