JP4024612B2 - Thermistor manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermistor manufacturing method suitable as a temperature detection element such as a temperature sensor.
[0002]
[Prior art]
Conventionally, a thermistor has been used as an element for a temperature sensor for measuring an exhaust gas temperature or the like of an automobile, and in recent years, there has been a demand for higher accuracy in temperature detection. As such a thermistor, for example, a bead type thermistor shown in FIG. 14 is known. The thermistor 101 is configured by extending a pair of electrodes 103 in parallel from the side surface (curved surface) of a cylindrical element body 102 serving as a detection unit, and the manufacture thereof is performed, for example, as follows.
[0003]
First, Y ₂ O _Three , SrCO _Three , Cr ₂ O _Three , Fe ₂ O _Three , And TiO ₂ Are weighed to a predetermined ratio, mixed by a wet method, dried, and then calcined. At this time, a predetermined amount of a sintering aid is added to the calcined powder, wet pulverized, and dried. Then, after drying, a predetermined binder is added to granulate the ceramic powder M.
[0004]
Then, using a mold 150 as shown in FIG. 15, ceramic powder M is press-bonded to the tip of a platinum or platinum rhodium alloy wire that becomes the long electrode 103 to form the element body 102. Here, FIG. 15 is a vertical cross-sectional view of the mold 150 and the thermistor molded body 111 during the pressing process, and FIG. 16 corresponds to the EE cross section, and the mold 150 is divided (partition) after the pressing process. It is explanatory drawing showing the press post-processing process to perform.
[0005]
That is, the mold 150 includes a female mold 160 for inserting and fixing the electrode 103 and filling the ceramic powder M therein, and a male mold 170 for pressing the ceramic powder M up and down using a pressing device (not shown). It is composed of The female mold 160 and the male mold 170 are configured so as to be divided vertically, and the female mold 160 includes an upper mold 161 and a lower mold 162 that form a through-hole 163 having a circular cross section in the vertical direction. Includes a cylindrical upper mold 171 and a lower mold 172 each having an outer diameter substantially the same as the inner diameter of the through-hole 163. In addition, a pair of semicircular cross-sectional long grooves 165 and 166 are provided in parallel to each other at a predetermined interval on the contact surface between the upper die 161 and the lower die 162 of the female die 160. These long grooves 165 and 166 are provided so as to communicate with the through hole 163 from one end of the side surfaces of the upper mold 161 and the lower mold 162, and when the upper mold 161 and the lower mold 162 are installed facing each other. In addition, a pair of insertion holes 164 parallel to each other for inserting the electrodes 103 are formed.
[0006]
Then, the upper mold 161 and the lower mold 162 are installed in combination, and the lower mold 172 of the male mold 170 is first inserted into the through-hole 163 from below, and the upper surface position of the lower mold 172 is the electrode insertion position. It is set at a predetermined position that is higher than (the central axis of the insertion hole 164). Subsequently, the ceramic powder M is put into the through-hole 163 from above, and the upper mold 171 is inserted and set from above the through-hole 163. The male mold 170 and the female mold 160 are inserted into the through-hole 163. A ceramic powder M is filled in the internal space S surrounded by each inner surface.
[0007]
At the same time, the lower mold 172 of the male mold 170 is lowered to a position where the vertical center of the filled ceramic powder M and the electrode insertion position (center axis of the insertion hole 164) match (overlap), The upper die 171 is also lowered, and centering is performed so that the distance from the electrode insertion position to the surface of the upper die 171 and the lower die 172 facing the ceramic powder M becomes equal.
[0008]
Subsequently, the two electrodes 103 are respectively inserted into the insertion holes 164, and their tip portions are protruded into the through holes 163, and are embedded in the ceramic powder M by a predetermined electrode insertion amount.
Then, the thermistor molded body 111 is formed by pressing the upper mold 171 and the lower mold 172 of the male mold 170 at a constant pressure with a predetermined pressure using a pressing device (not shown). At this time, the electrode 103 is pressure-bonded to the center in the vertical direction of the element body 102.
[0009]
Thereafter, the male mold 170 is removed vertically, and the female mold 160 is further divided vertically so that the thermistor molded body 111 is taken out. The thermistor 101 is obtained by firing the thermistor molded body 111 in a high-temperature atmosphere.
[0010]
[Problems to be solved by the invention]
However, as shown in FIGS. 15 and 16, in the method of manufacturing the thermistor 101, the pressing direction and the mold dividing direction (the female dividing direction) are the same direction, and the electrode 103 is the upper mold of the female mold 160. 161 and the lower mold 162 are arranged on the dividing surface. For this reason, when the mold is divided after the pressing step, a tensile stress in a direction away from each electrode 103 is applied to the element main body 102 due to a pressing force and a frictional force between the inner surface of each mold and the outer surface of the element main body 102. appear. As a result, there is a problem that cracks are generated on the electrode insertion portion or the outer peripheral surface parallel to the longitudinal direction of the electrode in the element body 102, which is weak in strength.
[0011]
The thermistor 101 has a configuration in which two electrodes 103 are inserted through the curved surface of the element body 102, and the electrode 103 and the element body 102 form an obtuse angle at the electrode insertion portion as shown in FIG. For this reason, when the position of the electrode 103 is shifted due to the clearance between the insertion hole 164 formed between the upper mold 161 and the lower mold 162 of the female mold 160 and the electrode 103, as shown in FIG. There is a possibility that the insertion length (electrode insertion amount) of the electrode 103 may vary. Such variation in the insertion length changes the volume of the element body 102 surrounded by the tip portion of the electrode 103, and consequently changes the resistance value of the thermistor 101, thus reducing the temperature detection accuracy. There was a problem. In addition, since the element body 102 and the electrode 103 form an obtuse angle at the electrode insertion portion as described above, the portion of the element body 102 positioned between the electrodes 103 and the electrode 103 are not positioned between the electrodes 103. Since the relative volume of the element main body 102 located on the obtuse angle side is different, there is a problem that peeling occurs between the obtuse angle side of the electrode 103 and the element main body 102 due to a difference in thermal shrinkage during firing (see FIG. 17). was there.
