US2859307A - Fuse link - Google Patents

Description

J. W. ENK

FUSE LINK Nov. 4, 1958 Filed March 21, 1957 FIG. 5.

FIG. 3.

FIG. 1.

United States Patent FUSE LINK John Enk, St. Louis, Mo., assignor to A. B. Chance Company, Centralia, Mo., a corporation of Missouri Application March 21, 1957, Serial No. 647,532

Claims. (Cl. 200-123) This invention relates to fuse links, particularly but without restriction for use in electrical power distribution systems, and with regard to certain more specific features, to links of this class adapted to respond with time delay to light overloads and instantaneously to heavy overloads.

Conventional fuse links of the above class generally contain at least one soldered connection which, upon heating by a current-heated wire, will with some predetermined time delay melt to provide desired relatively slow action in response to small overloads, and an additional fusible element or elements adapted to respond with fast action to greater overloads. Unreliable operation has been encountered in the case of small overload operation, particularly in the lower operating current ranges.

I have traced the unreliability of operation to the high temperature that sometimes occurs at the soldered end of the heating wire, causing it to soften the solder too quickly and the wire to pull out from it. It is accordingly an object of the present invention to prevent this condition. Another object of the invention is to produce a stronger soldered junction which can be manufactured more rapidly and at less expense and with closer operating tolerances upon slow action, particularly for lower operating current ranges. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

Fig. l is an axial section of one form of the invention;

Fig. 2 is an enlarged cross section taken on line 22 of Fig. 1;

Fig. 3 is a vertical section taken on line 3-3 of Fig. 2;

Fig. 4 is an axial section of another form of the invention; and,

Fig. 5 is an enlarged cross section taken on line 5-5 of Fig. 3.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawmgs.

Referring now more particularly to Figs. 1-3 of the drawings, numeral 1 indicates a conductive terminal, to the outer end of which is threaded a conductive head 3. The inner end 5 of the terminal 1 is in the form of a conductive cylinder, which at 7 is crimped around a suitable conductor wire 9 composed of, for example, copper. At 11 is shown a flexible braided conductive terminal wire which is crimped into one end of a conductive sleeve 13. The other end 15 of the sleeve is crimped around a second conductor Wire 17 composed of, for example, copper. The adjacent ends of the wires 9 and Faiented Nov. 4, 1958 17 are electrically connected by means of a junction block, shown in general by numeral 19.

Referring also to Figs. 2 and 3, the junction block 19 is composed of two crimped conductive members 21 and 23, each of which prior to crimping was in the form of a short tube, sleeve or cylinder of a conductive metal such as, for example, copper, and adapted to accept an end of one of the wires 9 or 17. After insertion of each wire with its end practically flush with the respective tube end, the tubes are crimped or compressed into the shapes shown in Figs. 2 and 3, i. e., into a troughor crescent-shaped cross section. The crimping is such that the members 21 and 23 compressively grip the respective wires 9 and 17 with permanent, tight low-resistance electrical contacts. Either or both members 21 and 23 may be provided with a cross crimp. In the illustration shown in Figs. 1 and 2, a single cross crimp 25 of this type is shown in the member 23 only.

After the members 21 and 23 have been crimped onto the wires 9 and 17, respectively, a mass of melted solder 27, having a suitable melting point, is applied to the convex side of member 23 and the concave side of member 21 applied thereto, suitable flux being used to form after cooling an electrically conductive and meltable solder joint between members 21 and 23.

To prepare the fuse link for use, an insulating tube 29 is applied to the terminal 1, being frictionally held in place by means of knurling 31 on terminal 1. A flange washer 33 may also be employed under head 3. As will be understood by those skilled in this art, the head 1 is held in the usual way by one terminal-engaging element of an expulsion fuse tube or the like (not shown), the terminal wire 11 extending from the open end of the expulsion tube and attached to another terminal-engaging element thereof. Spring-biased tensioning means connected to the expulsion tube usually applies tension to the terminal 11. Upon application of a substantial overload, one of the conductors 9 or 17, will fuse and break the circuit, the resulting generation of gas in escaping from the expulsion tube tending to separate the remaining portions of the conductor, thus clearing the circuit. The spring bias of the tensioning means aids in this result. v

On the other hand, should a smaller or so-called dragging overload occur, insufficient to fuse either of the conductors 9 or 17, one or both will be heated, the temperature rising accordingly. One or both wires are calibrated for this effect. This heat is conducted from one or both wires 9 and 17 to the crimped members 21 or 23, respectively. In these it is diffused and conducted to the solder 27. The heat-diffusing effect in the members 21 and/or 23 prevents any local overheating (high temperature) at the wire ends from prematurely melting the solder, thus preventing erratic action. If the overload continues for a sufficient time, the temperature will rise until the solder is melted, thereby breaking the circuit, the spring tension on the terminal wire effecting a mechanical separation after melting of the solder. Obviously, the existence of the spring tension requires a strong and reliable block such as 19 prior to fusing or melting action of the fuse link.

