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Патент USA US2408126

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Sept. 24, 1946?
Filed Aug. 18, 1942
2 Sheets-Sheet l
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Sept 24, 1946.
Filed Aug. 18, 1942
2 Sheets-Sheet 2
Patented Sept. 24, 1946
Hans Jay Rolfes, Melrose, Johannesburg,
Transvaal, Union of South Africa
Application August 18, 1942, Serial No. 455,235.
In the Union of South Africa September 11,
4 Claims. (Cl. 102-28)
This invention relates to means for safeguard
ing the electric igniters of blasting detonators
against accidental ?ring by electric currents or
spark discharges produced respectively in, or in
the vicinity of, the ?ring means of the igniter
by atmospheric electricity.
More speci?cally, the invention consists in
means for safeguarding as aforesaid electric ig
niters which includes a plug of material which
is grounded through the shell of the igniter or
detonator or otherwise and which comprises mi
It is obvious that a possible solution to this
nute metal or other electrically conductive par
ticles which in the mass are non-conductive to
problem is to surround the two electric leads of
voltages of the magnitude used for intentionally
the igniter at a position a safe distance from the
?ring the detonator and which in the mass be
come instantly conductive through coherer action
to currents or electric discharges at voltages of
?ring means thereof by a grounded mass of a
material, which may be termed the ideal mate
rial, and which will exhibit a high resistance at
voltages of the magnitude used for intentionally
?ring the igniter and a low resistance at volt
ages of the magnitude of the electrostatic charges
which produce the currents and spark discharges
One means of obtaining a solution of the prob
lem has already been proposed, the means con
sisting broadly in employing for the purposes of
the material surrounding the leads any material
which has the characteristic that its resistance
to electric currents or discharges is an inverse
the magnitude resulting from atmospheric elec
tricity along a locally con?ned path from the
lead or leads to ground.
The grounded mass may surround the electric
leads, e. g. igniter wires or wires of the blasting
circuit, at parts located inside and/or outside
the igniter, these parts being bared; or the igniter
wires or blasting circuit wires may be tapped by
insulated conductors having bared parts sur
rounded by the grounded mass.
The invention will now be described by way
of example with reference to the annexed draw
function of the voltage applied thereto. Amongst
materials having this property are, for example,
ings, in which:
galena, stibnite, carborundum, yellow crystalline
instantaneous electric detonator embodying the
Fig. 1 is a sectional view in elevation of an
iron pyrites and zincite.
This application is a continuation in part of
Fig. 2 is a sectional view in elevation of an
my copending application No. 422,452.
instantaneous electric detonator, enclosed in an
The object of the present invention is to pro 30 inert body or so-called wax primer, embodying
vide another means of solving the problem stated
the invention._
which will render available as the ideal material
Figs. 3 and 4 are sectional views in elevation
a class of materials other than those of which
of electric igniters for delay-action detonators,
the resistance is an inverse function of the ap
embodying the invention.
plied voltage as aforesaid, and which will afford 35 Fig. 5 is a diagrammatic view of an alternative
a particularly e?ective safeguard against cur
means for associating the igniter leads indirectly
rents or spark discharges produced in, or in the
with each other through a coherer mass.
vicinity of the ?ring means of the igniter by elec
Figs. 6 and '7 are diagrammatic views of two
trostatic charges caused by lightning or atmos
embodiments of this alternative means applied
pheric electricity in general.
40 to groups of detonators connected in series.
Figs. 8 and 9 are respectively a sectional ele
According to this invention, means for safe
guarding electric igniters of blasting detonators
vation, and a sectional plan, of a convenient prac
against accidental ?ring by electric currents or
tical form of the alternative means.
spark discharges produced respectively in, or in
Figs. 10 and 11 are respectively a sectional ele
the vicinity of, the ?ring means of the igniter 45 vation and sectional plan of an improvement in
by atmospheric electricity, comprises a grounded
the alternative means.
