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The existence of temperature difference during roasting

Release time:2019-12-12 From: Zhengnai Industry in China

The existence of temperature difference during roasting

The temperature difference is not only expressed at the end of the calcination temperature rise, but also in the whole process of calcination. The faster the temperature rise rate, the larger the temperature difference, not only the temperature difference in the height direction, but also the temperature difference in the horizontal direction.

Price of graphite electrode

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The result of ensuring the best temperature rise rate

The optimum temperature rise rate should ensure that the decomposition and polycondensation of the binder in the green body are carried out under conditions which are most favorable for the yield and product quality, that is, the number of bending, deformation and cracks generated is the smallest.

Relationship between green diameter and temperature rise rate

Under industrial production conditions, the diameter of the green body should first be considered, the green diameter should be increased, and the temperature rise rate should be reduced.

Container roasting of graphite electrode has the following advantages

  • (1) The heat transfer of the steel cylinder is fast, which is beneficial to make the temperature of the raw material up and down and the surrounding temperature rise relatively uniformly, and reduce the temperature difference. The faster heating temperature rise curve can be used without increasing the crack waste.
  • (2) The green body is fired in the container, and at the same flame temperature, the actual heating temperature of the green body can be increased by about 50 ° C than that of the direct furnace (a large amount of filler is surrounded).
  • (3) Although the steel cylinder is not sealed, it has a certain resistance to the discharge of volatiles, and a slight positive pressure is maintained in the steel cylinder, which is beneficial to increase the carbon residue rate of the coal tar.
  • (4) The roasting of the container can reduce the consumption of the filler
  • (5) to facilitate the mechanization operation of the roasting and unloading furnace, and also solve the problem that the dust on the furnace is large and the working conditions are poor.

The final difference in calcination temperature is large and crack

The large difference in the final temperature of the green roasting results in a large difference in the physicochemical properties of the calcined product, which is one of the reasons why cracking waste is easily generated in the graphitization process.

Internal defects during cooling

The thermal stress of the baked semi-finished product gradually increases in the direction from the center to the surface, and increases as the exit temperature and the semi-finished elastic modulus increase and the linear expansion coefficient increases. The internal defects of the semi-finished product during the cooling process are often the concentration points of various stresses.

Take the purpose of forced cooling of water spray

The forced cooling of water spray is adopted to shorten the roasting cycle and increase the production capacity.

Size of graphite electrode

Item Unit RP HP
300-500mm 550-800mm 300-500mm 550-700mm
Electric resistivity Electrode μΩm 7.5-8.6 7.5-8.8 5.5-6.8 5.5-7.0
Nipple 4.5-6.0 4.0-5.5
Bending strength Electrode Mpa ≥7.5 ≥6.5 ≥10.0 ≥8.5
Nipple ≥16.0 ≥18.0
Elastic modulus Electrode Gpa ≤9.0 ≤13.0
Nipple ≤13.0 ≤15.0
Bulk density Electrode g/cm3 1.54-1.62 1.62-1.70
Nipple 1.70-1.78 1.72-1.80
CTE(100-600℃) Electrode 10-6/℃ 2.20-2.60 1.80-2.20
Nipple 1.50-1.90 1.50-1.80
Ash % ≤0.3 ≤0.3