CA2118528A1 - Detonator packaging method - Google Patents

Abstract

ABSTRACT
DETONATOR PACKAGING METHOD

A non-electric detonator assembly wherein a detonator is located substantially along the axis of a coil of initiation tubing, the initiation tubing being woundsuch that it may be unwound by drawing from the centre of said coil.

Description

AUS 1529 ~ ~.18 ~ 2 8 ,, "

DETONATOR PACKAGING METHOD
The present invention relates to a method of packaging non-electric detonators and detonator assemblies.

One common form of non-electric detonator has a length of initiation 5 tubing which is crimped into the detonator shell to form a detonator assembly.The initiation tubing for this type of non-electric detonator generally comprises plastic tubing, lightly coated on the inside with a mixture of reactive powder which is capable of transmitting a shock wave which starts a delay element (if fitted) to burn and finally cause initiation of the priming charge, which initiates 10 the base charge in the closed end of the detonator shell.

Production of detonator assemblies by attachment of a detonator to its initiation tubing is~ a specialised process which is carried out by the manufacturer. Following manufacture the detonator assemblies are transferred to storage magazines from which they are exported to local or overseas 15 distributors or directly to consumers.
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Distributors and customers at larger mine sites are likely to require large quantities of detonator assemblies, often several thousand in a single load.
This requires th0 use of specially marked and fitted trucks which are dedicateclto the exclusive transportation of explosives and depending on local law, these 20 trucks may be limited in the quantities of detonators carried, the times of travel on public roads and the number of escort vehicles required.

Legislation in most countries includes such specific requirements for the transportation of explosives to try and minimize the likelihood of initiation of a detonator in transit. Such events can have many causes including mishandling 25 or truck accident. Most countries base their legislative requirements for transportation of explosives on the "Recomendations on the Transport of Dangerous Goods" issued by the United Nations and the United Nations prescribed testing codes for establishing the acceptablility of various packaging -2118~28 . ,~.

and transportation methods for dangerous goods.

With respect to the transportation of detonators, the UN's 1.4B Code of testing is generally accepted as the relevant criteria.
In general it is preferable that when detonators are packed together for storage5 and transportation that inadvertent initiation of one detonator will not lead to mass initiation of other detonators. In other words, compliance at least in partwith the following criteria is preferable;
1. initiation of a single detonator in a box of assemblies will not cause the instantaneous initiation of a significant number of other units (sometimes referred to as the "Case Test") and 2. if a box of assemblies is burnt, initiation of an individual unit will not cause instantaneous initiation of a significant number of other units (sometimes referred to as the "Bonfire Test").

To achieve the first objective the packaging must necessarily prevent a detonator from initiating either the base charge or the initiation tubing of a significant number of other detonators. With respect to the second objective, initiation tubes (which is generally made of plastic) will be non-functional before the temperature of the fire is high enough within the detonator to cause thermalinitiation. Hence direct initiation of detonators by shrapnel and shock is the major incident to consider.

Various attempts have been made in the past to minimize the likelihood of cross propagation of detonators whilst maintaining a practical packing density. For example, polystyrene packages have been approved by the UK
and Australian authorities for the transport of detonators comprising No.8~
delay elements (with no initiation tubing). These packages essentially consisted ~:
of a polystyrene lid and top which included cavities into which the detonators were laid 'top to tail'. The separation between the base charges of the detonators was about 50 mm and the package had overall dimensions of approximately 300 x 150 x 30 mm, however this type of packaging was not commercially practical for non-electric detonator assemblies as it would lead to uneconomic packing density.

UK and Australian authorities have also approved a method of packaging electric detonators having long lead wires which method consisted of forming the lead wires into a '~igure 8" coil and locating the detonator as far ~i 5 as possible inside the wire bundle. While this concept can be applied to electric detonators having long lead wires, it is not suitable for detonators having lead wires of shorter length which cannot provide enough separation between the detonators.

