JP4803651B2 - Method for manufacturing ceramic heater and method for manufacturing glow plug - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic heater in which a heat generating member made of conductive ceramic is embedded in a base made of insulating ceramic, and to a method for manufacturing a glow plug provided with the ceramic heater.

  A glow plug used as a starting aid for a diesel engine is a so-called metal glow plug that uses a heater in which an insulating ceramic powder and a metal heating coil are internally incorporated in a bottomed cylindrical metal sheath as a heater member. Has been used. In recent years, a ceramic glow plug using a ceramic heater in which a heat generating member made of conductive ceramic is embedded in an insulating ceramic base instead of such a heater is attracting attention from the viewpoint of heat resistance and durability. This is because the ceramic heater is excellent in durability over a long period of time and durability against rapid temperature rise.

  Due to the increasing environmental awareness on a global scale, which is increasing year by year, there is a demand for lower emissions of engines. In order to achieve low emissions, not only improvements to the engine itself, but also how to start and stabilize the engine efficiently is considered, and glow plugs are subject to more severe conditions and usage conditions. It is desirable to have the performance that can withstand. A ceramic heater is an example of a heater that meets such requirements.

  The ceramic heater is formed by combining an insulating ceramic and a conductive ceramic. There are a wide variety of types, in which the surface is heated by placing conductive ceramics that generate heat on its surface (see, for example, Patent Document 1). A heat generating member made of ceramic, a type in which a metal wire is incorporated as a lead wire for supplying power to the heat generating member (see, for example, Patent Document 2), and an all ceramic type in which the power supply lead wire is also configured as a conductive ceramic ( For example, it is various, such as patent document 3). (In this specification, the surface layer of the heater is a conductive ceramic as in Patent Document 1 is a surface heat generating type, and the surface layer of the heater is an insulating ceramic as in Patent Documents 2 and 3. The type in which the heat generating member is housed in the insulating ceramic is referred to as “internal heat generation type” for convenience.)

  In the surface heating type ceramic heater, the conductive ceramic constitutes the surface of the heater and is exposed, so there is a possibility that the characteristics of the heater may change if there is an adhering material on the heater surface, or external stress May cause cracks in the conductive ceramic. For this reason, especially in terms of durability, the internal heat generation type ceramic heater has an advantage. From such a viewpoint, it can be said that the internal heat generation type is preferable.

  By the way, as a method of manufacturing a ceramic heater, there is a method in which an unfired insulating ceramic is used as a base, and a conductive ceramic (and a metal wire) is contained inside and integrated, and then fired simultaneously. The type in which the metal wire is embedded in the insulating ceramic has a larger thermal expansion coefficient than that of the insulating ceramic or the conductive ceramic, so that a crack or the like is likely to occur and a defect is likely to occur. From this viewpoint, it can be said that the internal heat generation type, especially the all ceramic type, has an advantage in the manufacturing process.

According to Patent Document 3, the manufacturing method is as follows.
First, silicon nitride powder as a base is mixed and prepared with various materials and formed into a desired shape. Separately, a material to be a heating member is mixed and prepared, and a heating element pattern is formed in a desired shape on the substrate. The heater molded body thus obtained is fired in the range of 1700 ° C. to 1900 ° C. in an atmosphere having a nitrogen pressure of 1.5 atm or higher. Further, after the firing, hot isostatic pressure (HIP) firing is performed at 1600 ° C. to 1900 ° C. in an inert atmosphere of 1000 atm or more.
Special table 2003-503228 JP 2005-147533 A JP-A-10-106728

  When ceramic heaters were produced according to the above manufacturing method, those that could be produced “good” could have excellent durability. However, according to the present inventors' trial, it has been difficult to produce a “good” ceramic heater. This is thought to be based on the following differences.

