1. Field of the Invention
The invention relates to a method of recycling molding sand by mixing molding sand collected after use as a greensand mold with water and binder.
2. Description of the Related Art
In greensand molding, it is typical to recycle fatigued molding sand of a greensand mold which has been partly subjected to thermal deterioration by exposure to hot a molten material during molding of a product. As shown by way of example in FIG. 6, recycling of fatigued molding sand after having been used for a greensand mold includes several steps of disassembling a molding box to take out the greensand mold at step SA3 after forming a greensand mold in the molding box at step SA1 and pouring a molten metal into the greensand mold to mold a product at step SA2, collecting the entire part of molding sand having been used for the greensand mold at step SA4, and kneading and smoothing the collected molding sand mixed with water and a given amount of binder such as bentonite so as to revive or refresh thermally deteriorated part of the molding sand at step SA5. The revived molding sand is reused for another greensand mold at step SA1. During molding a product at step SA2, the greensand mold at its outer-shell portion is exposed directly to a hot molten material. In the prior art molding sand recycling, a binder such as bentonite is added to the entire amount of collected molding sand, which always needs a large amount of the binder, and leads to an increased cost of a greensand mold.
A water supply installation is used in the step of mixing the molding sand with water. For example, as described in Japanese Unexamined Utility Model Publication No. 3-9245 and shown in FIG. 7, a water supply installation 64 monitors the temperature or the like of molding sand 63 collected onto a belt conveyer 62 and smoothed with a scraper 61 and sprays or pours a desired amount of water into the molding sand 63 through a pouring nozzle 65. While the water supply installation can adjust an proper amount of water and pour it into the molding sand, a binder such as bentonite is added to the whole part of the molding sand, which always needs a large amount of binder and brings about an increase in cost of a greensand mold.