Calculation of the layer thickness ratio in the rolling of two- and three-layer strips from metallic powders

Summary The relationship of the velocities of powders in various hopper sections was determined experimentally. From these data, formulas have been derived for calculating the layer thickness ratio during the rolling of two- and threelayer strips, taking into account the nonuniformity of motion of the powders in the hopper. No effect of rolling velocity (within the range investigated) on the layer thickness ratio during the rolling of two-layer strips was noted in this study. Hence, the formulas proposed for calculating the layer thickness ratio are valid in a wide range of rolling velocities for two- and three-layer strips.     

Macromechanism of powder deformation in the incoherent zone during rolling

Conclusions Observation of the deformation of a free-flowing material through transparent hopper walls is a technique yielding a great deal of useful information and enabling the deformation behavior of powders to be studied in the lag zone (breaks in the velocity field, formation of arch structures, and the like). A binding link between the geometric and physical parameters of the powder rolling process is the initial powder compressibility. An increase in the intensity of the shear deformation of powders before the commencement of their irreversible densification suggests that impeded deformation zones may not be able to form above the angle of rolling.Translated from Poroshkovaya Metallurgiya, No. 9(237), pp. 1–7, September, 1982.     

金属粉末轧制

金属粉末轧制机理与传统的致密金属轧制机理不同 ,在这里适用的是粉末轧制前后粉末重量相等原理。粉末轧制变形区可简单地化分为粉末供料区和压实区。影响带材性能的主要因素有原始金属粉末的工艺性能和轧制工艺条件。     

锥辊非对称布置下轧制变形区参数的确定

锥辊非对称布置下轧制是利用不均匀轧制理论,高效、连续和大量生产螺旋物料的过程。轧制变形区是由两工作辊面构成。调整两辊的相对位置,就可得到不同旋向、不同尺寸(螺径和螺距)的螺旋物料。其原因是这种调整使两辊面所控制轧制变形区参数发生了变化。研究变形区并确定其参数,是轧机从“经验试轧法”过渡到高效、科学调整的理论基础,并使不均匀轧制理论研究和应用日趋完善。     

FEM Analysis of Physical Field in Level Rolling Process of Inversion Casting by ANSYS Program

Ininversioncastingprocessmothersheetisledthroughameltwhichthencrystallizesonthesurfaceofthestrip.Throughacoupleoflevelrollersabovethemeltthecastingstripisroughlyrolled,thefigureisshownintheReference[1].Levelrollingisveryimportantintheprocess.　　ThevaluesimulationtechnologyonthebasisofFEMhasbeenusedgraduallyinthefieldofmetalplasticforminginrecent20years.Thetheoriesareadoptedfromsmallelastic-plasticdeformationFEMtobigelastic-(viscidity)plasticdeformationFEM,andtheanalysistechnologyisbecomin…     

Formation of shear and densification zones during metal powder rolling

Conclusions Fluoroscopy offers the most effective means of obtaining comprehensive information concerning the deformation of metal powders during rolling. The process of powder densification in the region of deformation during rolling is composed of separate, distinct stages, which is linked with the fact that densification in the shear zone is accompanied by a process involving a decrease in density. The formation of slip bands in the impeded deformation zone of and structural blocks of powder is characterized by a certain periodicity. The size of structural blocks and periodicity of slip band formation are function of powder particle size.Translated from Poroshovaya Metallurgiya, No. 11(227), pp. 10–15, November, 1981.     

Cold and hot rolling of iron powder

Conclusions A BPMF atomized iron powder heated for 20 min at a temperature of 800, 900, 1000, or 1100°C is still characterized by good flowability, readily descends into the region of deformation, and can be rolled into strip. At a temperature above 1100°C this powder sinters into a bar, and can no longer be rolled. The mechanical properties of hot-rolled strips are an order higher than those of cold-rolled ones. Even so, the mechanical properties of strips produced by the hot rolling of the powder under the conditions of the experiments described are inferior to those of P/M parts shaped at room temperature and sintered under optimum conditions. In experiments on the hot rolling of powders between rolls with plain barrels it has proved impossible, because of axial splitting and edge cracking, to obtain nonporous strip of width up to 60 mm. The hot rolling of powders into narrow strips should be performed in closed passes; to reduce the cost of rolls, wide strips should be rolled hot between plain roll barrels, and their edges should then be trimmed.Translated from Poroshkovaya Metallurgiya, No. 10(226), pp. 13–18, October, 1981.     

