Note: Descriptions are shown in the official language in which they were submitted.
~ ~5~5
Title
,
Non-primary explosive detonator.
Technical Field
The present invention relates to a detonator for use as an
explosive device or for settin~ off other explosives and more .
specifically to a detonator of the non-primary explosive
type. Furthermore, the detonator according to the present
invention is of the type that comprises a hollow tube with
a closed end having a chamber containing a secondary explo-
sive base charge, an opposite open end provided with or
for the insertion of an igniting means, and an intermediate
confinement adjacent sai.d chamber and containing an explo-
sive charge for the initiation of a detonation of the
secondary explosive base charge via said igniting means
and optionally also via a delay composition. The novel and
characteristic features of the detonator according to the
invention are based on a special design of the confinement
~or the initiating charge and on the use of a secondary
explosive as said initiating charge, which features impart
to the detonator essential advantages as compared to
detonators which utilize primary explosives as
the initiating charge and also compared to prior non-primary
explosive detonators. The invention also relates to a
special initiating element for use in a non-primary explo-
sive detonator of the above-mentioned -type.
Background of the ~nvention
lJp to now detonators of the above-mentioned type in commer-
cial use ale generally represented by pyrotechnic delaydetonators which contain a srnall charge of a primary explo-
sive placed in contact on one side with a pyrotechn:ic delay
charge and on the other with a secondary explosive base
charge, to effect the transition from a relatively slow
non-violent chemical burning of the delay charge initiated
by an igniting means such as an electrical ~use head to a
detonation in said base charge.
In this connection it should be noted that for practical
purposes a primary explosive is defined as an explosive
substance which can develop complete detonation from a
flame or a conductive heating within a volume of a Eew
cubic millimeters of the substance, even without any con-
finement thereof. On the contrary, however, a secondary
explosive can be initiated to detonate by a flame or a
conductive heating only if present in very much larger
quantities or within heavy confinement such as a heavy
walled metal container, or by being exposed to mechanical
impact between two hard metal surfaces. Examples of
primary explosives are mercury fulminate, lead styphnate,
lead azide and diazodinitrophenol or mixtures of two or
more of these and/or other similar substances. Representa-
tive examples of secondary explosives are pentaerythritol-
tetranitrate (PETN), cyclotrimethylenetrinitramine (RDX),
cyclotetramethylenetetranitramine ~HMX),trinitrophenylmethyl- !
nitramine (Tetryl) and trinitrotoluene ~Tr~T) or mixtures of
two or more of these and/or other similar substances.
In a widely used method of producing a pyrotechnic delay
detonator according to the prior artJthe required weight
of secondary explosive for the base charge, typically
about 600 mg, is firstlpressed into the bottom part of an
outer metal shell having a closed bottom end. The required
weight of primary explosive, typically about 300 mg or less,
is then loosely filled into the shell on top of the base
charge and compacted by pressing into the shell. Said
primary explosive also contains a previously compacted
pyrotechnic charge which is thus left with its upper end
exposed an(l its lower end in close contact with the com-
pacted primary cxplosive.
When exposed to an igniting means such as a flame Erom an
electric fusehead, from a NONEL~tube or from a detonating
cord, inserted into the open end of the detonator shell,
the pyrotechnic charge starts burning at a rate that is
:~2~
typically of the order of 2-10 cm/s. As soon as the
burning pyrotechnic charge reaches the primary explosive
there is a rapid transition from burning to detonation
within said primary explosive. The resulting detona~ion in
turn initiates detonation in the secondary explosive base
charge.
Conventional detonators of the above type have several
serious disadvantages. These are primarily derived from
the extreme sensitivity of the primary explosive to impact
friction or flame initiation. Some of said disadvantages
are:
1. The presence of even a small charge of primary
explosive makes a conventional detonator hazardous
to handle because it is sensitive to mechanical
deformation or impact such as when accidentally
bent or impacted at the region of the primary
charge.
2. The manufacture of the primary explosive, the
handling of the same and the shell filling opera-
tions during manu-facture of the detonator are risky
operations which require extreme care and caution
which in turn means costly operations and expensive
plants.
3. The drainage of poisonous water containing fulminate,
lead or phenol Erom the process oE manufacture of
the primary explosive creates serious environmentc
pollutions if not controlled. ~urthermore as it is
not allowed to transport the bulk primary explosive
it is necessary for each detonator plant to set up
its own primary explosive plant which increases the
number of Polluted areas and also requires additio-
nal investments for environmental protection.
It is therefore an object of the present invention to eli-
minate or minimize the above-mentioned risks, pollutions
and high investments, which is accomplished by using instead
of the primary explosive a secondary explosive as an ini
tiating charge for detonators of the type referred to above.
