Warm bending mechanism of extrados and intrados of large diameter thin-walled CP-Ti tubes

In order to develop the warming bending technology of the large diameter thin-walled（LDTW） commercial pure titanium alloy CP-Ti tubes, the warm bending mechanism of the extrados and intrados of LDTW CP-Ti tubes was researched. By EBSD analysis and Vickers hardness test, the changes of microstructure and strength of the tubes at different bending temperatures of 293, 423 and 573 K, were analyzed. The results show： 1） The extrados of the bent tube deforms mainly by slip, along with few twinning, and the preferred orientation is similar to that of the initial tube; the intrados of the bent tube experiences compression deformation mainly by {1 012} tensile twinning, and the twinning makes the preferred orientation of wall materials change sharply. 2） The Vickers hardness values of both the extrados and intrados of the samples after bending increase greatly; the Vickers hardness values of the intrados are much higher than those of the extrados, and Vickers hardness values of the RD-TD planes are always higher than those of the RD-LD planes, which are related to the different deformation mechanisms.

Effects of process parameters on numerical control bending process for large diameter thin-walled aluminum alloy tubes

Numerical control(NC) bending experiments with different process parameters were carried out for 5052O aluminum alloy tubes with outer diameter of 70 mm, wall thickness of 1.5 mm, and centerline bending radius of 105 mm. And the effects of process parameters on tube wall thinning and cross section distortion were investigated. Meanwhile, acceptable bending of the 5052O aluminum tubes was accomplished based on the above experiments. The results show that the effects of process parameters on bending process for large diameter thin-walled aluminum alloy tubes are similar to those for small diameter thin-walled tubes, but the forming quality of the large diameter thin-walled aluminum alloy tubes is much more sensitive to the process parameters and thus it is more difficult to form.

Significance-based optimization of processing parameters for thin-walled aluminum alloy tube NC bending with small bending radius

Thin-walled aluminum alloy tube numerical control （NC） bending with small bending radius is a complex process with multi-factor coupling effects and multi-die constraints. A significance-based optimization method of the parameters was proposed based on the finite element （FE） simulation, and the significance analysis of the processing parameters on the forming quality in terms of the maximum wall thinning ratio and the maximum cross section distortion degree was implemented using the fractional factorial design. The optimum value of the significant parameter, the clearance between the tube and the wiper die, was obtained, and the values of the other parameters, including the friction coefficients and the clearances between the tube and the dies, the mandrel extension length and the boost velocity were estimated. The results are applied to aluminum alloy tube NC bending d50 mm×1 mm×75 mm and d70 mm×1.5 mm×105 mm （initial tube outside diameter D0 × initial tube wall thickness t0 × bending radius R）, and qualified tubes are produced.

Influence of deformation zone length on bending radius of SS304 tubes with small diameters manufactured via free bending-based active motion

In three and six-axis free-bending equipment,the deformation zone length(A)is a fixed mechanical structure parameter modified when the relevant structure is redesigned and manufactured.In this study,a six degree of freedom(6-DOF)parallel mechanism was used as the control mechanism of the bending die,and a new method of changing the deformation zone length(A)was proposed.Firstly,an idealized geometric model of free bending-based active motion was established.Then,the influence of the deformation zone length(A)on the bending moment and the bending radius of the tube was analyzed.In addition,the finite element simulation and a kinematic model of free bending-based active motion controlled by the 6-DOF parallel mechanism were established,and bending processes of the SS304 tube with different deformation zone lengths were investigated.Afterwards,the impact of the deformation zone length(A)on the bending radius,bending moment,wall thickness,and motion of the parallel mechanism were analyzed.Finally,experiments were carried out on the free-bending equipment based on the 6-DOF parallel mechanism.Experiments verified the rules in the theoretical analysis,finite element simulation,and kinematic simulation.

Forming limits under multi-index constraints in NC bending of aluminum alloy thin-walled tubes with large diameters

With increasing diameters of aluminum alloy thin-walled tubes (AATTs), the tube forming limits, i.e. the minimum bending factors, and their predictions under multi-index constraints including wrinkling, thinning and flattening have been being a key problem to be urgently solved for improving tube forming potential in numerical control (NC) bending processes of AATTs with large diameters. Thus in this paper, a search algorithm of the forming limits is put forward based on a 3D elastic-plastic finite element (FE) model and a wrinkling energy prediction model for the bending processes under axial compression loading (ACL) or not. This algorithm enables to be considered the effects of process parameter combinations including die, friction parameters on the multi-indices. Based on this algorithm, the forming limits of the different size tubes are obtained, and the roles of the process parameter combinations in enabling the limit bending processes are also revealed. The followings are found: the first, within the appropriate ranges of friction and clearances between the different dies and the tubes enabling the bending processes with smaller bending factors, the ACL enables the tube limit bending processes after a decrease of the mandrel ball thickness and diameters; then, without considering the effects of the tube geometry sizes on the tube constitutive equations, the forming limits will be decided by the limit thinning values for the tubes with diameters smaller than 80 mm, while the wrinkling for the tubes with diameters no less than 80 mm. The forming limits obtained from this algorithm are smaller than the analytical results, and reduced by 57.39%; the last, the roles of the process parameter combinations in enabling the limit bending processes are verified by experimental results.

