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防尘盖冲压模具设计【21张CAD图纸+毕业答辩论文】【冲压模具】

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关键词：: 防尘盖冲压模具设计全套 cad 图纸毕业答辩论文模具

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摘要：本设计进行了落料、冲孔、拉深复合模的设计。文中简要概述了冲压模具目前的发展状况和趋势。对产品进行了详细工艺分析和工艺方案的确定。按照冲压模具设计的一般步骤，计算并设计了本套模具上的主要零部件，如：凸模、凹模、凸模固定板、垫板、凹模固定板、卸料板、导尺、挡料销、导正销等。模架采用标准模架，选用了合适的冲压设备。设计中对工作零件和压力机规格均进行了必要的校核计算。此外，本模具采用始用挡料销和钩形挡料销挡料。模具的冲孔和落料凸模分别用不同的固定板固定，便于调整间隙；冲孔凹模和落料凹模则采用整体固定板固定。落料凸模内装有导正销，保证了工件上孔和外形的相对位置准确，提高了加工精度。如此设计出的结构可确保模具工作运行可靠和冲压产品大批量生产的要求。

关键词：复合模校核冲孔落料拉深。

Abstract：The design of the blanking and punching, drawing composite modulus design. This paper briefly outlined the Stamping Die current development status and trends. The product of a detailed analysis and the identification process. Stamping die design in accordance with the general steps to calculate and design the sets on the main mold parts, such as : punch and die. Punch plate, plate, Die plate and dump plates I. feet behind the sales, marketing and other derivative is. Die-standard model planes, to choose a suitable stamping equipment. Design work on the parts and specifications will press for the necessary checking calculation. In addition, the die block used only with marketing materials and Crook block behind the marketing materials. Punch and Die blanking punch were different plate fixed to facilitate adjustment gap; Punch and Die blanking die is used overall fixed plate. Blanking punch contents is a derivative sales, and guarantee the workpiece and the shape of the holes in the relative position accurately, improve processing accuracy. So the structure is designed to ensure reliable operation of die stamping products and mass production requirements.

Keywords : composite modules Check Punching Blanking Drawing.

1.绪论············································· 1

1.1冲压技术概念··································· 1

1.2我国模具技术的发展趋势························· 2

1.3 复合模的主要特点······························· 7

1.4 模具CAD技术·································· 7

1.5 本课题的来源及主要任务························· 8

2.冲压件的工艺分析······························ 9

2.1工艺方案的分析和确定····························10

2.1.1毛坯直径D的计算······························10

2.1.2 拉深次数n的计算······························10

2.2 工艺方案的确定··································10

2.3计算各工序压力、压力中心、初选压力机·············11

2.3.1冲裁力的计算···································12

2.3.2.初选压力机····································12

2.3.4.确定压力中心··································13

2.4冲压工序·········································13

2.5模具结构设计·····································13

2.5.1模具结构选择···································13

2.5.2模具工作部分的尺寸和公差的确定·················14

2.5.3 模具结构设计·································· 15

2.6整修工序·········································16

3.结论···············································19

4.致谢···············································20

5.参考文献·········································· 21

1 绪论

1.1 冲压技术概论

冲压是利用安装在冲压设备（主要是压力机）上的模具对材料施加压力，使其产生分离或塑性变形从而获得所需零件（俗称冲压件或冲件）的一种压力加工方法。冲压工艺与模具、冲压设备和冲压材料构成冲压加工的三要素。冲压是一种先进的金属加工方法，在国民经济的加工工业中占有重要的地位。与机械加工及塑性加工和其它方法相比，冲压加工无论在技术方面还是经济方面都具有许多独特的优点，主要表现如下[1]：

(1) 冲压一般没有切削碎料产生，材料的消耗较少利用率高，一般为70%～85%，易实现机械化和自动化；

(2) 在形状和尺寸精度方面的互换性较好。一般情况下可直接满足装配和使用要求；

(3) 冲压可加工的尺寸范围大、形状复杂的零件，而这些零件用其它方法是不可能或很难得到的，如薄壳件；

(4) 被加工的金属在冲压加工过程中产生加工硬化，金属内部组织得到改善，机械强度有所提高，所以冲压件刚度强度较好；

(5) 冲压时由模具保证了冲压件的尺寸与形状精度，且一般不破坏冲压材料的表面质量，而模具的寿命一般较长，所以冲压件的质量稳定，互换性好，具有“一模一样”的特征；

(6) 在大量生产的条件下，产品的成本低，经济效益较高；

(7) 冲裁过程能耗较低。

由此可见冲压制得的零件具有表面质量好重最轻成本低的优点。所以冲压在现代工业生产中，尤其是大批量生产中应用十分广泛。相当多的工业部门越来越多的采用冲压方法加工产品零件，如汽车、农机、仪器、仪表、电子、航空、航天、家电及轻工业等行业。在这些工业部门中，冲压件所占的比重相当的大，少则60%以上，多则90%以上。不少过去用锻造、铸造和切削加工方法制造的零件，现在大多数也被质量轻刚度好的冲压件所代替。有些机械设备往往以冲压件所占比例的大小作为评价结构是否先进的指标之一[2]。

