U.S. patent number RE31,953 [Application Number 06/221,920] was granted by the patent office on 1985-07-23 for method of charging a borehole.
This patent grant is currently assigned to Austin Powder Company. Invention is credited to Brooke J. Calder, Jr., David L. Childs, Donald W. Lyons, Roger N. Prescott.
United States Patent |
RE31,953 |
Calder, Jr. , et
al. |
July 23, 1985 |
**Please see images for:
( Certificate of Correction ) ** |
Method of charging a borehole
Abstract
A method of charging a borehole with at least first and second
separate sections of explosive material, which method comprises the
steps of providing a detonating cord extending into the borehole,
providing a first primer on a first carrier having a time delay
connection between the cord and the first primer, this time delay
having a first selected value, providing a second primer on a
second carrier having a time delay connection between a cord and
the second primer, the time delay of the second carrier having a
second selected value different from the first selected value,
sliding the first carrier and primer along the cord and into
detonation association with the first section of explosive material
and sliding the second carrier and primer along the same cord to
detonation association with the second section of explosive
material. Also the carrier for use in a method as described above
which carrier includes means for holding the primer, means for
slidably securing the carrier with respect to the detonating cord
whereby the carrier can move freely and longitudinally along the
cord, and means for supporting on the carrier an elongation
detonation element extending in a generally linear path from the
extending cord to the primer thereon.
Inventors: |
Calder, Jr.; Brooke J. (OH,
KY), Childs; David L. (Madisonville, KY), Prescott; Roger
N. (Lyndhurst, OH), Lyons; Donald W. (Madisonville,
KY) |
Assignee: |
Austin Powder Company
(Beachwood, OH)
|
Family
ID: |
26916286 |
Appl.
No.: |
06/221,920 |
Filed: |
December 31, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
740799 |
Nov 11, 1976 |
|
|
|
Reissue of: |
866277 |
Jan 3, 1978 |
04133247 |
Jan 9, 1979 |
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Current U.S.
Class: |
86/20.15;
102/318 |
Current CPC
Class: |
F42D
1/06 (20130101); C06C 5/06 (20130101) |
Current International
Class: |
C06C
5/00 (20060101); C06C 5/06 (20060101); F42D
1/06 (20060101); F42D 1/00 (20060101); F42D
001/08 () |
Field of
Search: |
;102/313,314,315,317,318,320,322,275.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; David H.
Attorney, Agent or Firm: Body, Vickers & Daniels
Parent Case Text
This is a division, of application Ser. No. 740,799 filed Nov. 11,
1976.
Claims
Having thus defined the invention, it is claimed:
1. A method of charging a borehole with at least first and second
separated sections of explosive material, said method comprising
the steps of:
(a) providing a detonating cord extending into said borehole;
(b) providing a first primer on a first carrier having an elongated
first time delay element with an inlet cord and extending between
said detonating cord and said first primer, said time delay element
having a first selected time delay value;
(c) providing a second primer or a second carrier having an
elongated second time delay element with an inlet cord and
extending between said detonating cord and said first primer, said
second time delay element having a second selected time delay value
different from said first time delay value;
(d) maintaining said inlet cord of said first time delay element in
slidable contact with said detonating cord;
(e) maintaining said inlet cord of said second time delay element
in slidable contact with said detonating cord;
(f) loading said first section of explosive material into said
borehole;
(g) sliding said first carrier and primer along said detonating
cord and into a position in said borehole where said primer is in
detonation relationship with said first section of explosive
material;
(h) loading a separating non-explosive decking material over said
first section of explosive material;
(i) loading said second section of explosive material into said
borehole; and
(j) sliding said second carrier and primer along said detonating
cord and into a position in said borehole where said primer is in
detonation relationship with said second section of explosive
material. .Iadd.
2. A method as defined in claim 1 wherein said maintaining steps
each includes the step of holding said inlet cord of a given delay
element and said common detonating cord in a common bore of the
carrier carrying said given delay element. .Iaddend. .Iadd.3. A
method as defined in claim 1 wherein said maintaining steps each
includes the step of holding said inlet cord of a given delay
element in sliding engagement with said detonating cord. .Iaddend.
