The Causes of Blowholes on Flange Castings and the Process Improvement Measures

The flange castings are thin-walled gray iron castings. The production process includes resin sand modeling without using metal flasks, making sand core by cold core box, making coated sand core by hot core box, leaching and painting the whole sand model with water based paint, drying the casting in the drying tunnel and smelting it in the medium frequency furnace. The main defect of this process is the pore, which will cause the defects of products, turning them into wastes and affect the production efficiency and yield of products.
 
The Causes of Blowholes
1. High gas evolution of the sand core
The inner cavities of castings are formed by the sand cores, and due to the thin wall, the complex shape and the use of high-strength coated sand, the gas evolution is particularly high.
2. High gas evolution of the sand model
Since cavities have great depth, after several drying processes, the bottoms of the cavities can not be totally dry and easy to produce a lot of gas when casting. In addition, resin sand will inevitably produce a lot of gas.
3. Poor exhaust performance of the sand model
For the exhaust area of a sand model is small, if the base area of the flange is enlarged too much, it will easily cause metal shortage.
 
Process Improvement Measures
1. Decrease the gas evolution of the sand cores made by cold core box
With the premise of guaranteeing the tensile strength of the sand cores larger than 1Mpa, adjust the resin compounding ratio of the sand cores made by the cold core box to decrease the gas evolution.
2. Decrease the gas evolution of the sand models
With the premise of guaranteeing the circulation and operating requirements of the sand cores, due to the upper columnar cores and the oil ducts of the inner cavities are coated with sand, develop the coated sand of low gas evolution, whose amount is better to be controlled about 12g/ml.
3. Change the method of painting the sand model
Change the painting method of the sand model from leaching and painting the whole sand model with the water base paint to leaching and painting the whole sand model with the water base paint plus brushing and coating parts of the model manually with the alcohol base paint. After coating the alcohol base paint, timely ignite with fire to ensure the two deep pore drying to decrease the gas evolution and reduce the occurrence the pore defects.