Propellant Powder Charge Having Finned Internal Configuration

Abstract

A method of manufacturing a finned, one-piece propellant powder charge in which an extruded or moulded cylindrical block of propellant powder is split into two or more cylindrical sectors along one or more planes containing the longitudinal axis of the block. Each sector is machined to form longitudinal grooves parallel to a plane of symmetry of each sector so as to divide each sector into parallel longitudinal fins integrally connected at their bases to the rim of the respective sector. The machined sectors are then joined to reconstitute the cylindrical block and the sides of the reconstituted block is then coated with a combustion inhibitor.

Description

This invention relates to a method of making a finned, one piece propellant powder charge.

Previously, propellant powder charges with quick burning times (<0.10 s) and very strong thrust surges have been obtained by using charges formed of thin sheets of powder whose composition, thickness and length have varied with the ballistic performance required, the sheets being bonded together by a combustion inhibitor often in the form of a lacquer surrounding the periphery of the sheets.

The production of a charge of this type is, however, time-consuming, expensive and subject to many uncertainties. In particular, it is very difficult to bond the sheets with the lacquer. Furthermore, when the sheets are long and very thin, they are liable to deformation and this renders their behaviour highly unsatisfactory.

The present invention is concerned with an improved method of manufacturing such powder charges.

Accordng to the present invention, there is provided a method of manufacturing a finned, one-piece propellant powder charge which comprises

A. SPLITTING AN EXTRUDED OR MOULDED CYLINDRICAL BLOCK OF PROPELLANT POWDER INTO TWO OR MORE SECTORS OF THE CYLINDER ALONG ONE OR MORE PLANES CONTAINING THE LONGITUDINAL AXIS OF THE BLOCK;

B. MACHINING EACH SECTOR TO FORM LONGITUDINAL GROOVES PARALLEL TO A PLANE OF SYMMETRY OF EACH SECTOR SO AS TO DIVIDE EACH SECTOR WITH PARALLEL LONGITUDINAL FINS INTEGRALLY CONNECTED AT THEIR BASES TO THE RIM OF THE RESPECTIVE SECTOR;

C. JOINING THE MACHINED SECTORS TO RECONSTITUTE THE CYLINDER BLOCK, AND

D. COATING THE SIDES OF THE RECONSTITUTED BLOCK WITH A LAYER OF A COMBUSTION INHIBITOR.

The propellant powder may be either a homogeneous powder, for example a double-base explosive (nitroglycerine, nitrocellulose) which may be extruded, calendered or moulded, or a compound powder formed of an oxidizing agent such as ammonium perchlorate, a reducing agent such as aluminium powder, and a rubbery binder such as polybutadiene.

Preferably, the cylindrical block of powder is split into two half-blocks along a plane passing through the longitudinal axis of the block. The flat surface of each half-block is machined to form each half of a central bore for the reconstituted block, the parallel longitudinal fins are then machined on each half block to the desired thickness, spacing and shape, the two machined half-blocks are bonded together, optionally by means of adhesive, to reconstitute the original cylindrical block, and then the sides of the reconstituted block are coated with a combustion inhibiting layer, for example a lacquer.

In one embodiment of the invention, the sectors of the block are machined to provide fins of different thicknesses. Preferably, fins of two different thicknesses are provided alternately in each sector. In this manner, a plurality of thrust performances can be obtained by means of a single block.

The invention will be illustrated, by way of example, by means of the following description, referring to the accompanying drawings in which:

FIGS. 1 to 6 are perspective views of a finned one-piece charge at various stages during production in the method according to the invention;

FIGS. 7 and 8 represent cross-sections through alternative one-piece charges which may be made according to the invention.

Referring to FIGS. 1 to 6, an extruded or moulded cylindrical block 1 (FIG. 1) of propellant powder of a given composition is split along its entire length into two half-blocks 2 (FIG. 2). In order to adjust the specific flow rate per unit of the gas passage cross-section and to restrict or, conversely, promote erosive combustion, a desired shape is imparted to the flat portion 3 of each half-block (FIG. 3) by milling.

Thin sheets or fins 4 (FIG. 4) are then formed in each half-block by machining; the thickness, spacing and shape of the fins having been determined by means of calculation. The fins in each sector are joined together at their bases through the annular periphery or rim 5 of the block.

The two half-blocks are then joined (FIG. 5) by means of adhesive 6 or a solvent (for example, nitromethane) which dissolves the propellant.

The reconstituted block is rolled to the desired diameter and its sides are coated with a combustion inhibitor 7 (FIG. 6).

