GB2218414A - High-duty smoke-producing bodies and projectile - Google Patents

Abstract

High-duty smoke-producing pressed bodies with wide-band camouflage effect are described and comprise red phosphorus, an oxidizing constituent which consists exclusively or preponderantly of a peroxydisulphate, preferably potassium peroxydisulphate, at least one reactive metal powder, preferably magnesium powder, and a binding agent. The bodies may each have the shape in plan view of the sector of a circle with the apex removed so that a plurality of the bodies can be packed into and fill a substantially cylindrical charge chamber in a smoke projectile while leaving free a central ignition channel.

Description

HIGH-DUTY SMOKEPRODUCING BODIES AND PROJECTILE FIELD OF THE INVENTION This invention relates to smoke-producing pressed bodies and to smoke projectiles containing such bodies.

BACKGROUND OF TRE INVENTION AND PRIOR ART German Patent Specification No. 19 13 790 describes a device for the ignition of a smoke-producing mass, which consists of individual bodies packed together. When ignited by an ejector charge, these bodies are discharged from housing and dispersed over a target area, the ignition taking place along the axis of the housing.

In this device the smoke-producing pressed bodies (smoke pressings) are briquetted in a known manner with the addition of a binding agent, stacked securely in position in the housing about an axial igniter tube and are formed with ignition channels, the igniter tube being combustible or formed with ignition cavities which contain an igniter material. The housing may be a warhead of ogive shape connected with the casing through the igniter tube.

On ignition of an igniter-and-detonator charge, the igniter tube ruptures at the preset breaking points, and the smoke-producing pressed bodies (smoke pressings) are thereby ignited and at the same time ejected. A particular advantage of such a device is that a multiplicity of individual smoke-producing bodies may be dispersed indiscriminately and widely over a target area. A disadvantage of this device however, is that it is not suitable for use as a high-duty projectile, this being due to the constructional arrangement of the device itself and to the shape and composition of the briquetted smoke pressings located within it. That is to say, upon firing such a device the briquetted pressingsdo not withstand the resultant stress and accordingly break into pieces.This process is still further promoted because of the fact that the smoke pressings are not wholly flush with the shell casing, since their outer circumferential edges, directed towards the shell margin, are not in the form of sectors of a circle but are straight-sided, and seen from the axial igniter tube they are formed with ignition channels which run radially outwards. These ignition channels formed in the incendiary bodies and the hollow spaces in the circumferential region of the projectile are indispensable for a clean and functionally correct ignition of the smoke pressings described in German Patent Specification No. 19 13 790, since these pressed bodies can only be ignited with sufficient reliability if the greater part of their surface is contacted by the ignition flame.On the other hand, these hollow spaces cause the pressings to break into pieces under the stresses occurring on firing, namely a pressure loading in an axial direction and a loading due to centrifugal force in a radial direction.

No data are given in the German Specification as regards the composition of the briquetted smoke pressings and the binding agent used in its production. It is possible to proceed on the assumption that the pressings contain red phosphorus and that in addition, the usual oxidizing constituents, reactive metal powder and binding agent are present.

In short, it follows accordingly, that the device for igniting a smoke or flame-producing mass described in German Patent Specification No. 19 13 790, especially as described with reference to Figures 1 to 7 and also Figures 4 and 5, is essentially therefore unsuitable for a high-duty projectile, because the briquetted smoke pressings present within it do not possess the requisite high mechanical strength.

In order to overcome this disadvantage, in default of the possibility of sufficiently raising the mechanical strength of suitable smoke pressings, projectiles for the reception of an ejectable payload have been developed, which, in their interior contain disposed along the axis of the projectile a compactly or loosely united self-supporting support structure subdivided into several compartments, these compartments being filled with an appropriate smoke-producing agent. Projectiles of this type have been described for example in German Offenlegungschriften Nos.

24 37 535; 25 25 553 and 25 31 364. The smoke-producing agent and/or incendiary agent contained in the compartments in these projectiles are at least partially protected from the high loadings occurring with the acceleration of the projectile, so that these projectiles in respect of their payload are high-duty projectiles.

