EP0008265A1 - Process for producing propellant plates partially coated with a combustion inhibitor - Google Patents

Abstract

1. A process for the manufacture of pyrotechnic charges from plates of powder having a thickness which is substantially constant, according to which process a viscous composition of a material which is an inhibitor of combustion is prepared for deposition on the plates, characterized in that : - said composition is prepared from a constituent selected from the group represented by organic resins which are moisture-polymerisable, and by silk-screening inks having a polyester base, to which is added at least one propellant stabilizer ; - a silk-screening screen is positioned on one of the faces of the powder plate, said screen having a series of apertures regularly distributed thereon ; - the viscous combustion inhibiting composition is applied to the screen and is spread thereon ; after which, - the screen is withdrawn so as to allow polymerisation of the combustion inhibiting composition disposed on the powder plate.

Description

The present invention relates to a method for manufacturing powder plates, partially coated with combustion inhibitor.

Propellant blocks are known, the outer surface of which is partially coated with a combustion inhibitor material. Thus, French patent n ° 2 276 555 filed on June 27, 1974 in the name of the Applicant, describes for example propellant blocks whose external surface comprises linear protuberances whose summits are coated with a layer of combustion inhibitor. These protrusions define between them notches which reduce the combustion thickness of these blocks.

The main purpose of the combustion inhibitor applied to the tops of these protrusions is to reduce the initial combustion surface of the propellant block, so that the overpressure generated at the start of combustion is limited, a goal which is also achieved by implementation of the techniques described in French patent n ° 2 299 519 filed on January 31, 1975 in the name of the plaintiff.

This combustion inhibitor can be applied by coating with a combustion inhibitor resin composition or by dipping in such a resin.

There are also known propellant charges made up of thin powder plates relative to the other dimen sions, intended in particular for propelling rockets, and the Applicant has discovered that such powder plates could be used for loading ammunition for tube weapons such as breech cannon, howitzer, recoilless cannon and rocket launcher, provided that these powder plates are partially coated with a combustion inhibitor.

For such a partial coating of combustion inhibitor to be effective, it is necessary that the latter be broken up into a large number of elements of combustion inhibitors of relatively small dimensions, of the order of magnitude of thickness of these plates. As a result, the application of such elements of combustion inhibitors is very difficult, if not impossible, to be carried out by conventional coating or soaking means.

The object of the present invention is to provide a method making it possible, in a very easy and very rapid manner, to partially inhibit powder plates having in particular a small thickness relative to their other dimensions, such plates being intended for particular to the pyrotechnic loading of weapons with propulsion tube.

• - on prépare une composition visqueuse de matériau inhibiteur de com-. bustion ;
• - on applique, sur l'une des faces de la plaque de poudre, un écran sérigraphique comportant une série d'ouvertures régulièrement réparties sur cet écran ;
• - on applique sur cet écran la composition visqueuse d'inhibiteur de combustion, et on racle cette composition sur cet écran, après quoi,
• - on retire l'écran pour permettre la polymérisation de la composition d'inhibiteur de combustion déposée sur la plaque de poudre.

According to the invention, this process is characterized in that:

• - A viscous composition of com- inhibitor material is prepared. bustion;
• - We apply, on one side of the powder plate, a screen printing screen comprising a series of openings regularly distributed on this screen;
• - the viscous combustion inhibitor composition is applied to this screen, and this composition is scraped on this screen, after which,
• - The screen is removed to allow the polymerization of the combustion inhibitor composition deposited on the powder plate.

The serigraphic screens used in the printing field are generally prepared from a fine mesh canvas covered by a mask consisting of a photosensitive resin. The openings of this mask are obtained by photoengraving. This technique makes it possible to make very small openings whose edges are remarkably sharp.

It is therefore possible, thanks to the process according to the invention, to partially coat plates of powder with a large number of elements of combustion inhibitor material distributed regularly over the surface of such plates.

Furthermore, a very large number of coating operations can be carried out from the aforementioned screen, so that the method according to the invention is particularly suitable for mass production.

