Papers by Author: Sheng Zhi Li

Abstract: A 3-D thermal-mechanical model was built to simulate the hot rolling process of medium plate, with the aid of nonlinear commercial FE code MSC.SuperForm on a company's actual process parameters. The hot rolling process of single-pass which slab thickness is 180mm was simulated, and the influence of pass reduction on metal flow, stress-strain field, contact stress and rolling force were researched. The study revealed that pass reduction should be at least 20% by increase depress in pass in addition to rolling efficiency. As that, rolling efficiency be increased, roll contact stress be brought down, and its service life be prolonged. And metal plastic strain enhanced, metal flow increased, but its strain field non-uniformly distributed, metal flow and plastic deformation would be strengthen by increase pass reduction, and the lateral broadening in the head is bigger than that in the tail.

Abstract: With the aid of commercial FE code MSC.SuperForm, the structural steel tube continuous rolling process of a typical hollow tube specification 152.5×12.5mm is simulated based on Bao Steel 152.5 main pass sequence of 140mm 8-stand mandrel mill, and the distribution characteristics of stress/strain, outline lateral spread, temperature changes of workpiece in continuous rolling process and distribution of stress/strain, friction of workpiece in deformation zone are analyzed. Analysis results indicate that deformation of workpiece along the width of the groove, especially at the top and the bottom of the groove is highly inhomogeneous due to the unequal draught and the longitudinal stress of special position (the top and the bottom of the groove) of workpiece is always an alternate state, in a tensile-compressive-tensile manner, and has a distinct rule. In the first stand, outline dimension of workpiece gradually increases during reducing process and early stage of wall thickness reduction, but it gradually decreases during middle-late stage of wall thickness reduction and tends towards stability at last. It is inhomogeneous that distribution of unit compressive stress and longitudinal strain of workpiece in deformation zone, and contact stress and total equivalent plastic strain are maximal in inner surface of workpiece contacting with mandrel. Temperature difference between the outer and the inner surfaces of workpiece is obvious.

Abstract: In continuous tube rolling process, wall thickness reduction per stand will be changed due to wall thickness fluctuation of pierced shell caused by piercing process, which results in changes in metal flow conditions and affects force parameters, deformation parameters, especially transverse wall thickness precision of rolled hollow tube. In this paper, with the aid of commercial FE code MSC.SuperForm, the high pressure boiler steel tube continuous rolling process of a typical hollow tube specification 133.0×4.0mm are simulated based on 133 main pass sequence of 89mm 6-stand semi-floating mandrel mill, and force parameters, equivalent plastic strain, transverse wall thickness precision, outline dimension and real roundness of rolled hollow tube are analyzed and compared on the condition of two different wall thicknesses of pierced shell. Analysis results indicate that force parameters increase with wall thickness of pierced shell, maximal rolling force, rolling moment and mandrel axial force increase 10% or so in the first three stands when rolling pierced shell of wall thickness 11.5mm compared to that of wall thickness 10.5mm. When rolling pierced shell of wall thickness 10.5mm, there exist front and back tensions among the third, the fourth and the fifth stands and outline dimension and real roundness of rolled hollow tube is slightly better. However, transverse wall thickness of rolled hollow tube at the bottom of groove is pulled thin obviously.

Abstract: The Fomichev plug is of characteristic producing equal unit-reduction of wall thickness along its perforation section during seamless tube piercing. This paper introduces the design of a novel Fomichev plug based upon the analysis of roll opening, taking into account for both feed angle and toe angle of a cone type piercer, then presents a 3-D coupled thermo-mechanical simulation of the novel Fomichev Plug’s performance characteristic during cone-roll piercing process, with the aid of FE code MSC.SuperForm. In comparison with conventional plugs, as FEM simulation result shows that the new plug makes the metal deformation distribute uniformly along its perforation section, which brings about well-distributed plug wear. The novel Fomichev plug is able to decrease the slip between the roll and workpiece and avoid rolling block owing to its smaller plug force, which can increase piercing efficiency so, moreover, analyzing stress distribution, it’s more suitable for metal deformation with fewer defects in tube piercing, makes resistance to metal elongation smaller, reduces wedge cleaving to tube billet, and prevents lamination defects during piercing high-alloy billet.

