The Defect Analysis Of Isolating Switch Shell By Low-Pressure Die Casting

Along with the development of power transmission equipment needs, GIS(Gas Insulated Switchgear)is widely used, the shell with aluminum alloy is one of the key components in transmission equipment. Currently, GIS shell was made by the process of low-pressure casting, it can produce the casting with high qualified rate, stable quality and high utilization rate of alloy. It's the development trend of producing the shell, the main limiting is casting defects in the process of production by low-pressure casting.This paper studies the problem of the shell in the production, the main three aspects were used to solve the defects of GIS shell. Firstly, through the development of low pressure casting process parameters management system for the shell, which to standard foundry technique was designed. Secondly, through the low-pressure casting foundry technique was designed based on the CAD/CAE system, in order to analyze stress distribution of isolating switch shell under uniform load condition, to find out the weak points, according to the results to guide the design of gating system; Two sets of plans was designed in this paper:"Arborization"gating system and circular crevice gating system; The simulation software of foundry was used to simulate the liquid metal filling and solidification process, and the defects were predicted. The determination of reasonable gating system solutions and low pressure casting process parameters: pouring temperature is about 700℃, mold temperature is 200~300℃, lift pressure is 0.04MPa, lift time is 15s, filling pressure is 0.055MPa, filling time is 30s, boost pressure is 0.08MPa, boost time is 15s, holding time is 120s. Finally, through the actual production process, in order to analysis defect of casting and find the solutions, and then the casting technology was optimized.Through the analysis of metallographic and mechanical properties, its shows that the shell metallurgical structure densification, and mechanical properties can be achieved:σb≥250MPa,δ≥1.4, HB≥90. Nondestructive evaluation and bulge test show that produced shell of GIS, the qualified rate of gas-tight test has reached up to 98%, which can fulfill the demand of GIS.