大型灰铸铁工作台导轨面铸造缺陷的防止措施

介绍了大型工作台铸件的结构特点,详细阐述了原生产工艺及导轨面出现的缩孔、缩松及气孔缺陷,通过对浇注系统设计、冒口补缩效果以及铁液凝固条件等方面进行分析,采取了以下措施:采用分层阶梯式浇注系统,使冒口晚于铸件热节处凝固,提高CE,增加废钢加入量和加大孕育量。生产结果显示:生产的205件大型工作台,只有6件产品因为缩孔、缩松和组织疏松等问题导致导轨面镶嵌导轨板,不良品率下降至2.93%。     

灰铸铁机床导轨面缺陷的补焊

某厂C6140机床是机加工生产中主要的设备之一,在使用过程中由于操作不当,造成机床导轨面的损坏,损坏部位在机床外侧距尾部约260 mm处,缺口大小为:长52 mm、深29 mm.使得机床无法正常工作.为了减少损失,尽快恢复生产,工厂决定尽快自行补焊.     

提高机床铸件床身导轨硬度的措施

根据对前阶段生产的铣镗床床身导轨所出现的问题进行分析,通过采取提高出炉温度、细化晶粒、合金化处理以及铸造工艺改进等措施,成功生产出各项力学性能均符合设计要求的床身铸件,其导轨硬度值不仅达到180～230 HB,而且加工前后以及薄厚断面的硬度值也相差很小.     

灰铸铁件裂隙状氮气孔及其防止

阐述了灰铸铁件裂隙状氮气孔的形成机理和防止方法，介绍了在含氮量高的铁液中加入钛铁以及通过改变炉料配比、减少白口倾向的防止缺陷的实例。     

采用锑和锰复合提高大型床身导轨硬度

介绍加锑提高大型床身导轨硬度的试验情况和生产应用结果。通过计算和铸件含锑量检查证明，加锑回炉铁反复使用，不会引起锑量无限地增加。     

孕育对高牌号灰铸铁件缩松的影响及其防止

孕育处理使灰铸铁共晶团数量增加，因而会引起内部缩松或外部缩陷等铸件不致密缺陷。笔者提出了防止这些缺陷的方法。     

石墨冷铁在铸造行业中的应用

我厂生产的铣床及铣镗类大中型灰铸铁件,如床身、工作台等;中小型球铁件,如压力机的导柱、铣床的拨叉等,采用粘土砂干模造型芯.其结构复杂,壁厚不均,综合性能要求高.采用铸铁冷铁作为激冷物效果不理想,易产生气孔、缩松、表面光洁度不好等缺陷.改用石墨冷铁效果好.     

高强度灰铸铁件典型质量问题探讨

铸造生产的困扰是因任何铸件的具体质量问题与缺陷表征及其原因是多种多样又彼此关联甚至相互对立。当生产高强度（HT300和HT350级）灰铸铁件时更为突出,较难处理的两对主要矛盾是：提高金属强度将引起石墨形态恶化;而材质性能的升高将加大铸件产生缩松的倾向并降低铁液流动性。本文拟就此进行分析并相应地探讨一些调解措施,有助于拟订调试工艺方案和分析问题。     

Shrinkage porosity and its relation to solidification structure of grey cast iron parts

Abstract

The purpose of this work was to investigate the relation between shrinkage porosity and the macrostructure. Based on results from an earlier investigation regarding shrinkage porosity and its characteristic features, a test casting was developed. The macrostructure was preserved using direct austempering after solidification heat treatment. Shrinkage porosity was found in regions where it was designed to occur. It was also found that this type of porosity is connected to the atmosphere via defects located on the surface, confirming earlier findings. Beneath the surface, it extends as a three-dimensional network through the casting. The shrinkage porosity was, in some cases, found along the boundaries separating primary crystals, and in some cases, it encircled separate primary crystals. A shrinkage porosity formation mechanism is proposed based on these observations, discussing the importance of a rigid columnar zone, movement of a local thermal centre and how pressure differences developing during solidification influence the formation of shrinkage porosity.     

Graphite nucleation control in grey cast iron

Abstract

A research programme has been undertaken to achieve a more detailed understanding of graphite nucleation control in grey cast irons, at different sulphur (0˙02–0˙1%), residual aluminium (0˙001–0˙010%) and zirconium (0˙001–0˙015%) levels in iron melts. It was found that three groups of elements are important to sustain a three stage model for the nucleation of graphite in grey irons:

(i) strong deoxidising elements (Al, Zr) to promote early formed very small microinclusions, oxide based, which will act as nucleation sites for later formed complex (Mn,X)S compounds

(ii) Mn and S to sustain MnS type sulphide formation

(iii) inoculating elements (Ca, Sr, etc.) which act in the first stage or/and in the second one of graphite formation, to improve the capability of (Mn,X)S compounds to nucleate graphite.

