EFFECT OF HIGH PRESSURE WATER BEAM PARAMETERS ON QUALITY OF DESCALED SURFACE

This work is focussed on hydraulic descaling of hot surfaces. Hydraulic descaling is a process when layers of oxides are removed from hot steel surfaces during continuous rolling. High pressure water beam is used. Quality of descaled surfaces is important for final quality of rolled product. Insufficient descaling causes drop of final quality, degradation of rolls and lost of yields. High-pressure water beam has two effects on a scale layer. The first effect is mechanical caused by impact pressure. The second one is a relatively intensive thermal shock depending on a set of parameters (water pressure, nozzle type, distance from the surface, inclination angle, speed of product moving). There are a lot of theories about principles of scales removing. Main task of this work is to make it clear which theory is acceptable and which is just ,,theory”. For this purpose mathematical modelling and experimental work were used. In experimental part, three types of experimental measurement were done. First one, measurement of dynamical effect of water beam – impact pressure. Second one, measurement of temperature drop when a product is passing under the nozzle. Measured data (temperatures) from this measurement are evaluated with inverse task and heat transfer coefficient is obtained. And the third experimental measurement is simulation of whole process of descaling. Quality of descaled surfaces is valuated according to amount of remained oxide scales. Data from firs and second experimental measurement are used as boundary conditions for mathematical modelling. For mathematical simulations, FEM (finite element method) system ANSYS was used. Obtained data from experimental measurement were applied on 2D and 3D models of basic steel material with layer of scale. Influence of theses data on final temperature, stress and strain fields were observed