The main disadvantage of these projectiles, however, is that the support structure for the protection of the ejectable payload represents a relatively expensive construction. At the same time, this leads to a reduction of the quantity of payload per unit volume which can be accommodated corresponding to the volume of the support structure present in the projectile and to an increase in the unusable dead weight of such a projectile.

Thus the disadvantage of previously proposed high-duty projectiles is that hitherto there has been no smoke pressing based on red phosphorus which will withstand the high mechanical loading which occurs on firing such a projectile, and for this reason the device described in German Patent Specification No. 19 13 790 is in practice not suitable as a high-duty projectile.

Pressed bodies based on red phosphorus have the further disadvantage that they only bumincompletely. There consequently exists in them an unfavourable ratio of phosphorus pentoxide (smoke producing agent) formed as the result of combustion to the quantity of phosphorus used. With increasing compaction of a pressed body of this kind this ratio becomes even worse, while at the same time the ignition capacity decreases further. However, such high compaction is an essential prerequisite to enable suitable smoke pressings to be installed in high-duty projectiles.

Phosphoric acid smokes are not only good screen producers in the visual range of the electromagnetic spectrum, but to a certain extent also in the infrared spectral range. The presence of molecular excitation bands in the wavelength range of 8 to 14 ym are essential if a smoke screen is to be impervious in the infrared region. The imperviousness of smoke screens could be substantially enhanced if the band spectrum of suitable red phosphorus based smoke charges could be spread in the requisite manner.

On the basis of the latest state of technology with sophisticated position finding devices for night vision and bad weather, for example thermal imagers and homing devices, which all function in the wavelength ranges of 3 to 5 fm and from 8 to 14 fm, the importance of obtaining a screening effect in the infrared in addition to the visual range is of increasing significance. A more effective smokescreen which will take account of these developments should therefore as far as possible cover both wavelength regions.

In addition an essential aim of modern tactical warfare is the screening of large areas within a short time from a relatively great distance. For this purpose suitably large calibre ammunition is fired for distances of up to approximately 30 km, but which, however, contains a high-duty payload (smoke pressings) capable of withstanding the forces which occur during such firing.

German Offenlegungschrift No. 20 48 583 describes a castable white smoke mixture, consisting of red phosphorus in a sufficient quantity for production of the smoke, a nitrate of an alkali metal in a sufficient quantity for oxidation of the mixture, magnesium in a quantity sufficient to generate heat to maintain burning of the phosphorus, and a polymer binder to bond the constituents together into a castable mass. This mixture preferably consists of 31 to 47 percent by weight of red phosphorus, 18 to 32 percent by weight of an alkali metal nitrate, preferably sodium nitrate or potassium nitrate, 4 to 5 percent by weight of magnesium and 25 to 35 percent by weight of binder together with a plasticizer.

In addition a cross-linking agent is preferably also present in a quantity of 10 to 20 percent by weight of the quantity of binder and plasticizer, and this is also prescribed for all the described Examples.

The above smoke mixture, by virtue of its phosphorus content, is also suitable, but to a limited extent, for the production of smoke, but has, on account of its relatively low phosphorus content, however, the disadvantage of low yield. This cannot be remedied by simply increasing the quantity of phosphorus, since a relatively large amount of the polymer binding agent together with the plasticizer and cross-linking agent must always be present, since otherwise the mixture ceases to be castable. All of the other constituents of this white smoke mixture are solids, so that the additionally present adjuvants must of necessity be liquid components.Thus this smoke mixture is not one which is convertible by simple pressing to pressed bodies, but one which is a castable composition, which, only after an indispensable hardening process, can be brought into a solid, although not compact condition.

Furthermore, the maximum phosphorus content of the mixture is very limited because of the need to use large quantities of adjuvants.

On burning such a white smoke mixture, the combustion products which arise as a result of the alkali nitrate content, range from nitrogen dioxide through other oxides of nitrogen to nitrogen itself, nitrogen dioxide showing excitable molecular bands in the wavelength range 8 to 14 P m. With an excess of reducing agent and high temperature, however, a substantially direct reduction to nitrogen takes place, only a small amount of nitrogen dioxide being formed. Such conditions, however, constantly arise in the combustion both of the above-mentioned smoke mixture as well as a smoke charge of the present invention. Nitrogen, however, is an inert gas, which is not burnable to a nitrogen oxide, so that with a smoke charge of this type no substantial band spreading and hence also no decisive improvement in the broad-band camouflage effect is achievable.

