NO20220611A1

NO20220611A1 - A detonator holder and a method for installing a detonator to an explosive

Info

Publication number: NO20220611A1
Application number: NO20220611A
Authority: NO
Inventors: Risto Rahkola
Original assignee: Oy Forcit Ab
Priority date: 2021-05-28
Filing date: 2022-05-24
Publication date: 2022-11-29
Also published as: FI20215629A1; CA3160528A1; AU2022203517B2; AU2022203517A1; FI131088B1; SE2250612A1

Description

A DETONATOR HOLDER AND A METHOD FOR INSTALLING A DETONATOR TO AN EXPLOSIVE

Background of the invention

The present invention is related to a detonator holder according to the preamble of claim 1, which is used for attaching a detonator to an explosive, particularly to an explosive having a hard plastic or metal cover. The invention is also related to a method according to the preamble of claim 10 for installing a detonator to an explosive. The object of the detonator holder and the method utilizing the same is to form a watertight structure in order to protect the explosive, to prevent the detonator from moving under external forces, and to align the detonator on the explosive such that the explosive power of the detonator is directed at the explosive.

Explosives designed to be safe are so unsensitive, that a detonator must always be used for detonating such low-sensitivity explosives. Conventionally, the detonator is pressed into the explosive mass of an explosive or into an empty cavity formed in the explosive intended for the detonator. However, retention of the detonator in such conventional installation methods is uncertain due to vibration or movement during the installation. As a result, an air gap is easily formed between the detonator and the explosive. As the detonator moves in a drill hole containing water, the water is able to enter under the bottom of the detonator, which may result in complete failure of the explosive or in partial power deficiency.

Nowadays, explosives are often formed by a viscous mass in which the detonator is planted. When the explosive mass is cold, it is difficult to set the detonator in place, and the cold mass does not necessarily form proper adhesion, allowing the detonator to move or even detach. A similar problem arises when using a hot explosive mass, which allows the detonator to be easily planted, but as the heat lowers the viscosity of the explosive mass, the explosive mass might not adhere to the detonator properly, allowing the detonator to move or even detach. When planting the detonator directly to the mass, resulting from a transverse pull on a shock tube or electrical conductor associated with the detonator, the detonator may be misaligned diagonally. In the worst-case scenario, this may result in total failure of the explosive.

The charge, i.e. the detonator and the explosive, may also have to be dismantled for some reason. Mechanical locking mechanisms for the detonator may have such a weakness that, once the detonator is attached, it is impossible or difficult to remove it without tools. Using force to remove a detonator is always a safety risk.

The presented problems have been attempted to be solved for instance as disclosed in patents EP 3 612 786, US 6 112 666, and US 9 115963 by locking the detonator with mechanical claws. In these solutions sufficient retaining is achieved only with detonators having certain lengths, which is not optimal as detonators may have varying lengths due to the detonators comprising different delay elements. The structures disclosed in said patents are also not watertight.

The worst consequence of the problems described above, for example in the mining industry, is that the blasting of a borehole full of explosives fails in part or completely. As a result of the failure, the charge must be disarmed, for example, mechanically. Regardless of the method of disarming, such work always poses a huge safety risk to the site.

Brief description of the invention

The object of the invention is therefore to provide a detonator holder with which the above-mentioned problems can be largely avoided.

This object is achieved in that the detonator holder and the method for installing the detonator according to the present invention have the features defined in the claims. More specifically, the detonator holder according to the invention is mainly characterized by what is set forth in the characterizing part of claim 1. Respectively, the method for installing a detonator according to the invention is mainly characterized by what is set forth in the characterizing part of claim 10.

Preferred embodiments of the invention are the subject of dependent claims.

The invention is based on that the detonator holder must fit tightly in place, while aligning the detonator in a watertight manner in a cavity in connection with explosive mass.

The invention provides significant advantages. The structure of the detonator holder is very simple and can be made of polymer at a low cost, for example by injection molding or 3D printing in mass production.

The invention makes it possible to attach a detonator to an explosive in a simple manner. Attaching a detonator to, for example, a powdered explosive mass is otherwise almost impossible without additional means requiring additional work, such as attaching the detonator to the explosive by taping, etc.

Due to its flexible construction, the detonator holder according to the invention remains in place despite vibration, pull, or other external forces, even if the load is many times the weight of the product. Nevertheless, the detonator holder installed in the explosive, or the detonator holder with a detonator arranged in it, can be safely removed, and reattached without special tools.

The present detonator holder installed in place also forms a watertight plug in the cavity of the explosive, both with and without the detonator provided therein.

