GB2182123A

GB2182123A - Explosive projectiles

Info

Publication number: GB2182123A
Application number: GB08624119A
Authority: GB
Inventors: Frederick Myles Young
Original assignee: Royal Ordnance PLC
Current assignee: BAE Systems Global Combat Systems Munitions Ltd
Priority date: 1985-10-22
Filing date: 1986-10-08
Publication date: 1987-05-07
Also published as: TR23273A; CN86106578A; CN1019142B; IL80202A; EG19933A; KR870004289A; EP0228769A1; GR3001018T3; IL80202A0; AU6340586A; US4760795A; IN169504B; JPS62116899A; GB8624119D0; CA1280315C; DE3670683D1; GR900300050T1; BR8605120A; AU602870B2; ES2003367A6

Abstract

An explosive projectile comprises a projectile casing, a high explosive charge filling a portion of the space inside the casing, an impervious case defining a detonation device cavity adjacent to a surface of the explosive charge, and located adjacent to the said surface of the explosive charge between the inside wall of the projectile casing and the impervious case, a pre-formed solid elastic sealant ring such that the seal effected by the sealant ring between the projectile casing and the impervious case is tightened if the pressure on the sealant ring from the material of the explosive charge increases.

Description

1 GB 2 182 123 A 1

SPECIFICATION

Explosive projectiles The present invention relates to explosive projectiles.

It has been known for many years to manufacture high explosive projectiles which comprise a type of gun-fired shell in various ways, one of which is that described as follows. A metal casing having an open upper end and a closed lower end forming a con tainer is partiallyfilled with high explosive material in a hot liquid state which is allowed to solidify by cooling or by pressing powder into a solid state in side the casing. A detonator booster cavity is later machined in the upper surface of the solid explosive charge so formed into which is inserted a cardboard liner, projecting above the charge.

The gap above the explosive charge between the wall of the casing and the liner of the booster cavity is then sealed with a bituminous composition which is applied in a soft mastic state and kneaded by a hand worked operation to occupy the corners of the gap and to adhere to and coat the adjoining surfaces of the casing, the liner and the explosive charge.

A detonator booster device is inserted in the cavity.

Finally, the open upper end is closed by a fuze which in operation interacts with the booster device to pro vide the required detonation of the explosive charge.

During their service life high explosive shells may be subjected to extreme environmental conditions, particularly high and low temperatures, and rough use eg drop, bounce, vibration, topple etc. These conditions can cause the explosive charge to crack and powder. High temperatures can cause expan sion and even melting of the charge. The bituminous composition seal is applied as described above to seal in the explosive charge to prevent it being con taminated by atmospheric moisture and other sub stances and to prevent the explosive material enter ing the fuze cavity region.

Explosive charge material entering this region is regarded as a serious safety hazard. Thefuze is nor mallyfitted in the shell casing by a screw thread joint.

If the explosive charge material becomes trapped be- 110 tween the threads of the fuze screwthread joint it may be initiated by (a) removing the fuze (eg for in spection purposes) or (b) acceleration of the shell on firing which can cause compression of the explosive material between the screwthreads. Such initiation can cause uncontrolled premature detonation of the main explosive charge.

Explosive shells manufactured bythe known method described above sufferfrom serious sealing problems. It has been found thatthe bituminous sealant material does not adequately contain the ex plosive material in all circumstances.

In cold conditions the bituminous material be comes very brittle and the seal is likelyto crackand break down allowing explosive material to escape.

The sealant particles themselves are a hazard since thefriction caused bytheir relative movementcould itself trigger an unwanted detonation. In hotcon ditions the sealant material softens and failsto con tain the explosive material in some cases. It has been found, for instance, that a known explosive composition containing TNT and RDX, which starts to soften at about WC and is in a flowable state above about 73'C exudes past the sealant material not only into the fuze cavity area but also onto the outer surface of the shell body where it is extremely hazardous. As a result, the bituminous material is unsuitable as a sealantfor use over a range of climatic conditions.

Considerable effort in this field has been put into solving these problems but no satisfactory solution has been found hitherto. Much of this effort has been directed at improving the bituminous sealant material.

Anothertechnique which has been investigated is to seal the cavity between the booster cavity liner and the casing wall with a polyurethane resin deposited in the gap in a softened uncured state to form an adhesive sealant coating similarto that of the bituminous material. Thistechnique suffers from the dis- advantages that uniform consistency of sealant polymer is difficuitto achieve, accessto the explosive charge, which may be necessaryfor inspection purposes in certain circumstances, is not easily obtained through the sealant once set and poly- urethane technology is relatively dangerous because of the toxicvapours which may be produced in the chemical reactions involved in the curing process.

