油泵齿轮壳铸造工艺及模具(芯盒)设计
油泵齿轮壳铸造工艺及模具(芯盒)设计,油泵齿轮壳铸造工艺及模具(芯盒)设计,油泵,齿轮,铸造,锻造,工艺,模具,芯盒,设计
油泵齿轮壳铸造工艺及模具(芯盒)设计课程设计说明书题 目:油泵齿轮壳铸造工艺及模具(芯盒)设计院 别: 专 业:材料成型及控制工程(模具CAD/CAM) 姓 名: 学 号: 指导教师: 日 期: 2014年01月10日 油泵齿轮壳铸造工艺及模具(芯盒)设计摘要对于载重汽车、卡车、消防车、牵引全挂车以及其改装车型等中型汽车而言,当前油泵齿轮壳的需求也越来越大,因此在油泵齿轮壳上也有比较高的要求,然而全国汽车生产量巨大,加上汽车配件量的需求也多,整车维修总量大,东风生产的各种油泵齿轮壳的产量仅能维持自身的供给,难以确保对外界的供给。因此本设计的目的,是让中小型企业拥有对中型货车油泵齿轮壳自行制造的能力,并且能以较低的设备成本投入,通过改善提高工艺性能的方案和控制模具(芯盒)精度等方式,来获取精度要求能与原厂生产油泵齿轮壳媲美的油泵齿轮壳。关键词:中型货车;东风汽车公司;油泵齿轮壳;工艺;模具;芯盒目 录1、零件及加工分析11.1.零件分析11.2.零件加工方案分析12、铸造方案的类型和确定22.1.铸造方式:22.2.制型方案:22.3.模腔数量32.4.砂型、砂芯材料选择:42.5.模样及芯盒材料:42.6.浇注系统形式选型:53、铸造工艺设计63.1.工艺设计参数:63.2.浇注位置:73.3.铸造分型面:83.4.砂型(型腔)上下模确定:93.5.砂芯设计:94、浇注系统设计104.1.浇注时间的确定104.2.阻流截面面积的确定114.3.内浇道设计134.4.横浇道设计134.5.直浇道设计144.6.浇注系统的分布145、芯盒设计155.1.芯盒的总体布局155.2.芯盒的主要结构设计155.3.芯盒的附具设计156、芯盒工装设计16参考文献17致 谢18 1、零件及加工分析1.1.零件分析1.1.1.零件主要结构分析:图1 油泵齿轮壳箱体汽车公司生产零件油泵齿轮壳箱体的零件图如图1所示,该油泵齿轮壳箱体是为一轴式结构,安装输出轴,是本箱体最为核心的部位。箱体左右两端平整,用以与其他零件相安装连接。1.1.2.制造工艺要求:根据实际生产中的要求,总体归纳为以下4点:1)工艺的实践性要强,操作要轻便;2)模具结构简单,制造容易;3)工艺和模具的经济性好;4)方便清砂。由此,本设计的设计原则必须遵循以上提及的4个总体要求。1.2.零件加工方案分析根据零件的结构性以及尺寸形位公差的要求,本设计箱体的总体制造方案分为两步:第一步为铸造;第二步进行各有加工要求的部位以镗、铣等基本的机械加工手段进行加工,最终达到图纸所要求的精度。2、铸造方案的类型和确定2.1.铸造方式:铸造方式多种多样,而在这些方式里面,较为普遍的而且实用性较高的方式主要为以下几种:砂型铸造、消失模铸造以及压铸。2.1.1.砂型铸造:砂型铸造成本很低,制作方便,能通过人工、机械造型,能满足一般铸件需求。但是一次铸造成型砂型必须重新制作,需要另设造型设备,不能铸造直径小于30mm以下的孔类部位。2.1.2.消失模铸造:铸造精度较高,能制作各种小孔类型的部位,适应于制作形状较为复杂的铸件,由于模样的高温融化,所以取件不须考虑型芯或型腔因结构复杂而造成取模障碍等问题。然而一次模样也是只能使用一次(因为在高温铸造过程中模样会融化消失),消失模自身的力学性能较差,容易变形。2.1.3.压铸:压铸的精度非常高,在高压下能轻松铸造至每一个精细的部位、角落和小孔等,能铸出结构复杂的工件。不过设备成本非常高,对铸造材料很有要求,铸铁类等材料均不宜进行压铸。方案确定:如上比较分析,本设计由于箱体铸件材料正好是铸铁,因此不能使用压铸方式;由于该箱体壁厚7-10毫米,消失模强度不足,在铸造操作过程中会变形,最终很可能导致铸件变形量超差。因此本设计选择砂型铸造。2.2.制型方案:本设计在2.1的铸造方式里已经确定为砂型铸造,因此型砂和型芯的制型方式也需要确定下来,普遍的制型方式主要有两种:手工造型和机械造型。2.2.1.手工造型:不用额外购买造型设备,在单件小批量生产中成本低。不过劳动强度高,操作人员数量大,制型精度难以得到保证,造型生产周期长。2.2.2.机械造型:造型速度快,造型精度高,适应于中、大批量生产。需要额外投入经费购买造型机,根据不同型号的造型机价格有所不一。方案确定:综合比较分析后,根据本设计生产实际需要,砂型精度要求比较高,手工造型无法满足这种要求,而且本设计规模为中、大批量生产,手工造型会导致工人劳动强度过大,需要操作人员也多,加上生产周期长,到最后成本还会过高。因此选择为机械造型,一次投资购买造型机,而造型机中,主要型号有Z145A Z148B Z230B其中Z145A适用的砂箱较小,制型数量有限,不能满足批量生产要求,Z230B造型机过大,用砂量大以及较耗费人力是主要缺陷,而型号Z148B造型机则能综合满足以上要求,能满足本设计箱体的生产规模,同时也能节省用砂量。因此造型机选为Z148B。2.3.模腔数量模腔数量是指一套铸型在一次装配并进行铸造后,所获得的铸件数量,这个参数直接影响到型腔和浇注系统的布局以及用以制造砂型的砂箱的大小的设计,因此此项选择不容缺失。2.3.1.一型一腔:一型一腔最大的特点就是铸件的空间所占用砂箱空间少,易于铸件及浇注系统在其内的布局。但是部分方向的吃砂量只为单一个铸型而设置,在本设计已确定的Z148B造型机中,这种布局会造成用砂量巨大浪费,而且单腔生产数量的难以满足较大生产规模的要求。2.3.2.一型四腔:较一型一腔式等批量生产更为节省用砂量,生产规模较大。然而由于要考虑砂芯和芯盒所要腾出的芯头尺寸的空间,有可能会因此而使得所选用的砂箱较大,因此浇注系统以及铸件摆放的方位需要有比较精细的安排,而且对铸造工装的装配精度要求较高。方案确定:由于本课题选择购买的造型机型号为Z148B,从用砂量的节省角度以及生产规模需求角度考虑,更适合于一型四腔。因此本设计选定一型四腔。2.4.砂型、砂芯材料选择:同一套砂型和砂芯虽然是铸造同一个铸件,然而各自负责成型部位不一样,工作的环境和工艺性能也有所不一,对材料的依赖性很高,因此合理地对砂型和砂芯的型砂材料的选择是提高铸造工艺性以及经济性的重要环节之一。