Possibilities for Renovation of Functional Surfaces of Backup Rolls Used during Steel Making

The paper presents the results of the research aimed at possibilities of renovation of functional surfaces of back-up rolls that are part of the hot strip rolling mill operating line using new types of additive materials. Experimentally, four melts of alloyed steel were produced in laboratory conditions from which four types of filler materials in the form of wires were made. They were made by pulling through dies to a diameter of 2.4 mm. The renovation of functional surfaces was performed on the batch of rolls with the outer diameter of 1000 mm and length 3000 mm. Cladding technology submerged arc welding (SAW) was applied for cladding of four spirals with 40 mm oscillation onto the base material of the 31CrMoV9 (EN 10085) sub-roll. The base flux marked WLDC 17-AWS A5.17-89 EM13K with basicity index 3 was used for cladding. The four-layer weld deposition was made to eliminate the effect of mixing the surfacing layers with the base material. The refurbished rolls were annealed after welding. Surface quality was assessed by visual inspection (VT) according to EN ISO 17637. The presence of internal errors was determined by ultrasound control (UT) in accordance with EN ISO 11666 and EN ISO 17640. The quality of the clad layers was analysed on metallographic sections using light microscopy. The microhardness of the individual clad layers was evaluated according to Vickers according to EN ISO 9015-2. Based on realized experiments it can be stated that the selected cladding parameter was suitable, and the overlay layers showed no surface or internal defects. Mechanical and tribological tests were carried out, but they showed significant influence of chemical composition of additive materials on mechanical properties, or wear resistance of the layers.

Study on a Large-Scale Three-Dimensional Ultrasonic Plastic Welding Vibration System Based on a Quasi-Periodic Phononic Crystal Structure

The uniformity of amplitude distribution and amplitude gain are two main factors affecting the performance of ultrasonic welding vibration system. In order to improve the uniformity of amplitude distribution and amplitude gain of welding surface to enhance the performance of the vibration system, a new design method of a large-scale three-dimensional ultrasonic plastic welding vibration system based on a quasi-periodic phononic crystal structure is proposed. In this method, the composite horn combined with a conical section and a cylindrical section can effectively improve the output amplitude gain of the welding surface. In addition, the method forms a quasi-periodic phononic crystal structure by slotting in a large-scale three-dimensional tool head, and utilizes the band gap property of the structure to effectively suppress lateral vibration of the tool head and improve the amplitude distribution uniformity of the tool head’s welding surface. However, when the size of the tool head is relatively large, the quasi-periodic phononic crystal structure cannot suppress the lateral vibration very well. Therefore, the paper processes fan-shaped slopes on the output surface of the tool head which can further improve the uniformity of the amplitude distribution and amplitude gain. Finally, the simulation analysis and experiments show that the design method can optimize the large-scale three-dimensional ultrasonic plastic welding system, improve the uniformity of the vibration distribution and increase the output amplitude gain of the welding surface.

Effect of Shoulder–Workpiece Interference Depth on the Quality of Friction Stir Welding of AA7075-T6 Aluminium Alloy

The joining of high strength aluminium alloy AA7075-T6 sheets of 3 mm thickness was an attempt utilizing friction stir welding process. The effect of interference depth between tool shoulder and surface workpiece on the welding quality and its effect on the mechanical and metallography properties of welded joints were studied. This process is carried out using a composite tool consists of a concave shoulder made of H13 tool steel and cylindrical left-hand thread with 1mm pitch pin (probe) made of cobalt-based alloy MP159. The dimensions of tools were 14mm shoulder diameter and the pin has 5mm diameter and 2.7mm length. The tool rotation speed and welding speed were 981 rpm 169 mm/min respectively, and the tilt angle was 2°. The range of interference depth between the shoulder and workpiece was selected (0.05, 0.1, 0.15, 0.2, 0.25, and 0.3) mm. various tests were executed to evaluate the welding quality. The results show that lack of filling defect appeared on the welding surface at the interference depth 0.05 mm. An invisible tunnel and lack of penetration in the bottom of the stir zone appeared when the interference depths were 0.1 mm and 0.15 mm. Defect-free welds obtained when interference depths were (0.2, 0.25, and 0.3) mm. The welding efficiency of the defect-free welds was in the range (85.3-92.3%) depending on the ultimate tensile strength of the parent alloy.

The effect of welded joint properties on the surface characteristics of laser-welded 2205 duplex stainless steel

Welded joints of poor welding surface quality are sensitive to stress concentrations, affecting both the tensile strength of workpieces and the fluidity of liquids and gases in pressure and liquid containers. Orthogonal experiments involving the laser welding of 1-mm-thick duplex stainless steel sheets were conducted using different electric current, pulse width and frequency values in order to analyse the effect of welding properties on the surface characteristics of the welded joints. Rapid judgement regarding the welded joint properties was made based on the observed welding surface quality. The results show that an even phase proportion and grain refinement are not necessarily guaranteed to provide good welding surface quality. A satisfactory welding surface quality characterised by a smaller spot pitch or spot pitch difference, smaller weld width, reduced surface roughness and valley depth of surface waviness implies better welded joint mechanical characteristics and a more even microstructure. The specimen with the most suitable welding parameters and the greatest heat input can reach the lowest volume fraction of ferrite phase of 42.5% and the highest tensile strength of 848 MPa, and its surface quality is the best.

THE AUTOMOBILE TIRES VULCANIZATION METHOD REPAIR PROCESS EXPERIMENTAL INVESTIGATION

In the article local repair automobile tires expediency by vulcanization means in mechanical damage carcass case is shown. It has been established that analytical and experimental data on determining the required temperature of the heating element have a significant discrepancy. It was found that on the vulcanization degree among all factors temperature and pressure on the welding surfaces are the most influential. After processing the experimental data and using the static methods, mathematical dependence of the temperature on the welding surface from the heating element temperature and on the welding surfaces as a second-degree polynomial is obtained. In order to verify the research results reliability, the control welding of the automobile tires with cord lateral rupture was conducted, which gave positive results.

Micro-Welding of Glass Substrate by YAG Laser – Effects of Substrate Temperature –

This paper deals with micro-welding of glass substrates using a YAG laser to prevent cracks. In order to fuse the glass substrates precisely using a YAG laser, a new glass welding method was proposed and developed in the previous report. In the method, two glass plates were made to overlap and the welded area of the glass surface was coated with absorbent. The YAG laser irradiated the surface, and the laser was absorbed in the coated area only. Therefore, only the coated area can be welded and the glass surface is expected to be clear. However, in the previous report, some micro cracks generated by the thermal shock of the YAG laser appeared on the fused area of the glass substrates. In this study, it is proposed that pre-heating the substrates decreses the heat shock, producing a crack-free surface of the fused area. In the pre-heated welding experiments, the substrate temperature and laser power are changed, and the welding surface and welding strength are evaluated. It is clarified from the experiments, that the glass plates can be welded without a crack using pre-heated welding.