mass of a material which offers a complete or
Referring to Figs. 1 to 4:
In Fig. 1, the insulated electric leads Ia, Ib pass
through a rubber plug 2 crimped in the mouth of
substantially complete resistance to voltages of
the magnitude used for intentionally ?ring the
igniter and which, on its being subjected to volt
ages of the magnitude of electrostatic charges
caused by atmospheric electricity, becomes locally
conductive through coherer action along a path
or paths permitting the passage therethrough of
the high voltage charge.
the copper or other conductive shell 4 of the
detonator. In the usual manner the detonator
shell 4 contains a fuze-head 5, a primary charge
6 and secondary charge ?I. The fuze-head 5 has
a bridge-wire 8 within the igniter composition or
bead thereof, and the one end of the bridge-wire
3 is connected to a bridge-pole 9 and the other
end to a bridge-pole I3. These poles 9, H! are
connected at soldering points M, �to the re
voltage charge from the leads Ia, lb, or either of
them, into the coherer plug l5.
When the detonator is ?red, the ?ring current
spective leads Ia, lb.
passes in the normal manner through the one
Parts i3, M of theleads la, lb respectively are
bared, as shown in the? drawings, and these parts
pass in spaced relationship through a plug I 5
provided within the detonator shell 4 between
the rubber plug 2 and the insulating sleeve or
lead, say la, across the bridge-wire S, and out
body 55 of the fuze-head 5.
The plug l5, hereinafter referred to as the
through the other lead I?, the bridge-wire being
heated to incandescence and ?ring the igniter
bead of the fuze-head 5. In other words, to the
voltage of the magnitude used for the ?ring cur
10 rent, the coherer plug I5 reacts as an insulator.
If, on the other hand, an electrostatic charge of
high potential is induced in the ?ring circuit con
sisting of the leads la, lb and bridge-wire 8, or if
this circuit is struck by a lightning discharge, the
ductive to Voltages of the magnitude used for in
tentionally ?ring the detonator and which in the 15 ?nely divided aluminium of the coherer plug I5
?coherer plug,? consists of ?nely divided alumin
ium particles which in the mass are non-con
mass become conductive through coherer action
to currents or electric discharges at voltages of
becomes at once locally conductive through co
herer action along outward radial paths from the
teeth I1, E8 to the wall of the detonator shell 4,
permitting the passage through these paths of
that ?nely divided aluminium used in the paint
trade is a particularly suitable material for the
coherer plug. Such aluminium appears to be in
the form of minute ?akes which have a ?lm of
charges its high potential to ground without any
flow of current being produced in the bridge-wire
8, or spark discharges being produced in the vi
the magnitude resulting from atmospheric elec
It has been discovered as a result of experiment 20 the high Voltage charge from the ?ring circuit
to ground. In this manner the ?ring circuit dis
grease or oxide over them, which may account 25 cinity of the fu'ze-head 5, such as would cause in
for their exceptional non-conductivity in the mass
to normal voltages. Preferably the aluminium
powder is mixed with oil to form a paste, or with
candescence of the bridge-wire or premature ig
nition of the fuze-head.
,By using the teeth IE, it or similar discharge
points, an effective safeguard is provided against
lique?ed paraffin wax to form a melt or heat plas
tic mass, so that the requisite amount may be 30 the consequences of a high voltage electric surge
which may arise in one lead only of the deto
squirted as a plug into the igniter shell. The alu
nator. The discharge teeth (say the teeth I?! if
the surge arises in the lead'l?) elfect complete
discharge of that surge direct to the detonator
tic materials, and, in any case, be used to replace
4, without any residual surge passing on to
the rubber plug or sealing means at the mouth of
the bridge-wire 8. In this case also, therefore,
a detonator, or alternatively it may be used in
there is no flow of current through the bridge
place of the insulation mass commonly employed
wire such as might cause incandescence and pre
for the leads or for part of the wires in the blast
mature ?ring of the fuze-head 5.
ingcircuit. .Other substances displaying coherer
action are ?nely powdered silver, nickel, iron, 40 The coherer mass may be used not only in the
minium ' powder may, on the other hand, be
mixed with rubber, or rubber-like or other plas
brass and cop-per and these substances can also be
used for the coherer plug, being preferably mixed
for this purpose with paraf?n wax or-other fusible,
powdered or liquid dielectric. Another material
which has been found suitable for the coherer
plug is graphite, preferably in de?occulated state,
mixed with a viscous neutral hydrocarbon such
as light lubricating oil to form a paste. ?Through
varying the amount of oil admixed with the
vgraphite, and by adding other inert materials
which may in?uence the physical properties vof
the paste, it is possible to vary to a large extent
the resistance to the ?ring current without im
pairing the coherer action with respect to the high voltage" discharges.
