The Process of Sand Mold Casting
The Process Flow of Sand Mold Casting
The production process includes making wooden models, sand molding, melting, pouring, sand falling, cleaning of sprue and riser, inspection, and storage.
Sand mold casting Methods
Sand mold casting methods can be classified as manual and mechanical methods. Manual methods, including sodium silicate sand casting, are characterized by convenience, flexibility, adaptability, and short preparation time for producing patterns, but have lower productivity, higher labor intensity, and less guarantee of casting quality, suitable only for small batch production of single units. Mechanical methods are the main methods for the mass production of sand molds, significantly improving labor productivity, working conditions, dimensional accuracy, and surface quality of castings, reducing machining allowances.
Understanding sand mold casting Process
In the production preparation of sand mold casting, a reasonable casting process plan must be made, and the casting process diagram must be drawn.
The casting process diagram is a graphic representation of the casting process plan using various process symbols in the part diagram, including the casting position, the mold parting surface, the number, shape, fixing method, and down-core sequence of the core, machining allowance, mold release angle, shrinkage rate, pouring system, sprue, and the size and layout of chills. The foundry process diagram is a basic process document guiding pattern (core box) design, production preparation, mold making, and casting inspection, including for silica sol casting. Based on the casting process diagram and the selected molding method, the sample diagram and joint box diagram can be drawn. The enlargement of dimensions on castings for machining is called machining allowance. The value of machining allowance on castings depends on the casting production batch, the type of alloy, the size of the casting, the distance between the machining surface and the reference surface, and the position of the machining surface during pouring. Using mechanical methods for molding, including silica sol casting, casting accuracy is improved, and machining allowance is reduced, while manual methods have larger errors and require larger machining allowances. Steel castings have rough surfaces and require larger machining allowances, while non-ferrous alloy castings are expensive and have smoother surfaces, requiring smaller machining allowances. The larger the size of castings or the distance between the machining surface and the reference surface, the greater the dimensional error, so the machining allowance should be increased accordingly. The surface of the casting facing upward during pouring has a greater probability of producing defects, and the machining allowance for this surface should be greater than that for the bottom and side surfaces.
Holes and grooves in castings: generally, larger holes and grooves should be cast to reduce machining time, save metal materials, and reduce thermal stress on castings, such as squeezing die casting. Smaller holes can be machined economically. Holes and slots that do not require machining on the part diagram should generally be cast.