铸造缺陷是怎么形成的

铸造缺陷是怎么形成的 铸造缺陷是怎么形成的 铸造缺陷首先应该判断是什么原因造成的 造成裂纹的原因很多 常见的有以下几点 1 气孔 特征 铸件中的气孔是指在铸件内部 表面或接近表面处存在的大小不等的光滑孔洞 孔 壁往往还带有氧化色泽 由于气体的来源和形成原因不同 气孔的表现形式也各不相同 有侵入性气孔 析出性气孔 皮下气孔等 Feature the pore often take place interiorly some smooth air hole exist in the surface or subsurface Sidewall sometimes exhibits oxidation colour Because the gas come from different source and different forming reason the exibit different formation such as ingressive pore precipitation pore subsurface pore 2 砂眼 渣孔 特征 缺陷处内部或表面充塞着型 芯 砂的小孔 称为砂眼 若缺陷形状呈不规则 内 部是渣或夹杂物 则称为渣孔 Sand hole inclusion hole Feature in inner or on the surface of the defect location some hole fill with sand which called sand hole If the defect represent irregular formation and filling with residue or inclusion which called inclusion hole 3 缩孔 缩松 特征 在铸件的厚断面 热节处或轴心等最后凝固的地方形成表面粗糙的孔洞 并且或多 或少带有树枝状结晶 孔洞大而集中的称为缩孔 小而分散的称为缩松 缩孔与缩松主要 是由于金属液在冷却凝固时所产生的液态收缩与凝固收缩远大于固态收缩 并在铸件最后 凝固的地方得不到金属液的补充所造成的 Shrinkage or looseness Feature on the thick section of casting hot spot or the axis center of the last freezing location rough holes often take place and more or less formed dendrite Big and concentrated holes are called shrink small and scattered are called looseness The reduction in liquid shrink is more bigger than in solid shrink during the metal liquid turning into solid and in the last location of freezing no metal liquid can be available for compensation 4 粘砂 特征 在铸件的表面粘结着一层很难清理的造型材料 粘砂分机械粘砂和化学粘砂两种 它们的区别是 机械粘砂是高温金属液渗入砂粒间的孔隙中而形成 化学粘砂是金属氧化 和造型材料形成的低熔点化合物 与铸件牢固地粘结在一起而形成 Adhering Feature on the surface of the casting there is a layer of model material which is different to remove Including mechanical and chemical adhesive The difference between these mechanical adhesive is formed when the high temperature metal liquid enter into the gap among sands when metal is oxidized and combined with the model material and form a combination with low melt temperature and bonded firmly 5 裂纹 特征 浇注好的铸件表面有直线或弯曲的裂纹 裂纹分热裂和冷裂两种 热裂的裂口多呈 曲折和不规则的形状 其断口表面呈浅黑色 有较深的氧化色 冷裂的裂口较直 铸件断 口表面有金属光泽而且比较干净 有时出现轻微的氧化色 铸件产生裂纹的主要原因是 冷却凝固收缩时受到阻碍而产生内应力 当内应力大于金属 材料的强度时 铸件就开裂形成裂纹 Crack Feature straight and curving crack take place in the casting surface Involving Hot crack and cold crack Hot crack breach mostly appear flexural and irregular form and the cross section appear light black and deep color oxidation The breach of cold crack appears straight section and have metal sheen and clear sometimes appear slightly oxidation color The reason of occurring crack is when the reduction is resistant by the inner stresss when freezing and when the inner stress is bigger than the metal tensile the crack will occur 6 变形 特征 长的铸件比较容易产生变形 如机床床身 柴油机的缸体 缸盖 由于铸件壁厚相 差太多 冷却不均 容易造成铸件变形 还有一些铸件是在加工好以后 存放一段时间后 出现变形 Deformation Feature longer castings are easy to deform such as lathe bed cylinder of diesel engine cover because of too much difference of the thickness cooling no uniformly this will result in casting deformation Some castings represent deformation after machining finished and stored for some time 7 硬度不均匀 特征 铸件表面经加工后 出现微观的凹凸 有的局部地方还有 发亮 的硬质点 铸件 的表面硬度相差较大 达 30 50HB 国外先进水平 5 10HB 硬质点部位的硬度可能超 过标准 铸件的硬度差大容易造成工作面磨损不均匀 导致机床加工精度差 柴油机工作 噪声大 Hardness uneven Feature after machining some protrude or and concave points appear some location have highlight hard point the surface has bigger differential hardness it can reach to 30 50HB advanced level 5 10HB the hardenss of the hard point may exceed the standard The difference of hardness will cause the uneven working face and result in inaccurate of the lathe machining make a big noise on diesel engine 8 球铁件不球化或球化不良 特征 铸件断口呈灰黑色 力学性能明显偏低 金相检查可发现石墨呈片状 铸件的残余 镁量和稀土量太低 这种状况一般是不球化 铸件断口仍呈银灰色 但有分散的灰黑点 力学性能偏低 金相检查可发现小部分石墨呈片状或蠕虫状 铸件的残余镁量和稀土量比 正常含量偏低 这种状况一般为球化不良 Feature the fracture section appears light black the mechanical property is obviously lower metallographic examination and find the graphite represent layered the remains of the magnesium and rare earth is too low this situation is called non spheroidation When fracture section appears silver grey and black point scattered mechanical property is low metallographic examination will find small part of graphite appears layered or worm form the remains of magnesium and rare earth is lower than normal this situation is called bad spheroidation 9 球化衰退 特征 同包铁液浇注的铸件中 前期浇注的球化良好 后期浇注的铸件球化不良 或者不 球化 Degraded spheroidation