常用的砂芯材料有:水玻璃砂,冷硬树脂砂,粘土砂,潮模煤粉砂方案确定:在本设计中,铸件外表面需要有较高表面质量,不应机械粘砂,因此外模砂选用潮模煤粉砂。而由于本设计中,油泵齿轮壳内部结构有内凸部位,如果用水玻璃砂或者粘土砂这些较硬的芯砂,将必须经过敲击才能逐步取芯,特别是粘土砂,如果粘在内部的内壁上,在敲击的过程中稍有不慎很容易会伤及铸件本体,加上该设计的油泵齿轮壳最薄的壁厚仅有7毫米,如此的敲击很容易会对其进行损害,所以水玻璃砂和粘土砂不大可取,然而冷硬树脂砂在铸造的冷却过程中,金属会逐步收缩包紧型芯,利用冷硬树脂砂与铁水接触表面的树脂砂层强度的丧失,相互之间的距离会收缩,从而减少铸件的收缩阻力,降低了铸件的内应力及日后工作过程中开裂的倾向。因此本设计中砂芯选用冷硬树脂砂。2.5.模样及芯盒材料:模样是用来对型腔成型的必要工具,芯盒是用于制作砂芯的母体。而这两者的材料各种各样,木制、塑胶、金属,各自的使用性能、制造成本、加工工艺以及加工难度也各不一样,正确的选择模样和芯盒的材料同样是直接影响零件最终制造成本的关键因素之一。芯盒材料分三种,木材,塑料和金属,其中金属是三者中最为昂贵的材料,加工难度也因模样或芯盒的外形尺寸而变化,有的可以通过压铸直接获得所需的成品,有的需要铸造后进行后机械加工或者热处理或者电镀加工等等方可投入使用。但金属耐磨性是三者中最高的,而且强度很高,在高压力的喷砂、压砂和振砂的工作条件下依然能保持结实的状态,尽管在批量生产工作后出现的小部分破损或者磨损,也能通过电焊的方式进行填补修复工作,通过电镀后在此进行机械加工也能恢复表面质量,因此维修效率和性价比都高。方案确定:结合本设计需求和对表格内容的分析,生产规模较大,如果用塑料和木材作为模样的话,长期进行造型工作中导致变形和失效。而选用金属的话将能满足长时间砂型造型工作而不被磨损和变形的要求。因此本设计选择金属作为模样材料,为了防锈需要,具体选择铸铝合金,牌号为ZL-106,而芯盒的材料牌号选定为ZL-108。2.6.浇注系统形式选型:浇注系统是整个铸造系统中重要的组成部分,不同形式的浇注系统会影响到灰铁金属液体浇注的流动状况以及和卷气情况,最终决定了铸件密度和内部质量。浇注系统分:全封闭式,半封闭式,开放式,三种。方案确定:由于本设计对铸件的铸造精度和表面质量有比较高的要求,因此不允许出现断续浇注的情况,而且浇注均匀,不卷气,而且冲刷力应足够大,因此应选择全封闭式浇注系统。即直流道横截面积必须大于横浇道横截总面积之和,横浇道横截面积之和必须大于内浇道总面积之和。而且在直流道底部必须设有直流道窝,在横浇道顶部要设有燕尾式斜角。3、铸造工艺设计在所有的工程设计中,工艺设计必不可少,而铸造工艺,主要就是根据铸造零件的结构特点、技术要求、生产批量和生产条件等,确定铸造工艺方案和工艺参数,绘制铸造工艺图,编织工艺卡等技术文件。铸造工艺设计的好坏,对铸件品质、生产率和成本起着重要作用,而铸造工艺设计也是本设计中的工作重点。3.1.工艺设计参数:3.1.1.铸件尺寸公差:本设计中得铸件尺寸公差,是从通过资料2 P39表2-12中获得的,根据实际生产的要求以及生产规模,铸件的公差定为CT11级,在此表格中具体每一个尺寸范围都有对应的公差值,单位为mm。而本设计的主要对象是芯盒,主要加工结构为内腔结构,在批量生产中,长期与型砂的摩擦和接触,都会带来一定的磨损。因此为了保留磨损余量,尽可能提高芯盒耐用度,特选择尺寸公差值为负偏差。3.1.2.铸件重量公差:本设计给定两个铸件加上浇注系统的总公称重量,范围在40100kg内,从资料2 P40表2-13中本设计取得铸件重量公差为12%。3.1.3.机械加工余量:通过资料中,结合P41表2-14 表2-15及P42表2-16的综合查选,根据最大尺寸100250mm范围内所对应的G级选择加工余量为2.0mm,为确保安全,特预为机械加工工人预留略多些的余量,取为2.5mm。3.1.4.铸件收缩率(模样、芯盒放大率):本设计的铸件收缩率是通过 资料 P43表2-17中获得的,此表格中有两个可供参考的栏目,分别是中国机械工程学会资料和美国铸造学会资料,两者略有不一,而本设计根据这是提供国内中小型企业的生产设计,应更趋于使用中国标准,因此参考表2-17中左栏的参数,条件为中小型件,受阻收缩,因此收缩率为0.7-0.9%。3.1.5.最小铸出孔槽:根据灰铸铁的材料特性以及现有实际生产经验,在本设计中,设定为铸出的孔直径不能小于,而由于本油泵齿轮壳箱体的倒档齿轮的卡槽为内部的盲槽,对日后机械加工不方便,因此该2个槽皆应直接在铸造时铸出。根据工艺参数,本设计的铸件图如图2所示,详见原CAD图或图纸。图2 油泵齿轮壳箱体铸件图3.2.浇注位置:铸件的浇注位置是指浇注时铸件在铸型中的位置,浇注位置需要考虑以下的原则:1)铸件的重要部位、重要加工面应该朝下或者呈直立状态;2)使铸件的大平面应该朝下;3)应保证铸件能充满;4)应有利于铸件的补缩;5)尽可能避免吊砂、吊芯或者单边悬臂式砂芯,便于下芯、合箱以及检验。经过综合的考虑,选择为图3的浇注位置,中注式。图3 中注式浇注位置3.3.铸造分型面:分型面是指两半铸型相互接触的表面,本设计中有以下方案如图4-A所示,分型面是则能大大提高模底板的通用性以及分型面的简易程度,分型面的平直意味着对模底板的通用性提高,只要是平直的底板即可使用,而且还会在两个大轴圆边上出现不可避免的工艺角,但由于其工艺角厚度非常小,能在铸造完毕后通过清理修配方式进行简单的处理即可达到要求。图4-A 分(模)型面3.4.砂型(型腔)上下模确定:由于浇注系统往往是设置在上砂型(型腔)中,砂型(型腔)上下模会因为铸件所占的高度不一而使得浇注系统占用的空间体积不一,再者静压力是否足够也是个需要考虑的要素。具体如图5-A图5-A3.5.砂芯设计:根据工艺参数的要求,砂芯的设计主要是随形成型。3.5.1.芯头形状设计:本设计中的芯头有2个,用以成型2个主轴孔的水平芯头,2个水平芯头皆为圆柱延伸体,顶部垂直芯头为垂直方向往上延伸的随形延伸体。3.5.2.芯头尺寸设计:由于砂芯长度最大尺寸接近200mm,高度最大尺寸也超过100mm,因此为了让砂芯拥有足够的强度,2个水平芯头皆设定为40mm,直径与图纸原加工部位直径一致,顶部砂芯高度也为40mm。