Technological Indicators of Operation of the Rotating-hearth Furnace in Conditions of Discontinued Production

The technological process for manufacturing seamless steel tubes in the Sisak Rolling Mill includes the heating of the charge for processing in the hearth-rotating furnace. Description of the furnace and its operation can be found in literature 1 . In the process currently applied for producing the tubes with the outer diameter of 168.3–356.6 mm the temperature is between 1280 and 1300 °C 2 . The thermal regime is monitored with an optical pyrometer. Measurements are made in a hollow shell after it is manufactured, and on its surface during reheating in the furnace. After heating the shells are extended into tube blanks by means of an elongator and subsequently rolled into tubes in a pilger mill. Provided all the other parameters are stable, the heating time in the rotating-hearth furnace will depend on the quality of the workpieces and on their dimensions as well as on their arrangement on the ring-shaped hearth (in two rows, in one row, or less often, in one and a half rows). In recent years, in addition to home-manufactured charge the Rolling Mill has made use of the continuously cast charge imported from Russia, Italy and the Czech Republic. The necessary technological adaptations that have been undertaken in accordance with the type of charge available on the market have caused occasional departures from the technologically imposed limitations 3 . As a result of periodic delays in the operation of the pilger mill due to mechanical trouble the firing intensity declines and the charge is left in the furnace chamber too long. The consequences may be manifold. Among the most frequent are excessive specific fuel consumption, undue scaling 4 , poor furnace productivity, and unplanned servicing. In this work we analyse the temperature regime in the rotating-hearth furnace.