Because it is a composite mold of molten model shell and sodium silicate sand mold, the sand dropping process of impeller investment casting sand casting is divided into two stages, namely, the cleaning of sodium silicate sand in sand casting and the alkali boiling cleaning of molten model shell.
1. Cleaning of sodium silicate molding sand for sand casting
Considering the type of impeller alloy, the nature, shape and size of sand casting mold and cutting conditions, in order to obtain dense metal structure in the hub and rim and improve the cooling conditions of impeller investment casting sand casting, the box shall be poured for 40 ~ 60min, and the sodium silicate sand mold shall be cleaned to accelerate the cooling of impeller investment casting sand casting outside the mold, To obtain the dense metal structure inside the wheel hub and rim. Impeller investment casting – sand casting is cooled outside the mold. After the temperature drops to 50 ~ 60 ℃, the sodium silicate sand mold and sand sleeve are cleaned by mechanical method.
2. Alkali boiling and sand cleaning of molten model shell
In order to prevent the slag generated by cutting from damaging the surface of impeller investment casting sand casting, especially the surface of impeller blade, the cleaning of molten shell between impeller investment casting sand casting blade is arranged after the vibration cutting of pouring riser.
Due to the small spacing and complex shape of impeller investment casting sand casting blades, it is difficult to clean the sand. In order to avoid damaging the impeller surface during sand falling, the alkali boiling process is selected for sand cleaning of impeller shell. However, neutralization treatment and clean water shall be carried out later to prevent rust spots.
See table for alkali boiling sand cleaning process of stainless steel impeller.
| Lye | Temperature / ℃ | Time / h | Neutralization and cleaning |
| W（Na OH）=15%～20% | Boiling | 4-8 | 90g chromium oxide + 30g sulfuric acid + 1.2g sodium oxide + 1kg water, temperature: 18 ~ 28 ℃, time: 2 ~ 3min, and then rinse with clean water after neutralization. |
Using the alkali boiling method, the mold shell between the impeller investment casting sand casting blades can be basically removed. If the alkali boiling effect between some impeller investment casting sand casting blades is not ideal, it can be easily cleaned by manual method.