US2773961A

US2773961A - Time delay fuse

Info

Publication number: US2773961A
Application number: US426077A
Authority: US
Inventors: Edward V Sundt
Original assignee: SUNDT ENGINEERING Co
Current assignee: SUNDT ENGINEERING Co
Priority date: 1954-04-28
Filing date: 1954-04-28
Publication date: 1956-12-11
Anticipated expiration: 1973-12-11

Description

Dec. 11, 1956 E. v. SUNDT TIME DELAY FUSE:

Filed April 28, 1954 United States Patent TIME DELAY FUSE Edward V. Sundt, Wilmette, 1li., assignor to Smidt Engineering Company, Des Plaines, Ill., a corporation of Illinois Application April 28, 1954, Serial No. 426,077

14 Claims. (Cl. 2043-123) The principal object of this invention is to provide an improved time delay fuse for electric circuits which provides substantially instantaneous action upon the occurrence of high overloads, which provides a time delayed action upon lower sustained overloads, which prevents needless fuse blowing on harmless overloads, which utilizes a new and improved principle of operation, which is of a new and improved construction, which is foolproof in operation, and which can be inexpensively manufactured.

Basically, the time delay fuse of this invention is a heat operated device wherein heat is generated therein through the passage of electric current and absorbed over time up to a calibrated point of fusion in order to secure the desired delay. Two physical factors are utilized to secure the time delay, the specific heat of the entire fuse element and the latent heat of fusion of a body of fusible metal purposely added to the element.

Briefly, the time delay fuse of this invention includes an electrically conductive fuse element formed from a fusible metal and having between its ends a receptacle portion and a resistance heating portion of limited cross sectional area adjacent the receptacle portion. A body of fusible metal of lower melting point than that of the fuse element is secured in the receptacle portion of the fuse element in intimate Contact therewith so as to provide high thermal conductivity therebetween. Electrical terminals are connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected.

A sustained overload in the electric circuit causes the resistance heating portion of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit. The heating of the resistance heating portion of the fuse element to the melting point thereof for breaking the electric circuit being protected is delayed by the specic heat and the latent heat of fusion of the body of fusible metal. ln this way substantial time delays in blowing of the fuse at the resistance heating portion thereof may be obtained. At the same time a high overload, such as caused by a short circuit, will substantially instantaneously blow the fuse at the resistance heating portion thereof.

Preferably, the fuse element of the time delay fuse of this invention includes a pair of spaced apart receptacle portions provided with the lower melting point fusible metal in each, an inner resistance heating portion extending therebetween and an outer resistance heating portion extending outwardly from each receptacle portion. Here, the delayed blowing of the fuse normally takes place at the inner resistance heating portion, where blowing conditions may be more readily calibrated and controlled, while instantaneous blowing may take place at any one or more of the three resistance heating portions. The fuse element may be encased in a tubular closure of electrical insulating material provided with metallic end 2,773,961 Patented Dec. 11, 1956 ICC caps to which the ends of the fuse element are electrically connected to form a cartridge type of fuse. Of course, other types of closures may be utilized.

The fuse element may be formed from a sheet of fusible metal and the receptacle portions may be substantially tubular in shape formed by suitably stamping and bending the sheet. The bodies of fusible metal may be secured in the tubular receptacle portions merely by dipping the fuse element in a molten pool of the lower melting point fusible metal. Substantially any kind of fusible metals may be used for the fuse element and the fusible bodies depending upon the fusing conditions to be met. They may be basic metals or alloys of metals, eutectic alloys being preferred for the lower melting point fusible bodies since their melting conditions may be more readily determined and calibrated. Preferably, the outer resistance heating portions of the fuse element are bent substantially normal to the axes of the cylindrical receptacle portions to compensate for thermal expansion and contraction.

Other objects of this invention reside in the details of construction of the time delay fuse and in the cooperative relationships between the component parts thereof.

