GB1580176A

GB1580176A - Solid propellent charge bodies

Info

Publication number: GB1580176A
Application number: GB2891274A
Authority: GB
Original assignee: DUPRAT Y G J FOURNIER A D; Le Coz J M
Current assignee: DUPRAT Y G J FOURNIER A D; Le Coz J M
Priority date: 1973-07-04
Filing date: 1974-06-28
Publication date: 1980-11-26
Also published as: FR2436121B1; FR2436121A1; IT1040552B; DE2431982C2; BE817264A; DE2431982A1

Description

(54) IMPROVEMENTS IN OR RELATING TO SOLID PROPELLENT CHARGE BODIES (71) We, YVES GUY JEAN DUPRAT, ALAIN DANIEL FOURNIER and JACQUES MICHEL LE COZ, all French citizens, of respectively 10, allee Cavalier, 18000 Bourges; 10 rue de Veauce, Saint-Doulchard 18230 and 17, avenue des Bigarelles, 18000 Bourges, all in France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to supported propellent charge bodies and to gas generators comprising the propellent charge bodies.

Gas generators generally comprise a body of solid propellant, particularly a body of solid propellant having a short combustion duration, for example less than 0.5 sec, which is fixed in a combustion chamber in the gas generator with the interposition of a support material, possibly carried by a rigid support structure, the support material, together with the support structure, if present, being hereinafter called a base. Such a base may be used in conjunction with a solid homogeneous propellent charge which may have one of a number of configurations. The charge can be formed of one or more elements which can be for example flat and assembled in a multilayer structure, solid or hollow cylindrical blocks or in the form of strips which may be flat or corrugated.In the following text, the expression propellent "element" is employed in the broad sense to mean an individual mass of propellant forming part of or the whole of a propellent charge body.

Gas generatores, find use, for example, in self-propelled missiles or rockets as the propulsion units thereof, recoil-less guns or weapons using solid propellent charges, pressuring devices employed to propel liquids, notably in large craft and in launching pads for missiles.

The assembly or positioning of propellent elements in the base must be carried out in such a manner that the propellent elements maintain a constant disposition with respect to the walls of the combustion chamber of the gas generator both during the passive life of the charge, that is when awaiting use, and during its active life, that is when the gas generator or a vehicle housing the same, is in use. Similar considerations apply to the disposition with respect to each other of individual propellent components of the propellent elements. During the passive life of the propellent elements, their structure must be resistant to shocks, particularly climatic and mechanical shock to which they may be subjected.Hence the propellent elements must be flexibly supported on the bases and possess unchanging mechanical and physicochemical properties in the wide temperature range to which the propellent elements may be subject, and over long periods of time. During the active life of the propellent elements, it is necessary to ensure that, at the instant of their ignition, the flow of gases does not impair the further combustion of the propellent elements, particularly by leaving unburnt propellent material so that the performance of the gas generator is lowered. In some cases, the propellent elements must be able to withstand considerable accelerations, as in the launching or firing of missiles containing them.

Various types of bases for propellent elements have been described, which generally differ both in their structure, which depends of course, on the configuration of the propellent element and, above all, in their composition so that the bases meet the aforesaid requirements to differing extents.

For example, there is proposed in United States Patent Specification No. 2,502,458, the use of a support material consisting of a hardenable bonding material, such as plaster of Paris. French Patent Specification No. 2,067,914 describes a method of adhesively bonding or assembling elongate propellent charge elements by bonding them over a very considerable part of their length, and on that face of the said blocks which does not burn, by means of a plastics material, for example a mixture of resin and glass fibre or of resin and asbestos.

In addition, the use of plastics materials having a polyester base has been proposed on a number of occasions. For example, French Patent Specification No. 2,061,802 discloses a mode of uniting masses of propellant in an element used in firing a micro-rocket which comprises seating the masses in a polyester prepolymer, which is cured. The cured polyester is preferably combustible. In French Patent Specification No. 1,351,422, the propellent element used in a rocket motor is formed of small tubes of propellant forming a bundle which is fixed and moulded at one end in a block of polyester or reinforced phenoplast. Finally, there have been described propellent elements consisting of profiled powder charge strips, on one of the ends of which there has been cast a polyester resin base for fixing the said element obtained in the combustion chamber of a propulsion unit.

