Analysis of fracture in high-temperature vacuum tube furnace

High-temperature vacuum tube furnace (HTVTF) is widely used for processing materials, developing new materials, and sintering various types of material under vacuum or gaseous conditions. A growing concern in engineering research communities and industries is that fracture occurs in the alumina tube after the furnace has run for few hours and this lead to a drainage of huge amount of money when the buyers replace the tube every time. To improve furnace tube longevity and performance in extreme temperature conditions, it is critical to determine the phenomena that take place inside the furnace and cylindrical alumina tube wall. In the present work, mathematical models are developed to understand the effect of stress concentration arising from thermal stresses in tube wall and heat-affected-zones (HAZ) of a HTVTF using multiphysics finite element software Comsol (Stockholm, Sweden). The combination of thermal stress with temperature difference determines the fracture region. Different air flow rates have been considered to find the critical thermal stress region inside the vacuum tube. Analysis suggests that lowering air flow rate and inserting a small copper pipe inside the first block to blow hot air on the second heat-affected zone (HAZ-2) will reduce thermal stress generation inside the tube and prevent the eventual fracture of the vacuum tube. It is expected that this study can lead to a better understanding of the complex phenomena of fracture alumina tube during operation of HTVTF. © 2009 ASM International.