JP2014089884A - Method for manufacturing ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of reducing a possibility of the occurrence of cracking in a ceramic heater.SOLUTION: An unfired compact is formed so that a ratio of density difference is 0.2% or more and 1.1% or less, the ratio of density difference being a ratio obtained by dividing a difference, which is obtained by subtracting the apparent density of a second part including the boundary between a conductive material and a molded ceramic material from the apparent density of a first part that is a part apart from the conductive material in the molded ceramic material and includes the surface of the molded ceramic material, by the total apparent density of a fired base substance obtained by firing an unfired compact.

Description

  The present invention relates to a ceramic heater used for a glow plug or the like.

  2. Description of the Related Art Conventionally, glow plugs including heaters that generate heat when energized have been used to assist in starting an internal combustion engine. A ceramic heater may be employed as the heater. As the ceramic heater, for example, a heater in which a heat generating element made of conductive ceramic is embedded in a base made of insulating ceramic is used. As a method for manufacturing a ceramic heater, for example, an insulating ceramic material powder is used to form a lower half-insulated molded body, the half-insulated molded body is set in a mold opening, and a conductive ceramic is used. There has been proposed a method in which a molded unfired heating element is placed on a half-insulated molded body, filled with a powder of an insulating ceramic material from above, and a ceramic heater before firing is formed by press molding.

JP 2007-226972 A

  However, ceramic has excellent heat resistance, but has a characteristic that it may break. Ceramic heaters are no exception, and cracks may occur in ceramic heaters.

  The main advantage of the present invention is to provide a technique that can reduce the possibility of cracking in a ceramic heater.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples.

[Application Example 1]
A method for manufacturing a ceramic heater, comprising: a base configured using an insulating ceramic; and a heating element embedded in the base,
Covering the conductive material that is a material of the heating element with an insulating ceramic material that is a material of the base body and includes a powdery portion;
The non-fired including the conductive material and a molded ceramic material that is a molded insulating ceramic material that covers the conductive material by press-molding the insulating ceramic material that covers the conductive material A step of molding the molded body of
Including
In the step of forming the green molded body,
A boundary between the conductive material and the molded ceramic material is determined from an apparent density of a first portion of the molded ceramic material that is away from the conductive material and includes the surface of the molded ceramic material. The difference obtained by subtracting the apparent density of the second portion including the density difference ratio, which is a ratio obtained by dividing the difference of the overall apparent density of the fired substrate obtained by firing the unfired molded body, The unsintered molded body is molded so as to be 0.2% or more and 1.1% or less,
Production method.

  According to this configuration, the apparent density of the first portion including the surface of the formed ceramic material and the boundary between the conductive material and the formed ceramic material are compared with the case where the density difference ratio is larger than 1.1%. Since the ratio (density difference ratio) of the difference between the apparent density of the second part and the second part is small, the apparent density of the second part is suppressed from being locally reduced. As a result, the possibility of cracks occurring in the base (particularly the second portion) can be reduced.

[Application Example 2]
The manufacturing method according to application example 1, further comprising:
When pressure is applied to the insulating ceramic material powder along one direction, a pressure at which cracks start to occur in the particles of the insulating ceramic material powder is 0.18 MPa or more and 0.36 MPa or less. It is characterized by being,
Production method.

  According to this configuration, a density difference ratio in the range of 0.2% or more and 1.1% or less can be easily realized.

  The present invention can be realized in various modes. For example, a ceramic heater manufacturing method, a ceramic heater manufactured by the manufacturing method, a manufacturing method of a glow plug including the ceramic heater, and a manufacturing method thereof It can be realized in the form of a manufactured glow plug or the like.

It is explanatory drawing which shows the glow plug as one Example of this invention. 4 is a flowchart of a method for manufacturing the ceramic heater 40. It is a perspective view of the shape | molded conductive material 220u. Schematic of shaping | molding of the half member 211u. Schematic of shaping | molding of the molded object 40u. It is the schematic of baking. It is sectional drawing (sectional drawing perpendicular | vertical to an axial direction) of the molded object 40u. It is sectional drawing of the metal mold | die for measuring a burst pressure.

A. Example:
A-1. Glow plug (ceramic heater) configuration:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory view showing a glow plug as one embodiment of the present invention. The glow plug 10 functions as a heat source for assistance in starting an internal combustion engine (for example, a diesel engine) (not shown). 1A is a longitudinal sectional view of the glow plug 10, and FIG. 1B is an enlarged sectional view showing a part of the glow plug 10 (a portion including the ceramic heater 40). The illustrated line CL indicates the central axis of the glow plug 10. Hereinafter, the central axis CL is also referred to as “axis line CL”, and the direction parallel to the central axis CL is also referred to as “axis line direction”. A first direction D1 in the figure is a direction parallel to the axis CL, and a second direction D2 is a direction opposite to the first direction D1. In a state where the glow plug 10 is mounted on the internal combustion engine, the end portion on the first direction D1 side of the glow plug 10 (more specifically, the end portion on the first direction D1 side of the ceramic heater 40) is in the combustion chamber. Inserted. Hereinafter, the first direction D1 side is also referred to as “front end side”, and the second direction D2 side is also referred to as “rear end side”. In addition, an end on the first direction D1 side of various members is also referred to as a “front end”, and an end on the second direction D2 side is also referred to as a “rear end”.

