Hot Steel Slabs Research Articles

Simulation of Spray Cooling on Hot Steel Slabs in Continuous Casting

Abstract Continuous casting is an important process to solidify molten steel. Efficient and uniform heat removal by water spray without cracking or deforming steel slabs is a major challenge during continuous casting. With the aid of computational fluid dynamics (CFD), the current study presents a numerical model of spray cooling for process understanding and improvement. The Eulerian–Lagrangian approach is utilized to track the movement of water droplets that are injected from a hydraulic nozzle. The initial droplet size is predicted by the linear instability sheet atomization (LISA) model and the droplet distribution satisfies the Rosin-Rammler distribution. Droplet-slab impingement is modeled by the wall jet model and the associated heat transfer accounts for both heat conduction and radiation. Heat transfer coefficient (HTC) on slab surface is validated against a hot-plate benchmark experiment and shows good agreement. The significance of spray standoff distance and spray direction on heat transfer is also investigated. The results indicate the existence of the critical standoff distance beyond which the cooling effect becomes negligible. Spray direction plays an important role in determining the heat transfer rate as well, and insufficient cooling is observed when droplets are sprayed against gravity. Additional 10% to 15% of water will compensate for such low heat transfer. The current study should benefit the steel industry by providing fundamental insights into the process. The current model can also be applied to other types of spray nozzles and can further improve the efficiency of future simulations.

Optimal Use of Physical Heat in Slabs Issuing from CCM

A method of using sensible heat of hot steel slabs issuing from a continuous casting machine (CCM) in which it is possible to eliminate slab heating in furnaces prior to rolling. For this, hot slabs at a certain time are sent to a thermostat, where the temperature is equalized along their section and length, whereupon the slabs can be fed to the rolling mill. This achieves a significant savings of fuel and eliminates heating and oxidation of the metal in the furnace. To implement this method, one must first solve several problems: put the continuous casting machine on one technological line with the rolling mill and establish diagnostics for surface quality of the slabs directly on the exit from the continuous casting machine. In addition, it is necessary to have a fairly accurate mathematical model to calculate the slab temperature field for stationary and non-stationary modes of casting. The mathematical model proposed in the article is somewhat simplified and serves mainly for the communication of the main ideas.

Pre-processing of data coming from a laser-EMAT system for non-destructive testing of steel slabs

Non destructive test systems are increasingly applied in the industrial context for their strong potentialities in improving and standardizing quality control. Especially in the intermediate manufacturing stages, early detection of defects on semi-finished products allow their direction towards later production processes according to their quality, with consequent considerable savings in time, energy, materials and work. However, the raw data coming from non destructive test systems are not always immediately suitable for sophisticated defect detection algorithms, due to noise and disturbances which are unavoidable, especially in harsh operating conditions, such as the ones which are typical of the steelmaking cycle. The paper describes some pre-processing operations which are required in order to exploit the data coming from a non destructive test system. Such a system is based on the joint exploitation of Laser and Electro-Magnetic Acoustic Transducer technologies and is applied to the detection of surface and sub-surface cracks in cold and hot steel slabs.

Thermal Printing for the 21<sup>st</sup> Century

Portable rental car transactions with receipts, faxed documents, drivers' licenses, and bar code labels on hot steel slabs at 600°C …are all printed with thermal printers. Notwithstanding the predictions of thermal printing's obsolescence for the last 10-15 years, the author explores some of the attributes of this technology which explain its robust nature, and its applicability well into the 21st century.

Conoscopic holography-based long-standoff profilometer for surface inspection in adverse environment

One of the more challenging applications of optical metrology is real-time dimensional control and surface inspection in industrial ap- plications, where strong requirements of cost, setup, and applicability in adverse environments greatly limit the number of applicable technolo- gies. This work shows an optic profilometer developed specifically for this purpose, the algorithms developed for efficient and accurate dis- tance map calculation, and an example of its use in a harsh steelmaking environment. This device, based on conoscopic holography, is able to obtain a distance profile of a target in a single shot, works at long dis- tance standoff 700 to 1200 mm, and still keeps good resolution under 0.2 mm with a very easy and reliable setup. The second part of the work focuses on a real example of this technology applied in an on-line in- spection system in steel continuous casting funded by the European Coal and Steel Community, and which is currently working in the Aceralia LDA steelmaking factory in Asturias Spain. The system is placed in the process line and performs on-line detection of surface defects over hot steel slabs above 800°C in the inspection point from a distance of 1200 mm. 100% of the production can be inspected without interfering with the process and without adding any delay. © 2006 Society of Photo-Optical

Development of Eddy Current Inspection System for Detection of Surface Defects on Hot Steel Slabs

An automatic inspection system has been developed for hot slab surface defects by the eddy-current technique. Because of hot-slab surface defects are very narrow, the eddy-current technique offers many advantages over the optical techniques1). But the conventional eddy-current inspection has two major problems.1)the noise caused by lift-off variation due to surface irregularities or oscillation mark.2)The noise caused by electric characteristic variation due to un-uniformity of surface temperature..To solve these problems, we have developed a unique probe coil configuration and found an optimum frequency to be applied and thereby obtained an S/N ratio ten times that of the conventional eddy-current inspection system.

Performance comparisons of contour extraction algorithms

Computer analysis of video images is a popular technique for noncontact measurement and inspection. These applications frequently require the identification and extraction of the contours of areas of interest in the image from which a variety of measurements can be made including location, orientation, and shape. Recent examples include detecting flaws in hot steel slabs, measuring surface defects in wood, finding growth traces in microbiology samples, and a host of applications in the area of robotics and flexible manufacturing. Several techniques for contour extraction are surveyed; a new algorithm is described and compared with previous methods in terms of number of calculations, memory requirements, and data structures. We show that the new algorithm performs significantly faster and is more robust at the expense of a small increase in memory. Due to its sequential nature, it is suitable for on-line execution during the raster scan of a TV sensor.

A Real-Time Automated Visual Inspection System for Hot Steel Slabs

This paper describes an inspection system designed to automatically detect and classify surface imperfections occurring on continuously cast hot steel slabs in a steel mill. The need to perform inspection at real-time throughput rates of 546 Kpixels/s using off-the-shelf components has led to the development of a unique architecture and algorithm set. The segmentation operations are done in a high-speed array processor front end. The imperfection classification is done in a mini-computer which uses statistical as well as syntactic/semantic classification techniques. The inspection system is currently undergoing evaluation in a steel mill.

Adaptive Threshold Estimation for The Inspection of Hot Steel

This paper outlines a practical method of automating the threshold selection for segmentation in a real-time image processing system. This system has been developed to perform on-line surface inspection of hot steel slabs, thereby reducing substantially the energy consumption of the steel industry (largest single user in the U.S.). The threshold selection scheme has been designed to provide suitable clutter rejection while regulating the system processing backlog. The discussion proceeds along the line of adaptive threshold design rationale, system architecture constraints and the ensuing implementation. Performance of the adaptive threshold is compared to that of fixed threshold schemes.