JP2005259595A - Electric contact and thermal protector using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric contact free from the possibility of melting and adhesion even at the end of its service life, and a thermal protector using the electric contact with greatly improved reliability and safety. <P>SOLUTION: The electric contact 10 includes a conductive layer 13 between a first main surface 11 and a second main surface 12 opposed to each other. The conductive layer 13 contains a conductive material, and further contains an electrically insulating material in a portion of the conductive layer 13 located near the first main surface 11 thereof. The volume ratio between the electrically insulating material and the conductive material in that portion falls within a range of 30:70 to 70:30. This electric contact 10 is used for the thermal protector. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrical contact with improved welding resistance and a thermal protector using the electrical contact.

  2. Description of the Related Art Conventionally, a thermal protector has been used as a device that protects an electrical device by detecting a thermal change that occurs when the electrical device such as a small motor is abnormal and opening and closing contacts.

  FIG. 3 is a partially cutaway cross-sectional view of a conventional glass-sealed thermal protector. In the thermal protector 30 shown in FIG. 3, a fixed-side internal lead wire 33 having a fixed-side contact 32 at the tip, a movable-side contact 34 at the tip, and a movable-side at the other end in the glass container 31. A thermally responsive element 36 to which the internal lead wire 35 is connected is disposed to face the stationary contact 32 and the movable contact 34 is detachably disposed. The fixed-side internal lead wire 33 and the movable-side internal lead wire 35 are supported by a glass bead 37, and the fixed-side internal lead wire 33 and the movable-side internal lead wire 35 are fixed-side external lead wires 38 in the sealing portion 31a. And connected to the movable external lead wire 39 by welding or the like. One ends of the fixed-side external lead wire 38 and the movable-side external lead wire 39 are led out of the glass container 31.

  Such conventional thermal protectors are used in electrical devices such as small motors, and the self-heating due to overcurrent in the event of device abnormalities and the increase in ambient temperature cause the thermosensitive element to reverse and return to the fixed and movable contacts. The device is protected by cutting off the current by opening and closing.

  Originally, surface damage due to arc discharge progresses as the frequency of electrical contacts increases, and even if the conventional thermal protector repeats switching operation until the end of its life, it cannot be predicted whether the failure mode is contact non-conduction or welding. Is the current situation. Here, if contact welding occurs, there is a risk of causing a failure in the electrical equipment to be protected.

  For this reason, in order to make the final failure mode of a thermal protector non-conducting, a thermal protector provided with a contact having a configuration in which an insulating fiber is sandwiched inside has been proposed (for example, see Patent Document 1).

However, in the thermal protector configured as described above, the contact is made by interposing a foreign substance called insulating fiber, so that the mechanical strength of the contact is inferior and the end of the insulating fiber is exposed to the outside of the contact. As a result of the opening and closing of the fabric, fiber scraps fall off between the contacts, and although the thermal protector is in a sufficiently normal state, the contact becomes non-conductive, and there is a problem that the electric device equipped with the thermal protector becomes inoperable.
JP 2000-311574 A

  Once the thermal protector has been activated due to an abnormality in the electrical equipment, it repeatedly opens and closes the contact at regular intervals until the cause of the abnormality is removed. Originally, the surface of an electrical contact becomes worn as the frequency of opening and closing becomes high, and there is a danger of eventually welding each other. However, if the contacts of the thermal protector are welded by a frequent switching operation, the function as a safety element is lost, and there is a possibility that the electric device may be damaged.

  The present invention solves such problems, and provides an electrical contact that does not weld even at the end of its life and a thermal protector using the electrical contact.

  The present invention is an electrical contact including a conductive layer between a first main surface and a second main surface facing each other, wherein the conductive layer includes a conductive substance, and the first main surface of the conductive layer is provided. An electrical insulating material is further included in the vicinity of the surface, and a volume ratio of the electrical insulating material to the conductive material in the vicinity is 30:70 to 70:30. It is an electrical contact.