  The glow plug 10 includes a metal shell 20, a middle shaft 30, a ceramic heater 40, insulating members 50 and 60, an outer cylinder 70, and a caulking member 80. The metal shell 20 is a member in which a conductive material (for example, a metal such as carbon steel) is formed in a cylindrical shape. The metal shell 20 has a through hole 25 extending along the central axis CL. The metal shell 20 includes a tool engaging portion 28 formed at the end portion on the second direction D2 side, and a male screw portion 22 provided on the first direction D1 side with respect to the tool engaging portion 28. It is out. The tool engaging portion 28 is a portion that engages with a tool (not shown) when the glow plug 10 is attached or detached. The male screw portion 22 includes a screw thread for screwing into a female screw of a mounting hole (not shown) of the internal combustion engine.

  The central shaft 30 is accommodated in the through hole 25 of the metal shell 20. The middle shaft 30 is a member in which a conductive material (for example, a metal such as nickel) is formed in a round bar shape. The distal end 31 of the middle shaft 30 is located inside the through hole 25 and is processed so that the outer diameter decreases in a stepped manner (hereinafter, the distal end 31 (the portion with the smaller outer diameter) is also referred to as the small diameter portion 31). The rear end 39 of the middle shaft 30 protrudes from the opening OP2 on the second direction D2 side of the metal shell 20 in the second direction D2. A ring-shaped first insulating member 50 is provided between the outer surface of the middle shaft 30 and the inner surface of the through hole 25 of the metal shell 20. Further, a ring-shaped second insulating member 60 is attached to the opening OP2 of the metal shell 20. The second insulating member 60 includes a tubular portion 62 and a flange portion 68 provided on the tubular portion 62 on the second direction D2 side. The cylindrical portion 62 is sandwiched between the outer surface of the central shaft 30 and the inner surface of the opening OP2 of the metal shell 20. The metal shell 20 supports the middle shaft 30 via these insulating members 50 and 60.

  A substantially cylindrical caulking member 80 is arranged on the insulating member 60 in the second direction D2 side. The middle shaft 30 passes through the caulking member 80. The caulking member 80 is swaged and fixed to the middle shaft 30 with its tip end face in contact with the flange portion 68 of the insulating member 60. Thereby, the second insulating member 60 is prevented from coming off from the middle shaft 30.

  An outer cylinder 70 is attached to the opening OP1 of the metal shell 20 on the first direction D1 side. The outer cylinder 70 is a member in which a conductive material (for example, a metal such as carbon steel) is formed in a cylindrical shape. The outer cylinder 70 includes a thin portion 71 and a thick portion 75 provided on the thin portion 71 on the second direction D2 side. The end of the thick portion 75 on the second direction D2 side is processed so that the outer diameter decreases in a step shape, and is inserted into the opening OP1 of the metal shell 20.

  A ceramic heater 40 is inserted into the outer cylinder 70. The outer periphery of the central portion of the ceramic heater 40 is held by the outer cylinder 70. The tip 41 of the ceramic heater 40 protrudes toward the first direction D1 from the tip of the outer cylinder 70, and the rear end 49 of the ceramic heater 40 protrudes toward the second direction D2 from the rear end of the outer cylinder 70. The rear end 49 of the ceramic heater 40 is accommodated in the through hole 25 of the metal shell 20.

  An electrode ring 90 is attached to the rear end 49 of the ceramic heater 40. The electrode ring 90 covers the outer peripheral surface of the rear end 49. The small diameter portion 31 of the middle shaft 30 and the electrode ring 90 are electrically connected by a lead wire 95.

  Next, details of the ceramic heater 40 will be described. FIG. 1B shows a more detailed cross-sectional view of the ceramic heater 40. The ceramic heater 40 includes a round bar-shaped base 210 extending along the axis CL, and a substantially U-shaped heating element 220 (also referred to as a “heating element 220”) embedded in the base 210. .

  The base 210 is formed using an insulating ceramic. In this embodiment, the material of the substrate 210 is silicon nitride. However, other insulating ceramics (at least ceramics exhibiting insulating properties after firing of the ceramic heater 40. For example, silicon fluoride) can be employed. The tip 41 of the base 210 is processed into a round shape.

  The heating element 220 is formed using a conductive ceramic. In this embodiment, the material of the heating element 220 is a ceramic in which tungsten carbide is mixed with silicon nitride as a main component.

  The heating element 220 includes two lead portions 221 and 222, a connection portion 223 that connects the lead portions 221 and 222, and electrode extraction portions 281 and 282. Each lead part 221, 222 extends in parallel with the axis CL from the rear end 49 of the ceramic heater 40 to the vicinity of the front end 41. The lead portions 221 and 222 are disposed so as to face each other with the central axis CL interposed therebetween. Hereinafter, of the directions orthogonal to the central axis CL, the direction parallel to the plane including the central axis CL and the two lead portions 221 and 222 is referred to as the X direction, and is orthogonal to the central axis CL and the X direction. The direction to do is called the Y direction.

  The connecting portion 223 is embedded in the tip 41 of the ceramic heater 40 and connects the tip of the first lead portion 221 and the tip of the second lead portion 222. The shape of the connecting portion 223 is a substantially U-shape that curves in accordance with the round shape of the tip 41 of the ceramic heater 40.

  A portion 223h on the first direction D1 side of the connecting portion 223 is configured such that the cross-sectional area is smaller than the cross-sectional areas of the lead portions 221 and 222. Therefore, at the time of energization, the temperature of this portion 223h of the connection portion 223 rises more rapidly than other portions. Thus, this portion 223h of the connecting portion 223 functions as a heating resistor (hereinafter also referred to as “heating portion 223h”).