According to the present invention an explosive projectile comprises a projectile casing, a high ex- plosive charge filling a portion of the space insidethe casing, an impervious case defining a detonation device cavity adjacentto a surface of the explosive charge, and located adjacentto the said surface of the explosive charge between the inside wall of the projectile casing and the impervious case, a solid pre-formed elastic sealant ring such thatthe seal effected bythe sealant ring between the projectile casing and the impervious case is tightened if the pressure on the sealant ring from the material of the ex- plosive charge increases.

By a "high explosive" charge is meant a charge of secondary explosive material which, when initiated provides a highly energetic brisant orshattering explosive effect as distinctfrom, forexample, a propellant effect. Charges of this kind are well known to those skilled in the art and examples of suitable known materials therefor are given below.

Theterm "solid" is intended to describe a ring madefrom a single continuous structure ratherthan a structure made up from a multiplicity& looselyconnected fibres etc. e.g. a felt. The ring could however comprise a composite material including embedded fibres,filler material forming a consolidated structure as well as being a ring formed from a single elastomeric material.

By"pre-formed" is meantformed before introduction into the projectile.

The present inventor has discovered that it is not necessaryforthe sealantto be in an adhesive state coating the adjoining surfaces of the explosive charge,the projectile casing and the detonation cavity liner (as in the known methods of manufacture), in orderto effect an adequate seal forthe explosive charge.

The present inventor has found that, surprisingly, 2 GB 2 182 123 A 2 use of a sealant ring as specified above in a projectile according to the present invention provides a good seal forthe explosive charge undervarlous climatic and environmental conditions and does not suffer from the problems described above. The present invention therefore provides a simple, neat and effective solution to the problem of sealing a high explosive charge in a projectile. The seal also provides an effective barrier against dust of the explosive mat- erial formed by vibration etc. of the projectile during handling.

UK Patent No. 1177813 describesthe use of a nonadhesive ring made of felt located between an explosive charge and a booster device butthe ring is provided for its cushioning ratherthan sealant effect and, because of the porosity of felt, does not adequately seal the high explosive material in a molten or vapour state or as a dust.

The projectile according to the present invention may,for example, be a gun fired explosive shell in which casethe internal diameter of the casing of the shell preferably tapers inward as the casing wall projects awayfrom the charge in the region beyond the charge, as in conventional shell casings, thereby assisting the sealing action of the sealant ring.

In the projectile according to the present invention the sealant ring is compressed into the gap between the casing and the impervious case under pressure from the explosive charge especiallywhen the charge material expands or exudes with a rise in temperature.

The sealant ring may have any suitable crosssectional transverse shape (as seen in a plane orthogonal to the circumference of the ring). For example,the transverse cross-sectional shape may be a solid circle oran annulus. Alternatively, the ring may have a more complex transverse cross- sectional shape. For example, it may have a bowed transverse crosssection whereby the surfaces of the ring are pressed aginstthe casing wall and impervious case surfaces by action againstthe bow under pressure from the explosive material.

Alternatively, the transverse cross-section of the sealant ring mayfor instance be chevron shaped or may approximate a trapezoidal shape, a U-shape or a G-shape or an inverted V shape.

One preferred form is a cross-sectional shape approximating an inverted V in which one limb of the V, for examplethe inner limb with respectto the axis of the ring, is substantially parallel to the axis of the ring 115 and the other limb is at an anglethereto.

The sealant ring may be spring assisted, eg by a metal spring. For example, where the sealant ring is approximately U-shaped or approximately G- shaped a metal spring may be used to force apartthe limbs of the sealant ring againstthe casing and impervious case. The spring may,forexample, be approximately U-shaped, inverted V-shaped orhelically coiled.

The spring assistance allowsthe sealant material to be chosen from a wider range of candidate materials and allows emphasis to be placed upon the attribute of long life rather than a combination of life and resilience. Thus, the sealant material, with spr- ing assistance, may be made of a long life polymeric material such as polytetrafluoroethylene at least in the regions where it contacts the casing and the impervious case. Where no spring assistance is provided the sealant ring maybe made from any of the rubbery polymeric materials conventionally used as elastomeric sealant ring materials, e.g. silicone rubber.

