The prediction of deformation length in cold roll-forming

Cold roll-forming is a process of forming metal from sheet, strip or coiled stock into shapes of essentially uniform cross-section by feeding the strips through successive pairs of rolls arranged in tandem. The deformation in cold roll-forming is quite complex and due to this inherent complexity of the process, the roll design and other decision-makings often involve a good deal of trial and error. The “forming angle” method, which is regarded as reasonably dependable for assisting in determination of the number of roll stations to form a bend, takes account of the intermittent deformation under each roll station only in a crude way. The present paper describes a method which predicts the deformation length under each roll station a priori by minimizing the deformation energy and assuming the material to be rigid-plastic. The theoretical results have been verified by roll forming channel sections from mild steel and aluminium strips and the agreement between the theory and the experiment has been found to be extremely good. The results also suggest that the deformation length depends on the physical parameters of the produced channel section but is practically independent of the mechanical properties of the workmaterial for the situations considered in the present investigation.     

小型专用拉弯矫直机的设计与工艺研究

镀锌薄钢带经常大量应用于冷弯型钢生产中,而在其生产过程中很容易出现板形缺陷。常见的辊式弯曲矫直设备通过单纯弯曲变形对钢带实施矫直,但无法胜任薄带复杂板形的矫正。拉伸弯曲矫直方法将拉伸和弯曲两种矫直工艺相结合,改变了钢带中性层的位置,经过多次拉直、弯曲能够实现钢带全截面延伸,能够同时实现钢带侧弯、波浪变形、坯料楔形等不良板形的矫直。为此我们开发了一种专门用于冷弯生产的小型拉弯矫直设备实现薄钢带的矫直功能。不但详述了设备机械、电气的研制与开发,而且采用有限元分析和现场试验相结合的方式,对特定产品的拉弯矫直工艺进行了研究。     

CO2 laser butt-welding of steel sandwich sheet composites

Steel sandwich sheets compared with conventional steel exhibit significant performance improvements such as lower density, higher specific flexural stiffness, and better sound and vibration damping characteristics. However, the main challenge for the broad industrial use is that the joining and assembling methods be used in such a way so as not to alter significantly these characteristics. In the present paper, a laser welding of steel sandwich is examined. The feasibility study of the laser butt-welding of sandwich steel sheets with a CO₂ laser beam has revealed that such an approach is possible. A theoretical model of the laser welding process is developed for the investigation of the laser beam impact on both the core and the outer steel layers of the sandwich material. The model presented is based on a novel idea for the simulation of the heat source through the finite element analysis for the estimation of the temperature distribution. Additionally, the effect on the quality of the weld, the strength of the welded sheet, and its damping characteristics are also experimentally investigated and prove that laser welding can be considered as an alternative joining process.     

Analysis of asymmetrical clad sheet rolling by stream function method

A mathematical model for asymmetrical clad sheet rolling is proposed by using the stream function method and the upper bound theorem to investigate the plastic deformation behaviour of sheets at the roll-gap. The curvature and thickness ratio of the rolled product and rolling power, effected by various rolling conditions such as roll speed ratio, roll radius ratio, initial thickness ratio and flow stress ratio of sheets, total thickness reduction, etc., are systematically discussed. Furthermore, experiments on asymmetrical clad sheet rolling are also conducted by employing aluminum, copper, and mild steel as layers of clad sheets. It is found that the theoretical predictions of the thickness ratio of the rolled products, rolling force, and rolling power are in good agreement with the experimental measurements. Through the study, it becomes clear that the proposed analytical method is applicable to simulate the asymmetrical clad sheet rolling processes and is able to offer useful knowledge in manufacturing clad sheets.     