  A first electrode extraction portion 281 is connected to a portion of the first lead portion 221 on the second direction D2 side. The first electrode extraction portion 281 extends from the first lead portion 221 toward the outer periphery of the ceramic heater 40 and is exposed on the outer surface of the ceramic heater 40. The exposed portion of the first electrode extraction portion 281 is in contact with the inner peripheral surface of the outer cylinder 70. Thereby, the outer cylinder 70 and the 1st lead part 221 are electrically connected.

  A second electrode extraction portion 282 is connected to a portion of the second lead portion 222 on the second direction D2 side. The second electrode extraction portion 282 is disposed closer to the second direction D2 than the first electrode extraction portion 281. The second electrode extraction portion 282 extends from the second lead portion 222 toward the outer periphery of the ceramic heater 40 and is exposed on the outer surface of the ceramic heater 40. The exposed portion of the second electrode extraction portion 282 is in contact with the inner peripheral surface of the electrode ring 90. Thereby, the electrode ring 90 and the second lead portion 222 are electrically connected.

A-2. Manufacturing method of ceramic heater:
FIG. 2 is a flowchart of the method for manufacturing the ceramic heater 40. In the first step S110, the material (conductive material) of the heating element 220 is molded (hereinafter, the molded conductive material is also referred to as “molded conductive material”). Specifically, a ceramic material (for example, a mixture of silicon nitride and tungsten carbide), a sintering aid, and water are mixed to generate a slurry, and powder is generated by spray drying. And a molded object is produced | generated by mixing a binder and the produced | generated powder and injection-molding a mixture. The binder is removed by heating and drying the formed body. Thus, the molded conductive material is molded.

  FIG. 3 is a perspective view of the molded conductive material 220u. As illustrated, the molded conductive material 220u includes unfired lead portions 221u and 222u, an unfired connection portion 223u, and unfired electrode extraction portions 281u and 282u. In this embodiment, the support portion 224 that connects the rear end of the first lead portion 221u and the rear end of the second lead portion 222u is also integrally formed. The support part 224 is provided in order to suppress breakage of the molded conductive material 220u. As will be described later, the support unit 224 is disconnected in step S190. Note that the support unit 224 may be omitted.

  In the next step S120 of FIG. 2, a ceramic material powder for the substrate 210 is generated. Specifically, a ceramic material (for example, silicon nitride), a sintering aid, and water are mixed to produce a slurry, and after adding a binder to the slurry, a powder is produced by spray drying.

  In the next step S130, an unfired half member is formed. The half member corresponds to one of two parts obtained by equally dividing the base 210 by a plane passing through the central axis CL. FIG. 4A is a perspective view showing a mold 300 for a half member. 4 (B) and 4 (C) are cross-sectional views of the mold 300 showing a part of the molding process. FIG. 4D is a perspective view of the molded half member 211u. 4B and 4C are cross-sections (BB cross-section in FIG. 4A) perpendicular to the longitudinal direction (axial direction) of the half member 211u.

  As shown in FIG. 4A, the mold 300 includes a frame-shaped outer frame 304, a lower mold 302 disposed below the outer frame 304, and an upper mold 306 disposed on the outer frame 304. , Including. The outer frame 304 has an opening 304h having a rectangular shape when viewed from the top to the bottom. The lower mold 302 includes a convex portion 302p that is inserted into the opening 304h from below. The convex portion 302p has a curved molding surface for forming the outer surface of the half member 211u. The shape of the convex portion 302p viewed from the top to the bottom is substantially the same rectangle as the opening 304h. The upper mold 306 includes a convex portion 306p that is inserted into the opening 304h from above. The convex portion 306p has a flat molding surface for molding the inner surface (the surface passing through the central axis CL) of the half member 211u. Further, the convex portion 306p has a molding protrusion 306x (FIGS. 4B and 4C) for forming a concave portion 211r (FIG. 4D) for fitting the molded conductive material 220u on the half member 211u. ))have. The shape of the convex portion 306p viewed from the bottom to the top is substantially the same rectangle as the opening 304h.

  When the half member 211u is formed, first, as shown in FIG. 4B, in the state where the convex portion 302p of the lower mold 302 is inserted into the opening 304h of the outer frame 304, A predetermined amount of the ceramic material powder CP is filled. Next, as shown in FIG. 4C, the convex portion 306p of the upper mold 306 is inserted into the opening 304h, and a force is applied to at least one of the upper mold 306 and the lower mold 302, whereby a predetermined pressure (several 10 MPa). The pressing direction is parallel to the Y direction. Thus, the half member 211u shown in FIG. 4D is formed.

  In addition, the order of shaping | molding of the shaping | molding electroconductive material 220u (S110) and shaping | molding of the half member 211u (S120, S130) can be set arbitrarily.

  In the next step S140 in FIG. 2, an unfired molded body is formed. This molded body is a molded body including a molded conductive material 220u and a molded insulating ceramic material that covers the molded conductive material 220u. FIG. 5A is a perspective view showing a molding die 400 of the molded body. FIG. 5B to FIG. 5D are cross-sectional views of the mold 400 showing a part of the molding process. FIG. 5E is a perspective view of the molded body 40u. 5B to 5D are cross sections (BB cross section in FIG. 5A) orthogonal to the longitudinal direction (axial direction) of the molded body 40u.

  As shown in FIG. 5A, a forming die 400 includes a frame-shaped outer frame 404, a lower die 402 disposed below the outer frame 404, and an upper die 406 disposed on the outer frame 404. , Including. The outer frame 404 has an opening 404h having the same shape as the opening 304h of the outer frame 304 (FIG. 4A). The lower die 402 has a convex portion 402p having the same shape as the convex portion 302p of the lower die 302 (FIG. 4A). The upper mold 406 has a convex portion 406p having a shape obtained by vertically inverting the convex portion 402p.

