JP2014164984A - Manufacturing method for ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce ceramic heater manufacturing failures.SOLUTION: A molding die is used, which includes: a fold molding part, which is provided for molding an unbaked fold that is to be provided as a fold after baking; and a pair of lead molding parts, which is provided for molding a pair of unbaked leads that are to be provided as a pair of leads after baking and of which each one end is connected with each of both ends of the fold molding part. By using this molding die, mold material is injected from the other end of each of the pair of lead molding parts. Thereby, an unbaked resistor that is to be provided as a resistor after baking is molded by injection molding. In the molding die, the minimum cross-sectional area in a range from a channel for injecting the mold material into the pair of lead molding parts to the pair of lead molding parts is 15 to 35% of the maximum cross-sectional area in this range. The injection molding is carried out under the conditions in which the fusing point of wax contained in the mold material is 70 to 80°C, and the temperature of the mold material when injection takes place is 125 to 150°C.

Description

  The present invention relates to a method for manufacturing a ceramic heater.

  Ceramic heaters are used for glow plugs and the like for internal combustion engines. The resistor of the ceramic heater used for the glow plug is generally U-shaped as a whole, and the heating part at the tip (the lower half of the U-shaped part) and the lead part (U-shaped) connected to the heating part Straight line portion extending from the lower half circle). In order to reduce the manufacturing cost, it is preferable that the heat generating portion and the lead portion are integrally formed by injection molding with a homogeneous material. In order to ensure the temperature rise performance of the heat generating portion while using a homogeneous material, a method is known in which the heat generating portion is thin and the lead portion is thick (for example, Patent Document 1).

JP 2009-287920 A

  The problem of the prior art is that the production defects are not sufficiently reduced. As a cause of the manufacturing failure, for example, jetting or the like can be cited. Jetting means that when the molding material flows from a small-diameter part with a small cross-sectional area into a large-diameter part with a large cross-sectional area in the molding die, the inflow tip part remains thick with the same outer diameter as the inner diameter of the small-diameter part. This is a phenomenon in which the molding material flows into the diameter portion and the molding material is filled from the back in the inflow direction at the large diameter portion. When such jetting occurs, the melting of the molding material previously filled in the molding die and the molding material filled later is deteriorated, so that the filling property is lowered, and the inherent defect of the molded body is reduced. May cause this.

  SUMMARY An advantage of some aspects of the invention is to solve the above-described problems, and the invention can be implemented as the following forms.

(1) According to one aspect of the present invention, a U having a folded portion having a folded shape and a pair of lead portions each having one end connected to both ends of the folded portion and extending linearly. A method of manufacturing a ceramic heater having a letter-shaped resistor is provided. In this manufacturing method, a folded portion forming portion that forms an unfired folded portion that becomes the folded portion after firing, and a pair of unfired lead portions that become the pair of lead portions after firing, and each end portion on one side Using a molding die having a pair of lead part molding parts connected to both ends of the folded part molding part, respectively, and filling the molding material from each other end of the pair of lead part molding parts An injection molding step of molding an unfired resistor that becomes the resistor after firing by injection molding; in the molding die, a flow for filling the molding material into the pair of lead portion molding portions The minimum cross-sectional area in the range from the path to the pair of lead portion molding portions is 15 to 35% with respect to the maximum cross-sectional area in the range; and the injection molding step is performed on the wax contained in the molding material. Point a is 70 to 80 ° C., the temperature of the molding material during the filling is performed in conditions that are 125 to 150 ° C.. According to this manufacturing method, manufacturing defects such as jetting can be reduced.

(2) In the manufacturing method of the said form, the said injection molding process is performed on the conditions whose temperature of the said molding material at the time of filling is 125-140 degreeC. According to this manufacturing method, manufacturing defects are further reduced. In the said temperature range, volatilization of the plastic material (DBP (dibutyl phthalate) etc.) contained in a molding material is suppressed. Therefore, when the molding material is reused, the change in the fluidity of the molding material is reduced, and manufacturing defects are reduced.

  The present invention can be realized in various forms other than the above. For example, it can be realized as a method for manufacturing a resistor.