小径管X射线焊缝图像缺陷识别算法

针对小径管X射线焊缝图像缺陷检测精确率低的现状,通过对图像进行特征分析并结合稀疏字典学习,提出一种基于图像分割的小径管焊缝图像缺陷检测算法.首先,对小径管焊缝图像进行两步图像分割获得感兴趣区域;其次,提取焊缝缺陷,得到缺陷疑似局部图像;最后,提出以不同类型原子间相关性最小为目标的小径管焊缝缺陷字典矩阵数学模型并使用K-SVD算法进行求解,利用该字典矩阵实现圆形缺陷、线形缺陷和噪声的分类鉴别.为提高系统实时性,使用并行编程对图像分割算法进行加速.结果表明,改进后缺陷字典矩阵对圆形缺陷识别成功率为0.974,线形缺陷识别成功率为0.967,且具有较快的识别速度,实现了小径管焊缝图像缺陷的有效识别.

房间空调器小管径室外换热器流路优化

随着空调器的快速发展和国际铜价的持续升高,制冷空调行业采用的换热器在向着小体积、低成本发展的过程中往往面临着性能衰减的技术瓶颈。为突破此瓶颈,以一款冷暖型房间空调器翅片管式室外换热器为研究对象,将其换热管外径由7 mm减小至5 mm并在此基础上优化其流路,最终实现Φ5 mm换热器性能达到初始样机水平并有效降低换热器成本。首先,分别在5种标准工况下测试初始样机性能;然后,利用CoilDesigner软件来分析小管径化对换热器性能的影响,仿真结果表明,在不改变流路布置的情况下,Φ5 mm换热器的换热能力略有提升,但制冷剂侧压降增大4~7倍;进一步地,有针对性地设计了5种流路布置方案来探究分路数、分路汇合位置等因素对换热器传热及压降特性的影响规律,总结了小管径翅片管式换热器流路优化的思路,并设计了3种Φ5 mm管径室外换热器流路优化方案。仿真评估3种方案的可行性后制作样机进行性能测试,实验结果表明:方案(3)性能与原换热器相当,同时其材料成本可降低34.6%。

核用小直径传热管衬管焊接TIG焊枪的设计及优化

随着我国核工业进入第3个30年发展阶段,核用设备的维修需求日益迫切。核用蒸汽发生器内部结构复杂,关键传热管结构管径小、管道长、拆卸安装难度大,传统修复方法难度极高。针对核用小直径传热管因长期处于高温高压工况而出现的腐蚀破坏问题,文中设计了一种全位置自动化TIG衬管焊接修复焊枪,并进行了焊枪可靠性验证和焊接修复试验。首先,提出了焊枪的总体结构设计方案,并阐述了所设计焊枪相对传统钨极TIG焊枪的优势;接着,完成了焊枪传动系统的设计与验证,所设计的传动系统体积小、空间利用率高;随后,对焊枪关键部位——导电轴进行了刚度理论建模、分析和实例计算,并通过有限元求解验证了理论模型的可靠性,在此基础上提出了焊枪结构的优化方法;最后,进行了现场挠度检测和焊接试验,验证了导电轴的刚度满足现场焊接工况,并用线性回归方程和挠度修正公式定量预测焊枪挠度变形,验证了所设计结构的合理性;焊接试验表明焊枪工作时传动系统的转速稳定可控,焊缝成形良好。文中所研制的焊枪能够满足核用蒸汽发生器不锈钢传热管的衬管焊接修复工艺要求。

小直径管幕工法横导洞施工现场试验及参数优化

对沈阳地铁市府大路站采用的小直径管幕工法进行研究,首先通过现场监测分析了车站横导洞施工对地表沉降和拱顶变形的影响,然后利用Midas GTS NX数值软件建立车站三维模型,并与监测数据对比验证了模型的准确性,最后分析了横导洞数量及施工顺序对地表沉降的影响.研究结果表明:横导洞开挖施工引起的地层损失率为0.08%,管幕结构有效地抑制了地表沉降;相比于其他开挖方案,采用先边后中的开挖顺序可有效减少地表沉降24.7%;当横导洞开挖数量为5~7时,引起的地表沉降差较小仅为8%,采用4个横导洞和3个横导洞施工时,相比于7个横导洞施工方案可分别减少地表沉降18.0%和28.3%.

