The advantages of EPC are dry sand molding, no binder is needed, the recovery rate of dry sand is high, the production cost of enterprise is reduced, but the quality of dry sand also determines the quality of casting. The requirements of EPC for dry sand performance mainly include high fire resistance, good soft dynamic property, good air permeability, low dust content and low pulverization degree.
The dry sand used for EPC in the industry mainly includes silica sand, forsterite sand, zircon sand, chromite ore sand, pearl sand, etc. Silica sand is the highest utilization rate of dry sand, but the crushing rate of silica sand is high, the dust content of added dust is also high, and its permeability is poor. When pouring, it affects the smooth discharge of foam pyrolysis products, which will affect the quality of castings. However, the utilization rate of non siliceous sand is not high due to its high cost and narrow application range. In recent years, the pearl sand is made from high temperature alumina raw material (bauxite) heated to high temperature melting state, and then atomized to recrystallize to form spherical pellet material. Baozhu sand has the advantages of high fire resistance, low expansion rate, round grain shape, good soft dynamic property and low dust content. It can prevent and reduce casting defects such as slag inclusion and blowhole. It is an ideal molding material.
Due to the existence of grooves and blind holes in the bearing and poor soft dynamic property of ordinary silica sand, it is difficult to vibrate and compact the steel casting of steel damping bearing by EPC process, which leads to collapse of box. Therefore, for this kind of bridge bearing products, 20 / 40 mesh Baozhu sand is selected in this design.