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In another attempt to provide a method of safe transportation of detonators, No.8 detonators with no initiation tubing attached have been stored in packages or blocks constructed of compressed paper. These packages are approximately 290 x 50 x 20 mm and holes 11 mm in diameter are drilled through the block in a pattern on 30 mm centres. The bottom of the block has a cardboard sheet stapled on and the top is covered with a cardboard sheet into which crosses are cut to line up with each hole. This allows the detonatorsto be pushed into the holes and be retained in place.

It has now been found tha~ non-electric detonator assemblies may be packaged in such a manner as to reduce the likelihood of one detonator initiating either the base charge or the initiation tubing of a significant number of other detonators. This packaging utilises initiation tubing to help protect the detonator any shock wave emitted from the detonator. The current invention ..
therefore provides a detonator located substantially along the axis of a coil of - .
initiation tubing, the initiation tubing being wound such that it may be unwoundby drawing from the centre of said coil. There is further provided a method of packaging non-electric detonator assemblies comprising a detonator and initiation tubing wherein said detonator is located substantially along the axis of a coil of said ini~iation tubing, the initiation tubing being wound such that it may be unwound by drawing from the centre of said coil.
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It is particularly preferred that the detonator is located within the coil of ;~

2118~28 initiation tubing such that any shockwave from the detonator base charge may be attenuated by the coil of tubing.

It will be apparent to those skilled in the art that a coil may be formed such that it can be unwound by drawing the free end from the outside of the coil or from the inside or centre of ~he coil. It is a feature of the current invention that the coil of initiating tube be able to be drawn from the centre.

The current invention further provides a method of packaging and transporting detonator assemblies which method comprises locating a .
. detonator substanitally along the axis of a coil of initiation tubing, the initiation tubing being wound such that it may be unwound by drawing from the centre of said coil and packing said detonator assemblies in alternate packing rows within a storage container.
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When a detonator is initiated, the majority of shrapnel occurs in two distinct areas. The first is in a ring that flows out from near the top of the detonator base charge and the second is in the form of a slug emitted axially from the bottom of the detonator. In air, radial shrapnel can cause initiation of an adjacent detonator at 120 mm separation and the axial shrapnel can cause initiation at least up to 300 mm separation. In other, low shrapnel areas, initiation of a receptor detonator appears to be of the order of 50 mm. ;; -The initiating tubing which is used to form the coil of the current invention may belong to the detonator being protected or it may belong to another detonator. The windings of the coil may optionally be at least partiallyenclosed by a coil container or alternatively a flange may be located at either end of the coil. Cylindrical plastic cages or shells having integral endplates may be used to enclosed or contain the coil and these are particularly preferred because they are convenient to produce by common industrial methods such as injection moulding.

2:118~28 The coil of initiation tubing may optionally be enclosed in a wrapping of polymeric film, paper wrap or the like. Other options include sliding a metal, cardboard or plastic sleeve over the coil and sticking, heat welding or solvent welding the ends of the sleeve to the flanges or end plates.

The detonator initiation tubing may be provided with a connector for attaching the initiation tubing of the coil of the current invention to other initiating explosives such as detonating cord, detonators ! other signal tubes.For example, the connector may comprise a J-hook for attaching initiation tubing to a mainline consisting of detonating cord. Alternatively the coil container or flange may include an appropriately shaped openings, slots or retaining means which can be used to serve an equivalent purpose.

The coil of initiation tubing can be formed by numerous means. In a ~ ~ ~
particularly preferred embodiment method of manufacture two flanges are ~:
located on a mandrill and positioned the required distance apart by two outer, locking rings. The initiation tube is then wound up and down the mandrill ~
between the two flanges. When the required amount of tubing has been --wound on, the free end of the tube is secured by, for example, sticking down with adhesive tape or pulling into a suitable notch in one of the flanges. A
length of heat shrink tubing is slid over the unit such that when heated in an oven or with a stream of hot air, the tubing shrinks to hold the coil and the two flanges together. One of the outer locking rings is then removed and the coil isslid off the mandrill. To finish the unit off a J hook or other su.~able connector :
is passed along onto the inner (or leading) end of the tube and a detonator is then crimped on. The detonator is then inverted and inserted through one of the flanges into the coil such that it lies substanitally along the axis of the centre of the coil.