冷轧钢板表面缺陷的形成原因

采用光学显微镜、扫描电镜、能谱仪等对冷轧钢板表面出现的大量长条状细线缺陷产生原因进行了分析。结果表明:出现大量的长条细线缺陷的原因是钢板在冷轧过程中被前几道次轧辊或输送辊辊道表面凸起物划伤,再经过后几道次继续轧制所致。     

Caracterisation du frottement outil–pièce en mise en forme à l'ambiante des aciers

Characterization of friction at the tool–billet interface in the cold forging of steel. A great number of steel billets used in the mechanical industry come from forging operations. That is to say that between the casting of the steel from the blast furnace to the ready to use billet, forging sequences such as drawing, backward and forward extrusions, stamping, etc., were involved, if necessary completed by cutting operations. The forging sequences, that can be carried out at or above room temperature, condition the integrity of the material. They are the source of residual stresses caused by plastic strains, that are usually needed to guarantee the good mechanical properties of the billets. On the other hand, they also imply severe conditions of contact which may lead to defects in the surface of the billets, such as scratches or cracks, or in core (tearing of sheets in stamping, etc.). The mastering of the conditions of contact is required in any optimization process of a fabrication line.     

Research and application of non-symmetrical roll bending control of cold rolling mill

The existing research of the flatness control for strip cold rolling mainly focuses on the calculation of the optimum adjustment of individual flatness actuator in accordance with the flatness deviation,which can be used for general flatness control.However,it does not work for some special rolling processes,such as the elimination of ultra single side edge-waves and the prevention of strip break due to tilting roll control overshooting.For the purpose of solving these problems,the influences of non-symmetrical work roll bending and intermediate roll bending on flatness control were analyzed by studying efficiencies of them.Moreover,impacts of two kinds of non-symmetrical roll bending control on the pressure distribution between rolls were studied theoretically.A non-symmetrical work roll bending model was developed by theoretical analysis in accordance with practical conditions.The model was applied to the revamp of a 1250 6-H reversible universal crown mill (UCM) cold mill.Theoretical study and practical applications show that the coordination utilization of the non-symmetrical work roll bending control and tilting roll control was effective in flatness control when there appeared bad strip single side edge waves,especially when the incoming strip was with a wedge shape.In addition,the risk of strip break due to tilting control overshooting could be reduced.Furthermore,the non-symmetrical roll bending control can reduce the extent of uneven distribution of pressure between rolls caused by intermediate roll shifting in flatness control and slow down roll wear.The non-symmetrical roll bending control technology has important theoretical and practical significance to better flatness control.     

冷弯型钢成型技术的发展现状

介绍冷弯型钢成型技术理论、成型工艺及冷弯成型计算机辅助设计（CARD）等方面的国内外发展现状,我国在冷弯型钢产业发展中存在的问题及对我国冷弯型钢技术发展的展望.     

Gap-free lap welding of zinc-coated steel using pulsed CO2 laser

CO₂ laser welding of zinc-coated steel sheets in the lap configuration has been a major research effort for the automotive industry for many years. The introduction of a gap between the sheets is one way of solving the zinc gas explosion problem. However, this requires sophisticated clamping devices and spacer materials. A homogeneous gap is therefore difficult to realise in high volume production. This paper describes a simple but useful approach for CO₂ laser welding of zinc-coated steel sheets in the lap configuration. By using a gated pulse mode, a seam welding process is developed that allows zinc-coated materials to be welded in a gap-free, overlap configuration. Laser seam welds in the lap configuration were produced in 0.7 mm-thick steel sheet with 7 μm zinc coating on both sides. A number of pulsed CO₂ laser welding parameters, including peak power, duty cycle, travel speed, pulse repetition rate, and pulse energy, were identified. Furthermore, the effects of pulsed CO₂ laser welding parameters on weldability were also investigated. The study shows that through the proper selection of welding parameters, it is possible to produce visually sound welds where porosity is still unavoidably formed. It was observed that decreasing the welding speed could reduce the porosity within the visually sound welds.     

