Numerical simulations using a boundary integral method are used to model three inviscid fluid flows with surface tension. The problems considered are the motions of a free drop, the self-similarity in the shape of inviscid pinchoff, and the evolution of a finite jet. Various shapes of drops are studied, and their frequencies of oscillation are compared to result in the literature. Non-linear shapes are evolved, simulating a drop after ejection from a finite jet, which determines whether the drop holds together or forms satellites. Special numerical techniques are added to the code for free drops in order to model the pinchoff process. Evidence is found for a similarity solution for inviscid pinchoff which adopts a double-cone shape with one cone angle greater than 90°. A novel result is that the two cone angles are always about 18.1° and 112.8° independent of the initial conditions. The potential far from the pinchoff region in the numerical simulations is shown to match with certain scalings expected from a similarity solution. A model of a finite axisymmetric jet evolving from a fixed nozzle is used to simulate various conditions of drop ejection. Driven by a time-dependent backpressure, the jet forms a neck due to surface tension and pinches off. Various backpressure functions are imposed which cause different shapes of jets to emerge. The model is intended to simulate a drop-on-demand ink-jet printing process for which the optimum result is a fast, satellite-free drop that can be ejected repeatably.

This thesis reports on experiments into whether abrasives, lasers or solvents can remove ordinary black toner-print from ordinary white office paper in a way that leaves the paper reusable. If it could be ‘un-printed’ then waste office-paper could be reused immediately, without the need for recycling. There has been no academic work on un-printing, but some relevant patents have been filed. The second chapter reviews these patents according to whether they remove, obscure or de-colour the original print. It is not clear from the patents whether toner-print can be removed by abrasives, lasers, or solvents without rendering the paper unusable. These three approaches are tested experimentally and the results reported in chapters 3, 4 & 5. Abrasives can remove toner-print with limited damage to the underlying paper by operating in an adhesive wear regime. This involves making ten passes with a fine P800 abrasive rubbing at high speeds (6 m/s) and low loads (0.3N). Longer wavelength lasers are able to remove the toner-print and leave blank paper undamaged by operating at 1 W and 10kHz in the 1064 nm wavelength and scanning across the surface eight times at 400 mm/s. Unfortunately the paper beneath the print is yellowed during removal. A 40:60 mixture chloroform and dimethylsulfoxide effectively dissolves toner without dissolving paper if agitated with ultrasound for four minutes.

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The hydrodynamics and mechanical behaviour of a soft nip between a rubber-covered roller and a rigid roller has been studied. The thesis reports the developments and the results of a combined theoretical and experimental investigation into the nip flow of Newtonian and non-Newtonian fluids operating under various roller mechanical engagements, speeds and other design parameters. The theoretical model has been developed based on a Finite Element method (FEM) to solve for the equation set of generalised pressure and plane strain elasticity equations under a pure rolling contact. Several numerical studies for Newtonian fluid were then carried out to verify the basis of the present model. As far as the author is aware, no published work has hitherto studied the effect of non-Newtonian fluid flow in a soft contact. The comparison between the present Newtonian and non-Newtonian models suggests considerable variation in the film thickness caused by the shear thinning action in the non-Newtonian fluid. Concurrently, an experimental programme was conducted using a real printing unit which was converted to an experimental test rig. The parameters that were measured were pressure, film thickness, speed and temperature. The results provide detailed behaviour of the rollers investigated, and these were used to verify the predicted nip behaviour. The measured results showed that very small speed differentials occur in the nip, and the hysteresis of the rubber was the major source of the heat build-up in the roller. Also, comparison of predicted and measured pressure showed close agreement for low levels of roller engagement and at low speeds. Systematic numerical case studies were carried out to ascertain the parameters which most affect the nip behaviour. Supported with the comparisons of published data where possible, the results showed that rubber modulus, roller engagement, viscosity and speed were the most influential parameters.

The prints produced by a web offset press are subject to significant variation due to transients, particularly during start up. This results in waste being produced that could be minimised if these phenomena were better understood. As run lengths become shorter, these become increasingly significant. The objective of this project was to identify the key factors that affect print quality during press start-up transients in order to minimise the waste and optimise the process. Three major experimental trials were carried out on full-scale web offset presses to study basic process variability, press transient response, and global inker thermal transients. Concurrently, a computer model of the inking system was developed to improve understanding of the process mechanisms. Extended transients were measured due to changes in the ink rheological properties caused by shearing in the ink roller train, the effect of which was aggravated due to low operating temperatures. The effect of form roller load was found to be insignificant. The result of ink key adjustment was also influenced by changes in the viscosity of the ink. Ink viscosity changes had the greatest effect on print variation and transient. By pre-shearing the ink, the transient and the print variation were reduced, halftone dot transfer was improved, and dot gain decreased. High press speed increased the temperature in the inker and affected significantly the cross-print density variation. The largest temperature changes of the inker components occurred at cold press start-up, where inker temperature control is critical to reduce transients. The flow of ink and water through the inker removes heat, which changes the ink viscosity and transfer. Inker thermal stability is a function of print duration, press temperature, water temperature, and ink temperature. Excessive temperature settings aid inker thermal stability but reduce print quality. The temperature of the ink was found to be the key factor for both inker stability and print quality. The computer simulation results showed that the key point of the inker is the ink feed mechanism. Subsequently, three different inker configurations were simulated that shared a common ink feed mechanism. The results showed a small influence of inker configuration on transient, but a pronounced effect on steady-state variation. The inker with the largest ink storage capacity was found to produce the least variation.

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