ARC EXTINGUISHING CHAMBER BASE OF MOLDED CASE CIRCUIT BREAKER

Abstract

The present disclosure relates to an arc extinguishing chamber base of a molded case circuit breaker and, more specifically, to an arc extinguishing chamber base of a molded case circuit breaker, manufactured using a thermoplastic resin. The present disclosure enables an arc extinguishing chamber base for forming a molded case circuit breaker to be manufactured using an aromatic polyamide-based thermoplastic resin, thereby enabling an increase in productivity, a decrease in component weight, a reduction in component production time, an eco-friendly effect, and recycling. Furthermore, component lifespan increases.

Claims

1. An arc extinguishing chamber base applied to a molded case circuit breaker provided therein with components and installed in a part of a circuit so as to shut off the circuit or allow a current to flow in the circuit, wherein the arc extinguishing chamber base is made of a material including a thermoplastic resin, and wherein the thermoplastic resin is an aromatic polyamide-based (polyphthalamide) resin having the following chemical formula: ##STR00003##

2. The arc extinguishing chamber base of claim 1, wherein the thermoplastic resin includes a PA66 (polyamide resin) material.

3. The arc extinguishing chamber base of claim 1, wherein the aromatic polyamide-based resin consists of 30 mol % or more and less than 100 mol % of aromatic dicarboxylic acid.

4. The arc extinguishing chamber base of claim 1, wherein the aromatic polyamide-based resin consists of aliphatic or cycloaliphatic C4-C15 diamine.

5. The arc extinguishing chamber base of claim 1, wherein the material further includes a metal material.

6. The arc extinguishing chamber base of claim 1, wherein the material further includes an inorganic filler, a heat stabilizer, an antioxidant, a light stabilizer, a flame retardant, and a colorant.

7. The arc extinguishing chamber base of claim 1, wherein the material of the arc extinguishing chamber base is composed of 30 to 75% by weight of the aromatic polyamide resin, 20 to 65% by weight of an inorganic filler, and 1 to 50% by weight of remaining constituents.

8. The arc extinguishing chamber base of claim 1, wherein the material further includes ball particles made of any one of ceramic, glass, and fiber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a schematic view illustrating a manufacturing process of BMC used in the related art MCCB.

[0038] FIG. 2 is a schematic view illustrating a manufacturing process of SMC used in the related art MCCB.

[0039] FIG. 3 is a cross-sectional view illustrating an injection molding machine used for manufacturing the related art MCCB.

[0040] FIG. 4 is a cross-sectional view illustrating a compression molding machine used for manufacturing the related art MCCB.

[0041] FIG. 5 is a cross-sectional view of an MCCB according to one embodiment of the present disclosure.

[0042] FIG. 6 is a perspective view illustrating an arc extinguishing chamber base applied to the MCCB according to the one embodiment of the present disclosure.

[0043] FIG. 7 is a cut view of an arc extinguishing chamber base applied to an MCCB according to another embodiment of the present disclosure.

BEST MODE OF CARRYING OUT EMBODIMENTS

[0044] Hereinafter, an MCCB according to one embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0045] FIG. 5 illustrates an MCCB according to one embodiment of the present disclosure, and FIG. 6 illustrates an arc extinguishing chamber base applied to the MCCB according to the one embodiment of the present disclosure.

[0046] Referring to FIGS. 5 and 6, an MCCB 100 according to the present disclosure is installed at a part of a line (circuit) to open and close the line when an overcurrent or fault current occurs. The MCCB 100 is equipped with a trip device to operate an opening and closing mechanism to automatically shut off the line in the event of a fault such as overload, short circuit, and the like, thereby protecting a load and the line.