工业发达国家对冷冲压生产工工艺的发展是很重视的.不少国家(如美国、日本等)模具工业产值己超过机床工业。从这些国家钢材构成可以看出冷冲压的发展趋势。钢带和钢板占全部品种的67%，充分说明冲压这种加工方法己成为现代工业生产的重要手段和发展方向。

冲压技术的发展特征是：

(1)冲压成形科学化、数字化和可控化；

(2)突出“精、省、净“三大优势；

(3)冲压成形可以实现全过程控制；

(4)产品从设计开始即进入控制，考虑工艺；

(5)冲压生产的灵活性和柔性。

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工件尺寸图.jpg

落料拉深模具总图.jpg

整形模总图.jpg

字数统计.jpg

内容简介：: 连铸连铸的发展二战之后，连铸发展非常迅速今天钢铁生产者普遍相信连铸至少和模铸一样在经济上是合理的，并且能与大部分高质量钢的生产系列相匹配。这项技术不断开发的目的在于改善钢的性能，这促使生产特殊高级钢时企业对其生产工艺过程不断进行调整。使用连铸系统的理由有： (l）和初轧机组（小型车间）相比，降低投资费用； (2）和传统的铸锭相比，提高10%的生产能力； (3）在整个铸坯长度上钢的成分较均匀；中心质量比较好，尤其是板坯；高的内表面质量，比其他需要昂贵的清理表而的工序节省； (4)高度的自动化； (5)益于保护环境； (6)较好的工作条件设备类型首台连铸机是立式连铸机，可是，由于横断面的增大，注流长度的增加，而且主要是随着浇注速度的增加，这种设备迫使厂房建筑高度增加。这些因素也导致了具有冶金影响的液相长度的大大增加。连铸坯的液相长度由下式决定： L=D2/4x2Vc这里，D=铸坏厚度(mm） x=凝固特征系数(mm/min1/2）对于全部的冷却长度这些值达到26-33。 Vc=拉坯速度( m分）为了减少厂房高度，首先研制出将钢水倒人立式结晶器中，并且在弯曲之前让钢水完全凝固的连铸系统，或弯曲时铸坯仍处在液相，这种系统随后发展为弧形结晶器，这是目前最常用的方法。立式连铸机和那些铸坯在完全凝固时被弯曲的连铸机都有一个长直的液相，这大大增加了成本。然而从维修的角度看，这些系统有冶金学优点。铸坯内部仍为液相就进行弯曲的连铸机比完全凝固后再弯曲的立式连铸机更好，它不需要修建与立式连铸机一样高的厂房。然而，液相弯曲系统要求更高的初期投资和更大的维护费用。弧形连铸机是考虑了投资费用和维护费用的折衷产物，而且可以在冶金上实现。连铸适合于生产任何横断而的产品：正方形的、长方形的、多边形的、圆形的、椭圆形断面都可以。也有些基本断面的例子，如管坯、板坯、大型坯、方坯。断面宽厚比大于1.6的铸坏通常称为板坯。方坯铸机生产正方形或近于方形、圆形或多边形断面，断面尺寸达到160mm的产品。较大断面或那些宽厚比小于1.6的产品用大型坯铸机生产。现在80 x 80到300 x 300mm的方坯以及50-350mm厚300-2,500mm宽的板坯都用这种方式生产。连铸比已经迅速增长，尤其在最近几年。这本质上是铸坯宽度和拉坯速度的增加。每个注流每分钟生产出的产品已超出了如下数据：板坯 5吨大型坯 1吨方坯 350kg最后，我们应该提到水平连铸机，它已经应用于有色金属和铸铁的生产，而且可以进一步开发用于钢的生产。R. Thielmann和R. Steffen针对用水平连铸机生产非合金钢和合金钢方坯的发展状况提出了一份综合报告。水平连铸机比传统连铸机有如下三个显著优势： (1)低的建筑高度和建设费用： (2)防止钢水二次氧化的方法简单； (3)由于钢水静压力非常低，没有铸坏变形。浇铸技术钢水由浇注大包注入中间包后流人敞口的水冷铜结晶器。首先结晶器底部用一个引锭杆塞住，然后由它将热的铸坯从结晶器拉出进人连续拉辊。铸坯从结晶器开始凝固,然后经过冷却系统，到达拉环辊，在拉辊中继续传送。引锭杆在进入切割装置之前或之后与铸环分离。切割装置可能是火焰切割机或热切割机，其行进速度与热铸坯相同，它将热铸坯切割成所需长度。使用中间包的目的是将确定的钢水量分流到一个或多个结晶器。这可以通过使用塞棒、滑动水口或其他力法控制的水口来实现。中间包的初始状态根据其耐火衬材料的不同可以是冷的、温的或热的。对于要求严格的钢使用浸入盒保护钢液注流以防止其氧化。结晶器不仅形成铸坯断面而且吸收一定的热量，使铸坯到达结晶器出口时坯壳有足够的运送强度。依据所铸铸坯的尺寸和形状，结晶器可以用铜管或硬质铜合金制成。按惯例，管状结晶器用于较小断面。结晶器的内表面可以使用铬或钼镀层以减少磨损并且适合于浇铸过程中从合金传热。结晶器的锥度是为了与钢的收缩、拉速和钢种匹配。现在使用的结晶器长度约为400 - 1,200mm,但通常在700 - 800mm之间。结晶器壁粘钢问题通常通过按正弦规律振动结晶器和加入润滑剂（油或连铸保护渣）以消除结晶器与钢水之间的摩擦加以解决。润滑剂，尤其是连铸保护渣，有一个附加的冶金功能。润滑剂的选择取决于所要求的质量和连铸条件；尤为重要的是所选择的连铸保护渣必须严格与质量工艺匹配。结晶器内钢液面可以人工控制或进行自动控制，两者中任何一种都可用于保持液面稳定或满足输人的钢水量，如与拉坯速度的变化相适应。人工控制通过调整中间包塞棒或流出速率实现。自动控制系统则可以通过放射测位仪或红外线放射仪或用安装在结晶器壁的测温探针测温来确定钢液面，并且通过操作水口塞棒机构（对于稳定流速）或控制拉辊速度（变化拉速）来补偿任何钢液面的变化。连铸中使用的引锭杆类型取决于连铸机的类型。立式连铸机可以使用刚性引锭杆，而组合式的或灵活式的引锭杆必须用于弧形连铸机。引锭杆与铸坯可以采用不同方式连接，一种是用连接部件（平板、螺钉、碎条钢）将钢液与引锭杆焊接在一起；另一种是在引锭杆头部铸造一个特殊连接头，它能使引锭杆像打开扣环那样进行脱锭。铸坯离开结晶器时的坯壳厚度首先取决于钢液与结品器的接触长度，它也依赖于结晶器的具体导热系数和钢水进人结晶器时的过热度。它可以由下面的抛物线公式进行精确计算：C=xt式中：C-坯壳厚度(mm) x凝固特性（mm/min1/2) t-凝固时间(min)铸坯在结晶器内或附近的凝固特性是20到26，它取决于操作条件；二冷区是29到33.离开结晶器时铸坯坯壳厚度约为铸坯厚度的8-10%，它取决于拉坯速度。结晶器下面的二冷区加速了铸坯的凝固过程。通常使用水进行冷却，但有时也用水和空气的混合物或压缩空气。为了适应冷却剂的流速，二冷区被分成很多部分。通过喷嘴将需要的水量喷到整个铸坏上。与铸坯断面和拉速有关的钢水静压力可能会太高，以至于铸坏不得不被支撑以防止鼓肚。在生产大型坯尤其是板坯的工厂，这种装置是很昂贵的。工艺控制由于生产率和质量的原因，在现代钢铁生产中，有一种转移费时操作的趋势，例如，将温度调整、脱氧和合金从熔化炉转到钢包处理站进行。这些操作在连铸过程中尤为重要，因为在这个过程中要严格控制温度和成分。连铸过程中进入结晶器的钢水温度控制要比常规铸造中的温度控制更精确。太高的过热度能导致拉漏或一种柱状结构，带来较差的内部质量。另一方面太低的温度会导致水口堵塞造成浇铸困难和产生不洁净钢。板坯连铸中间包温度通常在液相线以上5到20度，而方坯或大型坯则为5到50。这种不同取决于钢的等级，例如，小熔化炉中不锈钢板坯连铸过热度为45。在整个浇铸过程中，为使钢水温度保持在上面所说的范围之内，在钢包中温度的均匀性是最重要的。在浇铸以前为了保持钢包内钢液温度的均匀，需要搅拌，有时也进行清洗氮气或氩气可以带走热量，它们由钢包底部的多孔塞喷入或在独立的清洗站通过一个中空的塞棒喷入。在真空或清洗处理期间可以进行化学成份控制。在钢液均匀后，进行取样分析或用电动势法测量氧活度，在此基础上可以计算切屑的加入量以保证脱氧。加入切屑脱氧剂的最好方式是在搅拌熔池的同时保证高的速率（用惰性气体进行喷粉、喂线或喷丸）。通过小心除去钢包中的炉渣来减少对合金的需要。真空处理是实现良好钢包冶金的一种灵活、有效的手段，而低压处理是在浇铸前将氢或碳脱到很低的惟一方法。结晶器液面控制一台连铸机最重要的控制部分是保证铸坯拉出和部分冷却钢坯的生产能保持结晶器内钢液面的稳定（在几个厘米范围内波动）。这可以通过两种方式来完成：(1)称量中间包，从钢包到中间包的钢液流动速度自动变化以保持整个中间包重量不变。通过这个方式，从中间包流出的钢液速度是不变的。(2)要控制部分冷却钢坯的拉出速度以保持在结晶器中钢的液面大致不变。在连铸初期，通过操作者观察液面，并相应地调整中间包的塞棒来保持铸机中钢的上液面不变。