GB1599582A

GB1599582A - Forming and maintaining a lining on a gun barrel

Info

Publication number: GB1599582A
Application number: GB7495/78A
Authority: GB
Original assignee: Rheinmetall GmbH
Current assignee: Rheinmetall Industrie AG
Priority date: 1977-03-03
Filing date: 1978-02-24
Publication date: 1981-10-07
Also published as: GR66098B; DE2709247C2; NL7800888A; IT1095364B; JPS53110300A; JPS5921480B2; IT7820771A0; DK75578A; CH632837A5; FR2382419A1; PT67636B; ES467446A1; PT67636A; FR2382419B1; BR7801287A; NO780602L; BE864365A; SE7802288L; DE2709247A1

Abstract

In the case of a weapon with a barrel, the firing performance is improved by the powder propulsion charge, which produces the thermal and mechanical stress, having additives added to it of such a type and quantity that a cohesive, wear-resistant, high melting point coating is formed which has poor thermal conductivity and whose coating thickness is determined by a balance state between the formation of new deposit and erosion as a result of the thermal and/or mechanical stress.

Description

(54) FORMING AND MAINTAINING A LINING ON A GUN BARREL (71) We, RHEINMETALL Gesellschaft mit beschrankter Haftung, of Ulmenstrasse 125, 4 Dusseldorf 1, German Federal Republic, a Company organised and existing under the laws of the German Federal Republic, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment: The present invention relates to improvements in the use of ammunition to produce and maintain on the inner surface of a gun barrel a heat-insulating, erosion-inhibiting protective lining to protect it from the very high thermal and mechanical stresses to which it is subjected by the explosive charge of the ammunition.

To achieve this, in the past, additives have been admixed with the powder of the explosive charge of the ammunition which, when the charge is detonated, will be precipitated on the inner surface of the gun barrel either in a pure form or in the form of a chemical compound.

The use of such additives is mentioned in German Patent Specification No. 1,453,837, but it is mentioned that a serious disadvantage of the mixture of such additives in the powder of the explosive charge is that the amount which can be used must be limited to avoid unfavourably affecting the combustion characteristics of the charge. Therefore, according to that Specification, it is essential to weigh up carefully the effect of the additive substances and their influence detracting from the combustion characteristics of the powder forming the explosive charge, so that there is only comparatively little freedom in the selection and the quantity of such additives.

From this it follows that prior art proposals for the admixture of substances having a protective effect on the gun barrel with the powder charge of the ammunition only enable the intended effect to be achieved to a limited extent, so that separate and additional steps must be taken to coat the inner surface of a gun barrel, such as ionitriding, gas nitriding or depositing hard chromium in order to give the inner surfaces of the barrel an acceptable resistance to wear and erosion.

Surface protective coatings of metals, or with metal as the main component, have the disadvantage, however, that they have high coefficients of thermal conductivity, so that protection against thermal stress for the material of the barrel is imperfect. Experiments with non-metallic coatings experienced premature melting, evaporation or abrasion as a result of the extremely high surface temperatures caused by localised heat.

Because of the increasing performance demands on gun barrels due to the use of higher gas pressures, powders generating hotter gases, larger charges and higher rates of fire, however, the requirements regarding resistance to wear and erosion become ever greater so that the life of gun barrels is no longer adequate despite known protective methods.

The reason for this is to be seen in the fact that the surfaces are attacked on the one hand by the brief thermal loading and on the other hand by the mechanical loading, surface temperatures of the order of magnitude of up to 20000C being observed. Such temperatures are only tolerated by a few materials without melting.

Apart from a high melting point, other criteria for the adequate life of the inner surface of a gun barrel are resistance to high temperatures below the melting point and resistance to deformation. The chemical resistance of the material of the inner surface of a barrel or of a lining thereon to the hot gases generated by the explosive charge is also of importance.

It is an object of the present invention to avoid the above disadvantages of known techniques.

According to the present invention there is provided a method of forming and maintaining a heat-insulating, erosion-inhibiting lining on the inner surface of a gun barrel, wherein there is included in the powdered propulsive charge of ammunition to be used in firing the gun an abrasion-resistant metallic additive of low thermal conductivity and high melting point in a proportion by weight great enough to provide that each time the gun is fired lining material removed will be replaced by precipitated additive, the prevailing thickness of the lining, and therefore the temperature to which it is raised when the gun is fired, determining the amount of the additive precipitated each time the gun is fired so that the thickness of the lining remains substantially constant before and after successive firings.

Loss ofballistic performance resulting from the inclusion of non combustible additives in the explosive charge can be compensated by increasing the calorific value of the propellent powder without adversely affecting the considerably improved erosion-inhibiting effect.

