FR2640259A1 - Solid fuel propellant moulding system - with moulding block in sequence of sections with heat conductors attached to each - Google Patents

Abstract

A solid fuel propellant moulding system, designed to form a block contg. heat conductors which control combustion, consists of moulding an initial section of the block, forming a lengthwise portion of it, and placing one or all of the heat conductors against one or more of its surfaces. A second section of the block is then moulded, using a mould in which at lesat one part is formed by the heat conductor(s) of the initial section. Other sections of the block are made in the same manner. The heat conductors may be in the form of wires placed against the inner and/or outer surfaces of each section. ADVANTAGE - Simpler and more convenient block moulding.

Description

Process for manufacturing by molding a block of solid propellant with frontal combustion driven by heat conductors and block obtained by this process
The present invention relates to a method of manufacturing propellant blocks for rockets, missiles or more generally any machine propelled by a solid fuel, having a greatly increased combustion rate by incorporation of heat conductors in the propulsion units.

The invention more particularly relates to a method of manufacturing by molding solid propellant blocks with frontal combustion comprising heat conductors, preferably metal.

 It is already known, in particular from French Patent No. 1,349,125 and US Pat. No. 3,509,822, that the apparent rate of combustion of a propellant is greatly increased with respect to the intrinsic speed of this propellant, if thermal conductors are used. are incorporated into the propellant block. Indeed, these thermal conductors, which are generally wires or metal strips, modify the thermal field upstream of the flame front, because of the difference in conductivity between the propellant matrix and the thermal conductor. This modification of the thermal field induces a modification. the field of combustion velocities in the vicinity of the driver, and causes the formation of a cone centered on the driver.This creation of cones increases the combustion surface and therefore the amount of propellants.

Several modes of incorporation of these thermal conductors have been proposed. A first mode is to incorporate into the propellant matrix a certain amount of conductive wires of short length and in any distribution. In the second mode, only a few conducting wires are arranged in the longitudinal direction of the block and substantially perpendicular to its end faces. This last embodiment makes it possible to obtain a higher apparent and higher combustion rate.

Other studies, published in particular in French Patent No. 1,349,125, already cited, and the article "Influence of Long Metal Wires on Combustion of Dual-Base Propellants" of CHEN SHULING and
LIFENGSHENG published in "Combustion and Flame" No. 45 p. 213-218, 1982; - highlight the influence of the diameter of the conductor on the rate of combustion. Thus, it has been found that the highest apparent rate of combustion is obtained with wires of about 0.15 mm in diameter.

However, the manufacture of these propellant blocks by casting propellant in a mold, in which the yarns have previously been co-arranged and maintained in slight tension, has proved very delicate, particularly for viscous propellant compositions. . Indeed, the pressure exerted by the propellant composition causes the breaking of the son, which subsequently causes variations in the combustion of the blocks, and all the more so that the son are thin.

To prevent the breaking of the wires during the casting of the propellant composition, it is possible to reduce the tension exerted on the wires, but this leads to blocks having non-parallel wires between them and to the longitudinal direction of the block, and therefore the speed The combustion of the block has relatively large variations.

In addition, the arrangement of the son in the mold and their maintenance under tension required a relatively complex and bulky installation that hindered the casting of the propellant composition.

The object of the present invention is in particular to remedy all these drawbacks by proposing a manufacturing process by molding solid propellant blocks with frontal combustion, the combustion of which is controlled by small section thermal conductors without the risk of the conductors breaking during the casting. propellant.

For this purpose, the manufacturing method of the invention comprises the following successive steps
- Molding a first propellant composition, a first part of the block to be manufactured, this part being a longitudinal portion of the block, such as for example a crown, a central core or the like
- Have, in support on one or more walls of the first part of the already molded block, some or all of the thermal conductors
forming a second part of the block by casting a second propellant composition in a mold at least part of which is formed by the walls of the first part comprising the heat conductors
- and repeat these last two operations, if necessary, until the completion of the block in its entirety.

The method of the invention facilitates, therefore, the establishment of heat conductors. Indeed, as the thermal conductors are held in abutment against the wall of the first part, during the casting of the second composition, they are subjected to very low pressure forces, and the risks of rupture are substantially completely eliminated. .