  When molding the molded body 40u, first, as shown in FIG. 5B, the convex portion 402p of the lower mold 402 is inserted into the opening 404h of the outer frame 404. The half member 211u is placed on the convex portion 402p. The molded conductive material 220u is fitted into the recess 211r of the half member 211u.

  Next, as shown in FIG. 5C, a predetermined amount of ceramic material powder CP is filled in the opening 404h. Thereby, the molded conductive material 220u is covered with the half member 211u and the ceramic material powder CP. At this point, the insulating ceramic material covering the molded conductive material 220u includes a half member 211u and a powdered portion 212.

  Next, as shown in FIG. 5D, the convex portion 406p of the upper mold 406 is inserted into the opening 404h, and a force is applied to at least one of the lower mold 402 and the upper mold 406, whereby a predetermined pressure (several 10 MPa). The pressing direction is parallel to the Y direction. Thus, the molded body 40u shown in FIG. 5E is molded. By this press molding, the powdery portion 212 is molded.

  As shown in FIGS. 5D and 5E, the cross-section (cross-section perpendicular to the axial direction) of the formed molded body 40u is a shape obtained by rounding four rectangular corners (substantially elliptical). ). The length of the cross section of the compact 40u in the pressing direction (parallel to the Y direction) is shorter than the length in the direction perpendicular to the pressing direction (parallel to the X direction). Hereinafter, a portion of the molded body 40u corresponding to the material of the base body 210 is referred to as a “formed ceramic material 210u”. Further, of the formed ceramic material 210u, the portion of the half member 211u is also referred to as “first half portion 211u”, and the portion formed from the powdered portion 212 is referred to as “second half portion 212u”. Call.

  In the next step S150 in FIG. 2, the compact 40u is degreased. In this embodiment, calcination is performed at 800 degrees Celsius for 1 hour in a nitrogen gas atmosphere. Thereby, a binder is removed from the molded object 40u. In the next step S160, a release agent is applied to the outer surface of the molded body 40u.

  In the next step S170, the compact 40u is fired. In this step, firing by so-called hot pressing is performed. In the present embodiment, the compact 40u is heated and pressurized under a non-oxidizing atmosphere at 1800 degrees Celsius for 1 hour at a hot press pressure of 30 MPa. FIG. 6 is a schematic view of firing. 6A shows a cross-sectional view of the molded body 40u, and FIG. 6B shows a cross-sectional view of a fired body 40b obtained by firing the molded body 40u (each cross-sectional view is in the axial direction). It is a cross-sectional view orthogonal to. As shown in the drawing, the pressing direction is parallel to the X direction (pressure is applied to the compact 40u in a direction parallel to the X direction). In this step S170, a molding die having a recess having a shape conforming to the outer shape of the fired body 40b is used so that the cross-sectional shape of the fired body 40b after firing is substantially circular (not shown).

  In the next step S180 in FIG. 2, the fired body 40b is polished. Thereby, the outer shape of the fired body 40b is processed into a predetermined shape. In the next step S190, the end including the support portion 224 (FIG. 3) in the fired body 40b is cut, and the fired ceramic heater 40 is generated. When the support unit 224 is omitted, step S190 can be omitted.

A-4. About the apparent density distribution:
Next, the apparent density distribution in the substrate 210 will be described. FIG. 7 is a cross-sectional view (cross-sectional view perpendicular to the axial direction) of the molded body 40u. In the figure, two portions P1 and P2 of the molded ceramic material 210u of the molded body 40u are shown. These portions P1 and P2 are both part of the second half portion 212u. That is, these parts P1 and P2 are formed by compressing the powdery part 212 (FIG. 5C) by the molding in step S140 (FIG. 2).

  The first portion P1 is a portion that is separated from the molded conductive material 220u and includes the surface of the molded body 40u (molded ceramic material 210u). Specifically, the first portion P1 is a part of the surface of the molded body 40u (that is, the surface of the molded ceramic material 210u) (in this case, a specific direction parallel to the pressing direction when the molded body 40u is molded (here, , Y direction) side end portion 210u1), and the distance from the end portion 210u1 (the distance in the direction parallel to the pressing direction) is within the first distance t1.

  The second portion P2 is a portion including a boundary Ba between the molded conductive material 220u (particularly, the portion corresponding to the lead portions 221 and 222) and the molded ceramic material 210u. Specifically, the second portion P2 includes a part of the boundary Ba (end boundaries Ba1 and Ba2 that are ends of the boundary Ba on the specific direction (Y direction) side parallel to the pressing direction). The distance between the end boundaries Ba1 and Ba2 (the distance in the direction parallel to the pressing direction) is the second distance t2 and is disposed on the end portion 210u1 side of the formed ceramic material 210u when viewed from the end boundaries Ba1 and Ba2. The part that is within. The first end boundary Ba1 is a boundary with the first lead portion 221u, and the second end boundary Ba2 is a boundary with the second lead portion 222u. When the molded body 40u is molded, the first portion P1 comes into contact with the mold (upper die 406 (FIG. 5D). The second portion P2 is compared with the first portion P1 when viewed from the upper die 406. , Disposed inside the molded ceramic material 210u.

