JP7713893B2 - Main circuit conductors and switches - Google Patents

Description

This disclosure relates to a main circuit conductor and a switch having a structure in which contacts are crimped to a current-carrying conductor.

The main circuit conductor constituting the fixed contact conductor or the movable contact conductor of a switch such as an electromagnetic switch or a circuit breaker includes a current-carrying conductor and a contact fixed to the current-carrying conductor. Silver alloys are often used for these contacts. For example, Ag-WC-Gr sintered contacts and Ag-In ₂ O ₃ -SnO ₂ molten contacts are used as silver alloy contacts, and these are used according to the rated current or the breaking capacity. In addition, there are methods for joining the contacts and the current-carrying conductor, such as a method of crimping a rivet-shaped contact to the current-carrying conductor and a method of joining the current-carrying conductor and the contact with a brazing material, but crimping is more cost-effective and therefore more advantageous.

Patent Document 1 shows a structure for fastening a rivet-shaped base metal by crimping.

Japanese Patent Application Publication No. 10-223076

Crimping is advantageous in terms of cost, but there are problems with the occurrence of cracks or large deformation depending on the type of contact. For example, when a rivet-shaped sintered contact is crimped to a current-carrying conductor, the sintered contact will crack or become large in deformation. With such contacts, when subjected to thousands of impacts such as in a no-load endurance test, the contacts will chip or become easily detached, resulting in a lack of long-term reliability. In addition, if deformation is large, there is also the problem that the requirement that silver contacts be 0.5 mm or more thick as stipulated by the Electrical Appliance and Material Safety Act cannot be met.

This disclosure was made in consideration of the above, and aims to obtain a main circuit conductor that can ensure long-term reliability.

In order to solve the above problems and achieve the object, the main circuit conductor of the present disclosure includes a current-carrying conductor having a hole formed therein, and a rivet-shaped contact that is inserted into the hole of the current-carrying conductor and crimped. The main circuit conductor of the present disclosure is characterized in that, when the thickness of the current-carrying conductor is t and the crimping allowance after the contact is crimped is d, the crimping allowance d is determined so that t×( ^d1.4 )>2.3 and d+t<4.7 mm are satisfied, and the crimping allowance d increases as the thickness t of the current-carrying conductor becomes thinner .

The main circuit conductor disclosed herein has the effect of ensuring long-term reliability.

FIG. 1 is a cross-sectional view showing a tripped state of a circuit breaker according to a first embodiment; FIG. 1 is a cross-sectional view showing an on-state of a circuit breaker according to a first embodiment; FIG. 1 is a cross-sectional view showing a configuration of a rivet-shaped contact according to a first embodiment; FIG. 1 is a front view showing a state before a rivet contact is crimped to a current-carrying conductor according to the first embodiment; FIG. 1 is a front view showing a state after a rivet contact is crimped to a current-carrying conductor according to the first embodiment; FIG. 1 is a front view showing a state in which the rivet contacts cannot be properly crimped to the current-carrying conductor according to the first embodiment; 1 is a graph showing the results of a test in which a rivet contact is crimped to a current-carrying conductor in the first embodiment, the graph showing the presence or absence of cracks occurring at the contact, with the thickness of the current-carrying conductor on the horizontal axis and the crimping allowance on the vertical axis. FIG. 11 is a cross-sectional view showing a tripped state of a double-break circuit breaker according to a second embodiment. FIG. 11 is a cross-sectional view showing a configuration of an electromagnetic switch according to a third embodiment.

The main circuit conductor and switch according to the embodiment are described in detail below with reference to the drawings.

Embodiment 1.
Fig. 1 is a cross-sectional view showing a tripped state of the circuit breaker according to the first embodiment. Fig. 2 is a cross-sectional view showing an on-state of the circuit breaker according to the first embodiment.

1 and 2, the circuit breaker as a switch includes a handle 10, a switching mechanism 30, a fixed-side current-carrying conductor 6, a fixed-side contact 7 provided on the fixed-side current-carrying conductor 6, a movable-side current-carrying conductor 8, and a movable-side contact 9 provided on the movable-side current-carrying conductor 8. Details of the configuration of the switching mechanism 30 are not essential to this disclosure, so a description thereof will be omitted.