Teeth, projections, edges or other means may
be formed or provided on the igniter leads, at
their bared parts surrounded by the coherer
mass, and/or on the interior of the casing con
taining the said mass, or otherwise so as to con
stitute discharge points which promote the dis
charge of the high voltage charge from the leads
form of a plug enclosed within the igniter or
detonator shell, but also in the form of a plug or
layer surrounding the leads at a place outside the
igniter or detonator. Fig. 2 shows an applica
tion of this to a detonator enclosed in an inert
body or so-called wax primerZO. Reference nu
merals used in this ?gure similar to those used
in Fig. 1 refer to similar parts. In this embodi
ment, the coherer mass 2| is made in the form
of a layer interposed between the inert or wax
body 20 and a top inert or wax layer 22, The
leads la, lb are bared and formed with outwardly
directed discharge teeth at 23 and 24 respectively,
where they pass through the coherer layer 2|.
In function, the embodiment shown in Fig. 2
is similar to that already described with reference
to Fig. 1, and, as shown in Fig. 2, the toothed and
bared parts 23, 24 of the leads Ia, I10 are prefer
ably spaced outwardly from each other in the
coherer layer 2| so as to afford high voltage dis
charges a 'readier path to ground, 1. e. to the rock
or side of the borehole in which the wax primer
is inserted.
In Fig. 3, similar numerals again denote similar
or either of them into the said mass, as described 65
parts. The embodiment shown in this ?gure is
an electric igniter having a copper or other con
in my co-pending patent application No. 422,452.
The bared parts l3, I4 of the leads la, 1'? are
formed, in the particular example shown in Fig.
1, with pointed teeth ll, l8 respectively directed
diametrically outwards towards the wall of the
ductive cylindrical shell 30 into the lower open
end of which there is crimped a ?exible delay
fuze 3!, of which the other end (not shown) is
crimped in known manner in the mouth of a
detonator. A coherer plug 32 is in' this instance
inserted in the igniter shell 30 so as to surround
detonator shell 5. Any projections, edges or other
means adapted to constitute the discharge points
may be employed in lieu of the particular teeth
the solder points H, 12, the adjacent parts of
[1, I8 illustrated, so long as they ful?ll the pur
the bridge-poles 9, l0, and the bared lower ends
pose aforesaid of promoting discharge of a high 75 33, 34 of the leads la, lb. The upper end of the
to a group of series-connected detonators 6|.
The insulated conductors 53, 5'41 are in this in
stance led from the positive and negative wires
' to a delay-action detonator of the Eschbach type.
The construction of this detonator is similar to
that of the instantaneous detonator shown in
Fig. 1, with the exception that, between the fuze
head 5 and the primary charge 6, a delay compo
sition 3 is (e. g. antimony and potassium per
manganate) contained in a lead body 3!?) is pro
vided. Otherwise, similar reference numerals in
the two ?gures denote similar parts.
In any of the embodiments of the invention,
the detonator shell in preference to the casing 58.
Fig. 6 shows the application of the same means
igniter shell 30 is closed by a rubber plug 35
crimped therein.
Fig. 4 Shows the application of the invention
50??, 5|EL of the blasting cable, and the grounded
casing 58 is connected by separate conductors
59a, 59b and sleeves 60a, 60b to the ?rst and last
detonators of the series respectively. Otherwise
10 the arrangement is similar to that described with
reference to Fig. 5.
