A thermally expanded protective piezoresistor, a filler and a method for preparing the same

Abstract

The application belongs to the technical field of circuit protection devices, and discloses a thermal expansion protection varistor, which is arranged on a circuit board as a plug-in varistor to form a discharge branch circuit, comprising a shell and a varistor module arranged in the shell, the varistor module has two pins, the pins pass through an opening in the lower part of the shell and are connected to an external circuit structure to form the discharge branch circuit, the shell further has an expansion part and an expansion extrusion part, the varistor module has a breakable part at any position of the series-connected discharge branch circuit, the expansion part and the expansion extrusion part are arranged on the two sides of the breakable part respectively, the expansion part is expanded by heat to push the expansion extrusion part to break the breakable part to form an open circuit.

Description

Technical Field

[0001] This invention belongs to the technical field of circuit protection devices, and relates to a varistor, specifically a varistor with thermal expansion protection, a filler, and a method for preparing the varistor. Background Technology

[0002] A varistor is a voltage-limiting protection device. Utilizing its non-linear characteristics, when an overvoltage occurs between its terminals, the varistor clamps the voltage to a relatively fixed value, thus protecting downstream circuits. The main parameters of a varistor include: varistor voltage, current carrying capacity, junction capacitance, and response time. The response time of a varistor is in the nanosecond range, faster than a gas discharge tube but slightly slower than a TVS diode. Generally, its response speed is sufficient for overvoltage protection in electronic circuits. The junction capacitance of a varistor is typically in the range of several hundred to several thousand pF. In many cases, it is not suitable for direct application in the protection of high-frequency signal lines. When used in AC circuit protection, its large junction capacitance increases leakage current, which needs to be carefully considered when designing the protection circuit. The current carrying capacity of a varistor is relatively large, but smaller than that of a gas discharge tube. A varistor, abbreviated as VDR, is a voltage-sensitive non-linear overvoltage protection semiconductor element.

[0003] For onboard plug-in varistors, the conventional form consists of an inner core and two leads, encased in resin or other polymer materials, and connected to external circuits via the leads. Varistors are susceptible to degradation; during use, the originally formed current-carrying branch can short-circuit due to deterioration, leading to overheating and fire. Current technology typically includes an explosion-proof housing filled with a silica sand-based filler layer to prevent short-circuiting and fires caused by degradation, thus preventing external equipment malfunctions. This filler layer extinguishes arcs and provides heat insulation, preventing degradation and fire. However, while this structure prevents deflagration, if the varistor isn't replaced promptly, it remains in a short-circuit state, significantly impacting external circuits. Even with fuses in the external circuit, if the varistor's degradation level prevents the current from reaching the fuse's trip threshold, a safety hazard still exists.

[0004] Existing technologies include solutions with built-in fuses and other protective devices to provide additional protection. However, for such small plug-in varistors, manufacturing is difficult and costly, requiring changes to the internal structure. Furthermore, for explosion-proof varistors with a filler layer, the filling effect needs to be considered. Otherwise, the uniformity of the filler layer may be affected by the protective devices, potentially leading to a failure to achieve arc extinguishing and heat conduction. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a varistor with thermal expansion protection, a filler, and a method for preparing the same. By incorporating an expansion section and an expansion extrusion section inside, the varistor rapidly expands upon heating, breaking the structure with fragile parts to form an open circuit. This method has lower manufacturing costs while achieving better protection.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a thermal expansion-protected varistor, which is installed on a circuit board as a plug-in varistor to form a leakage branch. It includes a housing and a varistor module disposed within the housing. The varistor module has two pins, which protrude from the housing through an opening at the bottom of the housing and connect to an external circuit structure to form a leakage branch. The housing also has an expansion portion and an expansion compression portion. Any point on the series leakage branch formed on the varistor module has a breakable portion. The expansion portion and the expansion compression portion are respectively disposed on both sides of the breakable portion. When the expansion portion expands due to heat, it pushes the expansion compression portion to break the breakable portion, thus breaking the circuit.

