AU682552B2 - Detonator protector - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "DETONATOR PROTECTOR" The following statement is a full description of this invention, including the best method of performing it known to me:- AUS 1549 2 DETONATOR PROTECTOR The present invention relates to a protector for detonators and a method of packaging detonators for transport and storage.

Detonators may be broadly divided into two types, either electric or nonelectric, depending on the manner in which they are initiated. When detonators are attached to an initiation means such as electric leg-wires or signal tubing, the assembled unit is commonly termed a detonator assembly.

Electric detonators generally have a fusehead within the detonator shell, the fusehead being initiated by electric current transmitted along the legwires.

Non-electric detonators are commonly attached to a length of signal tubing, which comprises plastic tubing, lightly coated on the inside with a reactive powder which is capable of transmitting a shock wave to the detonator and thus initiating it.

While many different types of detonators exist, those used for civilian purposes generally comprise only a delay element (which is optional), a priming charge and a base charge which are enclosed within a metal shell. When an initiating shock wave or electric current is transmitted to the detonator, the delay element burns, then the priming charge is initiated and finally the base charge in :i the closed end of the detonator shell explodes.

0The storage and transpirt of dangerous goods such as detonators and detonator assemblies generally requires licenses and is regulated by law in almost :i all countries. Often manufacturers and large mine sites need to store hundreds of detonators in their magazines. Statutory requirements usually dictate many parameters such as the material of construction of the magazine, type of lighwing protection, security standards and the minimum distances of the magazine from other constructions.

Detonators are often transported from one site to another in specially marked and fitted trucks which are exclusively dedicated to the transportation of I- ~slC -r Iplp 3 explosives. Depending on local law, these 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 minimise the likelihood of initiation of a detonator in transit. Such events can have many causes including mishandling, lightning strike or road accident. Most countries base their legislative requirements for storage and transportation of explosives on the "Recommendations on the Transport of Dangerous Goods" issued by the United Nations plus the United Nations' prescribed testing codes for establishing the acceptability of various packaging and transportation methods for dangerous goods.

With respect to the transportation and storage of detonators, the United Nations' 1.4B Code of testing is generally accepted as the relevant criteria. In general it is preferable that when detonators are packed together for storage and transport, inadvertent initiation of one detonator will not lead to mass initiation of other detonators. In other words, compliance at least in part with the following criteria is preferable; 1. initiation of a single detonator in a box of assemblies will not cause the 20 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 S.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 in the bonfire test. With respect to non- S. electric detonator assemblies, initiation tube (which is generally made of plastic) will melt and become non-functional before the temperature of the fire is high c I enough within the detonator to cause thermal initiation. Hence direct initiation of detonators by shrapnel and shock is the major incident to consider.

When an unprotected 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.

Various attempts have been made in the past to minimise 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 "figure 8" coil and locating the detonator as far as possible inside the wire bundle. While this concept can be applied to electric detonators it is not suitable for non-electric detonators fitted with signal tube as the signal tube is an active component of the assembly.

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 I I R 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 detonators to be pushed into the holes and be retained in place.

In yet another attempt to provide a safe transportation holder and package for detonators US Patent No. 5,133,258 discloses the use of a holder having an internal cavity and surrounded by concentric, cylindrical elastomeric walls which are spaced radially from one another by concentric cylindrical spaces or air gaps.

In use, the detonator shell is flush with the walls of the cavity and this snug fit is sufficient to prevent the holder falling off the detonator.

It has now been found that detonators may be packaged in such a manner as to reduce the likelihood of detonator to detonator propagation of an explosion.

This is primarily achieved by providing a free volume around the base charge of the detonator to allow for initial expansion of the products of a detonation.

The current invention therefore provides a protector for use in the transportation and storage of detonators comprising, 20 a detonator holder which is open at one end for insertion of a detonator and closed at the other end, and which radially encloses the base charge of said detonator, at least one detonator retaining means integral with the detonator holder, and a first wall which is radially spaced around the holder, and wherein the holder and wall define a space, wherein in use, the detonator retaining means holds the detonator within the holder such that a free volume is provided around the base charge of the detonator.

II I LI ~Y 6 There is further provided a method of packaging detonator assemblies by inserting detonators in the protector of the current invention and placing the protected detonators on either side of an insert in a packing case such that the detonators point away from the detonator initiation means. Using this packaging method the shrapnel and shock waves from an exploding base charge is unlikely to impinge upon the initiation means of the detonator assemblies.

Where the initiation means is signal tubing it is important that the detonators are positioned such that if one detonator explodes it will not cause a shock front to pass along the signal tubing of neighbouring assemblies and initiate their attached detonators. While this packing arrangement can also be used for electric detonators, the packing arrangement is clearly not critical because no matter how close a detonator explodes to leg-wires, the detonation will not cause any flow of electric current in the leg-wires.

The protector of the current invention provides for a free volume around the base charge of the detonator and this free volume may optionally extend along the entire length of the detonator shell.

The protector may optionally comprise at least one outer wall which is radially spaced about the first wall, each pair of adjacent walls defining a space.

In a particularly preferred embodiment the protector of the current invention comprises one outer wall and the protector is constructed of high density polyethylene (HDPE). The provision of a free volume around the detonator, an outer wall and the use of HDPE as construction material has been found to be particularly advantageous. Using this embodiment of the protector, number 8* Sdetonators (which comprise 780 milligrams of pentrerythritol tetranitrate, PETN) 25 may be packed with an inter-detonator spacing of as little as 2 centimetres before a shock front from one detonator will initiate neighbouring detonators. Where no outer wall is provided the minimum inter-detonator spacing is 3.5 centimetres.

o°"S S. S o S -II -PI I The detonator retaining means may comprise any conveniently configured projections on the interior of the holder. Fins extending the length of the interior of the holder are particularly preferred.