.Iadd.4. A method of charging a borehole with at least first and
second separated sections of explosive material, said method
comprising the steps of:
(a) providing a detonating cord extending into said borehole;
(b) providing a first primer on a first carrier having an elongated
first time delay element with an input end and extending between
said detonating cord and said first primer, said time delay element
having a first selected time delay value;
(c) providing a second primer on a second carrier having an
elongated second time delay element with an input end and extending
between said detonating cord and said second primer, said second
time delay element having a second selected time delay value
different from said first time delay value;
(d) maintaining said input end of said first time delay element is
slidable contact with said detonating cord;
(e) maintaining said input end of said second time delay element in
slidable contact with said detonating cord;
(f) loading said first section of explosive material into said
borehole;
(g) sliding said first carrier and primer along said detonating
cord and into a position in said borehold where said first primer
is in detonation relationship with said first section of explosive
material;
(h) loading a separating non-explosive decking material over said
first section explosive material;
(i) loading said second section of explosive material into said
borehole; and
(j) sliding said second carrier and primer along said detonating
cord and into a position in said borehole where said second primer
is in detonation relationship with said second section of explosive
material. .Iaddend.
.Iadd.5. A method as defined in claim 4 wherein said maintaining
steps each includes the step of holding said input end of a given
delay element in sliding engagement with said detonating cord.
.Iaddend.
Description
This invention relates to the art of charging boreholes and more
particularly to a carrier for an explosive primer and method of
using same.
In using explosives to dislodge or heave material such as in a
quarry, is is quite common practice to drill a number of boreholes,
charge the boreholes with explosive material such as ANFO or
ammonium nitrate slurry, and the detonate the explosive material in
the boreholes in sequence to produce the desired movement of
material. Since material of the type used in boreholes generally
requires an intermediate primer of high explosive material for
detonation, various arrangments have been used for priming the
boreholes for detonation.
A common arrangement is to secure a detonating cord through the
normal opening in a primer and drop the primer and cord to the
lower portion of the borehole. Thereafter, explosive material is
placed into the borehole or the borehole is filled further with
explosive material. In some instances, the borehole is provided
with several sections of explosive material separated by
non-explosive material, such as soil. In these instances, the
primer is required for each of the separate explosive charges. To
accomplish this, as each section of charged explosive material is
deposited, a primer is dropped down along the detonating cord.
After several charges are in place and primed, the same detonating
cord can be used to explode all the primers simultaneously. This
simultaneously explodes each of the various explosive charges
within the borehole to provide maximum heave of the material being
moved. These concepts of charging and priming boreholes with
standard, available primers are well known and extensively used in
the field.
In some instances, maximum earth movement can be accomplished by
exploding or detonating various boreholes at different intervals
during a single detonation. To accomplish this, the trunk lines
used to denonate several detonating cords of different boreholes
are interconnected by time delay devices. Thus one group of
boreholes controlled by one trunk line can be detonated at a
slightly different time than another group of boreholes connected
to a separate trunk line. These time delay connections take a
variety of forms. Most commonly, they involve a time delay
cartridge which is generally cylindrical and has internal structure
which delays the propagation of a detonation wave therethrough for
a preselected time. The cartridges are often connected at opposite
ends to a relatively short section of commercial detonating cord.
Thus, to interconnect two trunk lines for different detonating
times, one of the time delay detonating cord sections is secured to
one trunk line and the other detonating cord section is secured to
the other trunk line. During detonation of one trunk line, there is
a time delay until detonation of the next trunk line. Also, there
are one piece molded time delay couplings which can be connected
between somewhat standard detonating cords to provide the same
preselected time delay. These cartridges or couplings are well
known in the art and can be timed for delays of approximately 5
milliseconds to upwardly of several seconds. Indeed, some time
delays are rated at zero time delays and they are often used for a
connection between a primer and a low energy type of detonating
cord, such as a detonating cord having a grain loading of less than
about 10 grains per linear foot. Also, such zero time delay devices
can be used with low energy detonating cord of the type having a
hollow tube with an inner cylindrical wall coated by explosive
material or filled with a combustible gas. In all instances, the
time delay devices provide a preselected time shift from the
somewhat instantaneous detonation occurring in a detonating cord.
The availability and use of these various time delay devices used
with detonating cords are well known. In addition, some time delay
devices may be used with electrical caps which can be used to
explode the high explosive of a primer for detonating the charge in
a borehole at a preselected time after an electrical signal.
In recent years, governmental regulations have been adopted which
affect the use of explosives of the type described above. One of
these regulations, which is becoming quite common, limits the
amount of explosive material which can be detonated at any given
time within a certain distance from an inhabited building or from a
highway or public transportation artery. This regulation has caused
certain modifications in the blasting techniques used in congested
areas or in areas adjacent specific structures. Compliance with
these regulations has resulted in the adoption of the concept of
detonating the material in a borehole at different times to prevent
a violation or regulations regarding the amount of explosives that
can be detonated at any given time. The first attempt to provide a
means of detonating several axially spaced explosive charges in a
given borehole at different and distinct times has been the use of
separate time delay electrical caps for detonating the primer in
each of the different axially spaced explosive charges in a single
borehole. This procedure involved the conversion of the detonating
systems into an electrical system. As is well known, there are
certain environments in which an electrical system is not
acceptable or completely satisfactory. For instance, when
electrical equipment is being used in the vicinity or during
electrical storms. When electrical lines are laid for a detonation,
these lines can act as an antenna and can be actuated in some
unusual situations by electromagnetic waves, such as radio waves.
