USING CAST ELECTROSLAG BLANKS INSTEAD OF FORGINGS IN FLANGE PRODUCTION

Abstract

Ring blanks of flange type are widely used in oil refining and the chemical industry for connecting various pipelines, which are made in accordance with GOST 12820-80 and GOST 12821-80 from steels 20, 09G2S, 10G2, 08Kh18N10T, and so on. These flanges work at high pressures and under severe climatic conditions with sharp temperature swings in the transporting media and therefore they are subject to inspection by the State Mining, Safety and Health Inspectorate. These products are usually made by forging, pressing, and casting by traditional techniques (open melting methods) followed by mechanical treatment. These standard technologies have advantages and shortcomings. The advantages of ones cast by traditional methods (open induction melting, electric arc melting) include highly accurate casting with minimal tolerances for subsequent machining and high metal use factors. Shortcomings of cast blanks are poor quality in the metal and difficulty in obtaining dense blanks, since on melting and pouring the metal, it becomes saturated with gases, nonmetallic inclusions, and harmful impurities; it also has structural and chemical inhomogeneity. For those reasons, casting is hardly ever used to make components performing critical functions. Components made by forging have higher quality metal, although they may inherit defects from cast items. Major defects of that technology are the high cost of the blanks, on account of the numerous intermediate operations (forging castings, cutting them into blanks, piercing the blanks, and finishing), as well as a low metal use factor and the need for expensive forging and rolling equipment. Hot deformation in making flange blanks is thus forced upon one in order to avoid the low quality of casting. A promising way of resolving this problem is to replace forged blanks by high-quality castings with minimal tolerances for subsequent machining. As these components have central through holes, it is best to use a new technology: centrifugal electroslag casting CESC [1]. The essential point is electroslag melting of an electrode in a melting vessel providing for accumulating the liquid metal and slag in appropriate amounts, with subsequent pouring into a rotating mold. The metal may be consumable electrodes of any shape and section. That technique has been used in making flange blanks for important uses. The electrode is melted under a flux, which is a mixture of calcium fluoride, electrocorundum, magnesite, and silica. That flux purifies the liquid metal in the vessel by removing sulfur and phosphorus and preventing environmental action, and also provides considerable fluidity with high cooling rates [2].