One or more additional rings may be used in conjunction with the sealant ring. For example, a cushioning ring may be interposed between the explosive charge and the sealant ring. The cushioning ring is provided to reduce back pressure on the explosive charge and to assist containment of bulk charge movement.

The cushioning ring may comprise a soft compressible material, e.g. a felt or foam, e.g. polyurethanefoam.

A metallised layer is preferably provided in conjunction with the sealant ring to act as a barrierfor vapour of the explosive material. For example, a metallised ring may be provided between the explosive charge and the sealant ring.

The metallised ring which may be located above or below (relative to the front end of the projectile when pointing upward) the cushioning ring where that is included may comprise a metal-coated plastics material, e.g. aluminium coated polyester. The metallised ring may itself form the base of a ring of cupshaped cross- section in which the cushioning ring is seated. The cup-shaped ring may be made of a plastics material, e.g. polyester coated on one or both surfaces at least on its base with metal, e.g. aluminium.

The impervious case in the projectile according to the present invention may be the liner of a cavity in which a detonation booster device is fitted. The cavity containing the case may extend into a slot previously machined in the surface of the explosive charge as in known shells. The liner may be an alumi- nium canister or alternatively a case made of a plastics material coated with metal, e.g. aluminium coated polyester, the metal coating being present on the inside and/or outside surface of the case at least in the portions which are adjacentto the explosive material.

The detonation device, e.g. booster, may be housed in a metal container as in known shells. The container may have tape or other cushioning material applied to its outer surface to prevent metal-tometal contact with the said impervious case. Such contact is highly undesirable because of the dangerousfriction itcan cause during assembly.

The high explosive charge in the projectile according to the present invention may comprise any of the high explosive materials known forfilling high explosive munitions. For example, it may comprise a conventionally used high explosive composition containing TNT (2,4,6-trinitrotoluene) and RDX (cycl o- 1,3,5-tri methyl ene-2,4,6-tri n itra m in e), togetherwith one or more known additives such as HM (cycl otetra methyl en etetratra n itra m i ne), HNS (hexanitrostilbene) and beeswax.

The casing innerwall of the shell may be coated with a known lacquer orvarnish to improve adhesion of the explosive material to the casing as is well 3 GB 2 182 123 A 3 known by those ski I led in the art, eg as described in UK Patent No 1, 295,486.

The projectile according to the present invention, may be a gun-fired shell, eg an artillery shelf, e.g. any calibre above 30mm, e.g. 76mm, 105mm, 4.5 inches or especially 155mm.

According to the present invention in another aspect a method of sealing a high explosive charge in the casing of a projectile such as a gun fired shell lo comprises (i) inserting a pre-formed solid elastic sealant ring through an opening of the casing and locating the ring in the space adjacentto the explosive charge and (H) depositing an impervious case defining a detonation device cavity adjacenttothe charge in the region not occupied bythe sealant ring, insertion and location of the sealant ring being carried out before, during orafter deposition of the impervious case so thatthe sealant ring occupiesthe space between the casing and the impervious case.

Preferably,the sealant ring is inserted and located before deposition of the impervious case to minimise distortion of the ring.

Embodiments of the present invention will now be described by way of examplewith reference tothe accompanying drawings, in which:

Figure 1 is a partly cross-sectional frontelevation of an explosive shell of known construction; Figure2 is a partly cross-sectional front elevation of a portion of an explosive shell embodying the pre- sent invention; Figures3to9 are cross-sectional front elevations of portions of various explosive shells embodying the present invention illustrating alternative sealant ring constructions.

In the prior art shell construction shown in Figure 1, a shell 1 comprises a casing 3 made of high tensile steel partiallyfilled with a charge of high explosive material 5 comprising the known composition manufactured according to the UK Ministry of Defence ser- vice use designation R1DX/TNTType G (CW3), a composition comprising RDX and TNTin the ratio by weight60:40 plus additives. An aperture 7 is machined in the uppersurface of the explosive material 5 and a cup shaped cardboard liner9 is inserted in the aperture 7,the base of the liner9 being separated from the explosive material 5 by a woollen felt layer 11. The space between the casing 3 and the finer 9 at the surface of the explosive material 5 is coated with a bituminous material 14 such as the known material having the UK Ministry of Defence service use designation RD 1284.