[0012]
On the other hand, what is shown in FIG. 19 is known as another structure of the thermistor. The thermistor 111 is configured by extending a pair of electrodes 113 from the upper surface (plane) of a cylindrical element body 112. In the manufacturing method of the thermistor 101 described above, the electrode 113 is inserted with the insertion direction thereof changed by 90 degrees, and the element body 112 is formed by pressing in the vertical direction.
[0013]
However, in such a configuration, since the press direction and the insertion direction of the electrode 113 are the same, when the load of the press is released, a so-called springback phenomenon occurs in which the element body 112 expands in a direction opposite to the direction of the press load, The insertion length of the electrode 113 with respect to the element main body 112 changes by the amount of the spring back. Since the amount of spring back also varies slightly depending on various factors such as the amount of ceramic powder charged, the insertion length of the electrode 113 varies depending on the manufacturing process of the thermistor 111. In addition, depending on the pressing direction, variation in shrinkage rate during firing of the element body 102 occurs, and thus variation in electrode insertion length after firing is promoted. The variation in the insertion length has a problem that the resistance value of the thermistor 111 is changed and the temperature detection accuracy is lowered.
[0014]
The present invention has been made in view of these problems, and provides a method for manufacturing a thermistor that can suppress or prevent the occurrence of cracks in an electrode insertion portion during thermistor manufacture and can suppress variations in resistance values. Objective.
[0015]
[Means for Solving the Problems and Effects of the Invention]
In view of the above problems, in the method of manufacturing the thermistor according to claim 1, in the pre-press treatment step, the side wall of the split mold is penetrated and extends toward the internal space formed when the mold is assembled. The electrodes extending in the longitudinal direction are respectively inserted into the pair of insertion holes, and one end side of the electrodes is embedded in a predetermined ceramic powder put into the internal space.
[0016]
As used herein, the term “split mold” refers to a mold that is configured so that at least a female mold divides an internal space and can be divided into a plurality of sections. It is formed by a region surrounded by the mating male mold.
Further, the “predetermined ceramic powder” means a powder composed of a plurality of predetermined compositions as described in, for example, Examples described later.
[0017]
Next, in the pressing step, this ceramic powder is pressed in one direction using a pressing device. At this time, an element body which is a press-molded body of the ceramic powder is molded, and a thermistor molded body in which a part of the electrode extends outward from the element body is obtained.
[0018]
Next, in the post-press treatment step, the mold is divided and the thermistor molded body is taken out of the mold and fired.
And in the thermistor manufacturing method of the said Claim 1, in such a series of processes, the press direction in the said press process and the division | segmentation direction (namely, mold split direction) of the metal mold | die in the said post-press treatment process are substantially. It is set so that it may become a right angle, and the division surface of a metal mold | die is provided in the position remove | deviated from the said insertion hole.
[0019]
According to such a configuration, the mold dividing surface is provided at a position away from the insertion hole. Because In other words, since the mold dividing surface is provided at a position that does not divide the insertion hole, it is possible to prevent the peeling force from directly acting between the electrode and the element main body when dividing the mold. Generation of cracks at the electrode insertion portion can be effectively prevented. Further, in this case, for example, if the pressing direction and the splitting direction are set to be parallel (in the same direction), the thermistor molded body is fitted and held in one mold after press molding due to its configuration. It is assumed that the thermistor molded body cannot be pulled out after the mold is split. However, in the present invention, since the pressing direction and the splitting direction are set to be substantially perpendicular, the area of the molded body fitted and clamped to one mold can be reduced. The thermistor molded body can be pulled out later.
[0020]
Also, Another form Similarly, in the thermistor manufacturing method, in the pre-press processing step, a longitudinal direction is formed in a pair of insertion holes extending through the side wall of the split mold and extending toward the internal space formed when the mold is assembled. Each of the electrodes extending in the space is inserted, and one end side of the electrode is embedded in a predetermined ceramic powder put into the internal space.
[0021]
Here, the “insertion hole” includes not only an insertion hole provided only in one of the divided molds but also an insertion hole formed when both molds are assembled.
Next, in the pressing step, this ceramic powder is pressed in one direction using a pressing device. At this time, an element body which is a press-molded body of the ceramic powder is molded, and a thermistor molded body in which a part of the electrode extends outward from the element body is obtained.
[0022]
Next, in the post-press treatment step, the mold is divided and the thermistor molded body is taken out of the mold and fired.
In such a series of steps, among the inner surfaces facing the inner space of the mold, the inner surface including the opening end of the insertion hole and corresponding to the electrode insertion surface of the element body has its surface direction of the electrode. It is comprised so that it may become substantially right angle with respect to the longitudinal direction of this, and the press direction in a press process is set so that it may become substantially right angle with respect to the longitudinal direction of an electrode.
[0023]
According to such a configuration, of the inner surface of the mold, the inner surface including the opening end of the insertion hole and corresponding to the electrode insertion surface of the element body is such that its surface direction is substantially perpendicular to the longitudinal direction of the electrode. Therefore, the shape of the electrode insertion surface of the element body to be molded is flat in a form orthogonal to the longitudinal direction of the electrode. For this reason, it is effective that each electrode insertion length in the element body changes relatively even if the electrode is displaced in a direction perpendicular to the longitudinal direction due to a clearance between the insertion hole and the like at the time of manufacture. Can be suppressed. In addition, since the electrode insertion surface is configured flat as described above, the electrode insertion portion between the element body and the electrode does not form an obtuse angle, so part of the element body is peeled off due to the difference in thermal shrinkage during firing. Can be suppressed.
[0024]
In addition, since the pressing direction is substantially perpendicular to the longitudinal direction of the electrode, the influence of the springback phenomenon in the longitudinal direction of the electrode is reduced, and variation in the insertion length of each electrode into the element body is reduced. In addition, it is possible to reduce the influence of variation in shrinkage ratio in the element body during firing. As a result, problems such as variations in the electrode insertion length of each electrode with respect to the element body do not occur.
