| The foundry technology could date from more than 6000 years ago in China. After entering the 21st century, the annual output of castings in China is increased every year. Green sand is the most diversified and well-known method used in metal casting operations until now. Casting plants create a hundred million tons of used green sand:about one ton of used green sand per one ton of castings. The total reclamation technology of used green sand is carried out for many years. The mold (core) sand strength of furan resin self-hardening sand (mixed with the total reclaimed sand) is far less the same index for the new sand. This issue has restricted the reclamation technology developing in the future. The modification technology of the total reclaimed sand which reclaimed from the used green sand contain furan resin self-hardening core sand is considered in the paper. The reclamation of used sand is the alternative with the lowest impact and leads to a saving of raw materials and a reduction of manufacturing residues.On the basis of previous study, the technical indicators (size distribution, grain shape, mud content) of reclaimed sand, which obtained by the process of "calcination of 700℃+ dry mechanical reclamation+micro-powder separation", is better than the same new sand. However, the acid request value is higher than the same new sand. The casting process performance of the furan resin self-hardening sand mixed by this total reclaimed green sand can’t meet the requirement of casting production. Therefore, the total reclaimed sand which reclaimed from the used green sand contain furan resin self-hardening core sand is chosen in the paper and the modification technology of reclaimed sand is studied by using the methods of experimental research and theoretical analysis. The equipment of SEM, ICP etc. is used in the study. The main factors that affect the performance of the total reclamation green sand are determined. The suitable modification process and process parameters for the modification of total reclamation green sand are explored, so that the total reclamation green sand mixed by furan resin self-hardening sand casting process performance better than the same index of new sand.The modification technology has proved to be a new ideas and method in the used green sand reclamation, and the suitable modification technology for the total reclaimed green sand is "modification process+drying process+mechanical reclamation+separation of micro-powder". In this treatment process, the adequate quantity of the modifier should be 1% of the mass of sand and the processing time of modified sand should be 90 min. At the same time, the aqueous solution of hydroelectric acid, sulfuric acid aqueous solution and benzene sulfuric acid aqueous solution are used as the modifier for modification process. The modified reclaimed sand is obtained by the same modification process and mixed with resin self-hardening sand. The results show that the modification effect of hydroelectric acid is the better than the other modifier. Its average tensile strength could reach 1.315MPa and the bench life is 5min, which superior to the same index of new sand. The modification effect of sulfuric acid solution is second. Its average tensile strength can be reach 1.233MPa, and the bench life is 4min, superior to the level of new sand. Benzene sulfuric acid modification effect is the worst one. Its average tensile strength is close to the level of new sand, which reaches 1.205MPa.The bench life is 4min.The results reveal that, in the same field of view, the number of bonded bridge of the modified sand mixed by the resin is increased significantly. The fracture mode changed from the prior to the cohesive fault. It can be concluded that the modification process can improve the number of the fracture surface of the bond bridge and improve the fracture mode. The performance of the casting process of the self-hardening resin sand mixed by modified sand is improved. |
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