Other objects and advantages of this invention Will become apparent to those skilled in the art upon reference to the accompanying specication, claims and drawing in which:

Fig. l is a perspective view of a time delay fuse constructed in accordance with this invention;

Fig. 2 is a sectional view taken substantially along the line 2-2 of Fig. l;

Fig. 3 is one form of a blank formed from a sheet of fusible metal from which the fuse element is fabricated;

Fig. 4 is another view similar to Fig. 3 showing another form of blank for fabricating the fuse element;

Fig. 5 is a perspective view of a fuse element formed into shape and including the bodies of fusible metal;

Fig. 6 is a sectional view taken substantially along the line 66 of Fig. 2;

Fig. 7 is a sectional view taken substantially along the line 7 7 of Fig. 2.

The time delay fuse of this invention is generally des ignated at 10. It includes a fuse element 11 formed from a sheet of fusible metal. The blank from which the fuse element is fabricated is illustrated in Fig. 3. It includes a pair of

parts

12 and 13 which ultimately form the substantially tubular cavities. Extending between the

parts

12 and 13 is a resistance heating portion 14 of limited cross sectional area. As illustrated the part 14 is provided with a cut-out 1S to limit the cross sectional area. When current is passed through the fuse element 11 the portion 14 of limited cross sectional area is heated thereby. Extending from the outer end of each

part

12 and 13 is a tab 16 and a tab 17, respectively. These

tabs

16 and 17 are provided with cut-

outs

18 and 19 for providing the tabs with a limited cross sectional area so that the

tabs

16 and 17 also form resistance heating portions of the fuse element 11. As shown in Fig. 4 the

tabs

16 and 17 may be made narrower to provide resistance heating portions of limited cross sectional area.

ln fabricating the ,fuse element the par-

ts

12 and 13 are formed into substantially cylindrical cavities as illustrated in Fig. 5. The

tabs

16 and 17 adjacent the outer ends of the `

receptacle portions

12 and 13 are bent substantially normal to the axes of the receptacle portions `as shown in Fig. 5. After the fuse element has been so formed or fabricated, it is then first dipped in a flux and immediately thereafter into a molten pool of `fusible metal of lower melting point. ln so doing, the fusible metal flows into the

tubular receptacles

12 and 13 and is maintained in there by capillary attraction. When the fuse element is removed from the molten pool, the fusible metal solidifies in .the receptacle portions and is thereby pemanently sccured therein in intimate contact therewith so as `to provide high thermal conductivity therebetween. The fuse element is then provided with `a rinse to remove excess tiux and it is then ready for incorporation into a suitable closure.

rllhe closure for the fuse element may include a tubular closure 25 formed of electrical insulating material such as glass or the like. The ends of the tubular closure 25 are preferably turned inwardly slightly as indicated yat 26 and 27. The fuse element is inserted in the closure 25 and

metallic end caps

28 and 29 are placed over the ends of the closure 25. The end caps 2S `and 219 are secured in place on the tubular closure 25 and are electrically connected to the ends of the fuse element il by means of solder indicated at 3@ and 3l. The end caps 2&5 and 29 therefore provide electrical connections for connecting the fuse of this invention into an electrical circuit to be protected.

When a sustained overload occurs in the electric circuit, it causes the resistance heating portions i4, )i6 and il/ of limited cross sectional area to heat the fuse element l?. and the bodies of fusible metal 27. and 23 substantially as a unit. The heating of the resistance heating portions of the fuse element to the melting point thereof for breaking the electric circuit being protected is delayed by the specific heat of the unit as a whole and the latent heat of fusion of the bodies of the fusible metal. in this way substantial time delays in blowing of the fuse at .the resistance heating portions thereof may be obtained. Since the resistance heating portion M is located between the bodies of fusible metal 22 and Z3 and will probably be of higher temperature than the other resistance heating portions lo `and l?, 4the fuse will blow on sustained overload conditions at this point rather than the other two points. At the same time a high overload condition such as caused by a short circuit will substantially instantaneously blow the fuse at any one or more of the resistance heating portions i4, 16 and i7. Because the resistance heating portions i6 .and 17 are bent substantially normal to the .axis .of the cylindrical receptacle portions l2 and i3, these bent portions may Hex upon expansion and contraction of the fuse element due to temperature conditions and therefore the fuse of this invention is fully compensated for thermal expansion and contraction and fatiguing of the fuse element is maintained at a minimum.