现在，通常用测量设备测量并自动地调整液面。下表中列出了几种测量液面的方法。在此对r射线（放射线）和红外法这两种方法作详细描述. 类型制造者备注r射线Distingtan Engineering(UK)应用广泛，可靠涡流NKK(日本）热敏电阻United States Steel仅用在USS机器红外Sert. Danielli广泛用在欧洲大陆电磁线圈Concast由这个表可以看出各操作方法的特点。为避免较强放射性同位素的应用，开发了红外线设备。这种探测器检测金属液面与结晶器后壁的连接处。当金属液面上升到观测范围内时，单个光电元件会收到更多的反射信号，此时输出增加。检测中断时可以采取特殊的措施来补偿。光电元件单元收到红外反射，输出一个电信号给控制单元，这个控制单元接着与操作者和连铸机相联系。操作者能够选择自动或手动控制，并且接收某个信号灯发出的操作指示。从液面返回的信号穿过夹缝罩，被圆柱面透镜聚焦到光电检测器。通过过滤除去波长1mm以下的反射光，以减少环境光和油焰的干扰。整个系统在冒口有两个探测仪，两个固定的光束检查钢液流股的每一边。通过改变夹缝间隔，可以调整光电元件检测到的两个区域的间距。在每一通道都装有三个光电检测器：第一个用上面描述的光束测定金属液面；第二个不收到光束而能进行温度漂移补偿；第三个通过夹缝观察正常钢液面上方位于主光束与金属流之间的一个小区域。它的作用是当金属流偏离中心位置，可能会干涉主光束时对其进行探测。两个主光束与液流界面探测间的平衡能够通过安装在单元后部的小电位计来调整。温度补偿以后，每一通道探测到的液面信号被输进一个选择最大信号的简单电路。因此这个单元总是控制两个液面信号中较高一个。如果液流传感光电元件发现液流向检测束移动时，它切断信号，并且元件转向进行控制另一个通道面。还有另一个特征，如果两个通道都被切断，例如被一个扇形金属流切断，单元转向记忆单元，相当于快速检查金属液面，防止突然控制失灵。在记忆单元释放时，液面逐渐下降，使操作者有足够的时间来调整。如果拉坯速度有一个大的跳跃，通过阻止自动运行，单元将给出一个从人工控制到自动控制的平滑转换。在从自功到手动的改变时，不提供无振动转换。在电缆有故障时，也有一个防止变到自动状态的保护。控制系统收到被选择过的液面水平信号，伴随比例和积分作用，直接给拉坯驱动单元输出一个电压信号。驱动单元产生与电压信号相对应的拉坯速度。连铸的益处操作步骤在连铸发展之前，只有钢锭为热加工成型的钢铁产品提供了初始原料。从炼钢炉到轧机的典型操作步骤是：（1）将钢水浇入钢锭模；（2）钢包运到浇铸平台，将钢水注人钢锭模；（3）将铸后锭模运到脱锭区脱锭；（4）运送钢锭到均热炉，加热到轧制温度；（5）从均热炉取出加热的钢锭，运送到初轧机轧制成半成品形状；（6）运送半成品钢到轧机。用连铸，只需如下更短的步骤： (1)从炼钢炉出钢到钢包； (2)钢包运到浇注平台，连续把钢水浇成半成品形状。 (3)运送半成品钢到轧机从较短的操作步骤获得的利益是人们采用连铸的主要原因；连铸增加了产量；提高了产品质量；节约能源；减少污染和降低了成本。产量从钢包中钢水到轧成半成品形状的产量提高在于三个方面金属废料的减少：初轧机；浇注；钢锭加热。对产量增加贡献最大的是无需初轧时钢锭切头、切尾。与浇铸操作有关的产量损失的减少，包括短锭，铸锭残头和一般的废钢的减少。由钢锭在均热炉中加热引起的氧化皮烧损也被避免了。质量冶金质量的提高包括在化学成分和凝固特征上变化小。除了在铸坯横切面上，改善碳、硫和合金元素偏析特性以外，沿着铸坯长度方向也没有什么变化（当将一炉钢水进行模铸时，每一支钢锭都有垂直偏析和组织变化，而连铸坯不仅是一块钢锭而且垂直方向上没有什么变化）。在现代连铸过程中，铸坯表面的质量要高于轧制半成品质量，轧制半成品的表面有例如结疤和疤痕等表面缺陷，因此，对铸锭的精整和产量的损失均降到最低程度。大多数连铸钢坯均无需经过任何修整就可进一步加工。因此能得到有较少的内部和表面缺陷、性能得到改善、更均匀的最终产品。能量连铸能够节约能量，因为连铸过程减少了在模铸过程中的能量消耗。这些包括在均热炉中的燃料消耗和初轧机的电能消耗。能量也可以通过产量增加来间接节省，因为它能减少用于生产大量半成品的原料钢的消耗。除此之外，人们正在关注将热的连铸坯直接热送到精轧机加热炉的实践，因此连铸坏的显热被节约了。污染连铸过程通过省略模铸工艺设备如均热炉减少了污染。成本连铸的资金和运行成本与模铸工艺相比均减少了。资金节约归功于省掉了模铸工艺所需要的设备。运行成本节约主要是较少的劳动力投人和较高的产量。炼钢连铸的炼钢操作与用电炉或碱性氧气转炉生产钢锭的炼钢操作相似，仅有某些不同，主要有两个： (1)温度控制； (2)脱氧实践。温度控制温度控制比模铸生产更关键。出钢温度通常更高，以补偿因运送到铸机的时间增加引起的热量损失，出钢温度要维持在一个较小的范围内，以避免温度太高时拉漏和温度太低时中间包水口过早凝固。浇铸温度也能影响铸坯的晶体结构。在整个浇注过程中采用均一且低的过热度可获得铸坯最佳晶体结构。为了达到此目的，必须进行使钢液温度均匀的操作。广泛使用的一种方法是利用钢包底部的多孔塞吹入少量氩气或将喷枪插人钢包液面下吹氩搅拌钢液。脱氧连铸钢必须完全脱氧（镇静）以防止在铸坯表面或接近表面的皮下形成气泡或气孔，气泡和气孔会导致随后轧制过程中产生裂纹。根据钢的等级和用途，采用如下两种方法脱氧： (1)对于粗晶粒钢加人少量铝，用硅进行脱氧； (2)对于细晶粒钢进行铝脱氧。硅镇静钢比铝镇静钢更容易浇铸，因为避免了氧化铝沉淀带来的中间包水口堵塞问题。为了生产高质量的产品，在连铸之前，进行钢包精炼正成为一种很普遍的操作。Continuous Casting出处From the Making, Shaping and Treating of Steel by William，McGrawHill Companies, Inc., 2002The Development of Continuous CastingContinuous casting was developed very rapidly after the Second World War. Steel-producers arc today generally convinced that continuous casting is at least as economical as ingot production and can match the quality of the latter across much of the production spectrum for high-quality steels. Continual development of the technique aimed at improved steel characteristics is leading to increasing adoption of the process in works producing special high-grade steels. The reasons for continuous-casting systems are:(1) lower investment outlay compared with that for a blooming train (mini-steelworks);(2) about 10% more productivity than with conventional ingot-casting;(3) high degree of consistency of steel composition along the whole length of the strand; better core quality, especially with flat strands; high inherent surface quality, leading to savings on an otherwise expensive surfacing process;(4) high degree of automation;(5) friendlier to the environment;(6) better working conditions.Types of InstallationThe first continuous-casting plants were aligned