  In Patent Document 3, an example of the manufacturing method is to obtain a heat generating member (heater molded body) by printing a conductive ceramic in a paste form, and the heat generating member is formed by forming a refractory metal compound into a heat generating body shape. It may be. Therefore, the present inventors previously formed a material constituting the heat generating member after firing, embedded the molded body in the material forming the insulating ceramic base after firing, and integrated the condition described in Patent Document 3 Ceramic heaters were produced by hot press firing and HIP firing at 1. However, few ceramic heaters produced by such a method could be produced “good”.

As a result of extensive research and trials by the inventors of the present invention, the following consideration was reached.
Since ceramic heaters, particularly those used for glow plugs, are rapidly heated, it is advantageous that the volume of the heat generating member is relatively large in order to uniformly heat the entire ceramic heater. It is preferable to make the heat generating member made of conductive ceramic relatively thick, and an attempt was made to produce a ceramic heater having such a configuration. However, even when hot press firing is performed in the production of a ceramic heater having a relatively thick heat generating member, firing in a state where a uniform pressure is applied to the entire ceramic heater is difficult. Therefore, since the ceramic heater is fired under non-uniform pressure, residual pores or the like are generated, resulting in a ceramic heater having defects. The effect of Patent Document 3 is that by performing HIP firing on such a ceramic heater, the substrate can be densified and a highly reliable ceramic heater can be expected.

  If the embedded heat generating member has a certain thickness unlike the paste, an adverse effect due to uneven pressure is likely to occur around the heat generating member. In order to eliminate the defects by HIP firing, a ceramic heater using a heat-generating member formed in a paste and a ceramic heater using a heat-generating member (molded body) formed thick in advance are good under the same conditions. Getting things is difficult.

  In order to realize a ceramic heater suitable for rapid temperature increase, the present inventors have found a specific shape and special firing conditions for the shape. An object of the present invention is to provide a method for manufacturing a ceramic heater for solving the above problems.

In order to solve the above problems, the present invention provides:
A method of manufacturing a ceramic heater comprising a structure in which a heat generating member made of a conductive ceramic is embedded in an insulating ceramic base mainly composed of silicon nitride,
The raw material that becomes the heat generating member after firing is injection-molded so as to have the above- described configuration to form an injection-molded body of the heat generating member, and the injection-molded body is integrally molded together with the insulating ceramic base by a pressing process. After forming things,
A first firing step of hot-press firing the integrally molded product at 1700 ° C. or higher;
A second firing step of performing HIP in a nitrogen atmosphere of 1500 to 1800 ° C. and 50 to 200 MPa after the hot pressing step;
It is characterized by providing.

  Further, a glow plug may be manufactured by electrically connecting a terminal metal fitting and a metal shell to one end and the other end of a heating member of a ceramic heater manufactured according to the present invention.

  With the ceramic heater manufacturing method described above, it is possible to manufacture a ceramic heater suitable for rapid temperature rise and a glow plug using the ceramic heater. In addition, in the manufacturing method of the ceramic heater of Claim 1, the structure which the metal lead wire and the electroconductive heat generating member are not connected in the inside of an insulating ceramic base is meant.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a glow plug 500 using a ceramic heater 100 manufactured by the manufacturing method of the present invention.

  The ceramic heater 100 has a rod shape extending in the direction of the axis O, and a heating member 20 made of ceramic that is fired in a substantially U shape and embedded in ceramic is embedded in the base 10 made of fired ceramic having insulation. It has a configuration. The front end (lower side of the drawing) of the heat generating member 20 has a U-shaped shape that is bent back and has a cross-sectional area that is smaller than the lead portions 21 and 22 that extend rearward. . On the other hand, on the rear end side of the heat generating member 20, electrode extraction portions 23 and 24 are formed from the lead portions 21 and 22 in the radial direction perpendicular to the axis O, respectively, so as to be exposed on the surface of the base 10. . The base 10 is an insulating ceramic base described in the claims, and the heat generating member 20 corresponds to a heat generating member made of conductive ceramic.

