ZG35CrMo material has poor casting performance, high solidification shrinkage and easy to produce shrinkage cavity and other defects. The pouring temperature of large steel castings is high, and the fluidity of liquid steel is poor, which is not conducive to mold filling; The molten steel is easy to oxidize, so the pouring speed should be increased. The plug rod ladle is used in the ladle, which has strong slag retaining ability. In this scheme, the slag retaining problem is not mainly considered, and the bottom pouring, open pouring system and single ladle single hole pouring scheme are selected. The diameter of the injection hole is 60 mm.

∑Ah ∶ ∑As∶ ∑Aru ∶ ∑Ag= 1∶ ( 1． 8 ～ 2． 0) ∶ ( 1． 8 ～ 2． 0) ∶ ( 2． 0 ～ 2． 2)

Where ah = 28.3 cm2, ∑ ah = 28.3 cm2, q = 90 kg / s.

#### 1. Pouring time

t = GL/Nq

Where q is the average pouring flow rate; GL is the weight of liquid steel in the mold, 1897. 431 kg; N is the number of leakage holes in ladle; T is the pouring time.

The calculation results show that t = 21.08 s, and in the case of sufficient mold filling capacity, a large number of tests show that the probability of sand hole and air hole defects is very small when the pouring time is controlled within 30 s, and sand hole and air hole defects will not appear in most cases. Therefore, the pouring time t = 21 s is selected.

#### 2. Checking the rising speed of molten steel

v = C/t

Where V is the rising speed of liquid steel level in mold; C is the height of the casting in the cavity, 545 mm; T is the pouring time.

The calculation results show that v = 25.95 mm / s, the minimum rising speed v ≥ 25 mm / s, so it meets the requirements.

#### 3. Residual head check

HM≥Ltan α ( Take α = seven °， L = 630 mm)

Where HM is the minimum residual head; L is the flow of liquid alloy; α It’s the pressure angle.

After checking, the residual head is sufficient.

#### 4. Determination of cross section area of each component in gating system

Sprue: 95 mm; As = 71 cm2， Σ As = 71 cm2。

Runner: see Fig. 2 for section shape and size, ARU = 70 cm2, Σ Aru = 70 cm2。

Ingate: see Figure 3 for section shape and size, Ag = 12 cm2, Σ Ag = 12 × 6 = 72 cm2。

The final cross-section ratio of each component is as follows:

∑Ah ∶ ∑As∶ ∑Aru∶ ∑Ag = 1∶ 2． 51∶ 2． 47∶ 2． 5

#### 5. Design of sprue socket

The diameter of the sprue pit is 1.4-2 times of the diameter of the lower end of the sprue, and the height is 2 times of it. In this scheme, the diameter of the sprue socket is 1.4d = 133 mm, and the height is 2D = 190 mm.

To sum up, the pouring time t = 21 s and the transverse diameter of the sprue are selected

Cross sectional area ∑ as = 71 cm2

The cross-sectional area of runner is ∑ Aru = 70 cm2

The cross-sectional area of the ingate is ∑ Ag = 72 cm2