US 3609621 A
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United States Patent Inventor Paul P. Danesl Attleboro Falls, Mass. App]. No. 4,380 Filed Jan. 20, 1970 Patented Sept. 28, 1971 Assignee Cable Electric Products Inc. Providence, RJ.
TIME DELAY FUSE 3 Claims, 4 Drawing Figs.
U.S. Cl 337/166, 3 37/ l 85 lnt.Cl .H01h85/10, l-lOlh 85/62 Field of Search 337/163,
References Cited UNITED STATES PATENTS 2,557,587 6/1951 Baenziger 337/166 2,506,304 5/1950 Ludwig 337/166 2,326,257 8/1943 Schmidt et al. 337/166 2,302,820 ll/l942 Von Liemdt 337/296 X Primary Examiner--Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorney- Max Schwartz ABSTRACT: A time delay fuse which is particularly adapted to eliminate failures during a short circuit test. The device uses a high refracting silicon material admixed with a metallic salt which acts as the heat sink. This material replaces the usual additional fusable metal, but will not dissolve or vaporize during a short circuit. Pressures are reduced and the fuse will not k gL mt ihsiwisq f l PATENIEDSEP28IBYI 3.609.621
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v INVENTOR PAUL P. DANESI ATTO N EY TIME DELAY FUSE My present invention relates to the electrical art, and more particularly to a time delay fuse.
The principal object of the present invention is to provide a time delay fuse which reduces the volume of fusable material in the fuse.
Another object of the present invention is to provide a time delay fuse which replaces some of the fusable material in the fuse with a high refractory nonfusable material.
A further object of the present invention is to provide a time delay fuse which will easily pass the Underwriters short circuit test by reducing the internal pressures in the fuse.
' A further object of the presentinvention is to provide a time delay fuse with a novel heat sink material which is simple and easy to apply to the fuse.
Another object of the present invention is to provide a novel time delay fuse which is simple in construction and easy and economical to manufacture and assemble.
With the above and other objects and advantageous features in view, my invention consists of a novel arrangement of parts, more fully disclosed in the detailed description following, in conjunction with the accompanying drawings, and more particularly defined in the appended claims.
In the drawings,
FIG. 1 is a vertical section of an S type time delay fuse embodying my invention;
FIG. 2 is a side elevation of the fusable link therefore;
FIG. 3 is a top plan view of the link; and
FIG. 4 is a side elevation of a fusable link for a standard type fuse.
It is good practice to provide some fuses with a time delay action to prevent unnecessary blowouts. For example, washing machine motors, starting under a heavy load, will draw more than the safe amperage but will then settle down while running. To prevent the fuse from blowing immediately, a time delay is provided. This is usually accomplished by adding an additional piece of metal to the fuse link, at one side, which acts as a heat sink and will draw off the initial heat to delay the burning out of the fuse. The Underwriters Laboratories require that such fuses give'out in a minimum of 12 seconds and maximum of 2 minutes. However, such fuses must also pass a short circuit test. This test suddenly pushes 10,000 amps@ 125 v. AC through the fuse. The link not only melts but vaporizes. Pressures build up within the body of the fuse. The test requires the fuse to hold without bursting or blowing off the cover or otherwise leaking the hot vaporized gases.
It is obvious that the time delay fuse, with its additional metal heat sink, builds up heavier pressures in this test than the standard fuse. The present invention provides a time delay fuse in which the heat sink comprises a nonfusable material thus not only not adding to the vaporized mass, but the material also encompasses some of the fusable material to actually reduce the pressures in the fuse to less than in a standard type fuse.
Referring more in detail to the drawings, the fuse shown in FIG. 1 is the new type S. The body portion is made of unglazed porcelain with the main threaded portion 11 and an enlarged head 12. The head 12 has an annular chamber with an auxiliary wall portion 13 at one side. The contact elements are made of copper alloy. The hollow body 14, extending through the portion 11, terminates in a restricted opening 15 which flares outwardly at the outer end 16. A hollow copper alloy contact element 17 is mounted in this end. It is formed like a hollow rivet, with its outer end flattened at 18 to form the bottom contact. It extends upwardly and flares out against the wall at l9 to be locked in place.
