Ductile Iron Society RESEARCH PROJECT No. 40 Survey of Greensand Properties of Member Foundries Mary Beth Krysiak Sand Technology Co. LLC, New Hudson MI Dr. Hathibelagal Roshan K & S Data Services LLC, Fox Point WI DUCTILE IRON SOCIETY Issued by the Ductile Iron Society for the use of its Member Companies – Not for General Distribution DUCTILE IRON SOCIETY 15400 Pearl Road, Suite 234 Strongsville, Ohio 44136 (440) 665-3686 SEPTEMBER 2007 Research Report Project #40 2007 Survey of Greensand Properties of Member Foundries A Cooperative Project of Ductile Iron Society And Member Foundries Reported by Mary Beth Krysiak Dr. Hathibelagal Roshan Ductile Iron Society Issued by the Ductile Iron Society Located at 15400 Pearl Road, Suite 234; Strongsville, Ohio 44136 Contents 1, Executive Summary - pdf 2. Survey report Part A - pdf 3. Survey report Part B pdf 4. Correlations - pdf 5. Sand data sheet for collecting info - pdf 6. Sand grain photos - pdf 7. Test data - XL 8. Sand tests and guide to controls – chart - pdf 9. Sand tests and guide to controls – chart - Word Sand Survey Report Executive Summary 1. The sand tests were done in one laboratory known to have many years of expertise in sand testing. During transport, regardless of how well samples are sealed, the samples age and while moisture content remains fairly stable, compactability drops as the moisture is absorbed further into the clay. In addition, the sands cool from the temperature at which they were in use at foundry. While the cooling effect could not be negated on a practical level, the sands were retempered or conditioned, prior to testing, to the reported target compactability at the foundry. This was done in a low energy mixer, so the water could be distributed with a minimum energy input into the sand in order to avoid altering the strength properties. 2. Because of the aging (temperature and compactability loss) and retempering, some of the green properties as measured may not match the values determined at the foundry. The tests affected include all tests run in the green state: green compression, green shear, permeability, dry compression, friability, cone jolt toughness, and Rowell flowability. These properties should be fairly close, however, the values in the foundry. If there are large differences, the reasons for the difference should be investigated. 3. All compositional tests performed on dried sand samples including MB clay, 25 micron and adjusted clay, AFS GFN, LOI, volatiles and the Silica Program sand composition data will be unaffected by aging and reconditioning and can be compared directly. Differences on these tests may be due to equipment or procedural differences between laboratories. 4. Standard AFS Handbook procedures were used for all work in the study. General Observations 5. In many sand systems, there were significant differences in composition between the two samples provided. This may be due to and not limited to: a. Large differences in sand to metal ratio of jobs run at that times b. Running a single mold line, with differences in core sand, new sand and metal poured per unit time c. Differences in number of molds per unit time (down time); new sand may be added even when molds are not shaken out. Unpoured molds also add variation d. Differences in dust collection due to operational variations e. Addition of materials in random fashion, slugging of spilled sand, dust collector fines etc. f. Changing bond and new sand addition drastically (on and off and in big steps) 6. There are wide variations between sand systems in many of the operating variables such as, MB clay, fines, LOI, moisture, AFS GFN, permeability etc. 7. At extremes of these values there may be problems either in mold making and or quality of the castings. 8. Even though the compactability is controlled at the muller, the compactability at the point of use is critical for good quality molds and castings. 9. It is a good idea to know the compactability change between the muller discharge and the point of use. When this difference changes, the causes of the change should be understood. 10. It must be kept in mind that, because this is data from 31 different foundries, all with different base sands, preblends, and sand system engineering, certain relationships or correlations may be different than what they are when viewing data from a single sand system. Property Relationships 11. At the clay levels foundry sand systems are operating, the green strength does not correlate to MB clay level. This is due to the fact that most of the systems in this study were high clay sands. Heine and Green have shown that at high clay levels, green strength does not increase further as clay is increased. In addition the sands were all tested in a narrow compactability range close to 40%.Bulk density (pounds per c.ft) decreases as. compactability (at the mold line) increases. Compactability is actually a measure of bulk density and is inversely related to it. Bulk density also correlated with specimen weight in this study. 