[0008] In conjunction with the first aspect, the present invention provides a first embodiment of the first aspect, wherein the pressure-sensitive module has an inner core, and the pins are connected to both ends of the inner core;

[0009] The expansion and compression part is a sheet body set on any pin. The breakable part is set on the pin with the expansion and compression part. Both the breakable part and the expansion part are located between the expansion and compression part and the inner core. When the expansion part is heated and expands, it pushes the inner core and the expansion and compression part to separate from the breakable part. The expansion and compression part is displaced towards the opening of the shell under pressure.

[0010] In conjunction with the first embodiment of the first aspect, the present invention provides a second embodiment of the first aspect, wherein the expansion part is made of a heat-expanding material with an expansion pressure of not less than 1.0 N / mm2 and a minimum thickness of not less than 1.5 mm.

[0011] In conjunction with the first embodiment of the first aspect, the present invention provides a third embodiment of the first aspect, wherein both pins are provided with a breakable portion, and a single expansion and compression portion is simultaneously connected to both pins. It should be noted that this method can be considered a preferred embodiment, as long as it is ensured that a short circuit is formed when one pin is disconnected.

[0012] In conjunction with the first embodiment of the first aspect, the present invention provides a fourth embodiment of the first aspect, wherein the two inner cores are wrapped with a filler layer, and the expansion portion and the breakable portion are both disposed between the filler layer and the expansion and extrusion portion.

[0013] In conjunction with the first embodiment of the first aspect, the present invention provides a fifth embodiment of the first aspect, wherein the two inner cores are wrapped with a filler layer, the expansion portion is disposed between the inner core and the filler layer, and the breakable portion is disposed between the filler layer and the expansion extrusion portion.

[0014] In conjunction with the first aspect, the present invention provides a sixth embodiment of the first aspect, wherein the two pressure-sensitive modules have an inner core, and the pins have a bonding conductive portion, which is connected to both ends of the inner core through the bonding conductive portion;

[0015] The inner core is also attached to both sides with expansion and extrusion parts. The expansion and extrusion parts are formed independently or combined with the encapsulation layer for blocking the encapsulation shell. The conductive body has fastening pins and connects the inner core and the attached conductive parts through the conductive body.

[0016] The expansion extrusion section also has a raised portion with a gap to the inner core's attachment surface, the expansion section filling the raised portion and separating the entire expansion extrusion section from the inner core when heated;

[0017] The shell is made of flame-retardant material, and the shell expands and deforms when the expansion part is heated.

[0018] The encapsulation layer is formed by encapsulating a blocky solid structure, particulate solid filler, or liquid material, and its adhesion to the shell is between 0.3 and 1.2 N / mm. 2 Within the specified range, when the expansion portion expands due to heat, the encapsulation layer expands and deforms or detaches from the housing.

[0019] In conjunction with the first embodiment of the first aspect, the present invention provides a seventh embodiment of the first aspect, wherein the breakable portion is a portion whose thickness or connection area is less than 50% of the pin cross-section;

[0020] Or a detachable connection structure consisting of two sub-parts of a pin that can be detachably connected;

[0021] Alternatively, it can be used as a connection structure for two sub-parts of a pin connected by low-temperature soldering.

[0022] Secondly, the present invention also discloses a filler, wherein a filler layer is formed within the housing of the aforementioned thermal expansion-protected varistor, comprising, by weight:

[0023] The filler is prepared by uniformly mixing 100 parts of 10-30 mesh quartz sand, 3-6 parts of ammonium polyphosphate, 2-5 parts of aluminum hydroxide and 0.2-2 parts of coated red phosphorus with 1-3 parts of binder.