  In the present embodiment, since the position of the first lead portion 221u in the Y direction is the same as the position of the second lead portion 222u in the Y direction, the second portion P2 has both of the lead portions 221u and 222u. (That is, the second portion P2 includes both the first end boundary Ba1 and the second end boundary Ba2). Suppose that the position of the first lead part 221u in the Y direction is different from the position of the second lead part 222u in the Y direction. In this case, as an end portion (end portion serving as a reference of the second portion P2) included in the second portion P2 of the boundary Ba, of the first end boundary Ba1 and the second end boundary Ba2, The end closest to the end 210u1 of the shaped ceramic material 210u is employed.

  During molding of the molded body 40u, pressure is directly applied to the first portion P1 from the molding die (FIG. 5D: upper die 406). The pressure transmitted through the portion closer to the mold (upper die 406) than the second portion P2 is mainly applied to the second portion P2.

In the first portion P1, since a strong pressure from the mold is applied to the powder particles of the ceramic material, the particles are easily crushed. And since the space | gap between particle | grains is filled up with the crushed particle | grain, an apparent density tends to become high. In the present specification, the apparent density means a value obtained by dividing the mass (g) of the sample by the apparent volume (cm ³ ) of the sample. The apparent volume means a volume including sample particles and voids between the particles.

  On the other hand, in the second portion P2, the pressure applied to the ceramic material particles is smaller than that in the first portion P1. This is because part of the pressure from the mold (for example, the upper mold 406 (FIG. 5D)) is caused by particle breakage at a portion (for example, the first portion P1) closer to the mold than the second portion P2. Therefore, in the second portion P2, the particles are less likely to be crushed and the voids between the particles are more easily maintained than in the first portion P1, and as a result, the apparent density of the second portion P2 is increased. Tends to be smaller than the apparent density of the first portion P1.

  Such a deviation in apparent density can cause cracks during firing of the molded body 40u. The second portion P2 having a low apparent density (hereinafter also referred to as “low density portion P2”) is more likely to be fragile than the first portion P1 having a high apparent density (hereinafter also referred to as “high density portion P1”). . Therefore, when the apparent density is not uniform compared with the case where the apparent density is uniform, the ceramic heater 40 after firing is more likely to crack. Even when firing by hot pressing is applied as the firing method, cracks may occur in the fired ceramic heater 40 if the low density portion P2 exists in the formed body 40u.

  In order to reduce the possibility of cracks, it is preferable that the difference in apparent density between the first portion P1 and the second portion P2 is small. Therefore, a test regarding a preferable range of the ratio of the apparent density difference was performed using a plurality of samples (details will be described later).

  In this embodiment, press molding is performed in each of a plurality of press directions orthogonal to the central axis CL (specifically, press molding in the Y direction (FIG. 5D) and press molding in the X direction). (FIG. 6)). Therefore, it is possible to easily manufacture the ceramic heater 40 having an approximately isotropic outer shape around the central axis CL.

A-4. First test:
Based on the above examples, seven types of samples (ceramic heaters) were generated and tested. Among the seven types of samples, the difference in apparent density between the first portion P1 and the second portion P2 is different (details will be described later). Items common to various samples are described below.
1) The particle size of the ceramic material powder produced in step S120 of FIG. 2 is about 100 μm. In this example, powder that passed through a sieve having an opening of 125 μm and remained on the sieve (75 μm) without passing through a sieve having an opening of 75 μm was used as the material of the substrate 210.
2) Dimensions of green body 40u (FIG. 7)
2a) Outer diameter L1 in the pressing direction (direction parallel to the Y direction) = about 4 mm
2b) Outer diameter L2 in a direction perpendicular to the pressing direction (direction parallel to the X direction) = about 7 mm
2c) Length in the axial direction = about 45 mm
Other matters are as described above as examples.

  The cross-sectional shape of the unfired lead portions 221u and 222u is a substantially circular shape in which the contour line includes a portion with a large curvature and a portion with a small curvature, and the diameter of the minimum circumscribed circle circumscribing the contour of the cross-section is about (In FIGS. 5 to 7, the cross-sectional shapes of the lead portions 221 u and 222 u are simply shown as circles in FIGS. 5 to 7). Moreover, the outer diameter of the fired body 40b after firing (FIG. 6B) was in the range of 3 mm to 3.5 mm. Table 1 shown below is a table showing test results of seven types of samples # 1 to # 7.

  The “density difference ratio” is a difference obtained by subtracting the apparent density of the second portion P2 from the apparent density of the first portion P1 of the unfired molded body 40u (FIG. 7) as the overall apparent density of the fired substrate 210. This is the percentage obtained by division (unit:%). When calculating the density difference ratio, the thickness (first distance t1) of the first portion P1 is 0.2 mm, and the thickness (second distance t2) of the second portion P2 is also 0.2 mm.

  The apparent density of the first part P1 and the apparent density of the second part P2 were measured using the degreased green compact 40u obtained in step S150 of FIG. The apparent density of the first part P1 was determined by measuring the mass of the molded body 40u (first mass) and the mass after scraping the first part P1 from the molded body 40u (second mass), The difference between the masses was calculated by dividing by the apparent volume of the first part P1. The apparent volume was calculated by measuring the dimension of the first portion P1. Similarly, the apparent density of the second portion P2 is also the same as the mass before scraping the second portion P2 from the molded body 40u (third mass) and the mass after scraping the second portion P2 from the molded body 40u (fourth mass). And the difference between the first and second parts) by the apparent volume of the second part P2. These apparent densities are calculated using the molded body 40u including the part to be cut in step S190 of FIG. 2, but the cross-sectional shape (FIG. 7) is between the part to be cut and the part to be left. ) Are approximately the same, the difference in apparent density is sufficiently small. Therefore, the calculated apparent density is equivalent to the apparent density of the unheated state of the base 210 of the ceramic heater 40 finally obtained.