The second contact element is also copper alloy and is in the form of a horseshoe shape 20 having a downwardly extending resilient contact portion 21 (dotted lines). This contact element 20 is positioned surrounding the upper end of the body portion 11 just below the head 12.
The fuse link 22, see FIGS. 2 and 3, is of a conventional fusable metal such as zinc. The link 22 has a short vertical portion 23 and then turns slightly to the left (FIG. 2) and then upwardly to form a long vertical leg 24. At the upper end it IS reentrantly bent to form a loop 25 and a short spaced parallel vertical leg 26. It then turns sharply to the right at a slight upward angle to form the link portion 27. Then there is another shorter upward and downward form to make the loop 28 at the right. As can be seen in FIG. 3, the fuse link 22 is flat and ribbonlike. At the link portion 27, it is tapered down at 29 to reduce the metallic conductive area and provide the fusable point of the device.
The fuse link 22 is mounted in the body 10 as shown in FIG. 1. The short bottom portion 23 enters the contact element 17 and the bottom end is soldered or otherwise electrically attached to it. The link is positioned at an angle to the left (FIG. 1) to allow sufficient room for the fusable portion 27. The short end loop 28 is mounted over the top of the auxiliary wall 13 and the free end of the link extends downwardly through an opening in the body 10 to contact the element 20 at this point. The element 20 is also provided with a tab portion 30 which extends through this opening to make the contact. A porcelain or other high refractory material 31 is poured into the space behind the auxiliary wall 13 to seal the opening, lock the link in place, and seal the contact between the link and the element 20.
All of the above construction is fairly standard. However, in accordance with the present invention, 1 now provide the link 22 with a time delay heat sink. This comprises a high refractory silicon material admixed with a metallic salt. The silicon itself, being a ceramic material, would not absorb any heat fast enough to form the necessary heat sink. However, applicant has found that the addition of a metallic salt will render it heat absorptive at a much higher rate. Furthermore, the rate can be controlled by the proportion of salt to the silicon. For example, a 50-5 proportion by volume will form a mixture which will satisfy the Underwriters tests. The mixture is positioned on the loop portion 25 as shown in FIG. 1 and in dotted lines in FIG. 2. The mixture 32 extends downwardly to cover all of the vertical leg 26 of the link, the parallel portion of the leg 24, and part of the fusable link portion 27.
Since it is close to the fusable link portion 29, its heat sink effect will act as the necessary time delay for the fuse. However, it will not vaporize during the short circuit tests and will prevent the material within it from vaporizing, thus, actually reducing the amount of vaporizable material in the fuse.
FIG. 4 shows the application of the present invention to a regular type fuse. Here the fuse link 33 is provided with the horizontal fusable portion 34 and two short loops 35 at each end. The material 36 is mounted to enclose the loops 35 to form a heat absorbing mass at each end of the link portion 34.
The present invention thus provides a heat sink material for a time delay fuse which replaces the metal now in use. This material not only is effective as a heat sink but is nonfusable and nonvaporizing to ensure the safety of the fuse and its ability to pass the short circuit tests. Other advantages of the present invention will be readily apparent to a person skilled in the art.
l. A time delay fuse comprising a porcelain housing, a fuse link mounted in said housing adapted to fuse under the excessive heat of a short circuit, said link comprising a thin ribbon of zinc material, and a mass of nonfusable material mounted on said link to absorb the heat and delay the fusing action of said link, said nonfusable material comprising a high refractory silicon admixed with a metallic salt in a predetermined pro portion to control the time of the delay.
2. A time delay fuse as in claim I, wherein said link is provided with an integral loop adjacent one end of the fusable portion of said link, said mass of nonfusable material encompassing said loop and a portion of said link fuse material.
3. A time delay fuse as in claim 2, wherein said high refractory silicon is admixed with a metallic salt in a 50-50 ratio.