In one method of manufacture, a cylindrical coil container is used instead of two flanges, the two end plates of the coil container having central holes toallow access and removal of a mandrill for coiling the init;ation tubing. One end of a suitable length of initiation tubing is fed into the coil container through a ~118~28 3 ~ `

slot in the wall and out through the hole in one of the end plates until about 50 mm of initiation tubing protrudes through the hole. A suitable mandrill is inserted through the hole in the end plates such that the initiation tubing is captured by the mandrill. The mandrill is then rotated such that the tube will 5 coil around the mandrill and be drawn in through the slot in the container.
When sufficient initiation tubing has been wound onto the mandrill the initiation tubing is cut off and the trailing end can either be attached to the outside of the coil container or drawn inside. The mandrill is then withdrawn leaving the leading end of the initiation tubing protruding from one of the end plates. It 10 would be particularly advantageous and cost effective to carry out the above method of assembly by a dedicated machine designed to thread, coil, cut and `
seal the tube automatically. These methods are generally all designed to produce a draw from centre coil but other suitable method will be readily apparent.
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Where used herein the term "alternate packing rows" refers to the packin~ of protectors such that no protector is located directly in alignment with other protectors in the rows above or below. In a preferred embodiment the units comprising protectors enclosing the detonator assemblies are packed in storage containers storage containers such as cardboard boxes or the like, 20 by arranging a base layer of units in a close packed or square packed array, then placing a second layer of inverted units such that they fill or point towards the interstitial spaces of the base layer. A third layer of units repeats the arrangement of the base layer and a forth layer repeats the arrangement of the second layer.

With this packing arrangment there is a low probability that the base of ;~ one detonator may be directed at the initiation tubing or the base charge of a second unit and the second unit could be initiated. However, whilst two units could fire, propagation to further units is unlikely. This packaging method willalso meet 1.4B transport requirements, if packed in an alternative manner, for 30 example, if the storage container included egg crate type inner separators.
The invention preferably provides a method of packaging that will allow a high .

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2 ~ 2 8 packing density in storage containers.

The invention further provides a method of locating the detonator of the non-electric detonator assembly of the current invention in a borehole, which method comprises the steps of;

- pulling the detonator out of the coil of initiation tubing, - drawing the initiation tubing from the centre of the coil such that the detonator can be inserted in a primer which is then located in a borehole, -- loading the borehole with explosive and - clipping the detonator protector housing to a main line such that an initiation front travelling along the initiation line will be transmitted along the detonator initiation tubing.

In a further embodiment of the method of borehole loading using the non-electric detonator assembly of the current invention, a detonator and connector are attached to either ends of the coil of signal tube. The detonator is pulled out of th0 coil of initiation tubing and the connector used to connectsaid signal tube to a separate length of signal tube or detonating cord or otherappropriate component.

The current invention will now be described with reference to the drawings in which Figure 1 shows sectional views of different arrangement of the coil of initiation tubing within a coil container; Figure 2 depicts a sectional view of the coil and coil container of Figure 1 (a) including a detonator which has been crimped onto the end of the inner end of the initiation tubing; Figure 3 shows the outside of the coil container of Figure 2(a) and 2(b); Figure 4 is a -25 section view of the detonator, coil container and coil of initiation tubing of Figure 3.

Figure 1 (a) is a sectional view of a coil of initiation tubing of the non-electric detonator assembly of the current invention. The detonator initiation ;! 2118~28 tubing (1) is coiled inside a cylindrical coil container (2) which has integral end piates (3a,3b) provided with central holes (4a,4b) to allow access and removal of a mandrill for coiling of the detonator initiation tubing as described above. In use the leading end (5) of the tube is withdrawn from the centre of the coil, through the hole (4a) in the end plate of the coil container.

