Research On The Law Of Steel Tube Wall Thickness Variation Of The Stretch Reducing Mill

It is regarded as very valuable to conduct researches on the reducing mill which is one of the deformation units of the seamless steel tube rolling-line, and attributed to heightening the capacity of the operation line, expanding the product mix, improving the product quality as well as cutting down the investment of equipment and tooling for the front area of the hot-rolling section.As the finishing step of the hot-rolling process of seamless steel tube, the reducing mill is mainly used to control surface quality and the final geometric accuracy. The reducing mill has a great variety of types. Up to now there have been plenty of research issues concerning pipe reducing mills throughout the world. In case of the tube rolling line located in Chengdu Seamless Steel Tube Co., Ltd., since it involves a rather broad product mix ( including light & heavy walled and large & small sized tubes in grades from the low carbon steel to the hi-alloy steels ) and features the special forging-rolling process, the reducing mill incorporated with it has to meet a rather crucial requirement, i.e., being capable of both efficiently reducing the tube bore and considerably improving the unsatisfactory surface quality and wall thickness of the tube as rolled with the pilger forging-rolling process. The research project focuses on identifying the law of steel tube wall thickness variation under operation of the group-driven, 3-high, 12-stand slight-stretch reducing mill in a bid to cut down the high rejection rate and degrading rate of pilgered tubes resulting from surface quality defects and inferior final concentricity respectively. The research project contributes to significantly enhancing the cost-effectiveness of the mill, freeing the circulating funds long-time lie idle caused by the degrading practice and providing a theoretical basis for improvement of the secondary processing technology. Based on the theoretical analysis of stress and strain during the deformation function of the stretch reducing mill,. the theoretical formulation of the steel tube W.T. variation is built up, and an experimental schedule is worked out. Accordingly, site measurements concerning such data as tube diameter, W.T. variation and elongation change are conducted, and all the elements responsible for W.T. variation such as diameter reduction rate, wall thickness coefficient, temperature and rolling speed schedule are analyzed. As a result, a regression math model with the diameter reduction rate and W.T. variation as critical regression factors is set up to meet the operationrequirements of the said mill. Based on the result of application of the model to the mill operation and in compliance of applicable steel tube standard, the limits to control W.T. during hot-rolling is determined as the basis for quality control of the production.Getting the theory well combined with relevant operational practice, the research project is significant to plant activities of steel tube production...