Also, many users are well accustomed to detonating cord and
somewhat hesitate to replace such systems with electrical systems
to comply with governmental regulations. Thus, there is a
substantial amount of effort devoted to the modification of the
detonating cord system into a system which will comply with
regulations and provide sequential detonation of separate charges
axially spaced within a single borehole. One of the most common
systems is to provide a separate time delay cartridge in the
detonating cord extending to each of several primers within the
borehole. This requires the use of separate and distinct down lines
extending to the different primers at axially spaced positions
within the borehole. This type of arrangement is time consuming and
costly. Another arrangement is to provide time delay cartridges at
the primers themselves and use several low energy detonation cords
extending from the upper trunk line to the separate primers within
a given borehole. This concept is not substantially different from
the concept of using time delay devices in the down line itself
since separate and distinct down lines are required for each primer
to produce the time delay required for sequential detonation of the
axially spaced charges.
STATEMENT OF INVENTION
In accordance with the present invention, there is provided a
method of charging a borehole with at least first and second
separated sections of explosive material, the method comprises the
steps of providing a detonating cord extending into the borehole;
providing a first primer on a first carrier having a time delay
connection between the cord and the first primer, the time delay
having a first selected value; providing a second primer on a
second carrier having a time delay connection between the cord and
the second primer, the time delay of the second carrier having a
second selected value different from the first selected value;
sliding the first carrier and primer along the cord and into
detonation association with the first section of an explosive
material; and, sliding a second carrier and primer along the same
cord and into detonation association with the second section of
explosive material.
In accordance with another aspect of the present invention, there
is provided a carrier for use in a method and apparatus as defined
above, which carrier includes means for holding the primer spaced
from the detonating cord a distance preventing the cord from
detonating the primer directly; means for slidably securing the
carrier with respect to the detonating cord whereby the carrier can
move freely and longitudinally along the cord; and, means for
supporting on the carrier an elongation detonation element
extending in a generally linear path from the extending detonating
cord to the primer.
In accordance with yet another aspect of the present invention, the
elongated detonation element of the carrier defined above includes
a time delay device having a selected time delay value. This time
delay value can be between zero and several seconds, such as 12
seconds.
The primary object of the present invention is the provision of a
method of detonating, in timed sequence, axially spaced charges of
explosive material in a borehole, which method uses a single down
line, uses standard detonating cord, uses standard time delay
devices and is easy to practice in the field.
Another object of the present invention is the provision of a
carrier for the primers used in the method defined above.
Yet another object of the present invention is the provision of a
carrier for a primer to be located in one of several axially spaced
explosive charges in a borehole, which carrier is easy to produce,
can support a time delay device having a variety of time delay
values and can slide freely into a desired position on a given down
line formed from a detonating cord.
In accordance with still a further object of the present invention,
there is provided a carrier as defined above, which carrier can be
used with similar carriers to secure a number of primers onto a
single detonating cord down line.
These and other objects and advantages will become apparent from
the following description taken together with the drawings
incorporated herewith.
BRIEF DESCRIPTION OF DRAWINGS
The present invention is illustrated in the accompanying drawings
in which:
FIG. 1 is a side elevational view of one embodiment of the present
invention;
FIG. 1A is an enlarged cross-sectional view taken generally along
line 1A--1A of FIG. 1. FIG. 2 is a bottom view taken generally
along line 2--2 of FIG. 1;
FIG. 3 is a pictoral view of the embodiment of the invention shown
in FIG. 1;
FIG. 4 is a partially cross-sectioned side elevational view showing
a slight modification of the embodiment shown in FIG. 1;
FIG. 5 is an enlarged cross-sectional view taken generally along
line 5--5 of FIG. 4;
FIG. 6 is a side elevational view showing a further modification of
the present invention;
FIG. 6A is a partial, enlarged cross-sectional view taken generally
along line 6A--6A of FIG. 6;
FIG. 6B is a cross-sectional view taken generally along line 6B--6B
of FIG. 6;
FIG. 7 includes several cross-sectional views I, II, III, IV
showing the preferred embodiment of the method used in accordance
with the present invention;
FIG. 7A is a graphic illustration of the time delay concept used in
the present invention with certain mathematical time delay
relationships;
FIG. 8 is a side elevational view showing still a further
modification of the present invention;
FIG. 9 is a side elevational view showing yet another modification
of the present invention;
FIG. 10 is an end view taken generally along line 10--10 of FIG.
