GB2255936A

GB2255936A - Tungsten projectiles

Info

Publication number: GB2255936A
Application number: GB9202528A
Authority: GB
Inventors: Cornelis Taal; Rene Oudelhoven
Original assignee: Rheinmetall GmbH; NWM de Kruithoorn BV
Current assignee: Rheinmetall Industrie AG; NWM de Kruithoorn BV
Priority date: 1991-04-23
Filing date: 1992-02-06
Publication date: 1992-11-25
Also published as: DE4113177C2; GB9202528D0; DE4113177A1

Description

2 2 5 -SY 3 0 1 - TITLE ProJectiles This invention relates to a method for

the production of a penetrator projectile primarily intended for use against armour.

In DE 3438 547-C2 there is described a heat treatment process for a prealloyed two-phase tungsten powder having a high. proportion of tungsten wherein a porous pre-form of compressed powder is sintered in the solid phase, with the sintering being followed by a heat treatment of between two and ten minutes in or with a liquid phase. The heat treatment in the liquid phase causes a rounding of the tungsten particles in order to increase their strength which is not accompanied by any appreciable granular growth.

Despite the increase in the strength of the starting material of the penetrator, however, mechanical processing such as turning or grinding unavoidably causes cracks in the tungsten particles close -'L.o the surface, and these fractures propagate themselves undbr loads so that the penetrator prematurely becomes useless.

An object of this invention is to provide a simple and economical process L?y which the propagation of cracks r_ in a penetrator can be avoided.

According to this invention there is provided a method for the production of a penetrator from tungsten heavy metal, in which method outer tungsten particle layers are removed by a corrosive process from the surface of the penetrator after processing to the final external geometrical shape.

This invention is primarily based on a simple method of removing the outer tungsten layers from the surface of the penetrator after the latter has been machined. Cutting operations on the external geometry of the penetrator can cause surface cracks in individual tungsten particles. Particularly with slender penetrators having a considerable length-todiameter ratio, the cracks in the particles concerned propagate themselves under tensile stresses accompanying the firing operation, under vbrational and flexural stresses occurring during the flight and also as a result of impact with a target, so that they cause the penetrator to fail prematurely. Laboratory tests have shown that when the outer granular layers are removed by a corrosive action process in accordance with the invention the notch impact strength of the penetrator is increased by about 20%.

This invention is explained and described in greater i 1 3 detail with reference to an example and the accompanying drawings.

In the drawings:

Figure 1 shows a penetrator wherein the external surface has undergone the final processing, and Figure 2 shows an enlarged diagram of a section of the penetrator referenced 1 in Figure 1.

Figure 1 shows a penetrator 10 which is made of bungsten heavy metal and of which the outer contour has been subject to a finishing process. The penetrator has a nose 12 and is---Laperedin a rear zone 14 to enable- a. tail unit (not shown) to be secured thereto. For force transmission by means of a sabot (not shown) the central part 16 of the penetrator is provided with positive interlocking means 18 comprising, for example, screw threading or annular grooves. The penetrator 10 is produced by a cutting process from a cylindrical body. This process is accompanied by the formation of notches and cracks in tungsten particles close to the surface and when subjected to stresses the cracks propagate themselves from these particles so that the penetrator shatters prematurely. Microscopic examination shows that particles in which initial cracks occur are mainly to be found in the two uppermost layers while the processing machinery causes no damage to the layers situated lower down. This is illustrated in Figure which is an enlarged diagram of the zone 1 of the penetrator 10 which is adjacent to the surface. The reference number 22 denotes the tungsten particles which are situated in the top two layers and which have suffered initial cracking, while the number 24 indicates the undamaged tungsten particles in the layers lower down.

According to this invention two layers are etched away from the surface of the penetrator. A chemical erosion process which has proved particularly advantageous is one with which the choice of acid mixture and the time for which it reacts with the penetrator material enables a certain defined rate of surface removal to be achieved.

The element tungsten is highly acid-resi-Sting. The maximum attack on the material is effected by a mixture of nitric acid (HNO3) and hydrofluoric acid (HF), the rate of removal depending largely on the concentration. A mixed acid of 50% by weight of HF and 50% by weight of HNO3 for example, is found to attack the heavy metal structure excessively, so that a corrosion process intended to ensure a defined rate of removal is difficult to control. An easily controllable reaction, on the 0 other hand, can be achieved by the use of the acid with a composition of 90% by weight of HF (industrial purity) and 10% by weight of HNO3 (industrial purity) for the corrosive processing.

During the said corrosion operation the acid mixture is at a temperature of between 20 and 50o C. This offers the advantage of enabling any change in the original strength properties in consequence of thermal action on the material to be avoided. The removal of material from the surface is governed not only by the composition of the acid mixture but also by the reaction time. For the corrosive removal of at least two tungsten granular layers, corresponding to a reduction of 100,,mrri in a penetrator of 120 mm calibre, a suitable time d be about 3 for the reaction with the acid mixture minutes. The penetrator is then rinsed under running water, and any tungsten particles not adhering thereto are removed with a brush.

6

Claims

1. Method for the production of a penetrator from tungsten heavy metal, in which method outer tungsten particle layers are removed by a corrosive process from the surface of the penetrator after processing to the final external geometrical shape.

2. Method in accordance with Claim 1, wherein at least two tungsten particle layers are etched away from the surface.

3. Method in accordance with Claim 'L or 2, wherein the corrosion process is effected chemically.

4. Method in accordance with any one of Claims 1, 2 or 3, wherein the corrosive process is carried out at a temperature of between 20 and 50o C.

5. Method in accordance with any one of the preceding claims, wherein the penetrator which has been finally processed in the required external geometry is immersed in an acid mixture, removed from the said mixture after a preselected period and rinsed with water, any tungsten particles riot adhering to the surface of the penetrator being removed from the said surface by brushing.

6. Method in accordance with any preceding claim, wherein the corrosive process is effected by an acid mixture prepared from 1-0% by weight of HNOs and 90% by weight of HF.

7. Method for the production of a penetrator substantially as described herein and exemplified with reference to the drawings.

8 A penetrator produced by the method of any preceding claim.