螺旋槽管材滚压成型过程的数值模拟及试验研究

利用ANSYS有限元分析软件,对螺旋槽管材滚压成型过程进行了数值模拟。根据有限元计算结果分析了螺旋槽管的主要结构参数对滚压力的影响规律。通过试验验证了用有限元法进行螺旋槽管材滚压成型过程模拟的可靠性,并得到了滚压力与槽深之间的对应关系,为螺旋槽管的二次加工提供了必要的实际指导依据。     

热轧薄板等间距纵向条纹产生机制及控制策略

 热轧过程引入的带钢表面等间距纵向条纹缺陷,经后工序酸洗、冷轧、连续退火等处理均无法彻底消除,严重影响成品表面质量。通过全流程缺陷演变研究及工艺试验,确认了该缺陷是由热轧精轧末机架工作辊辊面磨削螺旋纹在轧制过程中转印至带钢表面所致。磨削过程中砂轮平面与轧辊辊面曲线的接触匹配不当、磨辊工艺参数不合适等因素会导致磨削螺旋纹的产生。通过优化精轧工作辊CVC辊形及轧辊磨削参数,彻底消除了轧辊表面磨削螺旋纹以及由此导致的热轧薄板表面等间距纵向条纹缺陷。     

TC2钛合金管材工艺研究

对TC2钛合金管材研制中的两辊温轧、多辊冷轧变形程度及直径壁厚变形匹配关系、温轧加热温度、中间及成品退火温度、化学成分等对管材加工成形质量、组织性能等的影响进行了研究。研究结果显示，该合金两辊温轧、多辊冷轧性能优良，在直径壁厚变形匹配合理的条件下，温轧和冷轧道次变形达40％和30％时，未产生轧制开裂等加工缺陷；温轧加热温度550℃—650℃时，Al，Mn含量控制在标准中上限，Fe，O含量适中；退火温度850℃—900℃时，轧制产品质量和各项性能指标可满足技术标准要求。     

TC2钛合金管材工艺研究

对TC2钛合金管材研制中的两辊温轧、多辊冷轧变形程度及直径壁厚变形匹配关系、温轧加热温度、中间及成品退火温度、化学成分等对管材加工成形质量、组织性能等的影响进行了研究。研究结果显示,该合金两辊温轧、多辊冷轧性能优良,在直径壁厚变形匹配合理的条件下,温轧和冷轧道次变形达40％和30％时,未产生轧制开裂等加工缺陷;温轧加热温度550℃～650℃时,Al,Mn含量控制在标准中上限,Fe,O含量适中;退火温度850℃～900℃时,轧制产品质量和各项性能指标可满足技术标准要求。     

TC2钛合金管材工艺研究

对TC2钛合金管材研制中的两辊温轧、多辊冷轧变形程度及直径壁厚变形匹配关系、温轧加热温度、中间及成品退火温度、化学成分等对管材加工成形质量、组织性能等的影响进行了研究.研究结果显示,该合金两辊温轧、多辊冷轧性能优良,在直径壁厚变形匹配合理的条件下,温轧和冷轧道次变形达40%和30%时,未产生轧制开裂等加工缺陷:温轧加热温度550℃～650℃时,Al,Mn含量控制在标准中上限,Fe,0含量适中:退火温度850℃～900℃时,轧制产品质量和各项性能指标可满足技术标准要求.     

高线精轧及减定径辊箱进水分析及处理

分析精轧及减定径辊箱进水的原因和造成的危害,提出有效可行的处理措施,控制润滑系统的油品清洁度和含水量,确保摩根设备稳定运行。     

大直径管端定径工艺关键参数与仿真研究

采用内外模扩缩径的方案对管材端部进行定径精整,收到了良好的效果。初步研究了方案的结构参数,给出了定径力与被定径管材的屈服极限、原始椭圆程度的量化关系。对变形过程中与定径精度的相关因素进行了研究,为管端定径装备的系列化设计与金属变形工艺的优化奠定了基础。     