Therefore it will be realised that the smoke mixture described in German Offenlegungschrift No. 20 48 583 is, because of its composition, unsuitable for the production of a high-duty smoke pressing by simple pressing. This is due to the fact that the composition has a low phosphorus content which cannot be readily increased and which is too low to give a good smoke yield and does not allow of any appreciable improvement in the broad-band camouflage effect. This smoke mixture therefore has virtually all the disadvantages, which have already been mentioned above in connection with the other previously proposed smoke charges. Its relatively high content of adjuvants leads moreover to a considerable impairment of its ignition and burn-up characteristics.

BRIEF SUIARY OF TRE BxAX1\UION According to one aspect of the present invention there is provided a high-duty smoke-producing pressed body with wide-band camouflage effect, comprising red phosphorus, an oxidizing constituent consisting exclusively or preponderantly of a peroxydisulphate, one or more reactive metal ponders (as hereinafter defined) and a binding agent.

These smoke-producing pressed bodies, by virtue of their particularly high stressability, can be used in hilly accelerated projectiles and without the necessity for a special supporting structure to support the payload located therein, these smoke-producing pressed bodies having, despite their greater strength, improved ignition and burn-up properties and showing an enhanced camouflage effect not only in the visual, but also in the infrared range of the electromagnetic spectru.

According to another aspect of the present invention there is provided a high-duty smoke projectile, wherein a projectile body contains a smoke-producing charge and comprises means for igniting and ejecting such charge, and wherein the charge comprises a plurality of the smoke-producing pressed bodies just indicated, substantially filling a substantially cylindrical charge chamber while leaving free a centrally directed ignition channel.

Upon combustion of the present heavy-duty smoke pressing, the peroxydisulphate oxidizing constituent reacts with the red phosphorus with the liberation of gas and the formation of reaction products, which show absorption bands in the wavelength ranges of 3 to 5 ym and 8 to 14 tm.

The use of a peroxydisulphate in the production of the present smoke pressing makes it possible to form bodies of high strength, which have such a geometrical shape that they can be incorporated in the body of a suitable projectile to leave a central channel and no empty cavities, since in general the pressing can be ignited to the requisite extent. These peroxydisulphates are characterised by the fact, that they very readily release oxygen, as a result of which the ignitability of the smoke pressing is increased. This increased ignitability therefore permits the smoke pressings to be more compact and enables bodies of greater mechanical strength to be produced. Further, as a result of this, it is also possible to work with a greater quantity of binding agent, which likewise contributes to an increase in the strength of such smoke pressings. In the production of the present pressings by pressing under suitably high pressure, the peroxydisulphates, due to their ready decomposability, react to a certain extent with the red phosphorus to produce a small quantity of phosphoric acid.

This leads to a cross-linking (felting) of the entire pressed body and hence to a further increase in its strength, this effect being even further increased during storage.

Besides the above-mentioned improvement in the mechanical strength and reactivity of the present smoke pressings through the use of a peroxydisulphate, the use of such an oxidizing constituent also makes it possible to enhance the camouflage effect produced by combustion of the pressings. In the first place, the gases liberated by the reaction promote the disintegration of the structure thus promoting access to the composition by oxygen of the air. The escaping gases serve at the same time as carriers for the vaporizing phosphorus and facilitate its expulsion from the pressed body. In the second place, the conversion of phosphorus to phosphorus pentoxide is also increased by the high oxygen content of the oxidizing constituent and its readiness to liberate oxygen.

These two effects thus produce an increase in the smoke yield.

Moreover, there arise during the reaction, combustion products which show absorption bands in the wavelength ranges 3 to 5 Fm and 8 to 14 pm besides those of the compounds of phosphorus and oxygen. By the use of a peroxydisulphate as the oxidizing constituent, the absorption spectrum is broadened, and as a result, the camouflage effect in the infrared wavelength region is increased. Thus a two-fold increase in performance is achieved, namely by increasing the yield of phosphorus pentoxide and by a broadening of the absorption spectrum.