[0025]
For this reason, it is possible to suppress or prevent variation in the insertion length of the electrode with respect to the element body. As a result, variation in the temperature resistance value of the thermistor can be prevented, and the temperature detection accuracy can be kept high.
In addition, from the viewpoint of suppressing variation in electrode insertion with respect to the element body of each electrode, Claim 2 In the method for manufacturing the thermistor according to claim 1, the inner surface corresponding to the electrode insertion surface of the element body including the open end of the insertion hole among the inner surfaces facing the inner space of the mold It is preferable that the flat surface direction is substantially perpendicular to the longitudinal direction of the electrode.
[0026]
In addition, as described above, the mold is divided into a plurality of parts in the post-press processing step, but the direction in which the mold is divided and separated from the contact surface between the element body and the mold (that is, the mold division). When there is a corresponding contact surface that is parallel to the direction), a large frictional force is generated between the mold and the element body when the mold is divided, and a large tensile stress is generated in the element body due to the frictional force. It will be.
[0027]
Therefore, Claim 3 As described in the above, the inner surface facing the inner space of the mold is configured to have a shape that reduces the cross-sectional dimension in the direction in which the element body divides and separates the mold. Is preferred.
For example, as described in the embodiments described later, it is conceivable to configure the inside of the mold so as to have a tapered shape or a curved shape that decreases in the split direction.
[0028]
According to such a configuration, it is possible to prevent or suppress the generation of frictional force between the mold and the element body in the process of dividing the mold, and to effectively prevent the thermistor molded body from being damaged.
Furthermore, after the mold is divided in the post-press treatment step, the thermistor molded body is taken out from the mold. However, the thermistor molded body is provided at a position where the divided surface of the mold is removed from the insertion hole. Since it remains in the mold on the side where the insertion hole is formed, it is necessary to remove it from the mold.
[0029]
And when removing a thermistor molded object from the metal mold | die in the side in which the penetration hole was formed, the technique etc. which hold | grip a part of the thermistor molded object with a jig | tool (chuck), etc. are employable. However, when the thermistor molded body is gripped with a jig, it is necessary to grip it carefully, which is troublesome.
[0030]
Therefore Claim 4 As described above, in the post-press processing step, after the mold is divided, the electrode inserted through the insertion hole of the mold is directed from the side wall side toward the side where the internal space is to be formed. The thermistor molded body may be removed from the mold by extrusion.
[0031]
According to this configuration, the thermistor molded body can be easily taken out from the mold on the side where the insertion hole is formed.
further Claim 5 As described in the above, if at least the contact surface with the element body in each mold is pre-wrapped, the element body can be effectively prevented or suppressed from being crimped to the mold on its surface, The thermistor molded body can be removed from the mold with a small force.
[0032]
As used herein, the term “substantially right angle” includes a range of a predetermined angle centered on a right angle (for example, within ± 3 ° from a right angle) so that the effects of the invention can be obtained. And a right angle is desirable.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a plan view of the thermistor according to the first embodiment of the present invention, FIG. 2 is a side view seen from the A direction, and FIG. 3 is a side view seen from the B direction. For the sake of convenience, the upper and lower sides of the thermistor 1 shown in FIG. 1 are assumed to be the front and rear of the thermistor 1 (the side where the electrode 21 extends outward from the element body 10 is the rear). The description will be continued below with the direction to be performed as the vertical direction.
[0034]
As shown in these drawings, the thermistor 1 includes an element body 10 made of a ceramic powder press-molded body, and a pair of electrodes extending vertically from one side surface (electrode insertion surface) of the element body 10 and extending in parallel to each other. 21.
The element body 10 has a hexagonal column shape, and each side surface is formed flat. The cross section is composed of two long sides parallel to each other in the front and back and four short sides on the left and right connecting the long sides, and is formed so as to be symmetrical in the front and rear left and right. And it has the aspect by which the electrodes 21 and 21 were inserted from one side which has this long side. In the present embodiment, the length L1 in the front-rear direction of the element body 10 is 2.24 mm, the maximum width W1 in the left-right direction is 2.30 mm, the length W2 of the long side is 1.70 mm, and the thickness t (see FIG. 2). Is 1.24 mm. In addition, an angle (that is, a taper angle) α formed between each of the left and right short sides and a virtual line K in a direction parallel to the longitudinal direction of the electrode 21 is about 15 °.
[0035]
The electrode 21 is made of a platinum wire having a diameter d1 of about 0.3 mm extending in the longitudinal direction, and a portion having a length L (about 1.45 mm) at the front end thereof is inserted (embedded) in the element body 10. (The broken line portion in the figure: hereinafter, the length L of the inserted portion is also referred to as “electrode insertion amount”). The pair of electrodes 21 are arranged in parallel to each other with a space W3 (see FIG. 3) (about 1.10 mm) at positions symmetrical with respect to the element body 10. The total length L2 of the thermistor 1 including the element body 10 and the electrode 21 is formed to be about 5.50 mm.
[0036]
Next, the manufacturing method of the thermistor 1 is demonstrated based on FIGS.
First, a pre-pressing process for producing a ceramic powder used when the element body 10 is press-molded is performed.
In this press pretreatment process, first, Y having a purity of 99.9% or more and an average particle diameter of 1 μm. ₂ O _Three And SrCO having a purity of 98.5% or more and an average particle diameter of 1 μm. _Three Cr having a purity of 98.5% or more and an average particle diameter of 1 μm ₂ O _Three Fe with a purity of 98.5% or more and an average particle diameter of 1 μm ₂ O _Three TiO with a purity of 98.5% or more and an average particle diameter of 1 μm ₂ And (Y _1-x , Sr _x ) (Cr _1-yz , Fe _y , Ti _z ) O _Three , Weighed so that x = 0.070, y = 0.219, z = 0.05, mixed by wet, dried, and then held at 1400 ° C. for 2 hours for calcination To do.