Experimental investigation of transient and thermal effects on lubricated non‐conformal contacts

In this work, thermal and transient effects on non‐conformal lubricated contacts are investigated through experimental analyses. Experiments between a ball and a plane surface of a disc are described. Friction coefficients and film thicknesses are measured (the film thickness only for the glass‐on‐steel contact). A paraffin base mineral oil is used as a lubricant. First experiments are carried out under steady‐state conditions. To include effects due to different thermal properties of contacting materials, a steel‐on‐steel and a glass‐on‐steel contact with different slide‐to‐roll ratios are tested. If the contacting materials have different thermal properties, as in the case of a glass‐on‐steel contact, thermal effects like the temperature–viscosity wedge action could clearly be shown. It is found that the friction coefficients are influenced by the slide‐to‐roll ratio and the thermal properties of the contacting materials. Under transient conditions, the entraining velocity is varied with a sinusoidal law. Squeeze effects explain ‘loops’ of friction and film thickness found also in previous works. The formation of friction loops is related to the measured film thickness differences. However, also under non‐steady‐state conditions, thermal effects, like the temperature–viscosity wedge action, influence the friction coefficients. Copyright © 2007 John Wiley & Sons, Ltd.     

The prediction of roll load in cold roll-forming

Due to the inherent complexity of the cold roll-forming process, machine design procedures have remained highly empirical. There is little information available on the calculation of roll load, though a prior knowledge of this load is essential for the optimum design of the roll stands and the smooth forming of the strip. The present paper describes a semi-empirical method for calculating the roll load. The method is based primarily on equating the external work to the internal dissipation of energy. The estimate has also been modified to take account of the reverse bending of the deformed strip after it reaches the next roll station. The theoretical results have been verified by roll-forming channel sections of mild steel and aluminium and measuring the load with a specially designed quartz dynamometer. The agreement between theory and experiment has been found to be good in spite of the many assumptions which are necessary to simplify the analysis. The results also show how the roll load depends on the material properties, the geometrical parameters of the produced section and the machine dimensions.     

双相钢换热管与管板焊接工艺研究

采用管板自动TIG焊方法进行双相钢换热管与管板焊接工艺试验,通过着色检测、射线检测、焊喉尺寸测量、拉脱力试验、硬度试验等对焊接接头进行测试,从而确定了合理的管板焊接工艺,并掌握了双相钢的焊接特点。     

Analysis of deformation textures of asymmetrically rolled steel sheets

Asymmetric rolling has been studied to obtain the shear deformation texture of bcc steels through the thickness. Asymmetric rolling in which the circumferential velocities of two working rolls are different can be achieved by different roll radii at the same rotation rates, different roll speeds at the same roll radii and single roll drive. The deformation of steel sheets in the three different asymmetric rolling methods was analyzed by FEM. The deformation was used to calculate crystal rotation by full constraints Taylor model to predict the deformation textures. The texture evolution during the asymmetric rolling was measured and analyzed with the emphasis on the effect of shear reversions.     

海洋平台吊点失效分析及安全评定

用有限元方法对某海洋平台吊点焊接结构进行应力分析，计算结果表明，吊点最大等效应力出现在吊点板与筒体连接的纵向焊缝下端；同时，对吊点焊接接头进行裂纹敏感性试验分析和断裂韧度(COD)的测试。试验结果表明，该吊点用钢在厚度方向上无论是塑性还是韧度均较低，存在层状撕裂倾向。另外，依据BS6235规范对该吊点最大等效应力发生处的焊缝进行断裂性能安全评定，给出该处的容许缺陷尺寸。     

Analysis of sandwich sheet rolling by stream function method

A mathematical model for symmetrical sandwich sheet rolling is proposed by using the stream function method and the upper bound theorem to investigate the plastic deformation behavior of sheets at the roll-gap. The velocity fields derived from the newly proposed stream functions can automatically satisfy the volume constancy and the velocity boundary conditions within the roll-gap. Effects of various rolling conditions such as the thickness ratio and flow stress ratio of sheets, total thickness reduction, friction factor between the sheet and roll, etc., upon the thickness ratio of the rolled product, the relative length of the plastic region in each layer, rolling force and rolling power are discussed systematically. Furthermore, experiments on sandwich sheet rolling are also conducted by employing aluminium, mild steel and stainless steel as layers of sandwich sheets. It is found that the theoretical predictions of the thickness ratio of the rolled products and rolling force are in good agreement with the experimental measurements. Through the study, it becomes clear that the proposed analytical method is applicable for simulating the sandwich sheet rolling processes and is able to offer useful knowledge in manufacturing sandwich sheets.     