[0047] The MCCB 100 includes a case 110, a fixed portion 130 fixed to a power terminal 120 at one side of the case 110, and a movable portion 150 configured to be rotatable by a shaft 140, an arc extinguishing chamber 160 provided adjacent to contact portions, namely the fixed and movable portions 130 and 150, an opening and closing mechanism 200 configured to rotate the shaft 140 as a lower link (not shown) is interlocked by an upper link (not shown) connected to a handle 170, a trip mechanism 300 that operates the opening and closing mechanism 200 to shut off a current when an overcurrent and a short-circuit current are generated in the line, and a load terminal 400 connected to the trip mechanism 300.

[0048] When an overload occurred in the line of the MCCB having such a configuration is an overcurrent, a bimetal 306 fixed by a rivet begins to be curved or bent as heat is generated in a heater 307 provided inside the trip case 301.

[0049] As the bimetal 306 is curved, a gap between an adjustment screw 308 disposed on an upper portion of the bimetal 306 and a trip bar 309 becomes narrow, and eventually the adjustment screw 308 pushes the trip bar 309, thereby causing the trip bar 309 to rotate counterclockwise.

[0050] At this time, as a shooter (not shown), which is locked (or constrained) by the trip bar 309, is unlocked, the opening and closing mechanism 200 is operated, causing the MCCB 100 to be open.

[0051] FIG. 6 illustrates an arc extinguishing chamber base 500 applied to the MCCB 100 according to the one embodiment of the present disclosure. The arc extinguishing chamber base 500 is formed by injection molding or compression molding. The arc extinguishing chamber base 500 is provided with the fixed portion 130, the movable portion 150, the shaft 140, the arc extinguishing chamber 160, and the like. The opening and closing mechanism 200 is installed at an upper side of the arc extinguishing chamber base 500.

[0052] The arc extinguishing chamber base 500 of the MCCB 100 according to the present disclosure is molded by using a thermoplastic resin. Here, the thermoplastic resin may be an aromatic polyamide (e.g., polyphthalamide) based resin having the following chemical formula.

##STR00002##

[0053] The aromatic polyamide resin includes a repeating unit represented by the chemical formula. Here, 4<m<15, 50<n<1000, and each of M and N denotes an integer.

[0054] Such an aromatic polyamide-based resin contains a benzene ring, and the aromatic polyamide-based resin is, preferably, composed of 30 mol % or more and less than 100 mol % of aromatic dicarboxylic acid.

[0055] Conventionally, polyamide (PA) is generally used as an insulation material for electrical equipment products, which is excellent in electrical insulation, mechanical strength, heat resistance, abrasion resistance, flame retardancy, and moldability. In particular, among others, PA66 and PA6 have been widely used.

[0056] In addition, polyamide (PA) has been primarily used for cases of circuit breakers of low-voltage electrical equipment and switchgear products, but it has low heat resistant properties (melting point), making it difficult to be used instead of a thermoplastic resin material (melting point of PA6: 220° C., melting point of PA66: 260° C.)

[0057] Thus, in the present disclosure, aromatic polyamide, namely, polyphthalamide (PPA) is used for producing the case 110. The aromatic polyamide (polyphthalamide) has a similar molecular structure to the polyamide (PA). However, unlike a normal PA, the aromatic polyamide has an aromatic (benzene ring) structure, and thereby exhibits high rigidity and mechanical strength, an ability to maintain rigidity at a high temperature (Tm: 290° C.˜325° C., Tg: 90° C. 140° C.), high heat resistance, low moisture absorption, dimensional stability and low distortion, chemical resistance, and high property retention for an external environment.

[0058] An aromatic ratio of the material used in the present disclosure is 30 to 100 mol %, and an aliphatic carbon chain at both sides of an amide group has 4 to 15 carbon atoms.

[0059] In addition, even in the case of an alloy mixed with a material other than a polymerized polymer, an aromatic ratio (or molar proportion) of the entire alloy material may be in the range of 30 to 100 mol %.

[0060] The table below shows comparison of the arc extinguishing chamber base manufactured using SMC with the arc extinguishing chamber base 500 manufactured using PPA of the present disclosure.