Sectional drawing of a glow plug. The figure explaining injection molding of an unbaking exothermic member.

  FIG. 1 shows a cross-sectional view of a glow plug 500. The glow plug 500 includes a ceramic heater 100. The ceramic heater 100 has a shape extending in the direction of the axis O as shown in FIG. The ceramic heater 100 includes a base 10 and a heating member 20 as shown in FIG. The substrate 10 is made of ceramic and is insulative.

  The heat generating member 20 is embedded in the base 10 as shown in FIG. The heat generating member 20 is made of ceramic and is conductive. The shape of the heat generating member 20 is substantially U-shaped as shown in FIGS. 1 and 2 (described later). The U-shaped folded portion (lower semicircular portion) is a tip portion 25 as a part of the heat generating member 20. A portion connected to the distal end portion 25 and extending along the axis O is a pair of first and second lead portions 21 and 22 as a part of the heat generating member 20. The cross-sectional area of the tip portion 25 is smaller than the cross-sectional areas of the first and second lead portions 21 and 22.

  As shown in FIG. 1, a first electrode extraction portion 23 is provided on the first lead portion 21, and a second electrode extraction portion 24 is provided on the second lead portion 22. As shown in FIG. 1, the first and second electrode extraction portions 23 and 24 protrude outward in the radial direction and are exposed on the surface of the base 10. The first and second electrode extraction portions 23 and 24 function as a gateway for current supplied to the heat generating member 20. The second electrode extraction portion 24 is disposed so as to be electrically connected to the middle shaft 520 and the pin terminal 530. As shown in FIG. 1, the middle shaft 520 is inserted into a hole in the metal shell 510 without contacting the substantially cylindrical metal shell 510 extending along the axis O. The pin terminal 530 is a metal member fixed to the rear end portion of the middle shaft 520 by caulking. The 1st electrode extraction part 23 is arrange | positioned so that it may be earth | grounded. This grounding is performed through a male screw portion 511 or the like for screwing to an attachment target (for example, an engine). The male screw portion 511 is formed on the outer peripheral surface on the rear end side of the metal shell 510. With such an arrangement, a current can be passed to the heat generating member 20 through the pin terminal 530.

  As shown in FIG. 1, the first and second electrode extraction portions 23 and 24 are arranged so that the positions in the axis O direction are different from each other. Specifically, the second electrode extraction portion 24 is disposed on the rear end side (upper side in FIG. 1) than the first electrode extraction portion 23.

  The ceramic heater 100 is manufactured by kneading a molding material for a heating member (hereinafter also referred to as “molding material”), molding an unsintered heating member by injection molding of the molding material, molding an unsintered substrate by press molding an insulating powder, This is performed by a process in the order of forming, degreasing, hot pressing, and polishing of an unsintered ceramic heater using an unsintered heating member and an unsintered substrate. Hereinafter, the kneading of the molding material and the injection molding of the unsintered heating member will be described in detail. The molding material is produced by kneading silicon nitride powder, tungsten carbide powder and binder with a kneader. The proportion of the binder in the kneaded product is preferably 45 to 55% by volume. The binder configuration is preferably, for example, as follows. The constitution is such that wax (paraffin wax or microcrystalline wax or the like) is 50 to 80% by mass (59% by mass is particularly preferable), and plasticizer (DBP or DOP (dioctyl phthalate)) is 5 to 30% by mass (20 Mass% is particularly preferred), thermoplastic resin (polypropylene) is 20-30 mass% (20 mass% is particularly preferred), and lubricant (surfactant such as polyoxyethylene) is 1 mass%. The melting point of the wax is preferably 70 to 80 ° C.

As conditions for injection molding of the unsintered heat generating member, for example, when the total length of the flow path for injection molding (the total length of the unsintered heat generating member) is 42 mm, the injection speed is 12 to 40 cm ³ / s, and the mold volume is 8.0 cm ³ and the mold temperature is preferably 30 ° C. The total length of the flow path for injection molding is the length from the front end molding portion 225 to the filling flow path 227 (see FIG. 2).