  The apparent density of the entire fired substrate 210 was measured using the completed ceramic heater 40 obtained in step S190 of FIG. Specifically, the mass (fifth mass) of the remaining portion (base 210) from which the heating element 220 is removed from the ceramic heater 40 is measured, and the measured mass is divided by the apparent volume of the base 210, thereby obtaining the base. An apparent density of 210 was calculated. The apparent volume of the substrate 210 was calculated by subtracting the apparent volume of the heating element 220 from the apparent volume of the ceramic heater 40. Their apparent volumes were calculated using the measured dimensions.

The relationship between the measured apparent density Da of the first part P1, the apparent density Db of the second part P2, and the density difference ratio DR was as follows.
Da (g / cm ³ ): Db (g / cm ³ ): DR (%)
1.752: 1.689: 1.8
1.755: 1.707: 1.4
1.752: 1.714: 1.1
1.738: 1.707: 0.9
1.759: 1.735: 0.7
1.745: 1.738: 0.2
1.752: 1.748: 0.1

  The “density difference ratio” in Table 1 (the above density difference ratio DR) was calculated by processing five samples produced under the same conditions to measure each of the five masses described above. . “Crack determination” and “clearance determination” to be described later were performed using 800 samples (ceramic heater 40) generated under the same conditions. Since the generation conditions are the same, it can be estimated that the density difference ratios of the five samples and the 800 samples are almost the same as the density difference ratios shown in Table 1.

  “Crack determination” is an evaluation result of the total number of samples in which cracks are generated among 800 sintered samples (ceramic heater 40) generated under the same conditions (the same density difference ratio). Is shown. The A evaluation indicates that the number of samples having cracks is zero, and the B evaluation indicates that the number of samples having cracks is one or more. The presence or absence of cracks was confirmed by cutting the sample and observing the inside.

  “Gap determination” indicates an observation result (observation result using a microscope) of a section corresponding to the second portion P2 of the base 210 of the 800 samples. The A rating indicates that the voids between the particles are clogged with ceramic (eg, crushed particles) and the number of samples with the voids between the particles remaining is zero. The B evaluation indicates that the number of samples in which voids between particles remain is 1 or more.

  For the first and second samples (density difference ratios are 1.8% and 1.4%), the crack determination was “B evaluation” and the gap determination was “B evaluation”.

  For samples No. 3 to No. 6 (density difference ratios are 1.1%, 0.9%, 0.7%, 0.2%), the crack determination is “A evaluation”, and the gap determination is It was "A evaluation".

  For the sample No. 7 (density difference ratio is 0.1%), the crack determination was “A determination”, but the gap determination was “B determination”. Although no crack was generated in the vicinity of the boundary between the base 210 and the heating element 220, a gap remained. In addition, voids remained in the vicinity of the outer surface of the molded body 40u. Therefore, when a release agent is applied to the outer surface of the molded body 40u, the release agent can infiltrate into the inside from the outer surface of the molded body 40u unintentionally. Unintentional penetration of the release agent can make the substrate 210 brittle. Note that the reason why the void remains in the vicinity of the outer surface of the compact 40u in the sample No. 7 will be described later.

  As described above, the density difference ratio is preferably 0.2% or more and 1.1% or less. Specifically, the density difference ratios with which good test results were obtained are 1.1%, 0.9%, 0.7%, 0.2%, and between these two values. A range may be employed.

  If the density difference ratio is 0.2% or more and 1.1% or less, the apparent density Da of the first part P1, the apparent density Db of the second part P2, and the overall appearance of the baked base body 210 are obtained. It is estimated that the possibility of cracking can be reduced even if the density is different from the sample of the above test.

A-5. Second test:
Next, a method for adjusting the density difference ratio will be described. In the first test described above, the density difference ratio was adjusted by adjusting the strength of the ceramic material powder particles for the substrate 210. In order to adjust the strength of the particles, the composition of the binder was adjusted. In the second test, six types of ceramic material powder samples having different strengths were generated, and the relationship between the binder composition, strength, and density difference ratio was examined. The production method of the ceramic material powder is the same as the method of the above-described example (first test). Table 2 shown below is a table showing test results of six types of samples # 8 to # 13.

“Breaking pressure” indicates a pressure at which particles are broken (unit: MPa). The higher the burst pressure, the higher the particle strength. FIG. 8 is a sectional view of a mold for measuring the breaking pressure. The mold 500 includes an outer frame 504 having a cylindrical opening 504h, a lower mold 502 disposed below the outer frame 504, and an upper mold 506 disposed on the outer frame 504. . The lower mold 502 includes a protrusion 502p that is inserted into the opening 504h from below. The shape of the convex portion 502p is a cylindrical shape whose outer diameter is substantially the same as the inner diameter of the opening 504h. The upper mold 506 includes a protrusion 506p that is inserted into the opening 504h from above. The shape of the convex portion 506p is a cylindrical shape whose outer diameter is substantially the same as the inner diameter of the opening 504h. Specifically, the outer diameters of the convex portions 502p and 506p are 12 mm (the area of the end face is 113 mm ² ).

