US2688676A

US2688676A - Lag fuse construction and method and apparatus for making same

Info

Publication number: US2688676A
Application number: US275198A
Authority: US
Inventors: Gordon F Laing
Original assignee: ECONOMY FUSE AND Manufacturing CO
Current assignee: ECONOMY FUSE AND MANUFACTURING Co
Priority date: 1952-03-06
Filing date: 1952-03-06
Publication date: 1954-09-07
Anticipated expiration: 1971-09-07

Description

Sept. 7, 1954 Filed March 6, 1952 G. F. LAING LAG FUSE CONSTRUCTION AND METHOD AND APPARATUS FOR MAKING SAME 2 Sheets-Sheet l Patented Sept. 7, 1954 LAG FUSE CONSTRUCTION AND METHOD AND APPARATUS FOR MAKING 'SAME Gordon F. Laing, Delavan, Wis., assignor to Economy Fuse and Manufacturing 00., Chicago, 111., a corporation of Illinois Application March 6, 1952, Serial No. 275,198

4 Claims. 1

This invention relates to the construction and manufacture of lag fuses, and especially those of the type shown and described in my Patent No. 2,577,531, issued December 4, 1951.

The invention is primarily directed to construction techniques and apparatus for securing adherence between terminal links and a connecting central fusible element which characterize lag fuse constructions of this type. The invention also embraces desirable dimensional and volumetric relationships the better to secure open circuit conditions once a fusible element has been melted incident to circuit overload.

Although it has heretofore been the intention to solder terminal links to the fusible slug in lag 1 fuses, due to the relative low melting points of the metals involved, it has not been easily accomplished without embarking upon the rather costly procedures involved in preheating and holding the several parts at elevated temperatures for an interval of time necessary to secure the Welded union.

Since these practices are not regarded practicable under the limitations of commercial economy, other efforts to connect links to the slugs have resulted in loose connections which permit the metals to oxidize or corrode at the interface, aiiording a poor electrical contact and altering the capacity of the fuse thereby.

In many instances the connection is so loose as to permit the link elements to withdraw from the fusible slug, with obviously undesirable results. In this latter connection, the fibrous casings in which such fuses are assembled are responsive to changes in humidity, so that considerable expansion and contraction under operating conditions and for substantial intervals .of time subject the link assemblies to tension and compression, and in many instancess the forces of tension are sufiicient to loosen or destroy the contact between the links and fusible slug.

Other problems have arisen in relating the mass of the fusible slug element to the internal volumetric capacity of the casing in which it is installed to insure that the slug once fused on i overload to break connection between the link terminals will remainsniiiciently spaced from the latter 'eiiectively to maintain open circuit condi- :tion, irrespective of the position of the fuse in use.

In this latter connection there is no problem when fuses of this kind are used in :a vertical-or nearly vertical-attitude, since in such case the fused metal runs to one end of the interior of the casing surrounding one of the terminal links where it is adequately spaced from the opposite terminal link .to insure open circuit condition.

In the horizontal position, however, especially with the width of the terminal link disposed in a vertical direction, the melted segment can 'become dangerously close to the terminal links to incur the risk of accidentally maintaininga closed circuit condition beyond the limits of practical safety. Hereinafter, certain safeguards against this condition are disclosed.

Turning now to the drawings:

Figures 1 and 2 are longitudinal mid-sectional views of fuses made in accordance With the present invention, said sections being taken along planes disposed 90 degrees apart;

Figure 3 is a crosss-sectional view regarded along line 33 of Figure 1.;

Figures 4 and 5 are mid-sectional elevational and top plan views, respectively, of a mold designed to give effect to the present invention; and

Figures .6 and 7 are end and side diagrammatic views showing certain considerations of mass and volume entering into the practice of the present invention.

lhe type of lag fuse to which the present invention is directed is shown and described in my patent previously mentioned, so that it will be unnecessary to enter into a detailed description of the construction shown in Figures 1 to 3 of the drawings hereof, other than briefly to identify the several parts and their relation to the following description.

In these figures, 1-9 represents a cylindrical tubular fuse casing closed at each end by end disks ['2 and caps M, both of which are apertured to receive knife-blade terminals l5 in the usual way. The caps 14 are secured to the tubular body 46 by suitable fastenings, such as the screws I8. The interior of the casing is divided into three parts by two

partitions

20 and 22, respectively, to comprise end compartments '24 and 2B, which are usually filled with powder, and a central compartment 28. The partitions 20 .and 22 .areslotted centrally to receive fuse links 30 and Y32, which extend from the internal ends of the knife-blade terminals l6 into the central compartment 28, where they are connected, in the manner that will later be described herein, to a fusible slug 34.

This invention is concerned with securing a perfect soldered or welded joint between the inner ends of the fuse links 30 and .32 and the slug 34, which technique will be presently described, and is further concerned with the relation between the mass of the fusible link 34, the internal volumetric capacity of the central portion 28 of the casing, and the clearance between the slug metal 34 fused into a segment, and the inner ends of the

fuse links

30 and 32, which project into the central compartment 28. These latter considerations will be discussed in connection with Figures 6 and 7.