Figure 1(b) depicts initiation tubing (1) coiled inside a cylindrical cage (6) with integral end plates (7a,7b) and an odd number of vertical supports (8).
The two end plates have central holes to allow access and removal of a mandrill (9a,9b) for forming the coiled detonator initiation tubing as describedabove.

Figure 1 (c) depicts detonator initiation tubing (1) held in a coil between two end plates (10a,10b). Heat shrink material (11) has been used to secure the coil and end plates together.

Figure 1 (d) depicts the initiation tubing of Figure 1 (c). The detonator initiation tubing (1) is coiled between two end plates (10a,10b) but instead of heat shrink material being used to secure the coil and end plates together, a paper sleeve (12) encloses the entire assembly. The ends of the sleeve are glued (13a,13b) to the end plates.
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Figure 2(a) shows another sectional view of the initiation tubing of Figure 1 (a) with a detonator (14) crimped onto the end of the initiation tubing (5). The -detonator has been inverted and located within the coil such that the base ~ ~

charge is radially enclosed by the coil.
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Figure 2(b) shows the coil of initiating tubing, coil container and ~ ;~
detonator of Figure 2 with a J clip (15) attached to the detonator initiation tubing. The J clip may be attached to the signal tube or coil container in any convenient manner or integral with said coil containen Figure 2(c) shows the coil of initiating tubing, coil container and ,~

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- ~118~28 9 ::
detonator of Figure 2 with a second detonator (22) attached to the other end of the initiating tube. This detonator has a clip (23) attached.
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Figure 3(a) shows a side view of the coil container of Figures 2(a) and 2(b) to which has been added an optional detonator holder (16). The 5 detonator holder may be integral with the coil container or connected to the end plate by any convenient method including screw fittings, bayonet fittings, gluing or melt seaming. Figure 3~b) shows the coil container of Figure 3(a) rotated 1800 to show a recess (18) in the container which can be used to clip the assembly onto a main detonation line or similar. Figure 3(c) is an end on . . . 10 view of the detonator of Figure 3(a) viewed along the line BB'. The central hole (4b) in the end plate (3b) may optionally be closed off by a plug, cap or similar.

The dimensions marked on Figure 3 are estimated to be suitable for standard signal tube lengths up to 6 m and for detonator tubes of 60 to 90 mm length. Actual dimensions may be modified to suit the size of detonator and 15 length of initiation tubing.
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Figure 4 is a section view of the container of Figure 3 and shows a detonator located within the protector housing. The detonator is also shown in section view so that the delay composition (21), priming charge (20) and base charge (19) within the detonator shell can be clearly seen. The base charge is 20 located anywhere within the coil of intiation tubing but the centre of the coil is the optimal location. The initiation tubing of the detonator leads from the openend of the detonator, down the central cavity of the coil container and the restof the initiation tubing is coiled around in the coil container.

Example 1 25 The following example compares some optimal packing density for detonator assemblies of the current invention with packing densities for detonator assemblies of the prior art in respect of standard size packing cases. The preferred embodiment used in Example 1 is that depicted in Figure 2(b). The packing method of the prior art consisted simply of making loops in the , i~

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initiation tubing of the detonator unit and using a cardboard sleeve or elas~ic band to constrain the loops. The units were laid in the packing case with their detonators all pointing in the same direction and most detonators concentrated in specific areas of the case~

Case Size (mm) Prior Art Method Current Invention No. of Units No. of Units .
. 10 610 x 310 x 480 approx. 300 370 (6.1m initiation tubings) 440 x 310 x 250 approx. 100 180 (3.6m initiation tubings) It is clear from a comparison of the numbers in Table 1 that the method of packaging of the current invention may in certain circumstances be more efficient than the method of the prior art. ~ -It will be apparent to the person skilled in the art that packing comparisons will -vary depending on the size of packing case with the method of packaging of the current invention providing the potential for packing densities which are : ::
higher than those achieved using packing methods of the prior art. ~ ~

