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Патент USA US2411339

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NOV- 19, 1945-
Filed Dec. 16, 1942
Patented Nov. 19, 1946
ì, ' î - .
,2,411,339y f
` nrimNef MEANS
¿Hans .lay Rolfes, `Melrose,~'1`ransvaal, and Eric. i
Clifford’llalliday, Parktown North, Transvaal,- ,
‘- --
Union of'South Africa
Application December’lfî, 1942„ SerialrNo. 469,244
»- »
¿Inïthe Union of South AfricaSeptember 25, 1941
v1 claim. f
(C1. 1oz-f2s)
This invention relates gto rneansffor safeguarding-,the >electricfigniters of blasting detonators
against accidental' ñringçby electric currents or
spark discharges produced respectively in, or in
earthbut leavesa residual chargein'oneilead or
theA other, no` now of currentin the igniter orig-`
niters suilicient to `set off’thellatter, will result.
As will be -appreciated, the self-inductance
the vicinity or”, the iiring means of the igniter> by 5 meanslshould beas smallinïdímensions as is con
atmospheric electricity.
, '
Itfisobvious that a possible solution to this
problem isto surround thef two electricY leads of
sistent with its capability ofproducing the req
uisite choking. »effect~ Preferably, therefore, the
self-inductance means comprises a continuous-
the igniterat a position ia-saferdistanee from the
soft iron or other magnetic >ocre in the »form of
ñring meansthereof by` an earthed mass of a ma- 10 an oval link, ring, or the like on 'opposite halves
terial; whichgwill exhibit ahigh resistance at voltn
ages of the magnitude used fqriintentionally nring the igniter and a low resistance» at voltages
of Vthe magnitude of the electrostatic charges
of which the igniter or blasting circuit leads (en
closed in their usual insulated- covering)- are
wound»l 1@or the samerea'son, the one leady inthe
case vjust-mentioned ‘isvvoundin- the form of a
which produce the currents and spark discharges 15 right-hand fhelix and the .f other in a left-hand-
aforesaid. ,
‘ One means of obtaining a solution of the prob- .
lem 1in the Vmannerjust„indicatedis described in
the Yzzo-,pendingPatent,Application No. 455,235,
helix, so 'that theinductancesof thetwo helices
or coils add> together.
vThree embodiments of 4the invention will novv- »
lee-described, by'way of example, with reference
now Patent 2,403,125, viz. to Aemploy a material 20 to theannexed-drawing, in which:
which oñers av complete _ or substan-tially com-
Fig. l is-a sectional elevation of a combined-lil
plete resistanceto voltages oi the'magnitude used
for intentionally ñringthe Vigniter and which, on
its» being subjected to voltages of the magnitude
termeans andself-inductance means enclosed in
afiseparatel casing.
Fig-2 is an elevation, partly in section, of a self
of, electrostatic Charges caused by atmospheric »25 inductance. means enclosed in a container with a
electricity, becomes> locally conductive through
ñltel‘ means and detonator.
coherer; action along a path or paths permitting
' FigfS is a diagrammatic View of a self-'induct
the kpassage therethrough of the high voltage
ance means and ñlter meansapplied to a b1ast~
ing circuit including a groupof detonators.
In any Solution .as above, itis important that 30 Referríngrto 1 the drawing.:
thepath' V01“ :paths to earth aiîorded by the mass
In the embodimentshownin Fig. «1, the self-im
of material (which will hereinafter be referred to
dllCÈaTlCe means COIISiStS 0f a Soft-iron oval core
as the “ñlter means”) to high voltage charges
l which is elongated in the direction of its en
should be such as to ensure that as far as possi-
ClOSîYlg Coppel' Casing 2 S0 aS 150 fît neatly there
ble, the whole charge passes instantaneously to 35 Ín- O‘Il the ODDOSîte halves 0f the @Ore Í, the i11
earth, without leaving any residual charge in one
Sllïated igniter leads 3, 4 are WOlmd, the lead 3
lead or the other capable of producing a now of
current in the ñring means, e. g. bridge-wire, suf-
being Wound on the left-hand half of the core in
the fOI‘m 0f a right-hand helíX 3a and the lead 4
ficient to heat the latter to incandescence. It
being wound on the right-hand half in the form
may not be possible, however, to discharge the 40 of a left-hand helix 4a, so that the inductances
whole of the high voltage charge through the íil0f the ’GWG helices add ÈOgei'fhel‘.
ter means to earth in every case, e. g. in the case
of exceptionally heavy charges or charges of ex-
The 10We1’ ends 3b, 4b 0f the leads 3, 4 are 60n
nected to the igniter (not shown) and on the side
ceptionally high voltage.
