PHASE COMPOSITION, SUBSTRUCTURE AND RESIDUAL MACROSTRESSES IN THE SURFACE LAYER OF A TAPE OBTAINED BY ELECTRIC CONTACT WELDING

Методами рентгенографии и электронной микроскопии исследован поверхностный слой чугуна ВЧ50-2 после его обработки электроконтактной приваркой. В качестве присадочного материала использовалась лента из стали 50ХФА. Применялись технологии обработки с созданием промежуточного слоя из никелевого порошка ПГН-12Н-01 и без него. Получены результаты о фазовом составе, субструктуре и остаточных напряжениях. Исследуемая система состоит из фаз a - Fe и у - Fe . Параметры субструктуры (микродеформации и измельчение блоков) имеют одинаковые значения для различных режимов электроконтактной приварки. Остаточные напряжения носят растягивающий характер и уменьшаются при создании промежуточного слоя из никелевого порошкового материала. Основной механизм их образования - термические воздействия на материал, обрабатываемый электроконтактной приваркой. Установлено, что после электроконтактной приварки ленты могут образовываться трещины, их ориентация преимущественно параллельно обрабатываемой поверхности обусловлена наличием большого градиента температур. The surface layer of DI50-2 cast iron after its processing by electric contact welding has been investigated by methods of X-ray diffraction and electron microscopy. A 50HVA steel strip was used as a filler material. Processing technologies were used with the creation of an intermediate layer of nickel powder PC-12N-01 and without it. Results on phase composition, substructure and residual stresses are obtained. The system under study consists of a-Fe and у-Fe phases. Substructure parameters (microstrain and block refinement) have the same values for different modes of electrical contact welding. Residual stresses are of a tensile nature and decrease when an intermediate layer of nickel powder material is created. The main mechanism of their formation is thermal effects on the material processed by electrocontact welding. Cracks may form after electrical contact welding of the tape. They are oriented mainly parallel to the surface to be treated and are due to the presence of a large temperature gradient.

Road Traffic Safety: High-Quality Welding - Ensuring Cost-Effectiveness and Safety

Welding industry is one of the leaders in the field of investments in the development of technologies and innovations aimed at ensuring functional cost-effectiveness, improving safety and speed of movement in the digital age. Ensuring the reliability and safety of the railway tracks requires the development of new scientific approaches to the use of welding technologies in the construction and operation of a high-speed railway. The main criterion for evaluating efficiency of the new approaches is the quality of the resulting welded joints and the productivity of the welding processes used. Rail connections should be made in such a way from a technical point of view that there are no restrictions during operation, the service life of the rails is not reduced, the percentage of defects does not increase, and the noise level is within the normal limits. The purpose of the study is to substantiate the cost-effectiveness and safety of the introduction of new contact welding technologies in Russia. Technical and economic analysis of welding methods is given, including using the rail welding machines — a new generation of equipment for the contact butt welding of high-strength rails during the construction and reconstruction of a high-speed railway. The Up-to-date technologies are based on the process of contact welding by pulsating reflow, on the one hand ensuring high productivity of the process, and on the other — reducing the influence of the human factor on it. This is achieved through a set of options for controlling the welding process, with online monitoring of the operational characteristics, with the software for storage and the possibility of using robotic welding in the future in the field of digital doubles and processing archived data based on the artificial intelligence as part of the implementation of Smart City projects. Feasibility study is also presented concerning the efficiency of the introduction of contact welding technology by the pulsed reflow on high-speed railway projects of Russia based on reducing the rail joint failures and improving the characteristics of the welding process and safe operation.

Numerical Simulation Mode of Spot Contact Welding Processes

Цель рассмотрения численного метода заключалась в получении подробных данных, позволяющих оценить проведение сварочного процесса: изменение объёма сварного шва, радиуса сварного шва, радиуса зоны термического влияния. При проведении моделирования авторами выведены зависимости параметров точечной сварки низкоуглеродистой стали толщиной до 3,2 мм. Данные зависимости будут определять качество сварных швов. Соответствующее сочетание параметров точечной сварки обеспечит прочное соединение и хорошее качество сварки. The purpose of the numerical method consideration was to obtain detailed data allowing evaluating the performance of the welding process: changing the volume of the weld, the radius of the weld, the radius of the weld-affected zone. During the simulation the authors have derived dependencies of the parameters of spot welding of low-carbon steel up to 3.2 mm thick. These dependencies will determine the quality of the welds. The correct combination of spot welding parameters will ensure a firm joint and good welding quality.

Influence of various types of clays on velocity dependence of friction composites

The stick–slip phenomena of various types (halloysite, montmorillonite and wollastonite) of clay-based composite friction materials were evaluated in terms of their velocity-dependent friction response. Scanning electron microscopy of the contact patches suggested breakage of contact plateaus in the composites with halloysite, whereas relatively small contact patches were developed in montmorillonite-based friction composites. The presence of relatively harder ingredients such as magnesium oxide and iron particles on the worn surface have contributed to the stick–slip phenomenon. The presence of wollastonite in the composites leads to the ploughing effect during sliding. The intensity of creep groan remained controlled by the shear strength of the interfacial junction involving asperity contact/welding whereas dynamic groan remains predominated by the stiffness of the composites.

Improvement of the Acoustic Characteristics of Pneumatic Mechanisms for Contact Welding Machines

Welding production forms the basis of assembly production in many branches of industry. Welding equipment is the most numerous in the environment of assembly of transport engineering units. This equipment is used both at the initial stage of assembly operations and at the final stage. The most common machines are single-point and multi-point welding with pneumatic drive. Traditional disadvantage of welding machines using pneumatic drives is the presence of intense acoustic flows at the outlet of the energy carrier, the operating sound level of which significantly exceeds the established sanitary norms and worsens personnel working conditions. Among the sources of aerodynamic flows in contact welding machines, the most relevant noise is during technological release of energy from the pneumatic mechanisms of the welding machines control systems, including the existing fleet of contact welding machines. Standard noise mufflers in the contact welding machines, the acoustic elements of which are made in the form of porous metal bushings or pots, are working efficiently for a short period of time up to 200 hours, both domestic and foreign companies Festo, Camozzi, Pneumax. The reason is that when pulsed, technological release of compressed air containing oil particles, in the presence of external dust sources, the channels of porous sound-absorbing elements are clogged with a suspension of oil with the above specified particles and condensate. This leads to an increase in the hydraulic resistance of the muffler path, an increase in the back pressure in the silencing chamber, and, as a result, to the destruction of the acoustic element, which requires frequent replacement of the muffler. The results are presented concerning the development of new chamber mufflers for contact welding machines, which efficiently reduce noise, operate without maintenance for more than fifteen years without requiring replacement. They are recommended for various branches of industries operating pneumatic systems for various purposes.