Combination Of Process Conditions Research Articles

Computational Exploration of Microstructural Evolution in a Medium C-Mn Steel and Applications to Rod Mill

An ‘Expert System’ is proposed in this work to conduct computational exploration of the deformation and restoration behaviour of a medium C-Mn steel under high strain rate conditions, at elevated temperatures and complex strain paths that occur in rod rolling process. The expert system computes appropriate thermomechanical parameters necessary for describing rod rolling process in detail and then utilizes these parameters in mathematical models to determine microstructure evolution during a typical industrial-scale rod rolling process. Microstructure simulation in rod rolling is a challenging problem due to the fact that several softening processes may operate sequentially or concurrently during each deformation step. Different softening processes have very different impact on microstructure development and therefore it is important to investigate the particular combinations of processing conditions under which transition of operating softening processes occurs. In the present work, the transition from dynamic to metadynamic recrystallization is studied in detail based on the criteria of critical strain, austenite grain size and Zener-Hollomon parameter when the interpass (interdeformation) time is very short of the order of few milliseconds during the later stages of rod rolling. Computational results are subsequently validated by comparing the program output to in-plant measured microstructure data. The proposed expert system is designed as an off-line simulation tool to examine and assess the various options for thermomechanical process optimization.

Simulation of non‐isothermal melt densification of polyethylene in rotational molding

AbstractRotational molding involves powder mixing, heating and melting of powder particles to form a homogeneous polymer melt, as well as cooling and solidification. The densification of a loose powder compact into a homogeneous melt occurs over a wide range of conditions as the material passes from a solid state into a melt state. The numerical simulation of the non‐isothermal melt densification in the rotational molding process is presented in this work. The simulation combines heat transfer, polymer sintering and bubble dissolution models, and is based on an idealized packing arrangement of powder particles. The predictions are in general agreement with experimental observations presented in the literature for the rotational molding of polyethylenes. The simulation allows for systematic and quantitative studies on the effect of molding conditions and material properties on the molding cycle and molded part density. Results indicate that the densification process is primarily affected by the powder characteristics, which are accounted for in terms of the particle size and the particle packing arrangement. The material rheological properties become increasingly important as the powder characteristics lessen in quality. The simulation demonstrated that while certain combinations of processing conditions help reduce the molding cycle, they have a detrimental effect on the densification process.

ディスク型フリクション仮撚における糸の走行経路 （第１報） ディスク上を走行する糸の経路と張力の解析

Although the false-twisting by means of a friction disk unit is an efficient technique widely applied to manufacture the synthetic fiber yarns conventionally called `textured yarns', the fundamental mechanics operating in the processing, especially the relationship between frictional and extensional forces and paths which a yarn experiences when twisted, is not sufficiently in vestigated to date. This series of reports aims to establish a theory that describes the mechanical behaviors of a yarn in the false-twisting process using a friction disk unit, and to obtain basic information about the yarn path and the frictional forces acting on the yarn . In the theoretical part of this article, the forces balance equations, which determined a yarn path contacting with the toric surface of a single false-twisting-disk unit, were developed on the basis of differential geometry of curved surfaces. In the experimental part, the path shape of a yarn contacting with the toric surface of twisting disk was photographed and simultaneously the yarn tension was measured under several combinations of processing conditions : the yarn entrance direction and feed velocity, the rotational speed of the twisting disk, etc.The data obtained coincided fairly with analytical estimations and the presented scheme was confirmed to be valid for predicting the behaviors of a yarn in the false-twisting processing using a friction disk unit .

Processing of thallium-based superconducting tapes for high current density

Optimum thermomechanical processing conditions have been developed to achieve a high current density in powder-in-tube (PIT) thallium-based (Tl,Pb)-1223 and (Tl,Bi)-1223 tapes. Critical currents in excess of 25 A corresponding to a current density of 20 000 A/cm 2 have been achieved in these tapes at 77 K. Heat treatment and intermediate deformation sequences, heating rates, and starting precursor phase assemblages have been examined to optimize the current density. A combination of processing conditions that result in incremental densification, less microcracking and liquid formation in the early and final stages of thermomechanical treatment is found to result in the highest current densities.