9;
FIG. 11 is a top view taken generally along line 11--11 of FIG.
9;
FIG. 12 is a partially cross-sectional view illustrating the
preferred embodiment of the present invention;
FIG. 13 is a top view taken generally along line 13--13 of FIG.
12;
FIG. 14 is an enlarged cross-sectional view taken generally along
line 14--14 of FIG. 12; and,
FIG. 15 is an enlarged cross-sectional view taken generally along
line 15--15 of FIG. 12.
EMBODIMENTS OF THE INVENTION
Referring now to the drawings, wherein several embodiments of the
invention are illustrated together with the preferred embodiment
thereof, FIGS. 1-3 show a first embodiment of the present invention
wherein a carrier A constructed in accordance with the present
invention is used for supporting a standard primer B and for
guiding the primer longitudinally along a standard detonating cord
10 extending down a borehole C having an upper open charging end
12. In the preferred embodiment, down line or cord 10 is a standard
detonating cord of the type having a loading of about 12-60 grains
per foot with a propagation of somewhat over 20,000 feet per
second, and preferably 30-60 grains per foot. Such detonating cord
is generally not capable of detonating certain explosive material
of the type contemplated for charging in borehole C. This material
may take a variety of forms, such as ANFO or ammonium nitrate
slurry. Thus, in order to detonate the charge in borehole C, in
accordance with normal practice, a primer B is needed. This primer
is to be detonated by cord 10 for detonation of the charge of
explosive material. This concept will be described in more detail
with respect to FIGS. 7 and 7A. An upper trunk line T is used for
detonating cord 10 in accordance with standard procedure in the
field. The trunk line detonating cord has a strength of loading
somewhat similar to that of down line 10, although different linear
grain loadings could be used. A standard plastic detonating cord
coupling 20 is used to loop and hold down line 10 around trunk line
T as the down line extends vertically downwardly into borehole C.
As will be explained later, several carriers A are used in
providing several detonating positions within bore line C. Each of
these carriers can slide downwardly along down line detonating cord
10 to different positions within the borehole.
In accordance with the illustrated embodiment of the invention
shown in FIGS. 1-3, carrier A is an integral plastic structure
having a body portion 40 provided with an upstanding rib 42 and
vertically spaced support arms 44, 46. Rib 42 supports axially
spaced guide members, such as two pairs 50, 52 of slit rings 54,
46. Each of these rings has a cord inserting, lateral opening 58,
opening at opposite sides of each ring for the purpose of
preventing carrier A from being dislodged inadvertently from
detonating cord 10 as it moves downwardly or longitudinally along
the cord. Rings, 54, 56 each have a central opening 60 which allows
for the sliding association of carrier A with respect to the
downwardly extending detonating cord 10. The spacing d, shown in
FIG. 2, allows sliding movement of carrier A. The pair 50 of slit
rings 54, 56 is adjacent an upper end of carrier A and generally
close to the upper arm 44. By providing rings 54, 56 on the
opposite side of rib 42 from a primer B supported with the carrier,
the down line 10 can not directly detonate the primer. The spacing
between the down line 10 and the primer B is selected so that the
detonation of the down line does not cause an inadvertent,
direction detonation of primer B.
Referring now to the upper support arm 44, this arm supports a
tubular element 70 and includes primer support abutments 72, 74,
which are spaced to match the diameter of primer B. In the
illustrated embodiment, arm 44 adjacent abutment 74 is somewhat
flexible in a vertical direction, as indicated by the arrow in FIG.
3. This allows transverse insertion of primer B over an inclined
wall 76. An outboard eyelet 80 provided on arm 44 includes an
opening 82 for a purpose to be explained later. Lower support arm
46, which may also be somewhat flexible, supports two abutments 90,
92 spaced along arm 46 in a manner to generally match the diameter
of primer B. Again, an inclined wall 44 allows insertion of a
primer B into carrier A between the abutments 72, 74 and abutments
90, 92. To prevent transverse dislodging of primer A, there are
provided two spaced, somewhat arcuately configured resilient primer
support flaps 110, 112.
During use of carrier A, a linear detonating element 130 transmits
the detonation wave from detonating cord 10 to primer B along a
linear path extending from a position adjacent the upper portion of
carrier A to a position at the lower surface of primer B. This
detonating element includes, in the illustrated embodiment, a time
delay device in the form of a standard time delay cartridge 132
having an input side 132a and an output side 132b. The time delay
value for cartridge 132 can be selected to obtain the desired time
delay between the detonation of cord 10 and the detonation of
primer B. Cartridge 132 is connected to a first length of
detonating cord 134 and a second length of detonating cord 136. In
this embodiment of the invention, the detonating cord, shown in
cross-section in FIG. 1A, is somewhat standard and generally
similar to the detonating cord used for cord 10 and trunk line T.
