Reclamation Of Green Sand Containing Cold-box (or Hot-box) Resin Sand And Its Application

With the development of foundry technology, more and more moulding methods are appeared. At present, although the foundry technology has a long history which has been existed for 5000 years in China and now many kinds of chemical-bonded sand are developed very fast, the clay-bonded sand casting process, which has more unique advantage, is still become one of the most common casting process used in the foundry industry. As we know, all over the world, China has become the largest producer of castings which about 60% of castings are produced by the clay-bonded sand casting process. Furthermore, the phenomenon of the growing number of used clay sand thrown away, which has caused a huge waste of natural resources and also more and more pollution to our environment, has become a hot topic over the recent year. For instance, there is a growing tendency for the studying on the total reclamation of used green sand, which will cut down overall production costs and protect environment. So the foundryman has been showing an increasing interested in reclamation of used green sand. In a brief, the studying and application on the used sand reclamation is a great significance to sustainable development of the foundry industry.Two systems of sand reclamation are commonly used at present. One of the simple reclamation systems is one that reclaimed green sand returns back into green sand, by which only a proportion of the bentonite and other fines is removed from the sand. Another route is that reclaimed green sand is used to core sand, by which all binders were run at all reclaimed sand and at the same binder and catalyst level as in the new sand runs. In other words, the reclaimed green sand, which has a lower clay content than the same base sand, has been reused in core-making process.The methods of theoretical analysis combining with experimental studying are adopted in this paper. Based on understanding the development situation of used green sand reclamation technology which introduced at home and abroad, the properties of used green sand and the mechanism of reclamation are analyzed in detail. Consequently, in order to remove the bentonite from the sand grains and obtain the reclaimed sand, calcination followed by mechanical attrition was chosen as the process of reclamation which was determined by studying basement of our studying team. Though testing the physical properties of reclaimed sand, the feasibility of the reclamation process is evaluated. The adaptability of the reclaimed sand which were applied to cold-box (or hot-box) resin sand process is determined by studying its foundry technology performance. At last, the factors of affecting the reclaimed sans properties are analyzed.The experimental data are obtained by the reclamation of green sand containing cold-box(or hot-box) resin sand. From the results, it can be found that, the grain size distribution and the shape factor of the reclaimed sand is no significant differences which were compared with the base sand. The clay content data indicates that the reclaimed sand appear "cleaner" due to the presence of agglomerated grains and fines removal during reclamation. The acid demand value of the reclaimed sand is higher than that of the base sand.The application of reclaimed sand for cold-box(or hot-box) resin sand process are also studied. From the results, it can be observed that, the top value of tensile strength is obtained from the core sand prepared with the base sand. In other words, the tensile strength value of cold-box(or hot-box) resin sand process which prepared with the reclaimed sand is lower than that of the state of base sand. Although the foundry technology performance of cold-box(or hot-box) resin sand process which were prepared with the reclaimed sand is not very good, the reclaimed sand can still meet the casting process needs. Hence the reclaimed sand are satisfactory for the core-making process.Method of comparative analysis, which is based on the foundation of the chemical phase analysis of the base sand and the reclaimed sand, is adopted in the studying on the influencing factors of the reclaimed sand properties. Test results are obtained by fluorescent x ray spectroscopy, SEM and EDS analysis. It can be observed that the dead clay and dash which left on the sand grain surface increase the acid demand value of the reclaimed sand, while the resin core sand which contained on the used sand may be not affect the acid demand value. Thus, it is a good approach to improve the performance of the reclaimed sand, by controlling the content of dead clay which left on the sand grain surface.