What are the requirements of sand casting for structural design of castings?
Alloy good mobility, filling ability, casting is not easy to produce misrun and cold lap defects, but also can cast casting a minimum wall thickness is small. Different alloy, minimum wall can be cast in the casting under the conditions of a given thickness is different. When the casting wall thickness design that must be the big inch alloy: the minimum wall thickness to ", in order to ensure the quality of castings. The casting" minimum allowable wall thickness "mainly depends on the type of alloy, casting method and casting size. Table 5 - 1 for the minimum allowable casting wall thickness values. However, the casting wall is not too thick. Thick walled casting grain coarse, loose tissue, prone to shrinkage, mechanical properties decrease. Casting load capacity is not difficult with the cross-sectional area increases proportionally to the increase. The design thickness of the casting wall, will cause the metal waste.
What are the requirements of sand casting for structural design of castings?Answer: sand molding casting design, not only to consider the work function and mechanical performance requirements, must also consider the alloy casting properties and process requirements of the structure of the casting casting. Casting structure design is reasonable and has a great influence on the casting quality, productivity and cost of manufacturing. The structure of castings, if not satisfied with the performance requirements of casting alloy that will likely cause misrun and cold lap, shrinkage, porosity, crack and deformation defects.
In order to improve the bearing capacity of the casting without increasing the wall thickness, the structure design of castings should Choose a reasonable cross-section shapeIn addition, the interior of the casting bar or wall cooling conditions than the outer wall, the cooling speed is slow. In order to prevent the inner wall of the grain coarsening and internal stress, general wall thickness should be less than the outer wall. Table 5 - 2 cast iron outer wall and the inner wall and the maximum critical wall stiffener thickness. If the wall thickness of casting parts the difference is too large, thick wall metal will produce local accumulation of heat of formation, solidification shrinkage in the hot spot is easy to form defects such as shrinkage cavity. In addition, different cooling rates, easy to form thermal stress, the casting thin wall and thick wall joints crack. Therefore in the design of castings we should, as far as possible to make uniform wall thickness, to prevent the defects.In case the wall thickness of the casting is uniform, the allowance shall be taken into account. If the thickness of the parts on the parts is uniform, plus the allowance, the casting thickness of the machined surface will increase, while the casting hot knot will be very large
