Dynamic simulation of cooling stack and cooling circuit for converter gas cooling

Abstract

A dynamic simulation programme for the recooling circuit of converter gas cooling systems has been developed to assist in the design of new plant and efforts to increase the production capacity of existing plant. A suitable choice of independent variables (enthalpy h and pressure p) allows clear mathematical modelling and enhances the numeric performance of the model. The results have been verified by comparison with the operational data from existing steel plants. This simulation programme offers steelmakers the following advantages when seeking an increase in production: recalibration of existing systems and determination of maximum allowable heat input to the cooling circuit; proposals for modification of existing systems to increase the allowable heat input under constraints for optimal investment cost and installation downtime; design of new, low investment cost cooling systems tailored for existing plant infrastructure and local market conditions.     

Temperature effects in aluminium melts due to cavitation induced by high power ultrasound

Abstract

Extensive research has been carried out previously in ultrasonic (cavitation) melt treatment. Such treatment can reduce grain size and improve material homogeneity. However, it is still not well understood which of the mechanisms is responsible for cavitation aided grain refinement. For better understanding of the processes which take place during solidification under the influence of ultrasonic vibrations, it is very important to consider the change in the cooling conditions during such treatment and thermal effects which are generated in the cavitation zone and in the bulk of liquid. The current paper presents the results of an experimental work on temperature effects in aluminium alloys and their impact on resultant microstructures. The results are discussed based on heat flow, nucleation and fragmentation during solidification.     

Initiation of SCC in nickel base alloys in primary PWR environment: studies at Studsvik since mid 1980s

Abstract

Investigations on initiation of primary water stress corrosion cracking (PWSCC) in alloys 600 and 690 in simulated primary pressurised water reactor (PWR) environments, carried out since 1985, are reviewed. A large number of tests, mostly on reverse U bend specimens, some from steam generator tubes from operating PWRs, have been conducted for periods up to 33 000 h (4 years). Most exposures were at 365 or 330°C in either high purity water with hydrogen addition or simulated primary water (representing beginning of cycle conditions). Parameters investigated include: material (composition, heat treatment (mill annealed or thermally treated), carbide distribution, yield strength, grain size, etc.), environmental (hydrogen content, boron–lithium–pH, zinc) and experimental environment control techniques. Although the PWSCC mechanism has yet to be fully explained, these studies provide an overview of important parameters for crack initiation. The present review aims to survey the evidence for PWSCC initiation in nickel base alloys. It is concluded that, within the normal range for operating PWRs, the influence of dissolved hydrogen on initiation is small. However, a weak maximum in crack growth rate is observed at 15–25 ml H₂/kg H₂O; a corresponding minimum in crack initiation time has not been confirmed but cannot be excluded. It is concluded that hydrogen must be reduced to well below 10 ml H₂/kg H₂O to achieve significant benefits. Increasing the Li content from 2–2·5 to 3·5 ppm is shown to reduce crack initiation time by 30–50%. Lithium in the range 2·2–7·5 ppm has little effect on crack growth rate at ～1200 ppm B. Boron appears to have little influence on crack initiation or growth.     

The effect of cryogenic CO2 cooling on corrosion behaviour of friction stir welded AA2024-T351

Abstract

Cryogenic cooling with CO₂ was applied during friction stir welding of AA2024-T351 in order to reduce the temperature increase during welding, and thus improve the corrosion resistance of the weld. The effect of cryogenic cooling on corrosion susceptibility was investigated with gel visualisation, immersion tests and local electrochemical measurements. The most susceptible area for both uncooled and cooled welds was in the heat-affected zone (HAZ) region, which showed intergranular attack. Cryogenic cooling had no detectable influence on the degree of anodic reactivity in the weld region. However, it did decrease the width of the reactive HAZ.     

