Basic information of casting product for a high class valve body

1. Product structure and technical requirements

The diameter of valve body is ϕ 254 mm, the maximum outline size of the product is 1 292 mm × 867 mm × 814 mm, the net weight of the processed product is 2 430 kg, and the product structure is shown in Figure 1.

The material of the product is WCC. The mechanical properties of the product are that the yield strength is more than 275 MPa, the tensile strength is more than 485 MPa, the elongation is more than 22%, and the reduction of area is more than 35%. The pressure class is ansi2500, i.e. 42 MPa. The NDT testing requirement is 100% RT testing for the whole casting, and the testing level is ASME B16.34-2004 grade II. After the product is processed, it needs to carry out the hydraulic test, the pressure is 42.5 MPa, and it is qualified if there is no visible leakage defect within 10 min or the pressure maintaining equipment does not reduce significantly.

2. Main defects of castings in actual production

The valve body has three flanges, the maximum wall thickness of the flange is 120 mm, and the middle wall thickness of the valve body is 50 mm. In order to meet the modeling operability and realize the sequential solidification of the product, the horizontal modeling is adopted in the process design, each flange is provided with an open riser, and the middle part of the valve body is provided with two separate risers for feeding.

In order to ensure that the temperature field of molten steel in the cavity after pouring is distributed from the bottom to the riser from low to high, the gating system adopts split inlet. In the actual production, resin sand molding is used, the pouring temperature is 1580 ℃, and the pouring time is 60 s. The casting process diagram is shown in Figure 2.

(a) Three dimensional digital model (b) Air gouging casting

In the early stage of development, a casting process software was used to simulate and analyze the product, and no defects were found. In trial production, large quality problems were found in the casting during RT inspection, such as slag inclusion, porosity, shrinkage porosity and other defects at a, B and C in Fig. 3 (a), with defect depth of 40 mm. Fig. 3 (b) is the defect form after air gouging.