FR2494833A1 - Friction welded seal caps for grenade casings - involving thin coatings pref. of polyvinylidene fluoride or chloride - Google Patents

Abstract

Chamber of an explosive or smoke grenade or shell is sealed by rotary friction welding a cap on to a suitable annular land at the chamber mouth, both the cap and the land having a thin coating of thermoplastic material. The component surfaces may be pretreated to improve anchorage of their respective thermoplastic coatings. Pref. the coatings are only a few tengths of a mm thick. Pref. the coatings are of polyvinylidene-fluoride or -chloride. The rotary motion may be oscillatory. Pref. the seal and/or land interfaces are ribbed. This provides a better long term seal for protective sensitive contents, such as a charge of TNT, than a mechanically clamped seal with or without an ancillary seal profile such as a rubber 'O' ring. The quantity of heat necessary for fusing thin coatings is small enough not to affect the casing body of its contents significantly.

Description

SEALED ZERMEQURE PROCESS OF A DIE BODY
AMMUNITION AND N (#NITION BABRIQU3E ACCORDING TO THIS
PROCESS.

 The invention relates to an industrial method of sealing a munition body; it also relates to a munition manufactured according to this process.

 In the ammunition industry, there is the problem of ensuring the tightness of the charge stored in the body of the ammunition and, in particular, that of the sealed closure of the loading orifice for this charge. This problem is particularly critical when the charge of the ammunition is a trinitrotoluene-based explosive (TNT) or a smoke liquid such as carbon tetrachloride.

 In the past, the internal surface of ammunition bodies has been coated with a thin layer of a material such as asphalt, a low-coating material, easily deposited in a layer, but slightly permeable to TNT and exothermically reactive with that - the use of asphalt pavements has been the source of many accidents when an ammunition was accidentally heated. More recently, to overcome the drawbacks presented by asphalt pavements, it has been proposed to coat the internal surface of the bomb bodies with a thin layer of polyvinylidene chloride practically impermeable to TNT.

However, the problem remains of sealing the loading orifice after the explosive has been poured. the means proposed for sealing the loading orifice use O-rings or flat seals, or alternatively closing parts glued to the loading port. These closing processes are not entirely satisfactory; on the one hand, the seal obtained is sensitive to aging and degrades when the munition undergoes repeated thermal cycles and, on the other hand, these methods require precise machining operations. Here, it should be noted that metal-to-metal welds are excluded for reasons of safety of personnel and manufacturing premises, due to the significant temperature rises caused by this type of welding.

 The object of the invention is an industrial method of tightly closing a body of ammunition which does not have the aforementioned drawbacks and which aims to increase, notably, the safety of use of the ammunition.

 To achieve this object, in the method according to the invention, there is included in the loading orifice of the ammunition body a support means intended to provide a contact surface whose transverse dimension is relatively small with a closure part. with this orifice # the internal surface of this body of ammunition is coated, including the means of support of the piece of iron meture of this orifice; the internal surface of this body of ammunition, including the means for supporting the closure part, is coated with a thin adhesive layer of a thermoplastic material which is self-sealing by friction, this material being impermeable to the products constituting the charge of the ammunition and chemically not reactive to these products; a closure piece is made of a material identical to that used during the internal coating of the ammunition body or # oaéêdant the same coating as the ammunition body; after the loading operation of the ammunition body, the latter, equipped with its closure part, is fixed on a rigid support; a pressure force is then applied to the closure part and jointly a rapid and short-lasting rotational movement is imparted thereto. It results from the friction of the parts of the closure part and of the support means in contact, a local temperature rise which locally softens these two elements which are intimately welded, finally, the pressure force applied to the part is released. closing.

 Other characteristics and advantages which the invention provides will appear in the detailed description of the various operations implemented in the process, given with reference to the appended figures; in these figures, identical reference numerals indicate similar elements.

 Figure 1 illustrates the sealed closure method, according to the invention, of a munition body.

 FIG. 2a shows a first embodiment of the closure part / loading orifice connection of the ammunition body.

 FIG. 2b shows a second embodiment of the closure part / loading orifice connection of the ammunition body.

 FIG. 2c represents a third embodiment of your connection between the closing part and the orifice for loading the body of the ammunition.

 FIG. 2d shows a fourth embodiment of the closure part / loading orifice connection of the ammunition body.

 Figure 3 shows, in a sectional view, a munition manufactured according to the method of the invention.

 FIG. 4 represents an alternative embodiment of the part for closing the loading orifice of the ammunition shown in FIG. 3.