[0037]
And, this calcined powder has a mean particle size of 0.6 μm as a sintering aid. ₂ 1% by weight of the powder is added, mixed and pulverized by a wet method, and then dried to obtain a dry powder. Then, 15% by weight of PVB (polyvinyl butyral), 10% by weight of DBP (n-butyl phthalate), 50% by weight of MEK (methyl ethyl ketone) and 25% by weight of toluene and acetone are added to this dry powder. , Mixed and dried, and the powder obtained at this time is sized to obtain ceramic powder M for press molding.
[0038]
Subsequently, a mold is installed in preparation for the subsequent pressing process. In this pressing step, a split mold 50 shown in FIGS. 4 and 5 is used. FIG. 4 is an explanatory view showing a longitudinal section of the mold 50 in the pressing step, and FIG. 5 is an explanatory view showing a CC section thereof.
[0039]
That is, the mold 50 includes a female mold 60 having a through hole 65 penetrating the center in the vertical direction, and a male mold 70 inserted through the through hole 65.
The female die 60 is configured to be divided into two parts in the front-rear direction with the center of the through-hole 65 as a boundary. One of the divided portions constitutes a first female die 61 and the other constitutes a second female die 62. The through-hole 65 configured by assembling the first female mold 61 and the second female mold 62 has a hexagonal cross-sectional shape that is substantially equal to the cross-sectional shape of the element body 10. Further, the first female die 61 is provided with a pair of insertion holes 63, 63 that penetrates the center of the side wall horizontally. The insertion hole 63 is formed in a circular cross-sectional shape having an inner diameter that is substantially the same as the outer diameter of the electrode 21, and is disposed at the same height and in parallel with each other at substantially the same interval as the interval W3 between the electrodes 21, 21 described above. Has been. Therefore, the dividing surface of the female die 60 is at a position away from the insertion holes 63 and 63.
[0040]
On the other hand, the male mold 70 includes a first male mold 71 inserted from above along the through hole 65 of the female mold 60 and a second male mold 72 inserted from below into the through hole 65. . The first male mold 71 and the second male mold 72 are each configured in a hexagonal column shape having substantially the same cross-sectional shape as the element body 10. Then, the internal space S is formed in the mold 50 by assembling the female mold 60 and the male mold 70.
[0041]
The contact surface between the inner surface of the female die 60 and the element body 10 at the end face of each male die 71, 72 is lapped in advance so as to satisfy the center line average roughness (Ra) = 0.2 μm or less. Has been made.
First, the first female mold 61 and the second female mold 62 are assembled and the female mold 60 is installed. First, the second male mold 72 is inserted into the through-hole 65 from below, and the upper surface of the second male mold 72 is inserted. The position is set to a predetermined position that is higher than the electrode insertion position (the central axis of the insertion hole 63). Subsequently, the ceramic powder M is put into the through-hole 65 from above, and the first male mold 71 is inserted and set from above the through-hole 65, and the male mold 70 and the female mold are inserted into the through-hole 65. A ceramic powder M is filled in an internal space S surrounded by each inner surface of 60.
[0042]
At the same time, the second male die 72 is lowered to a position where the vertical center of the filled ceramic powder M and the electrode insertion position (the central axis of the insertion hole 63) match (overlap). The male mold 71 is also lowered, and centering is performed so that the distances from the electrode insertion position to the surfaces of the first male mold 71 and the second male mold 72 facing the ceramic powder are equal.
[0043]
Subsequently, the two electrodes 21 are inserted into the insertion holes 63, respectively, and their tips protrude into the internal space S in the through hole 65, and are embedded in the ceramic powder M by a predetermined electrode insertion amount L.
Next, the process proceeds to the pressing process. In this pressing step, the first male mold 71 and the second male mold 72 are moved at a constant speed of 4500 kg / cm by a pressing device (not shown). ² The thermistor molded body 11 is molded by pressing with the pressure of At this time, the electrode 21 is crimped to the center of the element body 10 in the vertical direction.
[0044]
Next, the thermistor molded body 11 is transferred to a post-press treatment process for taking out the mold 50 from the mold 50.
In the press post-treatment process, first, the first male mold 71 and the second male mold 72 are first removed vertically, and then the female mold 60 is divided to divide the first female mold 61 and the second female mold 62. . As shown in FIG. 6, the dividing direction is a direction in which the contact surface of the second female die 62 is separated from the element body 10, and is perpendicular to the pressing direction and parallel to the longitudinal direction of the electrodes 21 and 22. It has become a direction. In the present embodiment, the shape of the element body 10 is formed in a hexagonal cross section, and the inner surface shapes of the first female mold 61 and the second female mold 62 are also formed accordingly. For this reason, the inner surface of the second female mold 62 has a tapered shape that gradually decreases in the mold splitting direction away from the first female mold 61.
[0045]
Subsequently, as shown in FIG. 7, a pin-shaped member (not shown) is pressed from the outside of the first female die 61 against the end surface of the electrodes 21, 21 opposite to the element body 10, and pressed. The thermistor molded body 11 is removed from the first female die 61 (arrows in the figure).
[0046]
The thermistor 1 is obtained by firing the thermistor compact 11 thus taken out in the air at 1550 ° C.
As described above, in the method for manufacturing the thermistor 1 of the present embodiment, the pressing direction and the splitting direction are set so as to be substantially perpendicular, and the dividing surface of the die (female die 60) is the above. It is provided at a position away from the insertion hole (63, 63).
[0047]
For this reason, the thermistor molded body 11 can be pulled out by dividing the mold, and it is possible to prevent a peeling force from acting directly between the electrodes 21 and 21 and the element body 10 when dividing the mold. Of these, the occurrence of cracks at the electrode insertion portion can be effectively prevented. As a result, variations in the temperature resistance value of the thermistor 1 can be prevented, and the temperature detection accuracy can be kept high.