High proportions ofbinding agent are not necessary so that the effective additive can be increased in quantity.

More or less all metals and their compounds are suitable as additives and may advantageously be admixed with or added to the powder of the explosive charge in a dispersed form, so that it will be evenly distributed in the gun barrel upon firing. The additive melts, evaporates, dissociates and/or is sublimated as a coating on the inner surface of the barrel, with or without the formation of new compounds, in the highly tensioned, extremely hot gas atmosphere.

This procedure only leads to an effective lining thickness if more than a certain minimum amount of additive is used, which is considerably above the quantity of additive hitherto used.

An effective lining thickness is one which completely protects the subjacent barrel material from heat damage. Metallic oxides have proved particularly advantageous as additive materials, in which case surface coatings result which have a satisfactory adhesion to the inner surface of a gun barrel. Deposits of an adequate thickness can be obtained without reducing the calibre diameter to an unacceptable extent, which de posits have an extremely low thermal conductivity and a high melting point and have a very high resistance to abrasion at high temperatures.

According to an advantageous embodiment of the invention titanium dioxide is used as an additive, about 10 to 25% by weight ofthe additive being added to the explosive charge of ammunition, or at least that used for initial firing of the first few shots depending on prevailing ambient thermal conditions.

For further shooting, this value can be re.

duced to between 5% and 15% by weight de pending on internal ballistic conditions. In the course of regular use of the gun barrel one or more shots may be fired between a given number of other shots, the ammunition used for these special shots again comprising an increased proportion of additive, so as to achieve an in creased deposit on the inner surface of the gun barrel and so to compensate for a reduction in the thickness of the protective lining.

The noteworthy result of this method of coating is to be seen in the fact that a lining which has once been applied is admittedly at first partially melted during shooting despite its high melting point, as a result of its low thermal conductivity, but then is built up again by the dispersed and partially dissociated additive material entrained in the charges, the amount of additive material added during the first and during subsequent shots being so determined that a sufficiently thick protective lining builds up and is maintained. This means that the thickness of the lining is determined by a balance between removal as a result of thermal and mechanical stress and fresh deposit. This phenomenon can be explained, inter alia, by the fact that thicker protective linings reach higher temperatures than thin ones because of low thermal conductivity in the wall of a barrel.

Therefore thick linings are somewhat more subject to melting and removal than thin ones during shooting.

The protective lining can be applied immediately after manufacture of a gun barrel, for example during acceptance firing, in that following manufacture the barrel is subjected to at least one thermal and mechanical stress at least equal to that which will be experienced during regular use using an additive which differs in nature and/or amount from the additive which will be used in the ammunition intended for the subsequent firing of the gun.

As a rule, the amount of the additive used during this first stressing would be greater than during subsequent use, and, in addition, provision may be made for the proportion of the additive in the marginal regions of the explosive powder charge producing the thermal and mechanical stress to be greater than in the core region. It is also possible to provide a gun barrel with a protective lining preceding actual use.

The lining can be formed in the course of an acceptance shot or partially by manufacturing methods and partially by shooting. In this case, different kinds and amounts of explosive charge powder and sizes of projectile can be used for initial firing by comparison with ammunition intended for subsequent use.

WHAT WE CLAIM IS: 1. A method of forming and maintaining a heat-insulating, erosion-inhibiting lining on the inner surface of a gun barrel, wherein there is included in the powdered propulsive charge of ammunition to be used in firing the gun an abrasion-resistant metallic additive of low thermal conductivity and high melting point in a proportion by weight great enough to provide that each time the gun is fired lining material removed will be replaced by precipitated additive, the prevailing thickness of the lining, and therefore the temperature to which it is raised when the gun is fired, determining the amount of the additive precipitated each time the gun is fired so that the thickness of the lining remains substantially constant before and after successive firings.

2. A method as claimed in Claim 1, wherein the barrel is subjected during trial firing following manufacture to at least one thermal stress at least equal to that which will be experienced in subsequent use.

