The design scheme of the third type of pouring and shrinkage system adopts an integral inner gate, with a complete circle of inner gate body set at the top of the impeller shell, 5 steel liquid channels set at the top, and a similar horizontal gate on top. Considering the characteristics of centrifugal casting, it is made into a whole circular shape, with a gate cup at the top, as shown in Figure 2-52..

In order to ensure the complete filling of the semi-circular ring in the inner cavity of the impeller and form a filling mode that combines the inner and outer parts, a straight sprue is introduced at the center of the lower end of the circular transverse sprue, which is connected to the inner wall of the through hole with a diameter of 74mm using a four pronged internal sprue, as shown in Figure 2-53.

First layer: Apply mullite powder slurry for 35 seconds, sprinkle 80-100 mesh mullite sand, dry for 10 hours, with a drying room temperature of 23 ℃ and a relative humidity of 65%.
Second layer: Apply mullite powder slurry for 22 seconds, sprinkle 60-80 mesh mullite sand, dry for 12 hours, with a drying room temperature of 23 ℃ and a relative humidity of 65%.
Third layer: Apply mullite powder slurry for 15 seconds, sprinkle 60-80 mesh mullite sand, dry for 12 hours, with a drying room temperature of 23 ℃ and relative humidity of 50%. Blow air and tie iron wire.
Fourth layer: Apply mullite powder slurry for 14 seconds, sprinkle 30-60 mesh mullite sand, dry for 12 hours, with a drying room temperature of 23 ℃ and relative humidity of 50%, and blow air.
The fifth and sixth layers: apply mullite powder slurry for 14 seconds, sprinkle 16-30 mesh mullite sand, dry for 12 hours, with a drying room temperature of 23 ℃ and a relative humidity of 50%, and blow air. Sealing: Apply mullite powder slurry for 14 seconds, dry for 16 hours, dry at a temperature of 23 ° C and a relative humidity of 50%, and blow air.

For the convenience of sand cleaning, the first and second layers remain unchanged. Before applying the third layer, the inner cavity of the blade is filled with sand (60-80 mesh sand) for sealing (in the future, powder will be added to form a mud like seal), and then the third, fourth, and fifth layers and sealing layers are made. The difficulty of cleaning significantly improves after pouring.
c. Module Dewaxing:
After dewaxing is completed, take out the Impeller shell and immediately rinse it twice with boiling water to thoroughly remove any remaining wax and debris inside the shell.

When pouring, it should be taken out of the furnace together with the impeller casting mold shell. In order to minimize the decrease in pouring temperature of the steel liquid, after pouring the steel liquid into the tea shell package, immediately return the steel liquid to the furnace. After pouring the steel liquid into the tea pot package for the second time, pour it immediately. The teapot bag is shown in Figure 2-56.

Strict control: Pour one set of Impeller casting shells per pot.
Strict control: If there is any remaining steel liquid in the ladle, it must be poured back into the furnace.

Three thicker shrinkage gates are installed on the riser to facilitate wax removal, exhaust, shell shrinkage, and improve the shell making rigidity of the module.

e. Clear division of labor and coordinated cooperation: The three processes of roasting, smelting, and pouring are the key to producing impeller casting. In addition to strictly adhering to the process regulations, on-site production emphasizes unified command, close cooperation, and collaborative operation.

f. Insulation cooling to prevent cracking. Strictly limit the unboxing time, allowing the just poured castings to slowly cool in the iron box. At room temperature of 30 ℃, remove the casting impeller from the iron box 3 hours after pouring (if the unboxing time is also delayed in winter), and continue to cool naturally at room temperature until the mold shell is touched by hand without feeling hot, before vibration and peeling can be carried out. This can effectively prevent cracks from occurring, and water cooling should be avoided throughout the entire cooling process.

g. Civilized cleaning and standardized operation. During the process of removing the shell on the casting impeller, cutting off the sprue and process ribs, and removing the sand and oxide scale inside the casting cavity, it is necessary to handle it gently, stack it neatly, prevent damage to the blades, adhere to civilized cleaning, and operate in a standardized manner. Using a tracked shot blasting cleaning machine, the particle size of the shot blasting should not exceed 0.3mm. For residual coatings that are difficult to remove at the inner groove, they should be soaked in a slag removal solution.

The casting results are achieved by strengthening the control of process details in each process of investment casting, and producing high difficulty and high requirements Impeller casting under non vacuum melting and non vacuum pouring conditions. It is reported that Japan still uses stamping and welding processes to produce the same type of impeller casting.
Under the same process control conditions, for the integrity of filling, the overall internal sprue gating system is superior to the spherical riser and transverse sprue gating system, as shown in Figures 2-57 and 2-58.