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Патент USA US3056360

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Oct. 2, 1962
Filed Aug. 20, 1959
United. States Patent @‘
Lars Alfred Lindblad, Utiriksbacken 23, Grondal, Sweden
Filed Aug. 20, 1959, Ser. No. 835,10tl
Claims priority, application Sweden Oct. 11, 1954
3 Claims. (Cl. 102-28)
Patented Oct. 2, 1962
may be used, but an insulating lacquer coating is gen
erally preferable. The two conductors are closely held
together at juxtaposed ends, and this is effected by twist
ing the respective end portions 4 and 5. As is apparent,
the twisted wire portions can be brought so closely to
each other that the spacing between the wire parts 4 and
5 does not appreciably exceed the thickness of the insu
lating coating on conductor 1. The twisted conductor
The present invention relates ‘to electric igniters or
ends are embedded in an insulation body 6 which has
primers as used in connection with fuses for detonating
an explosive ‘and especially with fuses for ammunition.
10 preferably about a semi-spherical shape. Body 6 is ad
vantageously formed of a hardening insulation material
‘Igniters of the general kind above referred to, gener
of a kind such that the embedding of the twisted con<
ally comprise two conductors such as wire conductors of
ductor ends does not require ‘a temperature high enough
adequate current carrying capacity, the ends of which
to damage the insulating coating on conductor ll. There
are physically separated, but are electrically joined by va
thin conductive layer generally produced by plating and
coated with an ignitable explosive. The heating of this
coating when an appropriate current is applied to the
wire conductors, produces the desired ignition or priming
As is apparent, the adjacent ends of the wire conductors
must on one hand be separated from each other and on
the other hand they should be as close to each other as
possible so that a minimum energy is required to heat
the conductive bridge between the two- wire ends to‘ the
ignition temperature.
It has been found difficult in practice to reconcile the
aforementioned two conditions, the more so as igniters
as here involved are and ‘must be an inexpensive mass
are known many insulating materials suitable for the pur
pose, such as hardening synthetic resins. The end faces
of the two conductor portions 4 and 5 are bare and sub
stantially flush with the plane surface of body 6.
Body 6 may have a variety of suitable shapes other
than the illustrated semi-spherical shape provided only
that the conductor ends 4 and 5 are laid bare ?ush in
an outer surface of the body.
The igniter according to FIG. 2 differs from the igniter
just described only in that both conductors 1’ and 2'
including the twisted end portions ‘4' and 5' are covered
with insulation coatings 7 and 8 respectively. As is
apparent, the minimum distance between the two wire
ends laid bare in the plane surface of body 6 is twice the
thickness of the insulation coating whereas in the em
production item.
It is an object of the present invention to provide a 30 bodiment of FIG. 1 it needs to be only once the thickness
of the coating. But even twice the thickness of the coat~
novel and improved igniter of the general kind referred
ing is still much closer than was heretofore possible, and
to, the wire conductor ends of which can be safely placed
the use of insulation coating on each of the conductors
closer to each other than was heretofore possible so that
affords an additional safety factor against a direct short
igniters according to the invention can be activated by
circuit between the two conductors.
employing a minimum energy.
My ‘aforementioned two ‘co-pending patent applications
Another object of the invention is to provide a novel
describe in detail a suitable method of producing igniters
and improved igniter, the structural design of which lends
according to FIGS. 1 and 2. The arrangement of the
itself to placing the conductor wires and more speci?cally
conductive coating electrically bridging the exposed and
the ends thereof very close to each other by simple and
embedded wire ends can best be apprehended from FIG.
inexpensive production methods without a risk of causing
3. This ?gure shows an enlarged plan view of FIG. 2,
electric contact between the conductor wires at points
that is the bare ends of wires 4' and 5' covered with in
other than the ends bridged by the conductive layer.
sulation coating 7 and 8 respectively are ?ush with the
Still another object of the invention is to provide a
plane surface of body 6. A coating 9‘ covers all or part
novel and improved electric igniter in which the wire ends
of the plane surface of body 6 and in any event at least
are bridged by a conductive layer which can be produced
the surface area including wire ends 4’ and 5'. The
by a very simple and efficient manner without requiring
coating comprises a suitable binder such as a hardening
the use of high temperatures or plating operations involv
adhesive liquid into which are mixed discrete particles 9
ing the use of a bath aggressive to insulation material.
of an electrically conductive and magnetizable material
Other and further objects, features and advantages of
the invention will be pointed out hereinafter and set forth 50 such as iron particles. The particles are oriented to form
a multitude of continuous coherent pathways which
in the appended claims forming part of the application.
bridge the two conductor ends as is indicated in FIG. 3.
