Threshold temperature indicator

Abstract

A threshold temperature indicator and a method of use thereof, the threshold temperature indicator comprising a dual plate stack including a first plate and a second plate, each plate having a front surface and a back surface, wherein the front surface of each plate has a different color indicating a state of the apparatus or of the system, wherein the two plates are attached to each other using a temperature threshold material having a melting point substantially equal to a threshold temperature, and wherein a visual indication is provided by the threshold temperature indicator when the front plate falls off, after exposure of the threshold temperature indicator for a time interval at a temperature substantially equal to or above the threshold temperature.

Description

[0001] THRESHOLD TEMPERATURE INDICATOR

[0002] CROSS REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority from US provisional patent application serial number 63 / 087794 filed on August 28, 2024 with the US Patent Office and which is incorporated herein in its entirety for all purposes.

[0004] FIELD OF THE INVENTION

[0005] Various exemplary embodiments of the present invention relate generally to temperature indicators and, more particularly, to threshold temperature indicators that trigger a response or action when a temperature has exceeded a predetermined level.

[0006] BACKGROUND OF THE INVENTION

[0007] U.S. Pat No. 4,191,125 to Johnson ("Johnson") describes a freeze indicator which includes a frangible ampoule substantially filled with a mixture of water, a nucleating agent and a surfactant. Upon reaching the freezing point of water, the water mixture freezes fracturing the frangible ampoule. According to Johnson, a nucleating agent can be used to overcome the undercooling effect; a dye-printed pad can be employed to show a color change; and deuterium oxide may be added to raise the freezing point.

[0008] U.S. Pat. No. 4,646,066 to Baughman ("Baughman") describes an indicator device employing a tuned electrical circuit interrogatable by an RF signal in the microwave range or lower. The tuned circuit includes an element having an electrical property that changes in a predetermined fashion in response to a particular environmental parameter. Baughman suggests that various freeze-induced phenomena such as rupture of salinecontaining microcapsules or demulsification of liquids, for example, salad dressing, can provide a conductance change in the tuned circuit element which may be detected on interrogation, enabling freezing to be monitored.

[0009] US patent 7891310 describes temperature indicators providing a visual indication of exposure of the freeze indicator to a freezing or near-freezing temperature and their manufacture. The freeze indicators employ colloidal dispersions as active elements and include flexible freeze indicators, freeze indicators protected against drying out and freeze indicators employing core-shell composites, for example gold coated pigments as active indicator elements. The patent also describes indicators with exposure to a temperature above a threshold. Typical temperature indicators therefore are made with processes and compositions that have limited shelf life and / or have to be stored carefully prior to use. Such indicators also have generally small size such that they may not be readily visible from a distance.

[0010] SUMMARY OF THE INVENTION

[0011] A threshold temperature indicator is provided that is suitable for attachment to, or association with a surface of interest of an apparatus or of a system for monitoring the thermal state of the apparatus or system and provide a visual signal to a user of the threshold temperature indicator. The threshold temperature indicator may comprise a dual plate stack including a first plate and a second plate, each plate having a front surface and a back surface. The front surface of each plate has a different color indicating a thermal state of the apparatus or of the system. The two plates are attached to each other using a temperature threshold material having a melting point substantially equal to a threshold temperature. A visual indication is provided by the threshold temperature indicator when the front plate falls off, after exposure of the threshold temperature indicator for a time interval at a temperature substantially equal to or above the threshold temperature. While the term metal plate is used to describe the construction of threshold temperature indicator, it is understood that much thinner forms like metal foil may also be used.

[0012] In an embodiment, the first plate may comprise a thermally conductive material such as aluminum, steel, copper, bronze, platinum, and the like.

[0013] In an embodiment, the front surface of the first plate may be painted red, and the front surface of the second plate may be painted green.

[0014] In an embodiment, the first plate is a bottom plate configured to be attached at a back side thereof to the surface of interest and the second plate is a top plate.

[0015] In an embodiment, the first plate is divided in two parts each part having a different color on the front surface thereof, wherein the second plate comprises two separate top plates and each top plate is covering and is attached to a corresponding part of the first plate with a different threshold temperature material having a different melt temperature.

[0016] In an embodiment, the threshold temperature material may be an alloy, a metal alloy, or a metal.

[0017] In an embodiment, the metal alloy is a low melting point bismuth alloy. In an embodiment, the two plates are attached with connectors including rivets, plugs, threaded screws, and the like made of a metal alloy.

[0018] In an embodiment, the two plates are attached with twist wire made of metal alloy.

[0019] In an embodiment, the two plates are attached by soldering the metal alloy in-place.