It is true that more recently non-primary explosive detona-
tors have been disclosed and patented but generally these
new detonators have not come to any widespread general
use due to certain disadvantages o~ limitations. Among
such disadvantages and limitations are
that generally these previously known non-primary explosive
detonators are restricted with reference to the use of
the igniting means and with reference to the wall thick-
nesses of the detonator shell and the dimensions of theconfinement for the secondary explosive initiating charge and
that they are also generally relatively complex as to their
structures which influences upon the manufacture as well as
the operation thereo-f.
As prior art related to non-primary explosive detonators
or in connection therewith reference is made to the
following patent specifications:
US 3 212 ~39 discloses a blasting cap which contains
secondary explosives only. Tlle detonation of the
secondary explosive is caused by another secondary explosive
that is compressed and arranged in a con;Eined enclosure in
a steel tube having specific dimensions. This confined
enclosure provides conditions under which an electrical
ignitor i~nitcs the secondary explosive.
US 3 978 791 relates to a detonator device containing
secondary explosives only. Also in this case a compressed
secondary explosive, "donor secondary explosive", is
utilized but together with an impactor disc, a portion of
which is released and accelerated when said donor secondary
explosive is initiated by a bridge wire. The disc strikes
an acceptor secondary explosive with sufficient velocity
to produce detonation of the acceptor secondary explosive.
US 4 239 004 discloses a detonator device of a structure
similar to that of US 3 978 791 but the device also con-
tains a delay mixture charge that imparts to the device a
time delay before the donor secondary explosive is initiat-
ed.
~0 DE AS 1 646 340 discloses a detonator device for the ini-
tiation of a non-sensitive explosive, which contains a fuse
and a pyrotechnic time delay element and the essential fea
ture of the device is that it comprises a housing filled with
a secondary explosive and open at one end. The open end of
the housing is facing the delay element of the other part
of the device and removably attached thereto.
US 3 724 383 (1973) relates to a new method of initiation
of an explosive, viz. the use of a laser pulse that passes
through a fiber optic bundle (9) and a focusing bead (4)
to impinge upon a charge (11) of a secondary explosive
which is set into low order detonation. A second secondary
charge (10) is thereby set into low order detonation but
as said second charge is loaded in a gradient of increasing
density the velocity of the reaction increases very rapidly
and a high order explosion is obtained.
US 4 206 705 (1980) relates to an electrical initiator
wherein polymeric solid sul:fur nitricle (SN)X is utilized
as the sole explosive i.nitiating means thanks to its abili-
ty to act as an explosive as well as to conduct electrical
current.
US 3 661 085 discloses a new electric initiator structure
wherein the pyrotechnic or explosive mix contacts only
selected portions of the bridge wire, which means a sub-
stantially faster response time than that exhibited by con-
6 22gl9-532
ventional initlators. The explosive charges (primary and
secondary charges) are those charges which are conventionally
employed in such devices.
Disclosure of the Present Invention
As should be clear from the above-mentioned an object of the
present invention is -to provide a detonator which eliminates or at
least reduces the disadvantages of the primary explosive
detonators as well as eliminates or reduces the disadvantages of
the previously known non-primary explosive detonators or at least
offers a valuable alternative thereto. More specifically, there
is provided by the present invention a simple design of a non-
primary explosive detonator which is conductive to the transition
of a secondary explosive from burning to detonation, which offers
the advantage of being able to use to the fullest extent those
parts and technological equipments which have previously been used
in conventional detonators while using less expensive shell
materials and explosives and avoiding the risks associated with
the utilization of primary explosives. This in turn means a
versatility of a non-primary explosive detonator which has
hitherto not been possible in connection with the previously known
and rather restricted non-primary explosive detonators. Thus, ~or
instance the new detonator according to the present invention is
not as restricted as the known non-primary explosive detonators as
to the choice of ignlting means, seconclary explosives, shell
materials and thicknesses, etc. Still another object o~ the
present invention is to provide a detonator by which the time o~
the transition from ignition to detonation is shortened so as to
ensure the delay accuracy oE high precision detonators.
~'
6a 22~19-532
To these ends, the invention provides an initiating element Eor a
non-primary explosive detonator comprising a thin-walled
confinement and containing a pressed, secondary explosive
initiating charge, the confinement having an access permitting
ignition of said secondary explosive initiating charge via
igniting means, characterized in that an intermediate charge of
secondary explosive is arranged adjacent the initiating charge at
the opposite end from said access, said intermediate charge having
a lower pressing density than said initiating charge.
The invention further provides a non-primary explosive detonator
comprising a hollow tube with a closed end having a chamber
containing a secondary explosive base charge, an opposite open end
adapted for the insertion of an igniting means, and an
intermediate initiating element according to the preceding
paragraph, the secondary e~plosive base charge being arranged to
detonate by activating the igniting means to ignite said
initiating element.