4、浇注系统设计4.1.浇注时间的确定计算体积,单个铸件(机械加工余量已经算入)约为5.2kg 浇注系统给定重量为4.5kg,抛洒系数1.02得本设计中铸造总重量约为W浇=(5.2kg4件+4.5kg)x1.02=25.806kg4.1.1.浇注时间计算:通过查 资料1 P136表3-2查得适用公式为其中铸件厚度为7.0mm,所以S取1.95,而G则是铸造总重量(即4个铸件重量+浇注系统重量),G为25.806kg。代入运算4.1.2.浇注时间校核:通过 资料1 P136式3-1式中v液面上升速度(mm/s);h铸件浇注时的高度,此处为150mm;t浇注时间,已算出9.9s。代入运算然后查 资料1 P136表3-3校验,正好大于所要求最小液面上升速度15mm/s,所以浇注时间计算合理。4.2.阻流截面面积的确定阻流截面面积,通过 资料1 P137式3-2式中 阻流截面面积(cm); G 浇注系统(kg); 流量系数 t浇注时间(s); HP作用于内浇道的金属液静压头,一般取平均压头(cm)。4.2.1.铸件重量:浇注重量G为单个铸件重量+浇注系统,即=(5.2kg+1.1kg)x1.02=6.426kg4.2.2.流量系数的计算:先通过 资料2 P138表3-6取值,干型,结构相对简单,阻力取中等,因此取得0.48。然后在表3-7进行细分修正:1)从1280起每50C则+0.025,本设计浇注温度选为1400C,所以+0.05;2)本设计不设有冒口,此处不修正;3)根据设计从 资料2 P65表3-6查得薄壁灰铸件砂型铸造的浇注系统面积比例为,则不符合,所以此处不修正;4)阻流后浇注系统的截面面积比较均匀,没有明显的扩大,此处不修正;5)本设计单个铸件设有2个内浇道,-0.05;6)虽然本设计不设有冒口,但型砂特别是砂芯的型砂为自硬树脂砂,通气性较好,此处不修正;7)本设计为中间注入式,此处不作修正最终得出=0.48。4.2.3.平均压头Hp计算计算:通过 资料1 P138式3-3查得 式中C浇注时铸件高度,此处为43.5cm;P内浇道以上的铸件高度,此处,即为21.75cm;Ho内浇道以上的金属液压头,等于内浇道到浇口盆液面的高度(cm)。为确定Ho,需要先计算压力角。给定铸件与内浇道接触边缘至直浇道中心线距离为35mm,经过计算,L为150mm给定单个砂型的浇注高度为83mm,上下砂型相同。则有,则算出=28.8通过 资料3 P131表3-13查得高于要求值10,所以压力角符合要求,设计合理,得Hm剩余压头高度为40mm,Ho=83mm=8.3cm。最后代入公式由上面已完全确定的 G、Hp以及t,则可以代入原式计算即阻流截面面积为2.58cm。4.3.内浇道设计4.3.1.内浇道形状设计:由 资料2 P55图3-11,参考(a)方案,扁平梯形,因为本设计的铸件最小壁厚只有7mm,根据铸造的浇注系统设计原则,内浇道高度应该小于铸件的最小壁厚,而且本设计为中间注入式浇注,所以方梯形,高梯形,圆形内浇道均不适合。给定内浇道高度为12毫米,斜度约为2,在横截面中上下底长度近乎一致,为简化计算和模样加工,所以直接取为相等,即本设计的内浇道横街面积定为矩形。4.3.2.内浇道尺寸设计:考虑到应安全系数,阻流截面面积应该放大,取值为=258mm,即单个内浇道的截面面积为,即=129mm。又因h=12mm,所以b=35mm。长度视横浇道的尺寸而定。4.4.横浇道设计4.4.1.横浇道形状设计:横浇道横截面形状为等腰梯形,为阻挡最先进入浇道而且温度相对低的金属液体不进入型腔,因此本设计横浇道设有为倾斜末端。4.4.2.横浇道尺寸设计:根据设计从 资料2 P65表3-6查得浇注系统各浇道横截面面积比例为则(注:为两个铸件所有内浇道的面积代数和)则一边的横浇道横截面积为。由于本设计横浇道梯形为等腰梯形,设水平中线长度b,高度h=1.4b,得面积,即可求出b=20mm ,h=12mm。上下底分别相对中线,则上底长16mm,下底长20mm,高度取整12mm。4.4.3.横浇道长度设计:考虑到先到达液体应进入横浇道的末端,所以从内浇道之外延伸30mm,两内浇道之间间隔为80mm,则总长度为150mm。4.5.直浇道设计4.5.1.直浇道形状设计:本设计的直浇道为直通型的圆柱体形状,从砂型的顶部直接开通连接到横浇道上的形式。4.5.2.直浇道尺寸设计:同上横浇道设计,根据则可求出半径R为13.53mm,取整为13.5mm。即直浇道为。长度因为是直通式,所以设计为250mm。为避免在浇注过程中发生反冲紊流现象,在直浇道的底部,即下砂型的顶部开设半球型的直浇道窝,尺寸为SR13.5。4.6.浇注系统的分布内浇道分布设计,两内浇道应该正好与铸件的边缘接触。详细请见CAD铸造工艺图所示。直浇道分布在两个内浇道距离上的正中央,直浇道的外圆边缘与内浇道之间的距离已超过了1.5倍横浇道的高度,因此拥有足够的浮渣行程。5、芯盒设计5.1.芯盒的总体布局芯盒是用来制作砂芯的主要部件,在本设计中芯盒选为对开式芯盒,分为两大部分,上芯盒和下芯盒,直接靠双芯盒的分型。5.2.芯盒的主要结构设计5.2.1.芯盒分模面设计:芯盒的分模面可选与铸造的分模面一样,都可选择平面分型面和曲面分型面,然而由于芯盒要制作的砂芯部位包括了芯头,如果依然采用平线过渡的话,将会浪费型砂,由于砂芯的型砂是自硬砂,价格相对很昂贵,因此为了尽可能的让型砂都充分利用,分型面会随着芯头圆心所在的位置而发生变化。5.2.2.壁厚设计:根据 资料1 P275图6-19,经过计算,本设计芯盒的平均轮廓尺寸为约200mm,则芯盒壁厚取为10mm。5.2.3芯盒本体加强筋设计:芯盒本体加强筋取为与芯盒壁厚相当,为6mm,布置在芯盒急拐角、容易变形以及应力集中的部位。5.2.4.耐磨片设计:本设计的芯盒刮砂面顶端设有2根3mm厚的条形防刮窄片,使用锥沉头螺钉进行固定,以保证在不影响刮砂前提下又能紧固防刮片。5.3.芯盒的附具设计5.3.1.芯盒导向机构:本设计的芯盒是以定位销和定位套进行定位,采用的是自行设计的可换导套座及可换销座,该2个可换座的尺寸和装配关系详细请见可换套座的零件图以及芯盒装配图。6、芯盒工装设计芯盒工装设计重点在于夹紧装置,芯盒在合模之后,充砂之前,施加夹紧力是必不可少的。