GB2233972A

GB2233972A - Propellant powders

Info

Publication number: GB2233972A
Application number: GB8908704A
Authority: GB
Inventors: Francis Sydney Baker; Roy Edward Carter
Original assignee: Royal Ordnance PLC
Current assignee: BAE Systems Global Combat Systems Munitions Ltd
Priority date: 1989-04-18
Filing date: 1989-04-18
Publication date: 1991-01-23
Also published as: GB8908704D0

Abstract

A method of producing a propellant in a bail powder form comprises the steps of extruding lengths of propellant cord, cutting the lengths into strips or pellets, and spinning the strips or pellets whereby they tumble against one another and eventually develop into spherical or spheroidal granules.

Description

PROPELLANT POWDERS The present invention relates to propellant powders and their production.

Certain small arms ammunition and auxiliary charges for mortar bombs and the like employ so-called ball powder which comprises essentially spherical granules of propellant materials such as nitrocellulose optionally containing a small amount of additives such as nitrogylcerine or other plasticiser material.

The advantage of ball powder compared with propellant in other forms, eg. tubular pellets, is that it flows more easily in handling and filling machinery.

Ball powder is traditionally made by a dissolution process followed by precipitation in a stirred vessel. This known process has the disadvantages that the range of suitable formulations which it can be used to produce is limited and that a range of particle sizes are produced necessitating considerable sieving and wastage.

According to the present invention, a method of producing a propellant in a ball powder form comprises the steps of extruding lengths of propellant cord, cutting the lengths into strips or pellets and spinning the strips or pellets whereby they tumble against one another and eventually develop into spherical or spheroidal granules.

Ball powder made in this way allows a wider range of propellant formulations to be manufactured in a more controlled manner with unexpected propellant performance benefits as described hereinafter.

The spinning step may be carried out in a spheruliser such as is used for the production of microcapsules in the pharmaceutical industry. The size of the granules produced is controlled by the operational parameters of the spheruliser and in addition by the mechanical and rheological properties of the extrudate. The strips or pellets need to deform elastically under the applied forces, but after deformation the particles remaining should stable until dried or otherwise fixed.

The cord lengths may, as described in a copending UK Patent Application of even date by the present applicants, conveniently be formed by screw extrusion eg. from a co-rotating twin screw extruder followed by chopping to size in a known way. A multiplicity of cords may be extruded and chopped in this way at the same time by the same machine.

It is usual for ball powder to incorporate a moderator composition to control the burning rate characteristics of the propellant. Where the cords are produced by extrusion the moderator composition may be conveniently co-extruded together with the propellant composition as described in a copending UK Patent Application of even date by the present applicants. The moderator may be a coating on the lengths of propellant employed or alternatively it may be a central strip around which the propellant is formed.

Other known optional additives which may be added to the propellant employed to form the ball powder include flash suppressant, eg, a potassium salt such a potassium bicarbonate or sulphate, and antioxidant. Preferably, such optional additives do not form more than two per cent of the weight of propellant present.

By coating ball powder made in the manner described above with a suitable binding agent, eg. ethyl cellulose together with a solvent such as amylacetate, it is possible to form a bonded propellant mass where such a mass is required. For example, such a mass may be employed in the preparation of caseless ammunition for small arms where the propellant charge is moulded around the bullet or projectile. By using a binder having an inherent tendency to crumble, such a charge may be broken back into its constituent spheroids upon operation of a disruption charge when the ammunition is fired.

Low density, fast burning ball powder, one particular form of ball powder, made in the manner described herein, may be made by incorporating a volatile blowing agent or a soluble salt in the extruded composition or by injecting a gas at the extrusion die during the extrusion of the cords.

As described in the aforementioned copending UK patent application of even date by the present applicant, the propellant of the cords formed into ball powder may comprise a multi-compositional propellant, for example a fast burning composition may be coated on a slower burning composition by co-extrusion. Alternatively, a propellant composition may be coated with a moderator, eg. methyl centralite, in this way.

The sizes of the particles produced by the present invention will depend on the material composition and the processing conditions. However, particles having a typical average diameter of between 0.25mm and 3mm can be produced. The required diameter can however be obtained more repeatedly for all granules produced in a given sample compared with the prior art.

Claims

1. A method of producing a propellant in a ball powder form which comprises the steps of extruding lengths of propellant cord, cutting the lengths into strips or pellets.

and spinning the strips or pellets whereby they tumble against one another and eventually develop into spherical or spheroidal granules.

2. A method as claimed in claim 1 and wherein the spinning step is carried out in a spheruliser.

3. A method as claimed in claim 1 or claim 2 and wherein the lengths of propellant cord include a burning rate moderator co-extruded with the propellant composition of the cord.

4. A method as claimed in any one of the preceding claims and wherein the ball powder is coated with a binding agent to form a bonded propellant mass having an inherent tendency to crumple.