[0024] Thirdly, the present invention also discloses a preparation method for preparing the above-mentioned thermal expansion protected varistor, the specific steps of which are as follows:

[0025] After connecting the inner core and pins to form a pressure-sensitive module, the pins of the pressure-sensitive module are processed into easily breakable parts and then installed into the housing. Filler is then filled to form a filler layer. An expansion part and an expansion extrusion part are set at the bottom of the filler layer, and then glue is injected to fix and seal the product.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) The present invention provides a breakable part and an expansion part in the housing, so that after the varistor fails and deteriorates, it can use the heat generated by its continuous short circuit to quickly react and expand to disconnect the leakage branch, thereby forming a double protection with the varistor module, which can avoid the fire situation that may occur due to continuous short circuit.

[0028] (2) The present invention improves production efficiency and reduces production costs by using various expansion parts and expansion extrusion parts in combination, as well as various easily broken parts in a structural arrangement, while ensuring that the connection can be broken when heated.

[0029] (3) By optimizing the selection and ratio of the filler, the present invention can provide better explosion-proof effect, and at the same time, it can achieve better expansion and heat conduction effect in conjunction with the expansion part. Attached Figure Description

[0030] Figure 1 This is an external isometric schematic diagram of the varistor in its assembled state in an embodiment of the present invention;

[0031] Figure 2 This is an isometric view of the internal structure of the first type of varistor in this embodiment of the invention after the shell has been cut open;

[0032] Figure 3 This is a schematic diagram of the internal structure of the first type of varistor in this embodiment of the invention after the housing has been cut open;

[0033] Figure 4 This is an isometric view of the internal structure of the second type of varistor in this embodiment of the invention after the shell has been cut open;

[0034] Figure 5 This is a schematic diagram of the internal structure of the second type of varistor in this embodiment of the invention after the shell has been cut open;

[0035] Figure 6 This is an isometric view of the internal structure of the third type of varistor in this embodiment of the invention after the shell has been cut open;

[0036] Figure 7 This is a schematic diagram of the internal structure of the third type of varistor in this embodiment of the invention after the shell has been cut open;

[0037] Figure 8 This is a first isometric schematic diagram of the internal structure of the fourth type of varistor after the shell is cut apart in this embodiment of the invention;

[0038] Figure 9 This is a second isometric schematic diagram of the internal structure of the fourth type of varistor in this embodiment of the invention after the shell is cut open;

[0039] Figure 10 This is an isometric view of the internal assembly of the fifth type of varistor in this embodiment of the invention after the shell has been cut open;

[0040] Figure 11 This is an isometric view of the fifth type of varistor in this embodiment of the invention, after the shell and internal structure have been cut apart.

[0041] In the diagram: 1-Housing, 2-Pin, 3-Inner core, 4-Expansion section, 5-Breakable section, 6-Expansion and extrusion section, 7-Glue seal section, 8-Conductive bonding section, 9-Slot. Detailed Implementation

[0042] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0045] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0046] In the description of this application, it should be noted that the use of terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationships commonly used when the product is in use. These terms are used solely for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the use of terms such as "first" and "second" in the description of this application is only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0047] Furthermore, the use of terms such as "horizontal" and "vertical" in the description of this application does not imply that the component is required to be absolutely horizontal or suspended, but rather that it may be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but rather that it may be slightly tilted.

[0048] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0049] Example 1:

[0050] This embodiment discloses a varistor with thermal expansion protection, which is installed on a circuit board as a plug-in varistor to form a current-discharging branch, as shown in the reference. Figure 1 The device includes a housing 1 and a pressure-sensitive module disposed within the housing 1. The pressure-sensitive module has two pins 2, which protrude from the housing 1 through an opening at the bottom of the housing 1 and connect to an external circuit structure to form a leakage branch. The housing 1 also has an expansion part 4 and an expansion compression part 6. Any point on the leakage branch formed in series on the pressure-sensitive module has a breakable part 5. The expansion part 4 and the expansion compression part 6 are respectively disposed on both sides of the breakable part 5. When the expansion part 4 is heated and expands, it pushes the expansion compression part 6 to pull the breakable part 5 to break, thus forming an open circuit.