在实际生产中,转动对开式芯盒的夹紧手段以活节螺栓与蝶形螺母为主,有的企业甚至为了获得更大的夹紧力,采用涡轮蜗杆机械式锁紧,甚至气压液压式夹紧装置。而本设计由于铸件属于中小型尺寸,用砂量相对少,充砂涨型不大,因此不必采用涡轮蜗杆或者气液压夹紧装置,出于本芯盒外形结构特征,并非转动对开式芯盒,因此本设计的夹紧装置为一种自行设计加工的紧固套。此紧固套工作原理是以紧固套内壁在垂直方向7的斜面对本芯盒特设置的垂直方向7加强筋进行接触,角度为7所提供的自锁力足够承受两芯盒在水平方向的涨型力,能在不需施加任何外力的前提下确保紧固套本体不会往上反弹。可见图17 紧固套装配示意图,详细尺寸请见紧固套CAD零件图。参考文献1韩小峰.铸造生产与工艺工装设计.长沙:中南大学出版社,20102董选普.铸造工艺学.北京:化学工业出版社,20093吕振林.铸造工艺及应用.北京:国防工业出版社,20114杜西灵.铸造技术与应用案例.北京:机械工业出版社.2009.5胡成立.朱敏立.材料成型基础.武汉:武汉理工大学出版社.20016徐自立.周小平.杨雄.工程材料.武汉:华中科技大学出版社.20037李凯岭.机械制造技术基础.北京:清华大学版社,20108胡凤兰.互换性与技术测量基础(第二版).北京:高等教育出版社,20109金大鹰.机械制图(第3版).北京:机械工业出版社,201010成大先.机械设计手册(第五版).北京:化学工业出版社,201011Peikher.Casting:An Analytical Approach.Berlin: Springer Verlag,200512Mistler.casting practice.America:American Ceramic Society, 2000致 谢本设计是在我的指导老师的亲切关怀和悉心指导下完成的。他严肃的科学态度,严谨的治学精神,精益求精的工作作风,深深地感染和激励着我。从题目的选择到最终完成,老师都始终给予我细心的指导和不懈的支持。17Casting of Brake Disc and Impeller from Aluminium Scrap Using Silica SandMatthew S. ABOLARIN, Oluwafemi A. OLUGBOJI, Oladeji A. OGUNWOLEDepartment of Mechanical Engineering, Federal University of Technology, Minna, Niger State, NigeriaAbstractThe impeller blade and the brake disc were produced using sand casting method. Wooden patterns of the two castings were constructed incorporating the necessary allowances. Green and moulding technique utilizing locally available materials were used for preparing the moulds. Aluminium scraps were used as the casting material. Melting of the Aluminium scraps was obtained using a crucible furnace and finally pouring the molten metal into the sand mould to obtain the impeller and the brake disc.After fettling and cleaning, the two casting were found to be good. The casting yield was found to be 73.59% for the impeller blade and 85.1% for the brake disc which indicate that sound casting was achieved.KeywordsImpeller Blade, Brake Disc, Green Moulding, Crucible Furnace, FettlingIntroductionBreak disc and impellerThe brake disc is a device for slowing or stopping the rotation of a wheel. A brake disc, usually made of cast iron or ceramic composites (including carbon, kevlar and silica), is connected to the wheel or the axle. To stop the wheel, friction material in the form of brake pads (mounted on a device called a brake caliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against both sides of the disc. Friction causes the disc and attached wheel to slow or stop.An impeller is a rotor inside a tube or conduit to increase the pressure and flow of a fluid.Impellers in pumps. An impeller is a rotating component of a centrifugal pump, usually made of iron, steel, aluminum or plastic, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller transfers into pressure