In cases where the assembly of elongate propellent elements to form a propellent charge body with the aid of a single support structure has not been satisfactory, it has been found necessary to use at least two support structures, for example disposed one at each end of an assembled group of elements, or to use additional mechanical means for securing the elements together, such as elastic bands surrounding a bundle of elements, or rigid bracing means between the elements of propellent material.

The aforesaid arrangements have a number of characteristic disadvantages.

The support materials or "bonding agents" used in the formation of the bases employed do not have sufficient temperature stability, and their use is limited by considerable variations in their mechanical properties which may occur in use. For example, they are generally too rigid in the cold state, which results in their being fractured, thereby causing separation of component elements of the propellent charge body. The support materials often deteriorate in time, and modification of the ballistic properties and of the physical properties thereof occurs owing to the fact that the nitroglycerine or the plasticisers generally contained in the propellent elements, are absorbed by the plastics material comprised by the base.Likewise, chemical incompatibility often exists between the plastics material used for support purposes and the solid propellents used in making the propellent charge bodies. Finally, the quality of bonding between the support material and the elements of propellent material is generally different to the quality of bonding obtained between the base and the walls or the end of the combustion chamber of the gas generator.

According to the present invention, there is provided a supported solid propellent charge body comprising a base, as hereinbefore'defined having one or more masses of solid propellent material having a lateral surface adhering to a cured mass of silicone elastomer which forms the support of the base.

The present invention also provides gas generators comprising such propellent charge bodies. The propellent charge bodies are preferably homogeneous.

The base may itself comprise cured silicone elastomer, generally bonded to a support structure, and having embedded therein one or more masses of solid propellent material, for example an array of parallel corrugated strips of propellent material. Alternatively, the silicone elastomer material may only be employed at discrete locations on a support structure formed of other material and used to bond the masses of solid propellent material to the support structure. For this purpose, the solid propellent masses may be of solid or hollow rod form the ends of which are disposed in recesses in the support structure. Alternatively, the support structure may have a plurality of projections formed at the surface thereof and over which are disposed the ends of hollow rods of solid propellent material.

Any surface which is contacted by silicone elastomer is preferably coated with a layer of primer material to enhance the wetting thereof by silicone elastomer and ensure good adhesion thereto by the silicone elastomer, when cured and hence a strong bonding of the solid propellent mass(es) to the support structure.

The silicone elastomer which is employed in the present invention preferably has an ultimate tensile strength of at least 30 bars and an elongation at break of at least 80%.

The silicone elastomer is preferably curable at ambient temperature, i.e. at about 20"C, and is preferably capable of resisting a flame at 20000 to 30000C for at least two seconds.

The cured silicone elastomer preferably possesses a Shore A hardness of from 40 to 60.

The cured elastomer itself preferably possesses mechanical and physico-chemical properties which remain substantially constant in the temperature range in which propellent charges are employed, which generally is from -40"C to +600 C. It has high flexibility at sub-zero temperatures owing to the low embrittlement point of silicone elastomers. If the elastomer is curable at ambient temperature (in the neighbourhood of 20 C), heating of the propellent material, with concomitant risk of ignition thereof, will be avoided. The elastomer has good resistance to combustion gases generated during combustion of the propellent element. In addition, the elastomer is chemically compatible with double-base (homogenous) propellants, irrespective of whether the latter are moulded or extruded.Finally, it has been found that the elastomers have low affinity for nitroglycerine and for plasticisers contained in the propellant.

Consequently, propellent charge bodies comprising silicone elastomer have excellent resistance to mechanical and climatic environmental conditions, preserve the integrity of the propellent elements as such at the instant of ignition thereof, possess very good mechanical stability, when subjected to rapid acceleration and have very good storage properties. In addition, because the propellent material is maintained in its desired disposition so that it undergoes optimum combustion, unburnt portions thereof do not remain in the gas generator; hence there is increased propulsion efficiency and freedom from ejection of masses of unburnt propellent which may block apertures and nozzles.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 is a longitudinal section through the rear part of one form of gas generator embodying this invention; Figures 2 to 4 are each a longitudinal section through a propellent charge body embodying this invention; and Figure 5 is a plan view of the propellant charge body shown in Figure 4.