[0020] Another aspect of the present invention is directed to a method of using the inventive threshold temperature indicator , the method comprising attaching the back side of the first plate of the threshold temperature indicator via attachment means including high temperature double-sided tape or a high temperature adhesive or mechanical means such as screws and the like on the surface of interest of an apparatus or of a system, wherein the first and second plates are in a vertical orientation, and wherein the second plate of the threshold temperature indicator falls off and a colored front side of the first plate is revealed providing a visual signal to a user of the threshold temperature indicator.

[0021] These and other features and advantages of the present invention will become better understood from the detailed description in conjunction with the following figures,

[0022] BRIEF DESCRIPTION OF THE FIGURES

[0023] Fig. 1 illustrates a top view of the threshold temperature indicator according to an embodiment of the invention.

[0024] Fig. 2 is a side view of the threshold temperature indicator according to an embodiment of the invention.

[0025] Fig. 3 is a side view of a dual threshold temperature indicator according to an embodiment of the invention.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] According to the present invention, a threshold temperature indicator (also referred to herein as temperature indicator or simply indicator) is disclosed that provides a visual indication of exposure to a temperature above or below a threshold temperature. The threshold temperature indicator is attachable to a surface of interest of an apparatus or system and shows by a visual color change whether the temperature of the surface of interest is above or below of a specific temperature limit also referred to herein as the threshold temperature or signal temperature. The threshold temperature indicator of the present invention may be used in different industries.

[0028] According to an embodiment, the indicator comprises at least two plates held together with a material having a melting point equal or substantially equal to the desired threshold temperature (also referred to as the signal temperature). The material holding together the at least two plates may be referred to also as the threshold temperature material. The at least two plates may include a first plate and a second plate held together with the threshold temperature material. The first and second plates may also be referred to as a bottom and a top plate. A front side of the bottom plate may be colored to indicate a signal temperature. Also, a front side of the top plate may be colored with another different color to indicate a different signal temperature. For example, the front side of the top plate may be colored green, or white, or some other color to indicate a temperature for the surface of interest below the threshold temperature. The back side of the bottom plate may be attached to the surface of interest. For example, the back side of the bottom plate may be attached to the surface of interest using a high temperature double-sided tape or a high temperature adhesive or mechanical means such as screws and the like, however, the invention may not be limited by the means used to adhere the back side of the bottom plate of the threshold temperature indicator to the surface of interest.

[0029] The top plate may be held in place attached to the bottom plate by the threshold temperature material. The threshold temperature material may be an alloy. The threshold temperature material may be a metal alloy. The threshold temperature material may be a metal. In an embodiment, the threshold temperature material may be disposed between the top and the bottom plates forming a layer between the top and bottom plates. In another embodiment, the threshold temperature material may form columns (also referred to as pillars, plugs, or connectors) within through holes extending from the top plate to the bottom plate. In an embodiment, the threshold temperature material pillars may pass through the top and bottom plates and may be in contact with the surface of interest. In this way the bottom plate may be made of a less heat conductive material since the heat from the surface of interest may be transferred directly to the pillars of the threshold temperature material and cause them to melt and release the top plate if the temperature of the surface of interest reaches or exceeds the melting temperature of the threshold temperature material. Hence, the melting temperature of the threshold temperature material determines the threshold temperature (or signal temperature) of the threshold temperature indicator.

[0030] It is preferable to have the bottom plate made of a thermally conductive material such as a metal like aluminum, steel, copper and the like for better heat transfer between the surface of interest and the threshold temperature material. This may be particularly important when the threshold temperature material may not be in direct contact with the surface of interest, for example when it is disposed only as a layer between the top and bottom plates and is not in direct contact with the surface of interest because in that case the heat needs to be transferred via the bottom plate which is attached to the surface of interest to the threshold temperature material that is disposed between the top and bottom plates.

[0031] In a preferred embodiment, the threshold temperature material is formed into one or more connectors that are passed through the top and bottom plates and contact the surface of interest. Preferably, the bottom plate may be made of a material that is a good heat conductor, susch as a metal, for example aluminum and copper.

[0032] The top plate is not particularly limited but may also be made of same material as the bottom material for conductivity, adhesion, and other design reasons. It is possible for the top and bottom plates to be made of ceramic or plastic materials as long as the threshold temperature material (e.g., the threshold material alloy) is thermally connected to the surface of interest. For example, in an embodiment, a connection means includes attaching the top and bottom plates by fdling holes drilled in the top and bottom plates with the threshold temperature material. As the temperature is raised to the threshold temperature of interest, the threshold temperature material (e.g., the alloy or metal alloy) melts, releasing the top plate and exposing the front side of the bottom plate with the color indicating that the threshold temperature has been reached. It is possible to use two different colors applied adjacent to each other on the bottom plate, where each color is covered with a separate top plate and secured to the bottom plate with two different threshold temperature materials of different melting points. A lower melting point (for example 70 °C) alloy may be used to attach the top plate covering a typical “ WARNING” signal color such as yellow and a higher melting point alloy (for example 95 °C ) may be used to cover a “FAIL” signal color such as red to indicate failure.