These and additional objects oE the detonator as well as the
specific initiating element accordlng to the invention will be
readily understood by a person skilled in the art Erom the
following more detailed description oE the invention.
~z~
The characteristic eature of the non-primary explosive detonator
according to the present invention is that the confinement is
thin-walled and contains a secondary explosive initiating charge,
that the end of the confinement towards said chamber is open
or provided with a thin wall or an aperture or a recess for an
aperture to accelerate the burning of the secondary explosive
initiating charge to a shock wave that causes detonation of the
secondary explosive base charge, and an access, preferably at
the opposite end thereof~ which permits ignition of said second-
ary explosive initiating charge via the igniting means, saidaccess preferably being in the form of a hole allowing escape
of reaction product gases formed at the burning of the second-
ary explosive initiating charge.
Thus, hy the new design of the confinement containing the se-
condary explosive initiating charge it has unexpectedly turned
out to be possible to utilize such a great area of burning se-
condary explosive within the initiating charge that the burning
rate is increased to such a level as to create a strong shock
wave leading to detonation of the base charge. This is even
more unexpected as the confinement can contain a hole that per-
mits escape of reaction product gases formed at the burning of
the initiating charge, i.e. said hole means that energy is lost
through the escape of said gases. The access can be a means
allowing ignition of the secondary explosive of the initiating
charge, e.g. an electric resistance wire, with or without a
surrounding fusehead, buried within the confinement with elec-
trical connectors sealingly penetrating the conEinement wall.
However, an access in the Eorm of a hole simplifies ignition
and also involves the benefit of being able to utilize any
igniting means available within the detonator art. As was ment-
ioned above this represents a major advantage as compared to
currently known non-primary explosive detonators. Ihat is, the
structure of the confinement according to the present invent-
ion makes it possible to make the hole for the igniting meansas large as is necessary for the insertion thereof, in spite
of the energy losses through said hole. Although ignition
8 ~
means such as a fusehead can be positioned immediately at, in
or below the hole, it is suitable to provide an empty space
somewhere above the hole ~o buffer pressure build-up or allow
escape of some of the reaction gases from the initiation
charge. The space can be posi~ioned for example somewhere be-
~ween the hole and the ignition means such as immediately above
the hole or above a delay element adjacent the hole.
From the above-mentioned i~ can be gathered that the detonator
according to the present invention is adapted for use of any
known secondary explosive as the initiating charge
which also means that the ini~iating charge may even be
of the same secondary explosive as the base cha~ge, if
desired. Representative examples of secondary explosives
to be used as the initiating charge, and as the base chaTge,
are the above-mentioned secondary explosives PETN, RDX, HMX
Tetryl and TNT but the invention is not in any way limited
to these explosives only. To modify the reaction rate of
the initiating charge it may also be desirable to add to
these secondary explosives pyrotechnical materials, e.g.
aluminium powder OT potassium perchlorate, passivators,
e.g. shellac, or sur-face activators, e.g. a stearate.
According to an especially preferable embodiment, however,
the secondary explosive for the initiating charge is PETN
or RDX or a mixture of these two explosives. Moreover, said
secondary explosive for the initiating charge is preferably
extra fine as to particle size, i.e. finer than the explo-
sive for the base charge, which e.g. means that the explo-
sive for the initia~ing charge passes through a 250 mesh
sieve ~US Sieve Series) (~ <0.06 mm) while the explosive
for the base charge passes through a 150 mesh sieve
~2~<O.1 mm). The particle size can preferably be below 30 ~m
and most preferably below 20 ~m. Other preferable data for the
explosive to be used as initiating charge are: specific surface
5000-7000 cm2/g; pressing density 1.2-1.6 g/cm3, pre-ferably 1.3-1.6
g/cm3. Said data can be accomplised in a physical, chemical
or mechanical way. As to the base charge it is generally
9 ~ 5
conven~ional with reference to the above-mentioned proper-
ties, but it may also sometimes be suitable to use as said
base charge part of the above-mentioned specific composi-
tion used for the initiating charge and part of a conven-
tional secondary explosive.
According to an especially preferable embodiment of the
invention there is also used~ between the initiating
charge wi~thin the confinement and the base charge, e.g.
adjacent the aperture/an~ outslde said confineme~t, a
secondary explosive that is more loosely pressed than the
initiating charge. Compared to the above-mentioned range
of 1.2-1.6 g/cm3 this may mean a pressing density within
the range of/0.8-1.1 g/cm3, preferably around 1.0 g~cm3.
This normally means that this intermediate charge of low den-
sity will be surrounded by the initiation and base charges ofhigher density. Preferably the intermediate charge is better
confined than the base charge.
The end of the confinement facing the base charge is critical
for the function of the initiating charge~ This end can be
entirely open for best transmission of the shock wave to the
base charge, which is possible if the remaining parts of the
confinement are sufficient for transition into detonation of
the deflagrating secondary explosive. This end can also be
provided with a thin wall to increase confinement, cause shock
wave reflections with interferences and simplify manufacture.