when the outward movement of the fluid is confined by the pump casing. Impellers are usually short cylinders with an open inlet (called an eye) to accept incoming fluid, vanes to push the fluid radially, and a splined center to accept a driveshaft.MoldingMolding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern.A mold is a hollowed-out block that is filled with a liquid like plastic, glass, metal, or ceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape. A mold is the opposite of a cast. CastingCasting refers to the pouring of the molten metal into a mould, in which it cools and solidifies to produce an object of desired shape. However, the main casting methods available include: sand casting, in which liquid is poured into a shape cavity moulded from sand; die casting, in which the mould cavity is machined within metal die block; investment and centrifugal casting also exist. Moulding sand has a fairly low thermal conductivity so that the rate of solidification of liquid metal with a sand mould is fairly slow, given rise to a coarse crystal grain size. This of course makes the use of metallic mould more suitable in order to obtain a fine grain structure.Sand castingSand casting is one of the most popular and simplest types of casting that has been used for centuries. Sand casting allows for smaller batches to be made compared to permanent mold casting and at a very reasonable cost. Not only does this method allow manufacturers to create products at a low cost, but there are other benefits to sand casting, such as very small size operations. From castings that fit in the palm of your hand to train beds. one casting can create the entire bed for one rail car, it can all be done with sand casting. Sand casting also allows most metals to be cast depending on the type of sand used for the molds.Metal castings are vital components of most modern machines and transportation vehicles. Cast metals parts accounts for more than ninety percent of the weight of tractor and more than fifty percent of an automobile engine. Above all, casting provides a process of improving the mechanical properties of components or articles. Aluminium is used because it produces casting of good mechanical properties, such as good surface finish, light weight, fewer tendencies to oxidation, lending to modification, resistance to corrosion and its availability. This work covers the casting of brake disc and impeller blade using a properly prepared green sand mould, which is less expensive and gives less distortion and dimensional accuracy. Aluminum alloy is used because of its fluidity and good physical properties.Theoretical analysisBoth