Certain features of the present invention are disclosed
The orientation of the particles can be readily effected
but not claimed in my co-pending application Serial No.
by subjecting the same to a magnetic ?eld prior to the
535,944 ?led September 2, 1955 now Patent 2,907,100.
The present application is a continuationsin-part of 55 hardening of the coating liquid. Suitable arrangements
for magnetizing the coating material are fully described
my ‘co-pending application Serial No. 535,949 ?led Sep
in my aforesaid co-pending applications.
tember 22, 195 5, now abandoned.
In the accompanying drawing, several preferred em
As is evident, the orientation of magnetizable particles
bodiments of the invention are shown by way of illus
by a magnetic ?eld affords the advantage of a minimum
60 of conductive material for forming a conductive bridge
tration and not by way of limitation.
In the drawing:
between the two conductor ends. Accordingly, a mini
FIG. 1 is a perspective side view of an electric igniter
mum of energy is required to heat the coating when the
or primer according to the invention.
igniter is activated to set off an explosive charge. Clear
FIG. 2 is a similar view of a modi?cation of the ignitcr,
ly any solid conductive layer such as heretofore used,
must contain considerably more metal however thin it
FIG. 3 is a plan view of the igniter according [to FIG.
may be than the pathways formed by the oriented par
2 an an enlarged scale.
ticles. Accordingly, the current required to activate the
Referring now to the ?gures in detail, FIG. 1 shows an
igniter is correspondingly higher.
igniter comprising two electric wire conductors 1 and 2.
In order to ready the igniter for actual use, the plane
Conductor 1 is covered with insulation material and con 70
after having been coated with the conductive ma
ductor 2 is left bare. Any suitable insulation material
terial is further coated with a suitable ignitable explosive
such as acetylene silver.
Experience and tests have shown that ?nished igniters
according to the invention can be mass-produced so uni
formly that existing differences, if any, are negligible.
While the invention has been described in detail with
respect to certain now preferred examples and embodi
ments of the invention it will be understood by those
2. An electric igniter for use with a fuse for an ex
plosive, said igniter comprising two wire conductors, at
least one of said wires being covered with insulation
material, said wires being secured to each other in close
juxtaposition at one end and extending into the same
general direction from the juxtaposed end portions, a
body of solid insulation material, said juxtaposed wire
portions being embedded in said insulation body termi~
skilled in ‘the art after understanding the invention, that
nating ?ush with :a surface thereof, and a hardened coat
various changes and modi?cations may be made without 10 ing covering the surface portion including said exposed
departing from the spirit and scope of the invention, and
wire ends and comprising a binder and discrete electrically
it is intended, therefore, to cover all such changes and
conductive ‘and magnetizable particles magnetically oni
modi?cations in the appended claims.
ented into ‘direct contact one with another in the form
What is claimed as new and desired to be secured by
of metallically coherent pathways within the coating, said
Letters Patent is:
15 pathways constituting a conductive bridge within said two
1. An electric igniter for use with a fuse for an ex
exposed wire ends.
plosive, said igniter comprising two conductors, a body
3. An electrical igniter ‘according to claim 2 wherein
of solid insulation material, one end of each of said con
the portion of the insulation body covered with said coat
ductors being embedded in said body, the two embedded
ing is a plane surface portion.
ends terminating flush with a surface of the body close 20
to but electrically insulated from each other, and a coat
References Cited in the ?le of this patent
ing covering the surface portion including said two con
ductor ends, said coating including electrically conduc
tive and magnetizable discrete particles, magnetically
oriented into direct contact one with another in the form 25
of metallically coherent pathways within said coating,
said pathways constituting a conductive bridge between
Smits ______________ __ May 24,
MacLeod ____________ __ July 17,
MacLeod ____________ __ Sept. 11,
Scherrer _____________ _. Feb. 9,
said two exposed conductor ends.
Liebhafsky et al. _____ __ June 28, 1960
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