[0051] A preparation method is also disclosed for preparing the above-mentioned thermal expansion protection varistor. The specific steps are as follows: after connecting the inner core 3 and the pin 2 to form a varistor module, the pin 2 of the varistor module is processed to form a breakable part 5, and then they are installed into the housing 1 together. Then, filler is filled to form a filler layer. After setting the expansion part 4 and the expansion extrusion part 6 at the bottom of the filler layer, glue is injected to fix and seal to form the product.

[0052] Furthermore, an implementation method is provided, referring to... Figure 2 and Figure 3 The pressure-sensitive module has an inner core 3, and pins 2 are connected to both ends of the inner core 3; the expansion and compression part 6 is a sheet body set on any pin 2, and the breakable part 5 is set on the pin 2 with the expansion and compression part 6. The breakable part 5 and the expansion part 4 are both located between the expansion and compression part 6 and the inner core 3. When the expansion part 4 is heated and expands, it pushes the inner core 3 and the expansion and compression part 6 to separate from the breakable part 5. The expansion and compression part 6 is pressed and displaced toward the opening of the housing 1.

[0053] In this embodiment, the easily breakable part 5 is a structure formed by cutting a groove directly on one side of the pin 2, with a cross-sectional size smaller than 50% of the cross-sectional size of the pin 2 itself. Typically, its thickness after cutting the groove is only about 30% of the normal thickness. As long as this structure ensures that it has a qualified electrical conductivity, it can be made of a more easily breakable material and, in conjunction with the extrusion force generated by the expansion volume of the expansion part 4, four times the expansion volume, it can have a relatively stable breaking effect.

[0054] It should be noted that the diagram shown is for illustrative purposes only, indicating that the expansion portion 4, which encloses pin 2 on only one side, is depicted as a relatively standard block. In actual production, depending on usage requirements and manufacturing process specifications, an expansion portion 4, primarily composed of expansion material, can be formed by filling a portion with expansion material. It is not limited to this portion consisting solely of expansion material or being a separate expansion body. The expansion compression portion 6 works in conjunction with the expansion portion 4. It is fixedly connected to the pin 2 portion near the breakable portion 5. When subjected to force, it transmits the force to the pin 2 portion at the connection point, causing it to pull the breakable portion 5 and break. Its area and thickness are not limited; it can be any structure fixedly connected to the pin 2 portion and possessing force transmission capabilities.

[0055] Furthermore, another implementation method is provided, referring to... Figure 4 and Figure 5 To improve the sensitivity of expansion disconnection, one or more breakable parts 5 can be provided on each of the two pins 2. In this embodiment, the breakable part 5 also adopts the groove method. This structure can be directly cut to the corresponding position of the pin 2 during manufacturing. Its manufacturing method is simple and low cost. Moreover, it is fixed by filling or injecting glue in the housing 1 and remains stable under the action of no external force.

[0056] The expansion and extrusion part 6 is a thin sheet material with an area close to the opening area of ​​the housing 1. After fixing it directly to the two pins 2, the expansion part 4 is first fixed between it and the inner core 3, and then they are placed into the housing 1 together. Finally, glue is injected to form the sealing part 7 for fixation. At this time, the inner core 3 deteriorates and heats up. The expansion part 4 expands due to heat and applies extrusion force to the inner core 3 and the expansion and extrusion part 6. Since the housing 1 is a rigid material, it cannot deform. However, the opening with the sealing part 7 can deform or even break when subjected to external force. At this time, the inner core 3 remains stable relative to the housing 1, while the expansion and extrusion part 6 will move outward. At the same time, it pulls the pins 2 on both sides to break at the breakable part 5, thus forming an open circuit.

[0057] Furthermore, another embodiment is provided, wherein the two inner cores 3 are wrapped with a filler layer, and the expansion portion 4 and the breakable portion 5 are both disposed between the filler layer and the expansion and extrusion portion 6.