Fig. 7 shows another application of the said
means to a similar group of series-connected
detonators 62. The insulated conductors 53a, 54a
more than one grounded coherer plug or mass
may be used in association with the one detonator
or igniter. One form of this modi?cation is
are led from the blasting wires 58%, 5M and their
bared ends 55a, 56*1 inserted into separate coherer
masses 5'53, 5111 contained in separate grounded
casings 58a, 58?). This is a specially effective safe
guard against short-circuiting of the ?ring cur
rent, e. g. between the bared ends 56, 56 (Fig. 6)
of the conductors 53, 53 through the coherer
shown incorporated in the embodiment illustrat
ed in Fig. 3 where, in addition to the coherer plug
32 surrounding the bared parts 33, 34 of the leads
within the igniter shell 30, a second coherer plug
35 is contained in a separate copper or other
conductive sleeve or shell 31 which is crimped on
rubber plugs 38, 33 as an independent unit
mass 51.
The outside arrangement of the coherer plug
shown in the preceding Figs. 5 to '7 necessitates
that the construction of the plug should be ro
bust, in order to withstand rough handling. In
particular, the internal spacing of the bared ends
or mass is thus used, discharge of high voltage
of the conductors and the grounded casing must
charges from the ?ring circuit to ground may
not be disturbed during the charging operations.
take place through either one or other or both of
easily made assembly is illustrated
the said plugs or masses. In carrying out the in 30 A rigid
in Figs. 3 and 9. In this assembly, the bared
vention. steps may, if necessary, be taken to en
ends of the conductors 53, 54 are constituted by
sure that high voltage discharges should they oc
two strips 63, 64 of metal foil secured by an ad
cur, will not take place through the coherer mass
hesive to the opposite sides of an. I shaped piece
from one lead of the igniter or detonator across to
the other. A safeguard against this happening is 35 65 of cardboard or like insulating material, which
is a neat ?t into the metal casing 65. This in
the provision. of discharge points hereinbefore re
sulating piece 65 serves to position, and to main
ferred to, Should these points not be employed,
tain in position, the strips 63, 64 with respect to
as for example in the embodiment illustrated in
the wall of the casing 65, which is, itself closed
Fig. 3, a preventive against the occurrence of dis
at its top and bottom ends by sealing means 61, 68
charges between the leads, and consequent short
held in place by crimpings 69, ?H3. In the con
circuiting of firing current, is obtained by, for
struction shown in Figs. 8 and 9 a copper wire
example, either spacing the leads I 1?, l?D apart in
?ll is soldered at one end to the casing 66 and at
the coherer mass (as in Fig. 2) a distance which
its other end to a, copper ring or sleeve 12, for
is substantially greater than the distances be
connection to the detonator casing (as already
tween the respective leads and the detonator shell
described with reference to Fig. 5).
or ground, or inserting between the leads within
Although the bared ends of the conductors in
the coherer mass (as in the case of the upper
around bared parts 48, 4| of the leads la, lb out
side the igniter shell 38.
When more than one grounded coherer plug
coherer plug 36 in Fig. 3) a paper sheet 42 or
Figs. 5 to 9 have been shown as of ?attened
and 52 are shown within the discharge plug, these
points may be outside the said plug and insulated
from each other and from the igniter shell by
being surrounded by a rubber or similar plug.
Referring to Figs. 5 to 11:
the said ends and/or the casing or grounding
means may be provided with discharge points as
straight-edged shape, it will be understood that
other insulating element.
While, in the drawings, the soldering points H 50 these ends may be of ordinary round section or
described in our co-pending patent application
Under practical tests, my coherer protected
detonators have invariably been found capable of
being ?red, that is, intentionaly ?red, after they
have been subjected to a discharge of high voltage
In these ?gures, an alternative means of asso
ciating the igniter leads with each other is shown,
such means comprising a coherer mass or masses
static electricity either through one lead only, or
which does not, or do not, surround the igniter
leads directly, but which is or are contained in a
grounded casing or casings and surrounds or sur
round the bared ends of insulated conductors led
from the respective igniter leads.
