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Graphite Furnace Temperature Measurement

Release time:2019-11-04 From: Zhengnai Industry in China

Effect of furnace temperature distribution on product quality

The quality of graphitized products is mainly related to temperature. The temperature distribution in the core of the Acheson graphitization furnace is very uneven. Generally, the temperature in the lower part of the furnace core is several hundred degrees Celsius higher than the upper part. Therefore, the resistivity of the upper end of the same electrode during vertical installation Higher than the lower end. However, the graphite electrode produced by the internal heat tandem graphitization furnace has a small difference in temperature in the longitudinal direction or the diameter direction, so that the resistivity of different parts of a plurality of electrodes in a series of columns is substantially the same.


 

Graphitization furnace temperature measurement

The furnace core temperature of the graphitization furnace can be measured by thermocouple and automatic balance recorder below 1600 °C. It can be measured by optical pyrometer or photoelectric pyrometer at 1600 °C. The maximum range is up to 3200 °C. Due to the large amount of smoke in the graphitization furnace, corresponding measures must be taken during the measurement.
It is very important to choose the temperature measurement point of the Acheson graphitization furnace. It is necessary to select a representative temperature measurement point according to the purpose of temperature measurement.
 

Temperature point selection

It is necessary to select representative temperature measurement points according to the purpose of temperature measurement. For example, considering the temperature difference between the upper and lower sides of the Acheson graphitization furnace core, the temperature should be measured at least at three points. The internal heat tandem graphitization furnace does not use the resistance material, and the current almost passes through the tandem column composed of the calcined product, and the temperature generated at each longitudinal point of the tandem column is relatively uniform, so the temperature measurement of the internal heat tandem graphitization furnace Points can be reduced.

Parameter of UHP/HP graphite electrode


Item Unit UHP HP
300-500mm 550-600mm 700-800mm 300-500mm 550-700mm
Electric resistivity Electrode μΩm 4.6-6.2 4.5-6.0 4.5-5.8 5.5-6.8 5.5-7.0
Nipple 3.5-5.0 3.4-4.5 3.3-4.3 4.0-5.5
Bending strength Electrode Mpa ≥10.5 ≥10.0 ≥10.0 ≥10.0 ≥8.5
Nipple ≥20.0 ≥22.0 ≥23.0 ≥18.0
Elastic modulus Electrode Gpa ≤14.0 ≤14.0 ≤14.0 ≤13.0
Nipple ≤20.0 ≤22.0 ≤22.0 ≤15.0
Bulk density Electrode g/cm3 1.66-1.73 1.68-1.74 1.62-1.70
Nipple 1.75-1.82 1.78-1.85 1.72-1.80
CTE(100-600℃) Electrode 10-6/℃ 1.20-1.50 1.10-1.50 1.80-2.20
Nipple 1.10-1.40 1.00-1.30 1.50-1.80
Ash % ≤0.3

 

What is crack?

There are three kinds of cracks observed on the surface of the product: longitudinal crack, transverse crack and mesh crack. It is generally considered that the longitudinal crack is caused by the poor quality of the baked product, while the transverse crack or the mesh crack has a great relationship with the graphitization process, and the temperature difference is high. The induced stress is the main cause of cracking.
One of the causes of cracking is the large deviation in temperature rise across the furnace core.
 

Bending deformation

After the furnace is found, the large-size product has a bending deformation, which is generally a defect of the roasted product itself, and the small-sized product has found that the bending deformation has a certain relationship with the operation of the graphitization furnace in addition to the defects caused by the roasting product itself.


 

What are oxidation used for?

Product oxidation can be divided into two types: “water oxidation” and “wind oxidation”. Wind oxidation is caused by cracks in the insulation coating at the end of electrification. It is not treated in time, and air enters the furnace core. Water oxidation is due to the furnace wall. There are cracks, water that cools the conductive electrode penetrates into the furnace core or is excessively watered during cooling after power failure. Both of these oxidations are caused by operational reasons.
 

Bump or break

In the process of lifting, loading or unloading, the product will be damaged or broken due to various reasons. A small amount of damage will not affect the finished product with the specified size. Serious damage or breakage can only be used for waste disposal or for use. Processing non-standard products.

 

Silicon carbide on the surface of the product

When the proportion of quartz sand in the bottom material is too large, and the temperature at the bottom of the furnace is too high, the silicon vapor rises and chemically reacts with the surface of the product, leaving crystal silicon carbide crystals which are difficult to clean on the surface of the product, and has an influence on the processing. Sometimes a small amount of insulation leaks into the furnace core, and quartz sand reacts directly on the surface of the product to form silicon carbide.
 

Unsatisfactory resistivity

Resistivity is the main performance index of graphite electrode. Except for the quality of raw materials used, the resistivity is too large (beyond the specified index), mainly because the graphitization temperature does not meet the requirements.
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