冷轧工作辊的带状疲劳剥落

影响冷轧工作辊寿命的因素很多,失效形式也是多种多样的。为找出冷轧工作辊的主要失效形式,曾对某厂的冷轧工作辊使用记录进行一次统计与分析。结果表明:由于产生表面裂纹或剥落导致失效者,占总使用辊数的70％以上;由表面裂纹或剥落导致有效直径的损失,平均达60％以上,高者可达90％以上。     

热连粗轧机支持辊剥落影响因素的有限元分析

基于现有的剥落和磨损,分析2250轧机支持辊边部发生剥落的因素,采用数值计算与实测数据,建立三维有限元模型和辊系力学仿真。结果表明:接触疲劳是支持辊辊面剥落的主要因素,为有效预防支持辊的剥落和控制磨损提供了理论指导。     

轧制极薄材料的Cr5型锻钢工作辊及其制备方法的研发

工作辊在长时间的工作中会发生磨损硬化,利用淬火工艺处理后的锻钢具有较强的淬硬性、可塑性、韧性及硬度均匀性,从而提高了工作辊的抗磨损和抗剥落强度.文中对轧制极薄材料的锻钢工作辊进行研究分析,针对Cr5型锻钢工作辊制备方法进行研发,采用淬火工艺,从而改善工作辊的硬度和强度.     

锻钢冷轧工作辊表面裂纹扩展引起的剥落分析

对某钢厂因使用原因导致的锻钢冷轧工作辊表面裂纹扩展引起剥落现象进行分析,采用剥落形貌勘查、金相组织检测、线切割解剖等方法,研究损伤裂纹从扩展到最终剥落过程,并提出预防此类剥落事故的措施.     

热连轧机支承辊抗剥落研究与优化设计

为解决热连轧机支承辊辊身端部剥落问题,在深入分析剥落机理的基础上,提出辊间接触压力以均匀分布为目的的支承辊辊型设计.模拟计算和生产试验结果表明,采用文中所述的辊型优化设计技术可使辊间接触压力均匀分布,降低辊身端部压力峰值,消除端部剥落现象.该方法不仅为轧机支承辊辊型的设计与改造提供了理论依据,且优化辊型也具有进一步推广应用价值.     

冷连轧机工作辊综合应力场的解析、测试及剥落损伤的力学原因分析

本文用边界元法计算了工作辊的接触面力,给出了精确计算边界层域内应力的边界元法公式和计算表层淬火残余应力场的简便模型,从而计算了表层工作应力场与淬火残余应力场。通过工作辊综合应力场的计算得出了表层领域最大剪应力分布曲线,为工作辊剥落损伤原因的分析及改善措施提出了作者的见解。     

无限冷硬工作辊的磨削

针对无限冷硬工作辊在生产期间经常出现轧辊剥落,增加辊耗,影响生产等问题,制定了轧辊分级磨削制度,即根据下机轧辊的具体情况采取不同的磨削工艺。这样既减少了轧辊事故,又降低了轧辊消耗。     

70Cr3NiMo支承辊剥落事故分析及处理

对某钢厂一起支承辊剥落事故进行现场勘察,分析剥落事故的原因,针对实际情况将辊身整体车削,待缺陷完全车掉后继续上机使用。     

CSP热轧板带支撑辊堆焊修复及工艺条件保证

热轧板厂支撑辊因事故损伤造成辊面剥落,可对辊面进行堆焊修复。本文对修复工艺条件及修复质量进行了探讨。     

热连轧工作辊辊身剥落失效分析

针对某热连轧生产线无限冷硬工作辊在轧制服役期间辊身剥落及辊颈断裂事故,采用磁粉探伤、金相检测等技术手段进行失效分析,对轧辊制造过程中的质量控制和轧辊使用管理提出改进意见,通过规范操作规程,避免类似事故再次发生。     

Mechanics of roll edge contact in cold rolling of thin strip

Simulation of cold rolling of thin strip due to roll edge contact with oil lubrication was performed successfully using a developed influence function method. Roll edge contact and related surface roughness was discussed in this paper. The calculated rolling force, intermediate force and work roll edge contact force increase significantly when the reduction increases. The strip profile becomes poor with a higher reduction, and the calculated rolling forces are consistent with the measured values. A modified edge shape of work roll determined from the roll edge contact length and roll edge flattening value is helpful to reduce the work roll edge wear and to extend the work roll life. Surface roughness and asperity of the rolled strip are characterized by surface profilometer and atomic force microscope. The research shows that the surface roughness reduces with a higher reduction or rolling speed. The effect of the strip width on surface roughness is not significant.     