Example 2 ~ ~:
Example 2 illustrates the cross propagation characteristics of the current invention using the embodiment depicted in Figure 1 (c). A coil was formed ~ .
25 using 2.4m of initiation tubing which included top and bottom flanges 25 mm apart. A separate detonator was inserted into the coil, that is it was not crimped onto the signal tube which formed the coil. Three un~s were placed at right angles to each other to locate the base charges of the detonators as :
close together as possible. The middle detonator was initiated with a separate length of signal tube. Neither of the outer two detonaotrs was initiated. One of i: -;
the outer signal tube coils was initiated.

i Example 3 Example 2 was repeated with 2.4m initiation tubings with top and bottom flanges 40 mm apart. The result was the same as for Example 2.

Example 4 Example 3 was repeated with 2.4m initiation tubings with flanges 35 mm apart and the units located parallel to each other, that is the centres of each unit were 50 mm apart and supported by thin card. No propagation to either detonators or signal tubes occurred.

Example 5 Example 4 was repeated with 3.6m tubes with flanges 35 mm apart and the units located parallel to each other, that is the centres of each unit were 50mm apart and supported by thin card. No propagation to either detonators or signal tubes oocurred.
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Claims (2)

1. A non-electric detonator assembly wherein a detonator is located substantially along the axis of a coil of initiation tubing, the initiation tubing being wound such that it may be unwound by drawing from the centre of said coil.

2. A non-electric detonator assembly according to claim 1 wherein said detonator is located substantially along the axis of said coil of initiation tubing such that said initiation tubing is capable of attenuating a shockwave from the base charge of said detonator.

4. A non-electric detonator assembly according to claim 1 or 2 in which a container at least partially encloses the windings of said coil.

5. A non-electric detonator assembly according to any of the preceding claims which further comprises a connector for attaching said initiation tubing to other initiating explosives.

6. A non-electric detonator assembly according to any of the preceding claims wherein said detonator is attached to the end of said initiation tubing located nearer the centre of said coil.

7. A non-electric detonator assembly according to any of the preceding claims wherein detonators are attached to both ends of said initiation tubing.

8. A method of packaging non-electric detonator assemblies comprising a detonator and initiation tubing wherein said detonator is located substantially along the axis of a coil of said initiation tubing, said initiation tubing being wound such that it may be unwound by drawing from the centre of said coil.

9. A method of packaging non-electric detonator assemblies according to claim 8 wherein said detonator is located substantially along the axis of said coil of initiation tubing such that said initiation tubing is capable of attenuating a shockwave from the base charge of said detonator.

10. A method of packaging non-electric detonator assemblies according to claim 8 or 9 which further comprises at least partially enclosing the windings of said coil within a container.

11. A method of packaging non-electric detonator assemblies according to any of claims 8 to 10 which further comprises locating a flange at either end of said coil and enclosing said coil and flanges in a wrapping material.

12. A method of packaging non-electric detonator assemblies according to any of claims 8 to 11 which further comprises a connector for attaching said initiation tubing to other initiating explosives.

13. A method of packaging non-electric detonator assemblies according to any of claims 8 to 12 wherein said detonator is attached to the end of said initiation tubing located nearer the centre of said coil.

14. A method of packaging non-electric detonator assemblies according to any of claims 8 to 15 wherein detonators are attached to both ends of said initiation tubing.

15. A method of packaging non-electric detonator assemblies which method comprises;

locating said detonator within a coil of initiation tube according to any of of the preceding claims and packing said detonator assemblies in alternate packing rows within a storage container.

16. A method of locating a detonator in a borehole which comprises the steps of;
- pulling the detonator out of said coil of initiation tubing as described in any of claims 1 to 7, - feeding the initiation tubing out of said coil such that the detonator can be inserted in a primer which is then located in a borehole, - loading the borehole with explosive and - connecting the signal tubing to a main line such that an initiation front travelling along the main line will be transmitted along the initiation tubing to said detonator.

17. A method of packaging non-electric detonators as herein described with reference to the Figures.

18. A method of loading a borehole substantially as herein described with reference to the Figures.