Clay sand casting of common defects in the following a few basic and old sand has a direct relationship.Some of the problems arisen in the process of production, clay sand old sand due to thermal decomposition of each component in the process of recycling changing physical properties, such as use them without regeneration, will make the molding sand quality is not stable.Here are several kinds of clay sand molding with common defects of molding sand quality on:1. The porosity, water, cold insulationSand powder of derivatives become old together.Powder content exceeds a certain limit, the micro powder can cause clogging gravel gap sand permeability is poor, and invalid clay water absorption ability stronger than effective clay, take effective moisture from the effective clay.So when invalid clay content is large, to make the required water content will increase, increasing the sand water content, to some extent also increased the gas evolution of molding sand, because of the reduced gas evolution increases with the permeability, when the casting liquid of resistance increase.Bound to lead to invasive defects such as porosity, water is less than, cold-lap formation.