In this structure, the detonating cord forming the first and second
auxiliary detonating cord lengths 134, 136 include an inner core
140 formed from a high explosive material and an outer support
layer 142. This cord is standard detonating cord and is well known
in the explosive field.
Delay element 130 is supported on carrier A as shown in FIG. 1.
Basically, the first end of auxiliary detonating cord 134 is fed
through eyelet opening 82, through tube 70, around down line 10 and
back through tube 70. Thus, the opening in tube 70 is sufficient to
accept two portions of detonating cord 134. The second auxiliary
detonating cord 136 is threaded through a lower eyelet 96 of arm 76
having an opening 98 and through a lower access opening 100 in the
same arm. In this manner, the second length of detonating cord is
directed into the standard central bore provided during casting or
primer B. Detonating cord 136 is generally located about two to
four inches into primer B for the purpose of detonating the primer
in response to a time delay detonation transmitted through the
cartridge 132. By providing a loop of cord 134 at tube 70, th
element 130 has a sliding relationship with cord 10 and carrier A
can be dropped into borehole C without effecting the ability to
transmit detonation from down line 10 to detonating cord 134.
Detonation of cord 134 by cord directs the detonation wave to one
end of cartridge 132, which then delays the transmission of the
detonation wave for a desired, selected length of time. Thereafter,
the detonation wave appears at the output side 132b of cartridge
132. This delayed detonation is then transmitted to primer B
through detonating cord 136.
In summary, carrier A provides a means to produce a delayed
detonation of primer B by spacing the primer from down line 10 and
providing a linear element for transmitting the detonation from the
down line to primer B in a delayed manner. Also, the loop
connection between linear time delay element 130 and down line 10
allows easy sliding of carrier A to the desired actual position
within borehole C without destroying the detonation relationship
between cord 10 and element 130. The purpose of this function will
be explained later in connection with FIGS. 7 and 7A which relate
to a method of using carrier A and which method is another aspect
of the present invention.
As indicated, linear time delay device 130 extending between cord
10 and primer B is a somewhat standard unit and may have a time
delay value between ends 132a, 132b of a selected time value. These
values generally range between 5 ms and 12 seconds. Also, the
length of cartridge 132 is substantially less than one foot and
generally less than about four inches. Consequently, the time delay
is not created by extensive length of the elongated time delay
cartridge. For the purpose of this invention, the time delay caused
by the length of detonating cord 10 or the length of detonating
cord sections 134, 136 is disregarded. The detonation in this
detonating cord is considered to be instantaneous since propagation
of the detonation wave is approximately 0.05 ms or less per linear
foot. Thus, time delay, as used in this specification, indicates an
element, such as a standard time delay cartridge, which causes a
substantial time delay in a relatively short length. For instance,
a time delay of at least about 1.0 milliseconds per linear foot.
This substantially differentiates a time delay from the speed of
the detonation wave of a detonating cord used in illustrating the
preferred embodiments of the present invention. There is one
exception to the general statement regarding the time delay
concept. When using low strength detonating cords, the detonating
cord itself does not have the explosive strength required to
detonate a primer, under normal circumstances. Thus, it is
necessary, when using a low energy cord extending from cord 10 to
primer B, to provide a booster or cap between the low energy
detonating cord and the primer. This provides a three step
detonation involving the cord, the cap and then the primer. Thus, a
low energy cord such as one having a loading of high explosives
less than about 10 grams per foot, requires the use of a booster to
detonate primer B. In this instance, the booster or cap can be
provided with a selected time delay as described above. In other
words, the booster or cap at primer B can delay detonation of the
primer for a selected time generally in the range of at least 5 ms
after the booster or cap has been initiated by a low energy
detonating cord. In this particular instance, there may be a
requirement for somewhat immediate detonation as will be explained
in connection with the first stage of the method illustrated in
FIG. 7. In that instance, the time delay for the booster or cap
when using a low energy detonating cord as the interconnecting
linear element may have a time delay value of zero. A time delay
value of zero refers to a cap or booster time delay which has a
selected value which is substantially instantaneous. This is
distinguished from instantaneous detonation by the cord itself.
Thus, a time delay can be zero when using a booster or cap in
combination with a low energy detonating cord as a substitution for
linear element 130 as shown in FIGS. 1, 1A and 2. An embodiment
illustrating this concept is shown in FIGS. 4 and 5.
Referring now to FIGS. 4 and 5, the same carrier A is employed.