Turning now to Figures 4 and 5 of the drawing, there is here disclosed a mold designated generally at 40, which is composed of two

complementary half sections

42 and 44, either one of which may comprise the construction shown in Figure 4. Each of the half sections is formed to provide a principal molding cavity 46 centrally of the mold, and a pouring entry 48 which is connected to the principal molding cavity 46 by a throat or sprue 59 which is divided near its lower end into two

legs

52 and 54 which enter the cavity 46 proximate to the points at which the fuse links 36 and 32 extend therein. The principal mold cavity is connected with an overflow reservoir 56 by a central bottom sprue 58. A central riser 60 having a passageway 62 communicating with the exterior of the mold is provided above and in connecting relation with the principal mold cavity approximately centrally thereof so as to bleed off displaced air and gases which would otherwise be entrapped therein. The mold cavity is pierced at each of its ends by slots 64, in which the ends of fuse links are adapted to be confined so as to project in equal amounts into the principal mold cavity and substantially beneath the

divided legs

52 and 54 of the pouring entry 50.

The partitions 2E! and 22 for the casing in are first disposed upon the inner extremities of the terminal links, and these latter are then inserted in the apertures fill on opposite sides of the mold 43 so that the extremities of the links project oppositely into the mold cavity 46 thereof. The

mold halves

42 and 44 are then clamped or bolted together as by fastening means 66, which may be applied for this purpose.

Fused metal is poured into the mold through the entry 48 of the sprue 5B and

legs

52 and 54 so as to flow past the link terminals for a length of time and in amount sufilcient to fill the overflow reservoir 58, the principal mold cavity 46, and their connecting sprue 53. By the time these cavities are filled, the extremities of the fuse links will have been sufiiciently elevated in temperature autogenously to unite their surface metal with that contained in the cavity 45. The links are usually first coated with tin solder or similar metal of like purpose, the temperature of which will be adequately elevated by the excess of molten slug metal flowing past the fuse link terminals tightly to bond to the latter once the cast is set.

Upon cooling, the

mold elements

42 and 44 are separated and the joined parts removed therefrom, which, of course, include the metal appendage formed by the cavity 56 of the overflow reservoir which must be removed from the finished article by cropping and machining, or in any desired way.

Fuse links made in this manner have exhibited a perfect union between the several parts, possessing the requisite physical and electrical properties without recourse to heating and holding the mold and its contents of cast metal and fuse links at elevated temperatures to accomplish this purpose.

Referring now to Figures 6 and 7, there is diagrammatically illustrated formulae for proportioning the metal volume of fusible slugs similar to 34 in the foregoing description to the volumetric capacity of the casing in which it is disposed, similar to the compartment 28 previously described, so as to maintain open circuit clearance between the fused segment of the slug (after overload has melted the same) and the fuse link terminals in the central compartment irrespective of the position of the fuse assembly.

As shown, the slug 34 is represented as being formed to radius 1" and the internal radius of the compartment 28 is indicated at R, and its length is indicated by l in Figure '7 Manufacturing considerations entering into the production of the mold 40 make desirable forming the cavity 46, in which the slug 34 is shaped, with concave hemispherical ends, which, as shown in Figure 2, are scribed to radii n, which are equal to the radius of the slug r as shown in Figure 6. Otherwise, the slug may be square ended or conical at these portions. The cylindrical portion of the slug between the hemispherical ends of the example illustrated is indicated by the dimension h in Figure 7, and the clearance C between the fused segment of the slug 35 as shown in Figure 6 and the terminal of the fuse link is pre-established to afford the necessary clearance for the retention of open circuit conditions.

Now with these pre-established conditions, the correct relationship between the parts can be determined from the following, which are given on the second sheet of the drawings hereof, when the formulae are expressed as cubic equations:

(1) Volume of cylindrical part of slug=pi r h (2) Volume of spherical parts of slug=4.l89r

(being two hemispheres in which r =r) 0 in degrees is obtained graphically Where R and C are established.

h and l are selected. Solve for r.

(4) Volume of segment:

(5) (pi Wad-4.189%):

The foregong formulae, when expressed and solved as cubic equations, determine the diametric size of the fusible slug 34 and assure the proper clearance between segment and terminals in all positions of the fuse. Of course, the minimum proportions of the slug B must be that mass which affords the necessary capacity for the circuit with which it is associated. The maximum proportions must be those in which necessary clearance between the segment of the fused slug and the terminals is maintained to insure continued open circuit conditions in any position of the fuse in accordance with the preceding formulae.

I claim:

1. A lag fuse comprising a cylindrical casing divided into three compartments, terminals at each end of said casing, terminal links extending from said terminals across the end compartments, respectively, and terminating in the intermediate compartment, a slug of cast fusible metal autogenously united to the opposed end of said links within the intermediate compartment and being inseparably bonded thereto to afford optimum physical and electrical connection between said links at temperatures below its melting point.

2. The fuse construction of claim 1, in which said slug is formed with substantially hemispherical ends and is formed to a radius 7 determined by the following equation to afiord the requisite clearance C between the link ends which terminate in the intermediate compartment when the fuse is in a horizontal attitude with said links disposed with their greatest dimension of breadth substantially vertical and the metal segment resulting from the slug when melted:

2 3 pi R 01 (p1rh+4.189r) 360 said links outside of said mold, casting fused metal in said mold in sufi'icient mass autogenously to unite the cast metal with said links so as permanently to connect the latter together between the disk-like elements, relating the cubic volume of the space between said disk-like elements to the mass of cast metal uniting said 6 links to provide a fuse which will afford open circuit clearance after the cast metal has melted to disunite said terminal links irrespective of the position of the fuse when melting occurs.

4. The method of claim 3, in which open circuit clearance is accomplished by equating the mass of cast metal in terms of its volume with the cubic volume of said space according to the formula:

Total volume of cast metal:

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 878,869 Cole Feb. 11, 1908 1,669,071 Thomas May 8, 1928 2,486,798 Mollenhauer Nov. 1,4949 2,561,464 Cremer July 24, 1951 2,577,531 Laing Dec. 4, 1951