28,278 research outputs found
Vacuum based roll-to-roll oled coating for pilot level
No full textS.532-543Flexible OLED lighting enable new functionalities and market entry for automotive lighting applications. OLED does not replace LED, but complement each other perfectly Unique characteristics of the OLED must be used consequently! The roll-to-roll OLED fabrication is feasible on metal-, plastic- And ultra-thin glass web for different kind of target applications. Comparable power efficacy between R2R and lab-scale OLED is possible. Further reproducibility will be pushed within the EU PI-Scale project for S2S and R2R. Starting pilot production in Roll-to-Roll fabrication on barrier films and ultra-thin glass web coming soon feasible. Remove residual moisture in coils has an impact on reproducibility. Changes in the barrier film layer structure influences the winding behavior
Stability of rigid and deformable roll coating flows
No full textThis thesis is concerned with developing suitable models for the investigation of instabilities in rigid and deformable roll coating flows. Consideration is restricted to Newtonian, incompressible fluids in the absence of inertia. In each coating flow analysed the steady two dimensional base state solutions of the system axe explored before the stability of the system is considered.
The particular rigid roll coating flow that is studied in this thesis is the flow formed between an intermediate pair of contra-rotating rolls within a multiple roll coater. The
base state is modelled using lubrication theory and the flow domain is terminated with simple boundary conditions. It is found that the form of the meniscus location
solutions differ from those found in similax flows by previous workers and this motivates a detailed re-examination of the boundaxy conditions. A matched asymptotic analysis applicable for small capillaxy numbers Ca and small inter-roll gaps gives the leading order correction to the boundary conditions and it is found that the inclusion of the correction terms alter the results significantly. It is found that a critical roll speed ratio,
Sc exists beyond which no steady two dimensional solutions exist. A simple stability hypothesis predicts the upstream meniscus to be neutrally stable at Sc and this point is
associated with bead break. Under certain operating conditions the stability hypothesis predicts multiple steady states.
The lineax stability of this multiple roll coating flow is investigated. Special attention is given to the relationship between the wavelength of the disturbance and
the form of the boundary conditions. The main predictions of the stability hypothesis axe confirmed and an additional ribbing instability on the downstream meniscus is predicted.
The base flow of a deformable roll coater is investigated using lubrication theory for the fluid and a linear elastic plain strain model for the compliant layer. The boundary
conditions developed for the multiple roll problem are extended to higher values of Ca. A finite element method is developed to numerically solve the governing equations.
The effects of Youngs modulus E and layer thickness L on the steady state operation of the coater are investigated. Previous workers have used spring models to describe
the compliant layer with the implicit assumption that E and L-1 have the same affect. Here it is shown that E and L-1 have a different effect upon the meniscus location in the negative gap regime and hence the underlying assumption of all spring models is shown to be incorrect. The plain strain model is extended to include viscoelastic terms
and it is shown that these terms can account for the discrepancy between experimental results and previous steady state elastic theories.
The lineax stability of the deformable roll coater is investigated with the plain strain model being extended to account for lateral disturbances. The effect of E and L-1 on
the stability of the system is investigated and it is found that in keeping with the steady state results, they have a different effect on the stability of the system in the
negative gap regime. It is demonstrated that perturbations to the compliant layer play a negligible role in the stability analysis and it is shown how the viscoelastic extension to the base state can be incorporated
Rolling mill roll design
No full textIn this thesis, some previously published experimental and theoretical studies of hot rolling are reviewed. A thorough understanding of the available roll design methods, and conditions of their application is extremely important in order to achieve the objective of producing high quality rolled products. Successful hot roll design is dominated by the calculations of some important parameters, which describe two-dimensional (2D) or three-dimensional (3D) deformation in the workpiece. These parameters, such as roll separation force, torque, elongation, spread and draft, are discussed in detail. The method or formula for the calculation of each parameter is different for each set of different application conditions. A thorough study of these methods in different application cases will lead to the optimised design of hot rolled products. Finite Element (EE) is an important method which has been employed in the study of hot rolling. Design theory, commercial software and application cases have been described. 2-D and 3-D Finite Element Methods (FEM) for hot rolling simulation have also been discussed within the work. The current techniques and the problems of using the Finite Element system in hot roll design have been presented briefly. Possible solutions to these problems have also been discussed and there need to be considered in order to successfully apply Finite Element theory in hot roll design. An important alternative approach for hot roll design has been introduced in this thesis. A Matrix-based roll design system has been developed. It includes a Matrix-based system for flat and section roll designs. The realisation of the Matrix-based system is discussed. All the methods and formulae considered previously can be integrated in the proposed roll design system. The approach emphasizes the need for teamwork. The design procedure allows both less experienced designers and senior designers to benefit from participation. It is suggested that high quality rolled products could be achieved from optimised designs produced using this systematised the approach compared to the ad-hoc use of existing techniques, formulae and methods