Substantially any kind of fusible metals may be used, depending,y upon the fusing conditions to be met. For example, the fuse element il may be formed from sheet zinc or the like. Different ampere ratings of the fiusc element may be obtained by varying the thickness of the zinc sheet and in practical applica-tion this ranges from .OOlS to .015 inch for small fuses. Accordingly this design provides an inexpensive means for securing a great number of ampere, or intermediate ampere, ratings. In regard to the melting points of the

fusible metal bodies

22 and 23 it is .preferable not to have the melting point much lower than 288 F., which is the eutectic of tin and bismuth, nor is it desirable to have .the maximum more than 690 F., which is the eutectic of cadmium and silver. The eutectic of tin and lead, melting at approximately 360 F., is a good compromise temperature, and is high enough above normal ambient temperatures so that the blo-wing characteristics of the fuses are not influenced greatly thereby.

In service under operating conditions, the assembled fuse of this invention will carry 110% of rated current for a minimum of four hours. if the current is increased to any value from about 135% of rating and up to less than 400% of rating, the resistance heating portions of the fuse element generate enough heat to bring the fusible metal in the heat receptacles up to the melting point thereof. Up to this point, delay in fuse action is due principally to the specific heat of the fuse element and the bodiesv `of fusible metal. Above this point, the fusion metal is changed from solid to liquid., and no further temperature rise takes place until all cf the fusible metal has .changed state, and a further delay is thus obtained due to the latent heat of fusion. Depending on the alloy used in the bodies of fusible metal, this del-ay is several times that obtained by the specific heat only. At of rating, the fuse of this invention will blow in about one hours time while at 400% rating, the fuse will blow in about five .scconds time. Above 400% rating, the fuse will blow at a time inversely proportional to the overload.

While for purposes of illustration one basic form of this invention has been disclosed, other forms thereof may become apparent to those skilled in the art upon reference to this disclosure and there-fore this invention is to be limited only by the scope of the appended claims.

I claim as my invention:

l. A time delay fuse comprising an electrically conductive single piece fuse element formed from a fusible :letal having a predetermined relatively high melting point and having between its ends a receptacle portion and a resistance heating portion of limited cross sectional area at each end of and adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in the receptacle portion of the fuse element in intimate contact therewith so ,as to provide a high thermal conductivity therebetween, `and electrical terminals connected to the ends of the fuse element for incorporating the same in `an electric circuit to be protected, a sustained Voverload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit `being delayed by the specific heat .and the latent heat of fusion of the body of `the relatively low inciting point fusible metal.

2. A time delay fuse comprising `an electrically conductive elongated single piece fuse element formed from a fusible metal having a predetermined relatively high melting point and having between its ends a pair of spaced apart receptacle portions, a resistance heating portion of limited cross sectional area adjacent to and between the receptacle portions and a resistance heating portion at and adjacent to the outer end of each receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in each receptacle portion of the fuse element in intimate contact therewith s0 as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and latent heat of fusion of the bodies of the relatively low melting point fusible metal.

3. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a sheet of fusible metal having a predetermined relatively high melting point and having between its ends a substantially tubular part forming a receptacle portion and a tab of limited cross sectional arca extending from each end of the tubular part and each forming a resistance heating portion adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured `in the receptacle portion of the fuse element in intim-ate contact therewith so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portion of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and the latent heat of fusion of the body of the relatively low melting point fusible metal.

4. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a sheet of fusible metal having a predetermined relatively high melting point and having between its ends a substantially tubular part forming a receptacle portion and a tab of limited cross sectional area extending from each end of the tubular part and each forming a resistance heating portion adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in the receptacle portion of the fuse element in intimate contact therewith by dipping the fuse element in a molten pool of said lower melting point fusible metal so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portion of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and the latent heat of fusion of the body of the relatively low melting point fusible metal.

5. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a sheet of fusible metal having -a predetermined relatively high melting point and having between its ends a pair of spaced apart substantially tubular parts forming a pair of spaced apart receptacle portions, a part of limited cross sectional area extending between the tubular parts and forming a resistance heating portion adjacent to and between the receptacle portions, and a tab of limited cross sectional area extending from the outer end of each tubular part and each forming a resistance heating portion at and adjacent to the outer end of each receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in each receptacle portion of the fuse element in intimate contact therewith so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and latent heat of fusion of the bodies of the relatively low melting point fusible metal.

6. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a sheet of fusible metal having a predetermined relatively high melting point and having between its ends a pair of spaced apart substantially tubular parts forming a pair of the fuse element in intimate contact therewith by dip` ping the fuse element in a molten pool of said lower melting point fusible metal so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and latent heat of fusion of the bodies of the relatively low melting point fusible metal.

7. A time delay fuse comprising an electrically conductive single piece fuse element formed from a fusible metal having a predetermined relatively high melting point and having between its ends a substantially tubular receptacle portion and a resistance heating portion of limited cross sectional area at each end of and adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in the receptacle portion of the fuse element in intimate contact therewith so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portion of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit, and the heating of the receptacle heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and the latent heat of fusion of the body of the relatively low melting point fusible metal.

8. A time delay fuse comprising an electrically conductive single piece fuse element formed from a fusible metal having a predetermined relatively high melting point and having between its ends a substantially tubular receptacle portion and a resistance heating portion of limited cross sectional area at each end of and adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melt-ing point and secured in the receptacle portion of the fuse element in intimate contact therewith by dipping the fuse element in a molten pool of said lower melting point fusible metal so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portion of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit, and the heating of the receptacle heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and the latent heat of fusion of the body of the relatively low melting point fusible metal.

9. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a fusible metal having a predetermined relatively high melting point and having between its ends a pair of spaced apart substantially tubular receptacle portions, a resistance heating portion of limited cross sectional area adjacent to and between the receptacle portions and a resistance heating portion at and adjacent to the outer end of each receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in each receptacle portion of the fuse element in intimate contact therewith so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electr-ic circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric Icircuit being delayed by the speciiic heat and latent hea-t of fusion of the bodies of the relatively low melting point fusible metal.

l0. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a fusible metal having a predetermined relatively high melting point and hav-ing between its ends a pair of spaced apart Substantially tubular receptacle portions, a resistance heating portion of limited cross sectional area adjacent to and between the receptacle portions and a resistance heating portion at and adjacent to the outer end of each receptacle portion, a body of fusible metal having a predetermined relatively low melting point and in intimate contact therewith by dipping the fuse element in a molten pool of said lower melting point fusible metal so as to provide high thermal conductivity therebetween, and electrical terminals connected to the ends of the fuse element for incorporating the same in an electric circuit to be protected, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and latent heat of fusion of the bodies of the relatively low melting point fusible metal.

ll. A `time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a fusible metal having a predetermined relatively high melting point and having between its ends a substantially tubular receptacle portion and a resistance heating portion of limited cross sectional area at each end of and adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melting7 point and secured in the receptacle portion of the fuse element in intimate Contact therewith so as to provide high thermal conductivity therebetween, a tubular closure of electrical insulating material for the fuse element, electrically conductive caps secured to the ends of the tubular closure and forming electrical terminals for connecting the fuse in an electric circuit to be protected, means for electrically connecting the ends of the fuse element to the caps, said resistance heating portions of the fuse element being bent substantially normal to the axis of the tubular receptacle portion adjacent the ends thereof to compensate for thermal expansion and contraction, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the body of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specifi-c heat and the latent heat of fusion of the body of the relatively low melting point fusible metal.