[0048]
In addition, since the inner surface that forms the internal space S of the female mold 60 is configured to have a tapered shape that decreases in the mold split direction, the mold and the element body 10 are separated in the process of dividing the mold. It is possible to relieve the friction force between them, improve the releasability of both, and effectively prevent the thermistor molded body from being damaged.
[0049]
Further, after the first female mold 61 and the second female mold 62 are divided, the electrode 21 inserted through the insertion hole 63 of the first female mold 61 is moved from the side wall side of the first female mold 61 to the internal space S side. The thermistor molded body 11 is taken out by being pushed out. For this reason, the thermistor molded body 11 can be easily pulled out from the first female mold 61.
[0050]
The inner surface of the first female die 61 includes the open ends of the pair of insertion holes 63 and corresponds to the electrode insertion surface of the element body 10. Since it is configured to be flat so as to be perpendicular, the shape of the electrode insertion surface of the element body 10 formed in the pressing process is also flat in a form orthogonal to the longitudinal direction of the electrode 21. For this reason, as shown in FIG. 8, even if the electrode 21 is displaced in the direction perpendicular to the longitudinal direction due to the clearance with the insertion hole 63, the insertion length L itself with respect to the element body 10 is difficult to change. . That is, even if the electrode position is shifted to the left and right, variations in the amount of insertion of each electrode are less likely to occur.
[0051]
Further, since the pressing direction is substantially perpendicular to the longitudinal direction of the electrode 21, the influence of the springback phenomenon in the pressing process described above is small, variation in the insertion length of the electrode 21 into the element body 10 is small, and firing is performed. Since the variation in shrinkage rate at the time is also small, the variation in electrode insertion length does not increase after firing.
[0052]
For this reason, it is possible to suppress or prevent the variation in the insertion length of the electrode. As a result, variation in the temperature resistance value of the thermistor 1 can be prevented, and the temperature detection accuracy can be kept high.
Although the present embodiment has been described above, the shape of the thermistor 1 is not limited to the hexagonal cross-sectional shape, but may be other polygonal shapes such as an octagonal cross-sectional shape. In addition, the thermistor manufacturing method of the present embodiment can be applied to a thermistor having a circular cross section or an elliptical cross section, such as the thermistor 101 shown in FIG. In this case, specifically, the shape of the female die is changed so that the shape of the through-hole 65 having a hexagonal cross-sectional shape shown in FIG. 5 becomes another polygonal shape such as an octagonal cross-sectional shape, a circular cross-sectional shape, or an elliptical cross-sectional shape. At the same time, the male shape is changed accordingly.
[0053]
Even in such a configuration, the pressing direction and the splitting direction are set so as to be substantially perpendicular to each other, and the dividing surface of the mold is provided at a position away from the insertion hole. Further, the inner surface is tapered so that the cross-sectional dimension of the inner surface of the female mold in the mold dividing direction is reduced, and the electrode is pushed out from the side wall side of the first female mold toward the inner space side. As a result, the thermistor molded body is taken out. For this reason, the effect similar to the above can be acquired.
[0054]
In the present embodiment, the mold is divided into two parts for the male mold 70 and the female mold 60. However, the mold may be divided into a larger number. Even in this case, it is preferable that the inner surface facing the inner space of the mold is tapered so that the cross section of the element main body becomes smaller in the direction in which the mold is divided and separated.
[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 9 is a perspective view of the thermistor 201 according to this embodiment.
[0055]
As shown in the figure, the thermistor 201 is substantially the same as the thermistor 1 except that the shape of the element body 210 is different from the shape of the element body 10 of the first embodiment. For this reason, the same code | symbol is attached | subjected about the same component and the description is abbreviate | omitted.
[0056]
The element body 210 has a shape in which a hexagonal column is laid down, that is, its transverse section has a quadrangular shape, its longitudinal section has a hexagonal shape, and has substantially the same thickness and volume as the element body 10 of the first embodiment. The thermistor 201 is configured by extending a pair of electrodes 21 vertically and parallel to each other from one side of the hexagonal shape of the element body 210.
[0057]
Next, a method for manufacturing the thermistor 201 will be described with reference to FIGS.
First, a pre-press treatment step for obtaining a ceramic powder M used when the element body 210 is press-molded is performed. This is the same as in the first embodiment, and a description thereof will be omitted.
[0058]
Subsequently, a mold is installed in preparation for the subsequent pressing process. In this pressing step, a split mold 250 shown in FIGS. 10 and 11 is used. FIG. 10 is an explanatory view showing a longitudinal section of the mold 250 in the pressing step, and FIG. 11 is an explanatory view showing a DD section thereof.
[0059]
That is, the mold 250 includes a female mold 260 having a through-hole 265 penetrating the center in the vertical direction, and a male mold 270 inserted through the through-hole 265.
The female mold 260 is configured to be divided into two parts up and down with the center of the through hole 265 as a boundary, and one of the divided parts constitutes a first female mold 261 and the other constitutes a second female mold 262. The through-hole 265 formed by assembling the first female mold 261 and the second female mold 262 has a tapered shape so that it gradually decreases by a predetermined dimension in a direction away from the dividing surface. The cross section is rectangular. A pair of long grooves 264 and 266 having a semicircular cross-sectional shape are provided in parallel to each other on the contact surface between the first female mold 261 and the second female mold 262. These long grooves 264 and 266 are provided to communicate with the through-hole 265 from one end of the side surfaces of the first female mold 261 and the second female mold 262, and the first female mold 261, the second female mold 262, and the like. When the two are installed facing each other, a pair of insertion holes 263 having a circular cross section are formed. The insertion hole 263 has substantially the same inner diameter (having a predetermined clearance) as the outer diameter of the electrode 21 and is disposed at the same height in parallel with each other at substantially the same distance W3 as the distance W3 between the electrodes 21 and 21 described above. Has been.