1420mm连轧机精细冷却系统的应用

在五机架冷连轧机中,末机架轧辊分段冷却能够改善板形,有效消除板形缺陷,精确的轧辊冷却能够有效释放轧辊内应力,延长轧辊使用寿命,提高轧制带材板形质量和表面清洁度。以1420mm冷连轧机的板形控制系统为依据,针对轧制极限薄板时轧机震动和出口带材温度高等现象,综合分析该精细冷却控制系统的功能与应用效果。     

超声滚压对铝合金表面质量和耐磨性影响研究

使用多珠平面滚压加工刀具对叉车举升液压缸表面实施滚压加工和超声滚压加工。通过激光共聚焦显微镜、光学显微镜和显微硬度仪对加工后的试样进行表面三维形貌、金相组织和硬度表征的研究。开发相应的分子动力学模型并对加工前后的试样进行干摩擦试验,对比研究超声滚压对液压缸铝合金表面摩擦磨损性能的影响。试验结果表明,与滚压加工相比,超声滚压加工进一步降低了表面粗糙度。磨损结果表明,超声滚压加工改变了试样表面的微观结构,改变了试样的磨损机制,提升了试样的抗磨损性能,可有效提高液压缸使用寿命,降低泄漏量。     

Effect of roll gap change of oval pass on interfacial slip of workpiece and roll pressure in round-oval-round pass rolling sequence

This paper presents a study of the effect of varying the roll gap of oval pass in round-oval-round pass sequence on the interfacial slip of workpiece, entrance and exit velocities, stresses and roll load that the workpiece experiences during rolling, by applying analytical method, finite element simulation and verification through hot bar rolling tests. The results have shown that the roll gap variation of oval pass affects the interfacial slip of workpiece along the groove contact and the specific roll pressure. The optimum conditions in terms of minimum interfacial slip and minimum specific roll pressure, which might influence the maximum groove life, is obtained when the subsequent round pass is completely filled.     

A numerical study of fatigue life in non-Newtonian thermal EHL rolling–sliding contacts with spinning

This paper presents a study on fatigue life in non-Newtonian thermal elastohydrodynamic lubrication (TEHL) point contacts with spinning. A numerical procedure is developed and extended to rolling contact fatigue (RCF) life. The results show that the effect of entraining velocity on the RCF life is closely related to ellipticity. The RCF life first decreases steeply and then gradually with increase in slide–roll ratio. However, the RCF life may increase slightly at a large slide–roll ratio. Spinning is beneficial for reduction of longitudinal friction coefficient; however, even for smooth surface contact, the RCF life can be slightly reduced by spinning.     

Experimental study for roll gap adjustment due to roll wear in single-stand rolling and multi-stand rolling test

To investigate a correlation between the amount of wear and roll gap (pass height) adjustment, we performed a single-stand reversible pilot groove rolling test as well as rolling test in an actual rod mill. In case of the pilot rolling test, we designed wear contour (profile) and machined it on the original roll groove (i.e., roll groove with no wear) to make the roll groove worn down. For the actual rod mill test, we developed a measuring device which can detect the actual wear profile. To determine the amount of roll gap adjustment, we propose a model for equivalent roll gap decrement which reduces the increased exit cross sectional area due to wear. We applied the proposed model to multi-stand rolling (roughing train of POSCO No. 2 Rod Mill) as well as single-stand reversible rolling. The wear profile of rolls worn down at each stand in mill yard was measured at different roll tonnage. The pilot hot rolling test shows that variation of exit cross sectional area is almost linearly proportional to roll gap change while the roll gap decreases from reference roll gap (6.5mm) to 3.5mm. In an actual rod mill which has consecutive rolling system, relationship between tonnage (total amount of tons that the produced rod weighs) and roll gap change at a stand is dependent on the rolling type (oval-to-round or round-to-oval) together with the cross sectional shape of incoming workpiece.     

