Temperature limiting device

Abstract

The temperature limiting device comprises an outer container (2) defining a cup-shaped housing (3), closed by a lid (4), inside which a spring snap-in disc (6) and a bimetallic disc (7) are stacked. The lid (4) of the outer container (2) and the spring snap-in disc (6) each bear, respectively, a fixed contact (10) and at least one movable contact (11). The components of the temperature limiting device intended for the electrical contact function are coated externally, at least in part, with a surface layer (15) of electrically conductive paint.

Description

[0001] Description

[0002] TEMPERATURE LIMITING DEVICE

[0003] Technical Field

[0004]

[0001] The present invention relates to a temperature limiting device for protecting electrical apparatus and the like, as well as a method for manufacturing such a device.

[0005] Prior Art

[0006]

[0002] It is currently known, in the technical field concerning the production of temperature limiting devices designed to ensure the thermal protection of electrical devices or apparatus components such as electric motors and the like, the use of anti-overheating temperature limiting devices based on the use of a bimetallic disc capable of switching the configuration of a spring snap-in disc that correspondingly closes or opens an electrical circuit of the device to be protected. Such temperature limiting devices, in the specified field, are also referred to as bimetallic thermal switches.

[0007]

[0003] Specifically, the bimetallic disc is capable of switching from a low-temperature position to a high-temperature position, where it acts on the spring snap-in disc to open the electrical circuit and thereby interrupt the current and consequently the heating. Essentially, when the temperature detected by the bimetallic thermal switch exceeds the trip threshold, the switch’s bimetallic disc snaps, opening the circuit and interrupting the current. As the apparatus in which it is installed cools down, the thermal switch can automatically close again.

[0008]

[0004] A temperature limiting device of this type is illustrated, for example, in European Patent EP 0678891.

[0009]

[0005] This temperature limiter comprises an outer container defining a cup-shaped chamber, closed by a lid, inside which a bimetallic disc and a spring snap-in disc are stacked. The lid carries the switch’s fixed contact, while the spring snap-in disc carries the moving contact. Under normal operating conditions, i.e., at low temperatures, the spring snap-in disc presses the movable contact against the fixed contact, thereby closing the electrical circuit and allowing current to flow. However, when the temperature exceeds a predetermined threshold value, the bimetallic disc reverses its position, consequently displacing the spring snap-in disc. In this way, the movable contact detaches from the fixed contact and the electrical circuit opens, interrupting the flow of current and the heating.

[0010]

[0006] Document US 2013 / 271258 A1 describes another temperature limiting device of the same type.

[0011]

[0007] The temperature limiter is designed such that it itself constitutes an active component of the electrical circuit by means of the assembly of various elements that effectively perform the function of an electrical contact. Because of this characteristic, unlike sensors in thestrict sense — which are only traversed by signal currents characterized by low voltages and low amperages — bimetallic thermal switches can be connected in series with the apparatus they protect. Specifically, the electrical circuit of the bimetallic thermal switch is traversed by a current equal to the power consumption determined by the operation of the apparatus itself. Furthermore, the bimetallic thermal switch must be sized to be able to interrupt and, if necessary, restore the aforementioned electrical load for a minimum number of cycles depending on the application, understood as the opening and subsequent reclosing of the circuit.

[0012]

[0008] Currently, the components of the bimetallic thermal switch that are actively affected by the flow of electric current — that is, the conductive parts of the assembly — may be made entirely of a material with high electrical conductivity (such as silver or its alloys, copper or its alloys, gold or its alloys, and similar materials). It should be noted that we are referring to “solid” contacts, meaning the entire volume of the aforementioned components is made of the same material without any discontinuity; or they may be made of a material with poor electrical conductivity, such as brass, which is then coated on the surface via a galvanic process with a layer of conductive material that is very often silver or a silver alloy; in this case, the flow of electric current is primarily carried by the coating, while the solid body of the component performs the mechanical functions. This second construction method allows for the use of more efficient production technologies compared to the machining of solid materials such as silver and its alloys, enabling the creation of complex shapes by leveraging the significantly superior workability of materials like brass, which, albeit to a limited extent, offer superior mechanical performance compared to silver and its alloys or, more generally, compared to conventional metals used for electrical contacts, thereby reducing the use of precious metals.

[0013]

[0009] The coating of components with surface layers of electrically conductive material to serve as electrical contacts is achieved by means of galvanic or electrochemical processes, by immersing the component to be coated in a bath with a complex chemical composition and applying a specific electrical potential. These processes require large amounts of energy, occupy significant space in terms of production facilities, and generally produce substantial quantities of wastewater that must be properly managed and treated to prevent environmental harm. A further factor contributing to the process’s inefficiency stems from the fact that electroplating baths are subject to contamination by exogenous agents that may originate from the component itself intended for coating.

