Note: Descriptions are shown in the official language in which they were submitted.
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B~ICGROUND OF T~IF INVENTION
The prosent inVentiQn relates to electrical f`use-
li~cs for pro-tecting electrîcal and e:Lectronic equipment.
British Patent No. 1,304,629 in the name of
Olvis Smeltze1ceringen~ Fabriek~ N.V. and dated 1Oth May,
1971, describes a fuse element consisting o-f a very thin or
fine wire helically wound about a rlgidified insulating
core. The lat-ter serves to support the ~ire and prevent
sagging thereof and also provldes handling strength for the
fuse element. The core should be heat-resistlve and be a
good heat insulator and not maintain combustion, as well as
being an electrical insulator and should be thin so that
its heat dissipation can be sllbstantially ne~lected.
thin rigidifiod core made from a fibre or filament of glass-
fibre material has the required properties and its mana~e~
ability allows the core to be sufficiently thin for its
heat dissipation to be substantially neglected. The thin
wire is wound onto the thin ri~idified core in a multiplicity
of closely spaced turns. ~-
One disadvantage which has been experienced Wit}l
the type of fuse element comprising a thin core supporting
the windings of a thin fuse wire 9 is the relativelr high
resistance which results from a large number of turns of
the wire wound on the core and one objec-t of the present
invention is -to reduce or overcome -this disadvantage.
Another object is to provide a low resistance fuse element
o~ this type which has impro~ed time-lag or timè~delay
characteristics.
SU~RY OF T~ INV~NTION
From one aspect, the present inventlon consi~ts
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:in a f-lsc elemcnt comprislng:-
(a) a thin flexlble electrically inslllating andheat lnsulatlng filament core,
(b) R fuse windlng comprising a thin metal fllse
wire helically wound wlth a multiplici-ty of turns about
said core,
~ c) said winding including spaced lon~itudinal
sections disposed respectively at opposi-te ends of said
core and spaced apart by an intermediate section of said
windin~,
(d) each of said spaced sections including multiple
turns of said windin~, and
(o) mcarls short-circuiting the said multiplc turns
of each of said spaced sections,
(f) said short~circuited turns of saicL spaced ~ ~ _
sections bein~ electrically interco~nected by the active
turns of said in-termediate section of said winding.
It is only the acti~e -turns of the intermediate
section of the winding which cons-titute the fusible link
and these active turns may be relatively few in number.
The fuse element according to the lnvention is
particularly suitable for makin~ lo~r-resistance time~la~
fuse-links intended to rupture at lo~ current ~alues 9 for
example, below 7 ~mps, The thin flexible core is convenient-
ly made from a fibre or fil~nent of ~lass-fibre material
and its di~neter is preferably not greater than 0.030 inches.
The thin metal wire preferably has a well-defined melting
point and a diameter not greater than 0.015 inches.
The fuse element may be secured between electrically
conductive terminals at opposite ends of a cartricLge or
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container with its short-circuited sectloll~ eo.~lected to
the tcrminals9 -tho .intermediate sec-tion consisting of the
acti~o turns o~ the windirl~ being disposed approximately
midway be-tween the terminals in thc centre of the cartrid~e.
From c~-other aspeet, the inventioll consists in a
method of m~nufacturing a cartridge f~lse-link comprisin~
the steps of:-
~a) helically winding a thin metal fuse wire
with a multiplicity of turns about a thin fle~ible core
consisting of an electrically insulating and hea-t insulatin~
filament,
(b) short~circuiting mlll-tiple turns in two spaced
longitudinal sections of the windin~, and
(c) mountin~ the fuse element thus formed in a
tubular lnsulating cartridge with said short-cireuited
longitudinal sections in electrical contact ~ith electrically
conductive terl~inals secured to opposite ends of said
cartridge.
The fusa alement may be produeed by continuously
winding said f-use wlre abo~t a eontinuous filament~ cutting
-the wound filament into perdetermined lengths, and then
short-eireuiting the turns in spaced longitudinal seetions
of the winding at and ad~acent opposite ends of a cut
length so as to form said fuse element. Alternatively, it
~ay be produced by eontinuously windin~ said fuse wire about
a eontinuous filament 9 short~eircuiting the tu-r.ns in a
plurality of longitudirlal sections of the winding spaced ~-
apart along said filament 9 and cutting the wound filament
; at positions intermadiate the ends of consecuti~e short-
circuited longitudinal sections so as to :form said fuso
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1~7~373~
e lcmen t .