Since the fins can be machined to the desired lengths, shapes and thicknesses, the resulting finned one-piece charge has many advantages: satisfactory behaviour of the assembly, which forms a single unit since the fins are attached to the remainder of the block at their bases; highly reproducible performances since the block is wholly machined; a satisfactory filling coefficient; ease of adjustment of the performances obtained; and also the fact that the desired spacing of the two series of fins 4 can be maintained by means of combustible nitrocellulose felt, which is placed in the central bore before applying the coating of inhibitor.

By way of example, performances obtained with a finned one-piece charge prepared according to the invention, with the dimensional characteristics listed below in Table I, are given below in Table II.

The composition of the propellant powder used was as follows:

% by weight cake (60 parts nitrocellulose, 40 parts nitroglycerine) 93 "Centralite" 2 combustion catalyst 4 acetylene black (combustion accelerator) 1

The inhibitor lacquer was a polyester lacquer with a methyl-ethyl ketone peroxide catalyst and a cobalt naphthenate accelerator.

TABLE I

External diameter before coating 140 mm Internal diameter 136 mm External diameter after coating 144 mm Length 288 mm Powder cross-section: fins 5928 mm.sup.2 rim 867 mm.sup.2 Burning thickness: fins 3.8 mm rim 1.9 to 2 mm Powder density 1.63 Velocity at 20.degree.C and 300 bars 32 mm/s Initial pressure 410 Weight 3.2 kg Periphery 3000 mm Base area (6795 .times. 2) mm.sup.2 Area (3000 .times. 288) mm.sup.2 Total area 877,600 mm.sup.2 Nozzle area (K 410) 2140 mm.sup.2 Nozzle diameter 52.2 mm.sup.2

TABLE II

Time 0.06 s Weight burnt 3.2 kg Effective pressure 300 bars Thrust 110,000 N

in the embodiment illustrated in FIG. 7 of the drawings, the finned one-piece charge has fins of different, alternating thicknesses 4a, 4b, so that two different thrust performances (one for take-off and one for acceleration) can be obtained from a single block.

In the embodiment shown in FIG. 8 of the drawings, the finned one-piece charge is formed of four quarters 2a to 2d of a cylinder, machined to form fins 4, joined by means of adhesive 6 to reconstitute the cylindrical block, and whose sides 7 are coated with inhibitor.

Claims

What we claim is:

1. A method of manufacturing a finned, one-piece propellant powder charge which comprises

a. splitting an extruded or moulded cylindrical block of propellant powder into two or more sectors of the cylinder along one or more planes containing the longitudinal axis of the block,

b. machining the interior of each sector to form longitudinal grooves parallel to a plane of symmetry of each sector so as to divide each sector with parallel longitudinal fins integrally connected at their bases to the rim of the respective sector,

c. adhering the machined sectors to reconstitute the cylinder block, and

d. coating the exterior of the reconstituted block with a layer of a combustion inhibitor.

2. A method according to claim 1 in which the block of propellant powder is in the form of a right circular cylinder which is split into two semi-circular sectors for machining the fins thereon.

3. A method according to claim 1 in which fins of a plurality of thicknesses are machined on each sector.

4. A method according to claim 3 in which fins of two different thicknesses are machined alternately on each sector.

5. A method according to claim 1 in which the block of propellant powder comprises a double-base or compound explosive, said compound explosive being formed of an oxidizing agent, a reducing agent and a rubbery binder.

6. A method according to claim 5 comprising a compound explosive, wherein said oxidizing agent is ammonium perchlorate, said reducing agent is aluminum powder and said rubbery binder is polybutadiene.

7. A finned, one-piece, propellant powder charge comprising a cylindrical block of propellant powder exteriorly coated with a layer of a combustion inhibitor, said cylindrical block being composed of a plurality of substantially contiguous sectors along at least one plane containing the longitudinal axis of said block, wherein the interior of each sector contains a plurality of spaced parallel longitudinal fins of said propellant powder integrally connected at their bases to the rim of the sector thereby defining a void between a portion of said fins.

8. A finned, one-piece propellant powder charge of claim 7, wherein said cylindrical block contains two sectors.

9. A finned, one-piece propellant powder charge of claim 7, wherein said fins are of varying thicknesses.

10. A finned, one-piece propellant powder charge of claim 7, wherein said fins are of alternating thicknesses.

11. A finned, one-piece propellant powder charge of claim 7, wherein said clyindrical block comprises a double-base explosive.

12. A finned, one-piece propellant powder charge of claim 7, wherein said cylindrical block comprises a compound explosive formed of an oxidizing agent, a reducing agent and a rubbery binder.

13. A finned, one-piece propellant powder charge of claim 12, wherein said oxidizing agent is ammonium perchlorate, said reducing agent is aluminum powder and said rubbery binder is polybutadiene.