IE44743B1 - Trenching charge case - Google Patents

Description

The present invention relates to a trenching charge case' used for excavating trenches and other cavities in the earth or seabed.

It is known to localise the effect of an 5 explosion by the use of a charge case including a hollow metal cone around which explosive is packed and which is arranged with its open end directed towards the substrate < . to be excavated. Detonation of the explosive causes the cone to implode resulting in fragments of the cone being '10 directed onto the substrate. The cone employed is of the type known as a ballistic cone or Monroe cone and has an included angle of substantially 80°.

In order to achieve the desired result, there should be an appreciable air space between the substrate and the open end of the cone and the charge of explosive must be contained sufficiently long to allow the cone to implode before the case disintegrates. Known trenching charge cases therefore comprise a hollow outer casing and a cone which divides the interior of the casing into two separate compartments, one of the compartments receiving the charge of explosive and the other constituting the air space. As such trenching charge cases are primarily for ’ . use on the seabed) they have been fabricated by welding so as to ensure that the joints'used in the fabrication are watertight so that the cases have to be transported 447 According to the present invention, there is provided a trenching charge case having an outer casing, comprising upper and lower casing parts, and a hollow cone to fit within the upper casing part, having an annular depending flange at the base of the cone, the upper and lower casing parts having interengageable fastening means which enable the parts to be joined together to form the outer casing with the cone mounted within the casing between the upper and lower parts to lie with the apex of the cone within the upper casing part, so as to divide the interior of the casing into two separate compartments, in which the lower casing part comprises a wall located to depend below the lower edge of the cone, when the cone is joined together with the upper and lower casing parts, to support the case against a surface to be excavated so as to stand-off the lower edge of the cone from that surface, and in which said interengageable fastening means for connecting the casing parts together comprises a depending annular flange formed at the lower edge of the upper casing part, an annular recess formed on the exterior of the lower casing part at the upper edge thereof and providing a radially inner wall and a radially outer wall; said two walls of the recess being radially spaced apart by a distance such that, with the depending flange of the cone entered in the recess to abut against the radially outer face of the radially inner wall, the depending flange of the upper casing part can be entered into the recess between the depending flange of the cone and of said radially outer wall to abut against the radially inner face of the radially outer wall of the recess, to join the two casing parts together to form the outer casing with the depending flange of the cone clamped between them.

In a preferred embodiment of the invention, the annular flange of the upper casing part and annular recess of the lower casing part are formed with complementary screw threads so that the two parts of the casing can be screwed together. A sealing member may, if necessary, be . provided in the recess or a sealing compound such as a waterproof mastic composition may be employed to ensure a watertight connection between the casing parts.

Whilst the cone will normally be formed of metal, typically steel, one or other or both of the casing parts may be formed of a plastics material. To avoid electrical sparking arising from build-up of static, at least the upper part of the casing, into which explosive is introduced, is rendered electrically conducting by, for example the incorporation of carbon into the plastics composition.

The use of plastics for the casing parts permits the parts to be configured so as to produce optimum results, production of the casing parts by, for example, injection moulding, providing scope for the massproduction of parts which could not readily be fabricated from sheet metal.

The invention is further described, by way of example, with reference to the accompanying drawing which is a side elevation, partly section, of an underwater trenching charge case constructed in accordance with the invention.

The charge case shown in the drawing is formed from three components, an upper casing part 10, a lower casing part 12 and a hollow cone 14. The casing parts 10 and 12 are injection moulded from a plastics material which is rendered electrically conductive by the incorporation of elemental carbon and the cone 14 is formed of a metal, typically steel. The lower casing part 12 has an annular recess 16 to receive a depending peripheral flange 18 of the cone 14 and a depending flange 20 of the upper housing part 10, bearing a screw-thread on its outer face. It may be seen that the recess comprises a radially outer wall 16' bearing a screw-thread on its radially inner face, and a radially inner wall 16' with the two walls being spaced apart by a distance such that, with the depending flange of the cone entered in the recess to abut against the radially outer face of wall 16, the depending flange can be screwed into the recess by mutual interengagement of the screw-thread on the upper casing part and the screw-thread on the radially outer wall of the recess to join the two casing parts 10 and 12 together with the peripheral flange 18 of the cone clamped between the flange 20 and the wall 16 of the recess 16. A sealing member (not shown) may be positioned in the recess 16 or a sealing compound such as a mastic composition may be used to ensure a watertight seal between the two casing parts.

At the top of the upper casing part 10, which has an outwardly bowed frustoconical wall 22, is an opening 24 through which a charge of explosive may be introduced into the space 26 between the wall 24 and cone 14 and which may be closed by a resilient bung (not shown). Diametrically opposed holes 28 are provided near to the top of the upper casing part for co-operation with a clamp (not shown) by which the casing may be manipulated into position.

The lower casing part 12 has a substantially hemispherical wall 30 which defines with the cone 14 an air space 32. Around the exterior of the wall 30 is an annular trough 34 which is interrupted at two diametrically opposed regions 36 for rigidity and which is filled with ballast such as concrete when the charged case is to be used; the dimensions, in the axial direction of the case, of the trough and the hemispherical wall being substantially the same.

