大型造纸机铸辊爆裂原因分析

经过对大型造纸机爆裂铸辊进行宏观和微观分析,确定该铸辊材质不是铸钢,而是铸铁;铸辊爆裂是从铸辊连接螺孔根部开始的,此处组织比较疏松,出现了因片状石墨-铁素体电偶腐蚀而形成的准裂纹。经过4年时间的运行,裂纹扩展到临界尺寸时发生失稳爆裂。文中提出了防止该类事故发生的建议措施,以供参考。     

宝钢5000 mm宽厚板工作辊国产化研究

探讨了厚板常规高镍铬工作辊制备过程中易出现的问题,对外层材质、铸造难点、热处理工艺等进行了分析,研究了适用于厚板轧机工作辊材质及制造工艺。结果表明,工作辊的外层石墨形态呈球形,组织细小;芯部为牛眼状铁素体,组织与性能超过了常规高镍铬工作辊的要求。耐磨性、抗热冲击及抗冷热疲劳性能优于传统高镍铬工作辊,组织与性能均达到预期。经宝钢5 000 mm厚板轧线实际使用验证,达到或超过进口轧辊的技术指标。     

FO工作辊断辊的失效分析

热连轧精轧机组F0工作辊发生爆裂、断辊事故.检查了该辊首次使用前的检测情况,观察了断辊的断口形貌,对残留辊面、剥落碎块各部位进行了硬度、金相、电镜检测,结果表明,轧辊的断裂经历了短周期的轧制、裂纹扩展的循环过程,轧辊表面产生大量异常热疲劳龟裂；轧辊的硬度均匀性差；工作层碳化物由表及里呈鱼骨状生长,会助长表层龟裂沿径向扩展；结合层组织异常、铸造缺陷促使裂纹萌生、加速裂纹扩展,导致工作层的剥落、爆裂.     

减少冷铸轧辊上辊颈裂纹的新方法

冷铸轧辊的上辊颈裂纹,是造成废品主要原因之一。我厂于1980年采用暗冷铁,减少了上辊颈裂纹,基本上解决了这一问题。 一.产生上辊颈 裂纹的原因 冷铸轧辊的上辊颈裂纹,发生在辊身到上辊颈的过渡区域,离辊身上端面40～100mm范围内。裂纹绝大多数是横裂纹,有环裂和局     

H型钢轧机水平辊复合辊套的离心铸造

Ｈ型钢轧机的水平辊采用组合式镶套辊。该水平辊的复合辊套外层采用高硬度铸造半钢，内层采用石墨钢，离心铸造而成。经热处理，达到了内外层不同的硬度要求，具有良好的耐磨性。     

冷轧辊表面层内的石墨夹杂

<正> 独联体克拉玛托尔斯克工业大学对冷轧辊表面层内的石墨夹杂进行了定量分析,并研究了其分布特征,研究了石墨夹杂的生成特性,分析了石墨颗粒在零件     

MC5轧辊辊颈表淬开裂原因分析

分析了MC5轧辊辊颈表淬裂纹形成的原因.通过减少锻造火次,合理控制锤击力和锻比,适当降低辊颈表面淬火温度,防止轧辊辊颈出现表淬开裂.     

四辊板带轧机辊颈载荷分布及板形影响因素分析

板形是板带材产品的重要质量指标之一。辊系弹性变形是影响板形的主要因素,轧机辊颈载荷分布直接影响轧机的辊系弹性变形,因此精确分析辊颈载荷分布对板形控制和轴承使用有着重要的意义。针对实验室四辊可逆冷轧机,采用ANSYS/LS-DYNA有限元软件,基于显式动力学建立了耦合支撑辊轴承、轧辊和轧件的三维实体模型,分析了板宽、摩擦因数、张力和压下量等因素对支撑辊辊径载荷分布和板凸度的影响,对四辊板带轧机板形控制和轴承使用提供了理论支持。     

离心铸铁轧辊辊颈缺陷的焊补

在离心铸铁轧辊铸造过程中,上辊颈处有时会出现夹渣、夹砂等缺陷,为提高轧辊的成品率,本文研究了离心铸铁轧辊辊颈缺陷的焊补,通过试验选择了适合的焊条和焊接工艺,成功解决了离心铸铁轧辊辊颈的焊补问题。     