Ship roll stabilization control with low speed loss
No full textLarge roll motion induced by waves can severely affect the ability of vessels and the speed will loss due to added resistance which caused by ship motions, especially in moderate to high sea states. With increasing needs of fuel efficiency and greenhouse gas (GHG) emissions, the effect of added resistance on surface ship performance must be considered when a ship fin stabilizer control system is designed. In this paper, we investigate basic principles of added resistance in oblique waves and ship calm water resistance. An alternative approach for reducing speed loss while keeping the satify roll reduction percentage, is proposed by controlling both roll and roll rate at the same time. A double nonlinear generalized minimum variance (NGMV) controller is used for achieving this objective. Finally, the effectiveness of the method is demonstrated
Work Roll Cooling System Design Optimisation in Presence of Uncertainty
No full textOrganised by: Cranfield UniversityThe paper presents a framework to optimise the design of work roll based on the cooling performance. The
framework develops Meta models from a set of Finite Element Analysis (FEA) of the roll cooling. A design of
experiment technique is used to identify the FEA runs. The research also identifies sources of uncertainties
in the design process. A robust evolutionary multi-objective algorithm is applied to the design optimisation I
order to identify a set of good solutions in the presence of uncertainties both in the decision and objective
spaces.Mori Seiki – The Machine Tool Compan
Flow phenomena in fixed-gap and gravure roll coating systems
No full textThis thesis describes investigations into a number of coating processes using experimental, analytical and computational techniques.
The first problem, considered experimentally, is that of reverse roll coating with a liquid reservoir positioned directly above horizontally aligned rollers. Measurements
of the film thickness as a function of the height of fluid in the reservoir and speed ratio are presented. When the wetting line is located downstream of the nip, either
a decrease in the height of the associated hydrostatic head or an increase in the speed ratio causes a reduction in the thickness of the outgoing film. However, when the wetting line is located upstream of the nip the opposite is found to be true.
The bead-break instability in forward meniscus coating is considered both experimentally and analytically. Agreement between predictions from a simple mathematical model of the stable bead and experimentally determined meniscus positions
is seen to be excellent. A perturbation hypothesis is used to predict the onset of the bead-break instability, at which the upstream meniscus accelerates rapidly towards
the downstream one, so the two collide and the bead collapses. The results from the model compare well with experiments. An outline of a method for using the
bead-break instability as a design criterion is also presented.
Typically in a slot, blade or knife coater the downstream meniscus is assumed to pin at a corner of the coating device. In chapter 5, a series of experiments and a
corresponding computational study, are presented which illustrate that the meniscus can advance up the face of such coating devices (in this case a roll-flat plate system). Reducing the corner angle is seen to reduce the size of the climb region and the associated recirculation at this point at the downstream meniscus. It is also shown
that the meniscus can detach from the corner and retreat into the gap, which can in turn give rise to the ribbing instability.
An offset gravure coating arrangement is considered in chapter 6. The coating arrangement is split into two areas of study - the offset gravure nip and the kiss coating bead. An experimental investigation of the offset nip with the two rolls vertically aligned and running at the same speed in forward mode reveals two ways in which the metered film thickness can be influenced. Either increasing the nip force by pressing the two rolls together or decreasing the roll speeds causes a reduction in the metered film thickness. At higher speeds the metered film thickness is observed to asymptote to a limiting value, the value of which depends on the gravure pattern.
The reverse mode kiss coating bead operating at speed ratios greater than one is also investigated. Experiments reveal that under these conditions, all the fluid is
transferred from the roll surface to the web and the two make contact due to the generation of a sub-ambient pressure field within the bead. Two models based on lubrication theory are derived, one assuming an infinitely tensioned web and a second that incorporates the effect of web flexibility. The latter is found to give much better agreement with the experimental data. Finally a perturbation hypothesis is applied to these to models in order to predict the onset of the ribbing instability,
both of which are found to give reasonable agreement with the experimental data.
