Table 2. Casting Evaluations Casting
blasted to remove sand and oxidation. Te cored surfaces were then evaluated for veining, penetration and surface finish using the 1-5 scale (1 being preferred), shown in Table 2. None of the castings showed signs of gas or penetration defects, so all castings were rated a “1.” Level averages for the effects on
veining were plotted for the different variables (Figure 7). BIO appeared to have the greatest effect on vein- ing with I900, V400 and V2003 close behind. Te RIO and IL appeared to have the least effect. Lower binder lev- els produced less veining as did higher additives levels. Te effects on surface finish were
plotted for the different variables (Fig- ure 8). Te relative differences between castings and level averages were small, but the BIO, V400 and IL seemed to produce the best ratings. Te finer sand also produced a better surface finish. Surface Carburization Analysis:
Sections were cut from each casting to compare casting microstructures to the baseline castings. Quantitative evalua-
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16
Veining 1.25 2.25
2.00 3.25 1.00 1.00 1.50 2.00 1.50 1.25 1.50 1.50 1.75 1.25 2.75 1.75
Surface Finish 2.50 3.00
2.50 3.50 2.00 2.75 2.50 3.00 3.00 3.50 2.50 2.50 3.0
3.50 2.50 2.50
tion was difficult, but several differences were noted. Te castings shaken out in an hour had smaller grain sizes than those cooled for 24 hours. Tis would have been the result of faster cooling through the eutectoid transformation. Te photomicrographs also confirmed the surface finish results with the cast- ing from the cores with the coarser sand showing higher peaks and valleys and more retained sand grains.
Surface carburization as measured
by the percent pearlite was much more difficult to evaluate. Many of the castings showed increased ferrite on the surface, indicating decarburiza- tion. However, the decarburization appeared to be more prevalent on the castings produced with cores with the lower binder levels. Only the castings produced with V2003 and illmenite showed apprecia- ble surface carburization. Te interior structures were similar to that of the other castings, but these two additives contained only very low levels of any iron oxide materials. Tese castings also showed more carburization on the castings made with the cores with higher binder levels. Te results of these experiments
show that different sand additives should be used for specific mold/core properties. However, the effects of the sand additives on mold/core properties outlined by the results of this study are limited to the PUNB systems, as other binder systems have different mecha- nisms of reaction.
Fig. 7. Shown are the level averages for the effects on veining.
Fig. 8. Shown are the level averages for the effects on surface finish. December 2015 MODERN CASTING | 41
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