The Fluidity of Sodium and Strontium Modified Sand-cast Aluminium-Silicon Foundry Alloys

The fluidity of A319, A356 and A413 alloys has been measured using a sand-cast spiral in the 700°C to 750°C temperature range. Modification by either sodium or strontium has no detectable effect on the fluidity and does not change the temperature dependence of fluidity within this temperature range. Measurements at 745°C indicate that sodium levels up to 0.037 wt% or strontium levels up to 0.024 wt% have no effect on the fluidity of sand-cast A356 alloy.     

Rapid fabricating process of zinc alloy moulds based on vacuum casting process

Abstract

A rapid fabrication process was developed by combining stereolithography prototype, silicone rubber mould and vacuum casting process for zinc alloy moulds. Transfer coating mould was introduced as casting moulds reproduced from silicone rubber moulds. Vacuum casting process was applied to improve filling ability of complicated mould with fine pattern surface. Vacuum reduces the gas counterpressure in the casting mould cavity and then improves the filling ability.     

A Study of the Microstructure,Mechanical Properties and Weldability of Low-carbon Ductile Iron

Abstract

Low-carbon cast iron (1.7–1.8% C, 1.7–2.2% Si) test bars and castings were prepared in a production foundry for evaluation of their microstructures and mechanical properties. The experimental variables were (a) inoculant types and (b) heat treatment cycles. Results indicate that low-carbon ductile cast irons with graphite present in spheroidal/compacted form may be satisfactorily produced on an industrial scale, after appropriate inoculation. However, a short normalising cum tempering heat treatment is necessary for the development of optimum mechanical properties. Low carbon irons can be satisfactorily welded to similar grades of cast irons as well as to steel.     

Sensitivity study of IHTC on solidification simulation for automotive casting

Abstract

Interface heat transfer coefficient values between the mould/metal interfaces need to be precisely determined in order to accurately predict the thermal histories at different locations in automotive castings. Thermo-mechanical simulations are carried out for Al–Si alloy casting processes using a commercial code. The simulation results are verified with experimental data from the literature. Sensitivity studies show that the choice of the initial value of the interface heat transfer coefficient (IHTC) between chill/metal as well as the sand mould/metal interfaces has a marked effect on the cooling curves. In addition, having chosen an initial value of the IHTC, the analyses also show differences in the solidification rate of the casting alloy near the sand/metal and chill/metal interfaces, upon further cooling. The gap formation, which results in a change in IHTC from the initial value, does not affect the cooling curves in the vicinity of the sand/metal interface due to lower thermal conductivity of sand. However it is found to have a considerable effect in the chill/metal interfacial regions due to higher thermal conductivity of the chill. Based on these studies we recommend initial IHTC values of 3000 and 7000 W m^–2 K^–1 for sand/metal and chill (steel)/metal interfaces respectively, for application in casting simulations.     

A Dual Stream Model of Carbon Pickup based on Carbon Activity

Abstract

An improved model of carbon pickup (CPU) in cupolas was derived from a previous model. The improved model assumes that, upon melting, (1) the liquid iron and steel descend the cupola without intermixing (dual stream assumption) and (2) the instantaneous rate of change of carbon activity, a_c, is da_c/dt=k·(1-a_c), where k is a rate constant and 1 equals carbon activity in coke. The model involves a single temperature-dependent rate parameter which was determined from experimental data. The revised model accurately correlated CPU when the proportion of steel in the charge varied from 0–50%. The standard error was <0.10%C. Inputs to the model are the relative weights of the metallic charge constituents, their compositions, and tapped iron temperature. Outputs are the CPU for each charge metal and the overall CPU.     

铁液纯净度对铸铁件质量的影响

综述了微量元素Pb、Te、As、Ti对灰铸铁件组织和性能的影响规律以及对球铁件质量的影响情况;介绍了Ti、V、Pb、Te等元素含量与铸件加工性能的关系;认为可通过使用高纯生铁、优质铸造材料,优质废钢+增碳工艺的感应炉熔炼、冲天炉+感应电炉双联熔炼,利用RE消除微量元素的不利影响等措施来提高铁液的纯净度。     

Influence of Bismuth on Graphite Nodule Count in Thin-section Spheroidal-graphite Cast Iron

Abstract

Cast irons containing 3.8% C and 2.2% Si were melted in a graphite crucible using a high-frequency induction furnace. Nodularisation treatment was carried out at 1530°C by the addition of 1.6% Fe-Si-Mg alloy and various amounts of bismuth as metallic bismuth, bismuth oxide and bismuth sulphide. When the magnesium reaction subsided, the melts were post-inoculated with Fe-Si and then poured into CO₂ Process sand moulds. The occurrence of chilled structure and graphite-nodule counts were determined using an optical microscope and an image analyser. X-ray microanalysis and emission spectrochemical analysis were carried out to detect Bi in the graphite nodules and also in nodules extracted with dilute hydrochloric acid. The nodule count was enhanced by the addition of extremely small amounts of metallic bismuth, bismuth oxide and/or bismuth sulphide. Some heterogeneous phases containing Bi, Mg, Ti, Fe and Si, with diameters of 1 μm or less were observed at the centres of graphite spheroids using back-scattered electron imaging and an energy dispersion X-ray microanalyser. Graphite crystallises on these phases during eutectic solidification. It is suggested that large numbers of fine liquid bismuth particles contribute to the formation of graphite spheroids by acting on the substrate.     