六辊CVC冷轧机凸度控制能力分析及应用

 基于三维有限元建立了六辊CVC辊系模型,该模型耦合了CVC辊形曲线、辊间轧制力分布以及带钢的弹塑性变形和辊系弹性变形,通过迭代计算辊间轧制力及轧辊与轧件的弹塑性变形。通过实际轧制规程数据对比验证了模型的有效性,其模拟计算结果与实际数据的绝对误差在10 μm内,相对误差小于1%。采用该模型研究了板形控制机构如中间辊弯辊、中间辊窜辊和工作辊弯辊对带钢2次凸度和4次凸度的控制规律,并成功消除了生产现场宽薄带钢的边中复合浪缺陷。     

薄带材轧制的最小可轧厚度理论及数值模拟

 智能制造、电子通信等行业向微型化、集成化方向发展要求不断提升精密轧制带材产品质量,提高厚度精度控制是其中关键组成部分,因此,精密带材轧制过程接触变形区理论研究有着极其重要的意义。以Stone轧制力模型为代表的传统薄带材冷轧理论假设轧辊在接触变形区内保持圆弧状轮廓,利用Hitchcock公式求解接触弧长进而求得平均单位压力,并在此基础上建立了Stone最小可轧厚度理论。在试验及实际生产中很多学者发现有时Stone轧制力计算值与实际值相差甚远,这是由于某些轧制工况下接触变形区内存在中性区,轧辊圆弧状假设不再适用。中性区的存在使轧制力剧烈增大而带材金属延伸变形增加甚微,即轧制难度增大、轧制效率降低。通过对不同厚度薄带材轧制过程进行有限元分析,得到了不同道次压下率下接触变形区轮廓与接触压力分布的变化规律,带材初始厚度越小或道次压下率越大,接触变形区内中性区所占比例越大,接触压力分布趋于椭圆形分布;基于Stone轧制力公式建立了考虑轧制效率的薄带材最小可轧厚度模型,对于一定初始厚度与Stone最小可轧厚度比值,根据轧制工艺参数可计算接触变形区内恰好不存在中性区时的临界道次压下率,以此临界道次压下率为依据可确定高效轧制厚度范围及Stone轧制力模型的适用条件,为精密薄带材轧制生产过程提供理论指导。     

A mathematical model for flat rolling of austenitic steel at elevated temperatures

The paper is concerned with the mathematical model for the computation of the technological as well as force and energy parameters during rolling of austenitic steel sheets and strips at elevated temperatures. On the basis of the computation results obtained for 18–8 type chromium-nickel steel (marked 1H18N9T) universal nomograms have been designed for a wide range of strip width and roll diameters. They allow the evaluation of force parameters, energy consumption and average temperature in the roll pass depending on the reduction and strip initial temperature as well as strip relative thickness. The presented nomograms might be helpful in designing the technology for warm rolling of austenitic steel sheets and strips as well as conventional cold-rolling, taking into consideration thermal effects in the deformation zone.     

Theory and Practice of Rolling Metal Powders

The theoretical and technological fundamentals are considered for rolling metal powders. The equipment and production schemes for rolling powders is described as well as unit for feeding powder between rolls for the case of manufacturing two-layer strips. The main technological schemes for production copper rollings are presented.     

Three-layer copper-iron-copper strips of metal powder

Summary The experimental study of the effect of the dimensions of the feed mechanism and the properties of powder upon the relative thickness of copper and iron layers in pore-free strip was carried out. An equation is suggested for the calculation of the relative thickness of copper layers in pore-free strips prior to rolling; this equation takes into account the setting of the feed apparatus and the properties (volume weight) of powders. The calculated data is in good agreement with experimental results. The agreement of the three-layer metal-powder strip with the standard specifications is not worse than that of the strip made of laminated ingots.     

Simulation of contact stresses and forces during hot rolling of thin wide strips with allowance for a stick zone and elastic regions in the deformation zone

A new procedure for the calculation of contact stresses and hot-rolling forces for wide strips 0.8–1.5 mm thick has been developed and tested. This procedure takes into account the presence of a stick zone in the deformation zone and stress distributions in both elastic and plastic regions in the deformation zone. The average error in the force calculation according to the new procedure is 5%, which is more than two times smaller than the calculation error of well-known force calculation procedures. The developed procedure is used to simulate the contact stresses in the deformation zones of working stands in a six-stand 1700 mill during rolling of strips thinner than 1.0 mm. A number of new relations for the state of stress in a strip have been revealed upon simulation. Some of these relations are as follows: in the last stands, the length of elastic regions accounts for 10–17% of the total deformation-zone length; the maximum normal contact stresses are 1300–1400 MPa, which corresponds to the stresses in the deformation zones of cold-rolling mills; the stick-zone length accounts for 85–99% of the deformation-zone length; and the contact stresses in the stick zone are virtually independent of the friction coefficient. The developed calculation procedure can be used to optimize the technological regimes of wide-strip mills.     