Fig. 5 shows the application of this indirect
means to a single detonator. The leads 5!), 5| of I
the detonator 52 are respectively tapped by in
sulated conductors 53, 54, the ends 55, 55 of which
are bared and surrounded by a coherer mass 51
contained in a grounded metal casing 53. De
sirably, but not necessarily, the casing 58 is elec
trically connected to the detonator 52 by a con
ductor 59 and conductive sleeve 60. This en
sures that the detonator casing is not at a lower
through both leads simultaneously. In the latter
case, theoreticallyat least, a circuit permanently
conductive to the ?ring current is created from
one lead outwardly through the coherer mass to
the metal casing, thence round the wall of the
casing and inwardly through the coherer mass
to the other lead. That such a detonator was
found on test nevertheless to be capable of being
?red is clearly due to the fact that the (perma
nently reduced) resistance of the (outward) dis
70 charge paths in the coherer mass was still high 7
enough to divert a current through the fuze
head sumciently strong to ?re the same.
A means
of positively ensuring that the coherer detonator
may be ?red after simultaneous high potential
potential than the casing 58 and that therefore
discharges on both leads is shown in Figs. 10 and
discharge to ground will not take place through
2,408, 124
11. In these ?gures, the'said means is shown
applied to an outside coherer plug (as used, e. g.,
in the constructions shown in Figs. 5 to 9), but
it may equally well be applied to an interior
coherer plug as shown in Figs. 1 to 4. The means
comprises an insulating casing 13 which is closed
at the top by sealing means '13a and which con
by atmospheric electricity, comprising a coherer
mass which is in electrical cooperation with insu
lated conductive branches connected with each
lead of the igniter, said branches having bared ?
parts surrounded by the coherer mass, a conduc
tive grounded casing conductively connected to
a conductive shell of the igniter, the coherer mass
including a metal powder offering a substantially
tains the coherer mass 14 in which the bared
parts 15, 76 of the leads 11, 18 are inserted as
complete resistance to voltages of the magnitude
usual. At the portions of the casing 13 directly 10 used for ?ring the igniter and which, on being
adjacent to the bared parts 15, 16, interior con
subjected to voltages substantially higher than
ductors 79, 80 are disposed parallel to the said
said ?ring voltages, becomes locally conductive
parts and are respectively formed integral with
through coherer action along a path permitting
or conductively connected to exterior conductors
the passage of the high voltage charge.
BI, 82. With these separate conductors, even the 15
2. An electric igniter of a blasting detonator
permanent reduction in resistance of the dis
in combination with means by which it is safe
charge paths created by discharge from both
guarded against accidental ?ring by electric cur
igniter leads simultaneously cannot result in a
rents or spark discharges produced respectively
short circuit of the ?ring current occurring be
in, or in the vicinity of, the ?ring means of the
tween the bared parts of the leads via the casing 20 igniter by atmospheric electricity including leads
containing the coherer mass.
for the igniter common to a group of two or more
A5 is the case with coherer materials in general,
detonators, insulated branches tapped from said
the part or parts of the grounded plug or mass
leads and having bared parts, said bared parts
which has or have had its or their resistance re
being surrounded by a coherer mass which is in
duced by the coherer action caused by a high 25 electrical cooperation with each lead through the
voltage discharge may have the resistance thereof
insulated branches, said mass including a metal
restored to its normal high value by the plug or
powder offering a substantially complete resist
mass being lightly shaken.
ance to voltages of the magnitude used for ?ring
With the present invention, an electric deto
the igniter and which on being subjected to volt
nator is obtained which is substantially safe
ages substantially higher than said ?ring volt
against stray currents and which, in addition, is
ages, becomes locally conductive through a co
equally applicable to series, as to parallel, blasting.
herer action along a path permitting the passage
In the appended claims, the term ?electric
of the high voltage current, and a conductive
leads? is to be understood as including the wires
casing enclosing said mass and connected elec
of the igniter and/or the Wires of a blasting cir 35 trically to the ?rst and last of the detonators of
cuit, and/or conductors led from these wires.
the group when the groups are connected in series.
I claim:
1. An electric igniter of a blasting detonator
in a combination with means by Which it is safe
guarded against accidental ?ring by electric shock
or spark discharges produced respectively in, or
in the vicinity of, the ?ring means of the igniter
3. A construction as de?ned in claim 1, wherein
the mass is common to both leads of the igniter.
4. A construction as de?ned in claim 2, wherein
the mass is composed of ?nely divided aluminum
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