  When measuring the breaking pressure, first, 0.65 g of ceramic material powder is filled into the opening 504h in a state where the convex portion 502p of the lower mold 502 is inserted into the opening 504h of the outer frame 504. Next, the convex part 506p of the upper mold 506 is inserted into the opening 504h, and the powder is pressed by applying a downward force to the upper mold 506. Here, a series of processes are repeated in which the press die is slightly increased and then the upper die 506 is removed and the state of the powder (particles) in the opening 504h is observed. The particles were observed with a microscope, and the press pressure at the time when cracks occurred on the surface of the particles was recorded as the breaking pressure.

  As shown in Table 2, the breaking pressures of the 8th to 13th samples were 0.13 MPa, 0.16 MPa, 0.18 MPa, 0.27 MPa, 0.36 MPa, and 0.38 MPa, respectively. Sample No. 8 is produced using a wax-based binder. Samples Nos. 9 to 12 are produced by replacing a part of the wax binder with an acrylic binder. The proportion of the acrylic binder increases as the sample number increases. The sample No. 13 is produced using an acrylic binder without using a wax binder. As can be seen from Table 2, the breaking pressure can be increased by increasing the proportion of the acrylic binder. In this way, the breaking pressure can be adjusted by adjusting the amount of the wax binder used and the amount of the acrylic binder used.

  The “density difference ratio” in Table 2 is the same as the “density difference ratio” described in Table 1 above. Using each of the six types of samples (ceramic material powder), the density difference ratio was measured according to the same procedure as in the first test. As shown in Table 2, the density difference ratios of the samples Nos. 8 to 13 are 1.8%, 1.4%, 1.1%, 0.8%, 0.2%, and 0.1%, respectively. %Met. As shown in Table 2, the density difference ratio is larger as the breaking pressure is lower. The reason for this is as follows.

  When the burst pressure is low, the particles of the first portion P1 (FIG. 7) are easily crushed during press molding in step S140 of FIG. Accordingly, the apparent density of the first portion P1 is increased. Moreover, since the pressure from the upper mold 406 is absorbed by the first portion P1, the pressure applied to the second portion P2 becomes weak. Therefore, in the second portion P2, the collapse of the particles is suppressed and the apparent density is reduced. As a result, the density difference ratio increases.

  On the other hand, when the burst pressure is high, the particles of the first portion P1 are not easily crushed. Therefore, the apparent density of the first portion P1 is reduced. Moreover, since the absorption of the pressure by the 1st part P1 is suppressed, the pressure applied to the 2nd part P2 becomes strong. Accordingly, in the second portion P2, the crushing of the particles is promoted and the apparent density is increased. As a result, the density difference ratio is reduced.

  As explained in Table 1, the density difference ratio is preferably 0.2% or more and 1.1% or less. In order to realize such a preferable density difference ratio, the fracture pressure is preferably 0.18 MPa or more and 0.36 MPa or less (Table 2). Specifically, the burst pressure at which a good density difference ratio is obtained is 0.18 MPa, 0.27 MPa, and 0.36 MPa, and a range between any two of these numerical values may be adopted. In the case where another range is adopted as the preferable range of the density difference ratio, the range between two pressures arbitrarily selected from the breakdown pressure that realizes the density difference ratio of the preferable range as the preferable range of the breakdown pressure. Can be adopted.

  In addition, regarding the sample No. 7 in Table 1, the reason why the gap exists also in the vicinity of the outer surface of the molded body 40u (FIG. 7) is as follows. Since the density difference ratio of the No. 7 sample is small, the ceramic material powder having a high breaking pressure is used as the ceramic material powder of the No. 7 sample. Therefore, in the first portion P1 (FIG. 7), the particles are not easily crushed, and voids between the particles remain. As a result, the release agent can infiltrate into the inside from the outer surface of the molded body 40u unintentionally.

B. Variations:
(1) In the manufacturing method of the ceramic heater 40 described above, various conditions can be adopted as conditions used for manufacturing. For example, the type of the binder used to obtain the insulating ceramic material powder for the substrate 210 is not limited to the wax-based binder and the acrylic-based binder, and various other binders can be employed. Moreover, as a usage amount of the binder (a usage amount of each binder when plural kinds of binders are used), a breaking pressure in a preferable range (for example, 0.18 MPa or more and 0.36 MPa or less) can be realized. Can be determined experimentally. Further, the breaking pressure of the ceramic material powder for the substrate 210 may be less than 0.18 MPa or greater than 0.36 MPa. In any case, the method for realizing the density difference ratio within the preferable range (for example, within the range of 0.2% or more and 1.1% or less) is not limited to the method of adjusting the burst pressure, but other methods. Various methods can be employed. For example, you may adjust the combination of the press pressure for shape | molding the molded object 40u, and the filling amount of the powder of the material of an insulating ceramic.

  Further, the pressing pressure and the filling amount of the insulating ceramic material powder at the time of forming the half member 211u can be arbitrarily determined according to the specifications of the half member 211u. Similarly, the pressing pressure and the filling amount of the insulating ceramic material powder at the time of forming the unfired formed body 40u can be arbitrarily determined according to the specifications of the formed body 40u. As each press pressure, for example, a pressure within a range of 10 to 100 MPa can be employed. Further, the particle diameter of the insulating ceramic material powder may be larger or smaller than 100 μm. Moreover, as conditions for degreasing (calcination), any conditions that can remove the binder can be employed. For example, the temperature may be higher or lower than 800 degrees Celsius. The calcination time may be longer or shorter than 1 hour. Further, the hot pressing conditions can be arbitrarily determined according to the specifications such as the target density and shape of the ceramic heater 40. For example, the press pressure may be higher or lower than 30 MPa. Also, the firing temperature may be higher or lower than 1800 degrees Celsius. The firing time may be longer or shorter than 1 hour.

