1 Mold Design
According to the overall dimension of the product, the size of sand box is 550 mm × 1400 mm × 450 / 600 mm (inner cavity), 1 piece / box. The inner cavity of the product is designed to be molded with integral resin sand core. The mold is divided according to the maximum section of the casting. The parting mold and upper and lower box mold of the product are reasonably designed. The shrinkage rate of the mold is 1%. The ingate is set at the parting surface of the casting, and the machining allowance of the processing surface is 5 mm. The mold is designed with cast test block. The 3D mold design scheme is shown in Figure 1.
2 Core Design
According to the needs of parting, the inner cavity of the product is designed as an integral resin sand core. The design scheme of 3D sand core is shown in Figure 3. The following aspects should be paid attention to when designing sand core:
(1) The sand core is placed in the lower box to avoid core hanging.
(2) Core heads are designed for both upper and lower boxes. The gap between the core heads of the lower box is 1 mm, the radial gap between the core heads of the upper box is 2 mm, and the axial gap is 1 mm.
(3) The core bone is designed to enhance the strength and stiffness of the core.
(4) The single weight of sand core is 70 kg. Considering that the core needs to be lifted, lifting rings are designed.
(5) Design sand core vent and sand accumulation tank.
3 Gating System Design
According to the shape characteristics of the product, the intermediate pouring system is selected. In order to avoid the film damage, turbulence and collapse in the casting process, increase the size of ingate and runner, and reduce the flow velocity of liquid metal in the cavity, the semi closed gating system is selected. A slag accumulation ladle is added at the end of the runner, and two overlaps are designed.
The first lap joint is designed with foam ceramic filter screen, and the lap joint area is gradually reduced, so that the runner is in a full state, and the slag resistance effect of the runner is strengthened. The cross-sectional area ratio of gating system is s straight: s Cross: s inner = 1.0 ∶ 1.4 ~ 1.6 ∶ 1.25 ~ 1.35 φ The cross-sectional area of the two-way runner is trapezoidal, the cross-sectional area of the two-way runner is 2 260 mm ~ 2 and 1 300 mm ~ 2 respectively. The cross-section of the ingate is flat and thin, which can avoid the formation of hot spot;
The cross-sectional area of the control flow at the second lap joint is 1200 mm2. The results show that the amount of metal used for feeding in V-process casting is 60% less than that in normal wet sand molding, which is also suitable for ductile iron casting. In addition, the riser also has the function of exhaust to prevent the porosity defects on the casting surface.