Referring to Figure 1 of the drawings, a gas generator is shown as a rocket motor in a casing 1 having a combustion chamber 2 and a gas discharge nozzle 3. The compartment 2 contains two elements of propellent material, namely a hollow body 4 and an axial cylinder 5 seated in a support material 6 formed of cured silicone elastomer to which the propellent material adheres, and which, in turn, adheres to a supporting transverse wall member of the compartment 2 which serves as a support structure as aforesaid. The combination of propellent charge elements 4 and 5, the support material 6 and the transverse wall member can thus be considered to form a propellent charge body according to this invention.

The propellent charge bodies shown in Figures 2 and 3 each comprise a plurality of rod-like masses 7 of propellent material connected to a wall member 8 for use as an end wall of a combustion chamber or propellant compartment 2 in Figure 1, by means of a mass 9 of cured silicone elastomer. In Figure 2 the rod-like masses are solid rods seated in recesses 10 formed in the wall member 8. In Figure 3 the rodlike masses are hollow cylindrical rods seated over projections 11 on the wall member 8, the cured elastomer occupying the space between and bonding together the inner walls of the rod-like masses and the projections I 1.

Referring finally to Figures 4 and 5, a propellent charge body is shown which comprises a plurality of corrugated strips 12 of propellent material embedded in a base 13 of cured silicone elastomer moulded around their ends. As can be seen from Figure 5, the overall width of the strips 12 reduces from that of a central strip 12 so that an overall assembly of corrugated strips 12 which is obtained is cylindrical for fitting into a combustion chamber therefor.

The following Examples, in which reference is made to the aforementioned figures, illustrate the invention.

EXAMPLE I A propellent charge body having the shape of that shown in Figure 1, was prepared by sinking the ends of the hollow body 4 and cylinder 5 into a mass of uncured silicone elastomer, the methyl phenyl polysiloxane material available in France under the trade name PR 1930-2 from the Company Le Joint Francais. The elastomer occupied the dish-shaped forward end of the combustion chamber 2 of the gas generator. The introduction of the propellent material into the baseforming material and the adhesive bonding of the base material to the forward end of the combustion chamber took place simultaneously.

Before sinking in the elastomer material, the bodies 4 and 5 of propellent material were scoured with trichloroethylene, and were covered in their end regions with a priming layer formed of the priming material available in France under the trade name PR 1903-M, from Le Joint Francais and containing a silicone elastomer of similar chemical constituties to the aforesaid silicone elastomer PR 1930- 2. The end of the chamber was likewise scoured with trichloroethylene and provided with a priming layer formed of the same priming material. After drying of the priming material on the propellent material and the combustion chamber, the silicone elastomer was directly run into the chamber at ambient temperature, whereafter the bodies of propellent material were carefully lowered into the elastomer.The curing of the whole took place at ambient temperature, mechanical means being used to hold the propellant bodies in place during the curing stage.

As a variant of the aforesaid procedure, individual masses of propellant material can be adhesively bonded to the end wall of the combustion chamber by means of silicone elastomer disposed at discrete intervals or can be fixed to an end member which is subsequently fitted in the combustion chamber. This end member may be flat or of spherical form, and it may be formed with recesses 10 as illustrated in Figure 2, or with projections 11 as illustrated in Figure 3. In each of Figures 2 and 3 the silicone elastomer 9 provides a union between the rod-like masses 7 of propellant and the metal wall member 8.

EXAMPLE 2 A propellent charge body having the shape shown in Figures 4 and 5 was formed from an assembly of strips of propellent material having a corrugated profile and small thickness (of the order of a millimetre). The strips were mounted in a base consisting of the same silicone elastomer as that used in Example 1. The fixing of the propellent charge body in the combustion chamber of a gas generator may be effected by adhesive bonding using the same elastomer, or by any other method. To form the propellent charge body, the strips 12 were scoured with trichloroethylene and then coated in their end regions with a layer of the aforesaid priming material PR1903-M.The strips were arranged by means of a mechanical centring device in the disposition they were to have in the propellent charge body and, while maintained on this device, were carefully lowered into a mould which reproduced the external form of the base and contained the necessary quantity of silicone elastomer. After curing of the elastomer at ambient temperature, the body obtained was extracted from the mould and the centring device removed.

