best rp 700 mm graphite electrodes
Coefficient of thermal expansion of best rp 700 mm graphite electrodes and connectors
1 Coefficient of thermal expansion
For best rp 700 mm graphite electrodes and connectors, the coefficient of thermal expansion (CTE) is an important quality indicator. Electrode graphite has strong anisotropy, and their longitudinal CTE and transverse CTE are different, so their expansion behavior in these two directions is also different. The CTE index specified by the 700 mm graphite electrodes related standards refers to the longitudinal CTE value. Its value is measured using a quartz dilatometer in accordance with G.4-82 [1]. The test temperature range is 100～600℃. The calculation formula is :
α=ΔL /(K ×L 0×Δt )+correction coefficient where: ΔL — the expansion of the sample in the temperature range of 100～600℃, mm;
L 0-the length of the sample at room temperature, mm; Δt-the temperature rise
The range is 600℃-100℃=500℃;
K ———The magnification of the dilatometer.
The correction coefficient is the average thermal expansion coefficient of quartz at 100～600℃, and its value is ×10-6/℃.
Coefficient of thermal expansion (α
The value of) has a great influence on the behavior and consumption of the electrode in the steelmaking process. The thermal expansion behavior of electrodes and joints and their influence on steelmaking operations will be discussed below.
2 Thermal expansion of electrodes and joints
Thermal expansion of different types of electrodes
In order to understand the thermal expansion behavior of different types of electrodes, we take a sample from each of the Φ, HP and U HP electrodes in the axial direction, and measure their CTE according to the specified standards.
The relationship between ΔL /L 0 and temperature of these three samples. It can be seen from Table 1: For the RP electrode sample, before about 100℃, as the temperature rises, the product shrinks, and the product begins to expand beyond this temperature, and with the temperature rise, the expansion range is greater; for HP As for the electrode sample, the temperature at which it shrinks as the temperature rises has to continue until about 200°C. After that, as the temperature continues to rise, the product begins to expand, but the extent of expansion is smaller than that of the RP electrode sample. For the U HP electrode sample, the temperature at which it shrinks as the temperature rises has to continue to about 400°C. After that, as the temperature continues to rise, the product expands, and the expansion range is smaller than that of the HP electrode sample. The different thermal expansion behaviors of the three electrodes are mainly related to their raw materials. Needle coke molecules are arranged regularly, and the content of fiber components in the microstructure is high, and the content of inlaid form components is small. Since the capacity of the fiber component to accommodate expansion is more than 6 times larger than that of the inlay form, the U HP electrode produced from needle coke has a low thermal expansion coefficient. ; Thermal expansion in different directions
The thermal expansion of extruded graphite is anisotropic. In order to verify the anisotropy of the expansion of extruded graphite products, we used U
Take two samples along the axial and radial directions on the product joint, and mark them as A-1, A-2, C-1, C-2, and CTE test on 4 samples. The sample size is Φ20mm. ×50mm. The test data is shown in Table 2 (in Table 2, L 0=, the dial gauge reading is the difference in thermal expansion size between the sample and the quartz).
From the above data, we can get: α100～600 of sample A-1=0193×10-6/℃, α100～600=1121×10-6/℃ of sample A-2, α100～ of sample C-1 600=2186×
10-6/℃, α100～600=3112× of sample C-2
10-6/℃. It can be seen that the radial CTE is about 3 times the axial CTE. Figure 2 is a graph of the relationship between ΔL /L 0 and temperature of these four samples. It can be seen from Figure 2 that the radial specimen is almost always expanding with the increase of temperature, and the expansion range is small; while the axial specimen shrinks first with the increase of temperature, and does not start to expand until about 400 ℃, and the expansion range is large. This is mainly determined by the structure of the graphite material [3]. On the level of graphite, carbon atoms are bonded by covalent bonds and are not easy to expand; and between layers, carbon atoms are combined by intermolecular forces. Because the intermolecular forces are small, it is easy to Swell.
3& Impact on the performance of electrodes and connectors
(1) CTE and thermal shock resistance
Thermal shock resistance coefficient=K (thermal conductivity)×S (tensile strength)/
[α (Coefficient of Thermal Expansion)×E (Modulus of Elasticity)][4]
(1) Table 2&400T 4 joint thermal expansion test data
Temperature/℃
A —1
Dial indicator reading/μm (ΔL /L 0)/10-3A —2
Dial indicator reading/μm (ΔL /L 0)/
10-3
C —1
Dial indicator reading/μm (ΔL /L 0)/
10-3
C —2
Dial indicator reading/μm (ΔL /L 0)/
The formula (1) shows that the thermal shock resistance coefficient of the electrode is inversely proportional to its thermal expansion coefficient. In the process of steelmaking, the temperature at the center of the electrode is high and the temperature at the periphery is low, causing the center of the electrode and the periphery to expand asynchronously. When the stress caused by this asynchronous expansion increases to exceed the strength of the electrode, cracks will occur on the electrode, and as the cracks expand, they will eventually break off and fall off. Therefore, controlling CTE is of great significance for reducing the breaking loss of electrodes and joints.
(2) CTE matching problem between electrode and connector
In the steelmaking process, the joint temperature is always greater than the temperature of the electrode at the same horizontal position. As the temperature rises, both the electrode and the joint produce linear expansion. The condition for no gap between the connecting surface of the electrode and the joint due to expansion is: α joint axis <α electrode axis.
As long as the linear expansion coefficients of the electrode and the joint are properly matched, there will be no gaps on the connecting surface. At this time, most of the impact force generated by the collapsed material will be borne by the electrode body, and the probability of joint fracture will be reduced. On the other hand, to prevent the joint hole from expanding and cracking, it must meet: α joint radial <α electrode radial.
To meet the above two requirements, it is necessary to ensure that the raw materials for the production of joints are higher than the raw materials for the production of electrodes, especially the CTE of the former is smaller than that of the latter. In addition, the graphitization temperature of the joint should be higher than the graphitization temperature of the electrode.
In short, CTE is one of the important physical and chemical indicators of best rp 700 mm graphite electrodes and connectors. We should deepen our understanding of CTE, understand the thermal expansion behavior of best rp 700 mm graphite electrodes and connectors, and take necessary measures to ensure that the electrodes and connectors are CTE meets the aforementioned requirements.