4 resultados para Trench-Arc-Backarc system
em Aston University Research Archive
Resumo:
After a brief review of the various forms of thermal spraying equipment and processes, descriptions of the basic principles involved and the general functions for which thermally sprayed coatings are used are given. The background of the collaborating company, Metallisation, is described and their position in the overall market discussed, providing a backdrop against which the appropriateness of various project options might be judged. Current arc-spraying equipment is then examined, firstly in terms of the workings of their constituent parts and subsequently by examining the effects of changes in design and in operating parameters both upon equipment operation and the coatings produced. Published literature relating to these matters is reviewed. Literature relating to the production, comminution and propulsion of the particles which form the spray is discussed as are the mechanisms involved at impact with the substrate. Literature on the use of rockets for thermal spraying and induction heating as a process for feedstock melting are also reviewed. Three distinct options for further study are derived and preliminary tests and costings made to allow one option alone, the use of rocket acceleration, to go forward to the experimental phase. A suitable rocket burner was developed, tested and incorporated into an arc-spray system so that the sprayability of the whole could be assessed. Coatings were made using various parameters and these are compared with coatings produced by a standard system. Coatings were examined for macro and micro hardness, cohesive strength, porosity and by microstructural examination. The results indicate a high degree of similarity between the coatings produced by the standard system and the high velocity system. This was surprising in view of the very different atomising media and velocities. Possible causes for this similarity and the general behaviour of this new system and the standard system are discussed before the study reaches its conclusions in not proving the hypothesis that an increase in particle velocity would improve the mechanical properties of arc-sprayed steel coatings. KEY WORDS: Sprayed metal coatings, Electric arc spraying, High velocity flame spraying, Sprayed coating properties
Resumo:
Cascaded multilevel inverters-based Static Var Generators (SVGs) are FACTS equipment introduced for active and reactive power flow control. They eliminate the need for zigzag transformers and give a fast response. However, with regard to their application for flicker reduction in using Electric Arc Furnace (EAF), the existing multilevel inverter-based SVGs suffer from the following disadvantages. (1) To control the reactive power, an off-line calculation of Modulation Index (MI) is required to adjust the SVG output voltage. This slows down the transient response to the changes of reactive power; and (2) Random active power exchange may cause unbalance to the voltage of the d.c. link (HBI) capacitor when the reactive power control is done by adjusting the power angle d alone. To resolve these problems, a mathematical model of 11-level cascaded SVG, was developed. A new control strategy involving both MI (modulation index) and power angle (d) is proposed. A selected harmonics elimination method (SHEM) is taken for switching pattern calculations. To shorten the response time and simplify the controls system, feed forward neural networks are used for on-line computation of the switching patterns instead of using look-up tables. The proposed controller updates the MI and switching patterns once each line-cycle according to the sampled reactive power Qs. Meanwhile, the remainder reactive power (compensated by the MI) and the reactive power variations during the line-cycle will be continuously compensated by adjusting the power angles, d. The scheme senses both variables MI and d, and takes action through the inverter switching angle, qi. As a result, the proposed SVG is expected to give a faster and more accurate response than present designs allow. In support of the proposal there is a mathematical model for reactive powered distribution and a sensitivity matrix for voltage regulation assessment, MATLAB simulation results are provided to validate the proposed schemes. The performance with non-linear time varying loads is analysed and refers to a general review of flicker, of methods for measuring flickers due to arc furnace and means for mitigation.
Resumo:
Long period gratings have been inscribed in standard single mode fibre using a fs laser system, a fusion arc and a UV laser and a comparative study carried out of their thermal behaviour. The fs laser induced gratings can survive temperatures in excess of 800°C, however the inscription process can induce considerable birefringence within the device. Annealing studies have been carried out showing that below 600°C, all three grating types show a blue shift in their room temperature resonance wavelengths following cyclic heating, while above 600°C, the UV and arc induced LPGs exhibit a red shift, with the fs LPG showing an even stronger blue shift. High temperature annealing is also shown to considerably reduce the birefringence induced by the fs inscription process.
Resumo:
Long period gratings have been inscribed in standard single mode fibre using a fs laser system, a fusion arc and a UV laser and a comparative study carried out of their thermal behaviour. The fs laser induced gratings can survive temperatures in excess of 800°C, however the inscription process can induce considerable birefringence within the device. Annealing studies have been carried out showing that below 600°C, all three grating types show a blue shift in their room temperature resonance wavelengths following cyclic heating, while above 600°C, the UV and arc induced LPGs exhibit a red shift, with the fs LPG showing an even stronger blue shift. High temperature annealing is also shown to considerably reduce the birefringence induced by the fs inscription process.
