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Coking cause of filler

Release time:2019-12-17 From: Zhengnai Industry in China

Metallurgical coke is broken and used as roasting filler

After the metallurgical coke is broken, it is used as a roasting filler. Although the coke powder has poor thermal conductivity and high adsorption, it is not easy to be cleaned on the surface of the product. However, the use of coke powder as a filler will not cause blockage of the Shanghai flue. And so on.

Improve the bulk density and mechanical strength of the roasted product

The amount of expansion of the green body under the expansion force of the decomposition product decreases as the compressibility of the filler decreases, and the decrease in the adsorptivity and gas permeability of the filler facilitates the retention of a part of the asphalt decomposition product in the calcined product, thereby improving the The bulk density and mechanical strength of the baked product.
 

The relationship between the filler and the shrinkage speed of the green body

In the coking stage of the binder, in order to avoid the increase of the internal stress of the green body, it is necessary to minimize the shrinkage speed of the green body, and the smaller the adsorption property and the gas permeability of the filler material, the lower the shrinkage speed of the green body.

Coking cause of filler in graphite electrode

After the filler particles are pressed into the surface of the green body in a softened state, the adhesion to the filler is increased due to the partial extrusion of the binder to the surface of the green body. The green surface binder starts to be semi-coked at the same time as decomposition and polycondensation, and the adhered filler is coked on the surface of the baked product.
 

Factors related to the degree of coking on the surface of the baked product

The degree of coking on the surface of the calcined product is related to the binder content of the green body, the binder content is large, the plasticity of the green body is large, and the coking is severe. In addition, the smaller the particle size of the filler, the greater the anisotropy, and the more serious the coking. The coal pitch with higher softening point is used as the binder, and the coking degree is lighter under the same baking condition.

Relationship between coking degree and temperature

The degree of coking of the filler decreases remarkably with the increase of the heating rate in the initial heating stage of the calcination. This is because the relative expansion amount of the green body at the time of rapid temperature rise is reduced, and the amount of the binder discharged to the surface of the green body is reduced, so that the filler is in the raw state. The adhesion of the surface of the blank is reduced.
 

How to reduce the degree of coking

Before the furnace is installed, a layer of protective material is applied on the surface of the green body, which can reduce the adhesion of the filler to the surface of the green body and reduce the degree of coking.

Parameter of graphite electrode

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

The method of cleaning and coking after the roasting product is cooled

  • 1. Manual cleaning, that is, the worker uses a long-handled blade to shovel to coke. The coking is sometimes very serious, and the cleaning work is labor intensive.
  • 2. Use a special cleaning machine. The cleaning machine is equipped with a scraper device or a rubbing device. The burning products are automatically cleaned on the cleaning machine.
  • 3. Using a shot blasting machine, the fired product is placed in a specially designed iron box, and the iron shot is sprayed from the roasting product from several different angles, and the iron shot hits the surface of the baked product. Iron pellets can be recycled for reuse.
 

Secondary roasting definition

The secondary baking is a process in which the calcined product is immersed and then burned again to carbonize the pitch immersed in the pores of the calcined product.
 
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