Evaluation of Stresses in a Two-Layer Co-Extruded LDPE Melt Blown Film
Despite the fast growth of co-extruded film production, little research work has been devoted to this process. Films of LDPE, ULDPE, LDPE/ULDPE and ULDPE/LDPE were produced at various processing conditions. A continuous experimental set up was used to evaluate the in-plane birefringence during bubble formation. The data collected were used to derive the axial and transverse stresses. A non-isothermal Newtonian model that allows the determination of the kinematics and dynamics of the two-layer film blowing process was then used to calculate the axial and transverse stress. Generally the calculated stresses are in agreement with the experimental values.
Investigation of convective heat transfer in 9-layer film blowing process by using variational principles
Abstract In this work, coextrusion experiments utilizing an industrial 9-layer Brampton Engineering coextrusion film blowing line for LDPE/LDPE/tie/PA6/EVOH/PA6/tie/LDPE/LDPE film production has been performed in order to investigate the effect of cooling intensity on the bubble shape, temperature profile and final mechanical properties of the produced multilayer film. Obtained experimental data followed by theoretical parametric analysis were used to evaluate three different convective heat transfer models by using simple variational principle based film blowing model. For the studied processing conditions and given multilayer structure of the coextruded film, it has been demonstrated experimentally that reduction in the heat transfer coefficient leads to increase in Young’s modulus and yield strength. Secondly, it has been found that the variational principle based model can describe measured multilayer bubble shape reasonably well and finally, the Muslet & Kamal heat transfer model (Muslet and Kamal, 2004) provides more realistic behavior than Campbell heat transfer model (Campbell, 2014) or Constant heat transfer coefficient model, especially if the bubble has very high freezeline height.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.