As shown in Figures 1 and 2, when the handle 10 is turned on, the opening and closing mechanism 30 operates, the movable side current conductor 8 is rotated, the movable side contact 9 abuts the fixed side contact 7, and the movable side current conductor 8 and the fixed side current conductor 6 are in a conductive state. At the moment the movable side contact 9 touches the fixed side contact 7, the movable side contact 9 and the fixed side contact 7 are subjected to an impact caused by the closing of the movable side contact 9 and the fixed side contact 7. If a crack has occurred in the movable side contact 9 or the fixed side contact 7 due to this impact, the crack may progress due to several thousand impacts such as in a no-load endurance test, causing a defect in the movable side contact 9 or the fixed side contact 7, or the movable side contact 9 or the fixed side contact 7 may fall off.

Figure 3 is a cross-sectional view showing the configuration of a rivet-shaped contact 20 according to embodiment 1. The rivet-shaped contact 20 is a general term for the movable contact 9 or the fixed contact 7. Hereinafter, the rivet-shaped contact 20 will be referred to as a rivet contact 20. As shown in Figure 3, the rivet contact 20 has a base metal part 1 having a rivet shape and a contact 2 joined to the base metal part 1. The base metal part 1 has a body part 1a without a thread and a head part 1b having a larger diameter than the body part 1a. The boundary surface between the base metal part 1 and the contact 2 shows a joint surface 3 where the base metal part 1 and the contact 2 are joined by brazing, cold pressure welding, hot pressure welding, or the like.

The material of the base metal part 1 is, for example, copper, and preferably pure copper such as oxygen-free copper or tough pitch copper. The material of the contact 2 is a silver-based alloy, for example, Ag-WC-Gr, Ag-WC, Ag-In ₂ O ₃ -SnO ₂ , Ag-SnO ₂ system. As described above, there are various types of materials for the base metal part 1 and the contact 2, and there are also various types of methods for joining the base metal part 1 and the contact 2.

Figure 4 is a front view showing the state before the rivet contact 20 is crimped to the current-carrying conductor 5 according to embodiment 1. Figure 5 is a front view showing the state after the rivet contact 20 is crimped to the current-carrying conductor 5 according to embodiment 1. The current-carrying conductor 5 is a collective term for the fixed current-carrying conductor 6 and the movable current-carrying conductor 8. The current-carrying conductor 5 and the rivet contact 20 form the main circuit conductor. The material of the current-carrying conductor 5 is, for example, copper, aluminum, iron, etc.

As shown in FIG. 4, after inserting the body 1a of the base metal part 1 of the rivet contact 20 into the through hole 5a provided in the current-carrying conductor 5, a force is applied to the tip surface 1c of the body 1a of the base metal part 1 of the rivet contact 20 protruding from the current-carrying conductor 5 using a tool such as a punch 11 to perform crimping.

As a result, as shown in FIG. 5, the tip 1d of the body 1a of the base metal part 1 protruding from the current-carrying conductor 5 is deformed, and a crimped joint is performed. The thickness of the current-carrying conductor 5 is t, and the distance from the tip surface 1e of the rivet contact 20 after crimping to the current-carrying conductor 5 is d. Hereinafter, d is referred to as the crimping allowance. If the tip surface 1e of the rivet contact 20 after crimping is not flat, the crimping allowance d is determined based on the average position of each tip point that constitutes the tip surface 1e.

Figure 6 is a front view showing a state in which the rivet contact 20 cannot be properly crimped to the current-carrying conductor 5 according to embodiment 1. As shown in Figure 6, if the crimping allowance d is too long, only the vicinity of the tip surface 1c of the body 1a of the base metal portion 1 expands, so the through hole 5a of the current-carrying conductor 5 does not expand, and the base metal portion 1 moves relative to the current-carrying conductor 5, making it impossible to crimp the rivet contact 20 with the appropriate crimping strength.

FIG. 7 is a graph showing the results of a test in which the rivet contact 20 is crimped to the current-carrying conductor 5 in the first embodiment. The graph shows the presence or absence of cracks occurring in the contact 2, with the thickness t of the current-carrying conductor 5 on the horizontal axis and the crimping allowance d on the vertical axis. The crimping allowance d is in mm, and the thickness t of the current-carrying conductor 5 is in mm. The current-carrying conductor 5 is copper, and the contact 2 is Ag (85 wt%)-WC (12 wt%)-Gr (3 wt%). wt% is weight percent. When crimping, the contact 2 expands slightly and the diameter of the contact 2 increases, but in this test, the crimping was performed without restraining the outer periphery of the contact 2. A circle indicates a state in which there is no contact crack that can be visually confirmed, and a cross indicates the presence of a contact crack that can be visually confirmed. The threshold value a1 indicated by a white triangle is a threshold value for identifying whether or not there is a contact crack. When the crimping allowance d is smaller than the threshold value a1, there is a possibility of contact cracks occurring, and when the crimping allowance d is larger than the threshold value a1, there is no possibility of contact cracks occurring. The threshold value a2 indicated by a black triangle is a threshold value for determining whether the crimping force will become weak or not. When the crimping allowance d is larger than the threshold value a2, the crimping force becomes weak and an appropriate crimping force cannot be obtained, and when the crimping allowance d is smaller than the threshold value a2, the required crimping force can be obtained.

