轧辊再制造及其表面强化技术的研究进展

轧辊失效形式主要有辊身剥落掉块、大面裂纹、辊身和辊颈断裂等,通过对轧辊的修复和表面强化可以延长轧辊的使用寿命,减少轧辊的消耗并降低轧钢成本。综述了辊身修复和表面强化的几种表面处理技术的工艺、特点与用途;分析了堆焊层的作用机理和气泡产生的原因,指出了使用氮元素在堆焊中的作用;阐述了轧辊表面感应淬火获得较深的硬化层的限制性因素,指出残余应力的产生和分布还需要进一步研究;介绍了热喷涂技术裂纹产生的原因和机理,并讨论了激光重熔对减少热喷涂层裂纹和内应力的影响;总结了轧辊激光表面改性的近期研究进展,讨论了熔池流动性对熔凝层和熔覆层组织性能的影响;最后展望了现有技术的重点研究方向及3D打印技术在轧辊再制造和表面强化中的应用前景。     

热作模具的堆焊修复技术

简述了各种热作模具的工程背景和应用现状,介绍了堆焊工艺在热作模具修复中的作用,以及堆焊材料的分类特点及应用范围。详细阐明了热作模具的堆焊修复工艺过程,以汽车前轴辊锻模的堆焊修复为例,对整个堆焊修复过程进行了说明。     

铣齿设备芯轴翻转装置的设计与仿真分析

7MW风机偏航系统齿轮主轴的铣齿设备需要定期维护和检修,对其中的关键件芯轴设计了一种专用工具——翻转装置。根据芯轴的接口尺寸设计的翻转装置的结构具有翻转角度大、运动灵活、易于操作等优点。对翻转装置进行仿真分析可知,整体变形不大,能实现正常的使用功能,结构整体的安全裕度较高。翻转装置能满足铣齿设备芯轴的维护和检修功能。     

管线内表面堆焊成形一体化装置的研制

目的针对人工堆焊耐蚀耐磨合金层效率低、质量稳定性差等问题,研制一种管线内壁成形一体化成形装置。方法设计管线内壁堆焊制造焊接系统、枪体夹持系统、旋转系统、水平驱动系统和预热-后热处理系统,并将这些系统总装配合使用。结果实现了管线内壁堆焊制造的一体化成形。结论一次加工即可实现管线内壁预热、堆焊制造以及后热处理,极大提高了堆焊效率,同时能够保证堆焊层的成形质量。     

单齿辊破碎机水冷轴的改进

单齿辊破碎机(以下简称单齿辊)是烧结矿系统中不可缺少的设备之一。单齿辊是用来破碎从烧结机台车上卸下来的大块热烧结矿,并使其粒度符合工艺要求。单齿辊主要由以下几部分组成:电动机、定扭矩联轴器、减速机、柱销联轴器、齿辊部、篦板部及齿辊防尘罩等组成。如下图所示:     

尾减输入齿轮疲劳失效分析

对某发动机尾减系统尾减输入齿轮疲劳失效的原因进行了系统的分析。通过宏观检查、断口分析、金相检验以及受力分析等,确认了该齿轮的失效过程为：在大弯曲载荷作用下疲劳裂纹于锥齿中部齿根部位起始,裂纹初期沿径向呈15°左右的小角度疲劳扩展;齿部出现裂纹后,齿轮振动频率发生变化,进而导致齿轮出现节径型振动,使得裂纹逐渐沿径向疲劳扩展;出现径向裂纹后剩余齿由于截面减少以及起始部位已基本无渗碳层其强度较低等原因,导致剩余齿出现弯曲疲劳断裂。     

Bimorph变形镜10.6μm薄膜研究

基于压电驱动器的Bimorph变形镜是10.6 μm系统的一个重要元件.为了镀制薄膜,本文首先利用有限元软件对两种镀膜夹持方式与沉积温度进行了计算,对热应力产生的热变形进行了分析,选择了合适的镀膜夹持方式.为了预测bimorph变形镜受激光辐照后的温升,对单晶硅与石英玻璃制作的bimorph变形镜有限元模型进行了计算与分析.最后,利用光度计对镀制的薄膜进行了反射率测量.试验结果显示反射率测量值大于99.5％,满足实际系统的需要.     