According to a preferred version of the invention, the combustion inhibitor composition has a viscosity greater than 5,000 poises, and preferably between 10,000 and 20,000 poises.

Under such viscosity conditions, the inhibitor composition is deposited on the powder plate practically without spreading thereon, thus forming combustion inhibitor elements whose contours are perfectly clear. Therefore, during the mass production of such plates, one obtains for each of them a perfect definition of the combustion surface, and therefore, excellent regularity of the combustion surface of these plates.

Preferably also, the combustion inhibitor composition is produced from an organic binder which can be polymerized by humidity. Such a binder is advantageously chosen from polyurethane resins with polybutadien or polyether chains and silicone resins.

These binders are compatible with the pyrotechnic compositions used for the plates and, on the other hand, have excellent properties as a combustion inhibitor.

Other features and advantages of the invention will appear in the description.

• - La figure 1 est une vue en coupe d'une plaque de poudre au dessus de laquelle est disposé un écran sérigraphique,
• - La figure 2 est une vue en plan de l'écran sérigraphique,
• - La figure 3 est une vue analogue à celle de la figure 1, montrant l'application de la composition d'inhibiteur de combustion,
• - La figure 4 est une vue en coupe d'une plaque de poudre, partiellement revêtue par un inhibiteur de combustion,
• - La figure 5 est une vue de dessus de la plaque de poudre représentée sur la figure 4.

In the appended drawings, given by way of nonlimiting examples:

• FIG. 1 is a sectional view of a powder plate above which a screen printing screen is arranged,
• FIG. 2 is a plan view of the screen printing screen,
• FIG. 3 is a view similar to that of FIG. 1, showing the application of the combustion inhibitor composition,
• FIG. 4 is a sectional view of a powder plate, partially coated with a combustion inhibitor,
• - Figure 5 is a top view of the powder plate shown in Figure 4.

Referring to FIG. 1, the powder plate 1, constituting the elementary charge of a pyrotechnic charge, for example for projectiles of tube weapons, has a small thickness relative to its other dimensions.

• - on prépare, tout d'abord, une composition visqueuse de matériau inhibiteur de combustion,
• - on positionne au voisinage de la face 2 de la plaque de poudre 1, un écran sérigraphique 3 comportant une série d'ouvertures 4 régulièrement réparties sur cet écran (voir figures 1 et 2),
• - on applique ensuite, sur cet écran 3, la composition visqueuse 5 d'inhibiteur de combustion et on racle cette composition sur l'écran 3 au moyen d'une raclette 6 (voir figure 3).

To coat this plate 1, partially with a combustion inhibitor material, the procedure is as follows:

• - firstly, a viscous composition of combustion inhibitor material is prepared,
• a serigraphic screen 3 is positioned near the face 2 of the powder plate 1, comprising a series of openings 4 regularly distributed on this screen (see FIGS. 1 and 2),
• - Then, on this screen 3, the viscous composition 5 of combustion inhibitor is applied and this composition is scraped on the screen 3 by means of a squeegee 6 (see FIG. 3).

A powder plate 1 is thus obtained covered by elements 7 of combustion inhibitor material (see Figures 4 and 5). In this example, the elements 7 of combustion inhibitor material are constituted by identical rectahgles arranged in parallel rows.

The screen printing screen 3 is itself prepared in the following manner: There is, on a fine mesh fabric 8 made for example of polyester, polyamide or stainless steel, a layer of photosensitive resin 9 of a type known per se. Openings 4 are then made in this photosensitive resin layer 9 by a photoengraving process. This photoengraving is carried out by applying to the photosensitive resin layer 9 a cover comprising openings identical to the openings 4 to be produced and exposing the assembly to light. The exposed parts are then removed by a chemical process known per se.

Before applying the composition 5 of combustion inhibitor material to the screen printing screen 3, the latter is stretched a few tenths of a millimeter above the surface 2 of the powder plate 1, as indicated in FIG. 1.