Roller grooving in ball-rolling mills. Part 1

In ball rolling, the metal is deformed in rollers with helical grooves. Accordingly, the deformation zone may be dividing into the shaping section, where the blank is captured and rolled and the ball is formed, and the finishing section, where the ball is smoothed, its final dimensions are attained, and the links between balls are severed. For normal rolling, the shaping section is calibrated. In the present work, the roller grooving for a spherical blank is calculated, when the ball diameter is 125 mm. The initial data for grooving of the ball mill are presented.     

Improvement of the conditions of high-accuracy rolling of soft magnetic strips due to the application of a refined mathematical model of the process

The specific features of deformation during cold rolling are studied to develop a refined model for the cold rolling of precision soft magnetic strips. The results of development of the theory of cold rolling are used for highly worked thin strips to calculate and optimize the technological conditions of production of a wide range of precision strips applied in instrument making, electrotechnical industry, and so on.     

铸轧薄带的边部斜裂纹形成机理

 为了控制铸轧薄带产品质量,降低铸轧工艺本征裂纹导致的断带风险,针对铸轧薄带的边部斜裂纹展开研究,提出边部斜裂纹形成的直接原因为侧封与熔池间的换热使熔池边部的Kiss点高度局部提升。该处薄带进入铸轧塑性变形阶段的初始厚度局部增大,由此引发的斜向剪应力导致了边部斜裂纹的产生。建立了熔池的热-流耦合数值仿真模型,分析了Kiss点高度沿铸轧辊宽度方向上的分布规律,结果显示熔池边部的Kiss点高度高于熔池中心。建立了热-力耦合数值仿真模型,分析了变厚度薄带热轧时其塑性变形区内的应力分布状况,结果显示斜向剪应力集中分布于后滑区边部,其方向与后滑区金属的流动方向一致。仿真结果验证了所提出的边部斜裂纹形成机理的合理性。     

State of stress in the deformation zone during rolling of high-strength plate steel

A new mathematical model is developed for the state of stress in the deformation zone for plate rolling, including rolling under controlled conditions at a low temperature in the last passes. The stick zone during plate rolling is shown to account for 88–99% of the deformation zone, and the fraction of elastic regions in the deformation zone in the last passes at low temperatures can reach 12%. When the stick zone and elastic regions of the deformation zone are taken into account, the roll-force calculation error is less than 5–6.5%. The model developed can be used to optimize plate-rolling conditions, including the conditions of integrated deformation-thermal production.     

Research into an additional mechanism of lowering the pressure and increasing the compressions during the asymmetric rolling of strips of aluminum alloys

The variation in the longitudinal deformation of strips of aluminum alloys during symmetric and asymmetric rolling is investigated experimentally. The results revealed an additional mechanism by which the rolling pressure is lowered and the single compactions are increased during asymmetric rolling.     

The rolling coefficients of metal powders

Summary The investigation established that, in contrast to compaction in a closed die, the compressibility coefficient for the rolling of metal powders is not equal to the densification coefficient. The ratio of the compressibility coefficient to the densification coefficient for the rolling of metal powders gives the extension coefficient of the powder volume, the value of which is constant for each material being rolled and is always greater than unity.With a gravity feed of powder, the values of the compressibility and densification coefficients are uniquely determined by the maximum specific pressure and, consequently, by the strip density. When the rolling width, strip thickness, and angle of rolling are varied by changing the conditions of powder feed into the deformation zone at a given strip density, the rolling coefficients are not affected.     

Deep‐drawing quality of cold rolled sheet made of ferritically rolled hot strip

In the so‐called ferritic rolling the finishing is shifted down into the temperature region of ferrite, which enables a production of thinner hot strips (compared to the conventional hot rolling in austenite) with a changed texture development. The present study is focused on the effect of the process parameters of such initial warm rolled hot strips on the texture formation and hence on the deep‐drawing quality of the final cold strips. A special attention is given to the transmission of the hot strip texture to the cold strip. The investigation was carried out on commercial IF‐ and ELC‐steels by a laboratory simulation with the hot deformation simulator Wumsi (rolling simulated by the plane strain compression test). It was possible to optimize cold rolling and subsequent annealing by means of the measurements of the texture development during the ferritic (warm) deformation as well as the parameters of the processing route of such special production of cold strips by means of the calculation of r‐values. If compared with the conventional processing route, a considerable improvement of deep‐drawability with a diminished earing is achievable especially with the IF‐steel.