The protector of the current invention may be used as an independent unit or two or more may be joined together or manufactured together to form a set.

The protectors may be joined together by any convenient means such as sticking, heat welding or solvent welding protectors. Alternatively a single moulding or similar process may be used to form a set. Where the material of construction is an elastomeric substance the individual protectors may be joined by a web of the elastomer. Using sets of several protectors joined together may be advantageous where improved packing density is required.

It is particularly preferred that the individual protectors or sets be located in alternate packing rows. Where used herein the term "alternate packing rows" refers to the packing in which no protector is located directly in alignment with other protectors in the rows above or below. In a preferred embodiment the protectors are packed in storage containers such as cardboard boxes or the like, 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 20 arrangement of the base layer and a forth layer repeats the arrangement of the second layer.

C

With this packing arrangement there is a low probability that one o.:i detonator may be located in direct alignment with a second unit and that the second unit could be initiated. However, whilst two units could fire, propagation to further units is unlikely.

Ce This method of packaging is particularly useful for detonators without attached initiation means. Various packing densities can be obtained depending Son various parameters including the size of the detonator, the configuration of the I I~ X rs 8 protector, the dimensions of the packing case and the method of packaging of the current invention.

The current invention will now be described with reference to the drawings in which Figure 1 shows sectional views of one embodiment of the protector; Figure 2 depicts a plan view of an array of protectors; Figure 3 shows a sectional view along BB' of Figure 2; Figure 4 is a perspective view of detonator assemblies in a packaging case.

Figure l(a) clearly shows a cylindrical detonator holder having an open end (la) and a closed end (Ib) within which is located a detonator retaining means comprising several fins which are integral with the interior of the detonator holder. A wall is radially spaced around the holder and the holder and wall define a space The top of the wall and the holder form a junction Figure l(b) is a cross sectional view along AA' of Figure l(a) and shows the wall the holder and the fins In use a detonator would be pushed into the holder and held in place by the fins, the space between the detonator shell and the holder forming a free volume.

Figure 2 depicts a set of individual protectors held together by a web of material to form an array. Where the protectors are constructed of plastic, the entire array could be formed by a single injection moulding process with a web of the plastic joining individual protectors. In use detonator shells would be placed in the holders the tops of the detonator shells projecting above the tops of the protectors. When another set of protectors is placed on top of the first, the tops of the detonator shells would be located in the interstitial space Figure 3 is a cross sectional view along BB' of Figure 2 with detonators inserted in the protectors. The detonators are depicted in cross section to show each base charge priming charge (9b) and delay element (9c) located within each detonator shell (9d).

L I P-M Figure 4 depicts detonator assemblies packed in a box (10) using a preferred packaging method. The box includes an insert (11) about which the detonator assemblies (12) are packed. The initiation means (12b) of each assembly is formed into a loop and each detonator (12a) is located in a protector (13).

Bundles of detonator assemblies are held together by a rubber band (12c) located around their looped initiation means. As shown in the diagram, bundles of detonator assemblies are packed with their detonators on alternate sides of the insert, the detonators pointing away from the loops of initiation means.

While the invention has been explained in relation to its preferred embodiments it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

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a* o* o« II e rl

Claims (10)

1. A protector for use in the transportation and storage of detonators comprising, a detonator holder which is open at one end for insertion of a detonator and closed at the other end, and which radially encloses the base charge of said detonator, at )east one detonator retaining means integral with the detonator holder, and a first wall which is radially spaced around the holder, and wherein the holder and wall define a space, wherein in use, the detonator retaining means holds the detonator within the holder such that a free volume is provided arourd the base charge of the detonator.

2. A protector according to claim 1 wherein the free volume extends along ~the entire length of the detonator shell.

3. A protector according to claims 1 or 2 wherein the detonator retaining S' means comprises projections on the interior of the detonator holder. o

4. A protector for use in the transportation and storage of detonators according to any of claims 1 to 3 wherein at least two protectors are joined together to form a set of protectors.

A protector according to any of the preceding claims wherein the material of construction is high density polyethylene.

6. A protector for use in the transportation and storage of detonators according to any of the preceding claims which further comprises at least -a I 11 one outer wall which is radially spaced about the first wall, each pair of adjacent walls defining a space.

7. A method of packaging detonator assemblies in a packing case, each detonator assembly comprising an initiation means and detonator wherein the detonator is located in the protector of any of the preceding claims and wherein the protector enclosed detonators are placed on either side of an insert in a packing case such that the detonators point away from the detonator initiation means.

8. A method of packaging using the protector of any of claims 1 to 6 wherein protectors are placed in a storage container in alternate packing rows such that no protector is located directly in alignment with other protectors in the rows above or below.

9. A detonator protector substantially as herein described with reference to the S.Figures.

10. A method of packaging detonators substantially as herein described with rre tFu i reference to the Figures. S.. 0. i• Ld~, ABSTRACT A protector for use in the transportation and storage of detonators comprising, a detonator holder which is open at one end for insertion of a detonator and closed at the other end, and which radially encloses the base charge of said detonator, at least one detonator retaining means integral with the detonator holder, and a first wall which is radially spaced around the holder, and wherein the holder and wall define a space, wherein in use, the detonator retaining means holds the detonator within the holder such that a free volume is provided around the base charge of the detonator. S 0 o S S