Increasing pouring speed and reducing sand hole and air hole defects of large steel castings

① Increase the diameter of ladle nozzle and the size of gating system; ② Increase the number of ladle nozzles; ③ Increase the number of ladle poured at the same time.

(4) reasonably design the pouring system. More attention is often paid to the gating system of iron castings, because most iron castings are poured by turning over the ladle, and its gating system plays the role of slag retaining. Steel castings (especially large and medium-sized steel castings) are almost bottom pouring (i.e. ladle leakage pouring), which often ignores the importance of gating system. In fact, due to the high pouring temperature of steel castings, the secondary oxidation of molten steel and large volume shrinkage, more attention should be paid to the design of gating system. The following aspects should be paid attention to:

Open gating system is adopted to avoid serious splashing of steel flow directly to mud core (or sand mold) and steel flow.

For large and medium-sized steel castings, the inner gate should not be too scattered or too concentrated, and should be comprehensively considered in combination with the riser position. First, avoid the “physical hot spot” that cannot be fed due to the setting of the inner gate, and second, avoid the sand sticking caused by overheating at the inner gate. The best position of the inner gate is set under the riser.

During the pouring process, the filling molten steel shall have sufficient power to prevent the liquid level from “dead” and sundries from floating up. For example, tangent ingates are used for rotating body castings.

The setting of gating system shall be able to create a sequential solidification condition with reasonable temperature gradient distribution. For example, for castings with large height and size, a stepped gating system shall be adopted. However, special attention should be paid to avoid simultaneous steel feeding into multiple internal gates at the initial stage of pouring; The riser shall be re poured through the riser re pouring device to prevent the ladle from directly pouring above the riser.

(5) Control of pouring temperature. Reasonable control of pouring temperature is another important link to obtain high-quality castings. Generally speaking, large and medium-sized steel castings basically do not have cold insulation, insufficient pouring and other phenomena. Under the condition of ensuring normal pouring, the lower the pouring temperature, the more conducive to obtain high-quality castings.