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1、RollingObjectiveTo perform rolling process on an lead bar in order to observe the change in both the cross-sectional area and the general shape.Theory1. DefinitionFlat rolling or Rolling is defined as the reduction of the cross-sectional area of the metal stock, or the general shaping of the metal p
2、roducts, through the use of the rotating rolls 1. It allows a high degree of closed-loop automation and very high speeds, and is thus capable of providing high-quality, close tolerance starting material for various secondary sheet metal working processes at a low cost 1.2. Schematic Drawing of Rolli
3、ng ProcessFigure 1. Rolling Process 2The rolls rotate as illustrated in Figure 1. to pull and simultaneously squeeze the work between them. The basic process shown in Figure 1 is flat rolling, used to reduce the thickness of a rectangular cross section.Figure 2. Various configurations of rolling mil
4、ls: (a) two high, (b) three high, (c) four high, (d) cluster mill, and (e) tandem rolling mill 2.Various rolling mill configurations are available to deal with the variety of applications and technical problems in the rolling process. The basic rolling mill consists of two opposite rotating rolls an
5、d is referred to as a two-high rolling mill (Figure 2a). In the three-high configuration Figure 2(b), there are three rolls in a vertical column, and the direction of rotation of each roll remains unchanged. To achieve a series of reductions, the work can be a passed through from either side by rais
6、ing or lowering the strip after each pass. The equipment in a three-high rolling mill becomes more complicated, because an elevator mechanism is needed to raise and lower the work 2.Roll-work contact length is reduced with a lower roll radius, and this lads to lower forces, torque, and power. The fo
7、ur-high rolling mill uses two smaller diameter rolls to contact the work and two backing rolls behind them. Another roll configuration that allows smaller working rolls against the work is the cluster rolling mill.To achieve higher throughput rates in standard products, a tandem rolling mill is ofte
8、n used. This configuration consists of a series of rolling stands. With each rolling step, work velocity increases, and the problem of synchronizing the roll speeds at each stand is significant 2.3. General Overview of ProcessThe primary objectives of the flat rolling process are to reduce the cross
9、-section of the incoming material while improving its properties and to obtain the desired section at the exit from the rolls. The process can be carried out hot, warm, or cold, depending on the application and the material involved. The rolled products are flat plates and sheets. Rolling of blooms,
10、 slabs, billets, and plates is usually done at temperatures above the recrystallization temperature (hot rolling). Sheet and strip often are rolled cold in order to maintain close thickness tolerances.Basically flat rolling consists of passing metal between two rolls that revolve in opposite directi
11、ons, the space between the rolls being somewhat less than the thickness of the entering metal. Because the rolls rotate with a surface velocity exceeding the speed of the incoming metal, friction along the contact interface acts to propel the metal forward. The metal is squeezed and elongated and us
