The graphite electrodes play a major element in the process of making steel that is made using electric arc furnaces. They also constitute significant proportions of the total cost. Any technology that can extend their life span, improve their conductivity and enhance their longevity will be appealing to buyers, especially if it also helps save energy.
The high-quality graphite electrodes help improve the efficacy and productivity of steel manufacturing processes by their ability to withstand and evenly distribute heat in the EAF process, leading to an increase in productivity. Moreover, they are required to withstand physical pressure in the process of piercing the steel forging scrap, so it's important that their structural integrity be always maintained.
To ensure that the graphite electrodes are able to stand up to these conditions, the process of making them is controlled. This includes making of the raw materials, mixing and batching with baking and extrusion along with rigorous quality testing. Investing in high-quality electrodes that meet these standards may be expensive initially but the long-term financial benefits and reduced need for frequent replacements can offset the initial cost.
Hexagon recently completed a major test project aimed at improving the performance of electrodes at EAF plants all over the world. The research was carried out by NAmLab in collaboration with Hexagon and involved the evaluation and comparison of two kinds of electrodes namely AF-5 and EDM180. During the experiment the electrodes were put to a series of cutting tests, which included those that were performed on a metallic specimen. The experiment included not only testing the strength of the material on the electrodes, but also assessing electrical properties like resistivity.
The results of the machining tests were examined using a statistical approach, leading to the creation of regression models. The intensity of current (Ic) was determined to be the most important element in determining the efficiency of removal of materials. This was followed by time intervals (toff) and discharge duration. The roughness of the electrode's surface (Ra) was observed to significantly correlate with the effectiveness of removal of the material.
To evaluate the graphite electrodes, a conductive device was utilized to measure the voltage along a specific length of the test sample. This voltage is proportional to the conductivity of the graphite and the measurements were made with the lowest electric current to avoid any potential sample heating effects.
The graphite electrodes that were utilized in the tests series were impregnated with double pitch (1PI). The study revealed that the higher the quality of the electrode, the less its electrical resistance. In particular it was found that the 1PI electrodes exhibited the lowest values of resistivity under all test conditions. The electrodes that are higher grade are more homogenous in their structure. This decreases the porosity and opens up the density of the material. Hexagon has found that an increment of 10% in graphite grade could result in a reduction of 17 percent in electrical resistance. This is a key factor in EAF steelmaking. This leads to improved cutting and more efficient operations as well as energy savings.
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