Developing Techniques for Testing Magnetic Properties of Electric Steels. II. Variations in Magnetic Properties and Their Effect on Reliability of Testing Results (review article)

The paper presents experimental data concerning the magnitude and character of variations in magnetic properties of electric steels (among a number of sheets, within one sheet, over the length and width of a roll, etc.). The paper also considers effects of variations in magnetic parameters of steel on the quality of fabricated components and reliability of measurements of steel parameters conducted in accordance with the existing State Standards by testing one selected sample cut from single sheets of a batch, or from the beginning or end of a roll on an Epstein's apparatus. The inhomogeneity of magnetic parameters is a natural consequence of the instability of the technological process of the steel manufacture on all its stages and on the stages of its transformation (chemical composition, smelting conditions in which slabs for rolling are produced, regimes of rolling and annealing, etc.), therefore these parameters usually obey the law of normal distribution. Feasibility of more efficient methods of steel testing designed to optimize and improve the reliability of testing results is discussed.     

双金属复合板冷轧变形行为的Avitzur上限模式分析

应用Avitzur上限理论建立双金属冷轧塑性变形模式的数学模型。应用此模型计算变形区域的速度场、能量消耗及轧制力的上限解等变形行为,给出相关参数的相应计算公式。应用这些理论公式对铝-钢复合板进行分析,计算与试验结果得到较好的吻合。分析模型能够很好地应用于模拟双金属冷轧过程,并能为双金属复合板的生产提供一些有益的理论依据。     

镍铝青铜焊丝进行镁/镀锌钢板点焊的焊接性分析*

以镍铝青铜焊丝为填充材料,对AZ31B镁合金/镀锌钢板进行冷金属过渡点塞焊试验研究,分析镁板上孔直径对镁钢点塞焊接头力学性能的影响.并通过分析焊接接头微观组织及其元素分布状况来研究其连接机理。研究结果表明：使用镍铝青铜焊丝能够得到焊缝美观的镁/镀锌钢异种金属的连接接头。镁/钢板焊接接头的焊缝主要由α-Cu和CuAl₂组成,熔合区由镁的固溶体α-Mg以及Al₂Cu₃Mg₂和Mg₂Cu混合的金属间化合物组成。镁板上孔的直径对镁钢接头性能有很大的影响。随着镁板孔径的增大,镁钢点塞焊接头的最大抗拉载荷先增大后减小,且当镁板孔径为5 mm时接头的最大抗拉载荷达到最大为3.4 kN。焊缝金属和镁母材的连接处即熔合区存在大量脆性金属间化合物,使得镁/钢接头整体力学性能较差。     

Development of a new three-stage cold rolling manufacturing technology for grain-oriented silicon steel sheets

The purpose of this paper is to present some important parameters and new results, which control various stages of the manufacturing process to obtain new grain-oriented silicon steel sheets. A three-stage cold rolling method is employed for production. The results can be used to further reduce core losses of current silicon steel sheets by additional reduction of their thicknesses or increasing the silicon content of conventional grain-oriented silicon steel sheets without problems in the cold rolling stages.     

An approximate analysis of hot-strip rolling—A new approach

A new method of predicting the effect of rolling parameters on the roll pressure, roll force and power and energy consumption in hot-strip rolling is presented. This method is based on approximate solutions to the velocity, strain-rate and stress distributions in the roll gap. The degree of approximation was examined by comparison with finite element solutions. The theoretical predictions were compared with experimental data from hot rolling of steel strips and plates.