Abstract: In continuous tube rolling process, it has an obvious influence on the stability of rolling process, tools wear and the quality of rolled hollow tube that configuration of roll rotational speed per stand. In this paper, various roll working diameters per stand are determined by velocity integral method (VIT) and FEM respectively, and two roll rotational speed schedules are obtained correspondingly based on 133 main pass sequence of 89mm 6-stand semi-floating mandrel mill. With the aid of commercial FE code MSC.SuperForm, the high pressure boiler steel tube continuous rolling process of a typical hollow tube specification 133.0×5.2mm are simulated, and force parameters, transverse wall thickness precision, outline dimension and real roundness of rolled hollow tube and clearance between the mandrel and rolled hollow tube are analyzed and compared on the condition of two different roll rotational speed schedules, which provides scientific basis for configuring reasonable roll rotational speed per stand in pass design and optimization. Analysis results indicate that roll working diameter obtained per stand is smaller and roll rotational speed configured is higher correspondingly using FEM compared to VIT. Using FEM, there exist front and back tensions between stands and maximal rolling force, rolling moment and mandrel axial force decrease 10% or so in continuous tube rolling process, and outline dimension and real roundness of rolled hollow tube is better. However, transverse wall thickness of rolled hollow tube at the bottom of groove is pulled thin slightly, and clearance between the mandrel and rolled hollow tube is less than normal.

Abstract: Concerning the 3-roll skew rolling process of round billets, a 3-D thermo-mechanical coupled simulation is performed with the aid of commercial FE code MSC.SuperForm. The influence of the feed angle and inlet cone angle of the roll on the strain and damage filed are investigated. It is found that the distribution pattern of the equivalent plastic strain in the longitudinal section of the billet presents U-shape, and that the feed angle and inlet cone angle of the roll make difference in the gradient of deformation intensity in radial direction of round billet. The ring-shaped distribution of the damage field in transverse cross section of the billet indicates a high tendency for the ring-shaped inner crack to occur, instead of the center crack appearing in 2-roll skew rolling of round billet. The results show that the critical parameters to control the ring-shaped crack during the 3-roll skew rolling process are the feed angle and inlet surface cone angle of the roll. It should be avoided to use too large feed angles so as to reduce the tendency of annular inner crack in the actual rolling of high-alloy steels with poor hot workability.

Abstract: the aid of commercially available software MSC.SuperForm, a 3-D finite element model has been established to simulate the rolling process of steel tubes on the stretch reducing mill (SRM) with group centralized differential drive in certain factories. A special effort was made to analyze the fluctuation of transverse wall thickness uniformity. It was found that the wall thickness of each stand was accumulated in the original pass 50°~60° along the circumferential direction, which caused the formation of the inner hexagon defects and worsen. In view of this, this paper proposes a modified roll pass design method which uses the interactive technology of CAD graph curve and MATLAB equation. By means of decreasing the lateral curvature of roll pass contour curve to enlarge the contact length between the tube and groove, also the rolling process using the new pass system were simulated and analyzed. The results indicate that the design of such polygonal roll pass can be effective in improving the inner hexagon defects.

Abstract: The seamless steel tube continuous rolling process with 8-stand full-floating mandrel is simulated with the aid of commercial FE code MSC. SuperForm. The relationship is analyzed between the distribution of the transverse wall-thickness and the speed schedule of the rollers. The result shows that the transverse evenness of the wall thickness of the tubes can be enhanced by optimizing the speed schedule. Furthermore, by adopting meliorated method to measure the wall-thickness of the shell, the error is reduced while data reliability is increased. When using the existing equipments (mandrel mill), it is an effective way to improve the transverse wall-thickness accuracy of the shell tube by adjusting the speed schedule. Compared with present roll speed schedule, the transverse wall-thickness accuracy can be increased by 10% for the rolling of elongated shell with 152.5mm in OD and 6mm in wall thickness tube under the 3# speed schedule put forward in this paper.

Abstract: With the aid of commercial finite element analysis software MSC. Superform, the high pressure boiler steel tube continuous rolling process with 6-stand semi-floating mandrel is simulated, and the distribution characteristic of transverse wall thickness is analyzed. It indicates that it presents “M” shape that the distribution of transverse wall thickness of hollow tube along one-fourth groove periphery. Transverse wall thicknesses have low values at the top, the bottom and sidewall 45 degree or so of groove, and they have high values at the sidewall 23 degree and 67 degree or so of groove. Then the improved measure is put forward on the basis of analyzing the causes responsible for transverse wall thickness. By the comparison of the simulation results, they have been improved obviously that transverse wall thickness precision and real roundness of rolled hollow tube using the improved measure.

Abstract: The inner surface crack (ISC) defect easily occurs in seamless modified 9Cr-1Mo steel tubes rolled by the mandrel mill with high production efficiency. The reason for the formation of the ISC lies in both the properties of deformed material and rolling conditions. With the aid of commercial FE code MSC.SuperForm, the rolling process of modified 9Cr-1Mo seamless steel tube produced by the Mandrel Mill of Bao Steel in China was simulated, focusing on mechanical analysis of deformed metal. It was found from the simulation that the metal on the inner surface of the tube, in the position of 0 or 90 of the roll pass, experiences strong tensile stresses, especially the circumferential stress, which is closely related .to the strain behavior governed by the two-high pass caliber of the mandrel mill. Therefore an optimal design of the roll pass can be realized to decrease the tensile stress so as to relax the tendency to the ISC, which has been confirmed by the tests in Steel Tube & Pipe Company of Bao Steel.