[0033] When in use the threshold temperature indicator may be attached to a surface of interest may be a surface of an apparatus, or a system. The surface of interest may be oriented horizontally, vertically, or at any angle ranging from 0 degrees to 180 degrees relative to the horizontal plane. Preferably, the surface of interest may be oriented at an incline from the horizontal plane for facilitating the separation of the top plate (or second plate) of the threshold temperature indicator from the bottom plate (or first plate) when the surface of interest reaches the threshold temperature and the threshold temperature material melts. More preferably, the surface of interest may be oriented vertically for facilitating the separation of the top plate (or second plate) of the threshold temperature indicator from the bottom plate (or first plate) when the surface of interest reaches the threshold temperature and the threshold temperature material melts.

[0034] Referring now to FIG. 1, a plane top view of a threshold temperature indicator 100 is provided in a simplified schematic. The threshold temperature indicator comprises a top plate 102 (second plate) and a plurality of through openings 104. For example, in the embodiment illustrated in FIG. 1 four through openings are shown spaced apart from each other). The openings 104 may be filled with a threshold temperature material 204. See FIG. 2. The threshold temperature material may be, for example, an alloy, such as a metal alloy or a metal. The openings 104 with the threshold temperature material 204 may pass through the top plate 102 and the bottom plate 202 and the threshold temperature material 204 may contact the surface of interest 206. In an embodiment, the threshold temperature material may be formed as rivets or any similar type connector such as screws or plugs holding the plates together so long as the temperature of the surface of interest is below the melting point of the threshold temperature material making the connectors. As shown in the embodiment of FIG. 2, the lowermost surface of the connectors 204 may be in direct contact with the surface of interest. However, in some embodiments the connectors may not directly contact the surface of interest provided the bottom plate is made of a material that is adequately thermally conductive so that when the temperature of the surface of interest reaches the desired signal temperature the threshold temperature material of the connectors 204 may melt to free the top plate to separate from the bottom plate and fall off or move so that it does no longer cover the front side of the bottom plate and thus the color of the front side of the bottom plate can be seen by a user. The threshold temperature indicator at least in some embodiments, may comprise the top and bottom plates within at least partially transparent container or one that has a transparent window for allowing the user to see the color of the front side of the top plate when the top plate is in place and the front side of the bottom plate when the top plate has fallen off. The container may be sized to allow the falling off of the top plate and allow a user to see the color of the front side of the bottom plate.

[0035] Referring now to FIG. 3, according to an embodiment, the threshold temperature indicator may include a single bottom plate 102, covered by two separate top plates 302A and 302B. Each of the two top plates 302A and 302B may cover a different part of the bottom plate 102 and may be connected to the respective different part of the bottom plate 102 via one or more different connectors 304A and 304B respectively. The different connectors 304A and 304B may be made of different threshold temperature material having different melting points. The two different parts of the bottom plate 102 may have a front side with a different color, for example, one part may have a yellow color, and the other part may have a red color. The top plate 302A may be positioned above the yellow part of the bottom plate and may use connectors 304A made of a threshold temperature material having a lower melting point than the connectors 304B holding the top plate 302B which may be positioned above the red part of the bottom plate 102. The threshold temperature indicator of FIG. 3 may be referred to as a Dual threshold temperature indicator and may provide two different visual signals indicating a different thermal state (temperature) of the surface of interest 206 over which the back side of the bottom plate is attached to.

[0036] In the example embodiments of FIGS. 1-3 the surface of interest is a flat surface and is shown to have a horizontal orientation. Preferably, the surface of interest may be a vertically oriented surface of an apparatus or of a system so that when the threshold temperature indicator is attached to it the plates of the threshold temperature indicator may have a vertical orientation or at least some inclination relative to the horizontal to allow the top plate to fall off when the connectors made of the threshold temperature material are melted. Also, the back side of the threshold temperature indicator may in some embodiments (not shown) have a curved surface to allow to match the shape and curvature of the surface of interest.