[0060]
On the other hand, the male mold 270 includes a first male mold 271 inserted from above into the through hole 265 of the female mold 260 and a second male mold 272 inserted from below into the through hole 265. . Each of the first male mold 271 and the second male mold 272 is formed in a quadrangular prism shape having a cross-sectional shape substantially equal to the minimum cross-sectional shape of the element body 210. Then, by assembling the female mold 260 and the male mold 270, an internal space S2 is formed in the mold 250.
[0061]
The contact surface between the inner surface of the female mold 260 and the element body 210 at the end face of each male mold 271 and 272 is lapped in advance so as to satisfy the center line average roughness (Ra) = 0.2 μm or less. Has been made.
First, the first female mold 261 and the second female mold 262 are assembled and the female mold 260 is installed. First, the second male mold 272 is inserted into the through hole 265 from below, and the upper surface of the second male mold 272 is inserted. The position is set at a predetermined position that is higher than the electrode insertion position (the central axis of the insertion hole 263). Subsequently, the ceramic powder M is put into the through-hole 265 from above, and the first male mold 271 is inserted and set from above the through-hole 265, and the male mold 270 and female mold are inserted into the through-hole 265. A ceramic powder M is filled in the internal space S surrounded by the inner surfaces of 260.
[0062]
Then, the second male mold 272 is lowered to a position where the vertical center of the filled ceramic powder M and the electrode insertion position (the central axis of the insertion hole 263) match (overlap), and at the same time, the first The male mold 271 is also lowered, and centering is performed so that the distance from the electrode insertion position to the surface of the first male mold 271 and the second male mold 272 facing the ceramic powder M becomes equal.
[0063]
Subsequently, the two electrodes 21 are respectively inserted into the insertion holes 263, and their tip portions are projected into the internal space S in the through hole 265, and are embedded in the ceramic powder M by a predetermined electrode insertion amount L.
Next, the process proceeds to the pressing process. In this pressing step, the first male mold 271 and the second male mold 272 of the male mold 270 are moved at a constant speed of 4500 kg / cm by a pressing device (not shown). ² The thermistor molded body 211 is molded by pressing with the pressure of At this time, the electrode 21 is crimped to the center (center) of the element body 210 in the vertical direction.
[0064]
Next, the process proceeds to a post-press processing step for removing the thermistor molded body 211 from the mold 250.
In this post-processing step, the first male mold 271 and the second male mold 272 are first removed up and down, and then the female mold 260 is divided to divide the first female mold 261 and the second female mold 262. . As shown in FIG. 12, the dividing direction is the same as the pressing direction (the direction is opposite).
[0065]
In the present embodiment, the shape of the element body 210 is formed in a trapezoidal shape (longitudinal hexagonal shape), and the shapes of the contact surfaces of the first female mold 261 and the second female mold 262 are also formed accordingly. ing. For this reason, the contact surface of the first female mold 261 has a tapered shape that gradually decreases in the parting direction away from the second female mold 262.
[0066]
Subsequently, the thermistor molded body 211 remaining in the first female mold 261 or the second female mold 262 is removed, and the thermistor molded body 211 thus taken out is baked in the air at 1550 ° C. to obtain the thermistor 201.
As described above, in the method for manufacturing the thermistor 1 of the present embodiment, the inner surface of the female mold 260 includes the open ends of the pair of insertion holes 263 and corresponds to the electrode insertion surface of the element body 210. Since the inner surface is configured to be flat so that its surface direction is substantially perpendicular to the longitudinal direction of the electrode 21, the shape of the electrode insertion surface of the element body 210 formed in the pressing process is also the same as that of the electrode 21. It becomes flat in a form perpendicular to the longitudinal direction. For this reason, as shown in FIG. 8, even if the electrode 21 is displaced in a direction perpendicular to the longitudinal direction due to the clearance with the insertion hole 63, the insertion length itself with respect to the element body 210 is hardly changed. That is, even if the electrode position is shifted to the left and right, variations in the amount of insertion of each electrode are less likely to occur. In addition, since the pressing direction is substantially perpendicular to the longitudinal direction of the electrode 21, the influence of the springback phenomenon after the pressing process is small, variation in the insertion length of the electrode 21 into the element body 210 is small, and at the time of firing Therefore, the variation in the insertion length of the electrode does not increase after firing. As a result, variation in the temperature resistance value of the thermistor 201 can be prevented, and the temperature detection accuracy can be kept high.
[0067]
Also in this embodiment, the mold is divided into two parts for the male mold 270 and the female mold 260, but may be configured to be divided into a larger number. Even in this case, it is preferable that the inner surface facing the inner space of the mold is tapered so that the cross section of the element main body becomes smaller in the direction in which the mold is divided and separated.
[Example]
In order to confirm the effect of the present invention, the inventors of the thermistor according to each of the above-described embodiments and thermistors obtained by each of the conventional several types of thermistor manufacturing methods, the crack or the element body The defect occurrence rate (%) of partial peeling and electrode insertion length variation σ (mm) were inspected.
[0068]
Specifically, as shown in FIG. 13, with respect to Examples 1 to 3 according to the embodiment of the present invention and Comparative Examples 1 to 4, 100 thermistors were produced and inspected. The pressing speed in the pressing process at this time was set to 0.5 mm / s. The occurrence of cracks was confirmed by visually observing the thermistor with a magnifying glass, and the defect occurrence rate (%) was evaluated by the ratio of the number of thermistors with cracks to the number of thermistors produced. In addition, the electrode insertion length variation σ (mm) is obtained by imaging the internal state of the thermistor from above and below with an X-ray irradiation apparatus, and the length of the electrode insertion by the projector (the length of the electrode embedded in the element body). It means the inner length in the longitudinal direction) and the variation was evaluated by the standard deviation σ. Hereinafter, the test results of each example and comparative example will be described.