As variants of the foregoing procedure, other forms of component masses of propellent material may be used. There may be used an assembly of bodies of cylindrical form, in the form of tubes, flat strips or helically coiled strips.

EXAMPLE 3 In the construction of a propellent charge body of the type shown in Figure 3 there were used 200 tubes of homogeneous propellent. The overall propellent charge body measured approximately 140 mm in length and had the diameter of 70 mm. The weight of the propellent material was about 0.3 kg and the combustion time of this charge was about 10 milliseconds.

Environmental and firing tests were then carried out with the propellent charge bodies. To allow a comparison to be made between propellent charge bodies of this invention and those of prior art construction, there were used 48 charges comprising a base consisting of silicone elastomer, and 48 charges comprising a base consisting of polyester of conventional type filled with lithophone, both types being produced in the form indicated in the preceding paragraph.

These charges were subjected to vibrations at 50 Hz and to repeated impacts at a frequency of the order of I hertz for several hours. They were then kept either for 10 hours in an enclosed space kept at a temperature of 40"C, or for two days at a temperature of 50"C. Finally, the charges were subjected to a dropping test from a height of about 2 metres.

These tests had no effect on the charges comprising a cured silicone elastomer base.

On the other hand, it was found that even after being dropped from a height of only about 1 m, 33 charges out of 48 of those comprising a polyester base had undergone breakage of tubes of propellent material.

More than eleven of the charges had more than five broken tubes.

The charges which remained intact were fired at temperatures of -31.50C and +510C. Examination of the silicone elastomer bases after the firing tests showed that the bases had resisted combustion well and that all the propellent powder, and particularly that at the ends of the strips let into the base, had burnt. No flame was observed. The bonding of the propellent charge material to the end of the combustion chambers used in the firing tests was secure, no detached base being found after the firing.

During the firing of the propellent charge bodies having a silicone elastomer base there was obtained an initial velocity which was 4% higher at low temperatures (-31.5"C) and about 2% higher at high temperatures (+51"C).

WHAT WE CLAIM IS: 1. A supported solid propellent charge body comprising a base as hereinbefore defined having one or more masses of solid propellent material having a lateral surface adhering to a cured mass of silicone

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. same priming material. After drying of the priming material on the propellent material and the combustion chamber, the silicone elastomer was directly run into the chamber at ambient temperature, whereafter the bodies of propellent material were carefully lowered into the elastomer. The curing of the whole took place at ambient temperature, mechanical means being used to hold the propellant bodies in place during the curing stage. As a variant of the aforesaid procedure, individual masses of propellant material can be adhesively bonded to the end wall of the combustion chamber by means of silicone elastomer disposed at discrete intervals or can be fixed to an end member which is subsequently fitted in the combustion chamber. This end member may be flat or of spherical form, and it may be formed with recesses 10 as illustrated in Figure 2, or with projections 11 as illustrated in Figure 3. In each of Figures 2 and 3 the silicone elastomer 9 provides a union between the rod-like masses 7 of propellant and the metal wall member 8. EXAMPLE 2 A propellent charge body having the shape shown in Figures 4 and 5 was formed from an assembly of strips of propellent material having a corrugated profile and small thickness (of the order of a millimetre). The strips were mounted in a base consisting of the same silicone elastomer as that used in Example 1. The fixing of the propellent charge body in the combustion chamber of a gas generator may be effected by adhesive bonding using the same elastomer, or by any other method. To form the propellent charge body, the strips 12 were scoured with trichloroethylene and then coated in their end regions with a layer of the aforesaid priming material PR1903-M.The strips were arranged by means of a mechanical centring device in the disposition they were to have in the propellent charge body and, while maintained on this device, were carefully lowered into a mould which reproduced the external form of the base and contained the necessary quantity of silicone elastomer. After curing of the elastomer at ambient temperature, the body obtained was extracted from the mould and the centring device removed. As variants of the foregoing procedure, other forms of component masses of propellent material may be used. There may be used an assembly of bodies of cylindrical form, in the form of tubes, flat strips or helically coiled strips. EXAMPLE 3 In the construction of a propellent charge body of the type shown in Figure 3 there were used 200 tubes of homogeneous propellent. The overall propellent charge body measured approximately 140 mm in length and had the diameter of 70 mm. The weight of the propellent material was about 0.3 kg and the combustion time of this charge was about 10 milliseconds. Environmental and firing tests were then carried out with the propellent charge bodies. To allow a comparison to be made between propellent charge bodies of this invention and those of prior art construction, there were used 48 charges comprising a base consisting of silicone elastomer, and 48 charges comprising a base consisting of polyester of conventional type filled with lithophone, both types being produced in the form indicated in the preceding paragraph. These charges were subjected to vibrations at 50 Hz and to repeated impacts at a frequency of the order of I hertz for several hours. They were then kept either for 10 hours in an enclosed space kept at a temperature of 40"C, or for two days at a temperature of 50"C. Finally, the charges were subjected to a dropping test from a height of about 2 metres. These tests had no effect on the charges comprising a cured silicone elastomer base. On the other hand, it was found that even after being dropped from a height of only about 1 m, 33 charges out of 48 of those comprising a polyester base had undergone breakage of tubes of propellent material. More than eleven of the charges had more than five broken tubes. The charges which remained intact were fired at temperatures of -31.50C and +510C. Examination of the silicone elastomer bases after the firing tests showed that the bases had resisted combustion well and that all the propellent powder, and particularly that at the ends of the strips let into the base, had burnt. No flame was observed. The bonding of the propellent charge material to the end of the combustion chambers used in the firing tests was secure, no detached base being found after the firing. During the firing of the propellent charge bodies having a silicone elastomer base there was obtained an initial velocity which was 4% higher at low temperatures (-31.5"C) and about 2% higher at high temperatures (+51"C). WHAT WE CLAIM IS:

