Sliding wear behavior of copper alloy contact wire against copper-based strip for high-speed electrified railways

This paper reports the study of the sliding wear behavior of the Cu–Ag–Cr wire. Cu–Ag–Cr alloy is a promising contact wire material for high-speed electrified railways, which has an excellent combination of mechanical strength and electrical conductivity. Wear tests were conducted under laboratory with a special sliding wear apparatus, which simulated the tribological conditions of sliding current collectors on overhead wires in the railway system. The Cu–Ag–Cr alloy wire was slid against a copper-based powder metallurgy strip under unlubricated conditions. The same strip as those in the train systems were used. Worn surfaces of the Cu–Ag–Cr alloy wire were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDS). Within the studied range of electrical current, normal pressure and sliding speed, the wear rate increased with the increasing electrical current and the sliding distance. Compared with a Cu–Ag contact wire under the same conditions, the Cu–Ag–Cr alloy wire had much better wear resistance. Adhesive wear, abrasive wear and arc erosion were the dominant mechanisms during the electrical sliding processes.     

Effect of arc discharge on the wear rate and wear mode transition of a copper-impregnated metallized carbon contact strip sliding against a copper disk

Wear of the contact strip on the pantograph of electric railway vehicles is governed mainly by arc discharge occurring simultaneously with break of contact between the strip and trolley wire. As a step to clarify the wear mechanism of metallized carbon contact strips under the occurrence of contact break arc discharge, a detailed sliding wear test of 30 min duration was carried out for the combination of a copper-impregnated carbon strip and a copper disk at a sliding speed of 100 km/h. The worn surfaces of the strip and disk were observed every 5 min. The voltage drop and electric current were measured throughout the test, and the occurrence and energy of the arc discharge were evaluated for each revolution of the disk. The wear process is considered in terms of the wear mode transition, and the effect of arc discharge on the mode transition and wear rate of the strip is discussed.     

Friction and wear behavior of pure carbon strip sliding against copper contact wire under AC passage at high speeds

A series of tests on the friction and wear behaviour of pure carbon strip/copper contact wire with alternating current were conducted on a ring-on-block sliding tester at a high speed. The electric current, normal force and sliding velocity have distinct effects on the test results. The worn scar has the smallest size without electric current. The worn scar becomes larger with increasing electric current. Arc ablation pits, dark stream-lines of arc ablation, slipping marks, spalling blocks and the copper-like layer are found on the worn surfaces. Arc erosion, abrasive wear and adhesive wear are main wear mechanisms.     

电化学放电线切割加工方法实验研究

针对非导电硬脆材料的微细线切割加工,设计并搭建了电化学放电线切割加工装置,对电化学放电线切割加工过程中的电压-电流曲线与电极丝放电长度之间的关系进行了实验研究。实验结果表明,随着直流电压的增大,电压-电流曲线呈现出线性区、饱和区、跃变区和放电区等明显的区域性特征变化,稳定放电仅在电压高于一定值的放电区内发生,且电极丝放电长度越大,发生跃变放电时的临界电压越高。对普通玻璃和石英玻璃的加工实验表明,通过增大放电能量,能够获得更高的材料去除率,但也会导致工件加工精度和表面质量的下降。     

Friction and adhesion of stainless steel strip against tool steels in unlubricated sliding with high contact load

The strong tendency of stainless steel to adhere to other metals and to work harden makes it particularly difficult to form. A new slider-on-strip tribometer was used to study the tribological behaviour of traditional and new tool materials. The tribometer allows friction, workpiece adhesion on the tool surface and wear to be studied under conditions with low sliding speeds and high contact pressures. Several tool steels were tested using cold rolled stainless steel strip as a workpiece material. The results showed that the composition of the tool steel does not have a marked effect on the friction between the tool and the workpiece. However, the surface roughness and topography of the tool have a marked effect. Polishing of the tool surface to reduce the surface roughness reduces the friction between the tool and the workpiece.     

