EP4641611A1

EP4641611A1 - Filling mixture for fuse device

Info

Publication number: EP4641611A1
Application number: EP25169732.2A
Authority: EP
Inventors: Arjuna Shenoy; Jianhua Chen
Original assignee: Littelfuse Inc
Current assignee: Littelfuse Inc
Priority date: 2024-04-22
Filing date: 2025-04-10
Publication date: 2025-10-29

Abstract

A filling mixture for a fuse device is provided. The fuse device can include a pair of electrical terminals, a metal strip or wire element mounted between the pair of electrical terminals, a housing enclosing the metal strip or wire element, and the filling mixture inside of the housing. The filling mixture can include a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.

Description

FIELD

The present disclosure relates to a fuse device, to a filling mixture for a fuse device, to a method of providing a filling mixture for a fuse device and to a method of providing a fuse device with a filling mixture.

BACKGROUND

Large bore high power fuses are extremely sensitive to filler voids that are created during a manufacturing process, and as a bore of a fuse increases, a void fraction also increases. In some circumstances, a less than 2% increase in filler voids can lead to a 50% failure rate.
In view of the above, there is a continuing, ongoing need for reducing filler voids in fuses.

BRIEF SUMMARY

This Brief Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Brief Summary is not intended to identify key features or essential features of claimed subject matter or intended as an aid in determining scope of the claimed subject matter.
A fuse device according to the disclosure includes a pair of electrical terminals, a metal strip or wire element mounted between the pair of electrical terminals, a housing enclosing the metal strip or wire element, and a filling mixture inside of the housing. The filling mixture includes a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.
The lubricant can be thermally stable and electrically insulating.
The coefficient of friction of the lubricant can be 1 or less.
The coefficient of friction of the lubricant can be 0.3 or less.
The coefficient of friction of the lubricant can be 0.1 or less.
A mass of the lubricant in dry form can be 0.1% to 3% of a mass of the filler.
The lubricant can have a negligible impact on electrical properties of the fuse device.
The lubricant can increase a packing density of the filler.
The lubricant can be applied to the filler as a solid, as a liquid, as a solid powder, as the solid powder suspended in liquid, or as an aerosol.
The liquid or a gas in the aerosol can evaporate after application to the filler to leave a dry film that can cover at least some of the particles of the filler.
The disclosure also includes a filling mixture for a fuse device, including a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.
The lubricant can be thermally stable and electrically insulating.
The coefficient of friction of the lubricant can be 1 or less.
The coefficient of friction of the lubricant can be 0.3 or less.
The coefficient of friction of the lubricant can be 0.1 or less.
A mass of the lubricant in dry form can be 0.1% to 3% of a mass of the filler.
The lubricant can increase a packing density of the filler.
The lubricant can be applied to the filler as a solid power, as the solid powder suspended in liquid, or as an aerosol.
The liquid or a gas in the aerosol can evaporate after application to the filler to leave a dry film that can cover at least some of the particles of the filler.
The disclosure also includes a method which includes applying a lubricant to a fuse filler as a solid powder suspended in liquid or as an aerosol, evaporating the liquid or a gas in the aerosol, and coating at least some particles of the filler with a dry film that reduces a coefficient of friction of the particles of the filler. Preferably the resulting filler finds utility as filling mixture for a fuse device.
The method can further comprise filling a fuse device with the filler.
Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of a filling mixture in accordance with the disclosure.
FIG. 2 is a block diagram of an electrical fuse in accordance with the disclosure.
FIG. 3 is a block diagram of a surface mount electrical fuse in accordance with the disclosure.
FIG. 4 is a graph illustrating packing density vs. mass of lubricant in dry form in a filling mixture in accordance with the disclosure.
FIG. 5 is a box and whisker plot illustrating packing density for plain sand, doped sand, and lubricated doped sand in accordance with the disclosure.
FIG. 6 is a graph illustrating sand mass in an electrical fuse filled with doped sand and an electrical fuse filled with lubricated doped sand in accordance with the disclosure.
FIG. 7 is a box and whisker plot illustrating performance gain for an electrical fuse filled with doped sand and an electrical fuse filled with lubricated doped sand in accordance with the disclosure.
FIG. 8 is a flow chart illustrating a method in accordance with the disclosure.

