Baking and impregnation process for graphite production

Baking: It is a process in which the green carbon product is placed in a specially designed heating furnace for high-temperature heat treatment under the protection of the filler, so that the coal pitch in the green body is carbonized. The pitch coke formed after coal tar pitch carbonization consolidates the carbonaceous aggregate and powder particles together, and the roasted carbon product has higher mechanical strength, lower electrical resistivity, better thermal stability and chemical stability .

Bakting is one of the main processes in the production of carbon products, and it is also an important part of the three major heat treatment processes in the production of graphite electrodes. The baking production cycle is longer (22-30 days for one baking, 5-20 days for second baking), and Higher energy consumption. The quality of the green body baking has a certain impact on the quality of the finished product and the production cost.

The coal pitch in the green body is coked during the baking process, and about 10% of the volatile matter is discharged, and at the same time, the volume shrinks by 2-3%, and the mass loss is 8-10%. The physical and chemical properties of the carbon billet have also undergone significant changes. Due to the increase in porosity, the bulk density is reduced from 1.70g/cm3 to 1.60g/cm3, and the resistivity is reduced to 40-50μ.Ω.m from about 10000μ.Ω.m. The mechanical strength of the calcined billet is also greatly improved.

Secondary baking is a process in which the baked product is immersed and then baked again to carbonize the pitch immersed in the pores of the baked product. The production of graphite with higher bulk density requires two baking, and the joint blanks also need three immersion and four baking or two immersion and three baking.

Main types of baking furnaces: continuous operation-ring furnace (with or without cover), intermittent operation of tunnel kiln-inverted flame kiln, car bottom roaster, box roaster.

Firing curve and maximum temperature: primary firing - 320, 360, 422, 480 hours, 1250 ℃ secondary firing - 125, 240, 280 hours, 700-800 ℃ inspection of baked products: appearance knock, resistivity, bulk density, compressive strength, internal structure analysis.

Impregnation is a process in which the carbon material is placed in a pressure vessel, and the liquid impregnant pitch is immersed into the electrode pores of the product under certain temperature and pressure conditions. The purpose is to reduce the porosity of the product, increase the volume density and mechanical strength of the product, and improve the electrical and thermal conductivity of the product.

The impregnation process and related technical parameters are: baking billet-surface cleaning - preheating (260-380 ℃, 6-10 hours) - loading into the impregnation tank-vacuuming (8-9KPa, 40-50min) ——Inject bitumen (180-200 ℃)——Pressurize (1.2-1.5MPa,3-4 hours)——Return bitumen——Cooling (in or outside the tank)

Inspection of impregnated products: impregnated weight gain rate G=(W2-W1)/W1×100% , primary impregnated product weight gain rate ≥ 14% , secondary impregnated product weight gain rate ≥ 9% , tertiary impregnated product weight gain rate ≥ 5%.