12、ually changed in cross section. The amount of deformation that can be achieved in a single pass between a given pair of rolls depend on the friction conditions along the interface. If too much is demanded, the rolls will simply skid over stationery metal. Too little deformation per pass results in e
13、xcessive cost. Rolling involves high complexity of metal flow during the process. From this point of view, rolling can be divided into the following categories 3: Uniform reduction in thickness with no change in width: Here, the deformation is in plane strain, that is, in the directions of rolling a
14、nd sheet thickness. This type occurs in rolling of strip, sheet, or foil. Uniform reduction in thickness with an increase in width: Here, the material is elongated in the rolling direction, is spread in the width direction, and is compressed uniformly in the thickness direction. This type occurs in
15、the rolling of blooms, slabs, and thick plates. Moderately non-uniform reduction in cross section: Here, the metal is elongated in the rolling direction, is spread in the width direction, and is reduced non-uniformly in the thickness direction. Highly non-uniform reduction in cross section: Here, th
16、e reduction in the thickness direction is highly non-uniform. A portion of the rolled section is reduced in thickness while other portions may be extruded or increased in thickness. As a result, in the width direction metal flow may be toward the center 3.Hot RollingThe distinctive mark of hot rolli
17、ng is not a crystallized structure, but the simultaneous occurrence of dislocation propagation and softening processes, with or without recrystallization during rolling. The dominant mechanism depends on temperature and grain size. In general, the recrystallized structure becomes finer with lower de
18、formation temperature and faster cooling rates and material of superior properties are obtained by controlling the finishing temperature 1.Hot rolling offers several advantages 1:1) Flow stresses are low, hence forces and power requirements are relatively low, and even very large workpieces can be d
19、eformed with equipment of reasonable size.2) Ductility is high; hence large deformations can be taken.3) Complex part shapes can be generated.The upper limit for hot rolling is determined by the temperature at which either melting or excessive oxidation occurs. Generally, the maximum working tempera
20、ture is limited to 50C below the melting temperature. This is to allow the possibility of segregated regions of lower melting material 4.Cold RollingCold rolling, in the everyday sense, means rolling at room temperature, although the work of deformation can raise temperatures to 100-200C. Cold rolli
21、ng usually follows hot rolling. A material subjected to cold rolling strain hardness considerably. Dislocation density increases, and when a tension test is performed on this strain-hardened material, a higher stress will be needed to initiate and maintain plastic deformation; thus, the yield stress