Flue Gas Desulfurization Scheme To Recover Elemental Sulfur

A sodium-based flue gas desulfurization process, employing reductive burning and a Claus recovery system, has the advantage of producing elemental sulfur as a byproduct. This study optimized the process conditions for two steps in the proposed reaction scheme: (1) removing approximately one-sixth of the sulfur in the spent scrubbing liquor by a combination of acidification and evaporation and (2) precipitation of 50% of the remaining Na{sub 2}SO{sub 3}(s) by the addition of NaHCO{sub 3}/Na{sub 2}CO{sub 3} slurry. Several combinations of process conditions can be used to produce favorable results, but the optimum from a technical perspective is to add concentrated H{sub 2}SO{sub 4} to the spent liquor to 1.5% v/v, concentrate the mixture to 70% by weight, and then treat it with a >70% solids slurry of NaHCO{sub 3}/Na{sub 2}CO{sub 3}. The optimum from an economic perspective is dependent on the relative costs of H{sub 2}SO{sub 4} and the steam needed to concentrate the spent liquor.

Basic functionalization of polypropylene and the role of interfacial chemical bonding in its toughening

A reactive polypropylene (PP) containing oxazoline functional groups was prepared by the melt grafting of 2-iso-propenyl-2-oxazoline onto a PP homopolymer and used to introduce varying amounts of interfacial chemical reaction in PP/acrylonitrile- co-butadiene- co-acrylic acid rubber (NBR) blends. A technique has been successfully developed to control the rubber particle sizes of PP/NBR blends such that various PP/NBR blends with the same rubber particle size can be obtained by using different combinations of processing conditions and the amount of interfacial reaction. It has been found that moderate levels of interfacial chemical bonding are required for a transition from a brittle to ductile failure to be observed in PP/NBR blends. Blends without any interfacial chemical bonding showed no improvement in impact energy whereas up to a 13.5-fold improvement in impact energy (notched Charpy test) was observed for reactive blends above the brittle-tough transitions.

Effect of grain size and microstructure on magnetic properties of rapidly solidified Fe82.4Nd13.1B4.5 alloy

The effect of grain size on the magnetic properties of a rapidly solidified low boron Fe-Nd-B alloy, both in directly quenched and in the overquenched and annealed conditions, has been studied. The magnetic properties in the as-quenched crystalline state and changes occurring on annealing of the overquenched ribbons are discussed in relation to the microstructure. High values of the remanent magnetization, above 0.9 T (9 kG), in combination with coercivities of 1100 kA m−1 (13.7 kOe), have been observed for the directly quenched, isotropic single-phase ribbons, for certain combinations of process conditions. The mean-grain size for these ribbons measured on the roll contact side was found in some cases to be <20 nm, representing an essentially nanocrystalline structure. The enhanced remanence is considered to result from intergranular magnetic exchange interactions between fine adjacent grains. The overquenched ribbons were aged at temperatures between 500 and 800 °C for various times and these exhibited grain sizes in the range of 40–55 nm. Their magnetic properties depend on the annealing temperature and are generally lower than for the directly quenched ribbons though Br is still slightly enhanced at 0.85 T (8.5 kG). Apart from the effect of larger grains, the lower magnetic properties of the overquenched and annealed ribbons result from a slightly different phase constitution. Indirect evidence of this is provided by initial magnetization and coercivity measurements, using a VSM, which indicate that, on devitrification of the overquenched amorphous phase, a small proportion of soft magnetic phase was always present but which was not observed in the optimal directly quenched samples. Details of the phase transformations are discussed.

Prediction of Optimum Process Conditions for Rotomolded Products

Abstract This paper describes analytical and experimental work which has been carried out to identify optimum process conditions for rotomolded products. The mechanical performance of the moldings has been assessed using tensile impact tests. It has been found that changes in the oven temperature or oven time cause a very significant shift in the ductile-brittle transition for the SCLAIR 8504 grade of polyethylene used in the work. Optimum combinations of process variables can be clearly defined and used to establish a processing window for the material. The ROTOSIM computer simulation for the rotomolding process has been used to establish the best (most economic) combinations of process conditions to obtain the optimum mechanical properties. A single equation is presented to relate pool depletion time to some of the process variables.

P-type PtSi Schottky-diode barrier height determined from I– V measurement

We have shown that the method of analyzing the fundamental barrier height (flat-band barrier height at zero field) for n-type platinum-silicide Schottky barrier diodes can be extended to p-type Schottky barrier diodes. A mean flat-band barrier height of 0.272 ± 0.005 eV is obtained for p-type Schottky barrier diodes by relating the measured barrier heights and their corresponding ideality factors from I- V measurements. Nine different combinations of processing conditions were used in the fabrication of these devices so that the effects of different processes on the device characteristics could be evaluated.