A booster device or exploder 13 is located in the liner 9 and finally a fuze unit 15 is screwed into the upper end of the shell 1 at a screw thread joint 17 to close that end of the shell 1.

In operation the fuze unit 15 operates to activate the booster 13 which detonates the explosive charge at the required instant in time.

The shell 1 shown in Figure 1 has a construction which suffersfrom the disadvantages described above.

In Figure 2, in which parts which are the same as those in Figure 1 are given the same reference numerals, an improved sealing construction for the shell is shown. The cardboard liner 9 is replaced by an im- pervious case 21 made of aluminium or an aluminium al loy. The bituminous material 14 is replaced in the Figu re 2 construction by an elastomeric sealant ring 24, e.g. made of silicone rubber, of annular transverse cross-section between the case 21 and the shell casing 3. The ring 24 is forced upward into the tapering gap between the case 21 and the shell casing 3 under pressure from the explosive material 5, e.g. during expansion or melting at high tempera tures.

In Figure 3, in which partswhich are the same as those shown in Figure 1 are given the same reference numerals, an alternative improved sealing construction shown. In this casethe ring 24shown in Figure 2 is replaced by an elastomeric ring 27 of solid circular transverse cross- section. The case 21 in Figure 3 is the same asthat shown in Figure 2.

A cushioning ring, e.g. made of feltor a foamed plastics material, may be interposed between the ring 24 shown in Figure 2 or the ring 27 shown in Figure 3 and the explosive material 5. This is iHustrated in Figure 3 where the cushioning ring is shown with the reference numeral 29.

In Figure 4, in which parts are given the same refer- ence numerals as in previous Figures where the parts are the same, the ring 24-shown in Figure 2 is replaced by an elastomeric ring 31 having a transverse cross-sectional shape approximating a compressed bone shape ortrapezoid.

In Figure 5, a metal spring-assisted seal is shown replacing the ring 24 of Figure 2. The seal in Figure 5 comprises a ring 41 of approximately Ushaped transverse cross-section and an approximately Ushaped metal portion 43 insidethe limbs of the U of thering41 urging the limbs apart to facilitate sealing against the surfaces of the casing 3.

In Figures 6 and 7 alternative metal spring assisted seals are shown. In these casesthe ring 41 and metal portion 43 of Figure 5 are replaced respectively by (Figure 6) an alternative sealant ring 45 of an aiternative approximately U-shaped transverse crosssection togetherwith a metal spring 47 in the form of approximately an inverted Vwhich urgesthe limbs of the U of the ring 45 apart and by (Figure 7) a sealant ring 49 of approximately G-shaped transverse crosssection thetop and bottom of the G being urged apart by a coiled metal spring 51 againstthe case 21 and casing 3 respectively.

In the constructions shown in Figures 5to 7the rings 41,45 and 49 respectively may be made of PTIFE (polytetrafluoroethylene).

In Figure 8, an alternativeform of cushioning ring is shown (compared with thatof Figure 3). in this case the cushioning ring 29 is replaced by a com- posite ring comprising a foamed plastics portion 51, e.g. of expanded polyurethane deposited in a metallised portion 53 having a cup-shaped transverse cross-section, e.g. of aluminium coated polyester. The composite ring provides an additional barrierto vapour of the explosive material 5.

An alternative seal without a spring is shown in Figure 9. In this casethe exploder 13 is an explosive pellet separated from its aluminium alloy case 21 by a papertube 61. The exploder 13 is again seated in the case 21 by a felt layer 11. The seal between the 4 GB 2 182 123 A 4 casing 3 and the case 21 comprises a lip sealant ring 63 deposited on a barrierwasher or ring 65 comprising a surface metallised plastics material or metal eg. aluminium foil which in turn is deposited on a felt washer or ring 67. The ring 67 is deposited on the top surface of the charge 5.

In this casethe sealant ring 63 comprises a crosssectional shape approximating an inverted V having one limb parallel to the axis of the ring and the other limb at an angle thereto. The outer limb of the V makes contactwith the innerwall of the casing 3. The sealant ring 63 may be made for example of a silicone rubber.

We have found that in 155mm shells having a con- struction similarto that shown in Figure 3, but having a sealant ring which was a silicone rubber 0-ring of solid circular cross-section, when stored for long periods at 71'C, above thetemperature at which the high explosive material began to melt, and the problem of exudation of the explosive material was substantially eliminated. Such an over-test produces gross exudation with shells of the same explosive material sealed according to the prior art method illustrated in Figure 1.

