Semi closed gating system is adopted, and the proportion is as follows:

Σ a inside: ∑ a transverse: ∑ a straight = 1:0.8:1.2

The design of the ingate is the same as that of scheme I. the sectional area of the ingate is 22.5 cm2, and the size of the ingate is the same.

According to the section proportion of the open gating system, the cross-sectional area of the main runner is s = 0.8 × 1 × 22.5 = 18 cm2, and the cross-section shape and specific size of the runner are shown in Fig. 1.

The cylindrical sprue is adopted as the sprue. According to the section proportion of gating system, it can be known that:

Σ a = 1.2 ×Σ a = 1.2 × 22.5 = 27cm2, and the calculated diameter is d = 59mm. The section shape and specific size of the sprue are shown in Fig. 2.

To sum up, the three-dimensional diagram of the semi closed gating system is shown in Fig. 3.

As shown in Fig. 3, the total number of internal sprue, main runner and sprue of scheme 3 semi closed gating system is 1, 1 and 1 respectively.