  For example, when the electrode lead-out portions 23 and 24 are configured as a glow plug 500 as shown in FIG. 1, the electrode lead-out portions 23 and 24 are connected to the positive electrode and the negative electrode of a power source for causing the ceramic heater 100 to generate heat. Is to be done. In the form of FIG. 1, the electrode extraction portion 23 is electrically connected to the metal shell 510, and the electrode extraction portion 24 is electrically connected to the center shaft 520. The glow plug 500 is electrically grounded at one end side (electrode extraction portion 23) of the heat generating member 20 when the male screw portion 511 is screwed into an engine (not shown). On the other hand, a positive terminal of a power source (not shown) (for example, a battery) is connected to the pin terminal 530 fixed to the rear end of the middle shaft 520, and power is supplied to the ceramic heater 100, whereby the glow plug 500 functions to generate heat. .

Now, a method for manufacturing the ceramic heater 100 of the present invention will be described.
FIG. 2 is a flowchart showing each manufacturing process of the ceramic heater 100. Each step is expressed as “S”. As shown in this flowchart, first, a material is prepared for the ceramic heater 100 (S1). In the material preparation step S1, the material of the base 10 and the material of the heat generating member 20 are separately prepared. The process for preparing the material of the substrate 10 includes silicon nitride (Si3N4) powder having an average particle size of 0.7 μm, rare earth oxide (Er2O3) as a sintering aid having an average particle size of 1.0 μm, and CrSi2 and WSi2. This is a step of performing wet mixing and grinding for 40 hours in ethanol using silicon nitride cobblestone. In this way, the material of the substrate 10 is obtained. On the other hand, the process for preparing the material of the heat generating member 20 includes silicon nitride (Si3N4) powder having an average particle diameter of 0.7 μm, tungsten carbide powder (WC), rare earth oxide (Er2O3) as a sintering aid, and an organic binder as a solvent. To obtain a slurry, and after stirring and drying, a material powder is obtained in this way.

  S <b> 2 is a step of forming the obtained materials so as to form the general shape of the ceramic heater 100. The material of the base 10 obtained in S1 is press-molded into the divided molded body 310 shown in FIG. On the other hand, the material of the heat generating member 20 is injection molded into an injection molded body 320 shown in FIG.

  Next, the obtained divided molded bodies 310 and 310 and the injection molded body 320 are pressed to obtain an integrally molded body 350 (integrated pressing step S3). In this step, the injection molded body 320 is accommodated in the concave portion of one divided molded body, sandwiched by the other divided molded body 310 to be paired, and pressed by a press machine not shown to form an integrally molded body 350. (The integrally molded body 350 is shown in FIG. 4).

  In the next degreasing step S4, the binder contained in the integrally molded body 350 is removed. In this treatment, the integrally molded body 350 is subjected to a binder removal treatment for 1 hour in a nitrogen atmosphere at 800 ° C.

  Next, baking is performed. In this firing step, hot press firing S5 as a first firing step and HIP firing S6 as a second firing step are performed. Detailed conditions of these first and second firing steps will be described later. A fired body 400 is obtained through firing.

  Next, an end cutting step for cutting the rear end of the fired body 400 is performed (S7). As shown in FIG. 5, this step is a step in which the rear end of the fired body 400 is cut in a cross section perpendicular to the axis, and the heat generating member 20 is opened from the closed circuit.

  Furthermore, the ceramic heater 100 is completed through the centerless polishing step S8. The completed ceramic heater 100 is configured such that the ratio of the volume occupied by the heat generating member 20 to the base body 10 is 10% or more.

Now, the firing conditions of the first and second firing steps described above will be described.
The present invention enables the ceramic heater 100 to be manufactured without defects depending on firing conditions. Table 1 below shows firing conditions as Examples 1 to 4 and Comparative Examples 1 to 4. The materials, dimensions, etc. of the ceramic heaters 100 produced in the respective examples and comparative examples are all the same as those described above.