of the inductive helices 3a, ila remote from these
According to the invention we provide, in com.. 45 ends, the leads 3, 4 are bared for a short distance
bination with a filter means as aforesaid, a selfet parts 3c, 4° and SU-I‘I'Oul’lded by a ñlter means
inductance means located in the igniter or blast5. This means may C0nsîst 0f any earthed mass
ing circuit leads between the filter means and the
0f vmaterial which will exhibit, as aforesaid, a
igniter or igniters, whereby flow of current
high resistance at voltages of the magnitude used
caused in one lead or another by atmospheric 50 for intentionally ñring the igniter and a low re
electricity is choked back or prevented from
vsistance at voltages of the magnitude of the elec
reaching or setting off the igniter or igniters, In
>trostatic charges induced by atmospheric elec
particular, the self-inductance means ensures
that, even in cases in which the whole of the high
tricity. For example, the filter means 5 may be
a coherer plug as described in the co-pending
voltage charge does not pass instantaneously to 55 Patent Application No, 455,235, now Patent
spectively around the opposite halves of a mag
2,408,125, and the leads 3, 4 may, Whatever be
netic ring I9, the one lead I'I being wound as a
right-hand helix and the other lead I8 being
wound as a 1eft-hand helix. The magnetic core
I9 is located in the circuit between the detonators
I6 and a filter means 5 shown earthed diagram
e. g, discharge points constituted by outwardly
matically at 20. While the group of detonators
directed teeth 3d, 4d are formed on the bared
illustrated is a series-connected group, it is to be
parts 3C, 4c of the leads 3, 4 within the filter
understood that this filter and self-inductance
mass 5 shown in Fig. 1.
The casing 2 is closed at the ends by rubber 10 `means may be applied similarly to the circuit of
plugs 6, 'I or other sealing means secured in place » a parallel-connected group of detonators.
By this use of a self-inductance means in the
by crimping 8, 9 at the said ends, and a rubber
leads of the blasting circuit, the necessity for sep
plug or other sealing means I0 is provided be
arate self-inductance means in the leads 2|, 22
tween the ñlter mass 5 and core I.
With the means illustrated, high voltage elec 15 (Fig. 3) of the individual detonators I 6 can be
the filter means used, be provided or associated
with discharge points to promote or facilitate the
discharge of the high voltage charge from the
leads or either of them into the earthed mass;
trostatic charges induced in the lead 3 and/or
lead 4 will normally be discharged wholly and in
As the result of experiment it has been deter
stantaneously through the discharge points 3d
and/or discharge points 4d, and thence through
mined that the self-inductance means should
the filter mass 5 and the copper casing 2 to earth.
of 30 milli-henries or thereabout, i. e. 15 milli
henries or thereabout in each lead.
preferably have as a minimum a self-inductance
Any tendency for the high voltage charge to pass
down the lead 3 and/or lead 4 t0 the igniter is
If desired, the magnetic core may be made
prevented by the choking effect of the inductance
flexible to some degree, e. g. by building up lthe
means I, 3a and 4a. Thus, even in the case of
same from a length or strands of thin soft iron
exceptionally heavy charges, or charges of excep 25 wire.
tionally high Voltage, which might otherwise
It is to be understood that in the appended
leave a residual charge in one lead or the other,
claim the term “igniter leads” is intended to i11
clude the leads of either an individual igníter or
no ñow of current takes place through the lead 3
or 4 to the firing means or bridge-wire suñicient
to set off the igniter.
In the embodiment illustrated in Fig. 2, the in
the leads of a group of series-connected or par
ductance means consists of a soft-iron link or
core I I around which the leads 3, 4 are wound in
the form of right and left hand helices 3a and 4a
respectively. The inductance means is located
Within an aluminium container I2 which also
contains the ñlter means 5 and a detonator I3
(which latter may be of any known type, e. g.
instantaneous, Eschbach, or provided With a sep
arate igniter and intervening ñexible fuze) .
allel-connected igniters, and that by the term
“filter means” we signify a ñlter means as here
inbefore referred to.
We claim:
In a blasting unit, electrically-responsive firing
means, electric leads serving such means, a pri
mary safeguarding means in electrical contact
with such leads and electrically inert to normal
voltage ñring charge through said leads and fully
conductive to current flow from said leads of an
The 40 abnormal voltage current throughsaid leads, and
ñlter means 5 is adapted to be earthed, e. g. by
copper Wire I4 wound round the copper casing of
the detonator I3 and also connected if desired, as
shown diagrammatically at the points I 5, to the
a secondary safeguarding means between the ig
nition means and said primary means, said sec
ondary means being within the electrical influ
ence of the leads and preventing flow through
In function, as will 45 said leads to the ignition means of residual or
interior of the container I2.
be appreciated, the filter and inductance means
Shown in Fig. 2 are similar to those described
with reference to Fig. 1.
Fig. 3 shows the application of the invention to
the protection of a group of detonators I6. The 50
leads I‘I, IB of the blasting circuit are wound re
like current flow uncontrolled by the primary
means, said secondary means including a mag
netic core on which the leads are Wound in rela
tively-reversed helix form respectively.
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