Carbon material production technical problems & answers 4-- Baking

Carbon material production technical problems & answers 4-- Baking

I. Why should the raw billet be cooled immediately?

The raw billet produced just out of the molding machine are composed of plastic paste, containing binder coal tar pitch, which is convenient for viscous state, and the shape and size of the raw billet is not stable. Therefore, after leaving the molding machine, the raw billet should be immediately soaked in water and cooled in cold water, so that the raw billet's temperature can be reduced below the softening point of pitch. Graphite electrode, with coal tar pitch as binder, is widely used in electric furnace steelmaking. The pitch is re-cooled and solidified to a solid state, which stabilizes the shape, so that it will not be bent and deformed. The temperature of cooling water should not be higher than 30 ºC. Under normal circumstances, large-size blanks can be fully cooled after soaking in cold water for 3 ~ 5 hours and small and medium-sized blanks for 1 ~ 3 hours. The raw billet extruded in summer should be cooled for a longer time. 

II. How is the uneven density of the raw billet formed?

1. Carbon paste is thermoplastic and has a certain viscoelasticity. Its ability to transmit pressure is not as good as that of liquid. The pressure in the paste shows a decreasing trend, resulting in uneven raw billet density.

2. The friction between paste and mold wall and the friction between paste particles lead to pressure loss, uneven pressure distribution, and uneven density.

3. There are differences in the orientation of unequal axis particles in the surface and inside of the raw billet, which affects the uniformity of raw billet density.

III. What is baking?

Baking of raw products after molding is an indirect heating process with hot gas as fuel under the condition that the protective medium is isolated from the air in the baking furnace at a certain heating rate.

IV. What is the purpose of baking?

After baking the carbon products, the binder in the products is transformed into coke, and the coke carbon grid is formed between the carbon powder particles to connect them closely, forming a whole with fixed geometric shape, certain mechanical properties and physical and chemical indexes.

1. Eliminate volatile matter;

2. Reduce resistivity and improve conductivity of products;

3. Further shrink the volume and change its physical and chemical properties;

4. Create conditions for graphite chemical process;

5. Coking the binder coal tar pitch.

V. What is the essence of baking?

With the increase of temperature, the main changes in the pyrolysis and coking process of binder coal tar pitch are decomposition and polymerization.

Ⅵ. What are the basic requirements of baking process?

The calcined products must ensure that the coal tar pitch produces the maximum amount of coke. While producing the maximum amount of coke, the whole green body is heated and fed evenly, with correct geometric shape, and no internal and external defects (i.e., no internal and external cracks, no uneven carbonization of the product section, no bubbles, etc.).

VII. What are the heating stages of baked products?

The process of baking products is divided into:

1. Preheating stage;

2. The middle temperature stage of change intensification;

3. High temperature baking stage;

4. Cooling stage.

VIII. What are the causes of an explosion in a baking furnace?

1. Stop the exhaust machine, and the gas accumulates into explosive gas.

2. Put out the fire at low temperature. The temperature is too low, the flame is not extinguished, and the gas accumulates to form explosive gas.

3. The operation of low-temperature ignition is incorrect. When the air is sufficient, should be ignited first, then send gas, otherwise there is an explosion risk.

IX. What are the causes of cracked waste products produced in the baking process?

Generally speaking, due to the reasons of the previous process, many products have horizontal cracks and internal cracks. However, due to this process, longitudinal cracks are mostly produced in the products, and the causes of various cracks are as follows:

1. During molding, the material temperature is too low, the prepressure is insufficient, and the molding pressure is insufficient.

2. During the molding return, the paste is broken. although the surface is smooth, but the internal structure is not good.

3. The calcination degree of raw materials is not enough, or the ingredients are mixed with raw material blocks, resulting in secondary shrinkage during baking.

4. The plunger head of the press is coated with too much oil, and the nipples of the two pots of material cannot stick, resulting in cracks after baking.

5. The binder content of the product is too low, and the powder content is too high.

6. The paste is not kneaded evenly or there is water in the paste.

7. The heating rate is too fast.

8. The product is too close to the furnace wall when loading.

9. The furnace wall is partially leaked and heated too fast.

10. The upper layer is loaded with large-size (¢ 400mm above) low ash products.

X. Why does the baking furnace produce oxidized waste products?

1. The upper insulation of the product is too thin.

2. The furnace chamber leaks and the motor box is ventilated.

3. The filling material has too much moisture, and the blanking is not solid. During baking, it shrinks and sinks, exposing the products to oxidation.

4. The temperature is too high when it comes out of the furnace, and the products are not scattered in time in the cleaning site. For more carbon technical guidance, please contact us in detail.