The present detonator holder also always aligns the detonator arranged therein such that the detonating force of the detonator is applied to the explosive and is not, for example, directed at the protective cover of the explosive.

Other advantages of the invention will be apparent from the following detailed description of specific embodiments of the invention.

Brief description of the figures

In the following, preferable embodiments of the invention will be described in more detail with reference to the accompanying drawings, in which figure 1 illustrates a schematic axonometric view of an embodiment of the detonator holder as viewed from elevation obliquely behind,

figure 2 illustrates a side view of a longitudinal section A-A of the detonator holder of figure 1 installed in an explosive,

figure 3 illustrates a schematic axonometric view of a second embodiment of the detonator holder as viewed from elevation obliquely behind,

figure 4 illustrates a side view of a longitudinal section B-B of the detonator of figure 3 installed in an explosive,

figure 5 illustrates a top view of the detonator holder of figure 3, figure 6 illustrates a side view of the detonator holder of figure 3, figure 7 illustrates a side view of a third embodiment,

figure 8 illustrates a side view of the use of the detonator holder of figure 3 when installing the detonator, the explosive partially cut open for improved visibility,

figure 9 illustrates a completed installation of the detonator holder of figure 6, and

figure 10 illustrates a section of the detail C of figure 9, wherein the detonator holder is locked in place.

Detailed description of preferable embodiments

In the present figures, the detonator holder is not shown to scale, but the figures are schematic, illustrating the basic structure and operation of the preferred embodiments. In this case, the components indicated by reference numerals in the accompanying figures correspond to the components indicated by reference numerals in this specification. In the following description the terms 'substantially cylindrical', or 'cylinder' refer to the general shape of parts as illustrated in the figures and are not meant to be interpret as exact shapes as defined in geometry.

It is very important that the detonator used in blasting is placed in connection with the explosive during charging, as the most commonly used explosives are low-sensitivity explosives and require direct contact of the detonator with the explosive or a very small air gap between the detonator and the explosive. If water is able to enter the air gap between the detonator and the explosive, the worst consequence may be that, for example, the explosion of a borehole full of explosives fails. In general, a product failing completely or partially in blasting operations poses an immediate safety risk and figuring out the cause for failure alone can be time consuming and result in high costs. It is therefore important that the detonator can be reliably locked in place in connection with the explosive.

Figures 1 and 2 illustrate a first preferred embodiment of the detonator holder 1, which in this case comprises a body with a substantially rotationally symmetrical, preferably substantially cylindrical, outer mantle 2 with opposite and substantially parallel top 3 and bottom 4. The substantially cylindrical shape in this embodiment is a truncated cone shape. Of course, the detonator holder may comprise any truncated cone-shaped body, in which case it may have a crosssectional shape which is polygonal, for example rectangular or triangular, or oval.

The detonator holder 1 comprises a channel 6 extending through the detonator holder in the direction of its longitudinal axis. However, a thin, easily permeable protective film 7 may be provided in the bottom 4 to close the cylindrical channel. Preferably, permeability of this film is implemented such that the film comprises one or more sections with reduced thickness in order to facilitate penetration of the detonator 8 through the protective film, when the detonator is mounted on the detonator holder.

Figure 2 illustrates installation of the detonator holder into a cavity 10 in the explosive 9, wherein in this case it cooperates with a conical mouth of the cavity. For this purpose, the outer mantle 2 of the detonator holder is extended over substantially the entire cross-section of the cavity, both in terms of the crosssectional shape of the detonator holder and its outer diameter, which can be from 10 mm up to 50 mm.

Figures 3 to 7, in turn, illustrate a second preferred embodiment of the detonator holder 1, which also comprises a body with a substantially rotationally symmetrical, preferably substantially cylindrical, outer mantle 2 with opposite and substantially parallel top 3 and bottom 4. As described above, the detonator holder comprises a channel 6 extending through the detonator holder in the direction of its longitudinal axis. However, a thin, easily permeable protective film 7 may be provided in the bottom 4 to close the cylindrical channel. Preferably, permeability of this film is implemented such that the film comprises one or more sections with reduced thickness in order to facilitate penetration of the detonator 8 through the protective film, when the detonator is mounted on the detonator holder.