[0014] Disclosure

[0015]

[0010] The objective of the present invention is to solve the aforementioned problems by devising a temperature limiting device capable of ensuring a better environmental impact, as it requires lower energy consumption and significantly reduces wastewater production.

[0011] Within the scope of this objective, a further purpose of the invention is to provide a temperature limiting device with greater wear resistance.

[0016]

[0012] Another objective of the invention is to provide a temperature limiting device with a greater ability to extinguish the electric arc during operations involving the separation or closing of contacts under electrical load, thereby increasing the number of operations that can be performed and / or the maximum permissible current.

[0017]

[0013] A further objective of the invention is to provide a simple construction and operation temperature limiting device, featuring reliable performance, versatile application, and relatively low cost.

[0018]

[0014] The aforementioned objectives are achieved, according to the present invention, by the temperature limiting device of claim 1.

[0019]

[0015] The temperature limiting device comprises an outer container defining a cup-shaped chamber closed by a lid, inside which a spring snap-in disc and a bimetallic disc are stacked.

[0020]

[0016] Preferably, said outer container is made of conductive material.

[0021]

[0017] Preferably, said lid is made of insulating material.

[0022]

[0018] Alternatively, said lid is made of a combination of materials such that it is insulated from said outer container.

[0023]

[0019] The bimetallic disc is axially associated with said spring snap-in disc.

[0024]

[0020] The temperature limiting device comprises at least one fixed contact secured to said lid of the outer container and protruding in part below said lid, and at least one movable contact secured to said spring snap-in disc.

[0025]

[0021] Preferably, said lid is clamped against a ring-shaped spacer, which in turn rests peripherally on a ring-shaped shoulder formed internally by said outer container.

[0026]

[0022] According to the present invention, the components of the temperature limiting device intended to function as electrical contacts are externally coated, at least in part, with a surface layer of electrically conductive paint.

[0027]

[0023] The term “electrically conductive paint” refers to an organic coating, for example acrylic-, urethane-, or epoxy-based, with a progressively higher permissible operating temperature from the first to the third, in which conductive particles are dispersed; these particles are typically metallic in nature, such as silver, gold, copper, nickel, and the like, or organic in nature, such as graphite.

[0028]

[0024] Advantageously, said surface coating layer of the components intended for the function of electrical contact is made of an electrically conductive paint resistant to high temperatures.

[0029]

[0025] Advantageously, said components intended for the function of electrical contact comprise at least said outer container, said spring snap-in disc, said at least one fixed contact, andat least one movable contact.

[0030]

[0026] According to another aspect of the invention, the electrically conductive paint is advantageously supplemented with fillers that increase its wear resistance and its ability to extinguish the electric arc during operations involving the separation or approach of the contacts under electrical load.

[0031]

[0027] Preferably, the reinforcing action against wear mechanisms and the increase in resistance to erosion caused by the electric arc is provided by particles of refractory oxides (AIO2, SnO, CdO, and the like) finely dispersed in the organic matrix of the electrically conductive paint.

[0032]

[0028] The present invention also relates to a method for manufacturing a temperature limiting device that involves externally coating the components of said temperature limiting device intended for electrical contact, at least in part, with a surface layer of electrically conductive paint.

[0033] Brief description of the drawings

[0034]

[0029] The details of the invention will become clearer from the detailed description of preferred embodiments of the temperature limiting device, illustrated for illustrative purposes in the attached drawings, in which:

[0035] Figure 1 shows an axial section of the temperature limiting device according to the present invention;

[0036] Figures 1a, 1b, and 1c show enlarged details of the temperature limiting device in question;

[0037] Figure 2 shows an axial section of a different embodiment of the temperature limiting device according to the present invention;

[0038] Figures 2a and 2b show respective enlarged details of this different embodiment of the temperature limiting device.

[0039] Description of embodiments of the invention

[0040]

[0030] Referring first to Figure 1, the temperature limiting device according to the present invention is shown collectively as 1.

[0041]

[0031] The temperature limiting device comprises an outer container 2 defining a cup-shaped housing 3. The housing 3 of the outer container 2 is closed at the top by a lid 4, held in place by a peripheral folded rim 5 of the outer container 2. The outer container 2 is made of a conductive material, such as brass. The lid 4 is made of insulating material, such as ceramic or similar materials, or alternatively a combination of materials, including metallic ones, but such that it is insulated from the outer container 2.

