Process For The Surface Treatment Of Non Metallic Cases Such As Cartridges, And The So Treated Cases

Abstract

The invention relates to a process for surface treating porous combustible cartridge cases, said process consisting in applying a first barrier layer on the outer surface of the case, and, on this layer a water impervious layer so that the case is rendered moisture- and waterproof without modification of its porous structure.

Description

This invention relates to a process for the surface treatment of non metallic cases such as cartridges. The term cartridge is used herein to describe receptacles used in the ammunition techniques for explosive propellent charges, it being possible to give to said receptacles, shapes adapted to the weapons or their intended purposes, used in connection with the projectile proper or separated therefrom.

Such non metallic cartridges provided to burn with the propellent charge provide a problem in that the desired porous structure of the constituting material of the cartridge must have excellent break strength and storage stability. This is obtained by using synthetic materials or by solidfying combustible paper or cellulose raw materials. However, most pores are then closed, thereby slowing down the combustion process. An additional drawback results from the fact that the synthetic materials, i.e., the pasting products, are preventing a complete combustion of the constituting material of the cartridge, thereby causing detrimental effects through the barrel and a diminution of the initial velocity. It should be noted that the coating of the combustible cartridges with a protective lacquer layer against moisture action is detrimental in that said layer penetrates the constituting material of the cartridge to such a depth that the above drawbacks resulting from the manufacture method, namely the combustion slowing down, are still remaining.

It is an object of the present invention to protect such combustible non metallic cartridges against moisture in such manner that the cases will meet the strict requirements of the Military Authorities as regards their strength and their moisture resistance without any drawback when firing, i.e., without any detrimental effect upon the weapon.

For this purpose, this invention comprises substantially coating the cases made of porous combustible materials and more particularly the external surfaces thereof with a film of natural or synthetic swelling polymers or derivatives of such polymers, said film forming a barrier layer and, when said layer is set, coating it with a protective layer stable to moisture.

In preferred embodiments of the invention, the barrier layer is obtained by affixing a water swelling cellulose film. In addition, the barrier layer may be also made of synthetic or natural polymers or derivatives thereof having a structure chemically similar to that of cellulose, e.g., polyvinyl alcohol and esters and ethers thereof. As swelling means for forming the barrier layer, not only water, but also other gel-forming or dissolving liquids may be used according to this invention.

The barrier layer consisting preferably of water swelling cellulose or cellulose derivatives may be applied in high viscosity solution in a single operation or also in a low viscosity film. After drying of the first coating, the barrier layer is then made non porous by a second film.

The surface layer is applied as a protective layer above the barrier layer consists of a film forming rubber solution admixed with small amounts of bitumen and/or paraffin.

As combustible elements of cartridges, porous receptacles of cellulose derivatives, formed as known in accordance with the intended purpose, may be used. The porous receptacle which may also consist of nitrated fibers, is advantageous in that it has an external surface protected by a barrier layer consisting of a non porous film covering only the external surface and having consequently no effect upon the porosity. The external protective layer prevents the non metallic case from being damaged by any action of air humidity, water vapour or sea water.

Cartridges according to the invention have shown such a moisture resistance that after several hours in water at 20.degree. C or after an extended storage under a relative humidity of 95 percent, the ballistic requirements have been compltely fulfilled on test firings without observing any slowing down or detrimental effect upon the weapon.

As porous materials, there may be used also non combustible materials which, when exploding, are leaving no residue and are not damaging the weapon by corrosion or erosion.

The attached drawing shows by way of example a partial section of a case embodiment.

Reference number 10 indicates the porous combustible material forming a cartridge of corresponding sizes, e.g., a fuse case, a mine body or the like. The external surface of the porous body 10 is covered with the non porous barrier layer 11 in such manner that the barrier layer 11 forms a closed surface film. The protective layer 12 according to the invention is then applied on the barrier layer. The barrier layer and the external protective layer may be made in any known manner, e.g., by spreading or dipping.

Claims

What I claim is:

1. A process for the surface treatment of articles comprising

1. providing a porous combustible article,

2. covering said porous article on at least a portion of an external surface thereof with a porous film of a dissolved water swelling compound selected from the group consisting of natural polymer, synthetic polymers and derivatives of synthetic and natural polymers,

3. drying said porous barrier layer and

4. coating the said porous barrier with a film of a non-porous moisture proof composition as an outer protective layer.

2. A process according to claim 1, wherein polyvinyl alcohol and esters and ethers thereof admixed with dissolving or gel-forming liquids are applied as a barrier layer.

3. A process according to claim 1, wherein the barrier layer is applied as a low viscosity film to which, after drying, is applied a second film eliminating the pores.

4. A process according to claim 1, wherein a rubber film forming solution is applied as an outer protective layer.

5. A process according to claim 4, wherein small amounts of bitumen or paraffin are added to the rubber solution.