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General rule of asphalt segregation

Release time:2019-12-18 From: Zhengnai Industry in China

Pseudosegregation phenomenonin graphite electrode process

Asphalt segregation is a phenomenon produced by coal, bitumen and capillary action in the green body under the action of temperature, gravity and capillary action.

Causes of segregation of asphalt

Segregation of bitumen is the main cause of uneven axial and radial quality of the roasted product. The density of the green body is relatively uniform, but there is a big difference after burning, especially the difference in density between the two ends of the product is obvious.
 

Reasons why the filler is bonded to the baked product

In addition to gravity segregation, the coal bitumen in the green body also has “hot bleed out”, that is, when heated to a certain temperature, the volume expansion coefficient of the coal tar pitch after the sub-melting is larger than the volume expansion coefficient of the green body, so part of the coal tar pitch The outer surface is oozing out, and the oozing asphalt is adsorbed by the filler, which is also the reason why the filler adheres to the surface of the baked product.

General rule of asphalt segregation in graphite electrode

The general rule of asphalt segregation is: 1. The coarser the particle size composition of the green batching, the larger the segregation amount of the asphalt under the same cooking temperature. 2. Under the same composition of ingredients, the amount of asphalt is too much and the amount of segregation increases.
 

Effect of temperature on asphalt segregation

When medium temperature asphalt is used as the binder, the main temperature range of asphalt segregation is 100~250°C. Therefore, the maintenance time is too long below 250°C during roasting, which will increase the amount of asphalt segregation. When the temperature is higher than 250°C, the segregation rate of asphalt decreases. The amount of segregation also decreases.

Asphalt segregation phenomenon and softening point relationship

Separation is significantly reduced by using high softening point asphalt
 

Method of reducing the performance gap of the same product

When the ring furnace is fired, increasing the thickness of the top cover filler helps to reduce the temperature difference between the upper and lower sides, thereby reducing the difference in physical and chemical properties between the upper and lower ends of the same product.

Classification of graphite electrode

Item Unit UHP RP
300-600mm 650-800mm 300-800mm
Electric resistivity Electrode μΩm 4.8-5.8 4.6-5.8 7.8-8.8
Nipple 3.8-4.5 3.8-4.5 5.0-6.5
Flexural strength Electrode Mpa 10.0-14.0 10.0-14.0 7.0-12.0
Nipple 20.0-26.0 22.0-26.0 15.0-20.0
Elastic modulus Electrode Gpa 9.0-13.0 10.0-14.0 7.1-9.3
Nipple 15.0-18.0 15.0-18.0 12.0-14.0
Bulk density Electrode ≥g/cm3 1.68-1.74 1.70-1.74 1.53-1.56
Nipple 1.77-1.82 1.78-1.84 1.70-1.74
CTE(100-600℃) Electrode x10-6/℃ 1.1-1.4 1.1-1.4 2.2-2.6
Nipple 0.9-1.2 0.9-1.2 2.0-2.5
Ash   0.3 0.3 0.5

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