胎圈钢丝用盘条C82DA吐断问题原因分析

针对胎圈钢丝用盘条C82DA生产过程中出现吐断的问题,对轧制工艺参数进行了对比分析,并对材料的化学成分、金相组织及力学性能进行了检验。分析认为,导致吐断的主要原因是由于精轧机BGV、减定径TMB导卫和28#～30#轧槽磨损后没有及时更换,致使轧件在导卫中发生跑料,引起张力的瞬时急剧波动。通过及时更换BGV、TMB导卫,缩短28#～30#轧槽的过钢量,同时强化过程控制,月吐断由32次降至3次。     

轻型槽钢蝶式孔型设计

邯钢发明专利“轧制槽钢的蝶式孔型系统”中平轧弧形切深孔和弯腿蝶式槽形孔型侧壁斜度大、切槽浅、轧件好脱槽、使顶上卫板、缠辊事故大大减少,显著延长了轧槽使用寿命和换辊周期,提高了轧机作业率与机时产量,降低了辊耗与能耗,并可减少断辊事故,经济效益十分显著。该项技术应用于轻型槽钢的轧制时,技术上的优越性更加充分地显露出来。     

型钢轧辊冷却制度的改进

1 前言目前鞍钢乃至国内各大、中、小型轧机以及钢管等轧机的热轧工作辊的冷却都是采用一种落后的冷却方式,如在轧机上安装带孔的钢管或胶管对轧槽喷水。这种喷水方式使轧槽不能受到均匀冷却,因喷到轧槽上的水呈实心圆形,不能保证沿轧槽周边有均匀的温度场。这种情况易使轧槽内同一区域温差加大,使轧槽表面出现热应力,随之产生网纹和裂纹,进而造成轧槽表面成块脱落。短期内产生上述现象纯属冷却不均问题,严重影响产品表面质量。为了保证产品表面质量必须增加换辊时间,而影响轧机产量,因此从1960年开始,美国、前苏联等国家都进行新型     

Synergistic effects in the melting of DNA hydration shell: melting of the minor groove hydration spine in poly(dA).poly(dT) and its effect on base pair stability

We propose that water of hydration in contact with the double helix can exist in several states. One state, found in the narrow groove of poly(dA).poly(dT), should be considered as frozen to the helix, i.e., an integral part of the double helix. We find that this enhanced helix greatly effects the stability of that helix against base separation melting. Most water surrounding the helix is, however, melted or disassociated with respect to being an integral part of helix and plays a much less significant role in stabilizing the helix dynamically, although these water molecules play an important role in stabilizing the helix conformation statically. We study the temperature dependence of the melting of the hydration spine and find that narrow groove nonbonded interactions are necessary to stabilize the spine above room temperature and to show the broad transition observed experimentally. This calculation requires that synergistic effects of nonbonded interactions between DNA and its hydration shell affect the state of water-base atom hydrogen bonds. The attraction of waters into narrow groove tends to retain waters in the groove and compress or strain these hydrogen bonds.     

热轧无缝方管微张力定减径工艺研究

文章对内蒙古包钢西北创业普特钢管有限公司微张力定减径机的孔型系列规律进行分析研究,设计了生产热轧无缝方管的生产工艺、孔型参数及轧辊转速。经现场轧制规格为110 mm×110 mm×6 mm热轧无缝方形钢管产品检测结果表明：热轧无缝方管的外形尺寸和力学性能均满足相关标准要求,热轧无缝方管的定径生产工艺、孔型参数及轧辊转速设计合理可行。     

包钢生产热轧无缝方管的工艺设计

文章采用现场试验和数理统计相结合的方法,对包钢利用微张力定径机生产方管的孔型系列规律进行了研究,制定了微张力定径机生产方管的定径工艺参数,经现场轧制140mm×140mm方管实验证明:利用现有的12架微张力定径机组,对方管的定径工艺设计合理可行.     

