Design of exhaust system for sand casting

(1) When designing the exhaust system of sand mold casting, it should be based on the principle that the cavity gas and sand core gas should be discharged separately. Direct exhaust in the sand mold casting body should be avoided as far as possible to prevent sand holes from occurring in the sand mold casting.

(2) Before designing the exhaust system of sand casting, the molding and core making method and process formula shall be reasonably selected according to the structure and quality requirements of sand casting, and the sand core with low air generation and good air permeability shall be selected to prevent air hole defects of sand casting.

(3) In the design of sand casting exhaust system, not only the appropriate cross-sectional area of exhaust channel, but also the reasonable exhaust layout must be considered. It is a more convenient, economical and effective method to directly use exhaust filter at the plane part of sand casting body.

(4) When designing the exhaust system of sand mold casting, we should not only consider the optimization of gating 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 molding sand and sand core parameters, as well as the influence of pouring parameters of liquid metal and ignition air introduction during pouring on the exhaust capacity of sand mold casting. 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. Sand mold and sand core should not only exhaust well, but also have low gas generation and good air permeability.

(5) A reasonable exhaust system for sand casting is to discharge the gas in the mold cavity in time before the metal liquid in the mold cavity forms a surface oxide film. It is more critical to exclude the gas in the molten iron than the gas above the liquid level in the mold cavity and the gas of molding sand and core sand. The key to eliminate the gas in molten iron is to increase the surface temperature of molten iron and delay the formation of oxide film on the surface of molten iron. Properly increasing the pouring temperature, pouring speed and discharging cold iron liquid are conducive to increasing the top surface temperature of molten iron, delaying the formation of oxide film on the surface, eliminating the internal gas of molten iron and preventing air holes and gas shrinkage holes in sand castings.

(6) The design of gating and riser system and exhaust system of sand mold casting shall be in place, and the exhaust capacity and area of sand mold cavity and sand core shall be checked and optimized. For resin sand molding castings, high-pressure green molding sand molding parts and complex thin-walled sand castings such as cylinder, hydraulic pressure, turbocharger turbine shell and intermediate shell, the total exhaust area is often 1.5 ~ 2.5 times larger than the internal sprue and flow blocking area, so as to make the cavity gas discharge smoothly and ensure the quality of sand castings.

(7) The pouring system of sand mold casting shall be set reasonably, and the smooth exhaust of the mold cavity and the smooth flow of liquid metal into the sand mold shall be considered. The pouring system design gives priority to the middle injection or step pouring process to improve the liquid metal temperature in the upper part of the mold cavity and form a high and low liquid metal temperature gradient in the mold cavity, so as to create favorable objective conditions for the smooth overflow of gas in the liquid metal.

(8) The sand core structure of sand mold casting shall be designed reasonably and properly. The exhaust hole and vent channel are essential. The design of the core head of the sand core shall be large enough. The sand core and the sand mold shall be matched and sealed in place to ensure smooth exhaust and prevent metal liquid from entering the air outlet and blocking the exhaust channel. The sand mold casting shall have defects such as air hole and choking fire.

(9) Reasonable selection and setting of exhaust plug can make up for some shortcomings of core box structure or sand mold core structure, and get well formed sand core and mold.

(10) When designing the exhaust system of sand mold casting, it is necessary to theoretically calculate the exhaust capacity and exhaust area of mold cavity and sand core, and check and optimize them. It also needs to be verified in practice and not subject to the air hole defects of sand mold casting.

(11) In sand casting production, timely ignition and air introduction during pouring can discharge the gas generated in the mold cavity and reduce the air pressure generated in the mold cavity, which is conducive to the filling of liquid metal, and prevent air holes, fire choking, explosive sand sticking defects and liquid metal splashing safety accidents of sand castings.

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