The cone 14 is of the type known as a ballistic cone or Monroe cone and has an included angle of substantially 80°. When the charge case is positioned on the seabed over an area to be excavated and the charge of explosive in the compartment 26 is detonated, the cone 14 will implode, the fragments of the cone having a substantial component of velocity in the downward direction. The walls 22 and 30 will also rupture but the wall 22 which confines the explosive charge and which is acted upon by external hydrostatic pressure is designed to contain the explosion at least until the cone 14 has fragmented.

For use on dry land, the hemispherical wall 30 and ballast trough 34 may be omitted and replaced by a cylindrical er frusto-conical wall (not shown) extending downwardly from the recess 16. The wall 22 of the upper housing part may, if necessary, be reinforced to compensate for the absence of external hydrostatic pressure The invention therefore provides a trenching 10 charge case which is formed of a small number of easilymanufactured components and which may be supplied to a customer in component form. Each of the components of the illustrated embodiment is designed to be nestable with other identical components so that a set of components for several charge cases occupies only a small total volume. The two outer casing components are integrally formed with projections 38 to prevent jamming together of the nested parts.

Claims (17)

1. A trenching charge case comprising:A) an outer casing, the outer casing comprising an upper casing part and a lower casing part; B) a hollow cone to fit within the upper casing part, having an annular depending flange at the base of the cone, and C) interengageable fastening means to enable the upper casing part and the lower casing part to be joined together to form the outer casing with the cone mounted between the upper and lower parts thereof to lie with the apex of the cone within the upper part of the casing and so as to divide the interior of the casing into two separate compartments, the lower casing part comprising a wall located to depend below the lower edge of the cone, when the cone is joined together with the upper and lower casing parts, to support the case against a surface to be excavated so as to stand-off the lower edge of the cone from that surface; and said interengageable fastening means for connecting the casing parts together comprises a depending annular flange formed at the lower edge of the upper casing part, an annular recess formed on the exterior of the lower casing part at the upper edge thereof and providing a radially inner wall and a radially outer wall; said two walls of the recess being radially spaced apart by a distance such that, with the depending flange of the cone entered in the recess to abut against the radially outer face of the radially inner wall, the depending flange of the upper casing part can be entered into the recess between the depending flange of the cone and of said radially outer wall to abut against the radially inner face of the radially outer wall of the recess, to join the two casing parts together to form the outer casing with the depending flange of the cone clamped between them.

2. A trenching charge case as claimed in Claim 1, further comprising an annular ballast trough surrounding the lower casing part.

3. A trenching charge case as claimed in Claim 2, 5 wherein the depending wall is of a generally hemispherical form directed outwardly of the case and having substantially the same dimension in the axial direction of the case as the ballast trough, whereby the case may be supported against said surface by the underside of 10 the trough and by the exterior of the hemispherical wall at the apex thereof.

4. A trenching charge case as claimed in Claim 1, wherein said depending wall is of a generally cylindrical form. 15

5. A trenching charge case as claimed in Claim 1, wherein said depending wall is of a generally frustoconical form with the end thereof remote from the cone being the wider diameter end of the wall.

6. A trenching charge case according to any of the 20 preceding claims wherein said depending annular flange formed at the lower edge of the upper casing part is screw-threaded on its exterior face, and said radially outer wall of the annular recess of the lower casing part bears a screw-thread on its radially inner face, so 25 that the-depending flange of the upper casing part can be screwed into position in the recess by mutual interengagement of the screw-thread on the flange of the upper casing part and the screw-thread on the radially outer wall of the recess, to join the two casing parts and the 30 cone together. I

7. A trenching charge case as claimed in any of the preceding claims, wherein, in the assembled outer casing, means are provided to seal said recess against the ingress of dirt or moisture. **743

8. A trenching charge case as claimed in Claim 7, wherein said seal means comprises a seal member.

9. A trenching charge case as claimed in Claim 7, wherein said seal means consists of a sealing compound.

10. A trenching charge case as claimed in Claim 9, wherein said sealing compound is a mastic composition.

11. A trenching charge case according to any of the preceding claims, wherein at least one of the upper casing part and the lower casing part are formed of an electrically conductive plastics material.

12. A trenching charge case according to Claim 11, wherein the plastics material is one incorporating therein elemental carbon to render the material electrically conductive.

13. A trenching charge case as claimed in Claim 11 or 12, wherein both the upper casing part and the lower casing part are parts injection moulded from plastics material.

14. A trenching charge case as claimed in Claim 2 and any of the preceding claims 11 to 13, wherein the annular ballast trough is interrupted at diametrically opposed parts for rigidity.

15. A trenching charge case according to any of the preceding claims, wherein the two casing parts are formed so as to be nestable in other like parts whereby the parts for a plurality of the cases can.be stored and transported in compact, nested, form.

16. A trenching charge case as claimed in Claim 15 , wherein the exterior of at least one of the lower casing and upper casing parts is provided with exterior projections to prevent a plurality of the casing parts when nested from jamming together. 447 4 3

17. A trenching charge case substantially as hereinbefore described with reference to the accompanying drawing.