Abstract:
A polyamide molding composition filled with fine particulate metals for injection molding into practice hand grenades and shells which disintegrate into small pieces.

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention is polyamide compositions containing particulate metal fillers and the invention is particularly concerned with the application of these compositions to injection molded practice hand grenades and shells. 
     The state of the art of producing polyamide compositions containing fillers and processing these compositions by injection molding may be ascertained by reference to the Kirk-Othmer, &#34;Encyclopedia of Chemical Technology&#34;, 2nd Edition, Vol. 16 (1968) under the section &#34;Polyamides (Plastics),&#34; pages 88-105, particularly page 92--polylauryllactam (nylon-12), pages 98-99--injection molding and extrusion and pages 101-102--Powder Processing, the disclosures of which are incorporated herein along with U.S. Pat. No. 3,317,482 which shows the state of the art of polylauryllactam production. 
     The state of the art of practice hand grenades and shells comprising metal powder filled compositions may be ascertained by reference to U.S. Pat. Nos. 3,194,161; 3,369,486 and 3,463,047 the disclosures of which are incorporated herein. 
     According to the present invention a molding composition is provided which is densely filled with fine particulate metals and which can be worked into molded articles by injection molding. Such molded articles should be dimensionally stable under ordinary conditions, that is, they should not break, for instance when being dropped, while on the other hand they should disintegrate when subjected to a high force, for instance to an explosive, into the finest possible particles which practically can no longer be located a few meters from the disintegration site. In particular the molding composition should be practical in the preparation of training hand grenades or mortar shells. For those applications, the molded article must be of a weight corresponding to that of a well defined grenade or shell. 
     It is known to arrange the effectively disintegrating metal particles inside such ammunition in a thermoplastic such as polystyrene of low impact strength. As regards the previously known procedures, the metal splinters have been enclosed with a liquid plastic within a hollow mold, and then with the shell casing, by injection molding if desired. 
     This laborious procedure has been required so far because the known thermoplastics cannot be processed into densely filled molding compositions. 
     SUMMARY OF THE INVENTION 
     Having in mind the limitations of the prior art it is an object of the present invention to provide a composition which is filled with fine particulate metals, processable by injection molding machines, and which disintegrates into minute particles, this polyamide molding composition comprising: 
     5 to 20% by weight of polyauryllactam having a relative viscosity of about 1.6 to 2.2 (German Industrial Standard DIN 53 727); and 
     80 to 95% by weight of fine particulate metals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 of the drawing is an elevated view in cross-section of a practice hand grenade with the injection molded composition of the present invention and 
     FIG. 2 is a practice mortar shell of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 injection molded half body 1 is shown on the right and injection molded half body 2 is shown on the left. This hand grenade has a metal tube 3, a delay 4, a detanator 5, an explosive charge 6, and an ignition body 7. 
     The practice mortar shell of FIG. 2 has injection molded half body 9 on the right, injection molded half body 10 on the left, and explosive charge 11 in the center. 
     A suitable polylauryllactam is produced by hydrolytic polymerization as disclosed in U.S. Pat. Nos. 3,799,899 and 3,317,482.  Polylauryllactam obtained by anionic polymerization in the presence of metal fillers is too brittle and does not splinter into the required small particles. The relative visosity as measured by German Industrial Standard DIN 53 727 is between 1.6 and 2.2, especially between 1.6 and 1.8. The proportion of polylauryllactam in the molding composition is especially 5 to 15% by weight. Suitable fine-particulate metals are copper, bronze in the form of very fine powders or fragments of a size of less than 100 microns and approximately equal to 0.100 mm. In particular the metal proportion of the molding composition is between 85 and 95% by weight. 
     The ingredients are processable on kneaders into the molding composition, the polylauryllactam being prepared if desired in the form of granulates or as a powder. 
     Obviously dyes, lubricants, stabilizers and other accessories if desired are added to the molding compositions in conventional amounts as disclosed in Kirk-Othmer i.b.i.d. 
     Despite its high metal content the molding composition can be processed by injection molding machinery into molded articles. Obviously the molding composition can also be processed into other molded articles besides fillers for hand grenades or mortar shells. In many instances these compositions possess sufficient impact strength, for instance they are suited for the manufacture of sound absorbing plates. The density of the metal filled molded compositions amounts to 3.5 to 4.9 g/cm 3 , especially 4.2 to 4.5 g/cm 3 . 
     SPECIFIC EXAMPLE 
     13 parts by weight of polylauryllactam (relative viscosity 1.65) and 87 parts by weight of bronze fragments of a size of less than 100 microns are kneaded. The molding composition received in the form of granulates is processed by injection molding into two half bodies of a training hand grenade (FIG. 1).