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SUPERVISOR
Mohammad Hosein Fathi,Hossein Edris
محمدحسين فتحي (استاد مشاور) حسين ادريس (استاد راهنما)
 
STUDENT
Amir abbas Shakeri
اميرعباس شاکري حسين آباد

FACULTY - DEPARTMENT

دانشکده مهندسی مواد
DEGREE
Master of Science (MSc)
YEAR
1387

TITLE

investigation the Effect of CaO/ SiO2 and B 2O3/ Tio2 Ratioes in Fluoride Free- Mold Fluxes of Continuous Casting on Heat Transfer and Viscosity
Mould fluxes use in continuous casting. Mould fluxes are added to the top of continuous casting mould in order to cover the liquid steel and prevent thermal loss and reoxidation of liquid steel and to absorb floated liquid/solid inclusions from the liquid strand. Since the molten steel is at a temperature of around 1550?C, a temperature is established across the mould powder layer and the carbon in the flux starts to burn off, it starts sintering and then melts to form a liquid pool of flux, which prevents oxidation of the steel. The liquid slag infiltrates into the gap between strand and mould (aided by the mould oscillation). The liquid flux partially solidifies leaving a slag film consisting of a solid slag layer (ca. 1-2 mm) and a liquid layer (ca. 0.1 mm), which provides lubrication to the newly formed shell. In the continuous casting process, mold fluxes have an important influence on the surface quality of continuous casting slab. Especially, the surface quality depends on viscosity and heat transfer of the infiltrated mold flux between the mold wall and the solidified steel shell. Generally, the basic composition of mold fluxes is CaO–SiO2–Al2O3–Na2O–CaF2, in which fluoride mainly controls the viscosity, solidification temperature, and crystallization behavior of mold flux films. These characteristics directly influence the lubrication and heat transfer of a mold flux Film. Mould fluxes are designed to meet the requirements for specific steel grades and different steel plant conditions. However, in the course of its use, the volatilization and acidification of fluoride poses a significant health hazard, causes environmental pollution and intensifies the erosion to continuous caster. In this case, developing fluoride- free continuous casting mold fluxes is of great significance. At present, the research on fluoride-free mold fluxes is mainly concentrated on the heat transfer performance of fluoride-free mold fluxes and there has been little research on viscosity characteristics done of fluoride-free mold fluxes. The present work adopted TiO2 to take the place of fluorine in mold fluxes and studies its heat transfer performance. Heat flux simulation equipment was developed and the heat flux density of titanium- bearing mold fluxes containing TiO2 was measured; in addition, a solid slag film was obtained. The crystallization behavior was analyzed. In this thesis an attempt has been made to prepare mold powder using TiO 2 and B 2 O 3 instead of CaF 2 and investigate the influence of basicity, amount of TiO 2 and B 2 O 3 on the viscosity and heat transfer of the samples. For this reason, the different composition of fluoride-free mold fluxes was constructed. By means an apparatus that had been made for measuring heat flux of samples, based on the water cooled mold copper was constructed. Also, a viscosity characteristic of the samples was analyzed. As well as, micro structure of the formed slags during the experiments was analyzed. And the relationship between micro structures and heat transfer was investigated. Key worlds: Continuous Casting , Mold Powder, Mold Flux, Fluoride-Free
چکيده ترکيبات پودر قالب در ريخته گري پيوسته فولاد استفاده مي شوند. پودر هاي قالب را بر روي مذاب درون قالب اضافه مي کنند. دو نقش مهم پودر قالب روانسازي رشته فولاد منجمد شده و کنترل هدايت حرارتي بين قالب آب گرد و فولاد مذاب مي باشد. همچنين از پودرهاي قالب براي جلوگيري از اتلاف حرارت و اکسيداسيون مجدد فولاد مذاب استفاده مي شود. در فرآيندهاي ريخته گري پيوسته، براي حفظ سلامت سطح و کاهش ترکهاي سطحي شمش ريخته گري مطلوب است که شار حرارت کنترل شود که عمدتا اينکار توسط پودر قالب کنترل مي شود. به طور کلي ترکيب پايه پودر قالب CaO-SiO 2 -Al 2 O 3 -Na 2 O-CaF 2 مي باشد، که مقدار Al 2 O 3 آن کم مي باشد. در عصر جديد که انسانها به محيط زيست خود اهميت بيشتري مي دهند، استفاده از پودرهاي قالب فلوئور دار به دلايل صدمه زدن به محيط زيست، آسيب رساندن به سلامت انسان هايي که در تماس با اين پودر ها هستندو خوردگي ماشين آلات ريخته گري مداوم مخصوصا نازل آن، محدودتر شده است. در تحقيق حاضر سعي شده تا با استفاده از اکسيد هاي جايگزين مانند TiO 2 و B 2 O 3 به جاي CaF 2 پودرهاي قالبي ساخته شود و با بررسي اثر پارامترهاي بازيسيته، درصد TiO 2 وB 2 O 3 بر روي ويسکوزيته و انتقال حرارت نمونه ها گامي در جهت اين هدف برداشته شود. به همين منظور ترکيبهاي متفاوتي از پودر هاي قالب بدون فلوئور آماده شد و بوسيله دستگاهي که جهت اندازه گيري انتقال حرارت طراحي وساخته شد، مقدار شار حرارتي انتقال يافته توسط هر يک از نمونه ها اندازه گيري گرديد. همچنين خواص جريان يابي نمونه ها بررسي گرديد. ريزساختار سرباره هاي شکل گرفته در هنگام آزمايش بوسيله ميکروسکوپ الکتروني روبشي مورد مطالعه قرار گرفت و رابطه بين ريز ساختار و انتقال حرارت بررسي شد. همچنين فازهاي تشکيل شده در مراحل مختلف در پودرهاي قالب توسط پراش پرتو ايکس بررسي گرديد. کلمات کليدي: ريخته گري مداوم- پودر قالب- فلاکس قالب- پودر قالب بدون فلوئور- انتقال حرارت

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