Stellite12钴基合金热循环冲击前后拉伸断裂机理研究

对不同缺口的Stellite12钴基合金试样(700℃/20℃进行不同次数的热循环冲击和未冲击)进行原位拉伸,并结合试验数据的分析以及断口形貌的扫描电镜观察,分析了Stellite12钴基合金热循环冲击前后的拉伸断裂过程和断裂机理。结果发现:热循环冲击后不同半径试样的断裂过程略有不同,热循环冲击后的小圆弧缺口试样在缺口根部产生表面微裂纹,试样边缘及微裂纹两侧产生氧化微孔;原位拉伸时,该试样热冲击过程产生的裂纹先向试样厚度方向扩展,待厚度方向贯通,然后裂纹尖端的基体发生变形、黑相(白相)穿晶开裂、少量沿氧化微孔裂开,试样瞬间发生断裂;而经历热循环冲击后的大圆弧试样表面并未产生明显的裂纹,拉伸加载过程经历大圆弧根部基体变形、黑白相内开裂、边缘氧化微孔张开,试样突然断裂;对于未冲击试样,在加载过程中,试样的断裂过程经历基体变形、黑白相内部开裂,能量聚集到一定程度试样突然断裂。对于未热冲击的三种不同试样其断裂过程基本类似,仅仅是由于小圆弧半径的试样应力集中程度更大,从而使得其断裂应力低于平板以及大圆弧试样。     

Al-Cu合金在凝固过程中的变形速度对热裂纹形成的影响

本文采用自行设计的一种测试装置模拟热裂纹的形成过程。对A1—Cu合金热裂纹形成的温度和热裂纹形成时的临界断裂应力的研究表明,热裂纹形成的温度和临界断裂应力均与变形速度有着密切地关系:随着变形速度的增加,热裂纹形成的温度也相应地上升;而合金的临界断裂应力与变形速度的关系则存在着一个峰值。同时对热裂纹的形成条件进行了理论解析,当满足V<(KR/Es+β/τ-γ·R)·ι条件时,热裂纹将不产生。     

航空发动机变形齿的新材料设计与力学性能

为了克服航空发动机变形齿在循环使用过程中容易出现螺栓松弛和脱落等问题,本研究拟将呈梯度分布状态的形状记忆合金材料应用于航空发动机变形齿的设计中,构成由碳纤维复合板基片和形状记忆合金材料梯度复合而成的功能梯度变形齿装置。首先,给出了呈梯度分布状态的形状记忆合金复合材料层合板在变温作用下的热弹性本构模型;然后,对形状记忆合金层合板进行不同层数和组分含量设计,根据不同设计方案对航空发动机变形齿装置进行有限元建模,仿真分析该装置在变温作用下的应力分布、尖端挠度和应变分布等热力学性能;最后,结合正交分析,讨论不同设计因素对变形齿力学性能的影响。本工作可为形状记忆合金智能材料的进一步研究及其在航空航天等领域的工程应用提供理论基础与技术支撑。     

Fracture behavior of human molars

Despite the durability of human teeth, which are able to withstand repeated loading while maintaining form and function, they are still susceptible to fracture. We focus here on longitudinal fracture in molar teeth??channel-like cracks that run along the enamel sidewall of the tooth between the gum line (cemento-enamel junction??CEJ) and the occlusal surface. Such fractures can often be painful and necessitate costly restorative work. The following study describes fracture experiments made on molar teeth of humans in which the molars are placed under axial compressive load using a hard indenting plate in order to induce longitudinal cracks in the enamel. Observed damage modes include fractures originating in the occlusal region (??radial-median cracks??) and fractures emanating from the margin of the enamel in the region of the CEJ (??margin cracks??), as well as ??spalling?? of enamel (the linking of longitudinal cracks). The loading conditions that govern fracture behavior in enamel are reported and observations made of the evolution of fracture as the load is increased. Relatively low loads were required to induce observable crack initiation??approximately 100?N for radial-median cracks and 200?N for margin cracks??both of which are less than the reported maximum biting force on a single molar tooth of several hundred Newtons. Unstable crack growth was observed to take place soon after and occurred at loads lower than those calculated by the current fracture models. Multiple cracks were observed on a single cusp, their interactions influencing crack growth behavior. The majority of the teeth tested in this study were noted to exhibit margin cracks prior to compression testing, which were apparently formed during the functional lifetime of the tooth. Such teeth were still able to withstand additional loading prior to catastrophic fracture, highlighting the remarkable damage containment capabilities of the natural tooth structure.     