TABLE-US-00001 TABLE 1 SMC PPA Density (g/cm3) 1.73 1.65 Tensile strength (MPa) 39.54 196.11 Tensile modulus (MPa) 9862 20017 Elongation (%) 0.48 1.72 Flexural strength (MPa) 72.94 305.39 Flexural modulus (MPa) 9520 17829 Impact strength (KJ/m2) 11.02 8.64

[0061] It can be seen from the Table 1 that the MCCB 100 according to the present disclosure exhibits more improved mechanical properties, such as tensile strength and tensile modulus, than the related art MCCB manufactured using the SMC because the arc extinguishing chamber base 500 is molded by using the thermoplastic resin, namely, PPA.

[0062] The material of the arc extinguishing chamber base 500 includes an aromatic polyamide resin (A), an inorganic filler (B), a heat stabilizer (C), an antioxidant (D), a light stabilizer (E), a flame retardant (F), a colorant (G), and the like.

[0063] Here, the inorganic filler (B) may be carbon fiber, glass fiber, boron fiber, carbon black, clay, kaolin, talc, mica, calcium carbonate, aluminum hydroxide, and the like, and be coated with a coupling agent to improve interfacial adhesion with the thermoplastic resin.

[0064] A material is, preferably, composed of 30 to 75% by weight of an aromatic polyamide resin, 20 to 65% by weight of an inorganic filler (glass fiber), and 1 to 50% by weight of remaining constituents (or components).

[0065] The results of testing the material of the arc extinguishing chamber base 500 using a test piece are presented in Tables 2 and 3 below. In the following examples and comparative examples, only an amount (or quantity) of aromatic polyamide resin (A) was changed, and types and weight ratios of the inorganic filler (B), heat stabilizer (C), antioxidant (D), light stabilizer (E), flame retardant (F), and colorant (G) were the same. Here, the total weight ratio, excluding the aromatic polyamide resin (A), of the material was 55%.

[0066] In addition, in consideration of flowability and injection capability (efficiency) during a molding process, a PA66 material was polymerized with an aromatic polyamide resin (A) having an aromatic ring in its main (or backbone) chain instead of solely using the aromatic polyamide resin. [0067] Classification of “aromatic polyamide resin” in this test

[0068] (A1) Polyamide resin (PA6T): PA6T, an aromatic polyamide resin containing an aromatic ring in a main chain produced by polycondensation of terephthalic acid and hexamethylenediamine, was used.

[0069] (A2) Polyamide resin (PA4T): PA4T, an aromatic polyamide resin containing an aromatic ring in a main chain produced by polycondensation of terephthalic acid and tetramethylenediamine, was used.

[0070] (A3) Polyamide resin (PA66): PA66, an aromatic polyamide resin containing an aromatic ring in a main chain produced by polycondensation of adipic acid and hexamethylenediamine, was used.

[0071] In the Table 2 below, the ratio (mixed ratio) of (B+C+D+E+F+G) expresses a ratio of those components to the total weight percentage (100% by weight) of the material, and the ratio of A, expressed as weight percentage, is a ratio of the aromatic polyamide resins to one another in a state of excluding B+C+D+E+F+G.

[0072] According to the contents of Table 2 below, each constituent was added to be made in the form of a pallet, which was produced through twin-screw melt extrusion, and the pellet was dried at a temperature of 100° C. for 6 hours or more. Then, test pieces for property evaluations (standard ISO test specimen) were produced using an injection molding machine.