Since the wall also to some degree prevents shock wave trans~
mission to the base charge, it should not be too thick and is
pre~erably less than 3 mm and most preferably below 1 mm in
thickness. The wall can be smooth and uninterrupted. It can
also be prov:ided with an aperture, or a weakening for an
aperture, to thereby ampliy a shock wave and allow also a
weaky developed wave to penetrate the wall and cause ignition
of the base charge whereby the reliability will be improved.
In either design of the wall, it is preferred for reliability
reasons that the deflagration to de~onation transition takes
*/ 0.8-1.4, better between
r5 ~
1 0
c~?
p~ in ~he confinement at latest at the wall.
With reference to the aperture of the confinement for the
initiating charge the main purpose thereof, and its size
relative to the size of the initiating charge, is to
accelerate the burning of the initiating charge to such
extent that the burning gases create a shock wave that
causes detonation of the base charge. The cross-sectional
area as well as the shape of said aperture cannot be
exactly defined in general terms as these parameters are
dependent on other factors such as the material and wall
thickness of the confinement, types of secondary explosives,
amounts and configurations thereof, etc., but now that
the inventive idea has been disclosed the necessary or
optimum dimensions and shape of the aperture can easily
be established by a person skilled in the art by routine
experimental work. According to a preferable embodiment
of the invention, however, the cross-sectional area of
the aperture is substantially less than the average cross-
sectional area of the secondary explosive initiatingcharge, as this means a very rapid and accurate detonation
of the base charge. While referring to the above discussion
as to the exact dimensions of the aperture a typical
ratio between the cross-sectional area of the aperture
to that of the secondary explosive initiating charge is
from about 1:2,5 to 1:4 although it may sometimes also be
preferable to utilize a ratio that is less than 1:5. In
the case of circular cross-sectional areas the above-
mentioned ratios correspond to the ratios as to diameters
of from about 1:1.6 to 1:2 and less than about 1:2.3,
respectively.
Furthermore, a complete aperture need not necessarily
be present from the beginning as the invention works
also if said aperture is created during the operation of
the detonator. That is, according to another embodiment
of the detonator it contains a recess only for the aper-
S
ture to be formed bu~ s~ill the main function of thedetona~or is based on the shock wave generated during
the burning of the initia~ing eharge which in turn means
that the recess leaves typically a thin sheet or similar
which is burst by the accelerated gases.
Although it is possible that the column of secondary explo-
sive, when seen in the detonation direction, has a smaller
diameter of about the aperture size after the wall, it is
preferred that the diameter increases again after the aper-
ture, preferably to about the same diameter as before thewall. It is also preferred that the wall in which the aper-
ture is formed is short and preferably only of the above
mentioned wall thickness so that the aperture forms a short
restriction in the explosive column.
Th~ length of the initiation charge up to the wall or the
length
of the open-ended confinement is suitably sufficient for
transition into detonation of the burning secondary explo-
sive. The necessary length is quite short in the present
design and can be kept below S0 mm, is suitably between 3
and 25 mm and preferably~between 5 and 20 mm. Also the dia-
meter of the charge can be kept small such as below 15 mm
and preferably also below 10 mm.
According to another especially preferable embodiment
o-E the detonator according to the invention the confine-
ment containing the secondary explosive initiaking
charge is an element that is not integral with the shell
of the detonator tube but is separate from said tube.
This embodiment offers great advantages as compared to
the prior art as in this way the initiating charge can
be manufactured and handled completely separate from
the detonator up to the use thereof.
12
Apart from ~he obvious saety aspects therevf this means
for instance that the initiating element may even be adapted
to be incorporated into a currently available detonator of
the primary explosive type, the primary explosive initiating
charge being replaced by the new ini~iating elemen~ accord-
ing to the present invention.
With reference to the hole of the confinement or ini-
tiating element the cross-sectional area of said hole can be
of about the same size as, but i5 preferably
substantially less than the average cross-sectional area of
the secondary explosive initiating charge. However, as said
hole generally involves energy losses it should preferably
only be large enough to permit ignition of the initiat-
ing charge inside the confinement. A typical ratio bet-
15 ween the area of the hole and that of the initiating '~
charge is, however,~from about 1:2.9 to 1:6.3, ~Jhich
approximately corresponds to a diameter of from ~:1.7 to
1:2.5 in the case of circular cross-sectional areas. Llke
the aperture directed towards the base charge, the hole is
preferably short to facilitate rapid ignition of the large
diameterlinitiating charge column. As said above, entirely
diffe4rent ignition access means than holes can also be employed.