The structure of an RNA "kissing" hairpin complex of the HIV TAR hairpin loop and its complement

We have used nuclear magnetic resonance (NMR) to obtain the structure of an RNA "kissing" hairpin complex formed between the HIV-2 TAR hairpin loop and a hairpin with a complementary loop sequence. Kissing hairpins are important in natural antisense reactions; their complex is a specific target for protein binding. The complex has all six nucleotides of each loop paired to form a bent quasicontinuous helix of three coaxially stacked helices: two stems plus a loop-loop interaction helix. Experimental constraints derived from heteronuclear and homonuclear NMR data on 13C and 15N-labeled RNA led to a structure for the loop-loop helix with an average root-mean-square deviation of 0.83 (+/-0.10) A for 33 converged structures relative to the average structure. The loop-loop helix of the kissing complex is distorted compared to A-form RNA. Its major groove is blocked by the phosphodiester bonds that connect the first loop residue of each hairpin with its own stem, and it is flanked by two negatively charged phosphate clusters. The loop-loop helix has alternating helical twists between adjacent base-pairs. The base-pairs at the helix junctions are overwound and three base-pairs near the helix junctions adopt high propeller twists. All these changes reduce the distance needed for the bridging phosphodiester bonds connecting each stem and loop to cross the major groove of the loop-loop helix, and result in a deformed RNA helix with localized perturbations in the minor groove surface. The alternating helical twist pattern, plus other distortions in the loop-loop helix may be important for Rom protein recognition of the kissing hairpin complex.     

管材内螺纹成型有限元分析及换热性能试验研究

采用滚压成型的方法生产内螺纹管材，该方法不仅适于生产大直径管材，也可连续生产小直径盘管，并且生产效率高、内螺纹形状理想；用有限元方法对管材成型过程进行了分析，确定了理想的辊型参数。同时对滚压成型生产出的内螺纹管材的换热性能进行了试验研究，得到了各种参数对管材换热性能的影响规律。     

Structure of poly d(AI).poly d(CT) in two different packing arrangements

X-ray diffraction analysis of poly d(AI).poly d(CT) in oriented and polycrystalline fibers has revealed the DNA structure to be a 10-fold, right-handed, antiparallel, Watson-Crick base paired double helix in two distinct packing arrangements corresponding to one and two helices, respectively, in the unit cell. The helix pitch is 32.1 A and 32.4 A in the two cases, almost 1.5 A shorter than in classical B-DNA. The resulting B'-DNA geometry, described in terms of a tetranucleotide repeat which is conformationally similar to B-DNA, has its minor groove closely shut and major groove correspondingly widened, thus striking a sharp morphological contrast to B-DNA. According to difference electron density maps, a spine of hydration along the minor groove connects both strands and provides structural stability; ordered sodium ions and water molecules are actively involved in bridging the phosphate groups of neighboring helices. The crystallographic R-values for these two allomorphs are 0.26 and 0.20, respectively, for data up to 3.0 A resolution.     

The work hardening of surface layers during the sizing of sintered bushing

Summary An x-ray diffraction investigation established that the surface layer of porous parts undergoes work hardening during sizing. It is shown that, from the point of view of surface quality, the combined method of sizing has the advantage over the separate method that the densification and hardening of the outer and inner surfaces of bushings are not equal. The outer surface is hardened to a greater extent than the inner one.     

Different effects of nonintercalative antitumor drugs on DNA triple helix stability: SN-18071 promotes triple helix formation

The interaction of the nonintercalating bisquaternary ammonium heterocyclic drugs SN-18071 and SN-6999 with a DNA triple helix has been studied using thermal denaturation and CD spectroscopy. Our data show, that both minor groove binders can bind to the triple helix of poly(dA).2poly(dT) under comparable ionic conditions, but they influence the stability of the triplex relative to the duplex structure of poly(dA).poly(dT) in a different manner. SN-18071, a ligand devoid of forming hydrogen bonds, can promote triplex formation and thermally stabilizes it up to 500 mM Na+ concentration. SN-6999 destabilizes the triplex to duplex equibilirium whereas it stabilizes the duplex. The binding constant of SN-18071 is found to be greater than that to the duplex. The stabilizing effect of SN-18071 is explained by electrostatic interactions of three ligand molecules with the three grooves of the triple stranded structure. From the experiments it is concluded that SN-6999 binds to the triplex minor groove thereby destabilizing the triplex similar as previously reported for netropsin.