It was confirmed that 0˙07%S level is beneficial for graphite nucleation in grey irons with a lower incidence of carbides and undercooled graphite, compared to 0˙023%S cast irons. Low residual Al level (0˙001–0˙003%) results in higher chill and more undercooled graphite and lower eutectic cell count, in inoculated irons. A 0˙007–0˙010%Al content in the melt is important to sustain type A graphite nucleation and reduced chill. Not only inoculation but also the preconditioning (Al or/and Zr) of the base iron has a strong beneficial effect on the solidification pattern of cast irons. Both Al and Zr sustain the type A graphite formation with a lower degree of undercooling and free carbides. These elements were associated in a complex alloy (FeSi based), very efficient in preconditioning of grey irons for thin wall castings, at a low addition rate.     

灰口铸铁柱塞铸造缺陷的焊补

我厂橡胶分厂一台 16 0ｔ硫化平板机的柱塞因磨损严重多年老化等原因 ,已不能正常运转 ,需要更新。新铸造的毛坯在加工过程中 ,发现在其中间部位有一处约为 80ｍｍ× 10 0ｍｍ的大面积缺陷 ,经确定属浇铸流动性不好所造成的夹砂、疏松。缺陷位置的示意图见图 1。图 1　缺陷位置示意图1　缺陷分析柱塞体材质为ＨＴ2 0 0。由于灰口铸铁的含碳量较高 ,并含有较多的Ｓ、Ｐ杂质 ,强度低 ,塑性差 ,焊接性和焊后加工性能特别差。同时 ,柱塞的补焊区位于其中间位置 ,受热时有向外膨胀的倾向 ,补焊区受压 ,冷却时补焊区变为受拉力 ,随着补焊层的增加 …     

铸铁焊条在大直径铸铁阀门修补上的应用

我公司在阀门安装过程中,由于紧固时用力不均,导致与循环冷水泵出口相连的Dg500 PN1．6单向铸铁阀门的出口法兰根部沿周向出现裂纹,经检查发现裂纹长度有圆周长度的三分之二还多,裂纹深度基本上是贯穿性的,部分裂到法兰密封面上(图1中粗黑线),还有部分裂穿法兰螺栓孔之间(图1中虚黑线)．针对     

A comparison of dry and air-cooled turning of grey cast iron with mixed oxide ceramic tool

The present work compares the performance of a mixed oxide ceramic tool in dry and air-cooled turning of grey cast iron. First, the study was done in the range of process parameters where dry turning provided satisfactory performance. The contours of surface roughness and tool life were generated with the help of trained neural networks. A novel procedure of neural network training is used in this work. The study was extended to the range in which dry turning performed poorly in terms of tool life. Tool wear, surface roughness of the machined job and forces and vibration during the cutting were studied. It was observed that air-cooling significantly reduces the tool wear at high cutting speed. At higher cutting speeds, where the dry turning performs very poorly, the air-cooled turning provides an improved surface finish also apart from the reduction in tool wear. In all the cases, the cutting and feed forces get reduced in air-cooling. Thus, air-cooled turning of grey cast iron with mixed oxide ceramic tools offers a promising environment-friendly option.     

Study of shrinkage porosity in spheroidal graphite cast iron

This study aims at identifying the relationship between the shrinkage cavities and the solidification structure in spheroidal graphite cast iron. Cast samples specially designed to contain shrinkage cavities were used. The solidification macrostructure was revealed using the Direct Austempering After Solidification method, while the solidification microstructure was revealed by using colour etching. At the midsection of the pieces, the shrinkage cavities and the solidification structure were observed jointly. The study showed that the classification of shrinkage porosity found in literature does not correspond to the ductile iron solidification model recognized by most of the scientific community. Early solidification models, and therefore shrinkage formation mechanisms, were proposed in instances when there was not a thorough knowledge of the morphology of the solid phases during solidification. Nowadays, defects formation mechanisms can be described with higher accuracy. Therefore, an updated classification of shrinkage porosity for spheroidal graphite iron is proposed.     

Mechanism and estimation of porosity defects in ductile cast iron

Abstract

Although there are many works on the formation mechanism of porosity defects due to solidification in ductile cast iron, the formation mechanism is still not clear and decreasing the porosity defects is still a main issue in the industry. This paper critically reviews conventional explanations for the porosity formation including estimation methods. Based on the discussion the authors propose a formation theory where it considers gas and oxide entrapment during mould filling, expansion of outer part of casting due to graphite formation and pressure decrease in the inner part, followed by the growth of entrapped small gas bubbles. This mechanism can explain various facts in practice and be usable to estimate the defects. It also gives a good way to design effective risers. Future challenges are also discussed including the effect of inoculation on the fluidity of the mushy region.     

Gas absorption in grey cast iron during mould filling

Abstract

The effect of mould filling on the hydrogen and nitrogen concentration in grey cast iron has been investigated. A special mould was designed and the influence of several process and mould parameters, such as degree of turbulence, permeability, core binder and coatings, were studied. The hydrogen concentration increased during mould filling and the absorption was favoured by turbulent filling, low permeability and larger gas evolution from the mould and cores. In some cases, the hydrogen concentration in the iron after mould filling almost reached the solubility limit, which increases the risk that gas precipitates during solidification.

Exact values of the influence of mould filling on the nitrogen concentration could not be obtained, but some observations could still be conducted. The absorption of nitrogen seemed to be favoured by the same parameters as hydrogen.