Spray forming: Science and technology

Spray forming involves sequential gas atomization of a melt into a spray of fine droplets and their deposition on a substrate to build up a high-density preform. The rapid solidification inherent in spray deposition generates refined, equiaxed and low segregation microstructures. A number of promising features of this near-net shape manufacturing process are highlighted and compared, wherever possible, with the conventional casting and PM techniques. Some commercial nozzles used to create spray and mechanisms associated with spray generation are described. The consolidation of the droplets and the development of the microstructure in the deposit are primarily governed by the nature of the spray and the thermal state of droplets on the deposition surface. Several microstructural characteristics of the deposit are presented and their origin in spray deposition is discussed.     

一种悬臂式钢管喷印装置及其控制系统

本文介绍了一种用于成品钢管生产线上的悬臂式钢管喷印装置，它是一台结构和功能都较复杂的大型机电一体化设备。文中简介了它的性能、特点和工作原理，对其各部分机械装置的构成及动作以及喷印控制系统的组成和功能进行了较为深入的描述。     

横流环境中两孔热水浮射流数值模拟研究

为了达到热废水排放过程中热水快速稀释的目的,采用Fluent中Realizable k-ε模型基于SIMPLEC算法,研究了热射流过程中,射流孔间距、初始流速对射流流场、温度场的影响规律。研究表明:随着射流孔间距的增大,第1孔射流对第2孔射流影响程度逐渐减弱且第2孔射流的弯曲程度随之增加;射流与横流作用促使反向涡对的产生,加快了热水与环境水体的掺混度,横断面温度场出现"肾形"分布;当相对孔间距相同时,随着射流初始流速的增加,第1、2孔射流温度衰减速率随之增大;射流初始流速相同时,射流孔间距的增加对第1孔射流轴线温度稀释度影响较小,对第2孔射流的轴线温度稀释度影响相对复杂;S/D=2时,增大热射流的初始流速,为本研究中热水快速稀释的最优方案。     

中压分离器夹套部位接管组焊工艺

针对中压分离器夹套部位接管结构特点,分析了在制造过程中所面临的困难问题。介绍了为此而制定的特殊工艺方案以及方案的实施情况和结果。     

稳定段长径比对喷嘴雾化性能的影响

利用相位多普勒粒子分析仪,对BW J(Ⅲ)型干气雾化进料喷嘴的2种新型喷头雾化特性进行了冷态实验研究。在不同的喷嘴稳定段长径比下,对喷嘴的雾化粒径及喷射角分别进行了试验测量,并对雾化粒径和喷射角随长径比的变化规律进行了分析。同时,文中介绍了新型雾化进料喷嘴的结构、冷态试验研究装置和测量设备。结果表明,稳定段长径比对于雾化粒径及喷射角有比较明显的影响,试验结论为雾化喷嘴的设计提供了一定依据。     

基于梯度功能的陶瓷水煤浆喷嘴的设计

在分析水煤浆喷嘴工作特性和磨损机理的基础上,提出了梯度功能陶瓷水煤浆喷嘴的设计模型,’并对单向梯度功能陶瓷喷嘴的残余应力进行了有限元分析。结果显示,梯度功能陶瓷喷嘴内部的残余压应力能缓解喷嘴工作时的热应力,提高陶瓷喷嘴的抗热冲蚀磨损能力。     

Numerical simulation and experimental investigation of gas–powder flow from radially symmetrical nozzles in laser-based direct metal deposition

Laser-based direct metal deposition (DMD) is a solid freeform fabrication process capable of fabricating fully dense and metallurgically sound parts. The process has been greatly enhanced toward multi-directional deposition by the use of discontinuous radially symmetrical powder nozzles to supply the build material. Since many operational parameters depend on the gas–powder stream characteristics between the nozzles and the deposition point, an extensive understanding of the gas–powder flow is necessary. Three-dimensional (3D) multi-phase gas–powder flow structures of radially symmetrical nozzles are modeled using computational fluid dynamics methods. The obtained results are in good agreement with the experimental ones, and they provide a good insight into the process phenomena.     

基于PIV技术的七喷嘴气化炉流场研究

为研究七喷嘴气化炉的流场分布,建立了顶置七喷嘴气化冷模试验装置,采用激光粒子成像测速系统(PIV)在气化炉的上部、中部及下部视窗进行了流场测试,比较分析了颗粒流量、分散风流量对气化炉流场的影响。结果表明,在颗粒流量20~150 kg/h,分散风流量740~880 m3/h的工艺条件下,气化炉上部流场呈现自由射流特点,射流长度为40 cm,平均射流速度为25 m/s,中下部流场则以返混区为主,流速在8 m/s以下;颗粒流量增大会使得最大射流速度由40 m/s降低至15 m/s,且气化炉上部射流粒子束的径向脉动增强,造成射流弥散;分散风流量增大使得最大射流速度由25 m/s增至35 m/s,射流长度无明显变化。颗粒流量和分散风流量对流场的影响主要体现在气化炉上部,对中下部流场的影响逐渐减弱。     

Molybdenum disilicide-silicon nitride bushing nozzles tailor-made for basalt fibers production

A carefully comparative study of several ceramics compounds allowed the identification of MoSi₂ blended with Si₃N₄ as a suitable material for the realization of bushing nozzles, specifically designed for basalt fibers production. Degradation static tests were developed and performed to demonstrate the high resistance to oxidation at operating temperature of MoSi₂-Si₃N₄ composites with respect to alumina, zirconia stabilized with magnesia or yttria, pure MoSi₂, pure Si₃N₄, and MoSi₂ englobing SiC. Moreover, the MoSi₂-Si₃N₄ composites resulted resistant to corrosion and chemical inert with respect to oxidizing components present in basalt melts.Bushings in MoSi₂-Si₃N₄ were obtained by using hot isostatic pressing and were processed through mechanical drilling. The basalt fibers produced with the MoSi₂-Si₃N₄ bushing showed a constant diameter and a regular surface morphology. The bushing was recovered intact without defects or fractures demonstrating the efficiency of the selected material. Replacing platinum-rhodium bushings with ceramic ones could greatly reduce costs of basaltic fibers production and could encourage the use of these eco-friendly, natural fibers as reinforcement in lightweight polymer composites.