GB2096152A - High explosive substitute composition - Google Patents

Abstract

A high explosive substitute composition comprises Hardened Castor Oil, Kaolin, and additionally a finely divided solid inert filler material, especially Calcium Sulphate in the form of powdered Ground Anhydrite. Other inert filler materials can be included, e.g. Red Haematite (up to 60% by weight of the whole composition) and Rosin (up to 15% by weight of the whole composition). Kaolin is preferably present as between 5 and 50% most preferably between 10 and 40% by weight of total inert filler materials. The Hardened Castor Oil should preferably have a melting point in the range 83 to 86 DEG C. The proportions of the constituents are chosen to give the required density to the composition, normally between about 1.4 and 2.0 g cm<-3>.

Description

SPECIFICATION High explosive substitute composition This invention relates to high explosive substitute materials.

These materials are required to be used in practice and proof ammunition as an inert substitute for high explosive used in the corresponding live round. The practice ammunition should perform ballistically in as similar as possible a manner to the corresponding live round, in order to simulate the action of the live round as closely as possible. To do this it is important that the density of the substitute material corresponds closely to that of the high explosive which it replaces, and it is particularly important that the density should be substantially the same through the mass of the explosive substitute, as would be the case with the high explosive itself.

In practice, in order to achieve the required density it is necessary to employ an appropriately proportioned mixture of materials having respectively higher and lower densities than that required. It is also highly desirable that the mixture should be capable of being cast to form a homogeneous product of the required density.

A composition known to the Applicant which has been used in the past with some success comprises Technical grade Calcium Sulphate suspended in Hardened (Hydrogenated) Castor Oil. This manufactured grade of Calcium Sulphate has been available as soft material which was easily ground to a light, finely divided powder. High explosive substitute of the known composition using this ground substance is easy to pour when molten, the inorganic solid does not sediment and the moulding formers are easily removed after the casting has solidified. However, technical grade Calcium Sulphate is no longer available commercially in any substantial quantity, and the need therefore arises for an alternative substances or a completely new composition of high explosive substitute which can be used in place of the known composition.

Alternative compositions are known to the Applicant, comprising mixtures of paraffin waxes and various inorganic filler materials. One such known composition comprises Kaolin (known alternatively as China Clay) and Barium Sulphate. Since Barium Sulphate has a relatively high density while Kaolin has a relatively low density it is possible to adjust the density of the composition to a fine degree by adjustment of the relative proportions of these ingredients. In practice it is found that these compositions are highly viscous when molten and in order to pour them for casting it is necessary to add surface active agents such as lecithin or pentaerithritol dioleate particularly to counter the thickening effect of Kaolin. With these compositions it has been found that density control is very difficult, and pressing is necessary after casting so as to consolidate the cast mass.

A readily available source of large quantities of Calcium Sulphate is a naturally occurring mineral, Ground Anhydrite. This is however, a hard dense material which cannot be ground by normal commercial practice to a degree of fineness equivalent to the technical grade Calcium Sulphate. Thus sieve size ranges are coarser and specific surface areas are lower. When it was attempted to substitute Ground Anhydrite in the known composition comprising Hardening Castor Oil, although a satisfactory overall density could be obtained, the Ground Anhydrite was found to sediment severely in the molten composition, so that the density varied considerabiy through the depth of the cast product.In an attempt to produce a more even dispersion of the heavy solids in the organic vehicle, organic surface active agents such as lecithin and pentaerithritol dioleate were added, but this was found ineffective.

Further investigation showed that the suspension of Ground Anhydrite in Hardened Castor Oil was much lower in viscosity than the corresponding suspension of the technical grade substance. This suggested to the Applicant that a suspending agent might be capable of holding the coarser particles of Ground Anhydrite in a uniform suspension. Despite earlier experience with the known wax-based compositions, Kaolin was tried, and was found to be surprisingly effective as a suspending agent for the inert filler material, According to the present invention, a high explosive substitute composition comprises Hardened Castor Oil, Kaolin, and additionally a finely divided solid inert filler material.

