Browsing by Author "Prabhakar, Arun"

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    Fundamental investigation understanding casting of lead sheet
    (Cranfield University, 2020-04) Prabhakar, Arun; Jolly, Mark R.; Salonitis, Konstantinos
    Lead sheet is widely used in the construction industry for roofing and flashing applications. The roots of this process can be tracked back to the Roman times when sandcast lead sheets were used for a wide variety of applications. Sandcast lead sheets are characterised by their superior aesthetic performance and mottled appearance. These days such sheets are used for premium roofing and flashing applications in the heritage construction industry. Lead sheet is also manufactured using a type of continuous casting process also called as the ‘Direct Method (DM)’. This thesis focuses on a fundamental investigation of both these processes used for manufacture of cast lead. Just like any casting process, sand casting of lead sheet suffers from the presence of surface defects. In this study, a surface defect type, hereby referred to as ‘grooves’, has been investigated. The focus has been laid on the identification of the main factors affecting defect formation in this process. Based on a set of screening experiments performed using Scanning Electron Microscopy (SEM) as well as the existing literature, a number of factors affecting the formation of such defects was identified and their corresponding significance was estimated. Two-dimensional Computational Fluid Dynamics (CFD) simulations have been performed to simulate the melt flow and solidification stages of the lead sandcasting process. The effects of process parameters such as pouring temperature, screed velocity and clearance between the screed and the sandbed on the final quality of the lead sheet are investigated. Sheet quality is quantified by measuring the variance and the average of the final sheet thickness over the sandbed length. The CFD model has been validated against experimental results by comparing the evolution of the lead-sandbed interface temperature against data collected by thermocouples during the evolution of the process. The direct method of casting lead is a much more energy efficient compared to the conventional rolling process which requires a casting process before rolling to achieve the required thickness. This work also looks into the energy consumption in different stages of the DM process and suggests pointers for improvement. An energy audit of the process is conducted, and the consumption is analysed at different stages and compared with rolled lead. A two-dimensional numerical model of the DM process was developed and different process parameters affecting the thickness of the final cast sheet is studied. Effects of parameters like volume flow rate, heat transfer coefficient, speed of rotation of the casting drum and its immersion are investigated. The studies were conducted in collaboration with ML Operations, a cast lead sheet manufacturer based in Derbyshire and the findings of the study were implemented successfully.
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    Minimising defect formation in sand casting of sheet lead: a DoE approach
    (MDPI, 2020-02-13) Prabhakar, Arun; Papanikolaou, Michail; Salonitis, Konstantinos; Jolly, Mark R.
    Sand casting of lead sheet is a traditional manufacturing process used up to the present due to the special features of sand cast sheet such as their attractive sheen. Similarly to any casting process, sand casting of lead sheet suffers from the presence of surface defects. In this study, a surface defect type, hereby referred to as ‘grooves’, has been investigated. The focus has been laid on the identification of the main factors affecting defect formation in this process. Based on a set of screening experiments performed using Scanning Electron Microscopy (SEM) as well as the existing literature, a number of factors affecting the formation of such defects was identified and their corresponding significance was estimated using the Analysis of Variance (ANOVA) technique. The obtained results suggest that the most significant factor affecting defect formation in sand casting of lead sheet is the composition of the moulding mixture. Defect formation was also proven to be dependent on the sand grain fineness, the quality of the melt and some of the interactions between the aforementioned process parameters. Finally, an optimal set of process parameters leading to the minimisation of surface defects was identified.
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    Review of Non-destructive Testing (NDT) Techniques and their applicability to thick walled composites
    (Elsevier, 2015-10-27) Jolly, Mark R.; Prabhakar, Arun; Sturzu, Bogdan; Hollstein, K.; Singh, R.; Thomas, S.; Foote, Peter; Shaw, Andy
    A tier 1 automotive supplier has developed a novel and unique kinetic energy recovery storage system for both retro-fitting and OEM application for public transport systems where periodic stop start behaviour is paramount. A major component of the system is a composite flywheel spinning at up to 36,000 rpm (600 Hz). Material soundness is an essential requirement of the flywheel to ensure failure does not occur. The component is particularly thick for a composite being up to 30 mm cross section in some places. The geometry, scale and material make-up pose some challenges for conventional NDT systems. Damage can arise in composite materials during material processing, fabrication of the component or in-service activities among which delamination, cracks and porosity are the most common defects. A number of non-destructive testing (NDT) techniques are effective in testing components for defects without damaging the component. NDT techniques like Ultrasonic Testing, X-Ray, Radiography, Thermography, Eddy current and Acoustic Emission are current techniques for various testing applications. Each of these techniques uses different principles to look into the material for defects. However, the geometry, physical and material properties of the component being tested are important factors in the applicability of a technique. This paper reviews these NDT techniques and compares them in terms of characteristics and applicability to composite parts.
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    Sand casting of sheet lead: numerical simulation of metal flow and solidification
    (Springer, 2019-11-20) Prabhakar, Arun; Papanikolaou, Michail; Salonitis, Konstantinos; Jolly, Mark R.
    Sandcast lead sheets are characterised by their superior aesthetic performance and mottled surface. Lead sheet casting is widely used in the construction industry for roofing and flashing applications, while the roots of this process can be tracked back to the Roman times. In this study, two-dimensional Computational Fluid Dynamics (CFD) simulations have been performed to simulate the melt flow and solidification stages of the lead sandcasting process. The effects of process parameters such as pouring temperature, screed velocity and clearance between the screed and the sandbed on the final quality of the lead sheet are investigated. Lead sheet quality has been quantified by measuring the variance and the average value of the final sheet thickness over the sandbed length. The developed CFD model has been validated against experimental results by comparing the time evolution of the lead-sandbed interface temperature against data collected by thermocouples during the real-time process. The numerical results show that all of the aforementioned parameters affect the final quality of the cast product and suggest that superior quality lead sheets can be produced for a range of relatively low values of the pouring temperature and slow strickle motion.