500轧机空心导辊的焊接

500轧机的空心导辊是由20CrMoWV 钢管(辊身)和35锻钢(辊颈)焊接而成的。导辊的工作温度500℃左右,导辊的结构如图1所示。     

高血压、2型糖尿病并发牙周炎患者超敏C-反应蛋白及炎性细胞因子表达分析

目的: 观察高血压、2型糖尿病并发牙周炎患者血清超敏C-反应蛋白(high sensitive C-reactive protein,hs-CRP)、白介素-1β(interleukin 1β,IL-1β)、白介素-6(interleukin 6,IL-6)和肿瘤坏死因子-α(tumor necrosis factors-α,TNF-α)表达情况,探讨高血压、2型糖尿病对牙周炎发生与发展的影响。方法: 从某医院体检人群中筛选140名患者(单纯牙周炎组40名、高血压并发牙周炎组35名、2型糖尿病并发牙周炎组40名和2型糖尿病合并高血压并发牙周炎组25名)作为研究对象,记录其牙周探诊深度(probing depth,PD)、附着丧失(attachment loss,AL)、菌斑指数(plaque index,PLI)和出血指数(bleeding index,BI),并检测外周血hs-CRP、IL-1β、IL-6和TNF-α的浓度。结果: 2型糖尿病合并高血压并发牙周炎组PD、AL、PLI、BI指标检测结果高于单纯牙周炎组、高血压并发牙周炎组和2型糖尿病并发牙周炎组(P＜0.05),高血压并发牙周炎组和2型糖尿病并发牙周炎组高于单纯牙周炎组(P＜0.05);2型糖尿病合并高血压并发牙周炎组hs-CRP、IL-1β、IL-6和TNF-α检测结果高于单纯牙周炎组、高血压并发牙周炎组和2型糖尿病并发牙周炎组(P＜0.05),高血压并发牙周炎组和2型糖尿病并发牙周炎组高于单纯牙周炎组(P＜0.05)。患者血压、血糖水平与hs-CRP、IL-1β、IL-6和TNF-α水平呈正相关(P＜0.01)。结论: 高血压、2型糖尿病,尤其是高血压合并2型糖尿病并发牙周炎患者血清hs-CRP、IL-1β、IL-6和TNF-α水平较高,提示高血压合并2型糖尿病可能会加重牙周炎症发生与发展的风险。     

The role of hydrogen in weld cracking processes – a new look at the problem

The new welding method known as F-MAG, which has been developed based on the CO₂ gas-shielded arc welding method (MAG), increases deposition rate of weld metal. The F-MAG welding method is combined with hot-wire, as has been used in TIG arc- and laser-welding methods. F-MAG is performed using hot-wire which is inserted into the rear part of the weld pool made with the leading electrode. Hot-wire melts by both electrical heating of itself and heat of the weld pool. Multi-layered weld metals were prepared using F-MAG and MAG. Microstructures and mechanical properties of both as-weld and reheated zones in the uppermost layer of the multi-layered weld metals formed with F-MAG and MAG were examined and the effects of hot-wire on microstructures and mechanical properties were analysed. Both the as-weld and reheated zones of the weld metal formed with F-MAG consisted of acicular ferrite (AF), equiaxed ferrite and so on. Both strength and elongation in as-weld and reheated zones formed with F-MAG were superior compared with those formed with MAG. It could be suggested that strength increased by refinement of AF due to increase in the concentration of alloying elements being contained in the hot-wire. Larger elongation of the weld metal in F-MAG compared with that in MAG could be analysed in terms of the Aggregate of AF Laths with nearly Parallel Slip systems between neighboring AF laths (ALPS). The number of AFs contained in an ALPS formed with FMAG is larger than that with MAG, in spite of the sizes of ALPSs formed with MAG and F-MAG being almost same. Deformation occurs over a lot of AFs in the case of finer AF formed with F-MAG through the rotation of the tensile test piece during deformation, resulting in the larger elongation.     

Influence of tool inclination on brittle fracture in glass cutting with ball end mills

Glass milling is discussed with influences of tool inclination on brittle fracture. Cutting tests are performed to observe surfaces in the up-cut and the down-cut processes with a ball end mill inclined in the feed direction of the cutter. Brittle fracture occurs in the down-cut process at high feed rates. Then the machined surfaces in cutting with the ball end mills tilted in the vertical plane with respect to the feed direction are associated with those of the up-cut and the down-cut processes. The cutting forces are also measured to discuss brittle fracture with the change of the undeformed chip thickness. The scratches on the surface finished with the tilted ball end mill are shown in an analytical model with a notched edge shape. The maximum feed rates at which brittle fracture does not occur are shown with the tool inclination in the cutting tests.     

Mechanical Properties and Fracture Surface Morphologies in Unnotched Specimens of Rubber-PMMA Composites

Correlations between mechanical properties and microscopic features were investigated using unnotched specimens of rubber-PMMA composites in very low to medium range of cross head speeds. It is found that: (1) a trapezoid-shaped smooth region and fish scale-like texture with bands in rough region correlates with brittle failure in pure PMMA, while a quarter circle-shaped smooth region and hackle-like texture, and the presence of dimples and/or voids correlate with ductile failure in rubber-PMMA composites; (2) decrease in degree of roughness in rubber-PMMA composites can be correlated with decrease in Young’s modulus; (3) decrease in size of the smooth region with increasing speed can be correlated with decrease in modulus of toughness; (4) larger smooth region in rubber-PMMA composites containing more rubber correlates with higher modulus of toughness.     

