Method for joint modification of water glass for casting

The invention provides a method for joint modification of water glass for casting. The method comprises the following steps of: dissolving 0.3 to 1 mass percent sodium carboxymethylcellulose, 0.3 to 1 mass percent polyoxyethylated alkyl ether, 0.3 to 1 mass percent polyacrylamide and 0.2 to 0.8 mass percent dextrin in water, heating and stirring for 20 to 40 minutes; adding the water glass for casting in a mass ratio of 1:2-5, heating and stirring for 20 to 40 minutes and cooling to room temperature; and removing a surface dense membrane, adding 1 to 8 mass percent dipotassium phosphate, 0.1 to 1 mass percent lauryl sodium sulfate or alkyl sodium sulfonate and 1 to 6 mass percent nano-montmorillonite, stirring at room temperature for 1 to 2 hours and treating with pulse current for 30 to 120 seconds so as to obtain joint-modified water glass. The method has the advantages of effectively reducing the using amount of the water glass on the premise of meeting the use intensity of molding sand, reducing the retained strength of the molding sand, improving the collapsibility of the molding sand, increasing the recycling rate of used sand and lowering cost.