Search

This paper presents the main discussion during, and findings from, a symposium of the same title held in St Andrews, Scotland, in October 2014. Overall, there is good understanding of flexibles but a number of opportunities for improvement are identified. This paper presents a schematic of the road map developed by the delegates for improvement of methods, practices and tools to enhance the validation of flexible pipes and risers. [ABSTRACT FROM AUTHOR]

Here we report a simple design philosophy, based on the principles of bipolar electrochemistry, for the operation of microelectrochemical integrated circuits. The inputs for these systems are simple voltage sources, but because they do not require much power they could be activated by chemical or biological reactions. Device output is an optical signal arising from electrogenerated chemiluminescence. Individual microelectrochemical logic gates are described first, and then multiple logic circuits are integrated into a single microfluidic channel to yield an integrated circuit that can perform parallel logic functions. AND, OR, NOR, and NAND gates are described. Eventually, systems such as those described here could provide on-chip data processing functions for lab-on-a-chip devices. [ABSTRACT FROM AUTHOR]

Escherichia coli ribonucleotide reductase is an α2α2 complex that catalyzes the conversion of nucleotides to deoxynucleotides and requires a diferric-tyrosyl radical (Y) cofactor to initiate catalysis. The initiation process requires long-range proton-coupled electron transfer (PCET) over 35 Å between the two subunits by a specific pathway (Y122•→W48→Y356 within β to Y731→Y730→C439 within α). The rate-limiting step in nucleotide reduction is the conformational gating of the PCET process, which masks the chemistry of radical propagation. 3-Nitrotyrosine (NO2Y) has recently been incorporated site-specifically in place of Y122 in β2. The protein as isolated contained a diferric cluster but no nitrotyrosyl radical (NO2Y•) and was inactive. In the present paper we show that incubation of apo-Y122NO2Y-β2 with Fe2+ and O2 generates a diferric-NO2Y• that has a half-life of 40 s at 25 °C. Sequential mixing experiments, in which the cofactor is assembled to 1.2 NO2Y•/β2 and then mixed with α2, CDP, and ATP, have been analyzed by stopped-flow absorption spectroscopy, rapid freeze quench EPR spectroscopy, and rapid chemical quench methods. These studies have, for the first time, unmasked the conformational gating. They reveal that the NO2Y• is reduced to the nitrotyrosinate with biphasic kinetics (283 and 67 s-1), that dCDP is produced at 107 s-1, and that a new Y• is produced at 97 s-1. Studies with pathway mutants suggest that the new Y• is predominantly located at 356 in β2. In consideration of these data and the crystal structure of Y122NO2Y-β2, a mechanism for PCET uncoupling in NO2Y•-RNR is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The mould filling process and solidification of TiAl exhaust valves by centrifugal investment casting have been simulated. Two types of runner and gating systems are designed and analysed. In the preliminary design, a “tree-type” set up system is used and a significant amount of porosity is found in many valves of the simulation result. The fluid field simulations indicate that moulds are not filled well in the preliminary design, leading to the last hot spots deviating from the center line of castings. Casting defects deviated from the center line of the part, and the degree of deviation is affected by the mould filling process and temperature fields. Simulation results reveal that castings do not experience sequential solidification, so the design is not proper for the exhaust valve. Comparing the experimental and simulation results, the range of Niyama criterion in the centrifugal TiAl casting is defined, which is 0.14–0.20. Several key factors such as pouring temperature, mould temperature and rotation speed are studied in detail. An optimized design is developed in which valves are rearranged to reduce the neighboring heat radiation effect, and the gate size is enlarged to keep the feeding path open. Sound exhaust valves have been produced successfully using the optimized technique. [Copyright &y& Elsevier]

The present study describes the development of a horizontal and a vertical mould designed to produce thin ductile iron plates of 1·5–4 mm thickness. Both moulds used a non-pressurised configuration. The horizontal mould design was based on empirical rules, while the vertical mould was based on numerical simulations of fluid flow and thermal field, carried out using the software NovaFlow&Solid. The aim of both designs was to produce sound ductile iron plates that were large enough to make tensile test samples. The results show that the adoption of empirical rules and a non-pressurised configuration were not enough to guarantee proper filling. An optimised design was obtained through the use of mathematical modelling. [ABSTRACT FROM AUTHOR]

While the general mechanisms of hot tearing are understood, i.e. the inability of liquid to feed imposed strain on the mushy material, work continues on improving the understanding of the mechanisms at play. A hot tear test rig that measures the temperature and load imposed on the mushy zone during solidification has been successfully used to study hot tearing. The mould has now been modified to incorporate a window above the hot spot region to allow observation of hot tear formation and growth. Combining information from visual observation with load and temperature data has led to a better understanding of the mechanism of hot tearing. Tests were carried out on an Al–0·5 wt-%Cu alloy. It was found that load development began at about 90% solid and a hot tear formed a short time later, at between 93% and 96% solid. Hot tearing started at a very low load. [ABSTRACT FROM AUTHOR]

The present study concerns the development of a novel casting process for a heavy cast steel back-up roll. Total weight of the roll was 50 000 kg and the mould was about 7 m tall. A 'naturally pressurised' gating system was employed to avoid air and inclusion entrainment and to ensure smooth filling. In this way, high quality liquid steel was introduced into the mould. The gating system included an offset stepped pouring basin with stopper, hyperbolic tapered down-sprue with 113 mm entrance diameter and 63 mm exit diameter, radiused transition between vertical down-sprue and horizontal runner, and tangential ingate. The thickness of the sand lining of the cast iron dies at the barrel and journals was optimised by computer simulation to guarantee that the casting solidified progressively towards the feeder. In addition, all shrinkage was arranged to be completely located in the feeder by use of insulating boards and exothermic powder. The potential for sound castings to be produced with zero defects was demonstrated, although other castings appeared to require a sliding seal to allow the mould to contract longitudinally to avoid cracks. [ABSTRACT FROM AUTHOR]

There are many things that need to be considered when selecting the right feeder for a particular compounding operation. Dipl. Ing. R. Welsch of Brabender Technologie KG explains some of the basics and outlines some new developments. [Copyright &y& Elsevier]

The article presents a research that identifies the sources of carbon monoxide (CO) gas defects and determines a way to reduce or eliminate those sources. It focuses on five variables including pouring temperature, carbon equivalent, inoculant type, inoculant addition method and gating. It eliminates the CO gas defects that form in iron castings during solidification. It determines the conditions in castings associated with CO gas defects. It identifies the cause of those conditions and eliminates or controls them.