小管径管束外含空气的蒸汽冷凝传热特性分析

针对空气-蒸汽冷凝高效排热问题,本文采用CFD方法进行了小管径管束外冷凝传热特性分析。通过对不同管束结构进行建模并对管径为d、3排多列管等典型结构的综合分析发现:管间距较小时(≤2 d),空气层的叠加效应是影响小管径管束冷凝传热的关键因素,冷凝换热系数略低于大管径管束且明显低于单管。大管间距(>2 d)条件下,管束抽吸效应成为主控因素,使小管径管束冷凝传热系数高于大管径管束,甚至超过单管起到强化传热作用。管束结构布置方案对空气-蒸汽冷凝传热特性同样具有显著影响。

R32制冷剂在小管径水平管内的沸腾换热与阻力特性实验研究

针对污染小、能效高、可燃性差、低毒性的新型R32可替代制冷剂在水平管内低温工况下的沸腾换热特性开展研究,设计并自主搭建了管内对流沸腾相变换热实验系统,分别开展了3 mm、4 mm小管径水平管内低温R32沸腾换热的实验研究,探究了质量流速、热流密度、饱和温度等参数对R32对流沸腾换热特性的影响,分析了蒸干对沸腾换热系数恶化的影响机制。结果表明:3 mm内径管的沸腾换热相比4 mm通道平均提升约8%~12%,且高质量流速下的临界干度几乎与管径无关;相较传热特性,R32饱和温度对两相流动阻力更为敏感,饱和温度自13℃降低至11℃时阻力损失提高约23%;利用改进的Fang关联式,可实现小管径水平管内R32对流沸腾换热系数预测,88.56%的实验数据误差可控制在±10%范围内。

小管径顺排管束单元换热特性实验研究

小管径管束的管外对流换热系数对航空发动机用紧凑换热器的设计至关重要。为探究小管径光管管束的管外对流换热特性,设计了不同横向管间距比和流向管排数的顺排光管管束换热单元,并通过实验方法分析了管束横向管间距比、流向管排数和流动雷诺数对管束平均管外对流换热系数的影响。结果表明:经典换热经验关系式对小管径管束的管外努塞尔数预测误差基本在10%以内;不同横向管间距比下管束的管外换热努塞尔数随流动雷诺数增加的趋势不同,相比于大横向管间距比,小横向管间距比下管外努塞尔数在低雷诺数时增加更快,在高雷诺数时则增加更慢;管束的平均管外努塞尔数随着流向管排数的增加而增加,且小横向管间距比时管束流动更快达到充分发展状态。

基于NSGA-III算法的小管径翅片管式蒸发器高维多目标优化

以稳态分布参数法和NSGA-III算法为基础,提出一种翅片管式蒸发器结构参数与流路参数混合寻优的方法,并依此展开小管径蒸发器结构和流路参数的影响分析与流路的高维多目标设计优化。建立的小管径翅片管式蒸发器模型与实测数据的误差在4%以内,可以较好地用于小管径翅片管式蒸发器的计算。基于该模型进一步建立以结构参数与流路参数为自变量,换热量、制冷剂侧压降、空气侧压降以及成本为因变量的神经网络模型,并利用NSGA-III算法对模型进行优化求解,得到小管径翅片管式蒸发器在一定的结构参数变化范围内的最优结构参数及最佳流路。研究结果显示:管外径对小管径翅片管式蒸发器的换热量、制冷剂侧压降以及成本的影响程度最大;翅片间距对小管径翅片管式蒸发器的空气侧压降影响程度最大;翅片厚度对换热量、制冷剂侧压降、空气侧压降以及成本的影响程度均最小;流路主要影响蒸发器的换热量及制冷剂侧压降;制冷剂流路为二支路、三支路和四支路时,模型可输出综合性能最优的结构及流路特征。

小管径壁厚超声测量方法及测量不确定度分析

导管等管状类零件是飞机、发动机等产品的重要构件,这类构件承担着输送燃油、液压、氧气、冷气等任务,处于承压工作状态,需要保证零件的强度,才能保证产品的使用安全,壁厚作为直接影响强度的指标,通常对于其最小厚度有着严格的控制要求。但是常用的超声测厚在实际的小管径厚度现场测量时会出现测量数据不稳定甚至无法显示厚度数据的现象,导致超声测厚数据无法作为厚度评价依据。论文针对小管径管状类零件壁厚超声测量难题,通过对超声测厚机理的分析,提出频率、换能器直径、延迟块外形、换能器夹持工装等方面的改进建议,从而获得稳定有效的测量数据。同时对改进后的超声测厚提出基于蒙特卡洛方法的测厚不确定度分析方法,并通过试件进行测量不确定度的分析、评定,供从事小管径壁厚超声测量的检测人员参考。