ferrous and non - ferrous alloys can be cast using green sand method especially when greater tonnage of casting is required. The ferrous alloys cast by this process include cast iron and steel. The commonly non - ferrous alloys cast by this process are aluminum base, copper base and magnesium base alloys. The temperature of these alloys ranges from 680C to 450C.Melting and pouring are processes of preparing molten metal of the proper composition and temperature in foundary using appropriate melting furnace and pouring the prepared molten metal into the mould from transfer ladles. Furnace melting alloys in the foundry include lift out or tilting crucible furnace. For a particular casting alloy, the temperature of pouring is taken with a certain super heat above its liquids temperature. The super heat is chosen depending on the influence of super heat temperature on the structure and mechanical properties of metal, the thickness and extensions of the walls of casting, the liability of the metals to form films, the thermo - physical properties of the mould material and the initial temperature of the mould material, the forces that cause stirring of hot metal in the mould and other factors. The pouring temperature for aluminium alloy is 680C - 700C, for bronzes and brasses is 1000 - 1200C, for magnesium alloy is 700 - 800C, for steel is 1520 - 1620C and for cast iron is 1300 - 1450C.Material and MethodsMaterial usedThe brake disc of 260mm diameter and 15mm thickness and the impeller of 146mm diameter and 5mm thickness respectively were cast with the following materials: pattern material, mould material, aluminium scrap, and furnace.Pattern materialA wooden pattern was produced from the developed pattern drawing. A hard wood (mahogany) was use for the production of the impeller pattern. The pattern for the impeller was produced from the wood of initial dimension 200mm 150mm, putting into consideration the spacing of the characters, depth of each shape using the specified dimension on the patter drawing.In the case of the blade disc, two plywoods, each 2cm thick of 32cm32cm were glued and nailed together. A divider opened to a radius of 14cm was used to inscribe a circle in its centre, found by drawing diagonals from the plywood edges. Hardwood of 16cm16cm3cm was glued and nailed to the centre of the plywood, and a divider opened to 6.7cm was used to inscribe a circle for the bore to be drilled. Putty was used to fill all chipped imperfections and also in filleting the patterns sharp and rough edges, after it was filled to a smooth finish. Two coats of wood varnish were applied.Mould materialThe mould materials used is the