Wet sand casting defects and cooling methods: Cast iron automatic molding line: Sand temperature is generally controlled between 25-35°C. Within this temperature range, the performance of the molding sand is relatively stable, which can effectively guarantee the molding quality and casting quality.
In wet sand casting, excessively high wet sand temperature will cause the following defects in the casting:
Porosity defect: Excessive wet sand temperature will intensify the evaporation of water in the molding sand, and a large amount of water vapor will be generated during pouring. If these water vapors cannot be discharged in time, pores will form inside the casting.
Sand inclusion scarring: Excessive sand temperature will cause the water on the surface of the sand mold to vaporize and migrate rapidly, resulting in a decrease in the surface strength of the sand mold. Under the scouring and thermal action of high-temperature molten metal, the surface of the sand mold is prone to arching and cracking, and sand inclusion scarring will form after the molten metal penetrates.
Sand sticking defect: Excessive sand temperature will cause the anti-sand sticking materials such as coal powder in the molding sand to burn and decompose prematurely, and lose the anti-sand sticking effect. At the same time, high temperature will also enhance the fluidity of the molten metal, making it easier to penetrate into the pores of the sand mold, thereby causing sand sticking defects.
Sand hole defect: Too high sand temperature may lead to unstable sand performance. During the molding and handling process, the sand mold is more likely to drop sand. These dropped sand particles may be drawn into the molten metal during pouring, forming sand holes.
Decrease in casting dimensional accuracy: Too high wet sand temperature will cause uneven cooling and shrinkage of the sand after molding, resulting in changes in the size of the sand mold. During pouring, this dimensional change will affect the dimensional accuracy of the casting and cause dimensional deviations in the casting.
What factors will affect the temperature of wet sand and old sand?
Production process
Casting pouring temperature: The higher the pouring temperature, the more heat is transferred to the sand, and the temperature of the old sand will also increase accordingly. For example, when pouring steel castings, the temperature of the sand will rise significantly due to the pouring temperature of more than 1500℃.
Unpacking time: If the unpacking is too early, the heat of the casting and the sand has not yet been fully dissipated, and the temperature of the old sand will be higher; on the contrary, if the unpacking time is late, the sand has more time to dissipate heat and the temperature will be relatively low.
Molding compactness: When molding, the compactness is high, the air permeability of the molding sand is poor, and the heat is not easy to dissipate, which will increase the temperature of the old sand; low compactness means good air permeability, which is conducive to heat dissipation, and the temperature of the old sand is relatively low.
Environmental factors
Ambient temperature: When the ambient temperature is high, such as in high temperatures in summer, the temperature of the old sand will also increase; in cold winter, the temperature of the old sand is easy to decrease.
Ventilation conditions: Good ventilation can accelerate air flow, take away the heat in the molding sand, and reduce the temperature of the old sand; poor ventilation will cause heat accumulation, resulting in an increase in the temperature of the old sand.
Equipment and operation aspects
Sand processing equipment: Frictional heat will be generated when the sand processing equipment is in operation. For example, during the sand mixing process of the sand mixer, the friction between the stirring paddle and the molding sand will increase the sand temperature.
Transportation and storage: During the transportation of old sand, if the transportation distance is long, the time is long, and the heat dissipation conditions of the transportation equipment are poor, the sand temperature will increase; during storage, the poor insulation performance of the sand warehouse or the excessive storage volume will also affect the temperature of the old sand.
In terms of the characteristics of the molding sand itself
Water content: The evaporation of water in the molding sand will absorb heat. The old sand with high water content will take away more heat when the water evaporates, which will reduce the sand temperature; but if there is too much water, a large amount of water vapor will be generated at high temperature, which may cause the sand temperature to rise.
Sand particle size and composition: Sand with fine particle size and large specific surface area has relatively slow heat dissipation and is easy to increase in temperature; when the molding sand contains substances with high thermal conductivity, it will make the heat conduction faster and affect the sand temperature.
The methods to reduce the sand temperature are as follows:
Controlling the temperature of wet molding sand and old sand can start from process operation, equipment improvement, environmental adjustment, molding sand management and other aspects. The specific measures are as follows:
Optimize process operation
Adjust the unpacking time: According to factors such as the material, size and structure of the casting, reasonably determine the unpacking time to allow the casting and molding sand enough time to dissipate heat.
Use secondary cooling: After the casting falls out of the sand, the old sand is subjected to secondary cooling treatment, such as spraying water mist or using air cooling to accelerate the cooling of the old sand.