Another advantage of this method lies in the fact that it is possible to manufacture monocomponent or multicomponent blocks, and more particularly two-component, depending on whether the first and second propellant compositions are identical or different.

The heat conductors are preferably metal wires, but it is also possible to use metal strips, for example, or wires and strips made of a material having a thermal conductivity coefficient greater than that of propellant constituting the propellant unit.

The metal wires advantageously have a diameter of between about 0.1 mm and 1 mm, and are, for example, silver or copper wires.

In addition, the conductive wires are preferably held against the walls of the first portion of the block in a substantially tensioned configuration at least during the casting of the second propellant composition.

To facilitate the positioning and maintenance of the conductive son on the walls, it is advantageous to form grooves on said walls, in which will be arranged the conductive son.

The conductive wires are held either by fixing on the end faces of the first part, or by tensioning means, such as, for example, a spring connected to one end of the son.

Furthermore, the propellant compositions are either cast if their viscosity is low, or injected under pressure in the case of high viscosity. The injection under pressure of the propellant composition is possible with the method of the invention because the conductive son bear against a wall during the injection phase, and therefore are not subjected to forces that can cause them to break.

According to another characteristic of the invention, the first part of the block may have a section of any shape, but preferably this first portion has the shape of a tube or a bar. This tube or this bar may be cylindrical, in this case the conductive son are disposed on one or both walls of the tube, or on the wall of the bar, the second propellant composition being cast around the tube and the bar and to the inside of the tube.

The tube and the bar may also have a polygonal section, for example triangular, hexagonal, square or star-shaped in the preferred variant of the invention. In this case, the conductive son are advantageously arranged in the edges corresponding to the vertices of the polygons. The convex edges of the tube or of the bar are preferably chamfered to form a longitudinal groove for receiving the conductive wires.

Of course, the son can be arranged on the sides of the polygons without departing from the scope of the invention.

The method of the invention is a very flexible use, because it allows for blocks of very varied shapes, and to arrange the son son very easily and in a calculated and determined distribution, beforehand.

The invention also relates to a propellant block obtained by the above method, this block being characterized in that the conductive son are located in the separation surface between two different propellant flows.

Other characteristics, details and advantages of the invention will appear more clearly in view of the detailed description which follows, made with reference to the examples given for information only and to the appended drawings, in which
FIG. 1 is a cross-sectional view of a propellant block produced according to the method of the invention,
FIG. 2 is a diagram illustrating the progression of the combustion front of a propellant block in the vicinity of a conductive wire,
FIG. 3 is a view of the rear face of a propellant block produced according to the method of the invention,
- Figure 4 is a partial view in longitudinal section along the line IV-IV of Figure 3; and
- Figure 5 is a view of the rear face of another propellant block made according to the method of the invention.

In rockets, missiles or more generally, any machine propelled by a solid fuel, it is sought thrust fuel having high thrust characteristics. Furthermore, in certain types of gear, it is desired to have a high coefficient of filling, and for this purpose front-fired blocks are used. However, to reduce the diameter of these blocks, without thereby reducing the thrust characteristic, it is necessary to increase the combustion rate of the block. For this purpose, it is necessary to use front combustion blocks, whose combustion is controlled and accelerated by heat conductors.

The method of the invention makes it possible to produce such blocks, according to easy operations, with an incorporation of the heat conductors, in particular low-diameter conductive wires, without any risk of their breaking, and whatever the viscosity of the the propellant composition.

Referring to FIG. 1, the method of the invention consists in molding a first portion 2 of the propellant block 1 to be manufactured. In the example illustrated in Figure 1, this first part 2 is a thick walled tube whose inner section 10 is triangular. The propellant composition used to form this part 2 is a moldable composition, such as, for example, a composite propellant, or a homogeneous propellant molded in particular by the method of molding in situ or overall.

In the case of Figure 1, the part 2 of the block can be cast directly into an inhibitor sleeve 3, or in a mold and then inhibited at the end of manufacture, for example.

