J. Horsky

Optimal cooling of rolls in hot rolling

Abstract A laboratory experimental device was developed to allow full-scale measurements on roll cooling to be carried out. The full-scale tests use a complete configuration of rows of nozzles as in the plant conditions or prepared by a designer. The laboratory approach allows the design to be optimised or to compare old and new solutions. The tests provide a distribution of cooling intensity (heat transfer coefficient and heat flux) at the roll surface. The second step of the optimisation process is the usage of a numerical model for computation of temperature and roll crown in a hot rolling regime. A industrial typical rolling schedule is used to check the efficiency of cooling. A typical application of the experimental–numerical procedure is in improvements of cooling, in intensification of rolling and in design work. The paper shows how this approach can help in “making a decision” related to a prior plant application. Examples of the results and general recommendations for cooling are included.

Combined Inverse Heat Conduction Method For Highly Transient Processes

Combined inverse heat conduction task was developed. The task uses classical minimisation method in combination with optimisation method. The method was developed for the very steep changes of the measured temperature and the demand on precise results. Typical industrial applications are in descaling (removing oxides from steel surface by high energetic spray). The minimisation method is used as a basic method. The precision of this method is improved in the area of big temperature gradients by combination with optimisation method. The peaks of HTC of heat flux are computed precisely afterwards.

In‐Line Heat Treatment and Hot Rolling

In‐line heat treatment of rolled materials is becoming increasingly used at hot rolling plants. The advantage of this method is the achievement of required material structure without the necessity of reheating.This paper describes a design procedure for cooling sections for the purpose of obtaining the required structure and mechanical properties. The procedure is typically used for the cooling of tubes, rails, long products and plates.Microstructure and nature of grains, grain size and composition determine the overall mechanical behaviour of steel. Heat treatment provides an efficient way to manipulate the properties of steel by controlling the cooling rate. The rate of cooling is defined by a heat transfer coefficient (HTC). Good controllability of HTC can be reached using either air‐water or water nozzles. Thus, an on‐line heat treatment with the assistance of spray nozzles enables a manufacturing process that can improve product performance by increasing steel strength, hardness and other desirable c...

Development of accelerated cooling for new plate mill

Abstract The aim of the paper is to design the new wide plate mill. The work on the new cooling technology was supported by extensive laboratory testing while a simulator with full scale testing of cooling units was used. The principal objective of the investigation was to establish the design specification of equipment for accelerated cooling, particularly with respect to the product dimensions and steel grades. The possibilities of accelerated cooling are limited by technical parameters of cooling equipment such as thickness of water layer, flowrate, spray height, position of cooled surface to the nozzles and water or plate speed. These parameters were studied for different product temperatures and water impingement densities from 50 to 110 l s−1 m−2. The heat transfer coefficient was determined and compared for each case. There were three recognised significant cooling regions: water layer region, impinging jet region without water layer and impinging region with water layer, which must be taken into account. The application of the new cooling technology showed better flatness product and productivity higher than previous accelerated cooling system, even shorter cooling length. The rejection ratio by flatness problem of new mill was nearly half of the previous one.

Attainment Of More Precise ParametersOf A Mathematical Model For Cooling Flat AndCylindrical Hot Surfaces By Nozzles

The paper describes a method of improving parameters of an experimental data based mathematical model of cooling by water-nozzles using a neural network. Experiments are carried out using hot flat and cylindrical moving objects. These experiments simulate industrial applications such as cooling in continuous casting, cooling of products in hot rolling, and cooling of rolls in rolling technology. The measurements are evaluated using the inverse 3D task. The inverse task computes the surface temperature history and heat transfer coefficients. Using the heat transfer coefficients, the parameters for the mathematical model of cooling are obtained for a specific nozzle. Their correctness is verified using the computer simulation of the experiment. It has been found that for high temperatures the simulation based on experimentally obtained parameters is less precise than that for low temperatures. The analysis of the experimentally obtained data has shown that for high temperatures a much smaller set of data is available than for low ones. On the basis of comparison of the experimental data and the data obtained by computer simulation of the experiment, the correction for parameters is made, and more precise results of the mathematical model are obtained. The paper also describes the experimental methods used, the main characteristics of the inverse 3D task computing boundary conditions from the temperature history measured inside objects, and the method for correction of data obtained in the area sparsely described by the experiment. Advanced Computational Methods in Heat Transfer VI, C.A. Brebbia & B. Sunden (Editors)

Experimental Study of Leidenfrost Phenomena at Hot Sprayed Surface

An experimental study was prepared to find the relationship between Leidenfrost temperature and droplet size and velocity of impinging jets. The study is done for the case of steel surface cooling with two-phase nozzles. The sprayed surface moves under the spray at a velocity of 1 m/min. Cooling experiments were done for initial temperature of 1250°C. Thermal experiments are transient: internal temperature is measured and surface temperature and heat transfer coefficient distribution is computed by the inverse task. Droplet size and velocity of the impinging jet was modified by setting water and air pressures at the input of the nozzle. Spray parameters for each pressure combination was measured using a laser-doppler anemometer. The paper shows the results of the thermal and fluid flow experiment and the correlation between Leidenfrost temperature and flow parameters.The application of obtained results is expected for high temperature cooling especially in continuous casting.Copyright