EP0026511B1 - Method for manufacturing a composite barrel - Google Patents

Abstract

This barrel is characterized in that it comprises three layers superimposed without any break in continuity of surface contact between layers, namely: an internal layer of a refractory material; a core layer of a material the mechanical strength of which is higher than about 250 MPa at 900 DEG and an external layer of an alloyed steel. The invention relates also to a process for the manufacture of such barrel.

Description

The present invention relates to a method of manufacturing a composite gun.

• l'érosion et la corrosion par les gaz de combustion de la poudre propulsive ;
• la fatigue thermique due aux sollicitations mécaniques répétées à température élevée ;
• la friction provoquée par le passage du projectile qui, partant d'une vitesse nulle, acquiert une vitesse de plusieurs centaines de m/sec. en une milliseconde ;
• une pression Interne de plusieurs milliers de bars qui induit dans le canon des tensions mécaniques Importantes mais de courte durée.

Automatic weapons are mechanisms whose sub-assemblies and constituent parts are subjected to severe operating constraints. This is particularly the case with cannons and especially with the cannons of weapons used at very high rates, such as the guns of machine guns. In this case, the metal of the barrel is mechanically stressed while it is maintained at a relatively high temperature and in any case greater than 500 ° C. This rise in temperature is due to the combustion of the propellant powder and to friction. The available energy is mainly used to move the projectile, but a non-negligible fraction of this energy is transformed into heat which is dissipated towards the outside through the metal of the barrel which heats up strongly. In fact, the constraints can be summarized as follows:

• erosion and corrosion by the combustion gases of the propellant powder;
• thermal fatigue due to repeated mechanical stresses at high temperature;
• the friction caused by the passage of the projectile which, starting from a zero speed, acquires a speed of several hundred m / sec. in a millisecond;
• an internal pressure of several thousand bars which induces significant but short-lived mechanical tensions in the barrel.

• une résistance mécanique élevée à température ambiante et à 900 °C ;
• une bonne résilience jusqu'à - 60 °C ;
• un coefficient de frottement faible vis-à-vis des matériaux utilisés comme enveloppe des projectiles même à des températures de l'ordre de 1000°C;
• une résistance appréciable à la corrosion par les gaz de combustion des poudres propulsives ;
• une faible susceptibilité à la fatigue thermique ;
• une conductivité thermique importante ;
• une bonne aptitude à la mise à forme à l'aide des équipements classiques permettant de réaliser sans difficultés majeures le rayage interne et l'usinage externe.

These phenomena are well known to specialists and they have attempted by various means to find solutions to this complex problem, because if alloy steels (materials generally used for making cannons) allow weapons to function correctly at relatively low rates, they do not allow the application of high rates for a reasonable period of time. It follows that the life of a steel cannon used at high rates is relatively short. It can therefore be said that there is a real need to have a cannon allowing firing at high rates with an acceptable lifetime under these conditions. This gun should in fact have the following characteristics:

• high mechanical strength at room temperature and 900 ° C;
• good resilience down to - 60 ° C;
• a low coefficient of friction with respect to the materials used as the casing of the projectiles even at temperatures of the order of 1000 ° C;
• appreciable resistance to corrosion by the gases of propellant powders;
• low susceptibility to thermal fatigue;
• high thermal conductivity;
• good formability using conventional equipment allowing internal scratching and external machining to be carried out without major difficulties.

The object of the invention is to provide a method of manufacturing such a gun, the latter consisting of three superimposed layers without solutions of continuity.

• - pour la couche interne, le chrome, le tungstène, le niobium, le carbure de tungstène et similaires ou des alliages de ceux-ci ;
• - pour la couche médiane, des alliages à base de cobalt tels qu'utilisés entre autres dans la construction des turbo-réacteurs ;
• - pour la couche externe, des aciers alliés, par exemple au chrome-molybdène d'un usinage relativement aisé.

Materials suitable for making such a cannon are for example:

• - for the inner layer, chromium, tungsten, niobium, tungsten carbide and the like or alloys thereof;
• - for the middle layer, cobalt-based alloys as used inter alia in the construction of turbo-reactors;
• - For the outer layer, alloy steels, for example chromium-molybdenum of relatively easy machining.

The absence of continuity solutions is essential, without which there would be hot spots leading to premature destruction. Tests have shown that the superimposition of tubular layers by shrinking or mechanical assembly reveals thickness discontinuities, despite all the precautions taken to avoid them. However, a discontinuity of thickness less than 0.01 mm is sufficient to create a hot spot and lead to premature destruction.

A satisfactory method consists, in accordance with the invention, of threading three tubes, each intended to form one of the above-mentioned layers, and co-hammering them on the mandrel until all solution of continuity between said tubes disappears.

The absence of continuity solutions can easily be verified by microscopic examination of longitudinal or radial sections of the barrel. However, this destructive method does not apply to manufacturing control. In this case, the examinations are carried out by radiography or radioscopy or by ultra-sonic techniques.

Advantageously, a striped mandrel will be used for co-hammering, which makes it possible to obtain a striped blank and thereby reduces the manufacturing costs.

The test demonstrated that the life of the composite gun, determined on the basis of a firing accuracy criterion, was three times higher than that of the conventional gun.

Claims (3)

1. Procedure to manufacture a composite barrel composed of three superposed layers, consisting of sliding into each other three tubes, each destined to form one of the above layers and of co-hammering them on a mandrel, featuring that this co-hammering is carried on until any continuity solution between said tubes has disappeared.

2. Procedure according to claim 1, featuring the use of a striated mandrel.

3. Procedure according to claim 1, featuring that the materials to be co-hammered are selected so as to show elasticity characteristics of equal magnitude.