Papers by Keyword: Protective Atmosphere

Abstract: Micro-alloyed steels are widely used in the manufacture of critical welded structures operating under extreme conditions of the North. Microalloying of V, Nb and B is a simple and effective method of transferring known grades of structural steel and alloys to the category of increased and high strength, cold resistance, etc. The possibility of arc welding of steels grade 10CrSiNiAl and 15CrSiNiAl (10, 15ХСНДА in Russian), initially alloyed with trace amounts of niobium and vanadium to increase their cold resistance in carbon monoxide is considered. It is established that the use of the specified reducing atmosphere prevents the oxidation of the weld metal. The thermodynamic substantiation of the chemical reactions of microalloying elements proceeding in the weld pool, leading to the preservation of the steel composition, is presented. The chemical and metallographic analysis of welds was performed. The efficiency of using low-cost CO, or its mixtures with CO₂, as substitutes for expensive argon and helium, when welding micro alloyed steels is shown.

Abstract: A manufacturing process was developed using an electric through-type furnace for capillary tubes used for single-use injection syringes. The process flow diagram consisting of a number of sequential steps and tube heat treatment conditions in protective atmosphere of pure hydrogen providing also for the tube purging with inert gas were considered. The electric furnace installed capacity and heating element dimensions were found as a result of the thermotechnical calculations. Industry research was carried out with a view to optimize the annealing process of capillary tubes in the electric furnace. A choice of material for the muffle fabrication was justified. Temperature fields inside the muffles were evaluated. The optimal flow of protective gas and the maximum allowable flow of purging gas in the form of nitrogen and argon were determined. Mechanical properties were studied for tubes (stocks), welded at the medical goods fabrication plant in Tumen and fabricated at the Pervouralsky Novotrubny Plant. Test data were obtained for optimal rates of tube movement in the furnace, allowing production of capillary tubes, acceptable for medical needle fabrication after annealing. It was demonstrated that capillary tube heat treatment, ensuring the required condition of both outside and inside surfaces, as well as required mechanical properties, is possible with the use of nitrogen as protective (instead of hydrogen) and purging gases. At that probability of better tube surface condition significantly grows.

Abstract: The work deals with the research of wettability of lead-free solders for higher application temperatures. For the research of wettability, SnSb5, ZnAl4, ZnAl6Ag6 and BiAg11 solders were used on Ag, Cu and Ni substrates. The measurement was carried out in a controlled atmosphere by trigonometric method. Zn based solders wets none of the examined substrates. SnSb5 solder wets only Cu substrate with wetting angle of 54o. Soldering alloy BiAg11 wets all substrates, wherein the best results (23 o) was achieved on Ag substrate.

Abstract: Nowadays, a furnace designer has to meet the demands of the customer precisely to allow economical production at site. Repeatable high quality throughout millions of produced parts combined with high cost efficiency is needed to stay competitive. Thus the facility has to be changed from a black-box to a glassy furnace which records and controls all important process values that define the properties of the produced parts and the consumption of the facility. Current furnace designs offer a wide variety of layouts with unique advantages and disadvantages. Single type furnace designs are well known and need the lowest investments but they also take up a lot of space and do not offer a back-up solution during maintenance or in the event of malfunctions occurring. Twin type furnaces have a higher degree of flexibility as they still allow 50% production during downtime caused by maintenance or malfunctions, so availability is higher than with single type furnaces. Double layer furnaces, which are stacked versions of the twin type furnaces, only need half of the floor space but maintenance is more complicated on the upper level. An oxygen-free furnace atmosphere is essential for the production of components in process atmosphere in order to ensure high quality results with the minimum of scale and other surface defects. This is not possible in a multi-level furnace.

Abstract: In order to discuss chemical and physical reaction of A95 polycrystalline alumina fibers (PAF) during heat treatment and improve the properties, the influences of the protective atmosphere and heat treatment temperature on properties of PAF were researched. DT-TG, IR, XRD and SEM were adopted to characterize the fibers. The results show that in N₂ atmosphere, the carbonization and oxidation rates of the gel fibers decrease, the thermal decomposition process of the organics is extended and the crystal transformation temperature of alumina is enhanced. When the heat treatment temperature is lower than 1200 °C, the major phases of A95 PAF are mainly δ-Al₂O₃ and θ-Al₂O₃, but no α-Al₂O₃ appears.

Abstract: Behavior of hydrogen in steel during electroslag remelting process was investigated on a laboratory-scale unit. Results indicated that a considerable amount of hydrogen was picked up by the metal at the beginning of the process. Hydrogen content decreased with the increasing of ingot height. To avoid the hydrogen peak, anhydrous components must be used. Protective atmosphere combining with premelted slag was the optimal measure to control hydrogen in steel when the solid-starting technique was carried out. According to the results in the experiment it was not the crucial factor for hydrogen in steel remelted under protective atmosphere whether slag contained lime or not at actual remelting period.

Abstract: Sulphur hexafluoride (SF6) is widely used by the magnesium industry as a protective atmosphere. It has been demonstrated that SF6 prevents molten magnesium from further oxidation by reacting with magnesium to make the surface film on the magnesium melt denser. However, due to its high greenhouse effect (GWP=23900), the alternatives of SF6 must be sought. In this paper, 1,1-difluoroethane (commercially named HFC-152a), whose GWP value is only 140 and far lower than that of SF6, was tested to check its capacity of ignition-proof and further-oxidation-proof. Similar to SF6, the melt’s surface film formed in the protective atmosphere containing HFC-152a has a shiny metallic appearance. The surface film’s microstructure has been characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD’s results showed that the film contains only MgO and MgF2 phases while SEM showed their morphologies are uniform.