基于CFD方法的冷轧过程乳化液特性研究

应用CFD工具FLUENT建立冷轧过程乳化液内部压强及轧板所受压力求解分析模型,计算分析冷轧过程乳化液进口速度对乳化液内部压强及轧板所受压力的影响。模拟结果表明,乳化液内部压强随着乳化液进口速度的加大而增加,轧板所受压力也随之增加。通过对比生产现场的轧制力数据,得到乳化液的最优进口速度。通过分析不同油水混合比例乳化液的离水展着性,得到最优的油水混合比例,使得冷轧润滑效果最好,进而实现最优的板面质量。     

Mathematical model for cold rolling and temper rolling process of thin steel strip

A mathematical model for cold rolling and temper rolling process of thin steel strip has been developed using the influence function method. By solving the equations describing roll gap phenomena in a unique procedure and considering more influence factors, the model offers significant improvements in accuracy, robustness and generality of the solution for the thin strip cold and temper rolling conditions. The relationship between the shape of the roll profile and the roll force is also discussed. Calculation results show that any change increasing the roll force may result in or enlarge the central flat region in the deformation zone. Applied to the temper rolling process, the model can well predict not only the rolling load but also the large forward slip. Therefore, the measured forward slip, together with the measured roll force, was used to calibrate the model. The model was installed in the setup computer of a temper rolling mill to make parallel setup calculations. The calculation results show good agreement with the measured data and the validity and precision of the model are proven.     

Measurement of the forward slip in cold strip rolling using a high speed digital camera

The forward slip in strip rolling was defined as the relative difference between the roll surface speed and strip exit speed. It was always an important parameter because of its significant influence on friction and tension control. In this study a Phantom V3.0 digital high speed image acquisition and motion analysis system was used to record the movement of the roll and the workpiece during rolling. The pictures captured were analyzed to obtain the speeds of the roll and the workpiece along the roll bite, which then yielded the forward slip. The measurement accuracy has been validated by the mass conservation. The maximum relative error of the forward slip was only 1.6 %. The results have shown that the forward slip increased as the reduction increased for both dry and lubricated rolling. The roll speed did not change the forward slip in the case of dry rolling, but the forward slip was significantly reduced with roll speed when lubricated.     

A thermal analysis of strip-rolling in mixed-film lubrication with O/W emulsions

Increase of both roll and strip surface temperatures can significantly affect a rolling process, roll conditions and strip mechanical properties. A comprehensive thermal analysis in cold rolling, especially in a mixed film regime, is needed to understand how thermal fields develop in roll and strip during rolling. It requires a simultaneous solution of the mixed film model for friction in the roll bite and the thermal model for roll and strip thermal fields. This paper presents a numerical procedure to analyse strip rolling process using lubrication with oil-in-water (O/W) emulsions. The thermal model includes the effect of heat generation due to the strip deformation and frictional shear stress at the asperity contacts. The numerical analysis employs a coupled thermal model and a mixed film lubrication model for calculating the friction and the asperity deformation in the bite. The thermal model considers the initial temperatures of the roll and strip, temperature rise due to the strip plastic deformation and friction. While the O/W mixed-film lubrication model takes into account the effect of surface roughness and oil concentration (%vol) of the emulsion. The thermal effect is analysed in terms of strip surface temperature and roll temperature, which are influenced by rolling parameters such as reduction, rolling speed, oil concentration in the emulsion. The results of the parametric study indicate that the effect of oil concentration on the thermal field is relatively small compared to that of reduction ratio and rolling speed. The reduction ratio increases the maximum interface temperature in the roll bite. In the mixed film regime, rolling speed also increases the maximum interface temperature and alters the temperature field of the strip. The numerical procedure was validated against known experimental data and can readily be extended to hot rolling or used to analyse roll strip temperature subjected to different cooling system.