Investigation On Preparation Of φ700mm Ultra-High Power Electrode Nipple

φ700mm UHP graphite electrode is used in large volume UHP DC-ARC furnaceas high-temperature-resistance, electrical conducting graphite materials, which iswell-sold in domestic and foreign markets and has high value because of its high-techand complicated processing procedure. As now, just several graphite electrodemanufacturers in USA, Japan, German can produceφ700mm UHP graphite electrodewhile the domestic can not make it. During producing φ 700mmUHP graphite electrode, higher requirement toprepare nipple is needed because the nipple as joint bears higher smelting request.Therefore, the small-scale and middle-scale experiments were carried on in lab, usinghigh-grade petroleum needle coke----X-grade SUMITOMO coke as skeleton, Tianjinmodified pitch as binder, with various process formulas and two additives toinvestigate the preparing process and producing techniques. During small-scale experiments, the size distributions of formulas were selectedby trying measuring vibrated bulk densities of a lot of mixture. On basis of them, 9experimental formulas were designed and carried out. The suitable formulas wasoptimized by polarized light microscope and measured results of samples. Small-scale experiment shows that some formulas are gained by method ofmeasuring vibrated bulk density, whose characteristics are intermittent sizedistribution and continuous size distribution. Samples' properties based on formulasderived from intermittent size distribution are better than the ones based on formulasderived from continuous size distribution. For example, the bulk density is improved0.02~0.04 g/cm3,flexural strength is improved 19%~41%,specific electrical P Presistance is lowered 8%~22%. Compared with middle temperature coal tar pitch,modified pitch can apparently improve 0.02 g/cm3 of the bulk density and 10% of P Pmechanical strength of nipple samples because of 5% higher fixed carbon and binderstrength. Stearic acid should be prudently used because it lowers more than 16%mechanical strength of nipple samples although it could lower the softening point andviscosity of pitch so that it benefits for improving extrusion productivity. Addingproper additives of Fe2O3 could effectively inhabit the puffing in graphitization and B B B Bimprove mechanical strength of nipple samples. On basis of small-scale experiments, selecting proper process formulas,optimizing various procedure parameters, adding procedure of impregnation andre-baking, middle-scale experiments were carried out with polarized light microscopeand SEM, according to commercial production. Results of middle-scale experiments show that increasing content of fine particlein formulas could improve mechanical strength of nipple samples. Especially,increasing content of ultra-fine particle in formulas could increase more than 10% ofmechanical strength of nipple samples. Procedure of impregnation and re-baking is agood method to improve mechanical strength of nipple samples. But more times,improving amplitude gets less and less, and make coefficient of thermal expansionrise. Properties of final nipple samples are as follows: bulk density 1.87g/cm3, flexural P Pstrength 29.4MPa, Young's modulus 17.1GPa, coefficient of thermal expansion 1.50×10-6/℃, specific electrical resistance 4.9μΩm, which are close to those of foreign P Pφ700mmUHP graphite electrode nipple.