The electrode paste has problems during use, most of which are the overlapping effects of multiple factors. Among them, there is no shortage of U-turn phenomena.
Here, there are two situations that will not be discussed for the time being.
1. Operational factors during use (for example, carbon loss, erosion, etc.)
Two; loopholes in the production process (eg, different batches, inclusions, etc.)
Starting from the rationality of the process formula design, we focus on the following situations:
Let’s start with a phenomenon in our daily life. I think everyone has experienced such a thing; in the cold winter, we take a cold glass, and then pour hot water into the glass, what will happen What about the phenomenon? Why?
As a result, it is well known. In rare cases, the wall of the glass cup is cracked; in severe cases, the bottom end of the glass completely falls off.
In fact, this is because when the glass is under thermal stress, the heated bottom of the glass and the non-heated wall of the glass will generate a temperature gradient in an instant. At this time, if the glass material has poor thermal strain capacity, the heat cannot be taken away in time. The thermal stress is too concentrated, so it will cause the glass to crack and even the bottom end to fall off.
After all, the glass cup and the electrode paste are both inorganic and non-metallic and have similarities.
We return our thinking to the submerged arc furnace. The electrode is like a glass, and the powerful current is like hot boiling water. However, there is another important factor that exacerbated the U-turn.
Therefore, we introduced a physical quantity: the skin effect.
The skin effect is electrically defined as: when the conductor passes alternating current, the current density at the surface of the conductor is relatively large, and the current density inside and at the center is relatively small. This phenomenon is called the skin effect.
According to relevant data, the electrode paste has a skin effect if the diameter of the electrode paste exceeds 510 mm. And the larger the diameter, the more obvious the skin effect.
As you can imagine, a strong current passes through the electrode. The temperature of the electrode tip can reach about 3,500 degrees due to the generation of an electric arc, and the heat is conducted from bottom to top. In addition, the current passes through the electrode itself to generate resistance heat, the resistance of the material, and the surface of the furnace. Radiant heat; there is an inevitable skin effect. These superimposing factors make the temperature gradient inside and outside the electrode, up and down, to be large. At this time, if the electrode cannot take away the concentrated thermal stress in time, in the lighter case, the electrode will have surface cracks, peeling and falling off; in the worst case, it will turn around.
In order to improve the thermal shock resistance of the electrode paste, it should be considered from three aspects: reducing the generation of thermal stress, buffering the development of thermal stress, and enhancing the ability of thermal stress.
One, reduce the generation of thermal stress. Measures: high thermal conductivity, low coefficient of linear expansion and high strength (controversial)
Second, buffer the development of thermal stress. Method: low modulus of elasticity (controversial)
Third, enhance the ability of thermal stress. Ways: the addition of graphite material and the increase of the proportion, the appropriate increase of the size and proportion of the large-particle aggregate, the high volume density, the appropriate increase of the softening point of the asphalt, and the addition of additives with good thermal conductivity.