The combustion of the present smoke pressing results in the production of sulphur dioxide and to a small extent sulphur trioxide as well from the peroxydisulphate present as oxidizing constituent. Sulphur dioxide has a pronounced absorption band in the 8 to 14 fm range and sulphur trioxide has a pronounced absorption band in the range from 3 to 5 ym. Further reaction of this sulphur oxide analogously to the nitrate can lead to the formation of sulphur, although this, in contrast to the inert nitrogen, burns with the oxygen of the air to form a variety of oxides of sulphur, so that to a certain extent products are constantly being formed in a cyclic reaction all of which products contribute to the broad-band camouflage effect of such a smoke charge.Thus in contrast to the use of an alkali nitrate as the oxidizing constituent, the use of a peroxydisulphate has the advantage that in the reaction combustion products are formed which contribute to the desired band-spreading and give a substantially greater effect.

The peroxydisulphates, which may be used in the present pressed bodies, and examples of which are sodium peroxydisulphate, potassium peroxydisulphate and ammonium peroxydisulphate, are, as is well known, very reactive substances, and these have not been used hitherto for the formulation of smoke charges. At the beginning of page 4 of the already mentioned German Offenlegungschrift No. 20 48 583 there is for this very reason an express warning against the use of such highly reactive materials in the castable white smoke mixture therein described.The present smoke charge, due to its higher content of phosphorus and lower content of binding agent, is substantially more reactive than the smoke charge described in the abovementioned Offenlegungschrift and it is therefore to be regarded as extremely surprising that the highly reactive peroxydisulphates can actually be used without danger in such a highly reactive smoke charge.

As the foregoing discussion shows, the present smoke pressings provide for a broadening of the band spectrum to the entire wavelength range of 3 to 14 pm and thus for a substantial increase in the camouflage effect. The slight oxygen emission by, and high oxygen content of, the peroxydisulphates contributes in addition to a further improvement in the total smoke yield. The concealment (screening) effect resulting from the smoke produced by the present pressed bodies is thus significantly higher than that of corresponding bodies, which contain only red phosphorus and conventional oxidizing constituents, and which do not contain peroxysulphates.

In the present high dusty smoke-producing pressed body the oxidizing constituent can constitute 10 to 30 percent by weight of the pressed body; and as already mentioned above, can be exclusively or preponderantly a pero > g-disulphate. This means, that a minor quantity of the oxidizing constituent can also consist of another conventional oxidizing constituent. By this is to be understood any quantity of another such oxidizing constituent, which does not critically impair the desired properties of the present smoke pressing. Thus, for example, up to 30 percent by weight of the total quantity of oxidizing constituent present can consist of a conventional oxidizing constituent, and not a pero:ydisulphate.

Examples of such other oxidizing constituents include the conventional oxidizing constituents for smoke pressings of this kind, for example, nitrates, such as sodium nitrate or potassium nitrate, or powdered metallic oxides, such as copper oxide, iron oxides, molybdenum oxides end/or manganese oxides, and even powdered manganates and/or permanganates.

Thus the use of a peroxydisulphate in accordance with the invention in pressings based on red phosphorus above fulfils several functions, one of which is the possibility of utilizing a higher proportion of binding agent with an associated increase in strength of the corresponding smoke pressing. Whereas with conventional pressed smoke-producing bodies, namely such as have the usual oxidizing constituents, a troublesome impairment of the smoke yield takes place with a proportion of binding agent of only 5 percent by weight, the present high-duty smoke pressings, as a result of the presence of the peroxydisulphate oxidizing constituent, can contain up to 20 percent by weight of binding agent. In this connection, a binding agent content of up to 15 percent by weight is preferred and more preferably up to 12 percent by weight.