Linear element 150 is used as a substitution for linear time delay
element 130 as shown in FIG. 1. This linear time delay element uses
a standard low energy detonating cord 152 shown in cross-section in
FIG. 5. This cord can have low grain loading and have the form
shown in FIG. 1A. Consequently, a low energy detonating cord with a
loading of less than about 10 grams per foot can be employed. As an
alternative, and as shown in FIG. 5, the low energy detonating cord
can be of the type including a cylindrical tube 154 having an inner
cylindrical surface 156 with a thin layer 158 of high explosive
material. The cap or booster 160 is provided with a preselected
time delay between detonation of primer B and receiving the
detonating wave from cord 152. In this manner, as previously
described, low energy cord 152 can transmit detonation from cord 10
to primer B. Booster or cap 160 is inserted into the normal central
opening 162 of primer B in accordance with normal practice. This
cap can have any time delay value; however, in practice it is
generally greater than 5 ms and preferably between about 5 ms or 12
seconds. But in this particular embodiment, a time delay caused by
booster or cap 160 may have a zero time value to obtain detonation
substantially the same time as detonating cord 10. In using carrier
A with a low energy detonating cord 152 as the interconnecting,
time delay element, booster or cap 160 is inserted into bore 162 of
primer B after the primer has been located on carrier A.
Thereafter, low energy cord 152 is threaded through eyelets 96 and
80 and then through tube 70. The end of low energy detonating cord
152 is wrapped or looped around down line 10 and then threaded back
into and through tube 70. Prior to this operation, carrier A is
threaded onto down line 10 for free longitudinal movement along the
down line. The operation of the embodiment of the invention shown
in FIGS. 4 and 5 is similar to that described in connection with
the embodiment of the invention, shown in FIGS. 1-3.
Referring now to FIGS. 6, 6A and 6B, a further modification of the
present invention is illustrated. In this modicication, carrier X
is used for supporting primer B in a manner similar to the support
of the primer in carrier A. Carrier X is a unitary plastic
structure including an upstanding rib 170 having outwardly
extending arms 172, 174 and resilient flaps 176, only one of which
is shown. This structure is substantially the same as previously
described in connection with carrier A. Pairs 180, 182 and 184 of
slit rings 190, 192 are provided adjacent the outside edge of rib
170 to slidably support carrier on down line detonating cord 10.
Again, rib 170 provides spacing between detonating cord 10 and
primer B so that detonating cord itself will not directly discharge
primer B. Rib 170 also includes a plurality of laterally extending
cylindrical openings 200, 202, 204. Each of these cylindrical
openings receives a time delay cartridge 210 similar to the
cartridge 132 and booster or cap 160, as previously described. In
other words, a detonation wave at one end of cartridge 210 is
delayed before appearing at the opposite end thereof or before
causing detonation of the cartridge. The input ends 212 of
cartridges 210 are held by lateral openings 200, 202 and 204 in
detonation association with cord 10. In a like manner, the ouput
ends 214 of the time delay cartridges are inserted into specially
formed openings 216 within the side of primer B. Thus, the primer
is provided with axially spaced openings corresponding to openings
200, 202, 204. Of course, it is possible to allow the cartridges
210 to rest against the outer peripheral wall of primer B and still
cause detonation of the primer. In this particular embodiment, the
time delay for all cartridges 210, three of which are shown for
illustrative purposes, is the same. Consequently, upon detonation
of cord 10, the selected time delay of cartridges 210 expires
before detonation of primer B and therefore detonation of the
charge associated with the primer and the borehole C. To use
carrier X, carrier X is assembled onto cord 10. Thereafter,
cartridges 210 are inserted into openings 200, 202 and 204 and
primer B is snapped into the carrier. Then, carrier X can be
dropped into the borehole C by sliding along detonating cord 10.
This provides a sliding connection between carrier X and cord 10
without destroying the detonation continuity between the cord 10
and time delay cartridges 210. Thus, carrier X can be used in the
method similar to that shown in FIG. 7 in the same manner as
carrier A.
PREFERRED METHOD
Referring now to FIGS. 7 and 7A, the preferred embodiment of the
method practiced in accordance with the present invention is
illustrated. In accordance with this method, explosive charges 250,
252, 254 and 256 are deposited into borehole C as shown in view IV
of FIG. 7. This explosive material may be of any standard
composition such as ANFO or ammonium nitrate slurry, to name only
two. This material is generally immune from detonation by
detonating cord of the type having a strength in the neighborhood
of 30-60 grains per linear foot but is detonated by any of several
standard primers. The primers can be detonated by the detonating
cord 10. Each of the charges is in a separate axial location in
borehole C. These charges are separated by layers 260, 262, and 264
formed from various materials such as soil. Although not necessary,
a cap of earth or soil 270 may be applied above the uppermost
charge 256. In accordance with the present method, a carrier, such
as carrier A, constructed in accordance with the present invention
may be connected to the end of down line 10 by bringing down line
10 through the split rings 54, 56 and then upwardly through the
central bore in a primer B. Then, an appropriate knot K in cord 10
can be provided above primer B for holding the cord onto the
lowermost carrier A. This carrier is then dropped into borehole C.