The inner diameter (D) of the channel 6 of this detonator holder according to Figures 3 to 7 is typically 0.5 mm larger than the diameter of the detonator 8 to be mounted thereon, for example, for the common 7.5 mm diameter detonators, the inner diameter of the channel is thus 8.0 mm. The inner diameter (D) of the channel of the detonator holder may be constant or at least partially constant. Alternatively, the channel of the detonator holder is adapted to comprise a convexly expanding compression strip near the top end of detonator holder and expanding towards the top, cf. the area indicated by the broken line in Fig. 4. Further, the diameter of the channel may also substantially follow the outer diameter of the detonator holder.

The outer mantle 2 of the detonator holder 1 comprises at least two successive zones in the direction of the longitudinal axis 5. Figure 7 illustrates a truncated cone part 12 tapering from the top 3 towards the bottom 4 and a cylinder part 13 further connected to it and in this embodiment ending in the bottom. A functionally preferable embodiment is illustrated in figure 6, wherein the outer mantle 2 further comprises a conically tapered mounting portion 14 in its part adjoining the bottom 4. This conically tapered mounting portion 14 further facilitates guiding the detonator holder into place in the cavity 10 of the explosive 9, for example mechanically.

The body formed by the detonator holder 1 comprises at least one wedge-shaped slit 15 extending from the top 3 towards the bottom 4 and parallel to the longitudinal axis 5 of the body. Preferably, there are 2 to 6 of these slits such that they are arranged substantially symmetrically on a circumference 16 in the outer mantle 2 surrounding the channel. A preferred embodiment is obtained when there are two slits on opposite sides of the circumference, as illustrated in figures 1 to 7. The slits are preferably dimensioned so that at their widest point they are closed at least at the periphery 16 of the outer mantle 2 when the detonator holder is compressed into the cavity of the explosive 8. In this way, the detonator holder, together with the detonator mounted therein, forms a tight plug in the mouth of the cavity of the explosive. The length of the slit is in turn extended as far as possible in the direction of the longitudinal axis 5 towards the bottom 4. This results in a detonator holder that allows for greater tolerances while requiring as little force as possible to use even when the detonator holder is made of harder materials. It has been found that a preferable slit length is 50-95% of the length L of the detonator holder. The most preferred length is about 85% of the length L of the detonator holder.

The present detonator holder 1 is thus intended to be used for mounting a detonator 8 known per se on an explosive 9. Such an explosive can be formed, for example, by a pipe charge, a so-called booster used in connection with another explosive or a military explosive having a cover made of hard material. Figures 8 and 9 show an exemplary pipe charge/booster. The detonator can be an electric detonator, a shock tube detonator or a time fuse known per se, for instance.

The detonator holder 1 is intended to form a bond with which the detonator 8 is reliably and tightly attached to the explosive 9. For this purpose, the detonator holder must be of such a material that it is slightly flexible to be easily guided into the cavity 10 in the explosive, and also give in when the detonator is compressed into the channel 6. The detonator holder can therefore be made of, for example, a flexible polymer, an elastomer, or a flexible composite containing a polymer or an elastomer. The outer mantle 2 of the detonator holder can also be provided with fin-like means (not shown in the figures) projecting in a direction perpendicular to the longitudinal axis 5, which increase the friction between the outer mantle 2 and an inner wall 17 in the cavity 10. Parts of the cone and / or cylinder part of the detonator holder can also be reduced in thickness in its longitudinal direction and replaced with fins to save material without compromising watertightness.

The detonator holder 1 may also comprise a flange 18 projecting perpendicularly from the outer mantle 2 and in connection with the top 3. The flange is advantageous as it prevents the detonator holder from sliding entirely into the cavity 10.

The present detonator holder 1 is thus obtained by forming, for example, injection molding or 3D printing a body in which opposite and substantially parallel top 3 and bottom 4 are formed. These define between them the outer mantle 2 and the channel 6 in direction of the longitudinal axis 5 in the body.

The embodiment of detonator holder 1 according to figures 3 to 7 is manufactured to comprise a substantially rotationally symmetrical cylindershaped body. The channel 6 of this detonator holder is also shaped to be substantially cylindrical with a substantially constant diameter (D) and is provided with a thin film 7 adjacent to the bottom for closing the channel. In this connection the terms substantially cylindrical or cylinder refer to the general shape of said parts as illustrated in the figures and are not meant to be interpret as exact shapes as defined in geometry.

In this embodiment, the outer mantle 2 of the body comprises at least two successive zones formed in the direction of the longitudinal axis 5. The first zone is a truncated cone portion 12 tapering from the top 3 towards the bottom 4. The second zone is a cylindrical portion 13 extending from the cone portion 12 and ending in the bottom. In addition to these, at least one wedge-shaped slit 15 extending from the top towards the bottom in the direction of the longitudinal axis 5 of the body and tapering towards the bottom, and a flange 18 projecting from the outer circumference of the top are formed on the body.

