A new roll shifting strategy with varying stroke and varying step was investigated,Two characteristic parameters including cat ear height and gap contour smoothness were introduced to assess the effect of shifting strategy on roll wear,and the relation between characteristic parameters and shifting strategy was established.Both varying stroke and varying step can reduce cat ear height and gap contour smoothness,so the shifting strategy with varying stroke and varying step is better than the one with either varying stroke or varying step,Based on the effect of shifting control parameters on characteristic parameters of roll wear,the selection principle of these shifting control parameters was gained.A case study was conducted to validate the proposed roll shifting strategy,reducing uncontrollable quartic loading gap contour,improving strip profile and extending rolling length of a rolling campaign.
The variation of heat treatments including directed quenching and tempering off-line after controlled rolling(DQT) and quenching off-line and tempering off-line after controlled rolling(RQT) with microstructure and mechanical properties of a low-carbon microalloyed steel was compared and analyzed.For DQT,the quenched steel was obviously banded microstructure,with increasing tempering temperature,lath martensite coarsened,the cusp carbide precipitated at grain boundaries,the yield strength fluctuated slightly,and the fracture-separation was obvious.The impact toughness was better in the steel tempered at 500 ℃ for 1 h.In RQT,with increasing tempering temperature,lath martensite degenerated,intragranular and intergranular finer precipitations with smaller than 30 nm precipitated and grew up and were distributed dispersedly,the stripe-like carbides were distributed at grain boundaries,and the yield strength and tensile strengthen decreased obviously.The impact toughness of RQT process was much better than that of DQT process,and the comprehensive mechanical properties were better for the steel tempered at 500 ℃ for 1 h of RQT process.
Load distribution is a key technology in hot strip rolling process, which directly influences strip product quality. A multi-objective load distribution model, which takes into account the rolling force margin balance, roll wear ratio and strip shape control, is presented. To avoid the selection of weight coefficients encountered in single objective optimization, a multi-objective differential evolutionary algorithm, called MaximinDE, is proposed to solve this model. The experimental results based on practical production data indicate that MaximinDE can obtain a good pareto-optimal solution set, which consists of a series of alternative solutions to load distribution. Decision-makers can select a trade-off solution from the pareto-optimal solution set based on their experience or the importance of objectives. In comparison with the empirical load distribution solution, the trade-off solution can achieve a better performance, which demonstrates the effectiveness of the multi-objective load distribution optimization. Moreover, the conflicting relationship among different objectives can be also found, which is another advantage of multi-objective load distribution optimization.
Within the production chain of longitudinal profiled (LP) plates and tailor rolled blanks (TRB) ,variable gauge rolling (VGR) represents the vital important forming stage,in which shape and properties are tailored to satisfy customers′requirements.It is of vital importance to reveal the relationship between work-piece horizontal velocity and roll vertical velocity during VGR,which is not only a key point to understand the deformation law,but also an important content for setting VGR process parameters.It is proved that the simplified assumption of equal discharge per second condition (EDSC) breaks down during VGR.Due to this reason the differential equation of the workpiece horizontal velocity (VGR-V) is performed by keeping the material volume constant.To attain a comprehensive understanding of this underlying process in detail,numerical approaches based on finite elements method have been performed by utilizing the Abaqus Explicit.Rolling experiment is carried out which indicates that the numerical result coincides with the experimental result well.A fine spatial discretization of work-piece is essential for special emphasis has to be put on detecting different horizontal velocity of work-piece cross section,often leading to a hundred thousand degrees of freedom even for plane strain calculations.The data obtained by using Abaqus Explicit coincide with the results determined by theory.A theoretical basis on deformation parameters and mechanical parameters during VGR process is provided.
Roller leveling process of longitudinal profile (LP) plate is hardly studied because plate thickness changes.Deformation characteristics and residual curvature during LP plate leveling process were investigated based on curvature integral by elastic-plastic differences.It was found that entry intermesh section is reduced with increasing thickness and entry intermesh should be from 0.7 to 1.1 mm for LP plate with 42/54 mm in thickness.In order to get satisfactory flatness along longitudinal direction,small entry intermesh should be selected and exit intermesh should be 0mm.In addition,thickness section for LP plate which can be leveled by 11 roller leveler is from 24 to 60 mm.Finally,there is an intermesh schedule that could level LP plate with initial curvature less than elastic limit curvature.