[0069]
First, Example 1 shown in the figure is an inspection result when a thermistor is manufactured by the manufacturing method according to the first embodiment. That is, the shape of the element body is formed in a hexagonal column shape, the electrode insertion surface is a flat surface, the pressing direction and the dividing direction are set to be substantially perpendicular, and the dividing surface of the mold is formed from the electrode insertion hole. It is provided at a position that is off. Further, the inner surface facing the inner space of the mold is tapered so that the cross section of the element main body becomes smaller in the direction in which the mold is divided and separated. In addition, the dotted line in a figure has shown the boundary line at the time of dividing | segmenting a metal mold | die (hereinafter the same).
[0070]
The defect occurrence rate at this time was 0%, and the variation in insertion length was 0.006 mm, which was a very good result.
Next, Example 2 is an inspection result when a thermistor is manufactured by the manufacturing method according to the modification of the first embodiment. That is, the shape of the element body is formed in a cylindrical shape, and the electrode insertion surface is a curved surface. The pressing direction and the dividing direction are set so as to be substantially perpendicular to each other, and the dividing surface of the mold is provided at a position away from the electrode insertion hole. In addition, the inner surface facing the inner space of the mold is curved so that the cross section of the element main body becomes smaller in the direction in which the mold is divided and separated.
[0071]
The defect occurrence rate at this time was 2%, and a good result was obtained, but the result that the variation in insertion length was relatively large as 0.016 mm was obtained. This is presumably because the electrode insertion surface is a curved surface and the electrode insertion amount fluctuates relatively due to a deviation in the direction perpendicular to the electrode insertion direction.
[0072]
Example 3 is an inspection result when a thermistor is manufactured by the manufacturing method according to the second embodiment. That is, the element body is shaped like a hexagonal column lying sideways, the electrode insertion surface is flat, and the pressing direction and the dividing direction are set to be the same direction. Further, the inner surface facing the inner space of the mold is tapered so that the cross section of the element body becomes smaller in the direction in which the mold is divided and separated.
[0073]
The defect occurrence rate at this time was 20%, which was relatively large, but this was because the split surface of the mold was provided at the position of the insertion hole of the electrode, so that a tensile force was applied to the element main body when dividing the mold, This is probably because a peeling force was generated between the element body and the electrode. On the other hand, the variation in insertion length is as good as 0.007 mm.
[0074]
On the other hand, in Comparative Example 1, the element body itself has the same shape as that of Example 2 described above, and the electrode insertion surface is a curved surface, but the pressing direction and the dividing direction are set to be the same direction. Yes. For this reason, the taper shape as described above is not formed on the inner surface facing the inner space of the mold.
[0075]
The defect occurrence rate at this time is 50%, which is considerably large. This is because the pressing direction and the mold splitting direction are the same direction, so that a tensile force is applied to the element body during mold splitting, resulting in a peeling force between the element body and the electrode, and further, the inner surface of the mold. This is probably because the frictional force between the inner surface of the mold and the outer surface of the element body acts greatly, and the tensile force applied to the element body is further increased.
[0076]
In addition, the variation in insertion length is relatively large at 0.016 mm. This is similar to the case of Example 2 described above, because the electrode insertion surface is a curved surface. This is probably because the amount of electrode insertion fluctuated.
Next, Comparative Example 2 has a shape in which the element body is provided with a taper shape in the press direction relative to that of Comparative Example 1. That is, the electrode insertion surface of the element body is a curved surface, and the pressing direction and the dividing direction are set to be the same direction. Further, the inner surface facing the inner space of the mold is tapered so that the cross section of the element body becomes smaller in the direction in which the mold is divided and separated.
[0077]
The defect occurrence rate at this time is 30%, which is smaller than that of Comparative Example 1. This is presumably because the inner surface of the mold is tapered so that the frictional force between the inner surface of the mold and the outer surface of the element body is reduced, and the tensile force applied to the element body is reduced accordingly. Moreover, since it is larger than the case of Example 3, since the electrode insertion surface is flat in Example 3, the electrode insertion surface is curved in Comparative Example 2, Due to the difference in thermal shrinkage during firing due to the difference in the press body volume between the part between the electrodes in the element body and the outer part of the electrode located on the opposite side between the electrodes, peeling tends to occur at the electrode insertion part. It is thought that.
[0078]
Moreover, the variation in insertion length is relatively large at 0.015 mm. This is because the electrode insertion surface is a curved surface as described above. This is probably because the amount of electrode insertion fluctuated.
Next, in Comparative Example 3, the element body has a shape such that the element body of Comparative Example 1 is cut out on both outer sides of a plane parallel to the electrode, and the electrode insertion surface is a curved surface. The pressing direction and the splitting direction are set so as to be substantially perpendicular, and the pressing direction is the same as the electrode insertion direction. The tapered shape as described above is not formed on the inner surface facing the inner space of the mold.
[0079]
The defect occurrence rate at this time is 40%, which is smaller than that of Comparative Example 1. This is because, in Comparative Example 1, the pressing direction and the splitting direction are the same direction, so the portion of the element body expanded during pressing is pressed against the entire circumferential surface along the splitting direction of the mold. In Comparative Example 3, the pressing direction and the splitting direction are substantially perpendicular to each other, and the portion of the element main body that has expanded during pressing remains stuck to the two left and right surfaces along the splitting direction of the mold. For this reason, it is considered that the comparative example 3 has a smaller tensile stress (friction force) applied to the element body during the parting than the comparative example 1.
[0080]
On the other hand, the defect occurrence rate at this time is larger than that in Comparative Example 2. This is presumably because, in Comparative Example 3, unlike the case of Comparative Example 2, since the mold does not have a taper surface in the mold split direction, tensile stress (frictional force) due to frictional force increases.
Further, the variation in insertion length is considerably large as 0.062 mm. This is because the electrode insertion surface is a curved surface, so that the electrode insertion amount fluctuates relatively due to a deviation in the direction perpendicular to the electrode insertion direction, and the press direction is the same as the electrode insertion direction. Therefore, it is considered that the spring back occurred in the element body after releasing the pressing force, and the variation in the amount of electrode insertion was further increased.
