【作者】 顾菡妍；

【导师】 蒋建清； 方峰；

【作者基本信息】 东南大学 ， 材料加工工程， 2005， 硕士

【摘要】 高强度低松弛预应力钢绞线作为第三代高档建筑材料,被广泛应用于高层建筑、大跨度桥梁等现代化大型建筑。其中1860MPa级PC钢绞线是已商业化的钢绞线中强度级别最高,用量最大的品种。其生产过程是将高碳盘条通过连续7～10道次的连续冷拉拔形变而制成。由于现代化大生产的连续性,不同卷盘条通常采用电阻对焊的方法连接在一起,在生产过程中盘条电阻对焊区域容易出现拉丝断裂。通过对焊接区拉丝断口形貌的分析,结果表明,焊接区发生拉丝断裂的主要原因为:焊接引入的氧化夹杂物、焊接温度过高引起的组织过热以及焊接区表面润滑不良产生的表面缺陷。其中,表面缺陷的影响最大,还可能造成后续的绞线过程断丝。针对焊接区易产生表面缺陷的问题,研究采用磷化处理的方法来改善表面润滑性能,减少表面缺陷的产生。研究了氧化剂NaNO2和稀土促进剂La（NO3）3对磷化过程的φ-t曲线的影响,及磷化各阶段的磷化膜生长情况。结果表明,氧化剂NaNO2有明显的促进磷化成膜的作用,促进磷化过程的去极化,使成膜阶段的时间缩短;La（NO3）3可促使磷化膜形核;当NaNO2和La（NO3）3共同作用时,能综合二者的促进作用,起到良好的效果。研究了表面状态、表面活化处理、磷化处理时间、磷化液的成分对磷化膜膜重和形貌的影响,确定了一种低温快速磷化工艺。采用的磷化液配方:浓H₃PO₄（>85%） 5ml/L,Zn（H₂PO₄）₂ 55g/L,Zn（NO₃）2 70g/L,NaNO₂ 0.4 g/L,La（NO₃）₃ 0.05g/L ,处理温度为40℃,磷化时间为10min。对研制的磷化膜及皂化后磷化膜的摩擦性能进行了研究,结果表明,磷化膜在100N、150N和200N条件下均具有较好的减摩效果,尤其在载荷为100N时,其摩擦系数为0.4左右,而相同条件下未磷化处理样品的摩擦系数约为0.7;磷化膜皂化处理后,其摩擦性能更佳,摩擦系数均在0.2左右。生产性磷化试验表明,采用低温快速磷化工艺对盘条焊接区进行磷化处理,能有效地防止表面横向裂纹的产生。更多还原

【Abstract】 As high-grade structure material, 1860MPa prestressed concrete （PC） steel strand is widely used in modern construction, such as skyscrapers, large span bridges, and so on. It was made of high-carbon steel wires after drawing deformation. The bar to bar are connected by butt resistance welding in order to keep continuous drawing. Fracture often occurrs in the weld joint of the wire during drawing.Drawing fractures morphology were investigated and classified. Statistical results showed that the drawing fractures in weld joint were caused by three main reasons: 1) oxide inclusion brought about by welding process; 2) overheat structure caused by high temperature of heat treatment of welling process; 3) last but not lest, surface cracks occurred during drawing because of the destroy of lubricant coated layer in welding process. The surface crakes will also cause the fracture in the process of twisting. Thus a new phosphating process on weld joint surface is studied to improve the lubricant performance and avoid occurrence of surface cracks during drawing process.The effect of oxidative accelerant NaNO₂ and La（NO₃）₃ on potential （φ） vs time （t） relationships was studied. The growth process of phosphate coating was also observed. The result showed that NaNO2 can accelerate the growth of phosphate coating, and La（NO3）3 can accelerate the nucleation of phosphate. The better effect is obtained by using NaNO2 and La（NO₃）₃.The effect of process parameter on phosphating, such as surface conditions, activation process, time of phosphating and the component of solution on the weight and figure were tested. The experimental results showed that the best composition and process parameters are as follows, at 40℃and 10min, the composition of phosphating solution was H3PO4（>85%） 5ml/L,Zn（H₂PO₄）₂55g/L,Zn（NO₃）₂70g/L,NaNO2 0.4 g/L,La（NO₃）₃ 0.05g/L。The friction performance of the phosphate coating is studied as well. The result showed that the friction coefficient of the phosphate coating is about 0.4 when the load is 100N, but the un-phosphating sample is more than 0.7. The phosphate coating combined with sodium stearate and calcium stearate show a better fiction performance, and the friction coefficient is about 0.2.When the above phosphating process was used on the weld joint of wire, the result showed that the phosphate coating can eliminate surface transverse cracks.更多还原