  Table 1 shows the experimental results on the influence of the molding temperature (the temperature of the molding material when filled) on each defect. In the experiment, the presence or absence of jetting, the presence or absence of pores, and thermal shock resistance were evaluated. In the jetting evaluation, a case where jetting occurred was determined as “present”, and a case where jetting did not occur was determined as “absent”. In the pore evaluation, it was determined that “exist” when the pore occurred and “absent” when the pore did not occur.

  The conditions for the thermal shock resistance test are as follows. A voltage is applied to the heat generating member 20 so as to reach 1000 ° C. in 0.5 seconds from the start of voltage application, and the temperature is increased to 1350 ° C. while maintaining the temperature rising rate. Thereafter, the voltage application is stopped and cooling is performed for 30 seconds. These procedures are defined as one cycle. Even if 50,000 cycles were completed, if it was not disconnected, it was determined as “OK”. If it was disconnected before 50,000 cycles were completed, it was determined as “NG”.

  As shown in Table 1, when the molding temperature was 125 ° C. or higher (NO. 3 to 7), no jetting occurred and the thermal shock resistance was OK (within an allowable range). Therefore, the molding temperature is preferably 125 ° C. or higher.

  Further, as shown in Table 1, when the molding temperature was 150 ° C. or lower (NO. 1 to 6), no pore was generated. Therefore, the molding temperature is preferably 150 ° C. or lower. A pore is a small hole. As a cause of the occurrence of pores, volatilization of a binder and a plasticizer can be mentioned. This volatilization is accelerated as the molding temperature increases. For this reason, pores were not generated at a molding temperature of 150 ° C. or lower, whereas pores were considered to be generated at a molding temperature of 160 ° C. (NO. 7) because the binder and plasticizer were volatilized.

  The influence of the molding temperature on jetting and thermal shock resistance will be described. FIG. 2 is a cross-sectional view for explaining injection molding of an unfired heat generating member. A molding die 300 is used for this injection molding. The molding die 300 has a flow path for molding an unfired heating member that becomes the heating member 20 after firing. This flow path is divided into first and second lead part molding parts 221, 222, first and second electrode extraction part molding parts 223, 224, a tip part molding part 225, and a filling flow path 227. Can do.

  2A shows the state of injection molding when the molding temperature is 110 to 120 ° C. (NO. 1 to 2), and FIG. 2B shows the case where the molding temperature is 125 to 150 ° C. (NO. 3 to 6). ) Is a diagram for explaining the state of injection molding, and is a cross-sectional view showing a flow path for injection molding provided inside the molding die 300. FIG. FIG. 2C is a cross-sectional view of FIGS. 2A and 2B viewed from below. However, FIG. 2C illustrates only the flow path for injection molding.

  The molding material is filled into the flow path inside the molding die 300 through the filling flow path 227. As a result, the filling channel 227 is also filled with the molding material. The molding material filled in the filling channel 227 is removed after firing.

  The arrows shown in FIGS. 2A and 2B schematically show how the molten molding material flows inside the molding die 300. As shown in FIG. 2 (A), the melted molding material is formed through the filling channel 227 to form a first lead portion molding portion that molds an unfired first lead portion that becomes the first lead portion 21 after firing. 221 and a second lead part molding part 222 for molding an unfired second lead part that becomes the second lead part 21 after firing. Each flow goes to a tip portion forming part 225 that forms an unfired tip portion that becomes the tip portion 25 after firing.

  As shown in FIG. 2A, when the molding temperature is 110 to 120 ° C., the first lead portion molding portion 221 and the first lead portion molding portion 221 and the first lead portion molding portion 225 are slightly displaced from the vicinity of the front end to the rear end side. The molding material flowing through the two-lead part molding part 222 joins. The reason for joining at the position shifted to the rear end side in this way is considered to be that jetting occurs in the first lead portion molding portion 221 and the flow becomes faster than the flow of the second lead portion molding portion 222. Jetting here refers to the fact that when the molding material flows into the first lead portion molding part 221 having a larger inner diameter than the filling channel 227 via the filling channel 227, the inflow tip is solidified. This is a phenomenon that occurs because the molding material spreads into the inner wall of the first lead portion molding portion 221 and is not filled with the material, but vigorously flows into the first lead portion molding portion 221. The occurrence of such jetting can be confirmed by observing whether or not the molding material is sequentially filled from the boundary portion between the filling flow path 227 and the first lead portion molding portion 221 by short shot molding.

