The Relationship Between Rolling Mill Efficiency and Ambient Humidity and Temperature

Practice has shown that numerous factors can affect the efficiency of a rolling mill in daily operations, including environmental conditions such as temperature and humidity—both intrinsic and external.
Therefore, to improve the operational efficiency of the rolling mill, the narrow furnace tap hole is subject to stringent humidity requirements. When no steel is present and the door is closed, this can reduce air consumption and heat loss, thereby lowering fuel costs for coal and natural gas. If the ambient humidity in the rolling‑mill area is high, it increases the partial pressure of water vapor inside the furnace, reducing the effective driving force and making it difficult to maintain consistent heating. In such cases, it becomes necessary to extend both the length and width of the furnace, which in turn raises capital investment.
Regarding the selection of heating furnaces, appropriate relative temperature values vary. For instance, in a walking-beam reheating furnace, where the residence time of the steel billets is short, a rolling-type furnace requires greater driving force to achieve a higher heating rate. Typically, the partial pressure of water vapor at the gas outlet must be kept below half of the external material’s water vapor pressure. If a regenerative furnace is used, the water vapor fraction in the exhaust gas is generally about 60% of the billet’s surface water vapor pressure. For certain types of reheating furnaces, it is essential to maintain the required air velocity; therefore, when designing the furnace structure, both relative humidity and contact conditions should be carefully considered. To meet high‑velocity air requirements, a larger air flow can be employed to reduce relative humidity, thereby increasing the billet’s heating rate and minimizing heat loss.
The underlying reason is that the inlet temperature of the rolling mill must be carefully controlled to ensure that the steel billet quickly reaches the deformation‑rolling stage. Typically, the inlet temperature of the rolling mill should be maintained within an appropriate range—around 1150°C—allowing for variations in billet quality. Even among billets of the same type, deviations in inlet temperature can lead to differences in furnace conditions. Moreover, factors such as quenching heating temperature and holding time can vary from one billet to another. Consequently, during actual rolling operations, the rolling temperature must be adjusted according to specific process requirements.