DETAILED DESCRIPTION

A filling mixture for a fuse device in accordance with the present disclosure will now be described more fully hereinafter with reference made to the accompanying drawings.
In accordance with the disclosure, a fuse device includes a pair of electrical terminals, a metal strip or wire element mounted between the pair of electrical terminals, a housing enclosing the metal strip or wire element, and a filling mixture inside of the housing such that the filling mixture can include a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler. Advantageously, inclusion of the lubricant in the filler can increase performance, reliability, and manufacturability of the fuse device disclosed herein.
It is to be understood that the filler can include any filler as would be understood by one of ordinary skill in the art. For example, the filler can include silicate, sand, quartz sand, doped sand, doped sand with a binding material, undoped sand, melamine, and/or steatite.
The lubricant can be thermally stable. For example, the lubricant can be thermally stable after assembly of the fuse device including the lubricant, but need not be thermally stable while the fuse device is functioning and/or for a lifetime of the fuse device. The lubricant can be thermally stable after assembly of the fuse device including the lubricant, while the fuse device is functioning, and/or for the lifetime of the fuse device.
The lubricant can be electrically insulating. For example, an amount of the lubricant can cause the lubricant to be electrically insulating. The lubricant can include boron nitride, hexagonal boron nitride, Polytetrafluoroethylene (PTFE), molybdenum disulfide, tungsten disulfide, graphite, silicone oil (e.g., polydimethyl siloxane based), a silicone conformal coating, sodium (Na), potassium (K), magnesium (Mg), and/or calcium (Ca) fluoride salts, and/or other hydrocarbon-based oils. In particular, a low percentage of graphite can cause the lubricant to be electrically insulating.
The coefficient of friction of the lubricant can be 1 or less. Additionally or alternatively, the coefficient of friction of the lubricant can be 0.3 or less. Additionally or alternatively, the coefficient of friction can be 0.1 or less. In general, a lower coefficient of friction can lead to improvements in advantages of the filler mixture as disclosed herein.
It is to be understood that the coefficient of friction as discussed herein can include a static coefficient of friction. Additionally or alternatively, the coefficient of friction as discussed herein can include a kinetic coefficient of friction. Additionally or alternatively, the coefficient of friction as discussed herein can include the static coefficient of friction and the kinetic coefficient of friction.
The lubricant can have a negligible impact on electrical properties of the fuse device. In particular, , a design and a composition of the lubricant can be tailored to the fuse device to ensure the negligible impact on the electrical properties of the fuse device. That is, the fuse device can exhibit equivalent electrical performance regardless of whether the fuse device includes the filler by itself or the filling mixture (i.e., the filler that is coated with the lubricant). Such equivalent electrical performance can be seen during overload conditions. Peak arc current can be approximately 15% lower when the fuse device includes the filling mixture relative to when the fuse device includes the filler by itself.
The lubricant can increase a packing density of the filler. For example, the lubricant can increase the packing density of the filler by as much as 5%. As a specific, but non-limiting example, an average packing density of regular quartz sand is 1.70 g/ml. Doped sand is preferable in some applications, but due to additional chemicals, an average packing density of the doped sand is 1.61 g/ml. Advantageously, lubricating the doped sand as described herein can retain benefits of the doped sand, while increasing the average packing density of the doped sand to as much as 1.73 g/ml.
The lubricant can be applied to and/or mixed with the filler as a solid, a liquid, a solid powder, a solid powder suspended in liquid, or an aerosol. In particular, a low percentage of liquid lubricant can be functional. The liquid or a gas in the aerosol can evaporate after application to the filler to leave a dry film that covers at least some of the particles of the filler. In this regard, no ovens or heaters are necessarily required to cure the lubricant. Nevertheless, curing the lubricant can trap a doping compound, such as melamine or ammonium chloride, in or on the filler.
A mass of the lubricant in dry form can be 0.1% to 3% of a mass of the filler. As such, after evaporation, coating the filler with the lubricant can result in less 0.1% of added mass.
FIG. 1 illustrates a filling mixture 100 in accordance with the disclosure. As seen in FIG. 1, the filling mixture 100 can include a plurality of filler particles 102 or grains that make up a filler and a plurality of lubricant particles 104 that make up the lubricant.
The lubricant particles 104 in the filling mixture 100 can be bound film, that is, a dry film that is bound to one or more of the filler particles 102. Additionally or alternatively, in the lubricant particles 104 in the filling mixture 100 can be free, that is, not bound to any particular one of the filler particles 102.
FIG. 2 illustrates an electrical fuse 200 in accordance with the disclosure. As seen in FIG. 2, the electrical fuse 200 can include a pair of electrical terminals 202a, 202b, a metal strip or wire element 204a, 204b mounted between the pair of electrical terminals 202a, 202b, a housing 206 enclosing the metal strip or wire element 204a, 204b, and a filling mixture 208 inside of the housing 206. In particular, the filling mixture 208 can be the same as or similar to the filling mixture 100 of FIG. 1 and include a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.
It is to be understood that the electrical fuse 200 illustrated in FIG. 2 is exemplary only. For example, the disclosure can include and/or be used in connection with surface mount fuses.
In this regard, FIG. 3 is a block diagram of a surface mount electrical fuse 300 in accordance with the disclosure. As seen in FIG. 3, the surface mount electrical fuse 300 can include a pair of electrical terminals 302a, 302b, a fuse element 304, such as a metal strip or wire element, a housing enclosing the fuse element 304, and a filling mixture 310 inside of the of the housing. For example, the housing can include a top casing 306 and a bottom casing 308 enclosing the fuse element 304. Further, the filling fixture 310 can be the same as or similar to the filling mixture 100 of FIG. 1 and include a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.
