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Publication numberUS3261950 A
Publication typeGrant
Publication dateJul 19, 1966
Filing dateNov 30, 1964
Priority dateNov 30, 1964
Publication numberUS 3261950 A, US 3261950A, US-A-3261950, US3261950 A, US3261950A
InventorsKozacka Frederick J
Original AssigneeChase Shawmut Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Time-lag fuses having high thermal efficiency
US 3261950 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

July 19, 1966 F. J. KOZACKA 3,251,950

LAG FUSES HAVING HIGH THERMAL EFFICIENCY TIME- Filed Nov. 30, 1964 FIG.I.

INVENTOR= EMREDERICK J. KOZACKA,

BY WW ATTORNEY United States Patent 3,261,950 TIME-LAG FUSES HAVING HIGH THERMAL EFFICIENCY Frederick J. Kozacka, South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Nov. 30, 1964, Ser. No. 414,750 8 Claims. (Cl. 200-120) This invention is concerned with time-lag fuses, and more particularly time-lag fuses having sufficiently long time-lags to preclude blowing on occurrence of heavy starting currents in motor circuits.

It is one object of this invention to provide improved electric fuses of the above description which have a high thermal efficiency.

It' is another object of this invention to provide improved electric fuses of the above description which minimize heat flow in the presence of an arc-quenching filler, such as quartz sand having a high thermal conductivity.

Still another object of this invention is to provide timelag fuses of the above description avoiding the presence of any movable circuit-interrupting mechanisms, having a high interrupting capacity and concomitant currentlimiting action, and being of smaller size, or more compact, than comparable prior art fuses.

A further object of the invention is to provide highinterrupting capacity fuses including link-severing means which are predicated upon a metallurgical reaction be- .tween a metal having a relatively high fusing point and a metal having a relatively low fusing point, which fuses include means particularly effective for minimizing the dissipation of the heat generated therein, thus requiring for any given current rating fuse links having a relatively large mass and cross-sectional area, conductive to long time-lags.

A further object of the invention is to provide electric time-lag fuses whose current path has a relatively low impedance and includes improved means to oppose heat transfer away from the center region of the fuse structure in a direction longitudinally thereof.

These and other objects of the invention and advantages thereof will become more apparent from the accompanying drawings and the following description of a preferred embodiment of the invention.

In the drawings;

FIG. 1 is a top-plan View of an electric fuse embodying this invention;

FIG. 2 is a section along 2 -2 of FIG. 1;

FIG. 3 is a top-plan view of a sheet metal blank used for forming the fuse link structure of FIGS. 1 and 2;

FIG. 4 is a top-plan view of the vblank shown in FIG. 3 upon being provided with a link-severing overlay and appropriately folded; and

FIG. 5 is a side elevation of the structure of FIG. 4.

Referring now to the drawings, and more particularly to FIGS. 1 and 2 thereof, numeral 1 has been applied to indicate a tubular casing of insulating material closed on both ends by electroconductive terminal elements in the form of plugs 2, each provided with a blade contact 2a for insertion of the fuse structure into a fuse holder and an electric circuit. Casing 1 is filled with a pulverulent arc-quenching medium or filler 3, preferably quartz sand because of the high heat absorbing capacity of the latter, resulting in generation of high arc-voltages on blowing of the fuse. Terminal plugs 2 are provided with holes 2b allowing casing 1 to be filled with the arcquenching medium 3. These holes 25 are normally closed by sheet metal caps, each coextensive with one of Patented July 19, 1966 the holes 2b. The axially inner surfaces of terminal plugs 2 are provided with a plurality of parallel grooves 20 for receiving the axially outer ends of ribbon fuse links 4. Casing 1 houses four ribbon fuse links 4 which are submersed in the arc-quenching filler 3. Fuse links 4 are made of a current-limiting metal. The term currentlirniting metal is used as a term encompassing silver and copper and alloys thereof having substantially the same physical properties (conductivity, fusing point, specific heat, fusing i -t, etc.) as silver and/or copper.