According to the test results in FIG. 7, when the value of t×(d ^1.4 ) is greater than 2.3, that is, when the following formula (1) is established, it was visually confirmed that no cracks occurred in the contact 2 .
t×(d ^1.4 )>2.3 (1)

This result shows that when the thickness t of the current-carrying conductor 5 is thin, the force during crimping is easily transmitted to the contact 2, so it is necessary to crimp it shallowly (i.e., the crimping allowance d is large); however, when the thickness t of the current-carrying conductor 5 is thick, the force is not easily transmitted to the contact 2, so it can be crimped deeply (i.e., the crimping allowance d is small).

Moreover, as shown by the threshold value a2, when d+t≧4.7, the crimping force becomes weak and the contact stability is impaired, as shown in Fig. 6, and the conductor cannot be used as a main circuit conductor. Therefore, in order to obtain an appropriate crimping strength, the sum of the thickness t of the current-carrying conductor 5 and the crimping allowance d must be less than 4.7 mm, as shown in the following formula (2).
d+t<4.7 (2)

When a main circuit conductor that satisfies formula (1) is installed in a switch such as a circuit breaker or an electromagnetic switch, it can withstand thousands of shocks such as those in a no-load durability test, ensuring long-term reliability.

In addition, in the case of contacts with a Vickers hardness of 160 HV or less, if formula (1) is not satisfied, the contact 2 will be easily deformed when the rivet contact 20 is crimped, and depending on the shape of the contact 2, it will not satisfy the contact requirement of 0.5 mm or more for silver alloy contacts as stipulated in the Electrical Appliance and Material Safety Law.

In addition, when sintered contacts contain tungsten carbide, they are weaker against the impact force of crimping than the above-mentioned silver-based alloy contacts, and cracks are more likely to occur, and the effect of formula (1) is more pronounced. In particular, when the tungsten carbide content is 40 wt% or less, if formula (1) is not satisfied, the contact 2 is more likely to deform when the rivet contact 20 is crimped, and depending on the shape of the contact 2, the contact requirement of 0.5 mm or more for silver alloy contacts specified in the Electrical Appliance and Material Safety Law will not be satisfied. In addition, although sintered contacts are usually joined to the current-carrying conductor by brazing, in the first embodiment, the rivet shape is less expensive than brazing, and the characteristics of sintered contacts, which suppress temperature rise during current flow and have excellent welding performance, can be utilized.

Furthermore, when sintered contacts contain graphite, they are weaker against the impact force of crimping than the silver-based alloy contacts described above, and are more susceptible to cracking, making the effect of formula (1) more pronounced. In particular, when the graphite content is 2% or more, the effect of formula (1) is more pronounced, and they can withstand thousands of impacts such as those in no-load durability tests, ensuring long-term reliability. Furthermore, it is possible to take advantage of the characteristics of sintered contacts, which have an inexpensive rivet shape, suppress temperature rise when current is applied, and have excellent contact welding performance.

Tungsten carbide and graphite may also be included in the contact 2. In this case, the rivet shape is inexpensive, the temperature rise during current flow is suppressed, and the characteristics of the sintered contact, which has excellent welding performance, can be utilized.

Thus, according to the first embodiment, when the thickness of the current-carrying conductor 5 is t and the crimping allowance after the rivet contact 20 is crimped is d, the relationships t × ( ^d1.4 ) > 2.3 and d + t < 4.7 mm are satisfied. This prevents cracks from occurring in the contacts and prevents the contacts from becoming easily detached, ensuring the long-term reliability of the main circuit conductor.

Embodiment 2.
In the first embodiment, an example of a single-break circuit breaker has been described, but in the second embodiment, the main circuit conductor having the rivet contact 20 and the current-carrying conductor 5 described in the first embodiment is applied to a double-break circuit breaker. Fig. 8 is a cross-sectional view showing the tripped state of the double-break circuit breaker according to the second embodiment.