TABLE-US-00002 TABLE 2 Comparative example Examples (Present disclosure) (related art) Composition 1 2 3 4 5 1 A1 10 30 50 70 A2 70 A3 90 70 50 30 30 100 B + C + 55 55 55 55 55 55 D + E + F + G

TABLE-US-00003 TABLE 3 Comparative Examples example Items Properties 1 2 3 4 5 1 Basic Melting Point (° C.) 265 280 295 310 325 260 characteristies Original Tensile strength 185 190 190 195 200 185 physical (Mpa) properties Flexural strength 290 290 295 300 305 280 (Mpa) Impact strength 10 9.5 9.0 8.5 8 10 (KJ/m2) Insulation strength 24 24 24 24 24 24 (kV) Physical Tensile strength 95 100 110 115 120 80 properties (Mpa) after Impact strength 8 8 8.5 8.5 8 7 testing (KJ/m2) Insulation strength 20 22 24 24 24 18 (kV) Lifespan of part 10 20 25 35 60 5 (Year)

[0073] The original (or initial) properties of the test pieces after production were measured by performing pretreatment at 25° C. and relative humidity of 50% for 48 hours, and properties after the tests were measured after leaving the test pieces at 180° C. for 648 hours.

[0074] Here, the lifespan of part is obtained in the following manner. That is, accelerated life testing was conducted by leaving the test pieces for property evaluations in a gear aging oven at 160° C., 180° C., and 200° C. for 2400 hours, 648 hours, and 480 hours, respectively, in accordance with UL746-b (RTI testing), performing pretreatment on the test pieces under the same condition as the pretreatment above to measure properties, and calculating based on the measured results a time (year) taken for tensile strength properties of the test pieces to be reduced down to 40 Mpa under 100° C., which is an actual operating temperature condition of the arc extinguishing chamber base of MCCB (or simply, MCCB AEC BASE) using the Arrhenius equation. The calculated time is the lifespan of part. The tensile strength of 40 Mpa is the minimum property of tensile strength required for parts to be used in a product.

[0075] As such, the polypetalamide-based thermoplastic resin may be used in the arc extinguishing chamber base 500, and a material such as PA66 may be polymerized with the thermoplastic resin for molding.

[0076] Regarding the original properties among the properties in the tables above, a support force between polymers is increased by increasing the content of glass fiber or reinforcing agent, thereby increasing mechanical strength.

[0077] When the content of the PA66, PA6, PPA, or inorganic filler is the same, the properties of the test pieces are similar.

[0078] As the polypetalamide-based thermoplastic resin has a low property degradation rate overtime under a high-temperature operating environment, it can be a good replacement for a thermosetting material. In other words, maintenance of PPA properties rather than original properties is more important for the arc extinguishing chamber base 500. More specifically, it can be seen from the tables, the examples of the present disclosure have better part lifespan than the comparative example. In addition, the mechanical properties, such as tensile strength, impact strength, and insulation strength, are equivalent to or higher than those of the comparative example. Further, in the properties after the tests, the property degradation rate relative to the original properties is lower than that of the comparative example.

[0079] In the present disclosure, as the arc extinguishing chamber base 500 constituting the circuit breaker 100 is manufactured using the polyphthalamide-based thermoplastic resin, it may provide advantages, such as increased productivity, weight reduction of parts, a decreased part production time, eco-friendliness, and recycling.

[0080] In addition, as the PA66 material is polymerized with the polyphthalamide-based thermoplastic resin, the properties (mechanical properties) of the material are improved.

[0081] Further, the polyphthalamide-based thermoplastic resin consists of aliphatic carbon having 4 to 15 carbon atoms, and also consists of 30 to 100 mol % of a benzene ring, thereby greatly improving the properties of the MCCB (mechanical properties).

[0082] In particular, the thermoplastic resin manufactured with the above composition allows the lifespan of part to be increased, and the property degradation rate over time to be reduced.

[0083] FIG. 7 illustrates an arc extinguishing chamber base according to another embodiment. In this embodiment, a resin forming the arc extinguishing chamber base 500 includes ball particles 510. The ball particles 501 may be made of ceramic, glass, fiber, and the like. The ball particles 501 may be mixed prior to a plastic injection molding process. This allows mechanical properties such as pressure resistance, impact resistance, and thermal resistance to be further improved.