After curing the propellant composition constituting part 2, heat conductors 4 are fixed inside the first part 2, advantageously along the edges defined by the vertices of the triangular section of the tube, and resting against the wall of the first part 2.

These heat conductors 4 are preferably metal wires with a diameter of between about 0.1 mm and about 1 mm. These wires 4 are stretched on the wall of the tube 2. Their fixing is ensured by bonding, or preferably by fixing the ends of the wires 4 on the end faces of the block 1 and even more advantageously by a tensioning device, such as a tension spring (not shown) connected to one end of the wire, while the other end of the wire is connected to a fixed point.

Other modes of attachment can be used, without departing from the scope of the invention.

The next step of the process of the invention consists in pouring into the interior of the tube or part 2 of the block 1, a propellant composition to form the second part 5 of the block 1.

Thus, since the conducting wires 4 bear against the wall of the first part 2, the pressure forces generated by the casting of the propellant composition in the part 2 do not cause the wires 4 to break. Therefore it is possible to pouring propellant compositions having high or low viscosities, with small diameter or brittle threads.

Then simply harden the second part 5 of block 1.

It will be readily understood that the propellant compositions constituting the first 2 and second 5 parts of the block 1 may be the same or different.

This method therefore allows the realization of two-component combustion propulsion blocks driven by son.

Other embodiments are shown in Figures 3, 4 and 5.

In the variant shown in Figures 3 and 4, the first portion 2 also has a tube shape, but the inner section 10 of the tube, shown in phantom fine lines, is star-shaped. The conductive son 4 are arranged in the vertices 6 of the star, in the example shown, a vertex on two.

The second part 5 of the block is made by casting a propellant composition inside the first part 2, the walls of this first part acting as a mold.

In the variant shown in Figure 5, the first portion 2 has a crown shape, the conductive son 4 being disposed on its outer and inner walls. However, to obtain a better positioning of the son 4, grooves 7 are formed on the walls 10 of the first part, by machining, molding, for example.

It is thus possible, in this variant, to incorporate two rows of wires 4, the second part 5 being cast at one time, inside the ring 2 and around it, since the ring 2 is, of course , arranged in a mold (not shown).

These different variants show that the method of the invention makes it possible to produce blocks of various shapes, containing a large number of conductive wires 4. Thus, it is also possible, to make the block illustrated in FIGS. first the central core with a star section and arrange the son 4 on the tops of the star. Advantageously, the convex edges of the star are chamfered to form a groove equivalent to the grooves 7 illustrated in FIG.

Furthermore, the casting of the second part 5 can be carried out either by simple casting, in particular with a relatively fluid propellant composition, or by injection under pressure for high viscosity compositions.

As illustrated in FIG. 4, it may be advantageous to make cones 8 centered on each conductive wire 4 on the rear face of the block so as to increase the initial combustion initial surface and to enable the surface to be reached very quickly. stabilized combustion.

Indeed, and as illustrated in FIG. 2, the difference in thermal conductivity between the conductive wire 4 and the matrix 9 of the propellant modifies the profile of the combustion speeds around the wire 4, inducing the formation of a cone, centered on the conductive wire 4. This phenomenon considerably increases the combustion surface of the block and therefore the apparent velocity Va of combustion of the block measured parallel to the axis of the block. The phenomenon of formation of the cone stabilizes after a certain combustion time t2, then the cane thus formed, with an angle at the apex 2S, advances according to the apparent velocity Va of combustion of the block. The realization of the cones 8 on the rear face of the block 1 makes it possible to reduce the duration t 2 of stabilization of the combustion surface and therefore of the apparent combustion rate Va.

Other means also make it possible to reduce this duration t2, such as, for example, a grooving of the end face.