When the detonator holder 1 is used, it is first guided, as shown in the lower part of figure 8, until the truncated cone portion 12 of the outer mantle 2 meets the cavity 10 in connection with the explosive 9. This part of the installation can be facilitated by forming a conically tapered mounting portion 14 abutting the bottom of the outer mantle.

Thus, the detonator holder closes the cavity and the film 7 closing the channel 6 ensures sealing, whereby the explosive mass 19 of the explosive 9 is out of sight and protected from the environment. The explosive is now ready for storage and/or ready to be transported to its intended use location. Alternatively, the detonator holder can be provided separately from the explosive and be installed in its place when used.

In use location, the detonator 8 is first guided into the channel 6 of the detonator holder 1 as shown in figure 8, at the same time piercing the film 7 at the bottom of the channel. The detonator can now be pressed into the explosive mass 19 of the explosive 9. Once it has been ensured that the detonator is in sufficient contact with the explosive mass, the detonator holder is pressed into the cavity 10. This is done by compressing the conical part 12 towards the longitudinal axis 5, as a result of which the wedge-shaped slits 15 are at least partially closed and the diameter of the conical part 12 and the cylinder part 13 of the detonator holder is reduced over distance. See figure 10. This facilitates moving the detonator holder in the cavity 10 of the explosive. When the detonator holder is inserted into the cavity, the conical portion stops the movement depending on the force applied to the detonator holder, however, at the latest when the flange 18 meets the cavity. At the same time, the wedge-shaped slits 15 of the detonator holder at the mouth of the cavity are mainly closed and a watertight assembly is formed.

In the above-described installation method, as a result of the cooperation of the compressed cone part 12 and the inner wall 17 of the cavity 10, the detonator holder 1 locks into the cavity and the channel 6 extending through the body is compressed towards the longitudinal axis 5 of the body. The reduced diameter of the channel causes the inner wall of the detonator holder to be pressed against the outer surface 20 of the detonator 8 guided into the channel. The detonator holder ensures tightness and holds the detonator in place, while also ensuring that any lateral pull on the shock tubes or electrical conductors 21 leaving the detonator does not move the detonator excessively.

The conical part 12 is preferably dimensioned so that when the detonator holder 1 is pressed into the cavity 10, the wedge-shaped slits 15 are still slightly open on the top side 3. Such dimensioning allows the detonator holder inserted into the cavity to be removed safely, since the end of the detonator holder protruding from the cavity can still be pressed further together, whereby the tight grip formed by the detonator holder with the cavity is reduced and the detonator holder can be removed. Removal can be further facilitated by forming the channel 6 of the detonator holder to be conically expanding towards the top along the distance of the compression strip. Such a compression strip provides a small amount of room for movement at the top end of the detonator holder, which makes it easier to press the top of the detonator holder together by reducing the pressure on the detonator.

The operation of the detonator holder 1 was tested in practice using the embodiment of the detonator holder according to figure 3, to which a purpose-built measuring stick with a diameter of 7.6 mm was fitted. A Sauter FK50 force gauge was used for the measurements. The tests were performed at room temperature.

For reference two previously known explosive tubes from different manufacturers were also compared.

In the first comparison, five pieces of explosive tubes containing visible plastic explosive were selected. These explosive tubes had a hole in the explosive extending almost to the bottom of the explosive tube for attaching a detonator. In the test, a measuring stick simulating a detonator was pressed into the hole in the explosive, after which it was pulled out with a force gauge connected and the required force for removal was measured. The measured force before detachment averaged 11 N.

In the second comparison, five pieces of explosive tubes were respectively selected, the explosive of which was protected by a permeable plastic end plug. In the experiment, a measuring stick simulating a detonator was inserted into the explosive, after which it was pulled out with a force gauge connected and the required force for removal was measured. The measured force before detachment averaged 5 N.

The present embodiment of the detonator holder according to figure 1 was tested by using five plastic pipes having a diameter of 15 mm and length of 150 mm. In the experiment, a measuring stick simulating a detonator was attached to its place with the present detonator holder. The measuring stick connected to a force gauge was then pulled out of the pipe. Pull was continued until the measuring stick detached from the detonator holder or the detonator holder detached from the tube. The measurement reading obtained simulates the force required to remove the detonator. The measured force before detachment averaged 43 N.

It could therefore be concluded that the present solution requires a pulling force multiple times higher to detach the detonator from the explosive tube when compared solutions known from prior art.