The preferred reactive metal powder is magnesium powder, but instead of magnesium powder or in addition to it, other conventional reactive metal powders can be used. The term "reactive metal powders" as used in this specification includes not only conventional reactive powders of metals but also powders of the elements silicon and boron and their alloys, and for the purposes of the present specification, silicon and boron are regarded as metals. Thus examples of suitable metal powders are powders of aluminium, silicon, titanium, boron and their alloys with one another or with magnesium.

Depending upon properties which the present smoke pressing is required to have, the binding agent may be a soft or hard elastomer.

Examples of the former are elastomers based on Polyamide 12, which are obtainable from the firm CHEMISCHE WERKE HilLS AG under the trade name "VESTAMID". Examples of the latter are elastomer based on polyurethanes and polyvinylchlorides, which are obtainable from the firm HENKEL GmbH under the trade name "MACROPLAST". Especially preferred binding agents are those based on chlorinated rubber elastomers.

The present smoke pressings preferably consist of 55 to 75 percent by weight of red phosphorus, 14 to 22 percent by weight of peroxydisulphate as oxidizing constituent, 2 to 8 percent by weight of reactive metal powder and 4 to 20 percent by weight of binding agent. Preferably the oxidizing constituent is sodium peroxydisulphate, potassium peroxydisulphate and/or ammonium peroxydisulphate, potassium peroxydisulphate being most preferred, the reactive metal powder is magnesium powder and the binding agent is an elastomer.A particularly preferred smoke producing moulded body consists of approximately 65 percent by weight of red phosphorus, approx-nately 18 percent by weight of peroxydisulphate, preferably potassium peroxydisulphate, about 5 percent by weight of reactive metal powder, preferably magnesium powder, and about 12 percent by weight of an elastomer binding agent, preferably "VESTCD" or "HACROPLtST" .

The present high-duty smoke pressing preferably has the shape in plan view of a sector of a circle with the apex removed, so that after putting together the pressed bodies a closed cylindrical region with a central ignition channel is formed. The included angle of the sectors is preferably 450 The form of these pressings thus virtually corresponds to the form of the briquetted smoke and/or incendiary bodies described in German Patent Specification No.

19 13 790 but they differ, however, in that the outer limiting surface is not rectilinear but circularly arcuate and also in that the radial surfaces of the present pressed bodies are not formed with any recesses to form ignition channels between the individual layers of the pressings. Thus on filling up the body of a suitable projectile with the present smoke pressings, there is no empty space between the interior of the body and the central ignition channel or between the individual layers of pressings, which empty space would be conducive to breaking or crumbling of the pressed bodies under the heavy stresses which occur on firing a projectile of this type.The hollow space formed by the inner channel does not impose a stress on firing since the smoke pressings, as a result of the spin of the projectile are forced away from this hollow space and not forced into it, as in the case of the pressings in accordance with German Specification No. 19 13 790.

The present high-duty smoke pressings can be produced in a conventional manner, in which the individual constituents are first thoroughly mixed with one another and the resultant mixture is then moulded in conventional presses to form pressed bodies with the respective desired form. In general the present smoke 2 pressings are produced under a pressure of at least 4000 N/cm 2 preferably a pressure of 4500 to 5500 N/cm , have such a high strength, that they do not break with a loading of up to 18000 G, have a density in general of at least 1.5, preferably 1.6 to 1.75, and exhibit a breaking strength of at least 100 N, preferably of 140 to 320 N.

DESCRIPTION OF TEE DRAWINGS In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example, an embodiment thereof, and in which: Figure 1 is a longitudinal section through a projectile filled with smoke pressings in accordance with the invention, and Figure 2 is a cross-section through the projectile along the line A-E in Figure 1.

PREFERRED EMBODIMENTS Referring to the drawings, there is shown a smoke projectile consisting of a body 1, a head 3 with a time fuse 5 and an igniter-and-ejector charge 7, and a base 9, which is separable from the body 1 at a preset breaking point 11 in conventional manner.

A payload chamber formed by the body 1, the head 3 and the base 9 is bounded by a flush fitting sleeve 13 which is located on the inner casing of the projectile body 1. The sleeve is shown to consist of two identical half-shell elements 13a and 13b, but can also consist of three identical shell elements. The chamber is also bounded at its end facing the head 3 by a perforated support disk 15 and at its end facing the base by a basal perforated support disk 17. The payload is located within the sleeve 13 and comprises high-duty smoke pressings 19 disposed in tiers. The pressings have plane surfaces and, in plan view, have the shape of circular sectors which lie flush with the inner surface of the sleeve 13.

