GB2092720A - Explosive charge container - Google Patents

Abstract

An explosive charge container, especially for use under water as a unit in a string in seismic geophysical prospecting, comprises a cylindrical container body 1, preferably blow- moulded from polypropylene with a uniform wall thickness of not less than 1.5 mm, with a closed base end 2 and an open mouth end 3, each end having a shoulder 4, 5 and screwthreaded spigot 6, 7 and a moulded cap 10 in the form of an internally screwthreaded sleeve with a partition 11 between a connector end socket 12 and a closure end socket 13, the partition providing a seat 14 for the rim of the container mouth. Each cap 10 can close one container body 1 and connect it to another body end-to-end. <IMAGE>

Description

SPECIFICATION Explosive charge container This invention relates to explosive charge containers for use under water particularly, but not exclusively, for laying down charges to generate seismic waves in geophysical prospecting or exploration. Another potential use is for underwater blasting or demolition.

The invention is applied to containers for use as units in a string, for example as described in United Kingdom Patent Specification No.

1 453 884 and especially when the explosive is an ammonium nitrate powder converted, by heating in the containers, to a hardened form as described in United Kingdom Patent Specification No.

776 1 85. Both patents were taken out by Imperial Chemical Industries Limited.

The object of the invention is to provide moulded plastics containers which will withstand the hydrostatic pressure at depths greater than those at which existing containers can satisfactorily be used.

According to the invention, an explosive charge container, moulded from plastics material and suitable for use as a unit in string of such containers under external hydrostatic pressure, comprises a cylindrical container body having a closed base at one end and an open mouth at the other end, each end having a shoulder from which projects an externally screwthreaded coaxial spigot, and a cap in the form of an internally screwthreaded cylindrical sleeve with an internal transverse partition between a connector end socket, forming one end of the sleeve to fit the base end spigot of a complementary container body, and a closure end socket, forming the other end of the sleeve to fit and close the mouth end spigot of the container body, the cap sleeve partition providing, within the closure end socket, an annular seat which receives coaxially the rim of the mouth end spigot of the container body.

An important advantage provided by the invention is that the containers are basically of simple shape, suitable for blow-moulding from a high strength but flexible material such as polypropylene, with a substantially constant wall thickness giving a structure capable of flexure, such as during heat treatment of an ammonium nitrate charge, but when interconnected to form a string are resistant to and supported against distortion under hydrostatic pressure, particularly in the regions of the container mouths.

Other features of the invention will be described with reference to the accompanying drawings which illustrate, by way of example, preferred embodiments of the invention.

In the drawings: Fig. 1 is an elevation of one form of container body, with longitudinal ribs, Fig. 2 is a cross-section on the line Il-Il of Fig.

1, Fig. 3 is a half-sectional elevation of a cap, Fig. 4 is one end view of the cap, in the direction of the arrow IV on Fig. 3, Fig. 5 is the other end view of the cap, in the direction of the arrow V on Fig. 3, Fig. 6 is a half-sectional elevation of a cap with a detonator pocket, Fig. 7 is an elevation of part of a string of containers, assembled from bodies and caps as shown by Figs. 1 to 6, Fig. 8, on a larger scale, is a fragmentary longitudinal section showing in detail how a cap joins two container bodies end-to-end, and Fig. 9 is an elevation of another form of container body, with circumferential corrugations.

The container body 1, shown by Fig. 1, is cylindrical with a closed base 2 at one end and an open mouth 3 at the other end, each end having a shoulder 4, 5 from which projects a coaxial spigot 6, 7 with a respective external screwthread 8, 9.

A cap 10, as shown by Figs. 2, 3 and 4, is provided for each container body 1 and is in the form of an internally screwthreaded cylindrical sleeve with an internal transverse partition 11 between a connector end socket 12, to fit the base end spigot 6 of a container body 1, and a closure end socket 13, to fit over and close the mouth end spigot 7 of a container body 1.

As best shown in Fig. 8, the partition 11 is shaped so that it provides an annular seat 14, optionally having a resiliently deformable sealing gasket ring 15, which receives coaxially the rim of the mouth end spigot 7 of a container body 1 and supports it against deflection under external hydrostatic pressure. The seat 14 is an annular recess defined by the wall of the cap 10, a radial web portion of the partition 11 and a central hollow boss 1 6 which is moulded in the partition and projects into the closure end socket 1 3 of the cap. The hollow boss 1 6 also receives the base 2 of the connected container body 1 and this reduces the overall length of interconnected containers.

The container bodies 1 are blow-moulded from polypropylene, or other suitable high strength but flexible plastics material, and have a substantially constant wall thickness, preferably of not less than 1.5 mm.

In Fig. 1, the wall of the container body 1 is stiffened by longitudinal corrugations forming ribs 1 7 but in an alternative form, shown by Fig. 9, the container body wall has circumferential corrugations 1 7a which stiffen the body against crushing but permit some transverse flexure.