In addition, the apex angle 2 of the cone makes it possible to calculate the apparent velocity Va of the block from the intrinsic speed Vi of the propellant composition.
Va = (I)
Sin α
Therefore, the multiplying coefficient n of the combustion rate corresponding to the incorporation of conducting wires is given by the following formula II:
1
n = Va / Vi (II)
sin α
The apparent velocity Va is determined experimentally by the following formula
V = e = burned thickness (III)
a tcr burning time in regime
This multiplier coefficient can also be calculated from the combustion curves of the blocks, and in particular from a point in the diagram: combustion pressure as a function of time, and using the following formula (IV):
CD P d2
n1 = @ / @ Vi D2 (IV) in which: V. = intrinsic velocity of the propellant at the pressure P
CD = propellant flow coefficient q = density of the propellant
P = average combustion pressure
d = diameter of the nozzle neck
D = diameter of the block
Blocks, according to the variant represented in FIGS. 3 and 4, were manufactured according to the process of the invention with composite propellant compositions with a polybutadiene hydroxytelechelic (PBHT) binder and with a polyurethane binder, and thermally conductive metal wires made of copper or aluminum. money.

The results obtained from the firing of these blocks are summarized in the table below.

Nature <SEP> Nature <SEP>#<SEP> of <SEP> temperature <SEP> n <SEP> calculated <SEP> by <SEP> n1 <SEP> calculated
SEP <SEP><SEP><SEP> SEP <SEP> SEP <SEP><SEP><SEP> Formula <SEP><SEP> For <SEP>&alpha; = <SEP> arcsin <SEP> 1 / n <SEP> Observations
<tb> binder <SEP> yarns <SEP> (mm) <SEP> (C) <SEP> (II, III) <SEP> mule <SEP> (IV)
<tb> 1 <SEP> PBHT <SEP> Ag <SEP> 0.2 <SEP> - <SEP> 40 <SEP> - <SEP> 2.95 <SEP> 20
<tb> 2 <SEP>"<SEP>"<SEP>"<SEP> + <SEP> 20 <SEP> 3.5 <SEP> 2.9 <SEP> 20
<tb> 3 <SEP>"<SEP>"<SEP>"<SEP> + <SEP> 60 <SEP> - <SEP> - <SEP> 3.05 <SEP> 19
<tb> 4 <SEP> PBHT <SEP> Cu <SEP> 0.2 <SEP> + <SEP> 20 <SEP> 1.7 <SEP> 1.6 <SEP> 39
<tb> 5 <SEP> Polyurea <SEP> Ag <SEP> 0.3 <SEP> - <SEP> 40 <SEP> 4.5 <SEP> 4,4 <SEP> 13
<tb> thanne
<tb> Polyurea <SEP> Cu <SEP> 0.3 <SEP> - <SEP> 40 <SEP> 4.8 <SEP> 4.9 <SEP> 11.8
<tb> thanne
<tb> 7 <SEP>"<SEP>"<SEP>"<SEP> + <SEP> 20 <SEP> 5 <SEP> 5.2 <SEP> 11
<tb> 8 <SEP> PBHT <SEP> Ag <SEP> 0.2 <SEP> + <SEP> 20 <SEP> 3,11 <SEP> 3.36 <SEP> 17.3 <SEP> block <SEP > of <SEP> length <SEP> 255 <SEP> mm
<tb> 9 <SEP>"<SEP>"<SEP>"<SEP> - <SEP> 40 <SEP> 3.22 <SEP> 3.43 <SEP> 17 <SEP>"
<tb> 10 <SEP>"<SEP>"<SEP>"<SEP> - <SEP> 40 <SEP> 3.42 <SEP> 3.43 <SEP> 17 <SEP><SEP> Block of <SEP > length <SEP> 905 <SEP> mm
<tb> 11 <SEP> PBHT <SEP> Ag <SEP> 0.2 <SEP> + <SEP> 60 <SEP> 3.16 <SEP> 3.30 <SEP> 17.6 <SEP> block <SEP > of <SEP> length <SEP> 255 <SEP> mm
<tb> 12 <SEP>"<SEP>"<SEP>"<SEP> + <SEP> 60 <SEP> 2.99 <SEP> 3.05 <SEP> 19 <SEP><SEP> block of <SEP > length <SEP> 905 <SEP> mm
<tb> 13 <SEP> PBHT <SEP> Cu <SEP> 0.2 <SEP> - <SEP> 40 <SEP> 2.79 <SEP> 2.74 <SEP> 21.4 <SEP> block <SEP > of <SEP> length <SEP> 905 <SEP> mm
<tb> 14 <SEP>"<SEP>"<SEP>"<SEP> + <SEP> 20 <SEP> 2.71 <SE> 2.65 <SE> 22.2 <SEP>"
<Tb>
The combustion pressure of these blocks, observed during the shots, is substantially stable, which indicates that the wires have not broken and are arranged regularly in the block.