As clearly shown in FIG. 3 each fuse link 4 comprises an axially inner portion 4a and axially outer portion 4b. The axially inner portion 4a is provided with three transverse lines R, S, T of circular perforations. Each line R, S, T of perforations forms a point of minimum crosssectional area, or of minimum active width, respectively. The axially inner portion 4a has a larger cross-sectional area and a larger Width than each of the axially outer portions 4b. The cross-sectional area and the width of the axially outer portions 4b exceeds the cross-sectional area and the width of the fuse links 4 at the points thereof where these two parameters are reduced by virtue of the lines R, S, T of perforations. The center line S of perforations is associated with a link-severing overlay 5 having a considerably lower fusing point than the base metal-silver or copper-of which links 4 are made. The overlay metal may be tin, or appropriate alloys of tin, or indium.

The regions of fuse links 4 adjacent the transverse lines R and T of perforations are sandwiched between pairs of plates 6 of insulating material, preferably a syntheticresin-glass-cloth laminate, which are stapled together. Thus the regions of the fuse links 4 immediately adjacent the center lines S of perforations are exposed to the immediate action of the arc-quenching filler 3, whereas the arc-quenching filler 3 has no immediate access to the regions of the fuse links 4 adjacent the transverse lines R and T of perforations. Consequently different kinds of arc voltages, or arc voltages having different rates of rise and of decay, are generated at the center lines S of perforations, on the one hand, and on the axially outer lines R and T of perforations, on the other hand, as more fully explained in United States Patent 2,964,604 to P. C. Jacobs, Jr. et al., December 13, 1960 for Current-Limiting Fuses Having Compound Arc Voltage Generating Means, assigned to the same assignee as the present invention.

It will be noted that while the center portions 4a of fuse links 4 are perforated, the axially outer end portions or connector tabs 4b of fuse links 4 are not perforated.

The radially i-n-ner fuse links 4 are sandwiched between the radially outer fuse links 4, and the latter thus form thermal barriers, or shields, minimizing the escape of heat in radial direction from the radially inner fuse links 4. The latter are heated mutually, and also by the heat generated in the radially outer fuse links 4. Heat flow from the region of highest temperature adjacent the center lines S of perforations is minimized by reason of the fact that the axially outer portion 4b of fuse links 4 are folded, or bent, to form loops 4c substantially in the shape of the letter S, and substantially in the shape of the in- I verted letter S. The loops 40 shown to the left of FIG. 2 are i n the shape of the letter S, and the loops 4c shown to the right of FIG. 2 are in the shape of the inverted letter S. In other words, the axially outer portions or connector tabs 4b of fuse links 4 are folded in zig-zag fashion and form two serially related U-turns.

If the portions 4b of fuse links 4 were straight rather than folded and of equal length, this would result in a drastic increase of the heat flow away from the axially inner portions 4a of fuse links 4 in radial direction and in axial direction. The loops 4c as provided radically reduce the heat flow away from the central portions 4:: of fuse links 4, but do not significantly contribute to the generation of heat since they are not perforated, and since their cross-section or width is relatively large.

The cross-section or Width of the axially outer portions or connector tabs 4b of fuse links 4 must exceed the crosssection or width of the fuse links 4 at the points thereof Where their cross-section or active width is minimal on account of the presence of transverse lines R, S, T of perforations in order to compel arc initiation at the axially inner portion 4a of fuse link 4 and to preclude arc initiation at any point of the axially outer portions or connector tabs 4b of fuse links 4. The latter would be dangerous because it might result in back-burning of the are into terminal plugs 2.

It will be apparent from FIG. 3 that the axially inner portions 4a form shoulders 4d at the points of transition to the radially outer portions or connector tabs 4b.

The axially outer ends of the axially outer portions or connector tabs 41; are inserted into the grooves 2c in terminal plugs 2 and conductively connected to the latter by solder joints formed inside of said grooves.

The structure of FIGS. 1 and 2 achieves long timelags or time delays by the coaction of the following factors:

(a) Since the fusing point of the overlay metal is low, the temperature required at the centers of links 4 to cause the links to be severed by a metallurgical reaction between their base metal and their overlay metal is low.

(b) Since the sandwiching of radially inner fuse link portions by radially outer fuse link portions greatly reduces heat transfer away from the radially inner fuse link portions 411 of fuse link 4, relatively little heat generation is required to bring the overlay metal to the relatively low fusing point and to cause the links 4 to be severed by a metallurgical reaction.