Feature in the castings get from the same bucket the first solidified casting has the good sphereodation and the follower has bad spheriodation or non speriodation 10 石墨漂浮 含开花状石墨 特征 在铸件断口的上表面可见到一层清晰 密集的黑斑 金相检查可发现断面顶部石墨 球聚集 聚集层下部有时有连续的或者个别的开花状石墨 石墨漂浮严重削弱球铁的力学 性能 使强度 硬度 伸长率和冲击韧度都明显降低 Graphite floating including bloom graphite Feature a layer of clear and concentrated black spots can be seen on the cross section by metallographic examination graphite concentrates in the upper of section continuous or separate bloom graphite in the lower section Floating graphite severely decrease the ductile mechanical property and make tensile hardenss elongation impact obviously lower 11 反白口 特征 铸件断面心部出现白口 碳化物 而在冷却相对较快的外层部位 组织反而正常 产生这种缺陷的主要原因是 灰铸铁铁液含硫高 含锰量过低 不符合 Mn 1 7S 0 3 的 关系 另外 铁液吸收氢气或铁液中的石墨核心过少 硫 氢都容易向铸件中心偏析 而 它们又是反石墨化元素 阻碍石墨的生长 使铸件中心过冷到产生白口的温度才结晶 从 而使铸件中心产生白口 球铁小件出现反白口的原因往往是由于热节部位稀土和镁偏析 含量偏高 厚大球铁件心部出现碳化物则往往是由于心部凝固时间较长 石墨核心容易被 熔解消失所致 Reverse chill Feature the fracture section center appear white color carbide and in the our location having comparatively quick cooling speed the tissue is normal The reason is the grey iron contains higher sulfur and lower manganese not meet Mn 1 7s 0 3 relation Additionally rion liquid absorb hydrogen or has little graphite core Sulfur and hydrogen tend to segregation to center but they are also anti graphitized component resisting the graphite grow the center will not crystal until reach to the super cooling temperature This will result in reverse chill in the center Small pieces of ductile appear reverse chill just because the segregation of rare earth and manganese take place in the hot spot Carbide appear in the center of the thick ductile just because the center location freezing cost long time The graphite core easy is easy to be solved and disappear 不锈钢精密铸造的机械性能比铸铁高 但其铸造性能却比铸铁差 因为不锈钢 精密铸造的熔点较高 钢液易氧化 钢水的流动性差 收缩大 其体收缩率为 10 14 线收缩为 1 8 2 5 为防止铸钢件产生浇不足 冷隔 缩孔和缩松 裂纹及粘砂等缺陷 必须采取比铸铁复杂的工艺措施 Stainless steel precise casting The mechanical property of the stainless steel precise casting is higher than iron casting but the casting capability is bad than iron casting Because the melting point is higher for ss precise casting the steel liquid oxidized readily and bad flow capability big reduction volume reduction is 10 14 the linear expansion is 1 8 2 5 to prevent insufficient pour and cold lap and shrinkage and looseness as well as crack and adhering sand more complicated measures will be taken 1 由于钢液的流动性差 为防止铸钢件产生冷隔和浇不足 铸钢件的壁厚不能 小于 8mm 浇注系统的结构力求简单 且截面尺寸比铸铁的大 采用干铸 型或热铸型 适当提高浇注温度 一般为 1520 1600 因为浇注温度 高 钢水的过热度大 保持液态的时间长 流动性可得到改善 但是浇温过 高 会引起晶粒粗大 热裂 气孔和粘砂等缺陷 因此一般小型 薄壁及形 状复杂的铸件 其浇注温度约为钢的熔点温度 150 大型 厚壁铸件的浇 注温度比其熔点高出 100 左右 Because of the bad flow capability of the steel liquid to prevent cold lap and insufficient pouring the thickness can not be less than 8mm the pouring mechanism should be simple and the cross section larger than iron section adopt dry model or thermal model elevate the pouring temperature generally 1520 1600 Celsius when temperature is high the steel liquid will be overheated this will keep long period of liquid state but higher temperature will cause big crystal hot cract and pore and adhering sand etc defect So for some small size and thin wall and complicated form casting the pouring temperature is about 150 celsius above the melting point for large size thick wall castings the pouring temperature is 100 celsius above the melting point 2 由于不锈钢精密铸造的收缩大大超过铸铁 为防止铸件出现缩孔 缩松缺陷 在铸造工艺上大都采用冒口和 冷铁和补贴等措施 以实现顺序凝固 Because of the reduction of ss is bigger greatly than iron to prevent shrinkage looseness so riser and chill and compensation etc measurers are token to realize the freezing in order 3 此外 为防止不锈钢铸件产生缩孔 缩松 气孔和裂纹缺陷 应使其壁厚均 匀 避免尖角和直角结构 在铸型用型砂中加锯末 在型芯中加焦炭 以及 采用空 心型芯和油砂芯等来改善砂型或型芯的退让性和透气性 In addition to prevent castings from occurring shrinkage looseness pore and cracks made the thickenss even avoid sharp and right angle Add sawdust to Molding sand add coke to molding core and adopt hollow molding core and oil core to improve molding core collapsibility and air permeability 简介 1 特征 金属液充型后 在金属液的交接处融合不好 而且在铸 件中产生穿透的或不穿透的缝隙称为冷隔 多出现在远离流道的铸件表面上和 薄壁处 形状呈液体初流动时的形状 单挑光滑 边缘呈圆角 图 3 15 2 产生原因 1 合金的化学成分不合适 出炉与浇注温度低 金属液氧 化严重 流动性差 2 浇注系统设计不合理 内浇道的位置不当 断 面面积过小 数量小 直浇道的高度低 液体金属压头不够 3 由于 金属液的数量不够 或因跑火等原因 造成浇注中断 4 金属液在型 腔的流动受到阻碍 3 防止方法 1 严格按照熔炼工艺操作 防