The production technology of the isostatic graphite is different from the graphite electrode. The isostatic graphite need the raw material which has an isotropic structure property. It need to grind into finer powder,and use the cold press molding technology(the isostatic press molding is one kind of the the cold press molding) the baking cycle is very long,and for the high density,it need more times’ dipping and baking.and the graphitization cycle is more than normal graphite.
The main technology mainly includes:
1) raw material grinding
the particle size need to processed into 20 μm below. For now,the finest isostatic graphite particle size is 1μm,and it must need the superfine mill.
2) the kneading processing
make the powder and coal asphalt adhesive into fixed ratio,then put into the heating mixer to make it mixed,the purpose of this is to make the powder surface coated a layer of the pitch. After that get it out and cool it. Compared with the production of graphite electrode,the kneading time need longer,and the temperature need higher,and the QTY of the pitch need more.
The material after crushing,grinding,it will be screened into tens to hundreds of microns and mix it uniformly,then press it and mold it,prepare for the second-grinding.
Defferent from the extrusion molding and molded pressing,the isostatic molding is belong to the cold pressed molding. Press the raw material and make it into the rubber mould, use the high frequency electromagnetic vibration to make the powder pressed,then make it vacuum,put it into the high-pressure container with water or oil,then make the pressure to 100~200Mpa,at last,make it as a cylindrical or rectangular product.
5) baking and dipping
As the isostatic graphite compact structure,the baking temperature should heating-up slowly,and the temperature inside the furnace should also be controlled well,the heating-up speed should not beyond 1℃ /h,and the temperature difference in the furnace should below 20℃,and during the baking processing, it will take 1~2 month to meet the requistment.
After the baking processing, the volatile of the pitch discharged,there are some pores on the surface of the material ,so it need to be dipped,and it usually need many times to bake and dip.
6) the most important processing it the graphitization.
Heating-up to 3000℃,and it will take 1~1.5 month to make it. After this,the density,electricity conducting,thermal conducting and the erosion resistance will be improved better.