FIG. 1 illustrates the description of the method for closing an ammunition body according to the invention; this process comprising the following operations
- an ammunition body (1) is produced comprising
a loading opening (2) and at
this orifice is provided with a support means (3) for
keen to provide a contact surface whose
transverse dimension is relatively small
with a closing part (4),
- the internal surface of this body is coated with
ammunition, including the means of support of the
closure part, with a thin adhesive layer
te (5) of a waterproof thermoplastic material
ble to the products constituting the charge of
ammunition and chemically neutral towards
these products,
- we make a closing piece out of a mate
same as that used for coating
internal of the ammunition body,
- after the explosive loading operation
(6) in this ammunition body, the latter provided
of its closing part in contact on the
support means is fixed on a rigid support
(7),
- we then apply to the closing part,
a pressure force (F) perpendicular to the
plane of the contact and joint surface
ment we print a rotational movement (M)
fast and of sufficient duration in order to ramol
read locally the parts in contact with the
support means and closing part,
then we interrupt the rotational movement,
finally after a short time, we release the
pressure force applied to the workpiece
closing.

Among the usable thermoplastic materials, polyvinylidene fluoride has been found to have interesting physical and mechanical properties. It is available industrially in powder form; it can be deposited in a thin layer which is impermeable to many products, whether they are present in the solid, liquid or vapor phase, in addition, polyvinylidene fluoride is chemically neutral with regard to products highly reactive, like the
TNT or certain fumigants such as carbon tetrachloride. polyvinylidene fluoride adheres strongly, with certain precautions, to many metals, especially ferrous metals, with the exception of stainless steels. In addition, either by molding or by extrusion / blowing, it allows the production of shaped parts complex and can therefore be used for the manufacture of the closure part of the loading orifice. The physical properties of polyvinylidene fluoride are conserved over a wide temperature range, of the order of - 5000 to + 15000, which largely covers the range of temperatures used for ammunition.

The operation of coating a layer of polyvinylidene fluoride on the internal surface of a steel munition body requires, beforehand, a preparation of the surface to be covered if one wishes to obtain a perfect adhesion of this layer. ; this preparation of the internal surface of the ammunition body comprising the following steps
- sandblasting of the parties concerned,
- degreasing in hot alkaline solution followed
rinsing with water, - amorphous phosphating with fine-grained iron,
- passivating rinse with chromic acid and, finally,
air drying.

 The operation of coating the polyvinylidene fluoride layer can be carried out according to a known method, for example, by electrostatic spraying; this process makes it possible to obtain a uniform coating of the layer on complex shapes if care has been taken to eliminate the sharp edges of the body to be coated in order to avoid excessively large electric field gradients.

This coating process makes it possible to easily produce coatings of several tenths of a millimeter; however, a layer of polyvinylidene fluoride of two to three tenths of a millimeter is sufficiently impermeable to the various products used in the production of charges for ammunition.

 The manufacture of the closure part of the loading orifice can be carried out by molding the polyvinylidene fluoride powder or by electrostatic projection of a part made of a material such as steel preferably.

An extrusion blow molding process can also be used for more complex closure parts, as will be described elsewhere. In order to ensure a drive Bans sliding of the closure part, it can be provided with a drive means such as notches (8) as shown in Figure 1, these notches can be arranged at the periphery of the closure part and be formed either by indentations or by bosses.

 The surface of the parts of the piece of ironwork and of the support means of this piece which are in contact must have a sufficiently small transverse dimension to ensure rapid welding and the surface in contact must be large enough to provide an impermeable and mechanically resistant. Different profiles of these contacting parts are possible. As an illustration, a few examples of profiles have been shown in FIGS. 2a to 2d, in the case of a metallic closure part (4) covered at least in its part in contact with the support means (3) of a layer of a thermoplastic material.

 In Figure 2a, the support means (3) has a circular groove (3a) in which will be engaged a circular boss (4a) available on the closure part (4).

 In FIG. 2b, the circular groove (3a) has a flat at the bottom of the groove and the circular boss (4a) has a corresponding flat.

 In FIG. 2e, the support means (3) is constituted by a circular protuberance of the internal pa king of the loading orifice, this protuberance having a flat (32) on which a circular boss (4a) comes to bear available on the internal face of the closing part (4).

 In FIG. 2d, the support means (3) has a boss (3a) and the closure part (4) has a peripheral circular groove.

 The transverse width of the contacting surfaces can be between 2 and 5 mm, this width depending mainly on the size of the closure part. The applied pressure force can be of the order of 40 bars; it must be adjusted according to the profile of the parts in contact and the transverse width of the boss / groove couple.

 In the case where the closure part (4) is monolithic, the profile of the surfaces in contact may be similar to those which have just been described by way of illustration.