[0058] In another option, refer to Figure 6 and Figure 7 The two inner cores 3 are wrapped with a filler layer, the expansion part 4 is disposed between the inner core 3 and the filler layer, and the breakable part 5 is disposed between the filler layer and the expansion and extrusion part 6.

[0059] The filler layer comprises, by weight: 100 parts of 10-30 mesh quartz sand, 3-6 parts of ammonium polyphosphate, 2-5 parts of aluminum hydroxide, and 0.2-2 parts of coated red phosphorus. The filler is prepared by uniformly mixing the above materials with 1-3 parts of binder.

[0060] Furthermore, another implementation method is provided, referring to... Figure 8 and Figure 9 Two pressure-sensitive modules have an inner core 3, and pins 2 have a bonding conductive part 8. The bonding conductive part 8 is connected to both ends of the inner core 3. The two sides of the inner core 3 are also attached with expansion extrusion parts 6. The expansion extrusion parts 6 have a conductor, which connects the inner core 3 and the bonding conductive part 8. The expansion extrusion parts 6 also have a raised part with a gap between it and the surface of the inner core 3. The expansion part 4 fills the raised part and separates the entire expansion extrusion part 6 from the inner core 3 when heated. The shell 1 is made of fire-resistant soft material. When the expansion part 4 is heated and expands, the shell 1 expands and deforms.

[0061] It should be noted that, in this embodiment, the easily breakable part 5 is the part whose thickness or connection area is less than 50% of the cross-section of the pin 2;

[0062] Alternatively, it can be a detachable connection structure consisting of two sub-parts of pin 2; see reference. Figure 10 and Figure 11The figure shows a detachable connection structure, in which one side pin 2 includes two interlocking sub-parts, wherein the sub-part connecting the inner core 3 has a slot 9, and the other sub-part is inserted into the slot 9 and fixed by being covered by the expansion part 4.

[0063] Alternatively, it can be used as a connection structure for two sub-parts of pin 2 connected by low-temperature soldering.

[0064] In this embodiment, the expansion part 4 is made of a heat-expanding material with an expansion pressure of not less than 1.0 N / mm2 and a minimum thickness of not less than 1.5 mm.

[0065] To verify the technical advantages of the varistor in the above embodiments compared to existing technologies, a comparative example group of experiments was added for verification:

[0066] All experimental samples used MYN15-621K products and shells with dimensions of 15x12x25 mm. The filler consisted of 100 parts of 10-30 mesh quartz sand, 5 parts of ammonium polyphosphate, 3 parts of aluminum hydroxide, and 1 part of coated red phosphorus. These materials were mixed evenly with 1 part of adhesive. The easily breakable part 5 was made by breaking two pins 2 3-4 mm away from the pressure-sensitive body and then soldering them together using conventional soldering. Different expansion fasteners were added for comparative testing.

[0067] Experimental method: Connect the product to a power supply with a power of 30KVA, a test voltage of 550V AC, a short-circuit current of 15-16A, and connect an ammeter in series in the circuit to indicate the actual current and confirm whether the circuit is disconnected. Continue to apply 550V until the product is disconnected from the power supply.

[0068] Comparative Experiment Group 1:

[0069] The expansion block measures 10x6mm in size, has a thickness of 3mm, and an expansion pressure of 0.5N / mm². 2

[0070]

[0071]

[0072] Comparative Experiment Group 2:

[0073] The expansion block has a size of 10x6mm, a thickness of 3mm, and an expansion pressure of 1N / mm². 2

[0074]

[0075]

[0076] Comparative Experiment Group 3:

[0077] The expansion block measures 10x6mm in size and 1.5mm in thickness, with an expansion pressure of 1N / mm². 2

[0078]

[0079]

[0080] As can be seen in the example group, when the expansion pressure is lower than the specified value, even if the product has short-circuited and heated up, it cannot effectively cause the pin 2 of the fragile part 5 to detach, thus forming an effective open circuit. When the thickness of the material selected to achieve the set expansion pressure is insufficient, it also cannot effectively disconnect the fragile part 5.