As shown in Fig. 8, the circuit breaker includes, as fixed contacts, a first fixed contact 40 as a current-carrying conductor, a first fixed contact 41 provided on the first fixed contact 40, a second fixed contact 42 as a current-carrying conductor, and a second fixed contact 43 provided on the second fixed contact 42. The circuit breaker shown in Fig. 8 also includes, as movable contacts, a first movable contact 50 as a current-carrying conductor, a first movable contact 51 provided on the first movable contact 50, a second movable contact 52 as a current-carrying conductor, and a second movable contact 53 provided on the second movable contact 52. The first movable contact 50 and the second movable contact 52 are integral structures supported by the rotating shaft 54 of the rotor 55, and extend in opposite directions to each other. When the rotor 55 rotates clockwise from the state shown in FIG. 8, the first movable contact 50 and the second movable contact 52 rotate clockwise, the first movable contact 51 abuts against the first fixed contact 41, the second movable contact 53 abuts against the second fixed contact 43, and the circuit breaker enters a conductive state.

The main circuit conductor having the rivet contact 20 and the current-carrying conductor 5 described in detail in the first embodiment can be used as the fixed contact and the movable contact of the double-break circuit breaker shown in FIG. 8.

Embodiment 3.
In the third embodiment, the main circuit conductor having the rivet contact 20 and the current-carrying conductor 5 described in the first embodiment is applied to an electromagnetic switch. Fig. 9 is a cross-sectional view showing the configuration of the electromagnetic switch according to the third embodiment.

The electromagnetic switch as a switch includes, as fixed contacts, a first fixed contact 60 as a current-carrying conductor, a first fixed contact 61 provided on the first fixed contact 60, a second fixed contact 62 as a current-carrying conductor, and a second fixed contact 63 provided on the second fixed contact 62. The electromagnetic switch includes, as movable contacts, a first movable contact 70 as a current-carrying conductor, a first movable contact 71 provided on the first movable contact 70, a second movable contact 72 as a current-carrying conductor, and a second movable contact 73 provided on the second movable contact 72. The first movable contact 70 and the second movable contact 72 are integral structures supported by the plunger 74 of the electromagnetic actuator 75 and extend in opposite directions to each other. From the state shown in FIG. 9, the electromagnetic actuator 75 has a fixed core 76 and a movable core 77, and when a current flows through the coil 78, the fixed core 76 attracts the movable core 77. A plunger 74 is attached to the movable core 77. When the electromagnetic actuator 75 operates, the fixed core 76 attracts the movable core 77, causing the first movable contact 71 to abut against the first fixed contact 61 and the second movable contact 73 to abut against the second fixed contact 63, and the electromagnetic switch becomes conductive.

The main circuit conductor having the rivet contact 20 and the current-carrying conductor 5 described in detail in embodiment 1 can be used as the fixed contact and the movable contact of the electromagnetic switch shown in FIG. 9.

The configurations shown in the above embodiments are merely examples of the contents of this disclosure, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the spirit of this disclosure.

1 base metal portion, 1a body portion, 1b head portion, 1c, 1e tip surface, 1d tip portion, 2 contact, 3 joint surface, 5, 6, 8 current-carrying conductor, 5a through hole, 7 fixed side contact, 9 movable side contact, 10 handle, 11 punch, 20 rivet-shaped contact (rivet contact), 30 opening/closing mechanism portion, 40, 60 first fixed contact, 41, 61 first fixed contact, 42, 62 second fixed contact, 43, 63 second fixed contact, 50, 70 first movable contact, 51, 71 first movable contact, 52, 72 second movable contact, 53, 73 second movable contact, 54 rotating shaft, 55 rotor, 74 plunger, 75 electromagnetic actuator, 76 fixed core, 77 movable core, 78 coil, d crimping allowance, t thickness of current-carrying conductor.

Claims (7)

a current-carrying conductor having a hole;
a rivet-shaped contact that is inserted into the hole of the current-carrying conductor and crimped;
Equipped with
When the thickness of the current-carrying conductor is t and the crimping margin after the contact is crimped is d,
t × (d ^1.4 ) > 2.3, and d + t < 4.7 mm
Satisfied ,
A main circuit conductor characterized in that the crimping allowance d is determined so that the crimping allowance d increases as the thickness t of the current-carrying conductor becomes thinner . The main circuit conductor according to claim 1, characterized in that the contacts have a Vickers hardness of 160 HV or less. The main circuit conductor according to claim 1 or 2, characterized in that the contacts are sintered contacts and contain tungsten carbide. The main circuit conductor according to claim 3, characterized in that the contacts have a tungsten carbide content of 40% by weight or less. The main circuit conductor according to any one of claims 1 to 4, characterized in that the contacts are sintered contacts and contain graphite. The main circuit conductor according to claim 5, characterized in that the contact contains 2% or more by weight of the graphite. A switch characterized by using a main circuit conductor according to any one of claims 1 to 6.