An assessment of the control of finning (veining) defects in iron castings produced with phenolic - urethane cold - box bonded cores

摘要

The present work has revealed that in a casting presenting a severe finning situation with a phenolic urethane bonded core many of the techniques reported in the literature are not able to give freedom from finning. Indeed many of the techniques suggested made no difference or oniy a small difference to the results The results indicated some effects from the binder system and the sand type but, with the exception of the reclaimed greensand, the effects were minor. It was found that reducing the compacted density of the test cores reduced finning even within a practical band of density but the effect was also relatively minor. Only three sand additives were found that were adequately successful under the conditions used. These were dextrin. coal dust and a commerecial mineral blend. Of these only the dextrin and mineral blend were able to produce test castings entirely free of fins. All three additives were found to have disadvantages with dextrin having the most detrimental effects on other core properties (strength and gas evolution) and the commercial mineral blend having the least (except for worsening surface finish when used without a coating).The mineral blend produced the highest mixed sand cost with the dextrin also quite expensive. The coal dust presents a low cost option and is perhaps the best choice where finning is signififcant but not too severe. Dextrin would essm to suit cases of severe finning where core strength is not too critical and where high gas evolution would not be too damaging. The mineral blend would be best with smaller cores requiring high strength and / or low gas evolution and where the effect of the mixed sand cost would be largely irrelevant. One furtheer result of potential interest to some was that a mechanically reclaimed greensand used in a blend with new sand at 70% reclaimed 30% new produced a significant improvement in finning. This soulution would have the potential to reduce, rather than increase, the mixed sand costs despite the lower strength and increased resin demand. This technique could be a very viable solution for those greensand foundries where core sand input is high. The development programmme resulted in both an improved anti-finning coating and an anti-finning sand additive. The sand additive performed similarly to dextrin but would provide improvements in bainder consumption and mixed sand costs as well as reducing handling hazards. Both the coating and the sand additive may be commercialised afterfurther testing.