Low-speed sliding tests with nodular cast iron in contact with steel wire and a diamond tip

Scratch testing has been well applied towards the adhesion and failure testing of thin, hard ceramic coatings upon numerous different types of substrate materials. It is common that the test sample is scratched with a contact tip that will not easily deform, such as a Rockwell C diamond tip. Such tips are often not relevant to real, industrial cases, in which the materials of the two counter surfaces are both subjected to some degree of wear. The present paper describes the use of a scratch tester with a newly developed steel wire sample geometry replacing the conventional diamond tip, and the results of the effect of increasing load, loading rate and lubrication may have upon an industrially relevant nodular cast iron versus steel wire contact scenario.     

Experimental study of air squeeze effect on high-frequency friction contact

A special tribometer was developed which was used to test sliding friction force between PTFE-based composites and bronze with normal (out-of-plane) or transverse (in-plane) high-frequency vibrations under three different environmental pressures. The influences of environmental pressure, vibration amplitude and sliding velocity on sliding friction coefficient were studied. The results show that the effect of environmental pressure on reduction of sliding friction is outstanding. With the increase of vacuum, the reduction of sliding friction by high-frequency vibrations decreased, especially the reduction of sliding friction by normal vibration. The sliding friction coefficient with high-frequency vibrations slowed down as the vibration amplitude increased. With increase of sliding velocity, the time-averaged friction coefficient with transverse vibration increased.     

Influence of grease composition on rolling contact wear: Experimental study

This paper presents an experimental study on the influence of grease composition on rolling contact wear (RCW). Experimental tests for three greases and correspondent base oils were carried out on a twin-disc machine under pure rolling conditions. The following parameters were varied: base-oil viscosity, percentage of soap concentration and the presence of additives. The second aim of these tests is to analyse the use of artificial dents as a technique to evaluate RCW: prior to the tests, artificial dents were printed on one of the contacting surfaces. These dents were used to calculate the wear volume that is removed from the surfaces, based on the assumption that when the material is removed, the diameter of these dents diminishes. For each stop, images obtained using video-microscopy were analysed and the diameter of the dents, at a given number of cycles, was calculated. It was found that tests with different lubricants resulted in different damaged areas around the dents. Based on this, a comparison of this area growth throughout the fatigue cycles was used as a way to compare the influence of grease composition on RCW.     

Boundary lubrication with anti-wear additives: study of interface film formation by electrical contact resistance

It has been shown that a rapid measuring technique for electrical contact resistance (ecr) has potential applications in lubricant additives studies. In boundary lubrication of a metallic interface with zinc dialkyl dithiophosphate (DTPZn) or other anti-wear additives blended in the lubricant, anti-wear efficiency relies on interface film formation which acts also as an insulating barrier for electrical current. Investigations in the 1ω to 10 Mω range of resistance, with subsequent and appropriate ecr signal treatment and analysis, indicate that systematic use of ecr permits visualisation and study of interface film formation. This paper shows that two interface films can be detected, with two different levels of average ecr, 0–1 kω and 100k–10Mω. Discussion is based on an interface model and attempts to find what kind of further information on film formation may be obtained from ecr measurements     

Experimental study on micro electrical discharge machining of porous stainless steel

Various cutter strategies have been developed during milling freeform surface. Proper selection of the cutter path orientation is extremely important in ensuring high productivity rate, meeting the better quality level, and longer tool life. In this work, finish milling of TC17 alloy has been done using carbide ball nose end mill on an incline workpiece angle of 30°. The influence of cutter path orientation was examined, and the cutting forces, tool life, tool wear, and surface integrity were evaluated. The results indicate that horizontal downward orientation produced the highest cutting forces. Vertical downward orientation provided the best tool life with cut lengths 90–380 % longer than for all other orientations. Flank wear and adhesion wear were the primary wear form and wear mechanisms, respectively. The best surface finish was achieved using an upward orientation, in particular, the vertical upward orientation. Compressive residual stresses were detected on all the machined surfaces, and vertical upward orientation provided the minimum surface compressive residual stress. In the aspect of tool wear reduction and improvement of surface integrity, horizontal upward cutter path orientation was a suitable choice, which provided a tool life of 270 m, surface roughness (R _a ) of 1.46 μm, and surface compressive residual stress of ?300 MPa.     