We have found that in 105mm shells, having a construction similarto to that shown in Figure 9, when subjected to severe shock at low tem peratu res which caused break up of the filling, followed byvibration to makethe dust created migrate the dust was pre- vented from reaching the fuze cavity. Again such an overtestwould produce severe dusting in the fuze thread using the conventional design shown in Figure 1.

Claims

1. An explosive projectile comprising a projectile casing, a high explosive charge filling a portion of the space inside the casing, an impervious case defining a detonation device cavity adjacent to a surface of the 105 explosive charge, and located adjacent to the said surface of the explosive charge between the inside wall of the projectile casing and the impervious case, a pre-formed solid elastic sealant ring such that the seal effected by the sealant ring between the projectfle casing andthe impervious case is tightened if the pressure on the sealant ring from the material of the explosive charge increases.

2. A projectile as claimed in claim land wherein the projectile is a gun fired shell, the internal diameterof the casing of the shell tapering inward asthe casing wall projects away from the charge in the region beyond the charge.

3. A projectile as claimed in claim 1 or claim 2 and wherein the sealant ring comprises a solid ring comprising elastomeric material and has a transverse cross-section comprising a solid circle oran annulus.

4. A projectile as claimed in claim 1 or claim 2 and wherein the sealant ring has a transverse cross- sectional shape selected f rom a chevron shape, a bow shape, an approximate trapezoidal shape, an approximate U-shape or an approximate G- shape.

5. A projectile as claimed in claim land wherein the sealant ring comprises a lip seal having a trans- verse annular cross-section approximating an inver- ted V in which the limb of theV nearerthe axis ofthe ring is substantially parallel to the axis and the other limb of theV is atan anglethereto.

6. A projectile as claimed in claim 1, claim 2 or claim 4 and wherein the sealant ring is spring assisted.

7. A projectile as claimed in claim 6 and wherein the sealant ring has a transverse cross-section which approximates a U-shape and the spring assistance is provided by a metal spring having a transverse cross-section approximating a U-shape insidethe approximate U of the ring.

8. A projectile as claimed in claim 6 and wherein the sealant ring has a transverse cross-section which approximates a U-shape and the metal spring has a transverse cross- section which approximates an inverted V-shape inside the approximate U of the ring.

9. A projectile as claimed in claim 6 and wherein the sealant ring has a transverse cross-section which approximates a G-shape and the spring is a metal coil contained within the limbs of the approximate G.

10. A projectile as claimed in anyone of claims 6 to 9 andwherein the sealant ring is made of along life polymeric material.

11. A projectile as claimed in claim 10 and wherein the polymeric material is polytetrafluoroethylene.

12. A projectile as claimed in anyone of the preceding claims and wherein the projectile includes a metal lised ring in conjunction with the sealant ring.

13. A projectile as claimed in claim 12 and wherein the metal lised ring is located between the sealant ring and the high explosive charge.

14. A projectile as claimed in claim 13 and wherein the metallised ring comprises a metal coated plastics material.

15. A projectile as claimed in claim 14 and wherein the metallised ring comprises an aluminium coated polyester ring.

16. A projectile as claimed in anyone of the preceding claims and wherein a cushioning ring is located between the sealant ring and the explosive charge.

17. A projectile as claimed in claim 16 and wherein the cushioning ring is located in a ring of metal coated plastics material having a cup-shaped transverse cross-section.

18. A method of sealing a high explosive charge in the casing of a projectile as claimed in any one of the preceding claims, comprising (i) inserting a preformed elastic sealant ring through an opening of the casing and locating the ring in the space adjacentto the explosive charge and (ii) depositing an impervious case defining a detonation device cavityadja- centto the charge in the region not occupied bythe sealant ring, insertion and location of the sealant ring being carried out before, during or after deposition of the impervious cases so thatthe sealant ring occupiesthespace.

19. A method as claimed in claim 18 and wherein the sealant ring is inserted and located prior to deposition of the impervious case.

20. A method as claimed in claim 18 orclaim 19 and wherein the impervious case is deposited in an aperture provided in the surface of the explosive -c GB 2 182 123 A 5 chargeinsidethe projectileto locatethecase in position.

Printed for Her Majesty's Stationery Office by Croydon Printing Company W K) Ltd,3187, D8991685. Published by The Patent Office, 25Southampton Buildings, London, WC2A l AY, from which copies may be obtained.

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