Testing was conducted with these
four systems to compare the effects of the commonly used sand additives to the new engineered sand additives. Tis resulted in nine different mixes for each sand/binder system: 1. No additive 2. 1% woodflour base additive (BR W39)
3. 1% red iron oxide (RIO) 4. 1% starch base additive (AFX) 5. 2% black iron oxide (BIO) 6. 2.5% ESA1 (RS4) 7. 4% ESA2 (I950) 8. 6% ESA3 (IS 2011) 9. 6% older generation engineered sand additive (BR 14000F). Initially, each sand additive was
tested for bulk density and LOI. Tese tests confirmed the woodflour, starch and ESA3 additives have low density, and the woodflour and starch are pri- marily organic as indicated by the high LOI. Te additives were mixed with the North American sand as the high- est purity silica to show their effects on pH and ADV (Table 2). Te woodflour, starch and iron
oxides tended to drive the pH down (more acidic) and the engineered sand additives tended to increase the pH and ADV. Te older generation ESA (BR 1400 F) had the least affect on sand properties while the ESA3 had the greatest effect. Te researchers tested each of the sand/binder and additive combinations for tensile strength (psi), including the effects on benchlife and exposure to high humidity.
A number of interesting conclusions could be drawn from the data. Te most obvious was the consistently higher strengths with the European sand and 1.6% binder. Tis is undoubtedly the
result of the higher binder level. It may reflect a geographic practice or belief that higher strength is needed for their particular applications. Te North American sand/binder combination shows less loss of strength at elevated humidity and extended benchlife. Tis again may reflect a regional philosophy of designing binders to meet specific environmental conditions. Te strength loss with different additives is by no means consistent from additive to addi- tive or from sand to sand. Tis follows the belief that each system or facility tends to be a bit different. Te ESA3 material had the greatest
impact on strength and particularly on humidity resistance and benchlife. Tis is likely related to the high pH and ADV values. Tese losses could be overcome to some extent with additional binder, but that testing is beyond the scope of this paper. Te finer additives like starch and red iron oxide also showed significant strength losses. Tese effects likely could be overcome with slightly higher binder levels. Te ESA1 and ESA2 showed the least loss of strength. Additionally, the North American
sand mixes were tested for transverse strength because of the prevalence of transverse rather than tensile testing in some regions. Te transverse test pro- vides additional information about the flexibility or stiffness of the materials by measuring deflection. As shown with the tensile tests, all of
the additives caused a loss in strength. Te percentage loss seemed to vary compared to the tensile tests, but no particular pattern emerged. Some of the additives produced a small decrease in the amount of deflection while others increased the defection. Tis may indi- cate an impact on sand core stiffness.
British Cast Iron Research Associa-
tion (BCIRA) hot distortion tests were conducted on the North American mixes (Table 3). Te test heats the lower part of a small rectangular core and measures the deflection of the core from thermal expansion of the heated surface followed by contraction as the binders are ther- mally degraded against heating time. BCIRA results were mixed. Te
woodflour (BR W 39) and starch (AFX) additives had the greatest impacts: reducing maximum deflec- tion, time to maximum, time to zero and time to failure. Te iron oxide and engineered sand additives produced results similar to if not exactly the same as the sand without additives. Two-inch-diameter by two-inch-
high cylindrical cores were produced from the different mixes using standard methods, and the cores were molded and cast in duplicate at 2,650F (~1,455C). Tis test casting has been described and used extensively to measure veining and surface defects. Tis is a very severe test and some level of veining will occur on most surfaces (Table 4). Te castings were graded for veining
(Fig. 1), penetration and surface finish on a scale of one to five in 0.5 increments with one indicating very good quality and five indicating very severe defects.
American system showed the most severe veining problems followed by the European, South American and China systems. However, the high purity, round grain silica sand from North America has excellent molding and coremak- ing properties. Te South America and China systems provide lower strength and core making properties, but are more forgiving for veining defects. Te different sand additives also
3 Fig. 1. This graph shows the veining ratings for the different core mixes.
showed a wide performance range. Te woodflour generally showed the most veining, followed by the RIO, starch, BIO and ESA3. Te ESA1, ESA2, and older generation ESA showed mini- mal veining and good surface finish and penetration resistance. Te relative performance of the additives seemed
April 2013 MODERN CASTING | 39 Results and Conclusions
Te tests confirm different sands and binder composi- tions perform differently on a regional basis. Te North
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