钢丝滚道球轴承的点接触问题有限元仿真

以某型飞行器三轴仿真转台主轴轴系中的钢丝滚道球轴承为例,通过ANSYS对该滚珠．滚道间的非协调性接触问题进行有限元建模与仿真,发现最大接触应力发生在钢丝滚道的表面,而滚珠的最大接触应力发生在其接触面正下方短距离内。有限元分析结果有力地阐明了点蚀易在钢丝滚道接触表面形成并逐渐扩展的机理。本文的工作为进一步开展钢丝滚道的点蚀及磨损的实验研究提供了理论依据。     

Experimental research on electrical discharge machining characteristics of engineering ceramics with different electrical resistivities

Electrical discharge machining (EDM) is the extensively used nonconventional material removal process for machining engineering ceramics provided they are electrically conductive. However, the electrical resistivity of the popular engineering ceramics is higher, and there has been no research on the relationship between the EDM parameters and the electrical resistivity of the engineering ceramics that can be machined effectively by EDM. This paper investigates the effects of the electrical resistivity and the EDM parameters on the EDM performance of ZnO/Al₂O₃ ceramic in terms of the machining efficiency and the quality. The experimental results showed that the electrical resistivity and the EDM parameters such as pulse on-time, pulse off-time, and peak current had the great influence on the machining efficiency and the quality during electrical discharge machining of ZnO/Al₂O₃ ceramic. Moreover, the electrical resistivity of the ZnO/Al₂O₃ ceramic, which could be effectively machined by EDM, increased with increasing the pulse on-time and peak current and with decreasing the pulse off-time, respectively. Furthermore, the ZnO/Al₂O₃ ceramic with the electrical resistivity up to 3,410 Ω cm could be effectively machined by EDM with the appropriate machining condition.     

Experimental investigations into electrical discharge machining with a rotating disk electrode

In electrical discharge machining, when the provision of holes in the electrode is impracticable, flushing of the working gap poses a major problem. Use of a rotating disk electrode is proposed as a more productive and accurate technique than use of a conventional electrode. Material removal rate, tool wear rate, relative electrode wear, corner reproduction accuracy, and surface finish aspects of a rotary electrode are compared with those of a stationary one. The effective flushing of the working gap brought about by the rotation of the electrode remarkably improves material removal rate and machines surfaces with a better finish. Despite the prevalent high tool wear rate, the reproduction accuracy is least affected as the wear gets uniformly distributed over the entire circumference of the disk. Machining of a sharp corner is possible even with an aluminum electrode, whose relative electrode wear is greater than unity.     

多股螺旋弹簧三维接触摩擦研究

通过对多股螺旋弹簧在成形加载情况下的接触面上的状态分布进行深入分析,综合前人的研究,提出新型多股螺旋弹簧接触面模型,即包括空隙带、弹性带、摩擦带三种情形的分布模型.接着对这三种分布带的边界条件和接触判定条件在法向-双切线坐标系进行理论量化分析.     

Studies on fracture toughness of cold wire addition in narrow groove submerged arc welding process

Due to the faster joint completion rates coupled with good mechanical properties, narrow gap submerged arc welding (NGSAW) is widely used for fabrication of thick-walled pressure vessels. Several researchers are working on further increase in productivity in NGSAW. In this paper, we propose to increase the quality and productivity in NGSAW through cold wire addition without addition of heat input. Further toughness at sub-zero temperature is also enhanced. The improvement in toughness in cold wire NGSAW is demonstrated through different tests such as impact energy test, fracture toughness tests, plane strain fracture toughness test K _Ic, and crack tip opening displacement test.     

An investigation of contact problem between strip and work roll with a smooth straight surface during cold rolling

Under the assumption of elastic roller, and the neglect of heat transfer problem, this paper explores the distribution of elastic deformation of the work roll with initially smooth straight surface in the rolling area during the rolling process, and analyzes the effect of this deformation distribution on the strip shape after rolling.