As to the igniting means it has already been mentioned
that the detonator according to the invention permits the
use of any igniting means available within the detonator
area. As examples of such igniting means reference is made
especially to an electric fusehead, a low energy cord,
a NONEL tube, or other detonating signal transmission
lines or a safety fuse but as is said the invention is
not limited ~hereto.
In the case the igniting means does not provide at the
exposed surface of the initiating charge a sufficient
combination of high enough temperature and pressure with
*/ 1:1.1 to 1:6.3~ better from about
*/ 1:1.05 to 1:2.5, preferably from
13 ~ 2 ~
a long enough duration to ensure that the initiating charge
starts burning, then a special flame-conducting pyrotechnic
composition capable of being ignited by the wea~ igniting
means and also capable of igniting ~he ini~iating charge
to start burning may be placed in contact with the exposed
surface of the initiating charge. Such a ~lame-conducting
pyrotechnic composition may also be placed between a de-
lay elemen~ and the exposed sur~ace of the initiating
charge if the delay charge composition itself is not able
to initiate the initiating charge to start burning.
According to yet another embodiment of the detonator accord-
ing to the invention, in the case when the confinement is
represented by a separate element, said element comprises
a shell which may contain said hole and is open at ~he opPo-
site end thereof, and a separate cap or disk which fits
into said open end and contains said wall, aperture or recessO
In this way for instance the manufacture of the elements
can be facilitated economically by using existing tech-
nology and equipment. Preferably the cup or disc is kept
fixed against the shell, e.g. by being slightly oversized
in relation to the inner diameter of the shell.
Although the exact or desired con~iguration o~ the aperture
is determined by a person skilled in the art from case to
case a preferable cross-sectional area oE the a~erture or
recess may be a circular one. Moreover, it has been found
to be especially preferable for the aperture or recess to
include a surface of revolution, especially in the form
of a hemisphere, a cone or a paraboloid.
Yet another essential feature of the detonator claimed is
that it enables the use of a thin-walled confinement or
element, such as below 2 mm and even below 1 mm in thick-
ness, as well as the use of a similar thin-walled hollow
~ube. Yhis results in a large burning area of initiating
charge. The special design of the confinement with said wall or
$
aperture results i~ a reflection of the weak shock wave
accompanying the burning which additionally increases
~he shock pressure. The proviso ~or these features is that
the confinement is of a strong material, for instance of
steel. However, the detonator shell can be made of a very
cheap ma~erial such as paper or plastic. A preferred wall
thickness of the steel confinement part, which may con-
tain the hole is within the range of 0.5 - 1 mm, especial-
ly 0.5 - 0.6 mm. For that part of a steel confinement
which contains t~ael~aprerture or recess therefor a preferred
wall thickness is within the range of 0.3 - 0.25 mm for
said aperture part and 0.08 - 0.15 mm for said recess part,
respectively. The wall oraperture part can be designed in a
weaker material than steel since it represents a small fract-
ion only of the con-finement and since axial confinement is
supported by the explosive charges.
From the above disclosure it can also be seen that the
detonator can also include a delay substance or composi-
tion. As is obvious to a person skilled in the art delay
in this connection means time delay and the delay composi-
tion can be any of those delay compositions which are uti-
lized in the detonator field, e.g. a mixture of finely
ground ferrosilicon or silicon, red lead and burning speed
regulators. According to a preferable embodiment of the in-
vention the delay composition is incorporated into the con-
~inement or the separate initiating element which for in-
stance means that a separate initiating element can be manu-
factured which contains the initiating charge as well as
the delay composition for an easy incorporation into a de-
tonator tube. Alternatively a normal delay element, e.~.
containing a delay composition column in a thick-walled
metal cylinder, can be positioned above the initiating element.
According to another aspect of the invention there is also
claimed the above-mentioned separate initiating element and
the characterizing features of said elementare that it com-
prises a casing containing a secondary explosive initiating
charge and optionally a delay composition, the casing being
thin-walled and in the end intended to be positioned towards
the base charge being open or provided with a thin wall or
an aperture, or a recess for an aperture, for the accelerat-
ion of burning of said secondary explosive initiating chargeto a shock wave that causes detonation of the secondary ex-
plosive base charge, and a hole, preferably at the opposite
end thereof, which permits ignition of the secondary explo-
sive initiating charge via the igni~ing means.
The especially preferable embodiments of the initiating ele-
ment according to the invention have already been disclosed
and discussed above in connection with the detonator and
need not be repeated here. Thus, the essential features of
said embodiments are those features which are claimed in
claims dependent on the initiating element claim.
