2020 Volume 61 Issue 4 Pages 734-739
In recent years, casting molds made by additive manufacturing (AM) are increasingly applied to build prototypes and small quantity casting product. Devices and materials have been developed for accelerating the molding speed to achieve mass production using AM technology. Conventional AM molding methods using furan type hardening system adopt a combination of a liquid catalyst and binder. The sand wet by the liquid catalyst makes it difficult to increase the molding speed and apply artificial sands which have excellent refractoriness to the sand molding using AM technology.
This study developed a solid catalyst coated sand to improve the flowability of the sand and catalyst and to increase the binder hardening rate. The solid catalyst coated sand was made by covering sintered artificial sand with the solid catalyst of meta-xylene sulfonic acid after covering with the fine powder of anhydrous magnesium sulfate.
First, this study confirmed that the solid catalyst coated sand has good fluidity in fluidity tests. The reduction of the surface tension by the bonding of the powder anhydrous magnesium sulfate and the sulfate of the solid catalyst resulted in the dry state of the solid catalyst sand. Consequently, the catalyst sand showed good fluidity.
Secondly, in mold hardening tests, the solid catalyst coated sand hardened the mold quicker than conventional method. During the hardening reaction of the binder, water generated when furfuryl alcohols were bonded to each other was converted into a hydrate by anhydrous magnesium sulfate and absorbed. As a result, the reaction rate greatly improved compared with conventional methods that only release water outside the system.
Molds using sand additive manufacturing have been used for a long time, but the molding speed and size needs to be improved in order to apply high refractory granular material.
Finally, the ability to mold with this hardening system was tested with the AM molding apparatus using the binder jetting. The results of evaluating the characteristics of the mold showed that it has low thermal expansion and the unhardened part of the solid catalyst coated sand could be reused.
This Paper was Originally Published in Japanese in J. JFS 90 (2018) 280–285. Fig. 5, Fig. 7, Fig. 9, Table 1–Table 3 were slightly changed.