3. A method as claimed in Claim 2, wherein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. it is raised when the gun is fired, determining the amount of the additive precipitated each time the gun is fired so that the thickness of the lining remains substantially constant before and after successive firings. Loss ofballistic performance resulting from the inclusion of non combustible additives in the explosive charge can be compensated by increasing the calorific value of the propellent powder without adversely affecting the considerably improved erosion-inhibiting effect. High proportions ofbinding agent are not necessary so that the effective additive can be increased in quantity. More or less all metals and their compounds are suitable as additives and may advantageously be admixed with or added to the powder of the explosive charge in a dispersed form, so that it will be evenly distributed in the gun barrel upon firing. The additive melts, evaporates, dissociates and/or is sublimated as a coating on the inner surface of the barrel, with or without the formation of new compounds, in the highly tensioned, extremely hot gas atmosphere. This procedure only leads to an effective lining thickness if more than a certain minimum amount of additive is used, which is considerably above the quantity of additive hitherto used. An effective lining thickness is one which completely protects the subjacent barrel material from heat damage. Metallic oxides have proved particularly advantageous as additive materials, in which case surface coatings result which have a satisfactory adhesion to the inner surface of a gun barrel. Deposits of an adequate thickness can be obtained without reducing the calibre diameter to an unacceptable extent, which de posits have an extremely low thermal conductivity and a high melting point and have a very high resistance to abrasion at high temperatures. According to an advantageous embodiment of the invention titanium dioxide is used as an additive, about 10 to 25% by weight ofthe additive being added to the explosive charge of ammunition, or at least that used for initial firing of the first few shots depending on prevailing ambient thermal conditions. For further shooting, this value can be re. duced to between 5% and 15% by weight de pending on internal ballistic conditions. In the course of regular use of the gun barrel one or more shots may be fired between a given number of other shots, the ammunition used for these special shots again comprising an increased proportion of additive, so as to achieve an in creased deposit on the inner surface of the gun barrel and so to compensate for a reduction in the thickness of the protective lining. The noteworthy result of this method of coating is to be seen in the fact that a lining which has once been applied is admittedly at first partially melted during shooting despite its high melting point, as a result of its low thermal conductivity, but then is built up again by the dispersed and partially dissociated additive material entrained in the charges, the amount of additive material added during the first and during subsequent shots being so determined that a sufficiently thick protective lining builds up and is maintained. This means that the thickness of the lining is determined by a balance between removal as a result of thermal and mechanical stress and fresh deposit. This phenomenon can be explained, inter alia, by the fact that thicker protective linings reach higher temperatures than thin ones because of low thermal conductivity in the wall of a barrel. Therefore thick linings are somewhat more subject to melting and removal than thin ones during shooting. The protective lining can be applied immediately after manufacture of a gun barrel, for example during acceptance firing, in that following manufacture the barrel is subjected to at least one thermal and mechanical stress at least equal to that which will be experienced during regular use using an additive which differs in nature and/or amount from the additive which will be used in the ammunition intended for the subsequent firing of the gun. As a rule, the amount of the additive used during this first stressing would be greater than during subsequent use, and, in addition, provision may be made for the proportion of the additive in the marginal regions of the explosive powder charge producing the thermal and mechanical stress to be greater than in the core region. It is also possible to provide a gun barrel with a protective lining preceding actual use. The lining can be formed in the course of an acceptance shot or partially by manufacturing methods and partially by shooting. In this case, different kinds and amounts of explosive charge powder and sizes of projectile can be used for initial firing by comparison with ammunition intended for subsequent use. WHAT WE CLAIM IS:

1. A method of forming and maintaining a heat-insulating, erosion-inhibiting lining on the inner surface of a gun barrel, wherein there is included in the powdered propulsive charge of ammunition to be used in firing the gun an abrasion-resistant metallic additive of low thermal conductivity and high melting point in a proportion by weight great enough to provide that each time the gun is fired lining material removed will be replaced by precipitated additive, the prevailing thickness of the lining, and therefore the temperature to which it is raised when the gun is fired, determining the amount of the additive precipitated each time the gun is fired so that the thickness of the lining remains substantially constant before and after successive firings.

3. A method as claimed in Claim 2, wherein

during trial firing following manufacture of the barrel ammunition is used which has an additive differing in nature and amount from that included in ammunition intended for subsequent use of the gun barrel.

4. A method as claimed in Claim 3, wherein the amount of the additive of ammunition used for said trial firing is greater than that of ammunition intended for subsequent firing.

5. A method as claimed in any one of Claims 1 to 4, wherein the additive used comprises titanium dioxide.

6. A method as claimed in Claim 5 as appendant to Claim 4, wherein ammunition used for said trial firing comprises 10% to 25% by weight of titanium oxide in finely divided form and wherein ammunition intended for subsequent use comprises 5% to 1 5So by weight of titanium oxide in finely divided form.

7. A method as claimed in any preceding claim, wherein ammunition is periodically used which has a higher additive proportion than ammunition normally used.

8. A method as claimed in Claim 1 for forming and maintaining a heat-insulating, erosion-inhibiting lining on the inner surface of a gun barrel substantially as herein described.