Drawings
The detonator and the initiating element according to the
invention as well as the f~mctioning thereof will now be de-
scribed more in detail in connection with the drawings, in
which:
Fig. 1 is a cross-sectional view of one embodiment of a
detonator according to the invention;
Fig. 2 schematically shows the function of the detonator
shown in Fig. 1;
Figures 3-6 are cross-sectional views of different embodi-
ments of the initiating element according to the invention
without any delay compositions;
Figures 7-9 are cross-sect.ional views of other embodiments
of the initiating element according to the invention with
delay compositions~incorporated;
Figures lOa-1flg show cross-sectional views of different
embodiments of caps or dis~s of the initiating element
according to the invention;
Fig. 1la is a cross-sectional view of another embodiment of
a detonator according to the invention without any delay
composition;
16
Fig. 11b is a cross-sectional view of another embodiment
of ~he detonator according to the invention with a sepa-
rate delay composition;
Fig. 12a is a cross sectional view of yet another embodiment
S of the detonator according to the invention without any
delay composition;
Figl 12b is a cross-sectional view of another embodiment of
the detonator according to the invention with a delay com-
position and with an initiating element of the type shown
in ~ig. 9; and
Fig. 13 is a cross-sectional view of still another embodi-
ment of ~he detonator according to the invention.
Fi~stly, it should be noted that for all drawing Figures,
for an easy understanding thereof, similar reference nume-
rals are utilized for similar parts of the detonator andelements, respectively, in spite of the fact that said
parts may differ from each other as to configuration,
placings, etc. This also means that the presence and function-
ing of each separate part will not be repeated in connec-
tion with each Figure as the necessary information can stillbe easily gathered by a person skilled in the art. The
figures show the preferred embodiment of the initiating ele-
ment in which the access is a hole and in which the end facing
the base charge is equipped with a wall having an aperture,
The artisan will unders~and how these features can be
changed in accordance with the alternatives described.
More specifically, Figure 1 shows a detonator comprising
a hollow tube 1 with a closed end and an open end, the
closed end containing a chamber with a secondary explosive
base charge 8. In ~his connection, it should be noted that
the term chamber is not to be read li;terally, i.e. khe
chamber may well be a space only for the base charge, the
open end of said space being later restricted by the ini-
tiating charge to be described below. At the open end of
the tube I there is a plastic plug 10 containing an ignit-
ing means, in this case an electric fusehead 9. Adjacent
17
to the secondary base charge 8 the tube 1 contains the new
initiating element according to the invention which com-
prises a casing consisting of two parts, viz. an open-end-
ed shell 2 and fitted into its open end a smaller cap 3.
Within the casing there is a secondary explosive initiating
charge 7 at the end thereof towards the base charge 8 and
a delay mixture 6 at the opposite end of the casing. The
shell 2 contains a hole 4 intended for ignition via the
igniting means 9 and for the escape of gases formed at
the burning of the initiating charge 7. The cap 3 contains
an aperture 5 towards the base charge 8 for the accelera-
tion of the burning of the initiating charge 7 to a shock
wave causing detonation of the base charge 8.
The functioning of the detonator shown in Fig. 1 is schema-
tically shown in Figure 2. Thus, Fig 2 shows the transition
from the burning of the initiating charge 7 in the initiat-
ing element to a shock wave after the ignition of the deto-
nator. When exposed to the flame from the electric fuse head
9 the pyrotechnic charge 6 starts burning at a relatively
slow, non-violent rate. When the burning reaches the top of
the initiating charge 7, the pressure from the burning
sharply increases, some energy losses occurring due to the
leakage of gases G from the hole 4 and other energy losses
also taking place as a result of the plastic deformation of
the shell 2. On one hand, however, the energy losses are com-
pensated for by the accelerated burning of the initiating
charge 7, and on the other hand the gases ormed are still
confined by the deforrned shell 2, which in turn means that
the pressure in the burning region still continues to rise
so as to violently accelerate the burning to the formation
of a weak shock wave. This weak shock wave becomes very
intense after havîng reached the aperture 5 in the cap 3
wherein reflection of the shoc~ wave takes place~ The gases
passing-through the aperture 5 also get accelerated owing
to the contracted section of the aperture S, the pulse output
from the aperture 5 therefore producin~ a strong shock wave
W in the top part of the base charge 8 which causes the
required detonation of the base charge.
18
From the above-mentioned it is understood that one of the
preferred fea~ures of the invention is that the forced
acceleration of the burning is allowed to take place in a
non-closed confinement allowing escape of some reac~ion
product gases and possibly deformation of the casing wall.
This in turn for instance means that a relatively thin- !
walled casing can be utilized allowing a relatively large
cross-sectional burning area of the initiating charge.
In Figures 3-6 there are disclosed different embodiments of
the initiating element according to the invention, no time
delay composition being used within the element. The embodi-
ment shown in Fig. 3 is similar to that of Fig. 1, the only
difference being that said delay composition is not present.