  The present invention also includes a conductor portion having an electrical contact at the tip and a thermal response element having an electrical contact at the tip, and the electrical contact of the conductor portion and the electrical contact of the thermal response element are contacted and separated. A thermal protector arranged in a possible manner, wherein the electrical contact is used as at least one selected from an electrical contact of the conductor portion and an electrical contact of the thermally responsive element, and the first main surface is a contact surface. It is a thermal protector characterized by the above.

  INDUSTRIAL APPLICABILITY The present invention can provide an electrical contact that does not weld even at the end of its life and a thermal protector using the same that greatly improves reliability and safety.

  The electrical contact of the present invention includes a conductive layer between the first main surface and the second main surface facing each other, and the conductive layer includes a conductive material. Further, the conductive layer close to the first main surface (the vicinity of the first main surface of the conductive layer) contains an electrically insulating material. As a result, when the first main surface is a contact surface, the probability that the electrically insulating material is exposed to the contact surface portion increases as the conductive material of the contact wears and evaporates due to repeated opening and closing, and the opposing contact By touching the insulating material, the contacts become non-conductive, and welding of the contacts at the end of the life can be avoided. Note that the conductive layer may be composed of a plurality of layers.

  Moreover, the volume ratio of the said electrically insulating substance and an electroconductive substance needs to be 30: 70-70: 30, More preferably, it is 40: 60-60: 40. This is because, within this range, it is possible to reliably prevent welding at the end of the life while ensuring the electrical conductivity of the electrical contact at the normal time.

  Further, various materials can be used as the electrical insulating material, but alumina is most preferable. This is because alumina has the highest vapor pressure and is most stable against arc discharge between contacts.

  Since the thermal protector of the present invention uses the electrical contact of the present invention and has the first main surface as a contact surface, the contact becomes non-conductive at the end of the life of the thermal protector as described above, and contact welding is performed. By avoiding this, the safety of the device can be ensured.

  Further, when alumina is used as the electrical insulating material and the power supply voltage of the device in which the thermal protector is used is V (V) and the average particle size of the electrical insulating material is d (μm), d × It is preferable that 12> V is satisfied. This is because the alumina particles are not dielectrically broken by the power supply voltage applied between the contacts.

  In addition, the electrical contact of this invention may be used for both of the contacts which a thermal protector opposes, and may be used for any one. In particular, in a DC power supply device or the like, the degree of contact consumption may be greatly affected by the polarity of the contact, so it is desirable to determine a specific arrangement method according to the state of the device.

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

  FIG. 1 is a perspective view (A) showing an example of an electrical contact of the present invention and a partially enlarged sectional view (B) thereof. As shown in FIG. 1, the electrical contact 10 of the present embodiment includes a first main surface 11 and a second main surface 12 that face each other, and the first main surface 11 and the second main surface 12 are in contact with each other. A conductive layer 13 is formed therebetween. The conductive layer 13 is formed from, for example, a plurality of conductive layers 13a and 13b having different compositions. The conductive layers 13a and 13b are made of a conductive material. Further, the conductive layer 13a close to the first main surface 11 contains an electrical insulating material, and the volume ratio of the electrical insulating material to the conductive material in the conductive layer 13a is 30:70 to 70:30. It is set with a range. In addition, the conductive layer 13b close to the second main surface 12 is formed only from a conductive material.

  As the conductive material used for the conductive layer 13a, for example, a single metal such as Ag or an alloy such as Ag-Ni, Ag-Cd, Ag-Cu, Ag-W, Ag-Pd, Ag-Sn, Cu-W, or the like. Etc. can be used. In addition, alumina is used as the electrical insulating material. Other than alumina, oxides such as silica, magnesia, zirconia, and titania can be used. As described above, alumina with high vapor pressure is the most stable against arc discharge between contacts, and the effect of the present invention. Is perfect for revealing.

