Overcooling in overlap areas during hydraulic Descaling

Overcooling in overlap areas during hydraulic Descaling

Článek WoS

The production and processing of high-quality grades of steel are connected with the oxidation at high temperatures. Unwanted scales are formed on the steel surface, which is usually heated to over 900 °C. These scales are often removed by hydraulic descaling during the production. In most cases where long, flat products are produced, one row of descaling nozzles is used. As these flat jet nozzles are arranged in a row, the water spray from one nozzle interferes with the spray from the neighboring nozzles. This zone is called an overlap area and often even more scales remain here after the descaling process. An increased amount of the scales left behind results in a lower quality of a final product. A typical configuration with an inclination and twist angle of 15° was studied. Heat-transfer coefficients (HTC) and surface temperatures were measured in the overlap area and compared with the values obtained from undisturbed areas. It was found that the overlap area is grossly overcooled. The results were compared with a new configuration, where the twist angle was changed to 0°, and it was found that the overcooling was significantly reduced. The temperature measurement showed that an increased thickness of the scales in the overlap area can also be caused by surface overcooling because the scales change the material properties with the temperature, and they are therefore more difficult to remove. The new configuration with the twist angle of 0° seems promising for improving the quality of hydraulic descaling.

The production and processing of high-quality grades of steel are connected with the oxidation at high temperatures. Unwanted scales are formed on the steel surface, which is usually heated to over 900 °C. These scales are often removed by hydraulic descaling during the production. In most cases where long, flat products are produced, one row of descaling nozzles is used. As these flat jet nozzles are arranged in a row, the water spray from one nozzle interferes with the spray from the neighboring nozzles. This zone is called an overlap area and often even more scales remain here after the descaling process. An increased amount of the scales left behind results in a lower quality of a final product. A typical configuration with an inclination and twist angle of 15° was studied. Heat-transfer coefficients (HTC) and surface temperatures were measured in the overlap area and compared with the values obtained from undisturbed areas. It was found that the overlap area is grossly overcooled. The results were compared with a new configuration, where the twist angle was changed to 0°, and it was found that the overcooling was significantly reduced. The temperature measurement showed that an increased thickness of the scales in the overlap area can also be caused by surface overcooling because the scales change the material properties with the temperature, and they are therefore more difficult to remove. The new configuration with the twist angle of 0° seems promising for improving the quality of hydraulic descaling.

scales, steel, water, hydraulic descaling, overlapping, temperature, heat-transfer coefficient, surface

scales, steel, water, hydraulic descaling, overlapping, temperature, heat-transfer coefficient, surface

POHANKA, M.; VOTAVOVÁ, H.

2017

01.08.2016

Istitute of Metals and Technology

Ljubljana

1580-2949

Materiali in Tehnologije

50

4

Slovinská republika

575

578

4