The caps 10 are preferably moulded from polypropylene.

After charging with explosive, such as hardened ammonium nitrate as mentioned above, any required number of container bodies 1 and caps 10 can be screwed together to form a string as illustrated by Fig. 7.

At one end, and if required at intervals in a string of charged units, there is used a detonator cap 18, as shown by Fig. 6, having a detonator pocket 1 9 moulded as an axial extension from the boss 1 6 of the partition of a cap otherwise of the form shown by Figs. 2, 3 and 4.

In making up a string, container bodies with primer and main charges are incorporated as required, with closed-end caps or nose-pieces fitting the screwthreads of the container bodies or caps as the case may be.

The invention embodies important features described beiow.

Fig. 8 shows that the screwthreads 8 and 9, on the container body spigots, are of buttress thread form with their longer flanks, 18 and 79 respectively, sloping towards the container body in each case. This form of thread, through the lead presented by the flanks 1 8 and 1 9, facilitates engagement with the cap thread and is more resistant, than a corresponding V-thread or rounded thread, to axial deflection in the direction of longitudinal loading between the container body spigots and cap.

The over-all diameter of the cap 10 is not greater than that of the container body so that the cap does not project radially beyond the body and a string can be made up to a known maximum diameter without projections.

The lengths of the spigots 6 and 7 and of the cap sockets 12 and 13 are such that, as shown by Fig. 8, when a cap 10 and two container bodies 1 are screwed tightly together, the seat 14 makes sealing contact with the rim of the mouth end spigot 7 of one container body and the wall of the connector end socket 1 2 makes sealing contact with the shoulder 4 of the other container body.

Any necessary tolerance in the dimensions can be accommodated by an appropriate gasket ring 1 5.

It is known, from the above-mentioned United Kingdom Patent Specification No. 1 453 884, to provide a screwthreaded closure cap with ratchet stops to cooperate with similar ratchet stops on a container body and lock the cap against unscrewing. The present invention provides an improved form of a similar locking arrangement comprising well spaced wedge-shaped dogs 20 on the shoulder 5 and a ring of ratchet teeth 21 inside the rim of the closure end socket 13 of the cap sleeve. In order to engage with the dogs 20, the ratchet teeth 21 or the rim of the socket 13 must flex slightly and recover as the teeth ride over the inclined surfaces of the dogs. By spacing the dogs well apart, such flexure can take place at each dog without interference with the others and the provision of a ring of teeth provides only a small angular interval between successive locking positions and consequent positive holding in tight engagement when a cap is screwed home on to a container body.

Claims (9)

1. An explosive charge container moulded from plastics material and suitable for use as a unit in a string of such containers under external hydrostatic pressure, comprising a cylindrical container body having a closed base at one end and an open mouth at the other end, each end having a shoulder from which projects an externally screwthreaded coaxial spigot and a cap in the form of an internally screwthreaded cylindrical sleeve with an internal transverse partition between a connector end socket, forming one end of the sleeve to fit the base end spigot of a complementary container body, and a closure end socket, forming the other end of the sleeve to fit and close the mouth end spigot of the container body, the cap sleeve partition providing, within the closure end socket, an annular seat which receives coaxially the rim of the mouth end spigot of the container body.

2. A container as claimed by claim 1, in which the cap sleeve partition seat for the rim of the mouth end spigot is an annular recess defined by the wall of the sleeve, a radial web of the partition and a central hollow boss moulded in the partition so that it projects into the closure end socket of the cap and can receive the base of a complementary container body connected to the cap.

3. A container as claimed by claim 1 or 2, in which the screwthreaded portions of the container body spigots are of buttress thread form with their longer flanks sloping towards the Container body.

4. A container as claimed by claim 1, 2 or 3, in which the container body is moulded from polypropylene, or corresponding high strength plastics material, with a wall of axially or longitudinally corrugated shape but substantially constant thickness of not less than 1.5 mm.

5. A container as claimed by any preceding claim, in which the over-all diameter of the cap is not greater than that of the container body so that the cap does not project radially beyond the body.

6. A container as claimed by any preceding claim, in which the lengths of the container body spigots and cap end sockets are such that, when a cap and two similar container bodies which it interconnects are screwed tightly together, the cap makes sealing contact by its seat with the rim of the mouth end spigot of one container body and by its connector end socket wall with the shoulder of the base end spigot of the other container.

7. A container as claimed by any preceding claim, in which the cap sleeve partition is moulded with a hollow projection extending into the closure end socket to receive a detonator.

8. A string of containers, as claimed by any preceding claim, charged with explosive material, interconnected by caps end to end and with or without a priming charge or charges at intervals in or at one end of the string.

9. An explosive charge container as described with reference to and as shown by Fig. 1, or Fig. 9, and Figs. 2 to 7 of the accompanying drawings.