Thereafter, the charge 250 is deposited in the borehole and covered
by layer 260. Then, a second carrier A.sub.2 is connected, as shown
in FIGS. 1 or 4, and dropped down the detonating cord 10, as shown
in FIG. 7. When carrier A.sub.2 is in place, the explosive material
of charge 252 is deposited into borehole C. Then layer 262 is
positioned over charge 252. A third carrier A.sub.3 is then
assembled onto down line 10 and dropped into the borehole as best
shown in view I of FIG. 7. This process is continued until the
borehole is filled and charged as shown in view IV of FIG. 7.
Referring now to FIG. 7A, a timing graph or time layout plan used
in one embodiment of the present invention is illustrated. In this
embodiment, the time delay provided on carrier A.sub.2 is 25 ms.
Carrier A.sub.3 has an illustrated time delay of 100 ms and carrier
A.sub.4 has an illustrated time delay of 175 ms. Thus, with
instantaneous detonation of down line 10, the primers are detonated
in sequence. The first time spacing between carriers A.sub.1 and
A.sub.2 is approximately 25 ms. The other time spacings are 75 ms.
Thus, within 175 ms after detonation of cord 10 by trunk line T,
all explosive charges within borehole B are detonated. There has
been no instantaneous detonation of the total borehole, therefore,
governmental regulations regarding the amount of material exploded
within a given distance from an inhabited building or other
structure is satisfied by selecting the amount of explosive
material in the respective charges and by selecting the time delay
between detonation of the axially spaced charges. In practice, the
time delay between successive detonations is at least 8 ms and the
time spacing is generally less than time spacing used in FIG. 7A,
which is provided for illustrative purposes only. The illustrated
embodiment is used as an example because standard somewhat
inexpensive time delay devices are provided with the illustrated
time delay values. As previously indicated, the time in
milliseconds required to detonate along a standard detonating cord
is less than a value obtained by dividing the length of the cord by
20. This value is set forth in FIG. 7A. Since this value is
extremely small compared to the time delays used in the field and
as illustrated in FIG. 7, the delay in cord 10 can be
disregarded.
ANOTHER EMBODIMENT OF THE PRESENT INVENTION
Referring now to FIG. 8, still a further embodiment of the present
invention is illustrated. In this embodiment, carrier Y supports
primer B' in a generally horizontal direction for insertion into
borehole C, and includes a generally vertical rib 300 for
supporting axially spaced paris 302, 304 of slit rings 306, 308.
Thus, carrier Y is assembled onto detonating cord 10 in accordance
with the procedure used in previous embodiments of the invention.
Rib 300 separates the detonating cord from primer B' so that there
is no direct primer detonation. Spaced, generally resilient arms
310, 312 are each provided with spaced abutments 314, 316 which are
generally spaced from each other a distance corresponding to the
axial length of primer B'. Inclined walls 318 allows easy insertion
of primer B' in an axial direction. An upper flange 330 defines an
inclined support ledge 332 and carries an upper cord supporting
tube 334, similar to tube 70 of carrier A. Resilient flaps 336, one
of which is shown, are used to support primer B in carrier Y, as
illustrated in FIG. 8. An elongated time delay element 340 is
essentially the same as element 130, shown in FIG. 1. In accordance
with this structure, a time delay cartridge 342 is connected
between a first auxiliary detonation cord 344 and a second
detonation cord 346. The first auxiliary cord is looped around
detonation cord 10 after being passed through tube 334. The loose
end is then directed back through tube 334 to provide a detonation
connection with cord 10. A side bore 350 is provided in primer B'
and second auxiliary detonating cord 346 is directed from cartridge
342 through access hole 320 into this side bore 350. Thus, upon
detection of cord 10, cartridge 342 causes a time delay prior to
detonation of primer B' at bore 350 by detonating cord 346. This
modified carrier structure can be used in accordance with the
method illustrated in FIG. 7.