1. A supported solid propellent charge body comprising a base as hereinbefore defined having one or more masses of solid propellent material having a lateral surface adhering to a cured mass of silicone

elastomer which forms the support material of the base.

2. A charge body as claimed in Claim 1, in which the base consists of a cured mass of silicone elastomer having one or more masses of solid propellent material embedded therein, in part.

3. A charge body as claimed in Claim 2, in which a plurality of parallel corrugated strips of propellent material are embedded at their ends in the cured silicone elastomer.

4. A charge body as claimed in Claim 1, in which the base comprises a support structure which is formed with a plurality of recesses occupied by end regions of solid or hollow rods of solid propellent material each bonded to the wall df the respective recess by means of a cured mass of silicone elastomer.

5. A charge body as claimed in Claim I in which the base comprises a support structure which is formed with a plurality of projections entering end regions of hollow rods of solid propellent material each bonded to the respective projection by means of a cured mass of silicone elastomer.

6. A charge body as claimed in any one of the preceding claims, wherein a layer of primer material for enhancing the wetting of the solid propellent material by the silicone elastomer is disposed on the surface of the said mass of solid propellent material contacted by cured silicone elastomer.

7. A charge body as claimed in Claim 4 or 5, in which wetting of the support structure by the silicone elastomer is enhanced by a layer of primer material disposed on surfaces of the support structure contacted by silicone elastomer.

8. A charge body as claimed in any one of the preceding claims, which is housed in a gas generator which comprises a combustion chamber casing having outlet means for combustion gases produced in the combustion chamber and transverse wall means which, together with said cured mass of elastomer material forms said base.

9. A charge body as claimed in Claim 8, in which the gas generator is the motor of a self-propelled missile or rocket.

10. A charge body as claimed in any one of the proceding claims in which the mass(es) of solid propellent material is/are homogeneous.

11. A body as claimed in any one of the preceding claims, in which the cured silicone elastomer has an ultimate tensile strength of at least 30 bars.

12. A body as claimed in any one of the preceding claims, in which the cured silicone elastomer has an elongation at break of at least 80%.

13. A body as claimed in any one of the preceding claims, in which the silicone elastomer has been cured at an ambient temperature of about 20cm.

14. A body as claimed in any one of the preceding claims, in which the cured silicone elastomer has a resistance to flames having temperatures of from 2000 to 3000"C of at least two seconds.

15. A solid propellent charge body as claimed in Claim 1, substantially as described in either of the foregoing Examples I and 2.

16. A solid propellent charge body, substantially as hereinbefore described with reference to and as shown in, any one of Figures 1, 2 and 3 or Figures 4 and 5 of the accompanying drawings.