FIG. 2 is a partially cutaway sectional view showing an example of the thermal protector of the present invention. As shown in FIG. 2, the thermal protector 20 of the present embodiment includes a fixed-side internal lead wire 23 provided with a fixed-side contact 22 at the tip, and a movable-side contact 24 at the tip, in a glass container 21. A thermally responsive element 26 having a movable side internal lead wire 25 connected to the other end is disposed oppositely, and a fixed side contact 22 and a movable side contact 24 are disposed so as to be able to contact and separate. The fixed-side internal lead wire 23 and the movable-side internal lead wire 25 are supported by a glass bead 27, and the fixed-side internal lead wire 23 and the movable-side internal lead wire 25 are fixed to the fixed-side external lead wire 28 in the sealing portion 21a. And connected to the movable-side external lead wire 29 by welding or the like. One ends of the fixed-side external lead wire 28 and the movable-side external lead wire 29 are led out of the glass container 21.

  The fixed-side contact 22 uses the electrical contact of the present embodiment shown in FIG. 1 and connects the first main surface 11 to the contact surface and the second main surface 12 to the fixed-side internal lead wire 23. It is a surface. The contact surface of the movable contact 24 is made of, for example, conventionally used alloys such as Ag—Ni, Ag—Cd, Ag—Pd, Ag—Sn, Ag—Cu, Ag—W, and Cu—W, Alternatively, it can be formed from a single metal such as Ag.

  The thermally responsive element 26 includes a bimetal obtained by bonding two metal plates having different thermal expansion coefficients or a trimetal obtained by bonding three sheets. In general, a Ni-Fe alloy or the like can be mainly used as the metal on the low expansion side. Moreover, various alloys, such as Ni-Cr-Fe, Ni-Mn-Fe, Ni-Mo-Fe, Ni-Cu-Mn, can be used for the metal of the high expansion side.

  Hereinafter, based on an Example, this invention is demonstrated more concretely. However, the present invention is not limited to the following examples.

  First, an electrical contact was produced using a powder press method as follows.

  Silver powder having an average particle size of 4 μm was prepared as the conductive material for the conductive layer 13a, and four types of alumina powder having an average particle size of 5, 10, 20, and 40 μm were prepared as the electrically insulating material. The silver powder and four types of alumina powder were blended so that the volume content of alumina was 40% calculated from the theoretical density, and mixed uniformly to prepare four types of first mixed powder.

  Also, copper powder having an average particle diameter of 7 μm and Ni powder having an average particle diameter of 2 μm are prepared as the conductive material for the conductive layer 13b, and the weight content of Ni is 20% for the copper powder and Ni powder. The mixture was uniformly mixed to prepare a second mixed powder. The conductive layer 13b is provided in order to strengthen the bonding when fixing the contact by resistance welding in the production of the thermal protector.

Next, a predetermined amount of the first and second mixed powders are weighed, the first mixed powder is first put into a previously prepared die, and the surface of the charged powder is leveled by applying a slight vibration to the die. After that, after the second mixed powder was added and the surface was smoothed in the same manner, a punch was inserted and pressed at a pressure of about 600 kg / cm ² , and the square contact was 2.5 mm square and 1.5 mm thick. A molded body was produced. Similarly, a molded body having a diameter of 2.5 mm and a thickness of 1.2 mm and a curvature of 3R on the first mixed powder side was also produced as a round contact (not shown). This process was performed for each of the four types of first mixed powders, and four types of square contact and round contact compacts containing alumina powders having different particle sizes were produced.

  Next, each obtained compact was fired in a nitrogen atmosphere at 600 ° C. for 2 hours to produce an electrical contact.

  Subsequently, as shown in FIG. 2, the square contacts obtained by combining the square contacts and the round contacts so that the particle diameters of the alumina powders coincide with each other are used as the fixed contacts 22. Four types of thermal protectors were manufactured by arranging the contact as the movable contact 24 so that the layers containing alumina powder face each other. As the thermally responsive element 26, a bimetal obtained by bonding a Ni—Fe alloy plate and a Ni—Cr—Fe alloy plate was used. In addition, a Mn—Ni wire was used as the lead wire material.