主动免疫联合烯丙雌醇治疗原因不明反复自发性流产的临床疗效评估

目的:评价主动免疫联合烯丙雌醇(allylestrenol)治疗原因不明反复自发性流产(URSA) 的临床疗效, 为临床原因不明反复自发性流产的治疗寻求最佳方案。方法:435 例原发性原因不明反复自发性流产患者分为3 组。联合治疗组185 例, 接受主动免疫联合烯丙雌醇治疗;主动免疫组152 例, 单纯接受主动免疫治疗;烯丙雌醇组98 例, 只接受烯丙雌醇治疗;另有96 例继发性原因不明反复性流产患者, 为继发URSA 组, 全部接受主动免疫联合烯丙雌醇治疗。结果:联合治疗组妊娠成功率为92.05%,主动免疫组为71.43%, 烯丙雌醇组为31.51%, 继发URSA 组为86.76%(P<0.01) 。联合治疗对原发和继发URSA 的疗效相近(P>0.05) 。结论:在本研究中主动免疫联合烯丙雌醇治疗原因不明反复自发性流产疗效最好, 值得在临床推广应用。     

Corrosion of nonprecious metal alloys in dentistry in the presence of common saliva additives

Corrosion stability of metallic materials used in dentistry is a major concern; identification of materials combining high stability and good performance is needed. The corrosion resistance of representative nonprecious metal alloys frequently used in dentistry in contact with artificial saliva solution with various added substances encountered in foodstuffs and in materials used in dentistry, possibly influencing the corrosion has been studied in vitro with electrochemical impedance measurements. Values of obtained corrosion resistances are interpreted in terms of conceivable effects of the additives on the rate of corrosion; they are also compared with previous results obtained with these alloys and additives using breakthrough electrode potentials obtained from slow scan cyclic voltammetry reported before.     

Solution-cast blends of polyaniline–DBSA with EVA copolymers

Conducting blends of ethylene-vinyl acetate (EVA) copolymers with different vinyl acetate content and polyaniline doped with dodecylbenzenesulfonic acid (Pani–DBSA) prepared by three different procedures were prepared by solution-cast process. Blend films with EVA18 (with 18 wt.% of VA) presented gross-phase separation, resulting in a formation of Pani-enriched (glass-contacted film surface) and Pani-deficient (air-exposed film surface) layers. The use of EVA41 (with 41 wt.% of VA) resulted in blends with homogeneous conductivity (similar conductivity in both sides of the film). Better electrical performance was achieved in blends with Pani–DBSA produced by a redoping process. Concerning Pani–DBSA prepared by one-step polymerization, one prepared by inverted emulsion polymerization, resulted in EVA41-based blends with lower percolation threshold point and a more homogeneous morphology than that prepared with Pani–DBSA from aqueous dispersion polymerization.     

Technological special features of ultrasound welding polymer films

The design of permanent joints with fillet welds characterized by bevelling of the edges with the depth decreasing with an increase in the distance from the weld edge to the centre of the weld is proposed. The experimental results show that in producing permanent joints with the edge bevel of variable depth, the volume of the deposited metal is reduced by 35% with the corresponding reduction in the material requirement of the process without reducing the load-carrying capacity of the welded joint.     

Effects of compressing and remelting in SIMA processing on semi-solid structure evolution of an Al-Zn wrought alloy

Structure evolution of an Al-Zn wrought alloy in remelting processing in the strain induced melt activated (SIMA) semi-solid procedure was observed, and effects of factors, the remelting temperature, the holding time, and the compression strain, on structures and grain sizes of the alloy were investigated. The results show that (1) the proper temperature of remelting is in the range of 610 to 615 ℃; (2) the grain size in specimen with greater compression strain is smaller than that with smaller compression strain in condition of the same remelting temperature and holding time, and the grain size in local area with great local equivalent strain is smaller than that with small one; (3) liquid occurs in form of cluster in matrix during remelting and its quantity increases with remelting time increasing; liquid in specimen with great compression strain occurs earlier than that with small one, and quantity of liquid in the center of specimen with greater local equivalent strain is greater man that in the tw     

挤压铸造对Al-Cu合金显微组织及溶质分布的影响

研究了挤压铸造工艺条件下,工艺参数对Al-5Cu-0.4Mn合金显微组织及Cu元素分布的影响。结果表明,合金在25MPa压力下成形时,初生α-Al晶粒尺寸得到明显细化;浇注温度越高组织变得越粗大;升高模具预热温度,晶粒尺寸增大且分布不均匀。挤压铸造改变重力铸造条件下Cu的逆偏析现象,从铸件边缘往心部的Cu含量呈现增加的趋势,主要原因为晶间富铜液相在压力的强制补缩下,通过枝晶骨架通道被挤向铸件内侧。Cu在α-Al基体中的固溶度随着压力的增大而增加;沿径向远离铸件心部,α-Al晶内Cu含量逐渐增加。在挤压力为100MPa、浇注温度为680～730℃、模具温度为200℃的工艺条件下,可获得晶粒细小、组织致密、宏观偏析少的Al-5Cu-0.4Mn合金挤压铸件。