vertically; however, with larger cross-sections, increasing strand-length, and, above all, with increasing pouring-rates this type of construction leads to unreasonable building-heights. These factors also lead to a considerable increase in the length of the liquid phase which has metallurgical effects. The length of the liquid phase in a continuously-cast strand is determined by the following formula:L=D2/4x2VcWhere D =strand thickness (mm)x = solidification characteristic (mm / min1/2)These values amount to 2633 for the whole cooling length.Vc = casting rate (m /min)Efforts to reduce building-height first led to continuous-casting systems in which molten metal passed into a vertical mould and solidified completely before being bent or where the strand has been in the liquid phase and later to the bow-type installation which has a curved mould and is the system most used today. Vertical systems and those in which the strand is bent when completely solidified have long straight liquid phases and can lead to unacceptably high capital outlay.However, these systems have metallurgical advantages from the point of view of maintenance. A vertical system in which the strand is bent while still in the liquid phase has the advantage that the building need not be as tall as when the strand is bent after solidification; however, the liquid-phase bending system requires higher initial outlay and greater maintenance costs. The bow-type system represents a compromise between the costs of capital outlay and of maintenance and what can be achieved metallurgic ally.Continuous-casting is suitable for the production of almost any cross-section imaginable; square, rectangular, polygonal, round, and oval sections are all available. There are also some instances of preliminary sections for tubes and slabs, blooms, and billets. Sections with a breadth /thickness ratio greater than 1.6 are normally described as slabs. Billet-machines produce square or nearly-square, round, or polygonal cross-sections up to 160mm across. Larger sections and those with a breadth /thickness ratio less than 1.6 are cast in bloom-machines. Billets nowadays normally produced in this way range from 80 x80 to 300 x300 mm, and slabs are 50 - 350mm thick and 300 - 2500 mm wide.Continuous-casting output-rates have risen sharply, especially in the last few years. This is essentially because of increase in the breadth of the strand and in casting rate. The following outputs have been exceeded per section per minute:slabs5 tonesblooms1 tonesbillets350 kgFinally, we should mention horizontal continuous-casting systems which are already used for non-ferrous metals and cast iron and which are being further developed for steel. R. Thieimann and R. Steffen have produced a comprehensive report about the state of development of horizontal continuous-casting systems for producing billets from unalloyed and alloy steels. Horizontal continuous-casting systems have three important advantages over conventional continuous-casting system:(1) low height and cost of building;(2) simple means of protecting the melt against reoxidatioin;(3) no strand deformation because the ferrostatic pressure is much lower.Casting TechniqueMolten steel is poured from a casting ladle via a tundish into an open water-cooled copper mould. At first the bottom of the mould is closed off by a starting-bar, which then leads transport of the hot strand from the mould into the continuous withdrawing rolls. The strand, which starts to solidify in the mould, passes through a cooling system before it finally reaches the