Finally, the results of a systematic experimental investigation of reverse mode direct gravure coating is reported, where the web runs directly over a gravure roll surface. This wide ranging parametric study illustrates the effect of the operating parameters on the final film thickness. Key findings are that speed ratio, fluid properties and cell shape and size can significantly influence the final film thickness. For a fixed roll
speed it is observed that as the web speed is increased the gravure bead becomes unstable. This results in streaking on the web, and gives an upper limit to the speed ratio
Work roll system optimisation using thermal analysis and genetic algroithm
No full textIn today‟s highly competitive business environment it is vital to have smart and robust decision making framework for companies to be competitive or even to stay in the business. Profit margin increases is no longer a result of producing and bring more products to the market. Instead it is also a result of reducing cost, in particular tooling cost. In order to succeed with this, industry need to look in to innovative intelligent systems to enhance their process development so that maximum utilisation of tools can be achieved. Tooling is part of a process hence having an optimal process design is one ideal strategy for best utilising of tools. In design optimisation however presence of uncertainty in design variables and in the mathematical model (used for representing the real life process) is inevitable. For reliable design solution to be found this process complexity need to be addressed. The aim of this research is to understand work roll system optimisation and thermal issues within rolling system design, understand uncertainties and sources of uncertainties and develop Genetic Algorithm (GA) based solution frameworks so that a conscious decision, that prolong tool life can be made.
The thesis has proposed a framework for generating approximate models from numeric finite element (FE) data. Using the proposed framework a number of quantitative work roll system thermal analysis and optimisation models were generated and used in subsequent optimisation process. In the absence of a suitable multi-pass model that exhibits the features of a multi-stage process; confident decision making will not be possible. Hence the research has developed a quantitative multi-pass model to simulate the work roll system thermal analysis and optimisation problem that represents the relationships as well as inherited features between passes.
The research has developed a Genetic Algorithm based optimisation framework that deals with the constraint quantitative problem as well as the uncertainty, in the design space and fitness function. The research also proposed a post GA result analysis methodology for identifying the final best optimal design solution for the research many objective high dimensional work roll system problems in presence of uncertainty
The performance of the proposed frameworks was studied and analysed through case studies. The research also identifies future research directions in the subject area
Influence of cavity thickness and emitter orientation on the efficiency roll-off of phosphorescent organic light-emitting diodes
No full textThis article describes the first systematic investigation of how the efficiency roll-off in organic light-emitting diodes (OLEDs) is influenced by the position and orientation of the emitter molecules within the OLED cavity. The efficiency roll-off is investigated for two OLED stacks containing either the phosphorescent emitter Ir(MDQ)2(acac) or Ir(ppy)3 by varying the distance between emitter and metal cathode; a strong influence of emitter position and orientation on roll-off is observed. The measurements are modeled by triplet-triplet-annihilation (TTA) theory yielding the critical current density and the TTA rate constant. It is found that Ir(MDQ)2(acac) shows the lowest roll-off when the emitter is located in the first optical maximum of the electromagnetic field, whereas the roll-off of the Ir(ppy)3 stack is lowest when the emitter is positioned closer to the metal cathode. Measurement and modeling of time-resolved electroluminescence show that the different roll-off behavior is due to the different orientation and the corresponding change of the decay rate of the emissive dipoles of Ir(MDQ)2(acac) and Ir(ppy)3. Finally, design principles are developed for optimal high-brightness performance by modeling the roll-off as a function of emitter-cathode distance, emissive dipole orientation, and radiative efficiency.Peer reviewe
An experimental investigation of roll coating phenomena
No full textThis thesis gives an account of an extensive experimental investigation of the operation of a twin roll coater. Two distinct modes of operation are identified: Classical (fullyflooded inlet) and Meniscus (ultra-starved inlet). The former has been the subject of investigation for a number of years; the latter is less well known and would appear to have escaped the attention of the Coating Community at large prior to the research work reported here being carried out.
A detailed description of how the key features of an industrial roll coater can be reproduced using a piece of simple but well designed experimental apparatus, which
encapsulates all the necessary elements for an in-depth study of the flow, is presented. Various methods are used to visualise the flow. These include dye injection and novel
computerised particle tracking techniques, coupled with state-of-the-art image processing and High Speed Video photography.