[0037] Examples

[0038] Materials: For example, the following materials may be used:

[0039] 1) Background plate and foreground plate: 1 / 32" thick aluminum plate 2) Color: Red and Yellow acrylic spray paint

[0040] 3) Sealing adhesive: General Electric Advanced Silicone Adhesive

[0041] 4) Indicator temperature Alloy: 95C melting point, bismuth alloy Product code 2531A from Belmont Metals Inc, Brooklyn NY

[0042] 5) Indicator temperature Alloy: Woods metal, 70-76 Clow melting alloy. Product code 2502 from Belmont Metals Inc, Brooklyn NY

[0043] 6) Double-sided Tape: 9077, 3M High temperature double sided tape

[0044] Example 1 : A single temperature indicator was with 2, 0.75" x 1.5", 1 / 32" thick aluminum plates. Both plates had 0.125" diameter holes drilled at each of the 4 comers. One face of the background plate was painted red while the foreground plate was painted white. The foreground plate was placed on top of the background plate and Belmont metals 95C alloy was used to fill the aligned thru holes at each of the comers. 3M high temperature tape was applied to the back of the background plate. The indicator was affixed to an aluminum stand, to which heat was applied. As the temperature increased to 95C, metal alloy melted, and the foreground plate dropped exposing the red colored background plate. Example 2: A single temperature indicator was with 2, 0.75" x 1.5", 1 / 32" thick aluminum plates. Both plates had 0.125" diameter holes drilled at each of the 4 comers. One face of the background plate was painted yellow while the foreground plate was painted white. The foreground plate was placed on top of the background plate and Belmont metals 70 C alloy was used to fill the aligned thru holes at each of the comers. 3M high temperature tape was applied to the back of the background plate. The indicator was affixed to an aluminum stand, to which heat was applied. As the temperature increased to 70C, metal alloy melted and the foreground plate dropped exposing the yellow-colored background plate.

[0045] It is noted that although the invention is described with reference to specific example embodiments, many variations of these example embodiments and other embodiments may be envisioned by those with ordinary skill in the art of the invention without departing from the technical concepts and scope of the invention.

[0046] Figure Numerals

[0047] 100: Threshold Temperature Indicator

[0048] 102: Top plate

[0049] 104: Thru opening filled with threshold temperature alloy 202: Bottom plate

[0050] 204: Threshold metal material plugs or connectors

[0051] 206: High temperature adhesive 302 A: Top plate 1 302B: Top plate 2

[0052] 304A: Threshold Temperature Plug or connector 1 304B: Threshold temperature Plug or Connector 2

Claims

Claims1. A threshold temperature indicator suitable for attachment to, or association with, a surface of interest of an apparatus or of a system for monitoring a temperature of the surface of interest has gone above a threshold temperature, the threshold temperature indicator comprising: a dual plate stack including a first plate and a second plate, each plate having a front surface and a back surface, wherein the front surface of each plate has a different color indicating a state of the apparatus or of the system, wherein the two plates are attached to each other using a temperature threshold material having a melting point substantially equal to a threshold temperature, and wherein a visual indication is provided by the threshold temperature indicator when the front plate falls off, after exposure of the threshold temperature indicator for a time interval at a temperature substantially equal to or above the threshold temperature.

2. The indicator of claim 1, wherein the first plate comprises a thermally conductive material such as aluminum, steel, copper, bronze, platinum, and the like.

3. The indicator of claim 1, wherein the front surface of the first plate is painted red, and the front surface of the second plate is painted green.

4. The indicator of claim 1, wherein first plate is a bottom plate configured to be attached at a back side thereof to the surface of interest and the second plate is a top plate.5 . The indicator of claim 1, wherein the first plate is divided in two parts each having a different color on the front surface thereof; wherein the second plate comprises two separate top plates each top plate covering and being attached to a corresponding part of the first plate with a different threshold temperature material having a different melt temperature.

6. The indicator of claim 1, wherein the threshold temperature material is an alloy, a metal alloy, or a metal.7 . The indicator of claim 6, wherein the metal alloy is a low melting point bismuth alloy.

8. The indicator of claim 1, wherein the two plates are attached with connectors including rivets, plugs, threaded screws, and the like made of a metal alloy.

9. The indicator of claim 1, wherein in the two plates are attached twist wire made of metal alloy.

10. The indicator of claim 1, wherein the two plates are attached by soldering the metal alloy in-place.11.A threshold temperature indicator comprising:a dual plate stack including a first plate and a second plate, each plate having a front surface and a back surface, wherein the front surface of each plate has a different color indicating a state of the apparatus or of the system, wherein the two plates are attached to each other using a temperature threshold material having a melting point substantially equal to a threshold temperature.

12. A method of using the threshold temperature indicator of claim 1, the method comprising attaching the back side of the first plate of the threshold temperature indicator via attachment means including high temperature doublesided tape or a high temperature adhesive or mechanical means such as screws and the like on the surface of interest of an apparatus or of a system, wherein the first and second plates are in a vertical orientation, and wherein the second plate of the threshold temperature indicator falls off and a colored front side of the first plate is revealed providing a visual signal to a user of the threshold temperature indicator.

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