US2239390A

US2239390A - Fuse

Info

Publication number: US2239390A
Application number: US183489A
Authority: US
Inventors: Oscar H Jung; Paul E Heffelfinger
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-01-05
Filing date: 1938-01-05
Publication date: 1941-04-22
Anticipated expiration: 1958-04-22

Description

A ril 22,1941. 0. H. JUNG ETAL FUSE Filed. Jan. 5, 1938 2 Sheets-Sheet l rlllrlllli l HHUHHHHHHHIHI lie ferrule 4 by a drop of solder 82. The opposite end of the link, which projects into the thimble through the slot I 3, is embedded in a batch of fusible alloy ll of a lower melting point than that of the fuse link II. The alloy H is carried by a thermal con IS, the lower end of which projects into the cup rivet l0, and is electrically secured thereto by means of solder or other suitable material l6, preferably having a higher melting point than the alloy ll.

Positioned under the link I! is a flat spring ll provided at one end with an offset nose l8, which bears against the fuse link adjacent its connection with the thermal coil IS. The opposite end of the spring ll extends between the walls of the sleeve 2 and thimble 3 adjacent the link H. In carrying out the principles of the present invention, a disc is of substantially the same diameter as the interior of, the thimble 3 is positioned on the link adjacent its connection with the thermal coil I5, thus forming a shield between the link and coil, and also serving to create a compression chamber to within the thimble 3, as well as serving to aline and hold the thermal coil in central position out of contact with the inner wall of the thimble.

That end of the link extending between the telescoped walls of the sleeve 2 and the thimble 3 is provided with an insulating wrapping or cover M, which extends at 22 to provide a complete insulation between the fuse link i i and spring ill.

Figure 3 illustrates the present invention applied to a conventional type of one-piece plug, provided with a body 2| formed of moulded insu lating material, and in which the link it extends through an opening 26 formed in the body. The link is electrically connected to the metallic ferrule or contact 25 by solder 26. Above the solder the link issurrounded by suitable insulating material 24' poured into the opening 24. in this form of the invention one end of the hat spring l'l extends into a recess 2? formed in the casing 23 adjacent the opening 24. A notch or groove 28 is formed in the inner wall of the casing oppocartridge type iuse, comprising a casing 3i formed of insulating material, and provided with metallic end caps 32, which serve as contacts for reception in a conventional fuse clip. The thermal coil i is soldered or otherwise electrically connected to one of the caps 32, while the fuse link ii is connected to the opposite cap. A contractile coil spring 33, connected to the link M adjacent its restricted potential fusing portion, and to the cap 32 with which the opposite end of the link is secured, serves to space the severed ends of the link upon fusing, as will be later described.

Considering now the operation ofthe present invention, with particular reference to that formdisclosed in Figures 1 and 2, upon conditions of initial overload to which circuits are subjected upon the starting of a motor, or other electrical appliances, the link ii is prevented from blowing, in that it is proportioned to fuse within the range of approximately five times the full load rating of the device in the circuit, and upward to and including short circuit conditions. In the event of overloads below the foregoing values, the fusible alloy l4 softens and allows the spring ll to'withdraw the end of the fuse strip from the alloy, thus opening the circuit. When a short circuit occurs, the fuse element H, which is heavy enough to withstand starting currents or harmless overloads, will open in the manner described, and possibly in other exposed portions between the disc l9 and the insulating wrapper 2|. At the same time, the disc is will obstruct any tendency of the arc to burn upwardly on the link, and should the fusing occur in the link above the disc,- as upon short circuit or heavy overloads, the latter affords protection against the are carrying over to the thermal coil, thereby holding volatilization to a minimum.

While the discl9 may be formed of any insulating material, in practise the most desirable results have been obtained in the use of a material having arc-quenching and deionizing properties. In this respect black fibre has beeniound to be superior to white fibre, believed to be due to its ability to absorb and retain a greater amount of moisture. v

Inasmuch as the spring I l is spaced and insulated from the link ii, there is no tendency of the link welding itself to the spring upon fusing intermediate its ends, nor of the spring carrying the are along the link. A further advantage (112- I termined in insulating the link from the spring resides in the fact that harmless overloads heat the link II to such an extent that the spring becomes overheated when in contact with the same,

thus affecting its temper to the extent that'its resiliency is destroyed.

Heretofore, in conventional fuse structures of the type disclosed in Figure 1, it has been customary to merely project the bare fuse link between the telescoping walls of the casing sections,

and under such conditions it has been found that the are frequently has a tendency to travel the entire length of the link, causing the same to burn and volatilize, all of which creates excessive pressure, which either ruptures the casing or creates ignitions, causing the fuse to weld in the fuse holder due to a flash-over.

