Specific objective functions and algorithms are presented, which by means of dedicated finite element simulation software, calculate optimized control variables for an industrial Bridgman casting furnace. A gradient method and an evolution strategy have been integrated into an efficient optimization tool in order to minimize an objective function which characterizes the quality of directional solidified (DS) or single crystal (SC) turbine blades.
The goal is to minimize the manufacturing costs for a desired quality. For a dummy turbine blade geometry, the macrograin structures produced by the optimized withdrawal velocity profile and an equivalent constant velocity, which had the same total process time, are compared. This comparison shows that the developed optimization techniques are applicable to the casting of DS/SC turbine blades.
Easy opening of heat sealable tray and topfilm food packaging concepts is often realized by using a peelable seal layer. Peel strength needs to be strong enough to prevent the package from opening during and after storage, transportation and handling at different environmental temperatures. It also needs to be weak enough to be convenient for an ageing population. When designing packaging concepts, a balance needs to be found assuring food quality, safety and convenience. This study presents a method to evaluate and optimize peel performance of a packaging concept with polyethylene seal layer undergoing cool processing at −18 C and 4 C. A design of experiment approach is used as a basis. With a limited amount of tests, models are fitted and experimentally validated to obtain an optimal peel strength of 0.5 N mm −1 at an environmental temperature of 23 C. When measured during thermal treatment at −18 C and 4 C, the peel strength increased but no effect was seen once the seals are tested at 23 C after treatment. Bending of the bottomweb during the peel test slightly decreased peel strength while bending stiffness increased at low temperatures, suggesting a minor impact of bending of the bottomweb related to environmental temperature on the observed peel performance. Increased peel strengths during cool processing were clearly related to a change in seal failure mechanism. Besides cohesive peeling, partial delamination occurred in these stronger seals.
With the growing emphasis on minimization of global plastic waste, flexible fibrebased packaging has gained significant interest over the past few years. Heat-sealing technology is commonly applied for vertical form-fill-seal machine to provide tight closure of packages for maintaining food quality and shelf life. Several different seal bar geometries and adequate heat-seal parameters are required to improve the seal tightness of the packages. This study aims to compare the heat sealability of thermoplastic film (OPP/PE) and paper-based materials in vertical form-fill-seal machine using various seal bar profiles. The investigation includes seal strength measurement, understanding the causes of leak formation, seal tightness and inspection of the seal using scanning electron microscopy. Results reveal that OPP/PE material has exceptional seal strength and leakproof ability compared with paper-based materials. However, it has limited operating window because the material shrinks and coarsens at approximately 140 C. Sealing temperature and dwell time are found to be the major factors affecting the seal strength of paper-based material. Results reveal the PEcoated papers exhibit nearly twice the seal strength compared with the dispersioncoated paper. It was difficult to achieve good hot-tack values with dispersion-coated paper. During testing, all the paper-based materials experience delamination and fibre tear, and its severity increases with the increasing material grammage. As plateau temperature is reached, the fibre delamination remains relatively constant. The serrated geometry of seal bar design plays a significant role in providing a satisfactory airtight seal, particularly around the pouch's layer jump. However, flat seal bar designs are not recommended for gas tight applications for paper-based materials.
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