Reasonable exhaust system design and process preventive measures for sand casting

The design of exhaust system for sand mold casting should not only consider the optimization of pouring and riser system design and reasonable layout of exhaust system to make the exhaust of mold cavity and sand core unobstructed, but also pay attention to the control of sand mold parameters such as moisture, compactness, particle size, air generation, air permeability and drying degree of molding sand and sand core. There are also the pouring parameters of liquid metal, such as pouring temperature, speed and stability, and the influence of ignition and air introduction on the exhaust capacity of sand castings. These process design parameters, sand mold performance parameters and pouring parameters have a great impact on the quality of sand mold castings, which is conducive to prevent defects such as porosity and sand sticking. The sand core in the sand mold cavity should not only exhaust well, but also have low gas generation and good air permeability.

The reasonable exhaust system of sand mold casting is to discharge the gas in the mold cavity in time before the metal liquid in the mold cavity forms the surface oxide film. At the same time, due to the timely formation of the surface oxide film, the generation of sand sticking is avoided. Increasing the pouring temperature and keeping the high temperature molten iron baking the upper mold for a long time can delay the formation of oxide film, enhance exhaust and reduce pore waste, but it will bring sand sticking. By comprehensively considering the effects of exhaust system and pouring temperature on porosity and sand sticking waste, the balance point between them is found, so that when the molding sand parameters meet the process requirements, the best time for the formation of surface oxide film is found, and the rate of sand sticking and sand sticking waste is reduced.

In order to reasonably design the exhaust system of sand mold casting, the design of gating and riser system should be optimized first, and then the total exhaust area should be reasonable and correct. General total exhaust effective area ≥ minimum section of gating system Σ F resistance. For resin sand castings and complex thin-walled sand castings such as cylinder, hydraulic parts and turbocharger (volute and intermediate shell), the total exhaust area shall be large enough and the total exhaust effective area shall be large enough Σ Row f = (1.5 ~ 2.5) Σ F resistance, ensure smooth and timely exhaust of mold cavity and sand core, and prevent air holes and sand sticking defects of sand castings. The exhaust system design of sand mold casting can be divided into cavity exhaust system design and sand core exhaust system design.