FIG. 4 is a graph 400 illustrating packing density vs. mass of lubricant in dry form in a filling mixture in accordance with the disclosure. As seen in FIG. 4, as the lubricant is added to a filler, the packing density of the filler increases and can result in a density gain of anywhere from 1% to 5%. However, after some critical point, as more of the lubricant is added to the filler, the packing density decreases. Accordingly, the mass of the lubricant can range up to the critical point to achieve increases in the packing density of the filler. As seen in the specific, non-limiting example of FIG. 4, the mass of the lubricant in dry form can range up to somewhere between 0.1% and 0.2% of a mass of the filler to achieve increases in the packing density of the filler. However, when more than such a critical amount of the lubricant is added to the filler, the packing density begins to decrease. In some specific, non-limiting examples, less than 3g of the lubricant in wet form can be added to 200g of filler before being dried (i.e., a liquid can evaporate) to leave a dry film of the lubricant with a low additive mass coating at least some particles of the filler and optimally reducing a coefficient of friction of particles of the filler.
FIG. 5 is a box and whisker plot 500 illustrating packing density for plain sand, doped sand, and lubricated doped sand in accordance with the disclosure. Plot 502 represents the packing density in six exemplary trials for the plain sand, plot 504 represents the packing density in six exemplary trials for the doped sand, and plot 506 represents the packing density in six exemplary trials for the lubricated doped sand. Sampled maxima and minima for each of the Plot 502, the plot 504, and the plot 506 are represented by respective top and bottom bars, a sampled median for each of the Plot 502, the plot 504, and the plot 506 is represented by a respective inner line, and a sampled mean for each of the Plot 502, the plot 504, and the plot 506 is represented by a respective "x" mark. As seen, the doped sand reduces the packing density relative to the plain sand because of attributes of doping materials used. The doped sand can result in a loss of approximately 4% of the packing density. As such, while the doping materials increase general performance capabilities, reliability is reduced because a manufacturing and production yield is reduced. Advantageously, application of a lubricant to the doped sand as disclosed herein (i.e., the lubricated doped sand) can increase the packing density to match or even exceed the packing density of the plain sand while still maintaining increased general performance capabilities provided by the doped sand, thereby negating any manufacturing issues caused by the attributes of the doping materials.
FIG. 6 is a graph 600 illustrating sand mass in an electrical fuse filled with doped sand and an electrical fuse filled with lubricated doped sand in accordance with the disclosure. Distribution 602 represents the sand mass in the electrical fuse filled with the doped sand in nine exemplary trials, with point 604 representing an average thereof, and distribution 606 represents the sand mass in the electrical fuse filled with the lubricated doped sand in nine exemplary trials, with point 608 representing an average thereof. Weight is the first metric used to judge fuses filled in a manufacturing line, and low mass fuses below a threshold are rejected. Advantageously and as seen in FIG. 6, all electrical fuses filled with the lubricated doped sand have a higher mass than all electrical fuses filled with the doped sand. The lubricated doped sand can result in a final mass increase of approximately 2.5%.
FIG. 7 is a box and whisker plot illustrating performance gain for an electrical fuse filled with doped sand and an electrical fuse filled with lubricated doped sand in accordance with the disclosure. Plot 702 represents arc time in five exemplary trials for the doped sand, and plot 704 represents arc time in five exemplary trials for the lubricated doped sand. Of note, plain (undoped sand) is not tested because use thereof in fuses designed for use with doped sand can cause safety issues and activation failures. In FIG. 7, sampled maxima and minima for each of the Plot 702 and the plot 704 are represented by respective top and bottom bars, a sampled median for each of the Plot 702 and the plot 704 is represented by a respective inner line, and a sampled mean for each of the Plot 702 and the plot 704 is represented by a respective "x" mark. As seen, all arc times of electrical fuses filled with the lubricated doped sand are lower than all arc times of electrical fuses filled with the doped sand, thereby providing higher reliability and load protection in identical fuses with only a change in filler. The lubricated doped sand can result in an approximately 45% reduction of the arc time, and because lower arc times correlate with increased reliability and circuit protection, reducing the arc time as disclosed herein is advantageous.
FIG. 8 is a flow chart illustrating a method 800 in accordance with the disclosure. As seen in FIG. 8, the method 800 can include applying a lubricant to a fuse filler as a solid powder suspended in liquid or as an aerosol as in 802. The fuse filler can include silicate, sand, quartz sand, doped sand, doped sand with a binding material, undoped sand, melamine, and/or steatite. Additionally or alternatively, the lubricant can include boron nitride, hexagonal boron nitride, Polytetrafluoroethylene (PTFE), molybdenum disulfide, tungsten disulfide, graphite, silicone oil (e.g., polydimethyl siloxane based), a silicone conformal coating, sodium (Na), potassium (K), magnesium (Mg), and/or calcium (Ca) fluoride salts, and/or other hydrocarbon-based oils. In particular, the lubricant can be thermally stable, electrically insulating, increase a packing density of the fuse filler, have a mass that is 0.1% to 3% of the fuse filler, and/or have a negligible impact impact on electrically properties of a fuse device in which the lubricant and the fuse filler are included,
After the lubricant is applied to the fuse filler as in 802, the method 800 can include evaporating the liquid or a gas in the aerosol as in 804. Finally, the method 800 can include coating at least some particles of the fuse filler with a dry film that reduces a coefficient of friction of the particles of the fuse filler as in 806. Evaporating the liquid or the gas in the aerosol of the lubricant can leave the dry film as a remaining part of the lubricant. Furthermore, no ovens or heaters are necessarily required to cure the lubricant. However, curing the lubricant can trap a doping compound in or on the filler.
As used herein, an element or a step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited.

