Casting defects of a high class valve body

In the whole pressure pipeline system, valve is the key control device. Its main function is to connect or block the flow of various media in the pipeline, or change the flow direction of media, adjust the pressure and flow, and ensure the safe and normal operation of pipeline equipment.

Valves are widely used in engineering pipeline, petrochemical, power station and other fields. In the petrochemical field, the working conditions of valves are complex, and the circulating medium is usually corrosive. Therefore, the petrochemical transportation system has higher requirements for valve product quality than other working conditions, and the casting process design is difficult. Aiming at the casting defects of a kind of high-grade valve body produced in the actual production, the author uses the simulation software for in-depth analysis, puts forward the solving measures, and passes the actual production verification. The optimized process scheme can provide reference for the research and development of similar high class and large diameter valve body.

(1) The heating riser is used in the thick and isolated hot spot to improve the feeding capacity.

(2) The dichotomy method is used to set the inner gate of large and medium-sized steel castings, and the flow rate of the inner gate should be controlled within 0.6 m / s to ensure the smooth filling of liquid steel and avoid turbulence.

(3) The first strand of molten steel entering the mold is introduced into the slag collecting part by using slag collecting runner or slag collecting ladle to ensure the purity of molten steel in the mold cavity.

(4) The mold filling process was simulated. Through the analysis of porosity, niyama, secondary oxidation slag, tracking particles and other criteria, the actual production was carried out after the scheme was feasible, so as to improve the first pass rate of products.

The optimized process was tested in production. In the process of trial production, chromite sand was used to compact the thick parts, alcohol based zircon powder coating was used to keep the coating thickness at 2 mm, and several air outlet channels were set in the sand core to avoid casting defects such as porosity, shrinkage porosity and slag hole. Through RT testing, no internal defects were found, and all castings met the technical requirements of the products.

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