Characterisation of oxide films formed on Alloy 600 in simulated PWR primary water

Abstract

Long term exposure of austenitic nickel based alloys in the primary water of pressurised water reactors leads to the development of an oxide film that is generally considered to influence the stress corrosion cracking behaviour of the alloys. The structure, composition and thickness of the film depend on the chemical composition of the alloy and the exposure conditions. Previous laboratory tests have indicated that zinc can lower the susceptibility to initiation of primary water stress corrosion cracking of Alloy 600. In the present work, oxide films have been grown on polished samples of Alloy 600 (15 × 20 × 1 mm) under simulated beginning of cycle primary water at 303°C for periods between 485 and 725 h and their morphology, chemical composition and corrosion behaviour examined. Layers oxidised under stable chemical conditions were less porous and showed higher corrosion resistance. Samples oxidised for longer times showed higher transpassive potentials. Initial results from electrochemical data showed an influence of zinc on the corrosion susceptibility of Alloy 600 that requires further evaluation.     

Raising productivity of aluminium extrusion with nitrogen

Abstract

Nitrogen has been used for cooling and/or inerting aluminium extrusion dies for more than 35 years. Although it has not been widely investigated, the process is reported to improve quality and extrusion speed. Several techniques exist to apply the process in practice. Some of these techniques inert only the die exit. Others additionally use liquid nitrogen to cool the die and the exiting product simultaneously, and it is results from these techniques that are reported in the present paper. Although the gains to be made are very dependent on the profile being extruded and the design of the die set, the use of these techniques significantly improves all the measured parameters. In some cases increases in extrusion speed of over 100% are reported and in one case die life increased by 200%. Several methods of introducing the liquid nitrogen are described. Results are presented for each and the advantages of each technique are discussed. It is shown that liquid nitrogen injection via the bolster is particularly efficient when long runs can be extruded and when the peripheral conditions such as the section shapes, dimensional stability, die design and the plant as a whole, permit the extrusion speed to be increased substantially.     

Evaluation of melt quality of lead free copper alloy castings using cooling curve

Abstract

The melt quality of bronze castings such as JIS CAC406 has successfully checked by observing a fractured surface of specially designed test sample on the melting spot. Lead free copper alloy castings, however, are not successfully applied by this method because the fractured surface does not show a characteristic feature or colour. In this study, the cooling curve method cast into shell cup mould was applied to evaluate and establish melt quality. Melts, under various kind of atmosphere such as over oxidised, hydrogen absorbed, flux covered, adequately deoxidised and so on, were evaluated to check the cooling curve in a cup. Owing to the melting atmosphere, liquidus temperature and solidification behaviour showed a distinct difference. Another application of cooling curve method was carried out to deoxidising process in industrially clean melt. Phosphorus content necessary for and also during deoxidising process was well determined.     

Experimental investigation and numerical simulation of cooling process in water assisted injection moulded parts

Abstract

This report investigated, both experimentally and numerically, the cooling process in water assisted injection moulded parts. Experiments were carried out on a laboratory developed water assisted injection moulding system, which included an injection moulding machine, a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The resin used was semi-crystalline polypropylene. The in-mould temperature of the polymeric materials during the cooling process was measured. A transient heat transfer finite element model was adopted to simulate and predict the temperature variation within water assisted injection moulded products. Simulated results matched well with the experimental data. Experimental investigation and numerical simulations of a water assisted injection moulding cooling process can provide an improved understanding of the influence of water related parameters on the cooling process of water assisted injection moulded parts.     

Fracture strength of tensile loaded graphite–epoxy laminates containing cracks and circular holes

Abstract

A modified point stress criterion has been used to evaluate the fracture strength of tensile loaded graphite–epoxy laminates containing cracks and circular holes. The linear relationship between the asymptotic value of the centre cracked tension plate stress intensity factor and the fracture strength of the infinite plate was used for the evaluation of the characteristic length to predict the fracture strength of laminates having cracks and circular holes. The analytical based results were in good agreement with existing test results.     

Study of grain size and microhardness of submerged arc welded joint of AISI 1060 steel

Abstract

Change in microstructure, grain growth, hardness and residual stress in a weldment are very much dependent on the temperature distribution, peak temperature and cooling rate. In the present work, three-dimensional transient finite element analysis has been used to predict the cooling rate and peak temperature at different points of the submerged arc welded joint. Grain size and microhardness of the submerged arc welded joint of AISI 1060 steel were experimentally measured and explained on the basis of estimated peak temperatures and cooling rates.