Fusible links

A thermal fuse is comprised of a pair of internested, flat, thin metallic plates, each plate having peripheral upturned flanges along opposite edges of the plate. The flanges of the lower plate each have a notch formed therein and the upper plate has a tab extending transversely from each side through a respective notch. The notches each have a side inclined to the plate to form a ramp, the edge corners of the tabs being cammed up the ramp of the respective notches when the plates are pulled apart in a direction parallel to the plane of the plates, to lift the upper plate perpendicularly away from the lower plate so that the flat confronting surfaces of the plates are drawn apart.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is in the field of fusible links, of the break-away type 
that have a pair of metallic plates, soldered together and are then placed 
in a strategic location to monitor the existence of any fires and may form 
a part of fire prevention equipment, such as smoke detectors or safety 
devices. The soldered plates are placed under spring tension and when the 
ambient temperature heats the plates above the eutectic point of the 
solder, the plates separate. 
2. Brief Description of the Prior Art 
A recent advance in the art is disclosed in U.S. Pat. No. 4,055,829, issued 
to the applicant herein. That patent is directed to the problem 
encountered in the art of links tending to rejoin after the initial 
separation if there is a failure of the links to fully separate. While the 
device in that patent is an improvement over prior devices and is 
satisfactory in many respects, full and complete separation is not insured 
to the extent that this invention provides. Important to the correct 
operation of a fuse is that it respond accurately to a critical 
temperature. Separation of the fuse link components must be clean and 
abrupt. Shortcomings of previous fuses is the time delay, incomplete 
separation and lack of consistent response to a critical temperature. The 
present invention does so respond accurately and "cleanly", i.e., the 
separation of plates is abrupt upon reaching the critical temperature. 
SUMMARY OF THE INVENTION 
A pair of flat, thin overlapping, metallic plates each include peripheral 
upwardly extending elongated flanges along opposite plate edges. The 
plates each have ends that are adapted for attachment to spring members so 
that tension force exerted on the plates in the plane of the plates tends 
to pull them apart. Confronting flat surfaces of the plates are soldered 
together and are used with conventional fire control devices such that a 
rise in ambient temperature can cause heating of the plates above the 
eutectic point of the solder, whereupon the spring forces separate the 
plates and operate an alarm or other apparatus. 
Each of the flanges on the lower plate has a notch. Each notch has a side 
that is inclined 45 degrees to a flat surface of the plate to form a ramp 
edge. The upper plate has a tab transversely extending from each flange 
side that engages a respective notch. Upon heat in excess of a critical 
amount, the solder melts at its eutectic temperature and spring force 
causes relative sliding between the plates resulting in an edge corner of 
each of the tabs being cammed upwardly on its respective ramp edge, 
causing the upper plate to move upwardly and away from the lower plate. 
Since there is only an edge corner contact with the ramp between the upper 
and lower plates, sudden and complete separation occurs between the plates 
because the plates can more easily move relative one another. Cooling of 
the solder while the corners are on the ramp edges will not rejoin the 
plates. The spring force is sufficient to pull apart the plates, even if 
solder should cool quickly to form a joint. The sole point of direct 
engagement between the plates is through the ramp edges and tabs, and any 
inadvertent solder joint formation, occurring after melting between these 
surfaces is highly unlikely. Even if such inadvertent rejoining did occur 
any such joint would be relatively weak and overcome by the spring forces 
pulling the plates apart. 
In fusible links, separation of the links is insured upon a rise in ambient 
temperature to a critical temperature. It is necessary that this be 
achieved in a link where cost is small to make their use economically 
feasible 
It is an object of this invention to provide a low cost fusible link that 
is insured of complete separation when the eutectic point of the retaining 
solder is reached. 
Another object of the invention is to provide in a soldered link of the 
previous object, a sliding corner contact on a ramp edge to separate the 
links when the fusion point of the solder is reached. 
These and other objects will become more apparent from a description of the 
preferred embodiment in reference to the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawing, link 20 comprises a flat, thin plate 22 having 
elongated flanges 24,26 formed upwardly and outwardly from opposite edges 
thereof. Notches 28,30 are formed respectively in flanges 24,26. Notches 
28,30 have upwardly inclined ramp edges 32,34 respectively, each of which 
forms an angle of 45 degrees with plate 22. Adjacent the end 36 of plate 
22, is a circular opening 40 surrounded by upstanding circular flange 42. 
At end 36 and continuing along the plate is an upwardly and outwardly 
formed semicircular flange 44. Flanges 42,44 strengthen plate 22 and 
provide protection edges. The other end 46 (FIG. 3) of plate 22 is 
concave. 
The other link 50 consists of a flat thin plate 52 with peripheral flanges 
54,56 formed upwardly and outwardly from opposite edges thereof. The width 
of plate 52 is smaller than the width of plate 22 to enable it to be 
slidably internested therewith, as shown in FIG. 1. Tabs 58,60 are formed 
integrally with plate 52 and are coplaner with plate 52. Tabs 58,60 have 
edges 62,64 respectively. The lower corners of edges 62,64 are disposed to 
ride upwardly on ramp edges 32,34 respectively, when links 20,50 are 
pulled apart (FIGS. 1,5). Corner 68 of tab 60 is shown on ramp edge 34 in 
FIG. 5. Likewise a corner 66 of edge 62 rides against ramp edge 32. As a 
result the two plates are cammed apart when they are pulled in opposite 
directions. Opening 70 in plate 52 has a surrounding upstanding flange 72 
and is adjacent rounded end 74, of plate 52, around which flanges 54,56 
extend, and join one another. The end 76 of plate 52 is concave the same 
as end 46 of plate 22. 
In operation links 20,50 are joined in the position of FIG. 1 by fluxing 
and soldering in a manner well known in the art, the confronting surfaces 
of plates 22,52 being thus joined together. Springs 80,82 are next placed 
in openings 40,70 respectively (FIG. 3). Upon a rise in ambient 
temperature if the links 20,50 are heated to a temperature above the 
ambient temperature of the solder, the solder will melt, and then springs 
80,82 will pull the links 20,50 apart. The separation occurs when corners 
66,68 are cammed upwardly on ramp edges 32,34 respectively, lifting plate 
52 upwardly away from plate 22, breaking the contact therebetween. The 
minimum contact between links 20,50 at the corners 66,68 and edges 32,34 
enables the links to readily and completely separate. 
A feature of this invention is that even if the solder cools below the 
fusion point after separation of the plates there is virtually no 
possibility of the links recontacting and becoming resoldered, rejoined, 
or refused in the original condition. 
Although the invention has been described and claimed in connection with 
certain selected example embodiments, it will be understood that these are 
illustrative of the invention and are by no means restrictive thereof. It 
is reasonably to be expected that those skilled in this art can make 
numerous revisions and adaptations of the invention and it is intended 
that such revisions and adaptations will be included within the scope of 
the following claims as equivalents of the invention.