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The roasting process of graphite electrode

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

5 stages in the roasting process of graphite electrode

  • 1. The coal pitch is in a molten state, and the green body begins to soften.
  • 2. The volatile phase is discharged in a large amount,
  • 3. Asphalt begins to undergo strong polycondensation at the same time as decomposition.
  • 4. Semi-coking turns into a coke stage,
  • 5. High temperature carbonization stage.

Reasons for changes in properties of green bodies during roasting

The most important change in the greening process of the green body is the decomposition, polycondensation and morphological changes of the coal tar pitch, which causes a series of changes in the physical and chemical properties of the green body.

5 effects of calcination heating rate

  • 1. The heating rate of roasting affects the process of decomposition, polycondensation and carbonization of coal tar pitch.
  • 2. It affects the change of green form.
  • 3. The heating rate is too fast, the decomposition and evaporation rate of coal tar pitch is also accelerated, and the decomposition and volatilization amount increases. The char rate decreases, resulting in a reduction in a range of physicochemical properties.
  • 4. The heating rate of roasting has an important influence on the calcination yield.
  • 5. The crack of the product is directly related to the unreasonable heating of the roasting.

Product shrinkage during roasting

The apparent size of the green body during the roasting process is constantly changing and eventually manifests as shrinkage.

4 reasons for shrinkage

  • 1. Shrinkage is gradually produced as the calcination temperature increases, and the amount of shrinkage is related to the final temperature.
  • 2. The relationship with formula and molding pressure is more complicated.
  • 3. Shrinkage has a great relationship with the binder content and binder properties in the paste. Shrinkage is linear with binder content.
  • 4. The shrinkage of the green body is also related to the calcination process conditions to some extent.

Five factors to consider the calcination temperature

  • 1. Roaster structure.
  • 2. Temperature rise rate.
  • 3. Using the vessel to roast can shorten the roasting temperature rise time.
  • 4. Determination of the final calcination temperature.
  • 5 The effect of cooling rate and tapping temperature on the quality of the roasted product.

Heating curve for large size product selection

When producing large-size products, a heating curve with a long heating time should be selected.

Index of graphite electrode

Item Unit RP HP UHP
300-500mm 300-500mm 300-500mm
Electric resistivity Electrode μΩm 7.5-8.6 5.5-6.8 4.6-6.2
Nipple 4.5-6.0 4.0-5.5 3.5-5.0
Bending strength Electrode Mpa ≥7.5 ≥10.0 ≥10.5
Nipple ≥16.0 ≥18.0 ≥20.0
Elastic modulus Electrode Gpa ≤9.0 ≤13.0 ≤14.0
Nipple ≤13.0 ≤15.0 ≤20.0
Bulk density Electrode g/cm3 1.54-1.62 1.62-1.70 1.66-1.73
Nipple 1.70-1.78 1.72-1.80 1.75-1.82
CTE(100-600℃) Electrode 10-6/℃ 2.20-2.60 1.80-2.20 1.20-1.50
Nipple 1.50-1.90 1.50-1.80 1.10-1.40
Ash % ≤0.3 ≤0.3 ≤0.3

Reasons for using high quality asphalt as binder

The weight loss curve of high-quality asphalt with higher softening point begins to decompose and discharge volatiles is different from that of medium-temperature asphalt, so the green body produced by using high-quality asphalt as a binder is used.