Reasons And Measurement For Main Defects Of Large Size Castings With Thin Wall Thickness Molding With Furan Self-Cured Resin Sand

Through the comparison of the testing result of bolster and side frame, molding process without sand flask and with sand flask, as well as the comparison and analysis of casting defects, eventually, we found that the produc-tion of qualified casts was mainly affected by the maternal, technology and exogenous factors of resin bonded sand. According to microstructure analysis, cracks in bolster and side frame produced by Furan self-cured sand can be classified into shrinkage hot cracks and stress hot cracks. The primary reason is the synthetical effect of the high temperature function of Furan self-cued sand, thermal center of casts, penetration of sand casting stress existing in production. So we confirmed the measure in order to prevent the defects of casts. The result can be as follows: Adopting the Furan self-cured sand, the entironment's temperature of the workshop must be more than 10℃, entironment's humidity should be controlled below 60%, and range of the casting temperature was 1570℃~1580℃. The resin(SQG-100) and condensate(GS03) produced by Jinan Shengquan Co. were used in the molding sand. The content of resin was controlled in 0.75wt%~0.85wt%, and the content of condensate was 35 percent of the resin. But in the core sand, the primary resin (ZF-0.3-1-4) controlled in 0.95wt%~1.0wt %, and the condensate (GC01,GC02) whose content was 40 percent of the resin. Moreover, in the system of the molding and core sand, the reclaimed sand was 90 percent. Zircon flour was still used as the refactory aggregate of the modified water paint, with a granularity of 270 screen meshes. Binding agent Silicon contained series and water-solubility modified Phenolic resin were respective employed as the high temperature and the low-temperature agglomerates. The addition of Na-bentonite which actes as the defloccator was 1.0wt%~1.5wt%. The viscosity was 40s~50s(through a filler with an aperture of 4mm). The specific gravity was 1.8g/cm2~2.2 g/cm2 when the temperature got 20℃. The pH value was controlled within 8~10. The sedimentation stability was over 8 hours. The limitation of static shearing force was 0.5N/m2. The penetrability was an in leakage of 3~4 grits. The gas release was less than 15ml/g at 850℃. Chemical frozen iron was employed at the A and B part of bolster and the B part of side frame, which is favorable to the preventions of producing cracks. The advanced molding (core sand) sand technology such as the new type ester induration water glass self hardening sand and spasmolytol air hardening resin sand, together with Zircon sand which was better than Silicon sand on the chilling effect. According to these measure, have made the rejections of last reduce to 2% and tempering reduce to 5%, respectively.