withdrawing rolls, whereupon the hot strand takes over transport. The starting-bar is separated from the hot strand before or after it reaches the parting device. The latter, which may either be a flame-cutter or hot shears, moves at the same rate as the hot strand and cuts it into the lengths required.The purpose of the tundish is to feed a defined quantity of molten steel into one or more moulds. This can be done by using nozzles controlled by stoppers, slide-gates, or other means. The tundish may initially be cold, warm, or hot according to the nature of its refractory lining. Where difficult steels are processed the pouring stream is protected against oxidation between the submerged boxes. The mould not only forms the strand section but also extracts a defined quantity of heat, so that the strand shell is strong enough for transport by the time it reaches the mould-outlet. The mould may be made from copper tube or hard enable copper alloy, depending on the shape and size of the strand to be cast. As a rule, tubular moulds tire used for smaller sections. The interior surface of the mould may be coated with chronic or molybdenum to reduce wear and to suit heat-transfer from the alloy being cast. The mould is tapered to match steel-shrinkage and casting-rate and the type of steel concerned. Moulds used today range from 400 to 1200 mm in length overall, but their usual length is between 700 and 800 mm. The problem of steel adhering to the mould-sides is usually countered by oscillating the mould sinusoidally relative to the strand and by adding lubricant (oil or casting flux in an attempt to cut friction between the mould and the steel. The lubricant, particularly casting-flux, has an additional metallurgical function. The choice of lubricant depends on the qualities required and the casting conditions; it is particularly important that casting-flux should be chosen to match the quality-programme precisely.The level of steel in the mould may be controlled manually or by an automatic system. Either method may be used to keep the level constant or to match the incoming molten steel, i. e. to accommodate variations in casting rate. Manual control is affected via the stopper in the tundish or by varying the output rate. An automatic control system may meter radioactivity or infrared radiation or measure temperature via a probe in the mould wall to determine the steel-level and compensate any changes by actuating the stopper-mechanism (for constant pouring rate) or controlling the speed of the withdrawing rolls (varying casting rate).The type of starting-bar used for continuous-casting depends on the type of installation. Rigid starting-bars can be used in vertical systems, while articulated dummy bars or flexible strip have to be used in bowed installations. The starting bar can be connected to the hot strand in different ways, one is by welding the fluid steel using a jointing element (flat slab, screw, or fragment of rail) which is soluble in the starting-bar; another is by casting the connector in a specially shaped head in the dummy bar in a way that enables it to be released by unlatching.The thickness of the solidified strand shell on leaving the mould depends first of all on how long the steel is in contact with the mould, but it also depends on the specific thermal conductivity of the mould and on the amount of superheat that steel has when it enters the mould. It can be determined with fair accuracy using the following parabolic formula:C=x. T where C is the thickness of the strand shell (mm)x is the solidification