Analysis and modeling of sand casting structure of large turbine volute

Compared with other metal castings, sand casting has the advantages of low cost, simple production process and short production cycle. Such as automobile engine cylinder block, cylinder head, crankshaft and other castings are produced by sand casting process. The water turbine is generally composed of water diversion, water diversion, working, water discharge and non flow passage parts. The spiral case formed by sand casting has large stiffness and can withstand certain external pressure. It is often used as the supporting point of the water turbine, and the water diversion mechanism and its transmission device are directly arranged on it. This paper discusses the sand casting process design, solidification simulation and process optimization of single and small batch large turbine volute castings by sand casting.

Volute is a structural part of hydraulic turbine, which is used together with guide vane and runner. As a water diversion component, it is necessary to ensure that the water flow from the penstock is introduced into the water diversion mechanism evenly and axisymmetrically with small flow loss, so as to make the water flow force around the runner uniform; Make the water flow produce a certain circulation to meet the needs of the runner. The outline of the spiral case is shown in the figure, and the pipe is in the shape of “vortex” with gradual radius characteristics. The overall dimension of sand casting is 1622.5 mm × 814 mm × 1 510.3 mm, the thinnest part is the structural feature of sharp angle formed with the impeller in the cylindrical channel, with the maximum wall thickness of 110 mm. It belongs to a large sand mold casting with uneven wall thickness. The volute pipe is symmetrically arranged with 4 lugs, the inlet direction is provided with a flange, and the bottom of the central cylindrical ring is provided with a through circular hole with a straight diameter of 120 mm. The overall wall thickness of parts is uneven, which is prone to sand casting defects. According to the actual working conditions, after adding machining allowance on the important working mating surface, the sand casting weight is calculated to be 1972 kg.

(1) The structure and manufacturability of turbine volute are comprehensively analyzed. It is produced by sand casting and molded by resin sand core.

(2) The pouring system of turbine volute is designed, and the closed pouring system combined with no riser scheme is adopted to obtain a more feasible sand mold casting process scheme.

(3) AnyCasting was used to simulate and analyze the sand casting process of volute, the rationality of the overall design was determined, the solidification sequence of sand casting was obtained, the defect location of sand casting was predicted, and the defects were eliminated by adding cold iron through optimization design. Through simulation analysis, the correctness and effectiveness of the process scheme were determined.

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