A most effective inert filler material is Calcium Sulphate, particularly in the form of powdered Ground Anhydrite. Possible alternative inert filler materials for appropriate circumstances are calcium carbonate (e.g. in the form of ground limestone), silica and bauxite.

Other inert filler materials can be included in the composition. For example, up to 60% (by weight relative to the whole composition) of Red Haematite (Fe203) can be included in the composition for colouring, and to increase its density; up to 15% (by weight relative to the whole composition) of Rosin can be added, for the purpose of improving the adhesion of the hardened castor oil to the inorganic solids when the composition has solidified.

The inert filler material should preferably be sufficiently finely divided to pass 100% through a 60BS sieve.

The Hardened Castor Oil should normally have a melting point in the range 83 to 860C.

Normally the Kaolin is present in proportions between 5 and 50%, preferably between 10 and 40% by weight of the total inert filler material.

The proportion of the constituents in the composition as a whole will depend upon the composition density required.

For most purposes the density of the composition will be between about 1.4 and 2.0 g cm-3.

The composition and in particular the Kaolin constituent, should normally be substantially lead free because the inert compositions often come into contact with live explosives whose functioning could be impaired by the sensitising action of the lead salts.

Table 1 below shows the composition and certain physical properties of a technical grade Calcium Sulphate which was previously available from British Gypsum under the reference 2 ACS, and also shows similar details of two grades of Ground Anhydrite designated 6GA and 2GA respectively. Details of the 6GA and 2GA are based on figures as declared by the supplier, British Gypsum. Further details as found by the Applicant are listed for three samples of 2GA. 6GA although slightly finer than 2GA is no longer available commercially.

TABLE 1

2GA Found 2ACS 6GA 2GA Sample Sample Test Found Declared Declared 1 Sample 2 3 Loss on ignition (wtD/a) 0.5 to 0.9 1.9 1.9 1.6 1.6 1.5 Total Calcium as CaSO4 (wt%) 97 tb 99 97.1 97.1 98.7 99.2 99.2 Total Sulphate as CaSO, (wtO/o) 95 to 97 97.1 97.1 97.8 98.8 98.6 Total Calcium as CaSO, (wtO/o) 97 ti3 99 97.1 97.1 98.7 99.2 99.2 125cm (wt%) Retained when sieved through 240 BS sieve ie coarser than 63!n (vet%) 0.3-to 0.7 > 16 < 29 > 18 < 32 37 36 31 Specific surface area (cm2 9 l) 4000 to 5000 2000 to 3000 Table 2 below shows details of four high explosive substitute compositions each designed to have a density of 1.58 g cm-3, prepared as laboratory mixes numbers 1 , 2, 3 and 4. Mix 1 is a prior art mixture, Mix 2 illustrates the effect of substituting Ground Anhydrite for 2 ACS in the prior art mixture, and Mixes 3 and 4 are in accordance with the invention. A sample of each mix was allowed to solidify in a column, and the density of a slice from the top, middle and bottom of the column was determined to each mix. The composition of each mix can be expressed as follows: Component Weight Fraction (%) Hardened Castor Oil 36.4 Rosin 5.2 Finely divided iron oxide 0.2 Calcium Sulphate CaSO4 X Kaolin Y 100.0 The characteristics of the Kaolin and 2GA components of the compositions iisted in Table 2 as declared by their suppliers (i.e.English China Clays Ltd and British Gypsum Ltd respectively), are given below: Particle Size Wt% in 2GA Wt% in Kaolin (to DEF STAN 96-2) Coarser than: 125 ym (120BSS) 20 Nil Coarserthan: 63m (240BSS) 40 Nil Coarserthan: 53 ssm (300 BSS) 80 0.1 Coarserthan: 10 Mm ca100 12 Finer than 0.2 ,ltm Nil 8% The 2GA has a specific surface area of 2000 to 3000 cm2g-' compared with a value of approximately 9500 cm2g- for the Kaolin.As used in it mineral from Kaolin consists of hydrated alumino-silicate (kaolinite) with up to 1 5% Mica and traces of other clay minerals. The crystals of Kaolinite and Mica are thin plates having aspect ratios (diameter/thickness of from 5:1 to 50:1). This shape and aspect ratio are thought important to the success of Kaolin as a suspending agent in the organic medium.