Experiments reveal that the flow associated with the Classical mode of operation is essentially one-dimensional throughout the nip; Meniscus coating flow, on the other
hand, is uniquely two-dimensional, containing large vortical structures. Also the pressure distributions are found to be quite distinct. A fully-flooded nip results in a pressure profile which exhibits a characteristic maximum and minimum, while an ultra-starved nip produces one which is linear and entirely sub-ambient.
The transformation of the flow from one mode of operation to the other is then considered, a key feature of which is the behaviour of the upstream free surface which movesin to a minimum point and then out again as the flux is reduced, giving a non-singular result, that is, there are two non-dimensional values of the flux for each free surface position.
Finally, the subject of instability in roll coating is addressed, for both the Classical and Meniscus regimes. A number of new instabilities were observed using High Speed
Video photography and tentative explanations for their occurrence are given
Discomfort of seated persons exposed to low frequency lateral and roll motion
No full textPassengers of land transport are exposed to horizontal and rotational oscillations at frequencies less than 1 Hz which may cause vibration discomfort and motion sickness. Previous knowledge of human responses to motion is insufficient for predicting the discomfort caused by low frequencies. The objective of this thesis is to improve understanding of subjective responses to lateral and roll oscillation (presented in isolation and in combination) at frequencies less than 1 Hz in order to establish a predictive model of comfort.The first of five experiments tested the predictions of a conceptual model of motion sickness. Illness ratings were obtained over a 30-minute exposure to 0.2 Hz fully roll-compensated lateral oscillation where the point of full roll-compensation was either at the seat surface (i.e. ‘seat compensation’) or at head height (i.e. ‘head compensation’). Median illness ratings were greater during ‘head compensation’, showing some support for the motion sickness model, but differences were not statistically significant. Age, stature and body weight had no effect on illness ratings, but Asians were more than three-times as likely to experience ‘mild nausea’ than Europeans. It is concluded that differences in the position of full roll-compensation in transport vehicles are less important for motion sickness than inherent differences in passenger populations.The next four experiments used the method of magnitude estimation to determine the vibration discomfort caused by lateral oscillation, roll oscillation, and fully roll-compensated lateral oscillation with a variety of seating configurations. In the second experiment, lateral acceleration between 0.2 and 1.0 Hz caused less discomfort when sitting with a backrest than when sitting without a backrest on both a rigid seat and on a cushioned train seat; contrary to the predictions of current standards. In the third experiment, 0.25 to 0.4 Hz lateral acceleration in the plane of the seat caused similar discomfort regardless of whether the acceleration was due to lateral oscillation or roll oscillation through the gravitational vector, but above 0.4 Hz, discomfort from the roll was far greater. At frequencies less than 0.5 Hz, fully compensating the lateral acceleration with roll improved comfort compared to uncompensated lateral acceleration, but at greater frequencies, roll-compensation worsened comfort and caused discomfort similar to pure roll oscillation at 1 Hz.The fourth and fifth experiments examined differences in discomfort caused by the rigidity of the seat pan and the height of the backrest. In the fourth experiment, discomfort was greater on a soft foam seat than on a rigid seat during lateral oscillation below 0.63 Hz, during roll oscillation below 0.5 Hz and during fully roll-compensated lateral oscillation between 0.315 and 0.5 Hz. In the fifth experiment, discomfort was greater without a backrest than with a short backrest for lateral oscillation between 0.315 and 0.5 Hz. Contrary to current standards, discomfort was also greater without a backrest than with a high backrest for lateral oscillation below 1 Hz and for roll oscillation below 0.5 Hz. In addition, sitting with a backrest was beneficial for comfort with fully roll-compensated lateral oscillation between 0.4 and 0.63 Hz.The results of the five experiments were collated to provide recommendations for the improvement of current vibration standards. On the basis of experiment 1, a new multiplying factor for the prediction of vomiting incidence in an unadapted group of male Asian adults is offered. On the basis of the four discomfort experiments, modifications to current frequency weightings for lateral acceleration and roll acceleration are offered so as to extend the prediction to frequencies less than 0.5 Hz. Guidance for the prediction of discomfort with fully roll-compensated lateral oscillation is also provided. The thesis is concluded with recommendations for future research
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