(2) The shapes and dimensions of the base 210 and the heating element 220 of the ceramic heater 40 are not limited to the shapes and dimensions described above, and various shapes and dimensions can be employed. For example, the cross-sectional area of the connection part 223 may be the same as the cross-sectional area of the lead parts 221 and 222. Further, the second electrode extraction portion 282 (FIG. 1B) may be omitted. In this case, the lead wire 95 may be welded to the rear end of the second lead portion 222.

(3) The material of the heating element 220 is not limited to a conductive ceramic material, and other conductive materials can be employed (a material that exhibits conductivity after firing of the ceramic heater 40. For example, a high melting point metal (for example, , Tungsten (W), molybdenum (Mo), hafnium (Hf), rhenium (Re), etc., having a melting point of 2000 degrees Celsius or higher). In addition, the conductive material (material for the heating element) embedded in the unfired molded body 40u is not limited to the molded conductive ceramic material, and various types of conductive materials can be employed. In general, it is preferable to employ a conductive material formed in a predetermined shape. The shape of the conductive material may be determined according to the shape of the heating element 220 of the completed ceramic heater 40.

(4) The molded body 40u may be molded without using the half member 211u. For example, the entire periphery of the heating element material (conductive material) may be covered with a powder of an insulating ceramic material.

(5) As described above, the structure and manufacturing method of the ceramic heater are not limited to the structure and method described in the embodiments, and various modifications can be made. In any case, if the above-mentioned density difference ratio is within the above-mentioned preferable range (for example, within the range of 0.2% or more and 1.1% or less), the overall appearance of the baked substrate 210 is apparent. Since the uniformity of the density distribution in the green compact 40u based on the density can be improved, it is presumed that the possibility of cracking due to the apparent density deviation during hot pressing can be reduced.

(6) The configuration of the glow plug 10 is not limited to the configuration shown in FIG. 1, and various configurations can be employed. For example, the rear end 39 of the middle shaft 30 may be covered with a cap (not shown). As a method for manufacturing the glow plug 10, various methods including a step of fixing the ceramic heater 40 manufactured by the above-described manufacturing method to the metal shell 20 can be employed. The method of fixing the ceramic heater 40 to the metal shell 20 is not limited to the method of interposing the outer cylinder 70, and various methods such as a method of press-fitting the ceramic heater 40 into the through hole 25 can be employed.

  As mentioned above, although this invention was demonstrated based on the Example and the modification, Embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

10 ... Glow plug, 20 ... Metal fitting, 22 ... Male thread part, 25 ... Through hole, 28 ... Tool engagement part, 30 ... Middle shaft, 31 ... Tip ( Small diameter part), 39 ... rear end, 40 ... ceramic heater, 41 ... front end, 49 ... rear end, 40b ... fired body, 40u ... molded body, 50 ... first 1 insulating member, 60 ... second insulating member, 62 ... cylindrical part, 68 ... flange part, 70 ... outer cylinder, 71 ... thin part, 75 ... thick part, 80 ... crimping member, 90 ... electrode ring, 95 ... lead wire, 210 ... substrate, 210u ... molded ceramic material, 210u1 ... end, 211r ... recess, 211u Halved member, 220 ... heating element (heating element), 220u ... molded conductive material, 221 ... first lead part, 221u ... unfired first lead part, 222 ... second lead part, 222u ... unfired second lead part, 223 ... connecting part, 223u ... not yet 223h ... heat generating part, 224 ... support part, 281 ... first electrode extraction part, 281u ... unfired first electrode extraction part, 282 ... second electrode extraction Part, 282u ... unfired second electrode extraction part, 300 ... mold, 302 ... lower mold, 302p ... convex part, 304 ... outer frame, 304h ... opening, 306 ... Upper mold, 306p ... Convex part, 306x ... Molding projection, 400 ... Molding mold, 402 ... Lower mold, 402p ... Convex part, 404 ... Outer frame, 404h. ..Opening, 406 ... Upper mold, 406p ... Convex, 500 ... Mold, 502 ... Lower mold, 502p ... Convex, 504 ... Outer frame, 504h ... Opening, 506 ... Upper mold, 506p ... Projection, P1 ... First part (high density part), P2 ... Second part (low density part), CL ... Center axis (axis) )

Claims (2)

A method for manufacturing a ceramic heater, comprising: a base configured using an insulating ceramic; and a heating element embedded in the base,
Covering the conductive material that is a material of the heating element with an insulating ceramic material that is a material of the base body and includes a powdery portion;
The non-fired including the conductive material and a molded ceramic material that is a molded insulating ceramic material that covers the conductive material by press-molding the insulating ceramic material that covers the conductive material A step of molding the molded body of
Including
In the step of forming the green molded body,
A boundary between the conductive material and the molded ceramic material is determined from an apparent density of a first portion of the molded ceramic material that is away from the conductive material and includes the surface of the molded ceramic material. The difference obtained by subtracting the apparent density of the second portion including the density difference ratio, which is a ratio obtained by dividing the difference of the overall apparent density of the fired substrate obtained by firing the unfired molded body, The unsintered molded body is molded so as to be 0.2% or more and 1.1% or less,
Production method. The manufacturing method according to claim 1, further comprising:
When pressure is applied to the insulating ceramic material powder along one direction, a pressure at which cracks start to occur in the particles of the insulating ceramic material powder is 0.18 MPa or more and 0.36 MPa or less. It is characterized by being,
Production method.

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