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Reasons for large temperature fluctuations

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

The downdraft kiln is produced separately for each kiln in graphite electrode

The downdraft kiln is produced separately for each kiln, which requires 288-480h for one roasting cycle including furnace charging, heating, cooling, unloading and minor repair.

Advantages and disadvantages of downdraft kiln

The downdraft kiln has a simple structure and low investment, but the working conditions are poor when loading and unloading products, and the energy consumption is high.

Reasons for lower yield of downdraft kiln

When the downdraft kiln roasts large-size products, the yield is low. The main types of waste are cracks, followed by fractures, especially in a row of products close to the fire wall. This is mainly due to the furnace structure of the downdraft kiln. It is difficult to ensure uniform temperature rise, and the temperature measured by the thermometer broadcasted by the furnace door is larger than the actual temperature of the product.

Reasons for large temperature fluctuations in graphite electrode

When lump coal is used as fuel, the furnace temperature is affected by the structure of the furnace, the frequency of coal injection and the combustion condition, so the temperature fluctuates greatly.

Measures to improve the yield of inverted kiln products

  • 1. Improve the structure of the furnace
  • 2. Using lump coal as fuel
  • 3. When inserting the green body, it should be farther away from the fire wall.
  • 4. Adjust the position of the thermocouple
  • 5. Use container baking for large size products or high density products.

Tunnel kiln use process

The tunnel kiln is an industrial furnace with a relatively fixed calcination temperature field. The container is reinforced by the container. The green body is installed in the steel cylinder on the kiln car. The green material should be filled with filler material. The kiln car is pushed into the kiln according to the running schedule. And along the kiln bottom track, through the pre-tropical, burning zone (high temperature zone), cooling zone in sequence, the final kiln car is pushed out from the kiln tail, and the product and filler are discharged from the steel cylinder.

Tunnel kiln use

The tunnel kiln can be used for primary roasting of green bodies and for secondary roasting of impregnated products.

Index of graphite electrode

Item Unit UHP
300-500mm 550-600mm 700-800mm
Electric resistivity Electrode μΩm 4.6-6.2 4.5-6.0 4.5-5.8
Nipple 3.5-5.0 3.4-4.5 3.3-4.3
Bending strength Electrode Mpa ≥10.5 ≥10.0 ≥10.0
Nipple ≥20.0 ≥22.0 ≥23.0
Elastic modulus Electrode Gpa ≤14.0 ≤14.0 ≤14.0
Nipple ≤20.0 ≤22.0 ≤22.0
Bulk density Electrode g/cm3 1.66-1.73 1.68-1.74
Nipple 1.75-1.82 1.78-1.85
CTE(100-600℃) Electrode 10-6/℃ 1.20-1.50 1.10-1.50
Nipple 1.10-1.40 1.00-1.30
Ash % ≤0.3

The tunnel kiln is divided into 4 sections

The whole kiln is divided into four sections, (1) inlet isolation zone, (2) heating zone, (3) cooling zone, and (4) exit isolation zone.