l2. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a fusible met-al having a predetermined relatively high melting point and having between its ends a pair of spaced apart substantially tubular receptacle portions, an inner resistance heating portion of limited cross sectional area adjacent to and between the receptacle portions and an outer resistance lheating portion of limited cross sectional area at and adjacent to the outer ends of each receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in each receptacle portion of the fuse element in intimate contact therewith so as to provide high thermal conductivity therebetween, a tubular closure of electrical insulating material for the fuse element, electrically conductive caps secured to the ends of the tubular closure and forming electrical terminals for connecting the fuse in an electric circuit to be protected, means for electrically connecting the ends of the fuse element to the caps, said outer resistance heating portions of the fuse element being bent substantially normal to the axis of the tubular receptacle portions adjacent the outer ends thereof to compensate for thermal expansion and contraction, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and latent heat of fusion of the bodies of the relatively low inciting point fusible metal.

13. A time delay fuse comprising an electrically conductive elongated single piece fuse element formed from a sheet of fusible metal having a predetermined relatively high melting point and having between its ends a substantially tubular part forming a receptacle portion and a tab of limited cross sectional area extending from each end of the tubular part and each forming a resistance heating portion adjacent to the receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in the receptacle portion of the fuse element in intimate Contact therewith so 'as to provide high thermal conductivity therebetween, a tubular closure of electrical insulating material for the fuse element, electrically conductive caps secured to the ends of the tubular closure and forming electrical terminals for connecting the fuse in an electric circuit to be protected, means for electrically connecting the ends of the fuse element to the caps, said resistance heating portions of the fuse element being bent substantially normal to thc axis ol' the tubular receptacle portion adjacent the ends thereof to compensate for thermal expansion and contraction, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the ruse element and the body of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit beng delayed by the specific heat and the latent heat of fusion of the body of the relatively loW melting point fusible metal.

14. A time 4delay fuse `comprising an electrically conductive elongated single piece fuse element formed from a sheet of fusible metal having a predetermined relatively high melting point and having between its ends a pair of spaced apart substantially tubular parts forming a pair of `spaced apart receptacle portions, a part of limited cross sectional area extending between the tubular parts and forming a resistance heating portion adjacent to and between the receptacle portions, and a tab of limited cross sectional area extending from the outer of each tubular part and each forming a resistance heating portion at and adjacent to the outer end of each receptacle portion, a body of fusible metal having a predetermined relatively low melting point and secured in each receptacle portion of the fuse element in intimate cont-act therewith, a tubular closure of electrical insulating material for the fuse element, electrically conductive caps secured to the ends of the tubular closure and forming electrical terminals for connecting the fuse in an electric circuit to be protected, means for electrically connecting the chas of the fuse element to the caps, said outer resi e ating portions of the fuse element being bent substa illy normal to the axis ot the tubular receptacle portions adjacent the outer ends thereof to compensate for thermal expansion and contraction, a sustained overload in the electric circuit causing the resistance heating portions of the fuse element to heat the fuse element and the bodies of fusible metal substantially as a unit, and the heating of the resistance heating portions of the fuse element to the relatively high melting point thereof for breaking the electric circuit being delayed by the specific heat and latent heat of fusion of the bodies of the relatively low melting point fusible metal.

(References on following page) se s References Cited in the le of this patent UNITED STATES PATENTS Reynolds et al Oct. 13, 1908 Lippincott July 8, 1924 Bird Feb. 28, 1928 10 Steinmayer Nov. 7, 1933 Jung et al. Sept. 29, 1936 Baenziger June 19, 1951 Laing July 7, 1953 Baenziger May 11, 1954