The composition of the combustion inhibitor material 5 used must be sufficiently fluid to be able to easily pass through the meshes of the fabric 8. This composition must also be sufficiently viscous so that it does not spread over the surface 2 of the plate 1 after having passed through the openings 4 and the fabric 8 of the screen printing screen 3. Experience has shown, for this purpose, that the combustion inhibitor composition 5 must have a viscosity greater than 5000 poises, the best results being obtained when this viscosity is between 10,000 and 20,000 poises approximately.

The composition of the combustion inhibitor material 5 generally comprises a resin constituted by a base binder added with a curing agent. This composition comprises, on the other hand, inorganic fillers to ensure the thermal resistance of the inhibitor and to adjust the viscosity of the composition to the values indicated above.

This composition is essentially distinguished from the inks usually used in screen printing by the fact that it does not contain any solvent making it possible to adjust and maintain the viscosity of the ink before and during the scraping operation, certain solvents being liable to attack the surface of the powder plate 1. However, it has been found that certain screen printing inks with solvent may be suitable, for example polyester-based inks, provided that at least one of the inks is added to these inks propellant stabilizers, for example 5% ethyl-centralite for double base propellants.

Preferably, the base binder of the combustion inhibitor composition 5 is polymerizable with moisture.

In this way, if the constituents of the composition 5 are mixed in an anhydrous medium, the polymerization is blocked during the entire operation of applying the composition to the plates 1 and this, until the plates powder 1 covered by the elements 7 of combustion inhibitor are placed in a humid atmosphere. The combustion inhibitor composition 5 prepared before its application on the plates 1 can thus be used throughout the duration of the serial production cycle of a large quantity of powder plates 1 partially inhibited.

Among the moisture-polymerizable resins, there are in particular resins consisting of molecules whose chains terminate in isocyanate groups. Among these, polyurethane resins with polybutadien or polyether chains are preferred. However, it is also possible to use silicone resins.

• Exemple 1 : inhibiteur à base de polyuréthane :
  • - polybutadiène hydroxytéléchélique : 100 parties en poids
  • - dialcool à chaîne courte : 10 parties en poids
  • - diisocyanate : 20 parties en poids (le rapport fonctionnel NCO étant voisin de 2) OH
  • - agents de réticulation, anti-oxydant et catalyseur
  • - charges minérales contenat par exemple 50 parties d'oxyde de fer et de la silice ultrafine.
• Exemple 2 : inhibiteur à base de silicone nécessitant un primaire d'adhésion :
  • - résine silicone de base (diméthyl polysiloxane) : 100 parties en poids
  • - catalyseur : dibutyle dilaurate d'étain : 0,5 à 10 parties en poids
  • - charges : borax à taux d'humidité constant : 0 à 4 parties en poids, silice : 3 à 6% en poids.

Two examples of combustion inhibitor compositions which can be used are given below:

• Example 1: polyurethane inhibitor:
  • - hydroxytelechelic polybutadiene: 100 parts by weight
  • - short chain dialcohol: 10 parts by weight
  • - diisocyanate: 20 parts by weight (the NCO functional ratio being close to 2) OH
  • - crosslinking agents, antioxidant and catalyst
  • - mineral fillers, for example 50 parts of iron oxide and ultrafine silica.
• Example 2: silicone-based inhibitor requiring an adhesion primer:
  • - basic silicone resin (dimethyl polysiloxane): 100 parts by weight
  • - catalyst: dibutyl tin dilaurate: 0.5 to 10 parts by weight
  • - fillers: borax at constant humidity: 0 to 4 parts by weight, silica: 3 to 6% by weight.

To facilitate the attachment of the combustion inhibitor composition 4 to the face 2 of the powder plate 1, this surface is preferably degreased beforehand, for example by means of dichloroethylene.

The squeegee 6, used to allow the combustion inhibitor composition 5 to pass through the openings 4 of the screen printing screen 3, then through the meshes of the fabric 3, must not adhere to the composition 5. For this purpose , it is advantageous to use a neoprene reclette 6,

It can be seen in FIG. 3 that the passage of the squeegee 6 makes it possible to apply the fabric 8 to the surface 2 of the plate 1. This contact has the effect of printing on the surface 2 of the plate 1 the elements 7 combustion inhibitor, as shown in Figures 4 and 5.

