Internal recycling of scrap ferrous metal

Internal scrap is produced from the knock-off of feeders and runners, in quality control and in finishing operations. The relative amoimt of internal scrap produced can be calculated from the metal yield as defined and described in Section 3.10.1.3. In order to minimise residue production, internal scr is returned to the scrap metal feed of the furnace. 

For steel foundries, a 100 % use of return metal is uncommon, due to the amount of dissolved gas. Operators consider 60 % to be the maximum amount of return metal (feeders, scrap castings.) in the charge metal. Swarf and turnings may cause excessive molten metal oxidation. 

Internal scrap recycling may also be limited in the case of nodular base iron melting, as a high amount of silicon (about 1 % in most cases) is added in the liquid iron during the metal treatment. In some cases re-melting the whole internal scrap is not possible because the final silicon would be too high (typically 2.5 - 3 % in the castings). 

In the case of grey or nodular iron, lead or bismuth are very noxious for the properties of the metal after solidification. If there has been a pollution incident the returns (internal scrap) must not be recycled. 

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