铁液温度对球铁件质量的影响

结合河南、安徽等省二十多家工厂的调研结果，叙述熔炼温度、球化处理温度和浇注温度对球墨铸铁件质量的影响。指出与十多年前相比，冲天炉的熔炼温度和出铁温度提高了30～50℃，温度变化范围大为缩小，铁液含硫量也明显降低，但生产中应采取措施，确保不同铸件有恰当的温度范围。     

孕育剂对灰铸铁件不同性能的影响

灰铸铁添加合金元素后,结构复杂的铸件在铸造缺陷处试压过程中渗漏或使用过程中漏油,白口倾向导致机械加工性能恶化。用合适的孕育剂进行孕育是消除铸件铸造缺陷和改善铸件切削性能的重要措施。在保证冶金质量的前提下,在铁硅孕育剂的基础上添加其它元素的复合孕育剂进行孕育可以显著提高铸件的力学性能。配合铸造工艺,一些孕育剂对技术要求高的灰铸铁件进行孕育可以同时提高铸件的铸造性能、机械加工性能和力学性能。     

复合淀粉对铸铁件水玻璃砂溃散性的影响

针对铸铁件水玻璃砂溃散性差的现状进行了一系列工艺生产试验。结果表明：加入0．7％左右的自制复合淀粉，可明显降低铸铁件水玻璃砂的残留强度，改善其溃散性。     

The Horizontal Ohno Continuous Casting Process: Process Variables and Their Effects on Casting Stability

Abstract

Temperature profile measurements within a heated mould have been made during continuous casting of pure tin rod of 8.5 mm dia in an attempt to obtain an understanding of the influence of process variables on the position of the solidification front. It has been established that process variables such as casting speed, mould temperature and cooling position have a sensitive effect on the position of the solidification front. It varies linearly with casting speed for a given cooling position and mould temperature. The change in position of the solidification front in turn exerts a significant effect on the surface quality of the cast strand. It has been demonstrated that the solidification front should be brought well within the mould in order to obtain good dimensional and casting stability.     

Ti对灰铸铁件性能的影响

介绍了不同Ti量对中低CE灰铸铁件组织、力学性能和致密性影响的研究方法。试验结果表明:(1)一定量的Ti增加了铁液的过冷倾向,促进了灰铸铁件D型石墨的形成,湿型砂造型的D型石墨明显多于干型砂。(2)随着铁液中w(Ti)量的增加,中低CE灰铸铁件中D型石墨也不断增加。当D型石墨达到较高比例时,铸件中的厚大热节也大量出现D型石墨,CE较高的铸件力学性能增加;当CE降为3.66%,随着w(Ti)量增加,强度下降幅度较大。(3)随着w(Ti)量的增加,灰铸铁件的致密性下降,缩松几率明显增加。w(Ti)0.17%、w(Al)0.023%时,灰铸件缩松几率为70%。     

微量元素对大断面球铁组织与性能的影响

在实验室条件下,研究了添加一定量的合金A和合金B对φ590 mm×800 mm大断面球铁件组织和性能的影响,结果显示:当合金A的加入量(质量分数)为0.03%时,抑制大断面球铁件中石墨畸变的效果最佳;同时发现:强制冷却能进一步改善大断面球铁件的石墨形态和基体组织。     

煤粉的理化特性对铸铁件表面质量的影响

叙述了煤粉的理化特性,与煤粉有关的高温化学反应及对铸件表面质量的影响,根据生产实践,认为在原砂粒度与耐火度合适的前提下,适当地加入煤粉,可改善铸件表面质量。     

铁液冶金质量对机床铸件质量的影响

简述了铁液冶金质量对灰铁铸件质量的影响情况。为解决原用熔化设备和工艺生产的铸件所存在的质量问题,改用较大的冲天炉取代小型冲天炉,并采用优质冷压成型焦取代土焦,提高渗碳率,从而提高了铁液的冶金质量,在保证力学性能的前提下提高了碳当量,改善了铁液的铸造性能,从而消除了铸造缺陷,降低了废品率。     

工艺与材料对中小球铁铸件组织的影响

大批量生产中小球铁件时,生铁,废钢与球化剂对铸件的组织影响很大,合理的工艺与有效的措施,能够改善铸件的组织.     

EPC铸铁件表面皱皮缺陷的研究进展

在铸铁件消失模铸造生产中，经常遇到铸件表面出现皱皮缺陷，影响铸件的表面品质。结合工厂生产实践，论述消失模铸造铸铁件皱皮缺陷产生的机理、原因和防止的途径，并提出进一步研究的方向。     

球墨铸铁铸件的补缩工艺

通过分析和总结在生产实践过程中球墨铸铁铸件产生缩孔缩松缺陷以及成功解决办法,对球铁铸件凝固收缩理论提出理解和看法:铸件的补缩及缺陷产生取决于压力,由于球铁的凝固特性使石墨化膨胀和凝固收缩分离.薄壁件截面凝固差异不明显,石墨化膨胀压力无法有效利用,厚大件的截面凝固的差异大,容易实现石墨化膨胀压力的利用.铸造补缩工艺的设计原则就是提供并保持这样的压力,对薄壁要强调外部压力补缩,厚壁则充分利用石墨化膨胀压力自补缩.     

灰铸铁件表面缩松缺陷的防止

采用控制碳当量,提高硅碳比,并与成形冷铁技术相配合。实践表明,这些措施有效地防止了灰铸铁件的表面缩松缺陷     

磺酸硬化呋喃树脂砂对球铁件表层组织的影响

研究了用对甲苯磺酸(VISA)作催化剂的呋喃树脂自硬砂型生产稀土镁球铁件时,铸件表层出现的球化衰退现象及其影响囚素.结果表明:树脂砂中的对甲苯磺酸加入量和再生砂的回用量增加,球铁件表层片状石墨区的深度增大;浇注温度越高或铸件壁越厚大,球铁件表层的球化衰退越严重;球化衰退层的深度随稀土镁球化剂加入量增加而减薄.