  First, for comparison, the integrally molded body 350 is subjected to hot press firing for 2 hours under uniaxial pressure at 1780 ° C. and 25 MPa. Next, the HIP firing performed is performed in a nitrogen atmosphere with different firing temperatures and firing pressures (Comparative Example 1 does not perform HIP firing itself). The cross-section of each fired fired body 400 was observed, and the degree of remaining pores (residual pores) and the particle size were observed.

In Examples 1 to 4 in which the HIP firing conditions were 1500 ° C. or more and 1800 ° C. or less and the pressure was 50 MPa to 200 MPa, there were few residual pores, no abnormal grain growth was observed, and a good fired body 400 was obtained. Obtained. On the other hand, in Comparative Example 1 in which HIP firing was not performed, and in Comparative Example 2 in which HIP firing temperatures were less than 1300 ° C. and 1500 ° C., although no abnormal grain growth was observed, residual pores are examples of the present invention. Compared to 4, it was more. Moreover, about the comparative example 3 of the conditions which HIP baking temperature exceeded 1850 degreeC and 1800 degreeC, although there are few residual pores, it has grown abnormally and there exists a possibility that intensity | strength may fall. In Comparative Example 4 where the HIP firing pressure was as low as 0.9 MPa, the effect of reducing the residual pores due to HIP firing was small, and many residual pores were observed as in Comparative Examples 1 and 2.

As described above, when manufacturing a ceramic heater having a thick heat generating member in which the volume ratio of the conductive heat generating member to the insulating ceramic base is 10% or more, hot press firing at 1700 ° C. or higher is performed. It is effective to set the conditions for the HIP firing performed later to 1500 ° C. or higher and 1800 ° C. or lower and a nitrogen atmosphere of 50 MPa or higher and 200 MPa or lower.

  If a glow plug is manufactured using the ceramic heater manufactured in this way, a good one can be easily manufactured and also has excellent durability.

  Moreover, when manufacturing a ceramic heater in which the volume ratio of the heat generating member to the substrate is large as in the manufacturing method of the present invention, HIP baking is performed after the hot press baking, so that the heat generating member is formed before the HIP baking. It is possible to remove the microcracks and residual pores and manufacture a good ceramic heater. As a result, since cracks are formed, the resistance value of the heat generating member is slightly high, and even if variations occur, it is possible to reduce the adverse effects thereof.

FIG. 2 is a half sectional view of a ceramic heater 100 manufactured by the manufacturing method of the present invention and a half sectional view of a glow plug 500 manufactured using the ceramic heater 100. 3 is a flowchart showing each manufacturing process of the ceramic heater 100. It is a perspective view which shows the base | substrate 310 and the injection-molded body 320 before being integrated in an integrated press process. It is a figure which shows the integrally molded body 350 after an integral press process. It is a figure explaining the edge part cutting process performed after a baking process.

10 Insulating Ceramic Base 20 (Conductive Ceramic) Heating Member 100 Ceramic Heater 350 Integrated Molded Body 500 Glow Plug

Claims (2)

A method of manufacturing a ceramic heater comprising a structure in which a heat generating member made of a conductive ceramic is embedded in an insulating ceramic base mainly composed of silicon nitride,
In order to have the above-described configuration, the material that becomes the heat generating member after firing is injection molded to form an injection molded body of the heat generating member, and the injection molded body is integrally molded together with the insulating ceramic substrate by a pressing process. After forming things,
A first firing step of hot-press firing the integrally molded product at 1700 ° C. or higher;
A second firing step of performing HIP in a nitrogen atmosphere of 1500 to 1800 ° C. and 50 to 200 MPa after the hot pressing step;
A method of manufacturing a ceramic heater, comprising: For the ceramic heater manufactured by the method for manufacturing a ceramic heater according to claim 1,
A glow plug manufacturing method for manufacturing a glow plug by electrically connecting a terminal fitting and a metallic shell to one end and the other end of a heating member of the ceramic heater, respectively.

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