Research On Tundish Molten Steel Level Measurement Under The Condition Of Covering Slag Blocking

With the increase in quality requirements for the metallurgical products,the measurement of the molten steel level in tundish is increasingly becoming important.At the end of casting,the failure to accurately estimate the residual molten steel results in a huge waste of molten steel.As the weight of slag from the ladle remains unknown and unpredictable,acquiring the molten steel level in high accuracy and real-time is a worldwide difficulty.At present,the commonly used weighting method has a poor measurement accuracy due to the presence of slag.POSCO has developed the eddy current method but its technology has not been widely applied because of high cost and short service life arising from high temperature.To solve this problem,this thesis proposes a method for measuring the molten steel level via the combination of the measurement of height and thickness of covering layer.Firstly,the height of the covering layer is measured in real time using a laser range finder.Secondly,the thickness of the covering layer is sensed with a temperature tube based on temperature distribution.Lastly,the level is obtained on the basis of the difference between the height and the thickness.The major difficulty in this procedure is the acquisition of the thickness.It includes 3 cases:a)the temperature tube is used to sense the temperature gradient around the level;b)when the temperature information is blocked,the thickness of adhesive slag is employed to gain the level;c)when the adhesive slag,is fluent,the fluency distribution of the adhesive slag is useful for measurement of the thickness of the covering layer.At last,a device for measuring the molten steel level is developed,fabricated,and tested on site.The main content and the innovations are listed below:(1)measurement of the covering layer height using a laser range finderTo solve the hot slag radiation interference and the laser signal recognition,this thesis proposes a color-based filter.Based on the CCD imaging theory,the thesis analyzes the optical spectrum difference of the laser and the radiation,optimizes the optical system parameters capable of enhancing the color difference,and extracts the laser signal with the morphological image processing method.The proposed method achieves measurement of the covering layer height in high accuracy with a measurement error smaller than 2mm.(2)measurement of the slag thickness based on the temperature gradient on the temperature tubeBy inserting and lifting a temperature tube in the molten steel,the thickness of the covering slag can be acquired by an analysis of its temperature gradient.When the tube is lifted,the tube may have some slag adhered onto it.This adhesive slag blocks some temperature information.Thus,the thesis proposes a model matching method to acquire the blocked information and then measures the thickness.This method exhibits high accuracy and robustness with an error lower than 3mm.(3)measurement of the slag thickness when the temperature information is totally blockedWhen the temperature information on the temperature tube is totally blocked,the temperature gradient method will fail to measure the level.The thesis divides this case into 2 categories:a)when the adhesive slag is fixed,according to the different erosion mechanism of steel-tube and slag-tube,the adhesive thickness distribution is relative to the molten steel level.The thesis measures the adhesive thickness distribution with the surface temperature dropping characteristics and then obtains the covering layer thickness;b)when the adhesive slag is fluent,according to the different erosion mechanism of steel-tube and slag-tube,the fluency of adhesive slag distribution is relative to the molten steel level.The thesis measures the fluency of adhesive slag distribution with an optical analysis and then obtains the covering layer thickness.The results show that the method has a good accuracy when the covering slag on the measuring probe is flow or not flowing.The measurement errors in both cases are smaller than 3mm and 4mm,respectively.(4)Experimental research on the molten steel level measurement deviceThe device developed for measuring the molten steel level has been used in many steelmakers for more than 2 years.It has a high accuracy with a measurement error of molten steel level smaller than 5mm.In the example of Hanggang steelmaker,the continuous caster obtains extra 3 tons of molten steel at the end of casting.On the basis of this calculation,a steelmaker with an annual output of 10 million tons will gain extra 10000 tons of molten steel.