Study of non-metallic inclusions composition in rail joints welded seams, obtained at their contact arc welding

The quality of welded rail joints depends on various factors, in particular, on the type and quantity of non-metallic inclusions, formed at their contact arc welding. To check a hypothesis of the cause-effect of welded joint mechanical properties decrease and composition of non-metallic inclusions in the welded seams, their chemical and metallographic analysis accomplished. To study the non-metallic inclusions, samples of 90×30×10 mm dimensions used, cut of Э76ХФ steel rail head. After contact butt welding at MC-2008 machine, the samples were cut by electro-erosion method perpendicularly to the welding seam into two parts. One part of the sample was used for tensile test, the other – for metallographic analysis for non-metallic inclusions and structure of the welded joint. The microstructure of the welded butts studied after milling and intensive etching in the 50% water solution of hydrochloric acid. The microstructure was studied at the optical microscope OLYMPUS GX71 in the light field at magnification 100–1000 folds after etching in an alcohol solution of nitric acid. The chemical composition of all the revealed inclusions were determined at the scanning electron microscope MIRA 3. It was established, that silicon and manganese oxides were the basic components of inclusions, revealed in the welded seam, as well as oxides of aluminum, iron, titanium, chrome – to a less amount. In the samples seam microstructure the ferrite net, typical for rail butts, was not discovered, which is probably stipulated by their accelerated heating due to the small section of the samples.

Visual Investigation on the Arc Burning Behaviors and Features in Underwater Wet FCAW

The dynamic arc behaviors have a significant effect on the process stability and welded joint quality in underwater wet flux-cored arc welding (FCAW). In this study, clear underwater arc images are obtained by using a high-speed camera, which further reveal the complex physical process of underwater wet welding. The mechanism of underwater contact arc ignition is described in detail. Gas ionization and electron emission processes are carried out in bubbles generated by resistance heat. The dynamic arc behaviors are obviously different between bubble growth and separation stages. The high-speed gas flow in the bubble separation stage has a great disturbance to the arc. The arc shapes under water and in air under the same parameters are compared, and the mechanism of arc column shrinkage and arc length shortening is revealed from the aspects of water environment cooling, gas composition in bubbles, disturbance of gas flow, water pressure, and electric field strength.

Strain and Friction Effect on the Stress-Strain State in the Deformation Zone during Cold Rolling of Thin Beryllium and Aluminum Foils

The effect of strain and the friction on the stress-strain state in the deformation zone during cold rolling of thin beryllium and aluminum foils was investigated in this work. Calculations showed that material hardening has a significant influence on the contact pressure distribution along the contact arc. Although it, the distributions of hydrostatic stress and stress triaxiality are favorable for fracture prevention both beryllium and aluminum except narrow regions near the entrance and the exit of deformation zone for all considered cases (strain up to 40%, friction coefficient in range 0.03 – 0.3). The most favorable stress state is observed during cold rolling with a high friction coefficient (rolling without lubrication).

Belt-Drive Mechanics: Energy Losses in the Presence of Detachment Waves

The dissipative rolling friction moment in a simple belt-drive system is estimated both experimentally and computationally while taking into account the detachment events at the belt-pulley interface. Shear traction is estimated based on measurements of the shear strain along the contact arc. It is shown that the dissipative moment can be approximated by taking the difference between the shear traction and the load carried by the belt. A model is developed for analyzing the contributions of different components to this dissipative moment by considering both the volumetric and surface hysteresis losses. The computed rolling friction moment is found to be in good agreement with that estimated based on the experiments. It is also found that while the shear- and stretching-induced energy losses contribute the most to the dissipation in the belt drive system, the losses associated with the Schallamach waves of detachment make up a considerable portion of the dissipation in the driver case.

Establishment and Verification of the Cutting Grinding Force Model for the Disc Wheel Based on Piezoelectric Sensors

In this paper, a new model of cutting grinding force for disc wheels is presented. Initially, it was proposed that the grinding cutting force was formed by the grinding force and cutting force in combination. Considering the single-grit morphology, the single-grit average grinding depth, the effective number of grits, and the contact arc length between the grit and the workpiece comprehensively, the grinding force model and the cutting force model were established, respectively. Then, a universal grinding cutting force model was optimized by introducing the effective grit coefficient model, dependent on the probability statistical method and the grit height coefficient model with Rayleigh’s distribution theory. Finally, according to the different proportions of the grinding force and cutting force, the grinding cutting force model, with multi-particles, was established. Simulation and experimental results based on piezoelectric sensors showed that the proposed model could predict the intermittent grinding cutting force well. Moreover, the inclusion of the grit height coefficient and the effective grits number coefficient improved the modeling accuracy. The error between the simulation and experimental findings in grinding cutting force was reduced to 7.8% in comparison with the traditional model. In addition, the grinding cutting force can be divided into three segments; increasing, steadiness, and decreasing, respectively found through modeling.

Specifics of automatic switches commutation testing

We demonstrate that the most efficient way to extinguish the short-circuit arc is extinguishing inside the camera with an arc extinguishing grid, which splits it into several smaller arcs. The active resistivity of these partial arcs decreases the amplitude of the current of the short-circuit arc, decreases the angle φ between current and voltage, which decreases the amplitude of the return current and enhances the condition for the arc extinguishing. We analyze the process of arc extinguishing in the three-phase circuit. We would like to note that during the extinguishing of the arc in the first extinguishing pole resistance of electric arcs in two other poles deforms the voltage triangle decreasing the coefficients of the scheme from 1.5 to 1.3 according to the experimental data. This allows to decrease the difficulty of the tests for maximum commutation capability. Simultaneously, we consider the necessity of the selection and regulation of the wave parameters (amplitude coefficient and normal mode) of the test circuit according to the standard for test preparation. Taking into account the decrease of the coefficient of the scheme and the real wave parameters will allow to objectively estimate commutation capability and to optimize the parameters pf the contact arc extinguishing system of an automated switch.

Contact arc time – important parameter of DC high-speed circuit-breakers

The parameters of DC high-speed circuit-breakers (HSCB) and test methods are specified in the standards. These standards define requirements of the circuit breakers opening time and the total breaking time. During the direct current (DC) breaking after opening the contacts, the arc ignites, the voltage of which is so low that it does not limit the switched off current. The time in which this phenomenon occurs is defined as the contact arc time.The contact arc time has a significant influence on the breaking process. It can take up to over 40% of arcing time. Therefore, tests were carried out, which were to answer the questions about what and to a what extent affects the contact arc time.Since the standards for high-speed circuit-breakers do not refer to the contact arc time, definitions of this parameter are proposed in the article. Using this definition numerous tests of various factors have been carried out on contact arc time.The conducted research shows that shortening the DC breaking time through high-speed breakers is possible by limiting the contact arc time, which can be obtained by modifying the circuit breaker’s construction.