green sand mould and they include the following: silica sand, bentonite, and water. The chemical compound silicon dioxide, also known as silica, is an oxide of silicon with a chemical formula of SiO2 and has been known for its hardness since antiquity. Silica is most commonly found in nature as sand or quartz, as well as in the cell walls of diatoms. It is a principal component of most types of glass and substances such as concrete. Silica is the most abundant mineral in the earths crust. Green sand moulding which was used is a situation where the moulding sand remained moist until the metal is poured into it. Silica sand was sieved to obtain fine grain sized sand and to remove other foreign bodies in the sand. A specific quantity of the sand was fetched and bentonite was added as binder and mixed thoroughly with the sand. Water was then added to the already mixed mixtures, which were then thoroughly mixed together by hand to make ready for mould.AluminiumAluminium is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earths crust, and the third most abundant element therein, after oxygen and silicon. It makes up about 8% by weight of the Earths solid surface. Aluminium is too reactive chemically to occur in nature as the free metal. Instead, it is found combined in over 270 different minerals. The chief source of aluminium is bauxite ore.Aluminium is remarkable for its ability to resist corrosion due to the phenomenon of passivation and its low density. Structural components made from aluminium and its alloys are vital to the aerospace industry and very important in other areas of transportation and building. Its reactive nature makes it useful as a catalyst or additive in chemical mixtures, including being used in ammonium nitrate explosives to enhance blast power.FurnaceThe furnace used for the melting of the aluminium scrap is the Morgan furnace, which makes use of diesel oil for burning.MethodsAluminium was melted in a crucible furnace, an oldest and simple type of melting equipment. It was poured after melting into the mould earlier prepared for the two patterns. No melting treatment was carried out prior to pouring operation. After the pouring and solidification is completed, the two patterns were removed, cleaned and inspected for possible defects.CalculationsImpellerActual impeller diameter = 146mm, Shrinkage allowance used = 13mm/m, Machining allowance used 6mm.Diameter of pattern due to shrinkage = Impeller Diameter + (Shrinkage Allowance) (Impeller Diameter) = 146+ (13146/1000) = 146 + 1898/1000 = 146 + 1.898 = 147.898mm.Therefore, adding machining allowance, this diameter of the pattern becomesDiameter