As above made clear, it has heretofore been the practice to bury one or both wires such as 9 or 17 in a portion of the mass of connecting solder. This resulted in poor radiation from the solder-enclosed wire end, with premature temperature rise and erratic melting of the solder. This prevented close operating tolerances of the fuse link under slow-acting (solder-melting) conditions. By means of the present invention, each wire 9 and 17 is crimped into its respective sleeve 21 or 23, these sleeves functioning advantageously infour ways, namely:

the heat at the wire ends so asto prevent. localized erratic high temperature build-up in the solder;

(3) By reason of their trough shapes, to' provide a nesting whereby e p c fJSQI eI-J'Pining.isiacih: tated by laying one membersuch-as 2 1 intheoth'er mem;

ber 23duringthe soldering operation; and,

(4) To provide a gauge, as determinedby the length L of the elements 21 and 23 for the amount of wire end to be enclosed, this controlling accurately the amount of wire contained in the clinchingmernbersll and 25 and hence controlling the amount o f'locali'zedjheatingwithin these members.

An ancillary advantage of the trough or crescent shapes of the crimped membersZl and 23 is that they do not require as large asurroundingtube 29 aswould be the case if these membersll and 23 were crimped on the, wires in a plane. They are crimped flatwise onto the wires in order to increase the area to which solder is. attached. While they are not of plane fiatwise form, such a form is not excluded.

Another form of the ll'lVfiHtlOll'lS shown in Figs. 4 and 5. This has a conductive head 35, the inner end 37 of which is crimped to a heater wire 39 (such as Nichrome) and a strain wire 41' (such as steel), The latter is heldin a strain insulating member 43. A second strain wire 45 (such as steel) extends from member 43 through an insulating ceramic sleeve 47 about which the heater wire 39 is wound. Wires 45. and 39 at their lower ends are crimped inta crescent-shaped conductive member 49, as above described; Member 49 forms one ele-- ment of a junction block 51'.

A braided terminal wire 53 is crimped intothe lower end of a conductive tube 55. The upper end of the con ductive tube is crimped at 57 to two wires, one of which is a strain wire 59, composed, for example, of nickel steel, the other wire 61 being a conductor composed, for example, of copper. These wires 59 and 61 are crimped into a crescent-shaped member 63 which is formed as shown at 65. The length L of the members 49 and 63 determines the enclosed lengths of the crimped wires, their ends being flush with the ends of members 49 and 63. The members49 and 63 are again soldered together,

as shown at 67. The assembly between members 35 .and

57 is surrounded by an insulating sleeve 69,, the, lower end of which is provided with a bushing 71. A compression spring 73, reacting between the bushing 71 and the lower end of the crimped tube 55, serves. to tension the assembly within the tubewithout the requirement (as in the case of the Fig. 1 form) of an external tensioning spring.

In the form of the invention shown in. Figs. 4 and 5, heavy overloads instantaneously fuse both wires 59 and 61 to break the circuit. Light, or so-called dragging overloads, do not have this result, but cause heating of the in-circuit heater wire 39. Heat therefrom is in part radiated, but mostly conducted through the member 49. to the solder 67, which with time delay melts. In either event, the compression, spring 73 completes opening of I 4 the circuit by separating the fused or melted conductors, as the case may be.

In view of the above, it will be seen that the members 21 and 23, or 49 and 63, as the case may be, isolate the enclosed ends of their clinched and covered wires from the solder 27 or 67, respectively. Any erratic hightemperature heating at the enclosed wire ends is tempered as the heat is conducted through these members to the soldered connection between them. Also, these members predetermine the amount of covering on the wire endswhere clinched if, asv shown, the inserted wire ends; are brought flush with the ends of the tubes, which are crimped on the Wires to form members 21, 23, 49' and 63.

The solder employed such as 27 or 67 may be of any convenient formulation for the purpose. Various tin-lead formulations have been found to be satisfactory. While particular metals have been mentioned as examples for the various conductive, heater and strain wires, others may be used.

The members 21, 23, 49 and 63 may be ,referredto as heat-tempering sleeves, suggesting'their functions in p r -e.- venting localized solder melting and erratic, action.

In view of the above, it will be seen that the several;

objects of, the invention are achieved and other advantageous results attained.

As.vario us changes. could be madein the above-con structions without departing from the scope ofthe inyen:

tion, it is intended thatall mattercontained in the; above; description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting senser, I.claim:

1. A fuse link comprising'electrical conductorsatleast; one of which is adapted to fuse upon substantial overload andzatleast oneof which is adapted to heat upon smaller overloads ajunction block adapted electrically to-,con

nectv said'conductors, said block comprising tubular ele c.

trical and heat-conductive members connected to the 00113;, ductorsby fiatwise crimping thereof so as to form-heattempering pads, and a mass of solder joining said pads.

mass of solder joining said elements.

3. A meltable solder connection madeaccording to claim 2, wherein at least one of said flatwise elements-is transversely crimped.

4. A meltable solder connection made according to claim 2, wherein said flatwise elements are of trough shapes.

5. A meltable solder connection made according to claim 4, wherein at least one of said flatwise and troughshaped elements is transversely crimped.

References Cited in, the file of this patent UNITED STATES PATENTS 2,157,152 Triplett May 9,1939 2,256,360 Steinmayer et al Sept. 16, 1941 2,493,601 Smith Jan. 33,1950. 2,665,349 Sander Jan. 5,- 195.4

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