Claims

A fuse device comprising:
a pair of electrical terminals;

a metal strip or wire element mounted between the pair of electrical terminals;

a housing enclosing the metal strip or wire element; and

a filling mixture inside of the housing,

wherein the filling mixture includes a filler and a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.
The fuse device of claim 1, wherein the lubricant is thermally stable and electrically insulating.
The fuse device of claim 1 or 2,
wherein the coefficient of friction of the lubricant is 1 or less;

wherein the coefficient of friction of the lubricant is 0.3 or less;

wherein the coefficient of friction of the lubricant is 0.1 or less.
The fuse device of any of the preceding claims, wherein a mass of the lubricant in dry form is 0.1 % to 3 % of a mass of the filler.
The fuse device any of the preceding claims, wherein the lubricant has a negligible impact on electrical properties of the fuse device.
The fuse device of any of the preceding claims, wherein the lubricant increases a packing density of the filler.
The fuse device of any of the preceding claims, wherein the lubricant is applied to the filler as a solid, as a liquid, as a solid powder, as the solid powder suspended in liquid, or as an aerosol, preferably wherein the liquid or a gas in the aerosol evaporates after application to the filler to leave a dry film that covers at least some of the particles of the filler.
A filling mixture for a fuse device according to any of the preceding claims, the filling mixture comprising:
a filler; and

a lubricant coating the filler to reduce a coefficient of friction of particles of the filler.
The filling mixture of claim 8, wherein the lubricant is thermally stable and electrically insulating.
The filling mixture of claim 8 or 9,
wherein the coefficient of friction of the lubricant is 1 or less;

wherein the coefficient of friction of the lubricant is 0.3 or less;

wherein the coefficient of friction of the lubricant is 0.1 or less.
The filling mixture of any of the claims 8-10, wherein a mass of the lubricant in dry form is 0.1% to 3% of a mass of the filler.
The filling mixture of any of the claims 8-11, wherein the lubricant increases a packing density of the filler.
The fuse filling mixture of of any of the claims 8-12, wherein the lubricant is applied to the filler as a solid power, as the solid powder suspended in liquid, or as an aerosol, preferably wherein the liquid or a gas in the aerosol evaporates after application to the filler to leave a dry film that covers at least some of the particles of the filler.
A method comprising:
applying a lubricant to a filler as a solid powder suspended in liquid or as an aerosol;

evaporating the liquid or a gas in the aerosol; and

coating at least some particles of the filler with a dry film that reduces a coefficient of friction of the particles of the filler, to preferably provide a filling mixture for a fuse device.
The method according to claim 14, further comprising arranging the filling mixture in a fuse device.