The outline of the combustion inhibitor elements 7 thus deposited on the plate 1 is particularly clear, provided that the thickness of the screen printing screen 3 is less than about 0.2 millimeter.

The nature of the powder constituting the plate 1 is not critical. However, it is preferable that the latter is a homogeneous powder, such as for example a double-base propellant, constituted by a mixture of nitrocellulose, nitroglycerin and additives, this propellant being able to be covered by a thin layer of primer facilitating adhesion. subsequent to the inhibitor or which may be superficially impregnated with a combustion moderator.

From the above description of the process according to the invention, it appears that this process is particularly well suited to the mass production of pyrotechnic charges in plates partially coated with combustion inhibitor.

The number, shape and dimensions of the combustion inhibitor elements 7 applied to the plates 1 is not critical. These parameters depend, in fact, on the application planned for loading, and in particular on the desired modification for the initial combustion surface of these plates.

The preferred application of the invention is the partial inhibition of the propellant plates for the propellant charges of tube weapons, such as cannons and rocket launchers.

In such an application, the propellant plates 1 have a thickness generally less than 2.5 millimeters, and the largest dimension of the combustion inhibitor elements 7 is of the same order of magnitude as the aforementioned thickness. Furthermore, in such an application, there are a large number of these combustion inhibitor elements 7 on the propellant plates 1, distributed regularly, so as to cover more than 50% of the surface 2 of these plates 1. thus significantly reduces the initial combustion surface of these plates 1.

In this way, the maximum pressure of the combustion gases is appreciably reduced at the start of the firing, which makes it possible to considerably lighten the construction of the barrel tubes, rocket launcher and the like.

Of course, the invention is not limited to the examples which have just been described, and numerous modifications can be made to them without departing from the scope of the invention, the screen printing screen being able to be constituted by a multi-perforated sheet of nickel or stainless steel.

Thus, the method according to the invention is applicable to the partial inhibition of powder plates intended for pyrotechnic charges other than those of tube weapons.

Claims (12)

1. Method for manufacturing pyrotechnic charges from powder plates of substantially constant thickness, characterized in that: a viscous composition of combustion inhibitor material is prepared, a serigraphic screen comprising a series of openings regularly distributed on this screen is positioned on one of the faces of the powder plate, - the viscous combustion inhibitor composition is applied to this screen and this composition is scrapped on this screen, after which, - The screen is removed to allow the polymerization of the combustion inhibitor composition deposited on the powder plate. 2. Method according to claim 1, characterized in that the powder plate used is constituted by a homogeneous powder and preferably by a double base propellant. 3. Method according to any one of claims 1 or 2, characterized in that the powder plate used has a thickness less than about 2.5 millimeters. 4. Method according to any one of claims 1 to 3, characterized in that the combustion inhibitor composition has a viscosity greater than 5,000 poises and preferably between 10,000 and 20,000 poises. 5. Method according to claim 4, characterized in that the combustion inhibitor composition is produced from an organic resin polymerizable with humidity. 6. Method according to claim 5, characterized in that the resin consists of molecules whose chains terminate in isocyanate groups. 7. Method according to any one of claims 5 or 6, characterized in that the resin is chosen from polyurethane resins with polybutadiene or polyether chains and silicone resins. 8. Method according to claim 4, characterized in that the combustion inhibitor composition consists of a polyester-based screen ink to which is added at least one of the propellant stabilizers. 9. Method according to any one of claims 1 to 8, characterized in that the screen screen has a thickness less than about 0.2 millimeter. 10. Method according to any one of claims 1 to 9, characterized in that the screen printing screen comprises a large number of openings of geometric shape arranged parallel to each other. 11. Method according to any one of claims 1 and 5 to 7, characterized in that the application of the viscous composition of combustion inhibitor and the scraping of this composition are carried out in a dry atmosphere. 12. Method according to any one of claims 1 and 5 to 7, characterized in that after the removal of the screen printing screen, the powder plate partially coated with combustion inhibitor is placed in a humid atmosphere.

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