characteristic (mm/min1/2)t is the solidification time (min)The solidification characteristic in and near the mould lies between 20 and 26, depending on the operating conditions; for the secondary cooling-area the figure is 29 -33. The thickness of the solidified strand shell on leaving the mould is about 8 10% of the strand-thickness, depending on casting rate. A secondary cooling-area under the mould speeds up completion of the solidification process. The coolant usually is water but a water / air mixture or compressed air is also sometimes used. The secondary cooling area is divided into several zones to suit coolant flow rates. The necessary quantity of water is sprayed over the entire strand by spray-bars. The ferrostatic pressure may be so high in relation to the strand cross-section and the casting rate that the strand has to be supported to prevent buckling. The equipment for this is expensive in plants producing blooms and especially slabs.Process ControlFor productivity and quality reasons there is a trend in modern steelmaking to transfer time-consuming operations, such as temperature adjustment, deoxidation and alloying, from the furnace to the ladle treatment stations. These treatments are particularly important where the continuous casting process is involved because temperature and composition must closely be controlled.The temperature control of molten steel as it enters the mould needs to be more accurate in the continuous casting process than in conventional casting. Too high a superheat can cause breakouts or a dendritic structure, which is often associated with poor internal quality. On the other hand, too low a temperature may cause casting difficulties due to nozzle clogging and result in dirty steel. The steel temperature in the tundish normally lies between 5 and 20 above the liquids for slab casting and between 5 and 50 for billet or bloom casting. This differential depends on steel grade and, for example, is about 45t for stainless steel slab casting from small furnaces.In order to keep the steel temperature within the prescribed limits during the whole cast, temperature uniformity in the ladle is of paramount importance. Stirring is required before casting in order to destroy any temperature variations in the ladle, and rinsing is sometimes used. The heat is flushed with either nitrogen or argon, injected by means of a porous plug at the bottom of the ladle or through a hollow stopper rod at a separate rinsing station.Control of chemical composition can be performed during vacuum or rinsing treatments. On the basis of the analysis of a sample or of an electromotive force oxygen activity measurement made after homogeneity of the metal is attained, trimming additions can be calculated to ensure correct deoxidation. The best way to introduce trim deoxidants is at a high velocity (powder injection with inert gas, wire feeding or bullet shooting) while stirring the bath. Decreasing the need for alloys by careful exclusion of furnace slag from the ladle simplifies trimming. Vacuum treatment is versatile and useful to achieve for good ladle metallurgy. Low-pressure treatment, however, is the only way to remove hydrogen before casting or to decarburize to extremely low levels.Mould-level controlThe most vital part of the control of a continuous casting machine is to ensure that the withdrawal of the cast and the partially-cooled billet is such as to keep the liquid level in the mould constant (within a few centimeters). This is done in two ways.