[0042]

[0032] Inside the housing 3 of the outer container 2, a spring snap-in disc 6 and a bimetallic disc 7 are stacked. Under normal operating conditions, as shown in Figure 1, the spring snap- in disc 6, which has a slightly arched shape, rests peripherally on the bottom of thehousing 3 of the outer container 2; the bimetallic disc 7, which has a more arched shape, rests peripherally on the edge of the spring snap-in disc 6.

[0043]

[0033] As specified below, the spring snap-in disc 6 is preferably made of stainless steel coated with a surface layer of electrically conductive paint, instead of the traditional silver coating; the bimetallic disc 7 is preferably made of a sheet formed by bonding two different alloys, typically Fe-Ni and Mn-Cu-Ni.

[0044]

[0034] The lid 4 is clamped against a ring-shaped spacer 8, which in turn rests peripherally on a ring-shaped shoulder 9 formed internally by the outer container 2. In practice, the lid 4 and the spacer 8 are clamped together against the annular shoulder 9 by the folded edge 5 of the outer container 2, which has been suitably crimped. The spacer 8 is made, for example, of brass or similar material.

[0045]

[0035] The lid 4 has a fixed contact 10 of the thermal switch inserted axially in a manner known per se; the spring snap-in disc 6 in turn has a movable contact 11 of the thermal switch inserted axially. The fixed contact 10 is protruding below the lid 4; the movable contact 11 is protruding above the bimetallic disc 7 through an axial hole drilled in the bimetallic disc 7 itself.

[0046]

[0036] The contacts 10, 11 are made of metal, primarily brass and copper, coated with the aforementioned surface layer of electrically conductive paint.

[0047]

[0037] Under normal operating conditions, i.e., at low temperatures, the movable contact 11 is elastically pushed by the spring snap-in disc 6 against the fixed contact 10, thereby closing the electrical circuit and allowing the passage of current, as described below.

[0048]

[0038] The temperature limiting device is connected via appropriate cables to the outer container 2 and the fixed contact 10, respectively.

[0049]

[0039] According to the present invention, the components of the temperature limiting device through which electric current flows are externally coated with a surface layer 15 of electrically conductive paint. Hereinafter, the surface layer 15 of electrically conductive paint is also referred to simply as a conductive coating.

[0050]

[0040] Advantageously, said surface layer 15 coating the components through which electric current flows is made of a high-temperature-resistant electrically conductive paint.

[0051]

[0041] The said components through which electric current flows comprise at least the said outer container 2, the said spring snap-in disc 6, at least said one fixed contact 10, and at least said one movable contact 11 (see the enlarged details A, B, and C in Figures 1a, 1b, and 1c).

[0052]

[0042] In particular, it is possible to provide that all of the aforementioned components through which electric current flows are coated with the surface layer 15, or that only some of these components, for example only the contacts 10, 11, are coated with the layer 15.

[0053]

[0043] The operation of the temperature limiting device according to the present invention isreadily understood from the preceding description.

[0054]

[0044] Under normal operating conditions, the spring snap-in disc 6 and the bimetallic disc 7 are centered and locked between the base of the housing 3 defined by the outer container 2 made of conductive material and the lid 4 incorporating the fixed contact 10.

[0055]

[0045] The spring snap-in disc 6 constitutes the element through which the electric current passes and supports the movable contact 11, which is held in constant pressure against the fixed contact 10.

[0056]

[0046] The bimetallic disc 7, supported by the moving contact 11 passing through it, is capable of reacting to any changes in the temperature of the apparatus to be protected. When a preset switching temperature is reached, the bimetallic disc 7 snaps into the reverse position, with the concave side facing downward, and pushes the spring snap-in disc 6 downward.

[0057]

[0047] In this way, the connection between the fixed and movable contacts 10, 11 opens instantly, thereby halting the rise in temperature within the apparatus to be protected. Conversely, when the temperature drops and reaches the preset normal operating value, the bimetallic disc 7 snaps back to its initial position, and the contact closes again.

[0058]

[0048] Figure 2 illustrates a different embodiment of the temperature limiting device in which the lid 4 of the outer container 2 carries a pair of fixed contacts, indicated for clarity as 10a and 10b. The fixed contacts 10a and 10b pass through the lid 4 in parallel positions and are protruding in part from the lid 4 itself.

[0059]

[0049] Inside the housing 3 defined by the outer container 2, there is a circular movable bridge 12 arranged for abutment with the fixed contacts 10a and 10b. The movable bridge 12 is secured, by means of an axial rivet 13, to the spring snap-in disc 6 and the bimetallic disc 7, which are bundled together. Essentially, the movable bridge 12 performs the same function as the movable contact 11 in the previous solution. The movable bridge 12 is likewise coated with the aforementioned surface layer of electrically conductive paint.