Based on the large deformation—large strain theory, the update Lagrangian formulation (ULF) and the incremental principle were used to develop 3D elastic-plastic analytical model of aluminum strip rolling. The flow stress was considered the function of strain and strain rate to infer the governing equation containing the effect of strain rate.

Besides, in this article, we propose an iteration procedure to calculate the contact force between strip and work roll, and the contact deformation of the work roll. In the treatment of the contact problem, the work roll was regarded as a rigid body at the beginning of each step. The incremental displacement and contact force of strip nodes were first calculated, and then entered into the first iteration loop. The contact forces of strip nodes were allocated to the work roll to calculate work-roll elastic deformation. The elastic deformation of work-roll nodes would be compensated to the incremental displacement of the strip nodes (the work-roll deformation increment was added on the incremental displacement of strip node). Then the new contact nodal forces were derived from the finite element program of strip. The above procedures were repeated to incorporate the new contact nodal forces into the first iteration loop to obtain the new strip node incremental displacement. An error range was also designated as the comparison standard to compare the displacement increments of the strip from two iterations to determine whether the iteration was completed.

This paper considers the initial shape of work roll is straight and smooth. The elastic deformation distribution on the work roll surface in the rolling area is analyzed to serve as the basis for work-roll radius compensation. Finally, deformation of strip shape is also discussed.     

Experimental research on KDP crystal slicing with resin bonded diamond abrasive wire saw

This paper shows the development of software that calculates and generates the 3-D printing path for tissue engineering (TE) scaffolds. It is compatible with Fab@Home platform, which works with additive manufacturing (AM) extrusion processes. The software was named BioScaffolds PG; it allows obtaining 0/90^° architectures of square and circular scaffolds. In the software interface, the user can easily define the scaffold geometry, then, it generates a file with a continuous path, which can be exported to the 3-D printer software; the continuous path is an advantage since the 3-D printer does not need to stop the process between layers, minimizing morphological defects related to the AM process. Several tests were carried out to evaluate the compatibility between BioScaffolds PG and Fab@Home softwares. Furthermore, polycaprolactone (PCL) scaffolds were fabricated and morphologically characterized, where suitable scaffold morphologies were obtained. It was found that the software works properly and can be used in TE researching to reduce the computer-aided design (CAD) time usually required in this kind of applications.     

Experimental study of the disturbed layer generation during hot rolling contact of aluminum with steel

Effects of rolling passes and forward speed on the generation of disturbed layer on aluminum alloy sheet surfaces were investigated using a hot rolling simulator at forward speeds of −1% and 12% in presence of spraying emulsion. The results showed that at higher forward speed and number of rolling passes, the localized shear deformations become more pronounced on the surface. However, when the two rolling passes were in opposite directions, the localized shear deformations did not stick out, but were embedded into the aluminum surface. The defects generated were representative of the initial stages of the disturbed layer formation.     

Improvement of wire electrical discharge machining efficiency in machining polycrystalline silicon with auxiliary-pulse voltage supply

This study proposes a novel pulse voltage configuration, auxiliary-pulse voltage, for wire electrical discharge machining (WEDM) of polycrystalline silicon (polysilicon) used in solar cell production. It is developed with the objectives of reducing material waste due to the large kerf loss as well as achieving greater efficiency and better quality compared with conventional machining approaches. Experimental results show that compared with conventional-pulse voltage supply, the auxiliary-pulse voltage mode can avoid delay in electrical discharge during pulse-on time. Enhanced frequency of effective discharge for machining would increase machining speed, which would in turn reduce machining groove width, and obtain better surface roughness. In addition, parameters of significant influence on machining characteristics were examined with the Taguchi method, and the optimal combination levels of machining parameters were determined. In sum, our findings reveal that WEDM with auxiliary-pulse voltage supply is an effective approach to machining polysilicon with good quality and high efficiency achieved.