The t~lr.ns of tho ~lnding may be shor-t-circuited
in a mmlber of different ways. In a preferred form o~
the invent:ion, the spaced longitlldinal sections of -the
5 winding> are metallised wi-th a solder coating after the
winding s-tep. IIowcver, tlle scction~ may be short-circuited
by any other suitable me~ns.
The sbor-t-circuited sections of the fuse elemen.t
result in a considerable reduction in the elec-trica.l ~.
resistance of a fuse-linlc incorporating such a ~lse
elemen-t. The short-circuited sections also serve to
stiffen the fuse
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element and make it more manageable.
Whilst the thin metal wire is conveniently wound
onto the f lexlble core in a multipliclty of closely spaced
turns, it is also possible to provide the wire with an
insulating coating and to wind it on the core so that its
turns are in contiguous relation. The present invention
is equally applicable to such a constructlon, the insulating
cDating on the wire readily being destroyed in those sections
of the winding which are to be short-circuited by the
application of heat upon metallisation of the sections, or
any other means. An insulated wire is particularly
advantageous for producing very low current fuses, for example,
less than 250mA. The very flne fuse wires used at such
values tend to dissolve in the solder upon metallisation
and an insulating coating reduces or avoids this tendancy~
In order that the invention may be more readily
understood, reference will now be made to the accompanying
drawings, in which:-
Figure l illustrates, on an enlarged scale~
a piece of fuse element material made in accordance with
the invention, and
Figure 2 is an axial section through a cartridge
fuse-link embodying the invention.
DESCRIPTIO~ 0~ P~ ~ Rl~ ~M~UUIM~NIS
Referring to Figure l of the drawings, the use
element material is produced by winding a thin metal wire 1 `
having a well-defined melting poin~ for example a copper
or silver wire, about a thin flexible fibrous filament 2,
for example9 a glass-fibre thread. The wire is wound
on the core in a multiplicity of c`losely spaced turns.
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Consecuti~e longitudinal sections or regions 3 o ths winding
spaced at intervals along the core a~e then metallised
with a solder coating so as to short-circuit the turns
in those sections. The short-circulted sections 3 are
electrically interconnected by intermediate sections 4
having unshort-circuited or active turns. The fuse
element material may be readily manufactured by an automated
process.
The ratio of metallised to unmetalllsed sections,
the winding pitch, wire material and diameter and core
diameter can all be varied to obtain different current
rattngs and blowing or melting characteristics for the fuse
elements to be fonmed from the fuse material.
The fuse elemer~t material is formed into
individual fuse elements by cutting the material at
positions intermediate the ends of consecutive metallised
sections 3 so as to produce a fuse element having metallised
sections at opposite ends thereof interconnected by the
active ~urns of an intermediate section 4. The fuse
element thus produced may be mounted in a cartridge or
container of non-conductive material and be electrically
connected to end terminations which serve as electrical
terminals for connecting the fuse-link in an electrical
circuit~ One such cartridge fuse~link is illustrated in
Figure 2. It comprises a glass tube 6, or a tube made from
another insulating material, having metal end caps 7 which
ser~e as electrical terminals for conne~ing the use-link
in an electrical circuit. ThP fuse element 5 is moun~ed
in the tube by gripping the metallised sections 3 of
; 30 the element between the end caps and the tube at opposite
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ends of the latter. A sealing material 8 is provided on
the inside of each end cap between the adjacent end of the
tube and the end wall of the cap.
In the resulting fuse-link, only the relatively
few turns of the winding in the intenmediate section 4
perform the fuction of active fusing and the fuse-link
has considerably less electrical resistance than hitherto
kno~n fuse-links having a fuse element formed from fine
metal wire wound on a flexible insulating core. Moreover,
the metallised sections at each end of the fuse element
serve to stiffen the element and make it more manageable
during assembly of the fuse-link.
Whilst particular embodiments have been described,
it will be understood that various modifications can be made
without departing from the scope of the invention as defined
by the appended claims. For example, in an alternative
embodiment to that shown in Figure 2, ~he metallised ends
of the fuse element 5 may be soldered to the central
portions of the end caps 7 instead of being gripped between
the caps and the ad~acent portions of the tube 6.
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