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| Špánik J., Krochmal K. |
| PARAMETERS OF HOT EXTRUSION PRESSING OF ALPHA BRASS |
Abstract
Competition among producers of infantry ammunition is permanently forced to find ways of cost reduction at brass cartridges production. Changes from brass cups production made from rolled strips to production from pressed bars and wires are real ways of reducing material costs. Brass for deep drawing of type CuZn30 is used for production of cartridges and belongs to a group of alpha brasses. The brass for cold deep drawing of cartridges is applied due to its good cold formability. It is not the same for a hot formability of CuZn30 because it belongs to a group of the worst hot formable brasses. Parameters of hot extrusion pressing of CuZn30 given by literature have significantly limited the process of extrusion pressing from a particular point of view cross cracks formation on the extrusion surface, especially extrusion ratio and extrusion speed (output speed of extrusion from die opening). On the base of analysis of accessible literature from boundary values of extrusion pressing of CuZn30 brass were calculated parameters of extrusion pressing for operation press with a nominal force of 35 MN and container inside diameter of 210 mm. Realised experiments of extrusion pressing of CuZn30 have shown, that extrusion pressing in specific conditions at a higher extrusion ratio more than a value of 60 is possible. It was carried out the extrusion speed influences formation of cross surface cracks at hot extrusion pressing of alpha brass. A uniform criterion was searched for in order to consider predisposition of alpha brass to cross cracks formation at hot extrusion pressing. The criterion is mean deformation rate. Simultaneously, the critic value of mean deformation rate of 0,9 s-1 for hot extrusion pressing of alpha brass CuZn30 was determined. A function relation between extrusion ratio and extrusion speed pressing was defined, which specifies parameters of extrusion pressing. Image of dependence for brass hot extrusion pressed CuZn30 allow instantaneous determination of parameters of extrusion pressing enabling process of extrusion pressing without initiation of surface cracks.
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| Keywords: hot extrusion pressing|alpha brass|surface cracks|brass CuZn30|deformation rate|extrusion ratio|extrusion speed| |
| No 2 (2007), p. 236-243 |
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