12. Compacted density is influenced mainly by silica level, LOI, and ooltics. As compacted density increases, the rate of heat extraction would increase. 13. Metallics was also shown to correlate with compacted density. It must be understood, however, that whenever correlations are studied “correlation is not necessarily causation”. This is a good example. The metallics content of a molding sand is too low to truly influence compacted density. Yet the two correlate because sands with high compacted densities tend to be clean, high silica level sands. Sands with high levels of contamination (including inert fines, oolitic material and metallic contamination) generally have lower silica levels and lower compacted densities. 14. Permeability is affected by grain fineness but not to a great extent by clay level 15. Specimen weight is mainly affected by the ratio of the heavier component of silica to the light components (LOI level/carbonaceous material, and fluxing material as inert fines and oolitics). As the clay level rises it takes comparatively less moisture to reach a certain compactability, due to limited mulling of the sand. This is due to the fact that mulling cycles are short, and the moisture moistens the surface of the clay first. So the compactability can be reached even though the subsurface clay is drier. As the sand travels to the molding machine, the moisture has time to be further absorbed into the subsurface clay. 16. Inert fines are shown to strongly correlate with dead clay (the difference between Adjusted clay and MB clay). Sieve fines (200, 270 and pan material) correlated very strongly with AFS GFN. So, as expected, sieve fines mainly consist of fine particles of silica, and inert subsieve fines consist of dead clay or other non silica components. 17. Permeability related mainly to AFS GFN in this multi-system study 18. Dry compression correlated with average shakeout time. As the shakeout time increased, dry compression decreased. This is most likely due to a greater reduction in interlayer water with longer exposure to heat. The more interlayer water that is removed, the more difficult it is to re-hydrate the interlayer. 19. There were no strong linear correlations with Flowability, Friability and Cone Jolt Toughness and any other single factor, indicating that these properties are affected by more than one parameter. These properties and inter-relationships between multiple variables need to be better understood because there was a very wide range in the various sands in this study. Flowability ranged from 49% to 92%. Friability ranged from about 1% to 11%. Cone Jolt Toughness ranged from 36 jolts to 593 jolts. Complex inter-relationships of moisture, clay, and other properties control the toughness, friability, and flowability of the sand, and these inter-relationships are not, as yet, well understood. Changes in these sand characteristics, which we do not yet understand how to control, may contribute to sand control problems and casting defects in foundries. Further work, possibly including multiple linear regression studies, need to be undertaken so that foundries can understand how to control toughness, friability, and flowability. 20. Volatiles correlated inversely with Moisture Volatiles Ratio. The volatiles test is performed on a dried sample, so this most like reflects that sands with high volatiles also have higher LOI levels, and therefore higher moisture requirements. Since moisture is volatile and fresh carbons are volatile, pinholes become a problem at high moisture combined with high volatiles. This is particularly true if the moisture is high in relation to the volatiles, because this changes the mold atmosphere to oxidizing instead of reducing. 21. Volatiles correlated inversely with flowability. This most likely a reflection of the fact that sands with high volatiles tend to have high LOI, and therefore high moisture levels which reduce flowability.. 22. Metallics showed an inverse correlation with silica level. Again, this is due to the fact that cleaner/high silica level sands generally have lower levels of contaminants. 23. High moisture, low silica, low specimen weight sands tended to have lower mulling efficiencies. This is due to the fact that cleaner, low clay, low moisture sands hydrate more easily due to a lower moisture requirement. (Conversely, they may also dry out faster). 24. In terms of Heine Green Parameters, most of the sands in this study fell into the clay rich – moisture starved condition. 25. The Heine-Green Mulling Efficiency directly correlates to the easily calculated compactability to moisture ratio and inversely to Adjusted Clay. Again this is due to the fact that high clay sands have higher moisture requirements which are more difficult to satisfy. 26. The easily calculated MB to moisture ratio correlates inversely to Heine-Green Green Strength Efficiency.