EP0026511A2 - Method for manufacturing a composite barrel - Google Patents

Abstract

This barrel is characterized in that it consists of three superimposed layers without solutions of continuity, namely: an internal layer made of a refractory material; a middle layer of a material whose mechanical strength is greater than about 250 MPa at 900 ° C and an outer layer of alloy steel. The invention also relates to the method of manufacturing such a gun.

Description

The present invention relates to a composite gun and a method for its manufacture, a gun more especially intended for automatic weapons.

• 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 subsets 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 in the gun significant mechanical tensions but of short duration.

• 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 tem_- pératures 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 vis-à-vis the materials used as projectile casings 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 such a cannon. This consists, in accordance with the invention, of three superimposed layers without solutions of continuity, namely: an internal layer made of a refractory material; a middle layer of a material whose mechanical strength is greater than about 250 MPa at 900 ° C and an outer layer of alloy steel.

• - 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 process consists, in accordance with the in vention, to thread three tubes, each intended to form one of the abovementioned layers, and to co-hammer 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 ultrasonic techniques.

As the internal layer, given its raison d'être, can be relatively thin, that is to say have a thickness less than a millimeter, a variant of the method according to the invention consists in co-hammering the external layers and median, then to realize then the internal layer by carburizing, deposition in gas phase, vaporization under vacuum or electrodeposition, by taking all precautions to obtain a perfect adhesion, that is to say to avoid any solution of continuity.

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

In order to illustrate the invention without, however, reducing it to a single case, the following example can be given: a 7.62 mm caliber machine gun barrel was produced by co-hammering two tubes made for the inner tube d '' a cobalt-based alloy similar to those used in the construction of turbo-reactors and for the outer tube of a steel alloyed with Cr-Mo.

The operation was carried out on a striped mandrel made of hard material and produced a striped barrel blank. Through a choice judicious hammering parameters, the composite obtained was free of continuity solutions. The core of the blank was then chrome-plated under conditions capable of giving a coating whose adhesion was perfect. After machining the outside of the blank, the barrel obtained was subjected to a resistance shot and compared to a barrel absolutely similar in dimensional terms but completely made of the same steel alloyed with Cr-Mo as that used for the outer layer of the composite. This gun had received an internal coating of chrome produced by a conventional technique

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 (7)

1.- composite barrel, characterized in that it consists of three superimposed layers without solutions of continuity, namely: an internal layer made of a refractory material; a middle layer of a material whose mechanical resistance is greater than about 250 MPa at 900 ° C. and an outer layer of alloy steel. 2.- composite barrel according to claim 1, characterized in that the inner layer is made of chromium, tungsten, niobium, tungsten carbide or the like or an alloy of these materials. 3.- composite barrel according to claim 1, characterized in that the middle layer is made of a cobalt-based alloy. 4.- A method of manufacturing a barrel according to claim 1, characterized in that it consists of threading three tubes, each intended to form one of the above layers and to co-hammer on the mandrel until disappearance of any solution of continuity between said tubes. 5.- A method of manufacturing a barrel according to claim 1, characterized in that it consists in threading two tubes, intended to respectively constitute said outer and middle layers, to co-hammer them on the mandrel until all disappearance solution of continuity between said tubes and then making the internal layer by case hardening, vapor deposition, vacuum vaporization or electroplating. 6.- Method according to one of claims 4 or 5, characterized by the use of a striped mandrel. 7.- Method according to one of claims.4 or 5, ca characterized in that the co-hammered materials are chosen so as to have elastic properties of the same order of magnitude.