  On the other hand, in the second lead part molding part 222, unlike the first lead part molding part 221, jetting hardly occurs. This is because, in the second lead portion molding portion 222, the solidified molding material is captured by the second electrode extraction portion molding portion 224 that forms the unfired second electrode extraction portion that becomes the second electrode extraction portion 24 after firing. Because. The solidified molding material is captured by the second electrode extraction part molding part 224 because the second electrode extraction part molding part 224 is close to the filling channel 227. On the other hand, the first electrode extraction part forming part 223 for forming the unfired first electrode extraction part which becomes the first electrode extraction part 23 after firing is far from the filling flow path 227, so that it is near the filling flow path 227. Hardly captures the solidified molding material. As a result, jetting is more likely to occur in the first lead part molding part 221 than in the second lead part molding part 222.

  A weld is likely to occur at a portion where the molding materials flowing through the first lead portion molding portion 221 and the second lead portion molding portion 222 merge. The weld is a portion where the molding material flows in the molding die 300 and the molding material is insufficiently fused. Since the filling density of the molding material is low in the portion where the weld is generated, if the weld is a part of the unfired heat generating member and occurs at a portion corresponding to a portion where the heat generating member 20 generates a high temperature, there is a problem. May occur. The portion of the heat generating member 20 where the maximum temperature is reached is a position slightly shifted from the vicinity of the front end to the rear end side. Therefore, when the molding temperature is 110 to 120 ° C., there is a high possibility that a problem occurs when a weld occurs in a portion where the molding material flowing through the first lead portion molding portion 221 and the second lead portion molding portion 222 joins.

  On the other hand, as shown in FIG. 2B, when the molding temperature is 125 to 150 ° C., the molding material flowing through the first lead portion molding portion 221 and the molding material flowing through the second lead portion molding portion 222 are: It merges in the vicinity of the tip in the tip part molding part 225. As a result, even if the weld is generated, it is generated at a site different from the site where the maximum temperature is reached, so that the possibility of occurrence of a malfunction is low. The molding material flowing through the first lead part molding part 221 and the second lead part molding part 222 merges in the vicinity of the tip of the tip part molding part 225 because the first lead part molding part 221 and the second lead part molding part 222 are joined together. This is because the speed of the flowing molding material is about the same. The speed of the molding material flowing through the first lead part molding part 221 and the second lead part molding part 222 is about the same, unlike the case where the molding temperature is 110 to 120 ° C., because the molding temperature is high. This is probably because jetting is unlikely to occur in the molded part.

  Furthermore, since the molding temperature is high, the occurrence of weld itself can be suppressed. When the molding temperature is high, there is a high possibility that the molding material is sufficiently melted even when the molding materials flowing through the first lead part molding part 221 and the second lead part molding part 222 merge. If the molding material is sufficiently melted at the time of merging, the filling density is increased at the merged portion. As a result, the occurrence of welds is suppressed.

  In addition, when the molding temperature is high, solidification of the inflow tip portion in the first lead portion molding portion 221 can be suppressed, so that the occurrence of jetting is suppressed. Furthermore, when the molding temperature is high, the viscosity of the molding material decreases, thereby increasing the fluidity of the molding material. When the fluidity increases, the injection speed can be decreased. As a result, it is easy to suppress jetting by slowing the injection speed.

  As described above, this embodiment can suppress jetting. In the present embodiment, jetting can be suppressed by paying attention to the molding temperature and further adjusting the melting point of the wax.

  Further, as described above, the thermal shock resistance was OK when the molding temperature was 125 ° C. or higher (NO. 3 to 7). The reason is considered that jetting did not occur.

  The molding temperature is particularly preferably 125 to 140 ° C. (NO. 3 to 5). When the temperature is 140 ° C. or lower, the volatilization of the plasticizer is further suppressed. As a result, the change in fluidity when the molding material is reused is reduced. The smaller the change in fluidity, the more stable the production.