  A thermal protector was produced in the same manner as in Example 1 except that an electrical contact formed from a conventional Ag—Ni alloy was used as the movable contact.

  A thermal protector was produced in the same manner as in Example 1 except that an electrical contact formed from a conventional Ag-Ni alloy was used as the stationary contact.

(Comparative example)
A thermal protector was produced in the same manner as in Example 1 except that both the fixed side contact and the movable side contact were made of a conventional Ag-Ni alloy.

  Next, the thermal protectors of Examples 1, 2 and 3 and the comparative example are AC 110 V, 10 A, power factor 60% as the first condition, and AC 220 V, 15 A, power factor 80 as the second condition. A life test up to the end of life was performed using 50 samples per 1%, and the number of samples that finally reached contact welding was examined. The results are shown in Table 1.

  As can be seen from Table 1, in the comparative example, a considerable number of the 50 samples caused contact welding and reached the life end, whereas in Examples 1, 2 and 3, the life end by contact welding was reached. We were able to prevent considerably. In particular, among the samples of Examples 1 to 3, contact welding does not occur at all for samples satisfying d (average particle diameter of alumina) × 12> V (power supply voltage), and all the contacts are in a non-conductive state. It was the end.

  As described above, in the thermal protectors of Examples 1 to 3 according to the present invention, it was proved that even when the contact was repeatedly opened and closed until the end of its lifetime, the contact non-conductive state could be finally secured.

  In designing the contact material according to the present invention, a predetermined conductivity is required even in a layer containing an electrically insulating substance as a basic function of the electrical contact. In this example, the volume percentage of the alumina powder in the layer containing the electrical insulating material was 40 volume%, but the conductivity that does not affect the quality of the thermal protector when the volume percentage of the alumina powder is 70 volume% or less. Have confirmed. However, if the volume percentage of the alumina powder is less than 30 volume%, contact welding at the end of the life may occur.

  Finally, although the present invention has been described using a glass container type thermal protector, it is clear that the same effect can be obtained with a resin container type thermal protector, and the electrical contact of the present invention has a risk of contact welding. It can be applied to any contact relay device that bears it.

  As described above, the present invention can provide an electrical contact that does not weld even at the end of its life, and a thermal protector using the same that greatly improves reliability and safety, and its industrial value is It ’s big.

It is the perspective view (A) which shows an example of the electrical contact of this invention, and its partial expanded sectional view (B). It is sectional drawing which shows an example of the thermal protector of this invention. It is sectional drawing of the conventional thermal protector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrical contact 11 1st main surface 12 2nd main surface 13, 13a, 13b Conductive layer 20, 30 Thermal protector 21, 31 Glass container 21a, 31a Sealing part 22, 32 Fixed side contact 23, 33 Fixed side inside Lead wires 24, 34 Movable side contacts 25, 35 Movable side internal lead wires 26, 36 Thermally responsive elements 27, 37 Glass beads 28, 38 Fixed side external lead wires 29, 39 Movable side external lead wires

Claims (4)

An electrical contact including a conductive layer between opposing first and second major surfaces,
The conductive layer includes a conductive material;
The vicinity of the first main surface of the conductive layer further includes an electrically insulating material,
The electrical contact, wherein a volume ratio of the electrically insulating substance and the conductive substance in the vicinity is 30:70 to 70:30.   The electrical contact according to claim 1, wherein the electrical insulating material is alumina. A thermal unit including a conductor part having an electrical contact at a tip and a thermal response element having an electrical contact at a tip, wherein the electrical contact of the conductor part and the electrical contact of the thermal response element are arranged to be able to contact and separate A protector,
The electrical contact according to claim 1 or 2 is used as at least one selected from an electrical contact of the conductor portion and an electrical contact of the thermally responsive element, and the first main surface is a contact surface. A thermal protector.   When the electrical insulating material is alumina and the power supply voltage of the device in which the thermal protector is used is V (V) and the average particle size of the electrical insulating material is d (μm), d × 12> The thermal protector according to claim 3, which is V.

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