Figure 4 differs from Figure 3 in that the cap 3 is turned
in the opposite direction as compared to that of Fig. 3,
the walls of the open-ended shell 2 being extended beyond
the cap 3 to form an open-ended tubular space between the
cap 3 and the base charge 8. In last-mentioned tubular space
there is also preferably used a charge of the secondary
explosive 7 but having a lower density than that of the
ini~iating charge 7 within the initiating element. Examples
of useful densities in this respect are mentioned on p.9.
Figure 5 shows an element in the form of a closed casing 2,
the cap 3 having been replaced by a disk 3 within said
casing 2. In this special case the aperture 5 is present in
said disX 3.
Figure 6 shows a casing similar to that of Pig. 5 but with-
out any internal disk 3, the aperture 5 instead being made
through the wall of casing 2.
Figures 7-9 represent other embodîments of the initiating
elements which elements also contain delay compositions.
19
Thus, the element shown in Fig. 7 can be compared to that
of Figure 5 but with a delay composition 6 present within
the casing 2 at the end thereof adjacent the hole 4.
The element shown in Figure 8 is similar to the elements of
Fig. 3 and 4 and the only major difference relative to the
elements of last-mentioned igures is that a delay composi-
tion 6 is present within the casing 2.
Figure 9 represents an element with a special design of the
shell 2 which combines the functions of a delay element and
an initiating element.
Figure 10a-10g represent different embodiments of the cap
or disk 3. Fig. 10a shows a cap 3 of the type that has al-
ready been shown in Pig. 1 with an aperture 5 through the
wall of the cap 3. The cap shown in Fig. lOb differs from
that of 1Oa through the fact that the bottom end of the cap
3 contaïns a recess 5 only. Thus, the cap 3 of Fig. 1Ob
contains a thin wall adjacent the recess 5~ Fig. 10g shows
a cap without any aperture or recess at all.
Figures 10c-1OE show disks, for instance of a metal or a
plastics material, with apertures 5 having different confi-
gurations and cross-sectional areas. The disk shown in Fig.
10c contains an aperture 5 the cross-section of which is
circular. Fig. 10d shows a disk 3 with an aperture 5 con-
taining a surace of revolution in the form of a hemisphere,
while the disks according to Figures lOe and 10f are simi--
lar to that of Fig. 10d but with a surface of revolutionin the foTm of a cone and a paraboloid, respectively.
Although a preferable cross-sectional area of the recess is
a circular one said area can also be rectangular, rhombic
or any co~binations of two or more of these sections.
Figure 1la shows an instantaneous electric detonator with a
shell 1a of paper. Thus, it should be noted that one of
the advantages of the invention is that no particular require-
ments are to be set forth for the strength of the outer shell,
20~
which for instance means that the shell may be made of glass,
aluminium, s~eel, any alloy, paper or plastic. The bottom
end of the shell la is closed with sulphur or a plas~ic
plug 13. The connection of the shell la with the electric
5 fusehead 9 has been realized by a crimped linking of a
metal sleeve 14 with the plastic plug 10.
Pig. 1lb shows a delay electric detonator filled with an
outer secondary explosive base charge 8 at the bo*tom of
the outer shell 1a, followed by in turn an instantaneous
10 initiating element 2 and a delay composition 6 9 between
which there is a flame-conducting polytechnic composition
12 to accomplish a reliable ignition of the secondary
explosive 7 within the initiating element 2.
Figure 12a shows a non-electric detonator without any delay
15 composition which detonator is ignited by a low energy
cord or a NONEL tube 15. The shell 1b is of a plastics
material. Figure 12b is a metal-shelled non-electric delay
detonator with an initiating element similar to that al- I
ready shown in Fig. 9.
20 Figure 13 shows a secondary explosive blasting cap fixed
with a safety fuse 16, and where the flame-conducting
pyrotechnic composition 12 is incorporated into the ini-
tiating element 2.
Examples
25 EXAMPLE 1
A bras-shelled detonator similar to that shown in Fig. 1
was manufactured. The bottom end of the detonator was filled
with 650 mg of RDX as a base charge, and 300 mg of RDX and
250 mg of a pyrotechnic delay composition containing silica
30 powder and red lead were filled into the steel-shelled
initiating element. Upon initiation of the electric fusehead
the base charge of the detonator detonated and caused a
hole with a diameter of 12 mm in a 5 mm thick lead plate
placed in contact with the bottom surface of the detonator.
2 1
EXAMPLE 2
~en aluminium-shelled detonators were manufactured with the
same amounts of explosiYes as in Bxample 1 but with PETN
instead of RDX in the ini~iating element. Their ~imes from
electric initiation to detonation upon initiation were
160 ms ~milliseconds), 157 ms, 155 ms, 159 ms, ~63 ms, 164 ms,
161 ms, 166 ms, 1$4 ms and 167 ms, respectively.
