Papers by Keyword: High Vacuum

Abstract: This article discusses the problems of efficient removal of nitrogen in the vacuum tank degasser operating at the electric arc furnace shop of Uralskaya Stal (Ural Steel) OJSC in the course of manufacturing of high-quality low carbon steel grades by means of steel grades «2» and «T». In order to determine the reasonable and balanced treatment parameters that ensure the required level of nitrogen content in the above steel grades, an analysis of production data for the period of November-December 2016 has been carried out. This analysis is the basis for identifying the vacuum degassing parameters in compliance with the technological capabilities and well-balanced levels, which allow predicting the level of nitrogen content in steel. To assess the cumulative quantitative effect of the main parameters of vacuum degassing on nitrogen removal, there has been performed a regression analysis. As a result, there have been obtained multiple regression equations describing a rational combination of steel treatment parameters for achieving the required nitrogen removal level.

Abstract: In this paper, the fabrication of TiAl alloy powders by high-energy ball milling and heat preservation at low temperature and high vacuum using titanium powders of 30 micron and aluminum powders in the size of 9-12 micron. After being heated under the different time and temperature, the alloying of milled and heated powders of titanium and aluminum were investigated. The results show that the alloy powders with the main intermetallic compounds of TiAl and a small quantity of aluminum tri- titanium can be obtained through one hour high-energy ball milling and preserving heat 2 hours at 500°C, 3 hours at 600 °C in high vacuum. Furthermore, the transitional alloy phase Al2Ti was formed at 550 °C~600 °C, and it has an effect on the density of Ti-Al alloy powders in the diffusion synthesis. The fabrication of TiAl alloy powders with different density by sintering diffusion at low temperature and high vacuum is effective.

Abstract: The tribological properties of Plasma Nitrided (PN) rings were examined in high vacuum environment (1.6 x 10^-4bar) at 25°C, 200°C and 400°C. The high vacuum based pin on disc tribometer was used for this investigation. The two different sliders namely austenitic stainless steel type AISI 316LN (316LN) pin and Nickel based alloy coated (Colmonoy) pin have been used. The tribological parameters such as friction coefficient, wear mechanism and wear rate have been evaluated. The PN 316LN rings exhibits excellent wear resistance against 316 LN pin and Colmonoy pin at all temperatures. However, the PN 316LN ring vs Colmonoy pin pair shows better wear resistance than PN 316LN ring vs 316 LN pin pair. Whereas the untreated 316 LN ring vs 316 LN pin pair exhibits the combination strong adhesion and plastic deformation wear mechanism.

Abstract: The friction and wear properties of Polytetrafluoroethylene (PTFE) coatings before and after gamma irradiation were studied under vacuum conditions. Experimental results indicated that the friction and wear properties of PTFE coatings were improved by gamma irradiation. Results showed that the wear process of PTFE coatings before and after gamma irradiation consists of three stages. The steps for the irradiated PTFE are slightly longer than that for the non-irradiated samples. The friction coefficient of irradiated PTFE coatings reduces slightly compared to that of the non-irradiated samples. The friction coefficients of the PTFE coatings before and after gamma irradiation first increase with the increase of sliding velocity and then decrease with the increase of sliding velocity, and The friction coefficient of PTFE coatings before and after gamma irradiation decreases with the increase of load. The wear of irradiated PTFE coatings is slightly lower than that of non-irradiated PTFE coatings. The wear of PTFE coatings before and after gamma irradiation first decreases with the increase of sliding speed and then increases as the sliding speed increases. The wear of PTFE coatings first decreases with the increase of load and then increases with the increase of load. Scanning electron microscope (SEM) was utilized to investigate the worn surfaces.

Abstract: Compare to atmosphere die casting or moderate vacuum die casting process, use of the high vacuum die casting can enhance excluding gas volumes in the mold, improve the casting mechanical properties and density, and increase the fabrication feasibility for casting small feature size, shape, and higher quality of product. The process of high vacuum die casting for dumbbell specimens is established and implemented for evaluation of this innovative manufacturing technology. A transparent acrylic mold is fabricated to investigate the vacuum injection for vacuum die casting process and a metal mold is fabricated to test the real manufacturing of high vacuum die casting. To visualize the flowing pattern inside the mold under the consequence of evacuation processing, flow visualization experiments are conducted. Then, the specimen is molded by the high vacuum die casting process and the specimen castings are test by a universal testing machine for its loading-elongation relationship. The porosities of specimen casting are examined by scale weighting and direct visual inspection ways. Experimental results show that the high vacuum die casting process is effective to reduce the porosity (5.47% increment in weight) and to increase the strength (4.83% increment in maximum stress) of the investigated specimen. An obviously vortex roll is established along the centerline position of dumbbell specimen which may be became the source of porosity in real processing. Meanwhile, an excellent vacuum sealing is critical to the success of high vacuum die casting.

Abstract: Magnesium automotive components are currently produced by high pressure die casting. These castings cannot be heat-treated to improve the strength and ductility mainly due to the casting imperfections such as porosity and inclusions created by the air entrainment during the turbulent mold filing. These imperfections also prevent magnesium components to be used for highly stressed body components. Efforts were made to produce high integrity magnesium castings through a Super-Vacuum Die Casting process. The AZ91D castings were found to have very low porosity and can be heat-treated without blisters. The tensile properties of the castings were satisfactory. The mechanical properties and thermal analysis indicate that the conventional heat treatment procedure needs to be optimized for such thin sectioned and rapidly solidified castings which have very fine microstructures.