New material-saving technologies of pipe rolling on pilgrim units

In this work, based on the analysis of the process of hot pilger rolling of pipes of a wide range of sizes and grades from a round continuous cast billet, new and improved existing metal-saving technologies have been developed to reduce metal losses in the pilger head.Using scientific and patent sources of information in the field of pilger rolling and its mathematical modeling with the calculation of tables for rolling pipes of a wide range of sizes from a round continuous-cast billet with a diameter of 385-470 mm, metal losses into technological scrap on a pilgerstan are determined: a seed and a pilger head.On the basis of the results of the theoretical determination of metal losses in the process scrap on the pilgerstan: the seed and the pilger head, a forecast was made to reduce the weight of the pilger head, which was used to develop new material-saving technologies for pilger rolling of pipes, both thick-walled with D / S = 6 - 12.5, and thin-walled with D / S = 12.5 - 40. Metal losses in the pilger head are the main factor of increased metal consumption coefficients on pilger units, which reduces their competitiveness in comparison with other units when using round continuously cast billets as a starting material.The forecast for the reduction of metal losses in the pilger head made for the first time makes it possible to estimate the reserves for reducing the mass of the pilger head both by eliminating the underflow of the liner and trimming of the pipe end adjacent to the pilger head, and by means of individual parts of its profile part and predicting its decrease to the minimum possible size, ensuring the removal of the pipe from the mandrel using a gate device.To reduce the weight of the pilger head when rolling thick-walled pipes, it is recom-?ended to use improved technologies for butt-end rolling and rolling of the pilger head on the free section of the mandrel.The results of the studies and the proposed new material-saving technologies can be used on pilgrim units when rolling thick-walled (D / S = 6 - 12.5) and thin-walled (D / S = 12.5 - 40) pipes of a wide range of brands (carbon, alloyed, highly alloyed and special) from both continuous casting machine and forged and centrifugally cast billets, as well as ingots.

Influence of thermal state of the end area of multiple continuous-cast billet on cracking of the ends of hot-rolled breakdown at rolling

The authors have made an analysis of problems arising in the rolling of continuous-cast billets in the modern mini-metallurgical and rerolling plants. It is shown that the use of trio stands in rolling mills of these plants makes it necessary to obtain billets of multiple lengths from bars (most often of 12-meter length) produced in the rolling shop. The subsequent rolling of such multiple billets has revealed increased cracking of the front edge and, as a result, increased metal consumption. Analysis of the causes of these cracks has been made. It was indicated that this defect can appear as a result of a certain stress-strain state formed at the end of hot-rolled breakdown. It is caused by the presence of an uneven temperature field due to more intensive end cooling, to reduction mode in the trio stand and to the presence of axial defects in the continuous-cast billet. The study was conducted on the industrial medium-grade mill 500/370, as well as using mathematical modeling by finite element method. The influence of a set of technological factors, such as temperature of the billets heating before rolling, the time interval of their transportation on the site “heating furnace – first stand of the rolling mill” and parameters of the macrostructure of axial area of the metal were investigated. Calculations by the developed mathematical model have indicated the need to take into account the presence of a scale layer on the heated continuous-cast billet. It is shown that depending on the heating temperature and transport time, the temperature difference at the billet’s end compared to the heating temperature can be from 45 to 100 °C. It will lead to an uneven distribution of deformation resistance and unfavorable stress-strain state at the billet’s end. In addition, the presence of an axial defect can affect the cracking because of its shape and its transformation during reduction. Obtained experimental data allowed hypothesizing the mechanism of transformation of discontinuity defects into cracks at the billet’s end due to the conditions of continuous casting and cutting of billets during rolling in the reduction stand.

Influence of Different Factors on Withdrawal Speed of Continuous Cast Billet

The influence of the St.3sp, 40 and 85 steel grades chemical composition, temperature of the metal in the tundish ladle, billet cross-sectional dimensions (150 × 150 and 152 × 170 mm), the sulfur content in the metal on the speed of withdrawal of the billets from the CCM mold has been investigated. It was established, that the change of the metal temperature in the tundish ladle of the CCM has the greatest effect on the billet withdrawal speed, the change of carbon content in the steel and the billet cross-sectional dimensions influence in less extend, and the sulfur content in the cast steel does not affect at all.