[0081]
Next, in Comparative Example 4, the element body has a shape in which the outer flat surfaces of the element body of Comparative Example 3 are tapered. That is, the electrode insertion surface is a curved surface, the pressing direction and the splitting direction are set to be substantially perpendicular, and the pressing direction is the same as the electrode insertion direction. The inner surface facing the inner space of the mold is tapered so that the cross section of the element main body becomes smaller in the direction in which the mold is divided and separated.
[0082]
The defect occurrence rate at this time is 25%, which is smaller than that of Comparative Example 3. This is thought to be because the frictional force between the inner surface of the mold and the outer surface of the element body during mold splitting is reduced due to the tapered shape of the inner surface of the mold, and the tensile force applied to the element body is reduced. Although it is slightly smaller than Comparative Example 2, this is similar to the relationship between Comparative Example 1 and Comparative Example 3 described above, whereas in Comparative Example 2, the press direction and the splitting direction are the same direction. In Comparative Example 4, it is considered that the press direction and the splitting direction are substantially perpendicular.
[0083]
Further, although the variation in insertion length is considerably large as 0.065 mm, as in Comparative Example 3, this is a deviation in the direction perpendicular to the electrode insertion direction due to the electrode insertion surface being a curved surface, This is considered to be due to the springback due to the pressing direction being the same as the electrode insertion direction.
[0084]
From the above inspection results, it is effective to make the electrode insertion surface flat and to make the press direction perpendicular to the electrode insertion direction, in particular, to reduce variations in the electrode insertion length. confirmed. In addition, it is confirmed that making the press direction and the mold splitting direction perpendicular to each other and making the mold dividing surface away from the electrode insertion hole is particularly effective in suppressing the occurrence rate of defects. did it.
[0085]
As described above, the effectiveness of the thermistor manufacturing method according to the example of the present invention was confirmed.
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that embodiment of this invention can take various forms, as long as it belongs to the technical scope of this invention, without being limited to the said Example at all. Nor.
[Brief description of the drawings]
FIG. 1 is a plan view of a thermistor according to a first embodiment of the present invention.
FIG. 2 is a side view of the thermistor as viewed from the direction A in FIG.
FIG. 3 is a side view of the thermistor as viewed from the direction B in FIG.
FIG. 4 is an explanatory view showing a thermistor manufacturing method according to the first embodiment and a configuration of a mold used therefor.
FIG. 5 is an explanatory view showing a thermistor manufacturing method according to the first embodiment and a configuration of a mold used therefor.
FIG. 6 is an explanatory view showing a thermistor manufacturing method according to the first embodiment.
FIG. 7 is an explanatory view showing a thermistor manufacturing method according to the first embodiment.
FIG. 8 is an explanatory diagram showing the effect of the thermistor manufacturing method according to the first embodiment.
FIG. 9 is a perspective view of a thermistor according to a second embodiment of the present invention.
FIG. 10 is an explanatory view showing the thermistor manufacturing method according to the second embodiment and the configuration of a mold used therefor.
FIG. 11 is an explanatory diagram showing a thermistor manufacturing method according to a second embodiment and a configuration of a mold used therefor.
FIG. 12 is an explanatory diagram illustrating a thermistor manufacturing method according to a second embodiment.
FIG. 13 is an explanatory view showing an effect of the thermistor manufacturing method according to the embodiment of the present invention.
FIG. 14 is a perspective view of a thermistor manufactured by a conventional manufacturing method.
FIG. 15 is an explanatory view showing a conventional thermistor manufacturing method and a configuration of a mold used therefor.
FIG. 16 is an explanatory view showing a conventional thermistor manufacturing method.
FIG. 17 is an explanatory view showing a problem of a conventional thermistor manufacturing method.
FIG. 18 is an explanatory view showing a problem of a conventional thermistor manufacturing method.
FIG. 19 is a perspective view of another thermistor manufactured by a conventional manufacturing method.
[Explanation of symbols]
1, 201 ... thermistor, 10, 210 ... element body,
11, 211 ... thermistor molding, 21 ... electrode,
50, 250 ... mold, 60, 260 ... female mold,
61,261 ... first female mold, 62,262 ... second female mold,
63,263 ... insertion hole, 70,270 ... male,
71,271 ... 1st male mold, 72,271 ... 2nd male mold

Claims (5)

The electrodes extending in the longitudinal direction are inserted into a pair of insertion holes extending through the side wall of the split mold and extending toward the internal space formed when the mold is assembled, and then inserted into the internal space. A pre-pressing step of embedding one end of the electrode in the predetermined ceramic powder;
After the pre-press treatment step, the ceramic powder is pressed in one direction using a press device so that the electrodes are embedded in the element body, which is a press-molded body of the ceramic powder, at a predetermined interval. And a pressing step of forming a thermistor molded body in which a part of each of the electrodes extends to the outside of the element body, and
After the pressing step, the post-press treatment step of dividing the mold and taking out the thermistor molded body from the mold and firing it;
A thermistor manufacturing method comprising:
The pressing direction in the pressing step and the mold dividing direction in the post-press treatment step are set to be substantially perpendicular, and
The method of manufacturing a thermistor, wherein the mold dividing surface is provided at a position away from the insertion hole.   Of the inner surface facing the inner space of the mold, the inner surface corresponding to the electrode insertion surface of the element body includes an opening end of the insertion hole, and its surface direction is substantially perpendicular to the longitudinal direction of the electrode. The thermistor manufacturing method according to claim 1, wherein the thermistor is flat. The inner surface facing the internal space of the mold is configured so that the element body has a shape that reduces the cross-sectional dimension in a direction in which the element body is divided and separated. A method for producing the thermistor according to 1 or 2 . In the post-press treatment step, after the mold is divided, the thermistor molded body is pushed out from the side wall side toward the internal space side by extruding the electrode inserted through the insertion hole of the mold. The method of manufacturing the thermistor according to any one of claims 1 to 3 , wherein the thermistor is taken out from a mold. Method for producing a thermistor according to any one of claims 1 to 4, characterized in that said at least a contact surface with the element body in each mold, in advance wrapping.

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