The foregoing objections have been entirely overcome by the provision of the insulating'wrap per H, which surrounds that portion of the fuse link extending between the telescoping portions of the shell 2 and thimble 3. The wrapping may be of any pliable insulating material, suchas paper, asbestos, or the like. However, it is preferred to use a hygroscopic material, such as paper impregnated with a deionizing ingredient. Satisfactory results have even been obtained with gummed paper, which has a tendency to retain a sufflcient amount of moisture to efiectively cool or quench the are so that portion of the link extending between the sections of the casing will not volatilize.

Inasmuch as a slightly tapered fit is provided between the outer shell 2 and the thimble 3, a clamping or wedging action between the two apparently increases the smothering effect of the insulating wrapper, due to forcing the same into tight, intimate contact with the fuse strip.

In that form of the invention shown in Figure 3, the insulating filler 24' likewise serves to smother burning of the link, and prevents the arc,

from discharging or flashing past the casing.

In a cartridge type fuse, such as shown in Fig-- of the link as required in plug type From the foregoing explanation, considered in connection with the accompanying drawings, it is believed that the advantages of the present invention will be apparent, in that the same provides for the reduction of metal volatilized, thereby reducing the gas pressures generated, as well as the duration of the arc, which, because of the shields provided, is quickly quenched, and prevented from spreading to other parts of the connection between the fuse contacts, all of which reduces damage to the fuse casing, and the possibility cf fire hazard from ignitions and flashovers to a minimum.

Inasmuch as the resilient means provided, instantane usly spaces the severed portions of the connectic n between the contacts upon fusing, and in so doing raises the disc IS, with the assistance of pressure generated within the chamber or compartment 2!, the raised position of the disc serves as an indicator of the condition of the fuse. 2

Also, under all conditions of fusing, the link itself is slapped against the micawindow by the spring, which affords an additional and plainly visiblev indicator.

We claim:

1. A circuit interrupter comprising, a casing of,

insulating material, a pair of terminals carried by the casing, a heat generating element of rela-' tively high resistance connected to one of said terminals, a fusible link having one end connected with said heat generating element by a low melting point fusible material and its opposite end connected to the other of said terminals, said link being of lower resistance than said heat generating element and of greater resistance thansaid low melting point fusible material and a fibre disc located on said strip adjacent said thermal element to form a closed compression chamber within which the thermal element is located.

2. A circuit interrupter comprising, a casing of insulating material, a pair of terminals carried by the casing, a fusible link connecting said terminals, a flat metallic spring positioned under said link and normally under stress to part the severed portions of said link upon fusing, and heat insulation disposed between said link and sprins- 3. A circuit interrupter comprising, a casing of insulating material, a pair of terminals carried by the casing, a fusible link connecting said terminals, a flat metallic spring positioned under said link and normally under stress to part the severed portions of said link upon fusing, said spring being spaced from said link throughout substantially the entire portion of the link disposed within the interior of the casing and hearing upon the link adjacent its inner end, and insulation disposed between said link and spring.

4. A circuit interrupter comprising, a casing of insulating material, a pair of. terminals carried by the casing, a heat generating element concasing and bearing against the link adjacent its connection with said thermal element, and insulation disposed between said link and spring.

5. A circuit interrupter comprising a casing of insulating material, a pair of terminals carried by the casing, a thermal element connected to one of said terminals, a fusible link connecting said thermal element and the other of said terminals, a fibre disc located on said link adjacent its connection with said thermal element, said disc forming a closed compartment within which the thermal element is located, a flat metallic spring posl tioned under said link and normally under stress to part the link from the thermal element when the link is released therefrom, said spring being spaced from said link throughout substantially that portion of the link disposed within the interior of the casing and bearing against the link adjacent said disc, and insulation disposed between said link and spring.

6. A circuit interrupter comprising, a casing consisting of a pair of telescoping sections formed of insulating material, a terminal carried by each of said sections, a thermal element connected to the terminal carried by the inner section, a fusible link connecting said thermal element and the other of said terminals, said link extending between the walls of the telescoping sections, a wrapper formed of pliable sheet insulating material surrounding thatpart of the link extending between the telescoping sections whereby the wrapper is forced into intimate contact with the link, a fibre disc located on said link adjacent said thermal element, and forming a closed compression chamber within which the thermal element is located, a flat metallic spring positioned under said link and normally under stress to part the link from the thermal element upon release from the same, said spring being spaced from said material throughout substantially that portion of the link disposed within the interior of the casing, and bearing against the link adjacent said disc, and insulation disposed between said link and spring.

7. A circuit interrupter comprising, a casing of insulating material, a pair of terminals carried by the casing, a fusible link connecting said terminals, and a flat metallic spring positioned under said link and normally under stress to part the severed portions of said link upon fusing.

OSCAR H. JUNG. PAUL E. HEFFEIFIIIGER.