TABLE 2

s Weight fraction of CaSO4 (%) Density of solidified (X in composition) Weight fraction column g cm 3 Laboratory of Kaolin (%) Mix 2 ACS 2GA (V in composition) Top Middle Bottom 1 58.2 0 0 1.573 1.580 1.590 2 0 58.2 0 1.505 Not 1.971 recorded 3 0 45.7 12.5 1.581 1.603 1.672 4 O 41.6 16.6 1.597 1.600 1.610 It can be seen that substitution of 2GA for 2ACS resulted in severe sedimentation. In Mix 3 the addition of Kaolin has considerably reduced sedimentation, and in Mix 4, the addition of a higher proportion of Kaolin has further reduced sedimentation to the extent that Mix 4 is superior to Mix 1 in this respect. Mixes 3 and 4 were found to pour easily, and the casting was found to be well consolidated without the need for pressing. Obviously minor changes to the proportions of the components in Mixes 3 and 4 would result in compositions even closer to the density aim of 1.58 g cm-3.

Table 3 below shows the results of plant scale trials on three high explosive substitute compositions each designed to have a density of 1 .58g cm 3, prepared as plant trial mixes 5, 6 and 7.

Mix 5 illustrates the results of substituting 2GA in a prior art composition, and showed gross sedimentation of the inorganic filler. Mix 6 was prepared by remelting the product of the Mix 5 trial and adding Kaolin and extra organic material. As can be seen, very little sedimentation occurred. Mix 7 was prepared by remelting the product of the Mix 6 trial and adding further Kaolin, resulting in slightly higher density. The sedimentation in Mix 7 appeared very slightly inferior to that of Mix 6, but such a slight difference is not thought significant. Samples from each mix were solidified in a column, and the density determined for slices taken from the top, middle and bottom of each column.

TABLE 3

Composition of Mix (weight V/o) Density g cm~3 Trial Mix Hardened No. Castor Oil Resin Fe203 2GA Kaolin Top Middle Bottom 5 36.4 5.2 0.2 58.2 0.0 - Heavy Sedimentation 6 36.4 -5.2 0.2 41.7 16.5 1.55 1.56 1.56 7 34.8 5.0 0.2 39.8 20.2 1.57 1.57 1.59 Further plant trials have demonstrated that shells of calibre 76 mm, 1 05 mm, 120 mm, and 4.5 inches can be filled satisfactorily with compositions according to the invention. Such shells when fired in range proof, have given correct ballistics confirming that compositions according to the invention are of uniform density when solidified.

Claims (10)

1. A high explosive substitute composition comprising Hardened Castor Oil, Kaolin, and additionally a finely divided solid inert filler material.

2. A composition according to claim 1 wherein the inert filler material is Calcium Sulphate.

3. A composition according to claim 2 wherein the Calcium Sulphate is in the form of powdered Ground Anhydrite.

4. A composition according to any one of claims 1 to 3 including up to 60% (by weight relative to the whole composition) of Red Haematite.

5. A composition according to any one claims 1 to 4 including up to 1 5% (by weight relative to the whole composition) of Rosin.

6. A composition according to any one preceding claim wherein 1 00% of the inert filler material is capable bf passing through a 60 BS sieve.

7. A composition according to any one preceding claim wherein the Hardened Castor Oil has a melting point in the range 83 to 860C.

8. A composition according to any one preceding claim wherein the Kaolin is present in a proportion between 5 and 50% by weight of the total filler material.

9. A composition according to claim 8 wherein the Kaolin is present in a proportion between 1 0 and 40% by weight of the total filler material.

10. A composition according to any one preceding claim having a density between about 1.4 and 2.0 g cm-3.

1 A composition according to claim 1 and substantially as hereinbefore described.