Extending along the central axis of the projectile body 1 is a central ignition channel 21 which is formed by the individual pressings 19. Between the uppermost layer of the smoke pressings 19 lying nearer to the igniter-and-ejector charge 7 and the perforated support disk 15 is a perforated disk 23 of synthetic felt which acts as an elasticvolume compensator.

Figure 2 shows in section the projectile body 1, the half-shell elements 13a and 13b (of the sleeve 13) lying flush with the inner casing, the smoke pressings 19 and the central ignition channel 21 formed by the pressings.

In accordance with the present invention, the smoke pressings comprise red phosphorous, a peroxydisulphate as an oxidizing constituent alone or mixed with one or more other oxidizing constituents, one or more reactive metal powders, such as magnesium powder and a binding agent, preferably an elastomeric binding agent based on a polyamide or chlorinated rubber.

In the operation of the smoke projectile shown in the drawings, the projectile is fired and, after the lapse of a preset delay time, the time fuse 5 ignites the igniter-and-ejector charge 7 which is located in the head 3. The resultant jet of hot combustion gases immediately flows along the ignition channel 21 and ignites the smoke pressings 19 defining this channel and then exerts a gas pressure on the base 9. By this means the preset breaking point 11 between the body 1 and the base 9 is torn open and the entire payload ejected through the basal end of the body 1. The numerous ignited smoke pressings 19 present in the body 1 and sleeve 13 are liberated readily and scattered over a wide area, so that as they descend a thick smoke screen is drawn from above downwards.

Claims (12)

Claims:

1. A high-duty smoke-producing pressed body with wide-band camouflage effect, comprising red phosphorus, an oxidizing constituent consisting exclusively or preponderantly of a peroxydisulphate, one or more reactive metal powders (as hereinbefore defined) and a binding agent.

2. A smoke-producing pressed body as claimed in Claim 1, wherein the oxidizing constituent constitutes 10 to 30 percent by weight of the pressed body.

3. A smoke-producing pressed body as claimed in Claim 1 or 2comprising from 55 to 75 percent by weight of red phosphorus, 14 to 22 percent by weight of peroxydisulphate as oxidizing constituent, 2 to 8 percent by weight of reactive metal powder and 4 to 20 percent by weight of binding agent.

4. A smoke-producing pressed body as claimed in any one of Claims 1 to 3, wherein the peroxysulphate oxidizing constituent is sodium peroxydisulphate, potassium peroxydisulphate and/or ammonium peroxydisulphate.

5. A smoke-producing pressed body as claimed in any one of Claims 1 to 4, wherein the peroxydisulphate oxidizing constituent is potassium peroxydisulphate.

6. A smoke-producing pressed body as claimed in any one of Claims 1 to 5, wherein the metal powder is magnesium powder.

7. A smoke-producing pressed body as claimed in any one of Claims 1 to 6, wherein the binding agent is an elastomer.

8. A smoke-producing pressed body as claimed in any one of Claims 1 to 7, wherein the pressed body has the shape in plan view of a sector of a circle with the apex removed.

9. A smoke-producing pressed body, conprising approximately 65 percent by weight of red phosphorous, approximately 18 percent by weight of potassium peroxydisulphate, approximately 5 percent by weight of magnesium powder, and approximately 12 percent by weight of an elastomer binding agent.

10. A smoke-producing pressed body in accordance with Claim 1 substantially as hereinbefore described.

11. A high-duty smoke projectile, wherein a projectile body contains a smoke-producing charge and comprises means for igniting and ejecting such charge, and wherein the charge comprises a plurality of the smoke-producing pressed bodies claimed in any preceding claim, substantially filling a substantially cylindrical charge chamber while leaving free a centrally directed ignition channel.

12. A high-duty smoke projectile substantially as hereinbefore described with reference to the accompanying drawings.