 The loading operation of the ammunition body is entirely conventional and does not call for any particular description. This loading can be carried out by pouring the molten explosive or by decanting in the case of a smoke liquid.

In the case of an explosive charge, the welding operation of the closure part is carried out after solidification of the explosive, leveling of the end of the charge and, optionally, machining of a recess allowing the accommodation of a charge for initiating the explosion.

 The welding operation of the closure part on the support means of the loading orifice can be carried out at ambient temperature and, in an industrial manner, using a standard friction welding machine, available commercially. . Such a machine comprises a fixed frame and a vertical movable tool making it possible to jointly provide a pressure force and a rotational or translational movement perpendicular to the direction of this pressure force; generally, this tool carries a notch adapted to the corresponding notch disposed on the closure part. After the loading phase of the ammunition body, it is placed and immobilized on the frame of the machine and receives its closing part.

The machine tool applies pressure to the closing part and jointly drives it, for a short time, with an alternating rotational or translational movement. After the parts in contact with the closure part and the support means have softened, the rotational movement is interrupted and then the pressing force is released. The pressure force on the closing part can be of the order of a few tens of bars, the frequency of the alternating rotation or #translation movement of the order of 100 Hz and the duration of application of this movement. rotary less than 10 seconds. The values of these various parameters depend mainly on the size of the parts to be welded and, to a certain extent, on the nature of the thermoplastic material used. thermal conductivity of the material: allows rapid and localized heating to
surfaces in friction up to the temperature of
softening of the material, temperature which is
below dangerous temperatures for
the explosive,
- prevents the spread of overheating to
the load which is slightly behind
surfaces in contact.

 As indicated above, the charge of the ammunition body can consist of a liquid smoke product. The viscosity of these smoke products being always low, the heating of the smoke which is possibly in contact with the parts of the closure part is negligible during the welding operation of this closure part. In the case of sheath plunging into the explosive charge, there should be a clearance between the sheath which will be rotated and a housing in the explosive, in order to avoid contact with it.

 Figure 3 shows, in a sectional view, a munition such as an exploitive projectile, manufactured according to the process which has just been described. In this type of ammunition where one seeks the bursting and the fragmentation of the metallic body of the projectile, the charge of initiation of the explosion can be physically separated from the explosive charge by a thin wall, in a plastic material or even metallic, which does not disturb the propagation of the explosion.

In this FIG. 3, the projectile comprises:
- A metallic ammunition body (i) made of a material such as steel, this body comprising a charging orifice (2) of an explosive charge (6) which substantially fills the hollow part of the body; the charge of explosive may be tolite; the loading orifice comprises a support means (3) which is presented in this example as a circular shoulder of the wall of the loading port, this shoulder providing a relatively small contact surface with a piece (4) of closing of this orifice. The internal surface of the ammunition body, including the shoulder formed in the loading orifice, is covered with a thin adhesive layer (5) of a thermoplastic material. The closure part (4) is made of a thermoplastic material. identical to that used for the internal coating of the ammunition body; it is in the form of a cylindrical sheath which is housed in a recess made in the explosive charge, this sheath has a circular rim provided, at its external part, with drive notches and, at its internal part, with a circular boss allowing a small contact surface on the shoulder of the loading orifice, this edge of the sheath is intimately welded to the coating layer of the shoulder.

 The thermoplastic material which constitutes the internal coating layer (5) of the body is polyvinylidene fluoride and the thickness of this coating layer is of the order of a few tenths of a millimeter.

 In addition, the projectile can be equipped with its conventional elements: for example, for example #, a warhead rocket (9) which can be screwed into the loading opening (2) of the ammunition body, this rocket comprising, in particular, a relay load (9a) which is housed inside the closing part (3 #.

At the base of the projectile can be arranged stabilization fins or else a means of fixing (lo) of the propellant charge of the projectile, etc.
According to an alternative embodiment of the closure part (4), the latter, FIG. 4, comprises a metal part (4b) of cylindrical shape whose wall thickness is sufficiently small so as not to disturb the propagation. of the explosion; this metal part is covered with a thin adherent layer (4c) of a thermoplastic material identical to that used for the internal coating of the ammunition body.

On this closure piece, there are the circular boss or groove (4a) at the location of the weld with the support means disposed in the loading orifice, and the drive notches (8) used during the welding operation.

 A munition according to the invention can be manufactured in production centers and in distant times. For example, the raw ammunition body can be produced in a metallurgical plant, the operations of machining and coating a layer of a plastic material of the ammunition body and the operation of manufacturing the closure part. 11 orifice of loading can be made in an ammunition production center and, therefore, the body of ammunition is a manufactured object in itself; finally, the operations of loading and sealing the explosive charge can be carried out in an explosive materials production center.