不同轧辊尺寸下40Cr/Q345双金属环件成形过程有限元分析

目的 研究不同轧辊尺寸对40Cr/Q345双金属复合环件热辗扩成形过程的影响规律,并分析环件在辗扩变形过程中内、外层区域的协调变形机理,使辗扩完成后的双金属环件整体变形和温度分布趋于均匀。方法 基于ABAQUS有限元模拟软件,使用动态显式算法,建立双金属环件径-轴向轧制三维热-力耦合有限元模型,采用直径为70、90、110、130、150、170 mm的芯辊尺寸和直径为400、500、600、700、800 mm的驱动辊尺寸,分别研究两个主要的成形辊尺寸对双金属环件热辗扩成形过程的影响。结果 在研究的轧辊尺寸范围内,随着芯辊直径的减小,双金属环件整体温度分布趋于均匀,其变形均匀性明显提高,其中,环件外层40Cr金属塑性变形明显降低,内层Q345金属塑性变形显著升高;随着驱动辊直径的增大,环件整体温度分布均匀性有所降低,变形均匀性略有提高。结论 在双金属环件热辗扩成形过程中,较小的芯辊尺寸能够提高环件整体的温度分布均匀性,并能有效提高内层Q345金属的塑性变形程度,使环件整体变形更加均匀。较大的驱动辊尺寸会略微降低环件的温度分布均匀性,并通过改变内、外层金属的塑性变形程度使环件整体变形趋于均匀。     

铝/钢轧制复合有限元二次开发模拟与实验研究

目的 针对铝/钢两种金属性能差异大,轧制复合存在严重的变形不协调及结合强度低的问题,研究轧辊同径与异径及单辊驱动对复合板协调变形及结合强度的影响.方法 通过有限元二次开发进行模拟建模,并结合同步和异步轧制实验分析板翘曲机理.结果 与铝板接触的轧辊作为主驱动辊可使板变形更协调且结合强度更高,变形翘曲度为0.048,结合强度为34.2 MPa.结论 采用接触铝侧轧辊单侧驱动,双金属界面实现复合的位置更靠近轧辊出口,复合后的双金属界面间的剪应力和所受弯矩较小,制备的铝/钢复合板变形协调性更好,且结合强度更高.     

复合包套轧制工艺对难变形高温合金GH720Li组织的影响

研究了复合包套轧制工艺对难变形高温合金GH720Li组织的影响.结果表明:采用复合包套变形可以有效控制合金的轧制温度,减少轧辊与钢锭的摩擦力,改善难变形合金的表面质量及变形组织均匀性,防止轧制过程开裂.随着轧制变形量的增大,铸态GH720Li合金粗大的柱状树枝晶组织充分破碎,热变形后合金轧态晶粒度为ASTM5级,一次γ′相尺寸约为0.46μm,同时消除了低倍粗晶现象.经过热处理后GH720Li合金晶粒度为ASTM4级,改善了强化相γ′相的大小、数量及其分布状态,获得了良好的力学性能.     

高低瓦楞辊齿形尺寸参数研究

目的研究一种"高低瓦楞辊"组的齿形及具体尺寸,为制造高低瓦楞辊组提供设计参数,从而生产出高低瓦楞夹芯。方法在分析传统"等高瓦楞辊"齿形及有关标准尺寸参数基础上,预先确定基本尺寸参数值,并采用AutoCAD设计制图得出瓦楞辊齿形其他尺寸参数,然后模拟瓦楞辊滚压纸板过程,并测量纸板在瓦楞辊齿上的包角。按照纸板成形过程中张力的必要条件验算纸板成形的可行性,反复设计验算。结果得出了高低瓦楞辊齿形尺寸参数值。结论这种齿形尺寸参数的高低瓦楞辊能使纸板在瓦楞辊齿上的包角值为340°和332°,达到纸板成形过程张力要求,可作为高低瓦楞辊齿形尺寸参数。     

