Tham khảo tài liệu 'extractive metallurgy of copper part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 22 Melting and Casting About 95 of the copper currently produced in the United States has existed as cathode copper at some time during its processing Edelstein 2000 . The cathodes are produced by electrorefining pyrometallurgical anodes from ore and scrap and by electrowinning copper leached from oxide and chalcocite ores. To make it useful this copper must be melted alloyed as needed cast and fabricated. Much of the fabrication process for copper and its alloys is beyond the scope of this book see Joseph 1999 for more information. However melting and casting are often the last steps in a copper smelter or refinery. A discussion of these processes is therefore in order. Product Grades and Quality The choice of melting and casting technology is defined by a the quality of the input copper b the required chemistry of the desired product c the type of final product . wire or tube. Table lists the copper cathode impurity limits specified by various national standards Joseph 1999 ASTM Bl 15-00 . Customers usually require purer copper than in these specifications. Fortunately recent adoption of stainless steel cathodes for electrorefining and electrowinning has improved cathode purity to match these customer requirements. The tightest impurity limits in copper cathode are for selenium tellurium and bismuth. All three of these elements are nearly insoluble in solid copper. They form distinct grain boundary phases upon casting and solidification. 367 368 Extractive Metallurgy of Copper Table . Upper impurity limits for copper cathodes as specified in the United States Great Britain and Chile 1WCC . Impurity limits specified for the Southwire Continuous Rod SCR systems arc also shown. ASTM American Society for Testing and Materials BS British Standards ppm parts per million. Element ASTM B-l 15 BS EN 1978 IWCC High Grade SCR Southwire Classification System Grade 1 Grade 2 Class 1 Class 2 Class 3 Cu Ag Se ppm 2 10 2 2 4 8 10 Te ppm 2 5 2 2