~XAMPLE 3
An aluminium-shelled detonatoT with the same volume of
explosives as the one from Example 1 but with HMX instead
of RDX in the initiating element was manufactured. Another
difference relative to Example 1 was that a low energy tube
was used instead of an electric fusehead. Into this detona-
tor there was inserted an ANFO cartridge with a diameter of
3Z mm with a charge of 200 mg, and then another similar
cartridge was placed along the axial direction with a dis-
tance of 60 mm to the ~ottom end of the first cartridge.
The ANFO formula was diesel 4, sawn chips 4/ammonium
nitrate 92. Upon initiation of the NONEL tube the de*onator
and the cartridge detonated.
EXAMPLE 4
A steel-shelled detonator of the type shown in Figure 13
was manufactured and filled with 600 mg of RDX at the bottom
thereof, 200 mg of PETN in the initiating element and 80 mg
of a flame-conducting pyrotechnic composition containing
ferrosilicon and red lead. Upon the initiation of the deto-
nator by a safety fuse the base charge detonated and a fuse
with a length of 20 m, the end of which was lapped over the
detonator, got a complete detonation too.
EXAMPLE 5
A paper-shelled detonator was manufactured and filled with
650 mg of RDX at the bottom end thereof and with 220 mg of
HMX in the initiating element and without any pyrotechnic
composition. The detonator was lapped at one end thereof
with a use having a length of 1,2 m, the lat~er being filled
22 ~. ~ Q ~
with RDX in an amount of 13 g per meter. Upon initiation of
the NONEL tube the base charge of the detonator detonated
and the fuse was initiated too~ The data recorded by an
electric timer showed that the propagation time for the
detona~ion with a distance of one meter between the ~wo
points of the fuse was 142,3 microseconds, which is equiva-
len~ to a detonation velocity of 7027,4 m/s.
EXAMPLE 6
Ten paper-shelled detonators as shown in Figure 11b were
manufactuTed, and the base charges and secondary explosive
initiation charges *hereof were the same as in Example 2,
with the addition of 100 mg of a flame-conducting pyro-
technic composition 12 and a 300 mg delay charge consist-
ing of a pyrotechnic material containing ferrosilicon and
red lead. The delay times recorded upon initiation were
533 ms, 536 ms, 531 ms, 557 ms, 563 ms, 540 ms, 565 ms,
551 ms, 567 ms and 543 ms, respectively.
EXAMPLE 7
Detonators were prepared having an outer aluminium cap tube
with a length of 62 mm, a wall thickness of 0.5 mm and an
interior diameter of 6.5 mm. The tube contained a base
charge of 450 mg of RDX compacted to a density of about 1.5
g/cm 3 and an initiating element similar to the design shown
in Figure 4 with a steel shell of 17 mm length, an outer
21 diameter of 6.5mm, a wall thickness of o.6 mm and an upper
hole of 2.5 mm diameter. The shell contained in its upper
part a 200 mg initiating charge o about 5-15 ~m size PETN
powder compacted by a press force of 133 kg to a density of
about 1.4 g/cm and below this charge a 200 mg intermediate
charge of the same PETN powder compacted by a pressure
force of 70 kg to a density of only about 1.0 g/cm3. Between
the initiating charge and the intermediate charge a cup was
inserted having an outer diameter of about 5.4 mm, a mate-
rial thickness of about 0.5 mm, an aperture recess of 2.9
mm diameter and about 0.1 mm thickness. The entire cup
23 ~ 8~
being pressed as an integral structure from aluminium sheet.
The detonators were ignited by an electrical fusehead above
the initiating element hole. Detonation was obtained in all
four tested samples.
EXAMPLE 8
Example 7 was repeated but using a cup with a wall thickness
of 0.5 mm aluminium without an aperture or weakening. Two
detonations out of two were obtained.
EXAMPLE 9
lo Example 7 was repeated but using a cup prepared from 0.1 mm
brass sheet and having no aperture. Two detonations out of two
tests were obtained.
EXAMPLE 10
Example 7 was repeated but using a cup prepared from 0.25 mm
soft steel sheet and having no aperture. Two detonations out of
two tests were obtained.
EXAMPLE 1'1
Example 7 was repeated but using a cup prepared Erom 1.1 mm
aluminium sheet and having no aperture. Two detonations out of
two were obtained.
EXAMPLE 12
Example 7 was repeated but using a cup prepared Erolll 2.8 mm
aluminium sheet and having no aperture. One detonation out oE
one tested was obtained.
EXAMPLE 13
Example 7 was repeated but without any cul) or wall between
initiating charge and intermediate chargt-~. Six detonations
out oE six tested were obtained.
24 ~ 8
EXAMPLE 14
The initiating elements of example 7, comprising initiating
charge, intermediate charge and an aluminium cup with an
aperture recess in a O.S mm wall, were ignited separately
from the exterior tube and base charge of the detonator.
Four out of four initiating elements detonated.