[0060]

[0050] The spring snap-in disc 6 is held against a circular seat formed inside the housing 3 by a spacer ring 14.

[0061]

[0051] As described above, the components of the temperature limiting device through which electric current flows are coated externally, at least in part, with a high-temperature- resistant conductive coating 15 (see enlarged details D and E in Figures 2a and 2b).

[0062]

[0052] As in the previous case, if the temperature of the apparatus to be protected changes to the point of exceeding a preset switching temperature, the bimetallic disc 7 snaps into the reverse position, with the concavity facing downward, and pushes the spring snap-in disc 6 downward, opening the contact between the movable bridge 15 and the fixed contacts 10a and 10b.

[0063]

[0053] The temperature limiting device according to the present invention achieves the objectiveof ensuring a better environmental impact, as the energy consumption required is lower and waste production is significantly reduced.

[0064]

[0054] The temperature limiting device in question also features greater wear resistance and a greater ability to extinguish the electric arc during operations involving the separation or closing of the contacts under electrical load, thereby increasing the number of operations that can be performed and / or the maximum permissible current.

[0065]

[0055] This result is achieved through the inventive idea of externally coating the components of the temperature limiting device through which electric current flows with a surface layer of electrically conductive paint.

[0066]

[0056] The layer of electrically conductive paint effectively replaces all the functions of the galvanic coating used in the prior art, with the added advantage that the paint can be formulated with additives that increase its wear resistance and its ability to extinguish the electric arc during operations involving the separation or closing of contacts under electrical load, thereby increasing the number of operations that can be performed and / or the maximum permissible current.

[0067]

[0057] In particular, the reinforcing action against wear mechanisms and the increase in resistance to erosion caused by the electric arc can be provided by particles of refractory oxides (AIO2, SnO, CdO, and similar) finely dispersed in the organic matrix of the electrically conductive paint.

[0068]

[0058] The temperature limiting device described here by way of example is subject to numerous modifications and variations depending on specific requirements.

[0069]

[0059] In the practical implementation of the invention, the materials used, as well as the shape and dimensions, may be any as required.

[0070]

[0060] Where the technical features mentioned in each claim are followed by reference numerals, such reference numerals have been included solely for the purpose of enhancing the understanding of the claims and, consequently, they have no limiting effect on the scope of each element identified by way of example by such reference numerals.

Claims

Claims1. A temperature limiting device, comprisingan outer container (2) made of conductive material, defining a cup-shaped housing (3) closed by a lid (4), inside which are stackeda spring snap-in disc (6);a bimetallic disc (7) associated with said spring snap-in disc (6);at least one fixed contact (10) secured to said lid (4) of the outer container (2) and protruding with a portion thereof below said lid (4);at least one movable contact (11) secured to said spring snap-in disc (6); characterized in thatat least said fixed contact (10) and said movable contact (11) are coated with a surface layer (15) of electrically conductive paint.

2. The device of claim 1, wherein said surface coating layer (15) is made of a high- temperature-resistant electrically conductive paint.

3. The device of claim 1 or 2, wherein said outer container (2) and said spring snap-in disc (6) are coated with said surface layer (15) of electrically conductive paint.

4. The device of any one of the previous claims, wherein said surface layer (15) of electrically conductive paint consists of an organic coating based on acrylic, urethane, or epoxy, in which conductive particles of a metallic nature or also of an organic nature are dispersed.

5. The device of any one of the previous claims, wherein said surface layer (15) of electrically conductive paint is supplemented with reinforcing fillers that increase its wear resistance and its ability to extinguish the electric arc during operations involving the separation or closing of contacts under electrical load.

6. The device of claim 5, wherein said reinforcing fillers comprise particles of refractory oxides finely dispersed in the organic matrix of the electrically conductive paint.

7. A method for manufacturing a temperature limiting device, comprisingan outer container (2) made of conductive material, defining a cup-shaped housing (3) closed by a lid (4), inside which are stackeda spring snap-in disc (6);a bimetallic disc (7) associated with said spring snap-in disc (6);at least one fixed contact (10) secured to said lid (4) of the outer container (2) and protruding with a portion of it below said lid (4);at least one movable contact (11) secured to said spring snap-in disc (6);said method being characterized in that it comprises coating at least said fixed contact (10) and said movable contact (11) with a surface layer (15) of electrically conductive paint.

8. The method of claim 7, wherein it further comprises coating said outer container (2) and said spring snap-in disc (6).

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