 We now see more clearly the advantages of the closure method according to the invention; in fact, in addition to the fact that the charge of the ammunition is completely isolated from the environment, which notably increases the safety of the ammunition, the method lends itself to complete automation of the manufacture of the ammunition.

 the leaktight closing method as it has been described is in no way limiting and corresponds to an embodiment of the method, other variants are possible, in particular as regards the nature of the thermoplastic material of the internal coating of the ammunition body which may be vinylidene chloride; on the other hand, depending on the physical properties of the thermoplastic material used, the coating of the ammunition body can be carried out by centrifugation of an emulsion of this material, and the preliminary operation intended to prepare the surface to be coated depends on the nature ammunition body material; the shape of the closing piece depends on the additional function possibly provided by this closing piece; finally the coating of the internal surface of the metallic envelope of the body of the ammunition can be only partial and limited at the level of the support means, the rest of the surface being covered by a varnish.

 The method of tightly closing an ammunition body finds its application in the arms industry for the manufacture of extremely diverse ammunition such as artillery projectiles, aviation bombs, projectiles or smoke-producing containers, etc.

Claims (15)

CLAIMS 1. A method of tightly closing a body of metallic ammunition provided with a loading orifice and with a part for closing this orifice, characterized in that it comprises the following operations: - manufacture of a body of ammunition (i) whose loading orifice (2) comprises a support means <3) intended to provide a relatively small contact surface with a closure part (4), - coating of the internal surface of this body of munition, including the support means, of a thin adherent layer (5) of an impermeable thermo-plastic material and chemically neutral with respect to the products constituting the charge of the ammunition, - manufacture of a piece of closure (4) of which at least the part in contact with the support means is made of a material identical to that of the internal coating layer of the ammunition body. - loading of the charge of ammunition (6) in the body of ammunition, - mounting of the body of ammunition equipped with the closing part of the loading orifice on a rigid support, application on this closing part of a force of pressure (F) perpendicular to the contact plane of this part and of the support means and jointly of a relative movement (M) of short duration in order to obtain an intimate weld at the level of the contact of these two parts. 2. Method according to claim 1, characterized in that the thermoplastic material for coating the internal surface of the ammunition body is polyvinylidene fluoride. 3. Method according to claim 1, characterized in that the operation of coating the internal surface of the ammunition body is preceded by an operation of treatment of this surface aimed at increasing the adhesion of the coating. 4. Method according to claim 1, characterized in that the operation of manufacturing the closing part of the loading orifice comprises an operation making it possible to provide means for driving this part in rotation. 5. Method according to claim 4, characterized in that the means for driving the closure part are imprints. 6. Method according to claim 4, characterized in that the means for driving the closure part are bosses. 7. Method according to claim j, characterized in that the relative movement imparted to the closure part during the welding operation of the latter is an alternating movement. 8. Metal ammunition body comprising a loading orifice, characterized in that this loading profice comprises a support means intended to provide a contact surface with a closure part welded by friction and the internal surface of the ammunition body including this support means is covered with a thin adherent layer of a thermoplastic material. 9. Ammunition body according to claim 8, characterized in that the thermoplastic material for coating the internal surface of this ammunition body is polyvinylidene fluoride. 10. Ammunition body according to claim 8, characterized in that the thermoplastic material for coating the internal surface of this ammunition body is vinylidene chloride.  Ammunition containing a charge and comprising a metal body comprising a loading orifice provided with a closing part, characterized in that this loading orifice comprises a means for supporting the closing part; the internal surface of the body including the support means is coated with a thin adherent layer of an impermeable thermoplastic material which is chemically neutral with regard to the charge of the ammunition; the closure part is made, at least partially, in a thermoplastic material identical to that of the coating and is welded, intimately, on the support means of the loading orifice.  12. Ammunition according to claim 11, characterized in that the thermoplastic material is polyvinylidene fluoride. 13. Ammunition according to claim 11, characterized in that the thermoplastic material is vinylidene chloride. 14. Ammunition according to claim 11, characterized in that the charge of the ammunition is an explosive product. 15. Ammunition according to claim 11, characterized in that the charge of the ammunition is a smoke product. 16. Ammunition according to claim 11, characterized in that the closing piece of the loading port additionally allows the accommodation of a priming relay load. 17. Ammunition according to claim 11, characterized in that the thickness of the coating layer of the internal surface of the metal body is of the order of a few tenths of a millimeter.