Mechanism of warm and cold roll bonding of aluminum alloy strips

From a study of interfacial behavior at deformations up to 60%, a mechanism is proposed for pressure welding of aluminum strips by rolling at warm and cold conditions, where faying surfaces were first degreased and scratch-brushed. According to this mechanism, the scratch-brushed layers fractured coherently after entering roll gap at a reduction of approximately 21%, which is regarding to the threshold deformation for roll bonding of commercial pure (CP) aluminum strips, and some small cracks perpendicular to the rolling direction formed. As deformation proceeds and roll pressure increases, these cracks quickly expanded into fissures. This process allowed the bond to be established between the underlying metals, termed virgin metals, of base metal, which were extruded through the cracks and fissures at the scratch-brushed regions. Moreover by increasing the rolling temperature, threshold deformation required for bond formation decreases.     

轧辊表面激光处理技术的研究进展

轧辊是轧机的主要变形部件.总结了轧辊材质、主要工作形式及失效方式和轧辊表面处理技术应用概况,具体从激光淬火与重熔技术、激光合金化和激光熔覆3个方面介绍了轧辊激光表面处理(修复)技术的研究和应用现状,并展望了激光表面处理技术修复表面失效轧辊的发展前景.     

On the nature of plastic deformation generated by hydrostatic pressure in silicon single crystals

Macroscopic plastic deformation of silicon single crystals, caused by annealing at hydrostatic pressure and high temperature, was studied by X-ray topography and transmission electron microscopy. The analysis is given of elastic and thermal properties of material around surface cracks and scratches from which deformation process is propagated. The idea of elastic misfit between damaged self-strained material at cracks and scratches and defect-free silicon matrix, is introduced. On the basis of theoretical and experimental data it is concluded that the plastic deformation of silicon at high pressure consists of two processes. The first is a loss of coherency of cracks and scratches by the emission of dislocations at misfitting second phase precipitates present in silicon. The second is the macroscopic yielding from incoherent cracks and scratches at lower elastic strain energies.The presented mechanism explains also the deformation behaviour of silicon crystals subjected to tensile stress at high temperatures; the generation and propagation of dislocations at oxide precipitates before the macroscopic yielding [3].     

Bond strength evaluation of roll bonded bi-layer copper alloy strips in different rolling conditions

Roll bonding is a solid-state welding process to join similar and dissimilar metals and alloys and is widely used as a manufacturing process. In this study, bi-layer copper alloy strips were roll bonded at warm and cold conditions; and then the effects of parameters that create successful bonds, such as the amount of deformation by rolling and rolling temperature on the bond strength were investigated. For this purpose, faying surfaces were degreased and scratch brushed, being fractured coherently after entering roll gap at different reductions. As deformation proceeded and the roll pressure increased, these cracks quickly expanded into fissures. This process allowed the bond to be established between the underlying materials of the base metal layers, termed virgin metal, which were extruded through the cracks and fissures at the scratch brushed regions. The peel strengths of the bonds were measured and were found to increase when the rolling temperature or the thickness reduction are increased.     

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part II: Thermal stress analysis by FEA

A martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used as a glass roller failed prematurely after six rolling campaigns. A previous fractographic investigation showed that the failure of the roll was caused by thermal stresses associated with microstructural embrittlement of the steel casting. Crack nucleation took place on the internal surface of the roll and the crack propagated by ductile intergranular mode. In the present work, the thermal stresses distribution was investigated by a thermal elastic–plastic model using finite element analysis in order to associate the crack growth with the thermal history of the roll during service. The proposed methodology based on the assessment of thermal stresses by finite element analysis together with coupled thermal–mechanical non-linear modelling and calculations using non-linear elastic–plastic fracture mechanics allowed a better understanding of the stable and unstable growth of a longitudinal crack until the premature failure of the roll during its cooling to room temperature after the sixth campaign. The stable and unstable crack growth and the thermal history of the roll (heating up, glass rolling and cooling operations during the six campaigns of the roll) could be related using the proposed calculation.