The process of pouring the liquid metal of impeller sand mold into the mold is called pouring. The purpose of impeller sand casting is to obtain impeller sand casting with clear outline, accurate shape, smooth surface and intact internal structure. Therefore, correctly mastering the pouring process and reasonably organizing the pouring operation have a great impact on the quality of impeller sand casting.
a. Pouring method
The pouring method is determined according to the alloy type, production batch and the requirements for product quality. The dumping pouring method is selected in the research process of this subject. Since the total weight of the casting and pouring (riser) system is 290kg, a 300kg hanger ladle is selected for the ladle.
b. Pouring process
The pouring process of impeller sand casting mainly includes pouring temperature, pouring speed and so on.
(1) The ladle shall be newly lined, dried thoroughly and filled with molten steel after it is greater than 800 ℃;
(2) Due to the high chromium content in molten steel, chromium oxide inclusions are easy to be formed during pouring, which reduces the fluidity. Chromium oxide film also makes the sand casting of impeller easy to produce defects such as cold shut and surface wrinkle. When the molten steel temperature is too low and the pouring time is longer, the oxidation phenomenon is more serious. Therefore, the pouring temperature should be properly increased and the pouring time should be shortened. Tapping temperature 1620 ± 10 ℃, pouring temperature 1580 ± 10 ℃;
(3) Inspection in front of furnace: control melting, measure temperature, conduct sampling test after chemical cleaning, adjust composition, and pour plum blossom sample in front of furnace.
(4) Before tapping, argon shall be blown into the furnace. During tapping, argon shall be blown to the bottom of the ladle for degassing to purify the liquid steel. During pouring, the molten steel at the bottom of the ladle shall also be protected with argon to reduce oxidation;
(5) The pouring of impeller sand casting is slow first and then fast, and the filling time is 10 ~ 12s. In the pouring process, the drainage shall be accurate, the injection flow shall be stable and the collection flow shall be slow. In order to avoid excessive oxidation and absorption of molten metal, the ladle nozzle should be as close to the gate as possible during pouring;
(6) When the impeller sand casting molten steel is poured to the height of the riser, change the point to pour the riser. After the riser is filled, cover the riser and gate cup with special thermal insulation materials to facilitate continuous feeding;
(7) In order to obtain dense metal structure and improve the cooling conditions of impeller sand casting, the box is made after pouring for 1h to speed up the cooling of impeller sand casting outside the mold.