Infrared thermography of TMCP microalloyed steel skelp at upcoiler and its application in quantifying laminar jet/skelp interaction

Abstract

A series of area temperature maps were obtained from the upper surface of a moving thermomechanical controlled processed (TMCP) microalloyed steel skelp following laminar cooling using an infrared video camera. In addition, an emissivity probe was used to obtain both the emissivity and temperature at the mid-face of the moving skelp. Properly sampled infrared camera temperature measurements correlated well with both the measured probe temperature and with the process control pyrometer. A finite element thermal model of the system, in conjunction with the transverse skelp temperature profiles obtained from the infrared camera, was used to quantify the size and shape of the laminar cooling water jet's direct impact zone on the skelp. The region experiencing direct water impact was found to be constrained by the residual water present on the moving skelp.

Finite Element Thermal Analysis of Surface Cold Spots Observed during Infrared Video Imaging of a Moving Hot Steel Skelp

“…For the 8-14 µm spectral detection band used in the infrared video camera the change in emissivity that would account for the (≈ 75-100°C) temperature drop at the cold spots can be approximated [8] by: (1) where ∆T is the change in calculated temperature for a given change in emissivity (∆ε). Assuming the peak wavelength λmax is 3.32 µm (at 600°C) and the effective wavelength used for the measurement λ is11 µm, then for a ∆T = -100°C the value of ∆ε = -0.24 or an emissivity of 0.70.…”

“…A full description of the FE thermal model is given in reference [1]. The thermal model has been verified for a number of different strips thicknesses and processing conditions.…”

“…In a previous reported work undertaken by the authors [1], an infrared video camera was used to measure the area temperature profile of a steel strip surface immediately following laminar cooling but before strip upcoiling. Calibration (i.e.…”

Assessment of Oxide Descaler Functionality in a Steel Hot Strip Mill Using Infrared Video Imaging

“…In addition to observing realistic base metal temperatures, cold spots (i.e., localized low temperature readings significantly cooler (> 30 °C) than the surrounding steel) were also observed. Finite element (FE) thermal modelling of the skelp as it transits the laminar cooling system [7] was conducted to assess the validity of these cold spots. Thermal simulations included the effect of varying thicknesses (0 µm to 500 µm) of surface oxide films on the predicted temperature of the steel surface following laminar cooling.…”

“…At this specific stage in the process, an infrared video imaging system was employed. The temperature information obtained from the infrared video camera was primarily to assess skelp temperature and provide verification for finite element thermal modelling of the skelp as it transits the laminar cooling system [7]. However, additional information obtained from the infrared thermal images (i.e., the presence of apparent cold spots) was used to assess descaler functionality.…”