(c) Since the serially related U-turns 4c of links 4 result in a further drastic reduction of heat dissipation from the axially inner portion 4a of fuse links 4, the heat generation, or watt losses, required to bring the linksevering overlays to their fusing point is brought to an unprecedented low. In other words, considering a fuse structure as shown in FIGS. 1 and 2 having given watt losses, such a fuse structure tends to have but an extremely small minimum fusing current on account of its high thermal efficiency, i.e. on account of its small heat losses. In order to impart to the fuse structure higher minimum fusing currents, or a larger current-carrying capacity, respectively, the mass and cross-section of the axially inner portions 4a and that of the axially outer portions 4b must be significantly increased, resulting in a significant increase of heat storage capacity. This increase, in turn, results in a significant increase of time-lag, or time delay.

In the embodiment of the invention shown, the portions 4a and 4b of all four fuse links 4 are arranged in spaced parallel planes. Each of loops 4c encompasses three spaced planes and a separate groove 20 is provided in each plug 2 for each end of each fuse link. If desired, the number of grooves 2c may be reduced and each groove may receive the ends of two fuse links 4.

The structure shown in FIGS. 1 and 2 makes it possible to achieve time-lags, or time delays, in the order of to seconds at five times the rated current, though quartz sand is being used as arc-quenching medium in order to achieve reasonably high arc-voltages with a relatively small number of series breaks.

The structure shown in FIGS. 1 and 2 is similar to that shown in United States Patent 3,123,693 to Frederick J. Kozacka, March 3, 1964, Time-Lag Fuses of the Blade Contact Type, assigned to the same assignee as the present invention, inasmuch as both aim to achieve a high thermal efficiency by the provision of radially outer fuse link means forming thermal shields for radially inner fuse link means. However, in the structure of FIGS. 1 and 2 afar greater thermal efilciency is achieved by virtue of the presence of the axially outer fuse link portions or connector tabs 4b and the fashion in which these fuse link portions or connector tabs are folded.

The high thermal elficiency which is characteristic of the structure disclosed makes it possible .to greatly reduce the physical dimensions thereof relative to those of prior art fuse structures having comparable time-current curves and having an arc-quenching filler such as quartz sand combining high arc-quenching action with high thermal conductivity.

It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention as set forth in the appended claims.

I claim as my invention:

1. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of said casing;

(c) a pulverulent arc-quenching medium inside said casing; and

(d) a plurality of ribbon fuse link means of a currentlimiting metal inside said casing submersed in said medium conductively interconnecting said pair of terminal elements, said plurality of fuse link means including radially inner fuse link means and radially outer fuse link means sandwiching said radially inner fuse link means, said fuse link means having axially inner portions provided with transverse lines of perforations defining points of minimum crosssectional area substantially less than the maximum cross-sectional area of said axially inner portions, said axially inner portions supporting link-severing overlays of a metal having a relatively low fusing point, said fuse link means including axially outer portions having a cross-sectional area larger than said minimum cross-sectional area but less than said maximum cross-sectional area, said axially outer portions being folded to form loops substantially in the shape of the letter S and substantially in the shape of the inverted letter S.

2. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of the casing;

(c) a pulverulent arc-quenching medium inside said casing; and

(d) a plurality of ribbon fuse link means of a currentlimiting metal inside said casing conductively interconnecting said pair of terminal elements, said plurality of fuse link means including axially inner perforated portions arranged in substantially parallel spaced planes each supporting an overlay of a link severing relatively low fusing point metal, said fuse link means including axially outer connector tabs having a width smaller than said axially inner portions, said axially inner portions forming shoulders at the points of transition to said connector tabs, and each of said connector tabs including a zig-zag section situated between one of said axially inner portions and one of said pair of terminal elements.

3. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of said casing;

(c) a pulverulent arc-quenching filler inside said casing; and

(d) a plurality of ribbon fuse link means of a currentlimiting metal inside said casing submersed in said filler conductively interconnecting said pair of terminal elements, said fuse link means including axially inner perforated portions arranged in substantially parallel spaced planes each supporting an overlay of a link-severing relatively low fusing point metal, said fuse link means further including non-perforated connector tabs on the axially outer ends thereof having a smaller Width than said axially inner portions, said axially inner portions forming shoulders at the points of transition to said connector tabs, and each of said connector tabs forming two serially related U-turns.

4. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of said casing;

(c) a pulverulent arc-quenching medium inside said casing;

(d) a plurality of ribbon fuse link means of a currentlimiting metal inside said casing submersed in said medium conductively interconnecting said pair of terminal elements, said plurality of fuse link means including first fuse link means arranged relatively close to the axis of said casing and second fuse link means arranged relatively remote from the axis of said casing sandwiching said first fuse link means, each of said plurality of fuse link means including an axially inner perforated portion having a predetermined maxi-mum Width and supporting a linksevering overlay of a metal having a relatively low fusing point, each of said plurality of fuse link means further including a pair of connector tabs having a width less than said maximum Width of said axially inner portions, said axially inner portions forming shoulders at the points of transition thereof to said connector tabs, and said connector tabs being folded to form loops encompassing three spaced planes and being substantially in the shape of the letter S and substantially in the shape of the inverted letter S.

5. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of metal plugs each closing one end of said casing, each of said pair of plugs having parallel grooves on the axially inner end surface thereof;

(c) a quartz sand filler arranged inside said casing; and

(d) four ribbon fuse links of a current-limiting metal inside said casing submersed in said quartz sand filler, each of said four fuse links having axially outer ends inserted into said grooves in each of said pair of plugs, each of said four fuse links including an axially inner portion having transverse lines of perforations defining points of predetermined minimum cross-sectional area substantially less than the maximum cross-sectional area of said axially inner portions of said fuse links, said axially inner portion of each of said fuse links supporting a link severing overlay of a metal having a relatively low fusing point, said four fuse links further including axially outer non-perforated portions having a crosssectional area larger than said points of minimum cross-sectional area but less than said maximum cross-sectional area of said axially inner portion of said fuse links, and said axially outer portions being folded to form loops substantially in the shape of the letter S and substantially in the shape of the inverted letter S.

6. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of said casing;

(c) a pulverulent arc-quenching filler inside said cas- (d) fusible ribbon conductor means of a current-limiting metal inside said casing submersed in said filler conductively interconnecting said pair of terminal elements, said fusible conductor means being provided with transverse lines of perforations and supporting link-severing overlay means of a metal having a relatively low fusing point;

(e) additional fusible ribbon conductor means of a current-limiting metal inside said casing submersed in said filler conductively interconnecting said pair of terminal elements, said additional fusible conductor means being provided with transverse lines of perforations and supporting link-severing means of a metal having a relatively low fusing point, said additional fusible conductor means overlapping at least in part said conductor means to minimize substantially radial heat flow from said conductor means to said casing; and

(f) axially outer non-perforated connector tabs integral with said fusible conductor means and being folded to form adjacent to each of said pair of terminal elements, a pair of serially related U-turns of sufiicient size to significantly limit axial heat flow from the center region of said fusible conductor means to said pair of terminal elements.

7. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of said casing;

(c) a pulverulent arc-quenching filler inside said cas- (d) fusible ribbon conductor means of a current limiting metal inside said casing submersed in said filler conductively interconnecting said pair of terminal elements, said fusible conductor means being provided with transverse lines of perforations and supporting link-severing overlay means of a metal having a relatively low fusing point;

(e) additional fusible ribbon conductor means of a current-limiting metal inside said casing submersed in said filler conductively interconnecting said pair of terminal elements, said additional fusible conductor means being provided with transverse lines of perforations and supporting link-severing means of a metal having a relatively low fusing point, said additional fusible conductor means overlapping at least in part said conductor means to minimize substantially radial heat flow from said conductor means to said casing; and

(f) axially outer non-perforated connector tabs integral with said additional fusible connector means, and being folded to form adjacent to each of said pair of terminal elements a pair of serially related U- turns of sufficient size to significantly limit axial heat flow from the center region of said fusible conductor means to said pair of terminal elements.

8. An electric time-lag fuse comprising in combination:

(a) a tubular casing of insulating material;

(b) a pair of electroconductive terminal elements each arranged at one of the ends of said casing;

(c) a quartz sand filler inside said casing;

(d) a pair of substantially parallel ribbon fuse links of a current-limiting metal inside said casing submersed in said quartz sand conductively interconnecting said pair of terminals, said pair of fuse links being provided with transverse lines of perforations and supporting link-severing overlays of a metal having a relatively low fusing point;

(e) additional ribbon-shaped fusible conductors of a current-limiting metal inside said casing submersed in said squartz sand shunting said pair of fuse links, each of said pair of additional fusible conductors overlapping at least in part one of said pair of fuse links being provided with transverse lines of perforations and supporting link-severing overlays of a metal having a relatively low fusing point; and

(f) pairs of axially outer non-perforated connector tabs each integral with one of said pair of fuse links, each connector tab of said pairs of connector tabs being folded to form adjacent of each of said pair of terminal elements a pair of serially related U- turns of sufficient size to significantly limit axial heat flow from said pair of fuse links to said pair of terminal elements.