Still a further embodiment of the present invention, i.e. a carrier
Z, is illustrated in FIGS. 9-11. Carrier Z includes a vertically
extending rib 400 supporting an enlogated tube 402 spaced from a
downwardly opening cup 404 having a plurality of appropriate lugs
or other structures 406 for holding cast primer material 410 within
the cup. Thus, the primer material is not a separate primer but is
cast into a receptacle formed integrally with rib 400. To guide the
elongated time delay element on carrier Z, there is provided an
upper bracket 420 having spaced guide plates 422, 424 and a bore
426. Detonating cord 10 extends through tube 402 and bore 426 to
slidably mount carrier Z onto the cord. A pin 428 is spaced axially
from the aligned axes of tube 402 and bore 426. A tube 430
positioned at an angle and a vertical tube 432 having a bore 434
are used to support an elongated time delay device 440 of the type
having a time delay cartridge 442, a first detonating cord end 444
and a second detonating cord end 446. Detonating cord end 446 is
inserted into a bore 450 cast through primer material 410, as best
shown in FIG. 10. To assemble the elongated time delay device onto
carrier Z and deposit the carrier into borehole C, the detonating
cord is threaded through sleeve or tube 402, through bore 426.
Then, second end 446 of detonating element 440 is placed into
opening 450 in the cast primer. This locates the time delay
cartridge 442 within bore 434 of tube 432. Thereafter, the second
end 444 of the time delay element 440 is threaded through tube 430
around pin 428 and between spaced guide plates 422, 424. The
spacing of pin 428 from the normal position of cord 10 holds the
elongated time delay element adjacent to down cord 10. Thus,
carrier Z can be dropped into the borehole in a manner previously
described for performing the method as described in connection with
FIG. 7. The friction contact, if any, between the time delay
element and down cord 10 is relatively slight and is not sufficient
to prevent or inhibit downward movement of carrier Z into the
position necessary for a time delay discharge of primer material
410.
PREFERRED EMBODIMENT OF THE PRESENT INVENTION
Referring now to FIGS. 12-15, the preferred embodiment of the
present invention is illustrated. In accordance with this
embodiment, carrier P includes a molded plastic body 500 supporting
a cast in place primer material 502 in a generally cylindrical,
upwardly opening cavity 504. A center bore 506 is provided within
cast primer material 502. In accordance with this embodiment of the
invention, an outwardly extending, elongated wing 510 includes
parallel bores 512, 514 intersecting at an elongated slot 516. A
diametrically opposite wing 520 includes an elongated bore 522 with
a shoulder 524. These two diametrically opposed, radially extending
wings 510, 520 are joined by an arcuate, downwardly extending guide
plate 530 having an arcuate slot 532 with an outer periphery
defined by lips 534, 536. An elongated time delay element 540 is
provided for directing detonation between cord 10 and primer
material 502. As in other embodiments of the invention, this
elongated time delay element may take the form of a time delay
cartridge 542 having two auxiliary detonating cord sections 544,
546. The second of these sections is held within bore 506 by a
detent, illustrated as a stable 550.
In this preferred embodiment of the invention, cartridge 542 is
placed within bore 522 and rests upon shoulder 524. This prevents
downward movement of cartridge 542 beyond the position shown in
FIG. 12. Thereafter, the first auxiliary detonating cord section
544 is extended around guide plate 530 and in slot 532. In
addition, this detonating cord section is threaded axially through
parallel bore 512. The second auxiliary detonating cord section 546
is threaded into bore 506 and held therein by staple 550. Then
carrier P is threaded onto down cord 10 and dropped into the
borehole. Slot 516 allows sliding contact between cord 10 and cord
section 544. The width of this slot is substantially less than the
diameter of cords 10, 544 so that the cords remain in the
respective 512, 514. As in all carriers constructed in accordance
with the present invention, carrier P is deposited at a lower
position in the borehole. Thus, as the borehole C is filled, the
carrier goes to a different position longitudinally along down line
detonating cord 10. In this embodiment of the invention, there is a
side-by-side, generally elongated contact between the time delay
element and down cord 10. This is accomplished by the parallel
intersecting bores 512, 514 which are so dimensioned to maintain
relatively close contact between the two adjacent detonating cord
elements. Generally, the two cords are in sliding engagement, as
shown in FIG. 15. By providing shoulder 524, the downward movement
of carrier P which causes a certain upward pull on detonating cord
section 544 will not dislodge the time delay device.
The various structural features in the several embodiments of the
invention could be incorporated in other embodiments. For instance,
a low energy detonating cord with a time delay booster or cap could
be used as the time delay element in the embodiment shown in FIGS.
12-15. In that instance, the booster or cap would be held within
primer material 502 by detent 550 and the low energy detonating
cord would be wrapped into the circuitous path illustrated in FIG.
12. Other cross modifications of the various illustrated carriers
could be provided without departing from the intended spirit and
scope of the invention.
* * * * *