The performance of the present detonator holder 1 was also tested regarding its watertightness. The experiment was performed indirectly by filling the explosive tube with food salt (NaCl). Thereafter, a shock tube detonator known per se was attached to the explosive tube with the present detonator holder according to Fig. 1. The explosive tube with the detonator was immersed in tap water to a depth of 200 mm and the current electrical conductivity was measured. The explosive tube with the detonator was left in the water, after which the electrical conductivity measurement was repeated a week later. The electrical conductivity was 10 mS/m in the first measurement, and the measurement result did not change in the reference measurement performed 7 days later. It could thus be concluded that no salt had dissolved from the detonator tube, which would have increased the electrical conductivity. The joint formed by the detonator holder had remained watertight.

It will be apparent to those skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. Thus, the invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A detonator holder (1), characterized in that the detonator holder comprises

a body having an outer mantle (2) in the shape of a truncated cone, the body further comprising opposite and substantially parallel top (3) and bottom (4), which

body comprises a channel (6) extending through it in direction of its longitudinal axis (5), and in that

the body comprises one to six wedge-shaped slits (15) extending from the top (3) towards the bottom (4) in direction of its longitudinal axis (5), the slit or respectively slits (15) being formed so that when the detonator holder is inserted into a cavity in connection with an explosive, the slit (15) or respectively slits (15) close at least partially, squeezing walls of the channel (6) against an outer surface of a detonator (8) guided into the channel (6), as a result of cooperation of the outer mantle (2) and the cavity (10).

2. The detonator holder (1) according to claim 1, characterized in that the detonator holder comprises a body having an outer mantle (2) in the shape of a substantially right circular cone.

3. The detonator holder (1) according to claim 1, characterized in that the detonator holder comprises a body having a rotationally symmetrical outer mantle (2), wherein the outer mantle (2) of the body comprises at least two successive zones in the direction of the longitudinal axis (5), a truncated cone part (12) tapering from the top (3) towards the bottom (4), and a cylinder part (13) following it and further connected to it ending in the bottom (4).

4. The detonator holder (1) according to any of the preceding claims, characterized in that there are two slits (15) on opposite sides of a circumference (16) of the outer mantle (2).

5. The detonator holder (1) according to any of the preceding claims, characterized in that the outer mantle (2) is adapted to be conically tapered in its part adjacent to the bottom (4).

6. The detonator holder (1) according to any of the preceding claims, characterized in that the channel (6) is adapted to be conically expanding in the top end of the body (3) towards the top (3).

7. The detonator holder (1) according to any of the preceding claims, characterized in that a thin easily permeable film (7) is formed on the bottom (3), the film closing the channel (6).

8. The detonator holder (1) according to any of the preceding claims, characterized in that a flange (18) protrudes from the outer mantle (2) in connection with the top (3).

9. The detonator holder (1) according to any of the preceding claims, characterized in that the detonator holder (1) is made of a flexible polymer, an elastomer, or a flexible composite containing a polymer or an elastomer.

10. A method for installing a detonator (8) into an explosive (9), characterized in that the method comprises following steps:

forming a body having an outer mantle (2) in the shape of a truncated cone, the body further comprising opposite and substantially parallel top (3) and bottom (4), which

define between them the outer mantle (2) and a channel (6) in the direction of the longitudinal axis (5), and

forming one to six wedge-shaped slits (15) extending from the top (3) towards the bottom (4) in direction of the longitudinal axis (5), wherein when pressing the body into a cavity (10) in connection with the explosive (9), co-operation between the outer mantle (2) and an inner wall (17) of the cavity (10) is achieved, resulting in

the slit or respectively slits (15) closing at least partially, and the channel extending through the body being compressed towards the longitudinal axis (5) of the body, such that

the channel having a reduced diameter (D) is compressed against an outer surface (20) of the detonator guided into the channel.

11. The method according to claim 10, characterized by forming a body having an outer mantle (2) in the shape of a substantially right circular cone.

12. The method according to claim 11, characterized by forming a body having a rotationally symmetrical outer mantle (2), wherein the outer mantle (2) of the body comprises at least two successive zones in the direction of the longitudinal axis (5), a truncated cone part (12) tapering from the top (3) towards the bottom (4), and a cylinder part (13) following it and ending in the bottom (4).

13. The method according to any of the claims 10 to 11, characterized by forming the outer mantle (2) to be conically tapered in its part adjacent to the bottom (4).

14. The method according to any of the claims 1 to 13, characterized by forming the channel (6) to be to be conically expanding in the top end of the body (3) towards the top (3).