No references cited.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Examiner.

Non-Patent Citations
Reference
1 *None
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3425019 *Sep 5, 1967Jan 28, 1969Chase Shawmut CoMiniaturized cartridge fuse for small current intensities having large time-lag
US4216457 *Aug 8, 1978Aug 5, 1980Gould Inc.Electric fuse having folded fusible element and heat dams
US4219795 *Oct 18, 1978Aug 26, 1980Gould Inc.Fusible element for time-lag fuses having current-limiting action
US4300281 *Jan 29, 1980Nov 17, 1981Gould Inc.Method of making electric fuse having folded fusible element and heat dams
US4651119 *Jun 28, 1985Mar 17, 1987Gould Inc.Electric fuse heat dam element having stiffening ribs
US4935716 *Apr 24, 1989Jun 19, 1990Cooper Industries, Inc.Fuse having a ball plug
US4949063 *Apr 24, 1989Aug 14, 1990Cooper Industries, Inc.End closure system for high speed fuse
US4951026 *Apr 24, 1989Aug 21, 1990Cooper Industries, Inc.Weld projections on fuse terminals
US4972170 *Nov 15, 1989Nov 20, 1990Cooper Industries, Inc.High speed fuse
US5736918 *Jun 27, 1996Apr 7, 1998Cooper Industries, Inc.Knife blade fuse having an electrically insulative element over an end cap and plastic rivet to plug fill hole
US5841337 *Jan 17, 1997Nov 24, 1998Cooper Technologies CompanyTouch safe fuse module and holder
US5905426 *Jan 8, 1998May 18, 1999Cooper Technologies CompanyKnife blade fuse
US5963123 *Dec 29, 1998Oct 5, 1999Cooper Technologies CompanyKnife blade fuse
US6054915 *Feb 17, 1998Apr 25, 2000Cooper Industries, Inc.Compact touchsafe fuseholder with removable fuse carrier
US6157287 *Mar 3, 1999Dec 5, 2000Cooper Technologies CompanyTouch safe fuse module and holder
US7479866Mar 7, 2005Jan 20, 2009Littelfuse, Inc.Low profile automotive fuse
US7928827Jun 23, 2008Apr 19, 2011Littelfuse, Inc.Blade fuse
US8077007Dec 13, 2011Littlelfuse, Inc.Blade fuse
US20050015953 *Jul 21, 2003Jan 27, 2005Yaron KeidarMethod for making a spiral array ultrasound transducer
US20050212647 *Mar 7, 2005Sep 29, 2005Goldsberry Timothy RLow profile automotive fuse
US20090179727 *Jul 16, 2009Littelfuse, Inc.Blade fuse
Classifications
U.S. Classification337/160, 337/163, 337/229, 337/161, 337/158, 337/251
International ClassificationH01H85/055, H01H85/00
Cooperative ClassificationH01H85/055
European ClassificationH01H85/055
Legal Events
DateCodeEventDescription
Jun 15, 1983ASAssignment
Owner name: GOLUD INC 10 GOULD CENTER ROLLING MEADOWS IL 60008
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:I-T-E IMPERIAL CORPORATION;REEL/FRAME:004167/0716
Effective date: 19821227
Owner name: GOULD INC
Free format text: MERGER;ASSIGNOR:I-T-E IMPERIAL CORPORATION;REEL/FRAME:004167/0705
Effective date: 19830607
Owner name: I-T-E IMPERIAL CORPORATION A DE CORP
Free format text: MERGER;ASSIGNORS:AIRMATIC - BECKETT HARCUM INC - THE CHASE SHAWMUT COMPANY COMPONETROL INC - DATAMETRICS INC - EFCO DIE CASTING CORPORATION - GENRE REALTY INC - IMPERIAL EASTMAN CORPORATION - INDUSTRIAL DESIGN INC - RUNDEL COMP;ONENTS INC - TERAC CONTROLS INC;REEL/FRAME:004167/0712
Effective date: 19761130