of the pattern = Machine allowance + Diameter of pattern due to shrinkage = 6 + 147.898 = 153.898mm.Brake discActual blade disc diameter = 260mm, Shrinkage allowance used = 13mm/m, Machining allowance used = 6mm.Diameter of the pattern due to shrinkage = Disc diameter + (Shrinkage allowance) (Brake discDiameter) = 260 + (13260/1000) = 260 +3380/1000 = 260 + 3.38 = 263.38mmAdding machining allowance, thus diameter of the pattern becomesDiameter of the pattern = Machine allowance + Diameter of pattern due to shrinkage= 263.38+6 = 269.38 = 269 mmCasting Yields - The casting can be evaluated using casting yield, which determines the percentage use of metal in casting.Casting Yield = WC/(WC + WG+WR)Where WC = Casting Weight, WG = Gating Weight, WR = Riser Weight.For the impeller,Casting Weight, WC = 0.418Kg.Weight of gating and riser, WG + WR = 0.15Kg.Casting Yield = 0.418/(0.418+0.15) = 0.418/0.568 = 0.7359 100 = 73.59%For the brake disc,Casting Weight = WC = 2.0KgWeight of gating and riser = 0.35KgCasting Yield = 2.0/(2.0+0.35) = 2/2.35 = 0.851 100= 85.1%Result and DiscussionA casting free of defects can be obtained if the pattern is properly designed, the mould properly prepared and the melting and pouring processes correctly carried out. In this work, due to unavoidable errors, some defects were noticed on the cast impeller blade and the brake disc. Both the external and the internal surface of the casting were relatively rough compared with the degree of smoothness expected of the brake disc. However, the external surface was machined to obtain a higher degree of smoothness while for internal surface; there was little or nothing which could be done to improve the smoothness. In the case of cast impeller, it was only the edge that was rough. A file was use used in filling the edges in order to smoothen it.ConclusionIn the course of this work, effort was made to produce locally the impeller and brake disc from aluminum scraps and to ensure that they conform to specification required. The green sand mould prepared gave the rough surface of the two castings, this may be due to the fact that no additives were added or proper percentage composition was not used. The defects found on the two casting may be due to entrapped air and poor surface finish of the mould, though the defects are minor. The cast yield for the impeller and the brake disc indicates that sound casting was achieved.References1 Mikhailow A. M., Metal Casting, First edition Mir Publishers, Moscow, 1989.2 Howard E. B., Timothy L. G., Metal Handbook, Desk edition, America Society for Metal (ASM) USA, 1992.
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