From the various tests carried out, it appears that the multiplying coefficients of the combustion rate of the propellant blocks obtained by the method of the invention have the following mean values
n = 3.5 for silver wires of diameter 0.2 mm and one
Pc = 67 bars
n = 2.65 for copper wires of diameter 0.2 mm and one
Pc = 50 bars.

Moreover, blocks made according to the process of the invention have undergone, without deterioration, heat treatment cycles.

Thus, the method of the invention makes it possible to manufacture Ex plue and with good reliability blocks of propellant with frontal combustion driven by thermal conductors, and in particular the realization of such blocks with very viscous and even pasty propellant compositions. . In previous processes, making wire-driven combustion blocks from viscous or pasty propellant compositions was very difficult because the wires were often broken during the casting of the propellant composition.

Claims (17)

claims 1. A method of manufacturing by molding a block of solid propellant with frontal combustion driven by heat conductors, characterized in that it comprises the following successive steps  - Molding a first propellant composition, a first portion 2 of said block 1 to be manufactured, said portion 2 being a longitudinal portion of said block 1;  disposing on one or the walls of said first part some or all of said heat conductors  forming a second portion representing a second portion of said block 1, by casting a second propulsive composition in a mold at least a portion of which is formed by the walls. Having said leads 4 of said first portion 2;  - repeat the last two steps until completion of the total block. 2. Method according to claim 1, characterized in that the aforesaid heat conductors 4 are fixed against the walls 10 of said block portions in substantially tensioned configuration, said conductors 4 being son. 3. Method according to claim 1 or 2, characterized in that grooves 7 are formed on the surface of the walls 10 of the aforementioned block portions, the son 4 conductors being arranged in these grooves 7. 4. Method according to one of claims 1 to 3, characterized in that the first part 2 above is a tube of any section, the son 4 aforementioned conductors being disposed on its inner face and / or outer. 5. Method according to claim 4, characterized in that the transverse internal section of the aforementioned tube is a polygon, the son 4 aforementioned conductors being preferably arranged in the vertices of the polygon. 6. Method according to claim 5, characterized in that the aforementioned polygon is a triangle or a star-shaped polygon. 7. Method according to claim 4, characterized in that the wall of said tube has a polygonal shape, preferably a star, the son 4 conductors being arranged on the edges of said wall. 8. A method according to claim 7, characterized in that a longitudinal groove is formed on each are convexe of the wall of the aforesaid tube, for receiving the son 4 aforementioned conductors. 9. Method according to one of claims 1 to 3, characterized in that the first part 1 above is a bar. 10. The method of claim 9, characterized in that the aforesaid bar has a polygonal section, preferably triangular or star-shaped, each convex edge of said wall comprising a longitudinal groove for receiving the conductive son 4. 11. Method according to one of the preceding claims characterized in that the son 4 conductors are mounted in a substantially tensioned position on the walls 10 of a said part of the block during the casting of another part of said block, by fixing their ends on the end faces of said portion of the block. 12. Method according to one of claims 1 to 10, characterized in that the aforementioned four conductor son are maintained in a substantially tensioned position on the walls of a said part of the block during the casting of another part of said block by tension means such as a spring connected to at least one end of said wires. 13. Method according to one of the preceding claims characterized in that the first and second propellant compositions are identical. 14. Method according to one of the preceding claims, characterized in that the propellant composition forming the second part of the block above is injected under pressure. 15. Method according to one of the preceding claims, characterized in that the conductive son have a diameter of between about 1/10 mm and about 1 mm. 16. Solid propellant block with frontal combustion driven by heat conductors, characterized in that it is obtained by the method according to one of the preceding claims. 17. propellant block according to claim 16, characterized in that the aforementioned heat conductors 4 are located in the separation surface 10 between two propellant flows.