  Next, the experimental result about the influence which the cross-sectional area ratio in the shaping die 300 gives to each malfunction is shown. In the experiment, the presence or absence of jetting and the tip filling property were evaluated. In the jetting evaluation, a case where jetting occurred was determined as “present”, and a case where jetting did not occur was determined as “absent”. In addition, in the tip filling property evaluation, it is confirmed whether or not the molding material is filled up to the unfired tip in the unfired heating member after injection molding. “NG”, and the case where no filling failure occurred was determined as “OK”.

  As shown in Table 2, when the cross-sectional area ratio in the molding die 300 is 15 to 35% (NO. 14, 15, 18, 19, 22, 23), jetting did not occur and the tip filling property Was also good. The cross-sectional area ratio is the ratio between the minimum value of the cross-sectional area in the range from the first and second lead portion molding parts 221 and 222 to the filling flow path 227 and the maximum value of the cross-sectional area in that range. . The section mentioned here satisfies that the direction of the normal line coincides with the direction of flow of the molding material.

  When the cross-sectional area ratio is less than 15% (NO. 10, 11), the pressure loss during material filling is large. As a result, although jetting did not occur, the filling property of the molding material at the tip of the unfired heat generating member was poor, which is not preferable. On the other hand, when it exceeds 35%, since the cross-sectional area ratio is large, jetting does not occur even if the molding temperature is low, and thus the present invention may not be applied. When the end surfaces of the first and second lead portions 21 and 22 are exposed on the rear end surface of the heat generating member 20, the tensile stress between the first and second lead portions 21 and 22 is increased when the exposed area is increased. It may become large and cracks may occur. For this reason, the crack which generate | occur | produces in the heat generating member 20 can also be suppressed by making a cross-sectional area ratio into 35% or less.

  In addition, when determining the maximum value of the cross-sectional area, a portion including the first and second electrode extraction portion molding portions 223 and 224 is excluded. The portion having the smallest cross-sectional area is any cross-section of the filling channel 227 in the case illustrated in FIG. 2.

  The present invention is not limited to the above-described embodiments and examples, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and examples corresponding to the technical features in each embodiment described in the summary section of the invention may be used to solve part or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be performed as appropriate. If the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Base | substrate 20 ... Heat generating member 21 ... 1st lead part 22 ... 2nd lead part 23 ... 1st electrode extraction part 24 ... 2nd electrode extraction part 25 ... Tip part 100 ... Ceramic heater 221 ... 1st lead part shaping | molding part 222 ... second lead part molding part 223 ... first electrode extraction part molding part 224 ... second electrode extraction part molding part 225 ... tip part molding part 227 ... filling channel 300 ... molding die 500 ... glow plug 510 ... metal shell 511 ... Male thread 520 ... Middle shaft 530 ... Pin terminal

Claims (2)

Method of manufacturing a ceramic heater comprising a U-shaped resistor having a folded portion having a folded shape and a pair of lead portions each having one end connected to both ends of the folded portion and extending linearly Because
A folded portion forming portion that forms an unfired folded portion that becomes the folded portion after firing, and a pair of unfired lead portions that become the pair of lead portions after firing, each one end portion of which is the folded portion, respectively. By using a molding die having a pair of lead part molding parts connected to both ends of the molding part, and filling the molding material from each other end of the pair of lead part molding parts, An injection molding process for molding an unfired resistor that becomes a resistor by injection molding,
In the molding die, the minimum cross-sectional area in the range from the flow path for filling the molding material to the pair of lead part molding parts to the pair of lead part molding parts is the maximum cross-sectional area in the range. 15 to 35%,
The said injection molding process is a manufacturing method of the ceramic heater performed on the conditions whose melting | fusing point of the wax contained in the said molding material is 70-80 degreeC, and the temperature of the said molding material at the time of filling is 125-150 degreeC. The method for manufacturing a ceramic heater according to claim 1, wherein the injection molding step is performed under a condition that a temperature of the molding material at the time of filling is 125 to 140 ° C.

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