(1) The tundish is weighed and the rate of feed to the tundish from the ladle varied automatically to keep the total tundish weight constant. In this way the rate of feed from the tundish is constant.(2) The rate of withdrawal of the partially cooled billet is controlled so as to keep the level of liquid steel in the mould roughly constant.In the early days of continuous casting the level of the top of the liquid steel in the caster was maintained constant by an operator viewing it and adjusting the tundish stopper accordingly. It is now normal to have a means of finding the level using a measuring instrument and automatically adjusting the level. The table below lists several ways in which the level is detected. Two of them, the gamma-ray (radioactive) and the infrared methods will be described in detail.The operation is self-evident from this diagram. The infrared device was developed in order to avoid the use of powerful radioactive isotopes. The detector views the junction of the metal level with the back wall of the mould. As the metal level rises within the field of view more radiation is received by the single photocell and an increased output is obtained. Special provisions are made to compensate for interruption of the view of the metal. The photocell unit receives the infrared radiation and provides an electrical signal to the control unit, which is in turn connected to the operators unit and the casting-machine drives. The operator can select automatic or manual control and he receives indication of the operating rod from signal lamps. The radiation emitted from the liquid steel is collimated through a slotted mask and then focused on to a photo detector by a cylindrical lens. The light is filtered to eliminate radiation below a wavelength of 1 mm, so reducing interference from ambient light and oil flames.The entire system is duplicated within the had with two detectors and two fit beams normally arranged to view either side of the steel stream. It is possible to adjust the spacing between the two areas seen by the photocells by changing the slot spacing in the mask.There are three photo detectors fitted for each channel: the first measures the metal level using the beam described above; the second receives no light and enables temperature drift compensation; and the third looks through the slot at a small region above the normal metal level and between the main beam and the metal stream. Its purpose is to detect the metal stream if it wanders from a central position and is in danger of interfering with the main beam. The balance between the two main beams and the threshold level of the stream detectors can be adjusted with small potentiometers mounted in the back of the unit.The level signal detected by each channel is fed, after temperature compensation, to a simple circuit which selects the largest signal. Thus the unit always controls on the higher of the two level signals. If the stream-sensing photocell sees that the teeming stream is moving towards the detection beam it blocks the signal and the unit switches to control on the other channel. There is an additional feature that if both channels are blocked together, for example by a fan-shaped metal stream, the unit switches to a memory, equivalent to the fast detected metal level, and prevents a sudden loss of control. As the memory decays the metal level gradually drops allowing the operator ample time to intervene.The unit gives a smooth transition from manual to automatic control by preventing automatic operation if there would be a large jump in withdrawal speed at changeover. It does not provide bumpless transfer