小口径低碳钢-不锈钢复合钢管焊接新工艺

某小口径低碳钢-奥氏体不锈钢复合钢管的制造项目,由于钢管口径太小,无法选择“先基层,再过渡层,最后覆层”的常规焊接工艺填充顺序,而只能考虑单面焊双面成形,即先焊接覆层,后焊接基层。通过深入研究低碳钢-奥氏体不锈钢复合板常规焊接工艺的机理,以及分析不能直接在不锈钢表面堆焊碳钢的原因,探索性地引入工业纯铁作为新型过渡层填充材料。利用纯铁含碳量低的特性,避免了焊接接头中出现晶间腐蚀、热裂纹和冷裂纹倾向等问题,其塑性、韧性好的特点也进一步克服了直接在不锈钢表面堆焊碳钢会出现的裂纹问题。通过一系列试验验证了此工艺的合理性,从而获得了一种全新的焊接小口径低碳钢-奥氏体不锈钢复合钢管的方法。

渤海油田325″有缆智能工艺优化研究

针对渤海油田传统分层注水技术无法即时进行数据采集及在线调配的问题,本文提出了325″有缆智能工作筒的结构设计,通过力学计算以及水嘴优化设计,开发了一种适用于渤海油田分层注水的小直径智能工作筒,对配套的流量计以及在线验封技术开展了理论分析研究,确保优化设计后的工艺能实现有效分层注水。

采用小管径蒸发器的除湿机性能及成本分析

由于铜价的高涨,小管径蒸发器是当前降低除湿机成本的有效技术手段之一。基于实验对分别应用7.0 mm/5.0 mm管径蒸发器的除湿机进行性能特性和成本分析,并针对5.0 mm管径蒸发器的优化设计方法进行比较。研究结果表明:在相同的测试工况下,分别应用7.0 mm/5.0 mm蒸发器的除湿机的整机运行功率与制冷剂量呈现负相关;而整机除湿量和表示除湿机能效的EF值(Energy Factor)随制冷剂量的降低呈现先升高后下降的趋势,存在最佳制冷剂量,应用5.0 mm管径蒸发器的除湿机最佳制冷剂量较7.0 mm管径蒸发器至少要低4.76%;分流设计对提升整机除湿量和EF值的优势最为明显,可分别提升11.04%和10.98%;在满足相同除湿量和EF值的设计要求条件下,5.0 mm管径蒸发器的总成本较7.0 mm管径蒸发器下降了9.66%。

V型小管径换热器仿真及实验研究

多联机在家装市场的广泛应用,对室内机换热器尺寸提出了更高的要求。换热器铜管、翅片规格和安装角度等对室内机换热能力影响显著。针对某款室内机换热器,首先利用CFD仿真软件研究了不同换热器角度的风场分布,而后分别通过实验研究了Φ7 mm与Φ5 mm管径的换热器风阻与换热能力。CFD仿真研究发现,限定空间内V型54°风场分布最优;实验结果表明,限定空间内V型54°制冷和制热能力最优。考虑机组宽度上增加幅度对机组运输有一定的影响,实际应用的换热器夹角宜在51°~57°范围内。

锅炉受热面产品不同规格T91材料里氏与布氏硬度设备检测对比研究

里氏硬度计检测效率高,但其测量精度受到设备设定和多种外界因素影响,一般低于实际硬度,特别是对于锅炉受热面小管,误差较大。本文针对不同规格的锅炉受热面小径管T91材料开展同位置里氏与布氏设备的对比研究,分析两种设备测量值的差异。通过对比过程和结果表明,布氏设备测量稳定、准确,但在采用C型设备进行测量时建议使用辅助工装进行定位,以保证设备测量探头与管子轴线对中垂直;管子表面打磨状态对测量硬度值影响不大;不同检测人员的里氏测量值变化不大。不同布氏与里氏测量对比差值与管子壁厚存在一定的规律,管子壁厚越薄,对比差值越大,里氏测量值更偏低;管子壁厚越厚,对比差值越小,里氏测量值更偏高。

薄壁小口径管热丝TIG焊缺陷的预防控制

电站锅炉蛇形管壁薄小口径管对接,大量采用热丝TIG焊工艺,操作不当,容易产生层间未熔合、焊穿、小焊道成形差等焊接缺陷。分析了产生缺陷原因,通过优化坡口设计,优化坡口加工,调整热丝TIG焊焊机旋转方向和送丝位置,优化内壁通气保护措施、优化焊接规范参数,提高了焊接接头的性能,接头质量明显改善。