Strip cooling control for flexible production of galvanized flat steel

The work is devoted to the problem of flexible small-scale production of galvanized steel of various sizes on a continuous hot-dip galvanizing unit with varying productivity. The main focus is on the heat treatment of steel strip, the requirements for which limit productivity. In conditions of disturbances, it is necessary to proactively control the heat treatment using models, or to reduce the speed of the strip to ensure that the requirements are met. Unlike most of the works that focus on heat control, this work focuses on strip cooling. Based on the analysis of production data of the Magnitogorsk Iron and Steel Works, it is shown that violation of the cooling requirements leads to the appearance of defects in the zinc coating. Dependence of the probability of defects occurrence on the strip temperature is given. Problems of cooling predictive control are formulated using models in the absence of temperature control of the cooling section cavity. For each of the tasks, the model structure and the method of its tuning are determined according to the data accumulated over a significant period of the unit operation under conditions of uncontrolled systematic disturbances. The structure of the cooling control system is proposed by estimation of the cooling section cavity temperature as a controlled variable. The temperature estimate is determined from the model. The lack of measurement of the cooling section cavity temperature is not a problem then varying productivity. The results of the models tuning are presented according to the data of the Magnitogorsk Iron and Steel Works continuous hot-dip galvanizing unit. The proposed structures of the models and methods for their adjustment can be applied in the development of models for metal heating in furnaces.

An Ice Vest, but Not Single-Hand Cooling, Is Effective at Reducing Thermo-Physiological Strain During Exercise Recovery in the Heat

Sports limit the length of breaks between halves or periods, placing substantial time constraints on cooling effectiveness. This study investigated the effect of active cooling during both time-limited and prolonged post-exercise recovery in the heat. Ten recreationally-active adults (VO2peak 43.6 ± 7.5 ml·kg−1·min−1) were exposed to thermally-challenging conditions (36°C air temperature, 45% RH) while passively seated for 30 min, cycling for 60 min at 51% VO2peak, and during a seated recovery for 60 min that was broken into two epochs: first 15 min (REC0−15) and total 60 min (REC0−60). Three different cooling techniques were implemented during independent recovery trials: (a) negative-pressure single hand-cooling (~17°C); (b) ice vest; and (c) non-cooling control. Change in rectal temperature (Tre), mean skin temperature (T¯sk), heart rate (HR), and thermal sensation (TS), as well as mean body temperature (T¯b), and heat storage (S) were calculated for exercise, REC0−15 and REC0−60. During REC0−15, HR was lowered more with the ice vest (−9 [−15 to −3] bts·min−1, p = 0.002) and single hand-cooling (−7 [−13 to −1] bts·min−1, p = 0.021) compared to a non-cooling control. The ice vest caused a greater change in T¯sk compared to no cooling (−1.07 [−2.00 to −0.13]°C, p = 0.021) and single-hand cooling (−1.07 [−2.01 to −0.14]°C, p = 0.020), as well as a greater change in S compared to no cooling (−84 [−132 to −37] W, p < 0.0001) and single-hand cooling (−74 [−125 to −24] W, p = 0.002). Across REC0−60, changes in T¯b (−0.38 [−0.69 to −0.07]°C, p = 0.012) and T¯sk (−1.62 [−2.56 to −0.68]°C, p < 0.0001) were greater with ice vest compared to no cooling. Furthermore, changes in in T¯b (−0.39 [−0.70 to −0.08]°C, p = 0.010) and T¯sk (−1.68 [−2.61 to −0.74]°C, p < 0.0001) were greater with the ice vest compared to single-hand cooling. Using an ice vest during time-limited and prolonged recovery in the heat aided in a more effective reduction in thermo-physiological strain compared to both passive cooling as well as a single-hand cooling device.