22、 increases. However, the ductility of the material as expressed by total elongation and reduction of area drops because of the higher initial dislocation density. Similarly, strength coefficient rises and strain-hardening exponent drops. Crystals (grains) become elongated in the direction of major d
23、eformation 1.Cold rolling has several advantages 1:1) In the absence of cooling and oxidation, tighter tolerances and better surface finish can be obtained.2) Thinner walls are possible.3) The final properties of the workpiece can be closely controlled and, if desired, the high strength obtained dur
24、ing cold rolling can be retained or, if high ductility is needed, grain size can be controlled before annealing.4) Lubrication is, in general, easier. Rolling Problems and DefectsThe main problem during rolling process is the calibration of rollers. This calibration faults may occur in case of used
25、bearings and may affect the thickness of parts. A simple classification is as here below:a. Lengthwise Occurring DefectsChange of rollers speedMaterial temperatureRoller temperatureInlet thicknessMaterial propertiesEccentric and conical rollersUsed bearingsb. Transversally Occurring DefectsParallel
26、position of rollersSurface geometry of rollers轧 制目的：为了观察在执行轧制过程中铅条的横截面积和一般形状的变化。理论：1. 定义 扁平孔型轧制或者轧制被下定义为金属原料代表性面积的缩小，或金属制品通过旋转轧辊的一般成形。它允许一个闭合循环自动化的高程度和高速度，而且因此能够为各种以一个低成本工作程序的中级金属片提供高质量, 小公差的原材料.12. 轧制过程的示意图 图1 轧制过程2轧辊旋转如图 1 所示同时地在他们之间进行拉压工作。在 图1 所示的基本过程是扁平孔轧制，通常用来减少矩形断面的厚度。图2.各种结构的轧钢机：(a)二辊式轧机，(b)
27、三辊式轧机（c）四辊式轧机，（d）多辊式轧机，(e)串联式轧机。各种结构的轧机可处理轧制过程中的各种应用和技术问题。基本轧机是由两个反向旋转的两个轧辊组成,这被称为二辊式轧机(图2a) 在三辊的结构中图2(b),有三个在同一垂直列的且旋转方向保持不变的轧辊。可以通过任意方向升降钢带轧槽来完成一连串的轧制工作。这些设备在三辊式轧机中变得更加复杂,因为升降机构需要升降功2轧辊工作的接触长度因为较小半径轧辊而被缩短，并且这样可以减小力，扭矩功率.这种四辊轧机使用两个更小直径的轧辊轧制材料并且在它们后面有两个支承辊.在多辊式轧机的轧辊的结构允许有更小的工作辊。为完成更高吞吐率的标准产品，经常使用串联轧
28、机。它的结构由一连串的轧钢机架组成。经过每个轧制阶段，轧制速度都会增加，并且轧辊速度在每个机架上的同步问题都是有意义的。3. 关于过程的一般看法扁平孔型轧制主要目的是减小引入原料的横截面积，改变它的道具并在轧辊出口处获得所期望的截面。这个过程可以执行热轧冷轧，依靠应用程序并与原料有关。轧制产品为板材。块钢 、厚平板、坯段和金属板的轧制通常是在再结晶温度以上的温度下进行的（热轧）。薄板和条钢经常进行冷轧为了维持小公差的厚度。基本的扁平孔型轧制由金属通过两个反方向旋转轧辊且两辊间的空隙小于输入金属尺寸构成的，.因为轧辊以超过金属进入速度旋转，沿着接触表面的摩擦力驱动金属前进。金属被压榨拉长并经常改
29、变截面尺寸。变形量单一通过一对依靠沿摩擦力接触面的特定轧辊完成。如果有咬入量过多，轧辊将完全刹车结束文具金属。过小的变形量会导致成本的增加。轧制包含金属在轧制过程中变形的高复杂性。从这个观点来看，轧制可以分为以下种类3： .厚度统一宽度无变化：这里，这种变形是平面变形，那是，在这个轧制方向上和薄板厚度上。这种类型的轧制发生在条钢、薄板、或金属薄片。 厚度统一宽度增长：在这里，在轧辊旋转方向上被拉伸，在宽度方向上被伸展并且在厚度方向上被均匀的压扁。这种类型在块钢、坯钢、和厚板的轧制过程。 适度的不均匀的横截面变形：在这里，金属在轧辊的旋转方向上被拉长，在宽度方向上被拉伸，并且在厚度方向上被不均匀
30、压缩 高度不均匀的横截面变形：在这里，在厚度方向上的缩小是高度不均匀的。一部分辗压断面在厚度方向上被缩小的同时，另一部分辗压断面被挤出或在厚度上增厚。因此，在宽度方向上金属可能向中心流动3。4. 热轧热轧特色的标志不是明确的结构，而是同时发生的位错传播和软化过程，在轧制过程中有或者没有在结晶。其主要机理依赖于温度和颗粒的大小。一般情况，在结晶结构在小的变形温度和更快的冷却速度和在控制终轧温度情况下获得的好原料会变得更好。热轧机的几个有利提议1：1） 流动应力是低的，因此势力和功率需求相应的也小，并且非常地的工件也能使设备保持适当的尺寸2） 可延展性高，因此大的变形是实现。3） 能够产生复杂零件
31、热轧机的上限尺寸取决于材料的融化温度或过氧化的出现。通常，工作的最大温度是小于融化温度的50度。这是低熔点物质所允许的隔离地方4。5. 冷轧冷轧的日常含义，意思是在室温下轧制，虽然工作是变形温度会提高100-200C.冷轧机常常在热轧机之后，原材料进入轧机发生加工硬化。位错密度增加，但用这个变硬的材料进行拉伸试验时，需要用更高的压力和提供可塑性的变形；因而，屈服应力增加。尽管如此，原材料的延展性-总延伸量和截面变形-铁豆因为更高的最初的位错密度。同样地强度系数增加，机械加工硬化指数下降。在主变形方向上的结晶体变得拉长1。热轧机的几个有利提议1 :1） .在没有冷却和氧化的情况下，能够获得小公差
32、和更好的表面质量。2） 薄墙是可能的.3） 加工件的最终形状能被接近控制并且，如果希望获得高强度在冷轧过程中是能保持的，或如果需要高延展性，退火前颗粒大小是能保持的。4） 润滑油通常是微降的。 6. 轧制的问题和缺点主要问题是在轧制过程中轧辊的校准。这个校准错误可能发生在如果用轴承和可能影响零件的厚度。下面是一个简单的分类 ：a.纵向事故过失轧辊速度的改变原材料的温度轧辊温度进口速度原料模型异型和圆锥型轧辊轴承使用b.横向事故过失轧辊的水平位置轧辊的表面几何形状。内蒙古科技大学本科生毕业外文翻译题 目：轧 制学生姓名： 张 升学 号：200540401337专 业：机械设计制造及其自动化班 级：机2005-3班指导教师：关丽坤 老师