when changing from automatic to manual. There is also protection against changing to automatic when there is a cable fault.The control system receives the chosen level signal and, following proportional and integral action, outputs a voltage signal directly to the withdrawal drive unit. The drive creates a withdrawal speed proportional to this voltage signal.Benefits of Continuous CastingSequence of Operations-prior to the development of continuous casting, ingots provided the only starting material in wrought-steel products. The typical sequence of operations from the steelmaking furnace to the rolling mills was:(1) Tapping liquid steel into ingot molds.(2) Transferring ladle to pouring platform and teeming liquid steel into ingot molds.(3) Transferring filled molds to stripping area for ingot removal.(4) Transferring and charging ingots into soaking pits and heating to rolling temperature.(5) Removal of heated ingots from soaking pits and transfer to primary mill for rolling into semi-finished shapes.(6) Transferring semi-finished shapes to subsequent rolling mills.Using continuous casting, the following much shorter sequence of operations is required:(1) Tapping liquid steel from a steelmaking furnace into a ladle.(2) Transferring the ladle to a casting platform and continuously casting liquid steel into semifinished shapes.(3) Transferring the semi-finished shapes to rolling mills.The benefits derived from the shorter sequence of operations provided the main impetus for the adoption of continuously casting; increased yield; improved product quality; energy savings; less pollution; and reduced costs.Yield Increased yield from liquid steel in the ladle to the semi-finished rolled shape results from a reduction in scrap generation in three areas: the primary rolling mill; the pouring operation; and ingot heating. The major contribution to the improved yield is the absence of crop losses corresponding to the ingot top and bottom location when an ingot is rolled in the primary mill. Reduction in yield losses associated with the pouring operation includes short ingots, ingot butts and general pit scrap. Scaling losses associated with ingot heating in the soaking pit are also avoided.Quality Metallurgical quality improvements include less variability in chemical composition and solidification characteristics. In addition to improved segregation characteristics of carbon, sulfur and alloying elements across the section of a continuously cast shape, there is also less variability along the length of the cast shape. (In casting a heat into ingots there are a multitude of individual ingots each with their associated vertical segregation and structural variability, whereas a continuous cast strand is not only as one ingot but also an ingot which has less variability in a vertical direction.) In modern continuous casting, the surface quality of the cast shape is superior to that of a semi-finished rolled shape with respect to surface defects such as seams and scabs, and, consequently, conditioning requirements and yield losses are minimized. A majority of continuously cast steels can be further processed without any conditioning. Thus, an improved, more uniform finished product can be obtained with fewer internal and surface defects.Energy Energy savings are achieved with continuous casting because of the elimination of the energy-consuming steps in the ingot process. These include fuel consumption in soaking pits and the electric power requirements for operating the primary r

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