[0081] This invention is not limited to the optional embodiments described above, and anyone can derive other various forms of products based on the inspiration of this invention. The specific embodiments described above should not be construed as limiting the scope of protection of this invention; the scope of protection of this invention should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A thermal expansion-protected varistor, configured as a plug-in varistor on a circuit board to form a bleed current branch, comprising a housing (1) and a varistor module disposed within the housing (1), the varistor module having two pins (2) and the pins (2) extending out of the housing (1) from an opening at the lower part of the housing (1) and connecting to an external circuit structure to form a bleed current branch, characterized in that: The housing (1) also has an expansion part (4) and an expansion squeezing part (6). Any part of the series of leakage branches formed on the pressure-sensitive module has a breakable part (5). The expansion part (4) and the expansion squeezing part (6) are respectively arranged on both sides of the breakable part (5). The expansion part (4) expands when heated and pushes the expansion squeezing part (6) to pull the breakable part (5) to break and form a circuit. The pressure-sensitive module has an inner core (3), and the pins (2) are connected to both ends of the inner core (3); The expansion and compression part (6) is a sheet body set on any pin (2). The breakable part (5) is set on the pin (2) with the expansion and compression part (6). The breakable part (5) and the expansion part (4) are both located between the expansion and compression part (6) and the inner core (3). When the expansion part (4) is heated and expanded, it pushes the inner core (3) and the expansion and compression part (6) to separate from the breakable part (5). The expansion and compression part (6) is pressed and displaced toward the opening of the housing (1).

2. The varistor for thermal expansion protection according to claim 1, characterized in that: The expansion section (4) has an expansion pressure of not less than 1.0 N / mm. 2 It is made of a heat-expanding material, with a minimum thickness of not less than 1.5 mm.

3. The varistor with thermal expansion protection according to claim 1, characterized in that: Both pins (2) are provided with a breakable part (5), and a single expansion and compression part (6) is connected to both pins (2) at the same time.

4. A varistor for thermal expansion protection according to claim 1, characterized in that: The two inner cores (3) are wrapped with a filler layer, and the expansion part (4) and the breakable part (5) are both disposed between the filler layer and the expansion extrusion part (6).

5. A varistor for thermal expansion protection according to claim 1, characterized in that: The two inner cores (3) are wrapped with a filler layer, the expansion part (4) is disposed between the inner core (3) and the filler layer, and the breakable part (5) is disposed between the filler layer and the expansion extrusion part (6).

6. A varistor for thermal expansion protection according to claim 1, characterized in that: The breakable part (5) is the part whose thickness or connection area is less than 50% of the cross-section of the pin (2); Or as a detachable connection of the pins (2) of the two sub-parts of the detachable connection structure; Or it can be used as a connection structure for two sub-parts of pins (2) connected by low-temperature soldering.

7. A varistor for thermal expansion protection according to claim 4 or 5, characterized in that: The filler layer comprises, by weight: The filler is prepared by uniformly mixing 100 parts of 10-30 mesh quartz sand, 3-6 parts of ammonium polyphosphate, 2-5 parts of aluminum hydroxide and 0.2-2 parts of coated red phosphorus with 1-3 parts of binder.

8. A preparation method, characterized in that: The specific steps for preparing the varistor with thermal expansion protection as described in claim 6 are as follows: after connecting the inner core (3) and the pin (2) to form a varistor module, the pin (2) of the varistor module is processed to form a breakable part (5), and then they are installed together into the housing (1), and then filler is filled to form a filler layer. After setting an expansion part (4) and an expansion extrusion part (6) at the bottom of the filler layer, glue is injected to fix and seal to form a product.

Images