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By Erica Zhu Feilong Jiangli
The materials used in making molds are called molding materials. The sand molds are mainly molded sand and core sand, which are composed of sand, binder and additives.
1.Molding materials should have the following properties:
（1）Plasticity: molding sand and core sand are easy to form under the action of external forces.
（2）Sufficient strength: molding sand and core sand are not easy to destroy under external force.
（3）Fire resistance: molding sand and core sand are difficult to soften, sinter and adhere at high temperature.
（4）Permeability: molding sand and core sand must be easy to ventilate after compacting.
（5）Concession: molding sand and core sand can be compressed when cooled.
2.Pattern and core box
The pattern and core box are tools for making moulds and cores.
The shape of a casting to form a shape equivalent to the external shape of the casting. The core forms the inner cavity shape of the casting, and the core box is the tool for making the core.
Sand moulds and core boxes are used for multi-purpose wood casting. Metal mold, plastic mold and other patterns for special casting.
According to the different methods of modeling operation, it can be divided into:
（1）Manual molding: sand filling, compacting, mold lifting and so on mainly have the manual completion, the operation is flexible, the productivity is low, mainly uses in the single piece small batch production. There are many specific methods of manual modeling: whole mold modeling, three-box modeling, scraper modeling, false box modeling and so on.
（2）Machine Modeling: Mechanization of sand filling, compacting and moulding, high productivity and large investment, mainly used for mass production
4.Technical problems to be solved in sand casting
（1）The choice of pouring position: the main processing surface and large plane of the casting should be facing down, and the part of the Dian wall of the casting should be placed at the bottom.
（2）Selection of parting surface: plane parting surface should be adopted as far as possible, the number of parting surface should be as small as possible, so that all or most of the castings are placed in the same sand mold.
（3）Drawing inclination and casting fillet: In order to start the mold conveniently, the mold should have a certain drawing inclination, the higher the mold, the smaller the slope value: the inner wall inclination is larger than the outer wall inclination. In order to prevent the casting from producing stress and cracks at the wall joints and corners, the casting wall joints and corners should be designed into rounded corners.