The roof of an electric arc furnace used for precious metals recovery was dome shaped and lined with Kala Brick from Harbison-Walker. Once the furnace attained the operating temperature of 2400°F, the roof typically lasted for a maximum of five weeks. After about one and a half weeks, the roof started to “heave” because of its dome shape, causing cracks to appear on the roof’s outer surface. Hot spots were also observed on the surface and their temperatures ranged from 300 to 600°F when measured with a hand held optical pyrometer. The roof had to be invariably repaired after nearly three and a half weeks.
Emisshield ST-4 (US Patent 6,921,431) was applied to the electric arc furnace’s roof. The performance of the roof was studied in the weeks following the application and the results analysed.
After three weeks, surface skin temperatures were measured but no “hot spots” were found. The temperature on the surface was uniform, at a value of 300°F. The engineer who was in charge of the furnace attributed the disappearance of hot spots to the energy re-radiated by the Emisshield® Ceramic/Refractory ST-4. Besides, there was no cracking that used to occur on the surface after one and a half weeks.
Five weeks after the application of Emisshield, the furnace roof was taken down as was normal practice. However, even then no hot spots were found on the surface. Only a minimal amount of cracking was observed, causing the engineer to remark that the furnace roof would have possibly lasted three to four weeks more. Based of his opinion, the furnace roof was coated again and allowed to run until it failed. Cracking started only in the sixth week and the furnace functioned for eight weeks in total. Use of Emisshield® ST-4 thus increased the life of the Kala Brick used in the furnace.
Improved refractory life achieved by coating the furnace roof with Emisshield® ST-4 allows users to cut down material and labour costs. Another benefit is improved productivity as replacement of a roof causes a furnace go out of service for about four days.
This information has been sourced, reviewed and adapted from materials provided by ANH Refractories Europe.
For more information on this source please visit ANH Refractories Europe.