Roasting Isostatic Graphite Impregnation Process Research And So On

Isostatic pressing formed graphite, also called Sangao graphite or special graphite, is a kind of graphite with high strength, high density and high purity, which is widely used in fields such as metallurgy, chemical industry, aircraft industry, electronic industry and nuke industry. Especially, large size isostatic pressing formed graphite with superior quality can be used in high-tech and new technique field and is honoured as the most promising material in the21th century because of its widespread application prospect.The paper prepared raw material for the last process of making isostatic pressing formed graphite, which was graphitization, by multi roast and dipping of isostatic pressing perform body and coal pitch. Through measuring methods including TG-DSC analysis, SEM analysis and XRD analysis, properties and both apparent structure and micro structure of products made in every stage were analyzed and compared to each other. In addition, the mechanisms of affecting properties of products were also discussed.It was proved by experiments that the coking value of preformed body could be efficiently raised by roasting under inert gas atmosphere. Moreover, changes of preformed body under different temperatures were revealed by analyzing TG-DSC curve. When the temperature was under200℃, the body only slightly swelled because of softening of it and thermal decomposition in it, while no significant change of its physical and chemical properties happened. When the temperature was between200℃to600℃, volume of the body shrinked most obviously because of the drasticly reacting complex reactions, which suggested the heating rate should be decreased. When the temperature was between800℃to1200℃, the body was gradually getting stable because coking of the body had completed essentially, which suggested remaining the highest temperature for some time and then cooling down under control to the room temperature. Finally, based on above analysis and conclusion, theoretical heating curve of single-pass roasting of isostatic press preformed body was fixed.Through single factor experiments one to ten, which were designed to study influences on properties of roasted products of cover, heating rate and roasting time, optimum conditions of single-pass roasting of isostatic press preformed body were obtained.Optimum values of three technological parameters of impregnation technology were obtained through orthogonal experiments. The dipping temperature should be200℃and the pressure should be1.5MPa keeping60minutes. In addition, it was also concluded that influences on dipping of temperature, pressure and pressure maintaining time successively diminished. Through analyzing TG-DSC curve of heating coal pitch, it was revealed that thermal properties of coal pitch were similar to that of isostatic pressing preformed body. After analyzing TG-DSC curve of coal pitch, the roasting heating curve of preformed body after dipping was fixed for the purpose of reducing cost and improving work efficiency.Properties of products such as density, mechanical strength and so on were improved as number of times of dipping and roasting increased, while the improving range decreased. On the basic of experiments, it was concluded that the best times for roasting and dipping were respectively4times and3times.