This page contains a Flash digital edition of a book.
All melts contained a small number of large reacted re- fractory inclusions. The particle size of 0.15–0.25 mm (0.015–0.025 cm) indicated that the area fraction of this type of inclusions dominated the count. The other principal large inclusion was a metallurgical spinel, either in the form of long chains or as more compacted round inclusions. In addition, all melts con- tained fine and homogenously distributed alumina needles. The amount of oxide films increased significantly from Melt 1 to Melt 3 as one might expect. Micro- graphs from various types of inclusions as well as of oxide films are given in Fig- ure 6. RPT samples were taken in order to determine the bifilm index. A summary of the bifilm indices is shown in Figure 5(b). The bifilm index was in the range of 40 to 60 mm (4 to 6 cm) for all the melts. The graph does not show any trend, with an increase in oxide levels when the hy-


drogen level is kept constant. However, the scatter in the results increases and is significantly larger for the melt with the highest scrap addition.


Figure 4. Temperature vs. time readings from thermocouples in the step mould die (TC1-TC8) and ladle (TC9).


(a)


(b) Figure 5. Melt quality analysis results from (a) PoDFA tests and (b) bifilm index investigations.


(a)


(b)


Figure 6. Optical micrographs (a-b) taken from PoDFA residues, underline the presence of oxide films, porosity, reacted refractory, metallurgical spinel and alumina needles.


44 International Journal of Metalcasting/Spring 2012


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91