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This thesis is concerned with issues relating to the development of an active sealing system for hydraulic actuators where the sealing elements can be radially extended and retracted to vary the friction and leakage characteristics. In order to determine the feasibility of the active sealing concept it is necessary to establish that varying the seal geometry may achieve useful improvements in the friction-leakage trade-off and that a practical method of achieving this seal extension can be realised. Experimental and simulation approaches for seal friction prediction have been developed and active seal prototypes produced to demonstrate the concept. <br /> Experiments were carried out to measure the constant velocity friction for single-lip and double-lip seals over a range of sliding speeds and sealed pressures with special consideration applied to the instroke-outstroke direction dependence. Additional experiments were performed with sinusoid motion to provide an indication of the transient friction characteristics. Friction was shown to increase towards the end of the outstroke cycle and decrease once the instroke motion began. <br /> Tribology simulations were produced based on the results of a FEA simulation of the rod-seal contact pressure. Empirical friction-load relationships and novel contact mechanics approaches for high loads were considered. Simulations based on the Reynolds equation including standard inverse EHL theory and the GW-average Reynolds lubrication are also presented. Experimental agreement could be improved if loading is assumed to transfer to the fluid to maintain a fluid film. A hysteresis friction model was also developed in attempt to improve the prediction of speed dependent friction. <br /> Two active seal prototypes were produced, each with an adjustable external pressure supplied to the outer circumference of the sealing element. Constant velocity friction measurements for different external pressures and the transient response following step changes in this pressure are presented.

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Heat sealing is commonly used for making form-fill-seal packages fabricated from thermoplastic films. One of the challenges frequently faced by the industry is inadvertent contamination of the film–film interface by the product during filling, an event that can compromise package seal strength and integrity. In the present study, the effects of dwell time (0.5–1.5 s), jaw pressure (28–1,860 kPa), jaw configuration, jaw temperature (150–180°C), and liquid (water and oil) on the interface temperature and seal strength of a linear low-density polyethylene (LLDPE) film were investigated. In the presence of liquid contaminants, jaw pressure played an important role in displacing the liquid from the seal area allowing the formation of intact seals. Within the experimental conditions investigated, interface temperatures of 130–140°C resulted in optimal seal strength for both water-contaminated and clean film specimens. Thermophysical properties of LLDPE and the contact angle between the contaminant liquid and the polymer films were invoked to explain the seal strength behaviour of the liquid-contaminated LLDPE seals. Further, finite element analysis (FEA) heat transfer models were developed to describe the heat transfer phenomena for LLDPE film during heat sealing, when a liquid contaminant layer is present or absent at the film-film interface. The model predicted the observed temperatures well with root mean square errors (RMSE) ranged from 1.6 to 2.5°C. The FEA approach can potentially be applied to analyze the effect of different contaminant liquids on transient heat transfer during heat sealing. In the second part of this thesis research, an UV-activated oxygen indicator was developed to detect the headspace oxygen within sealed package. The detector involved encapsulating TiO2 nanoparticles, glycerol, and methylene blue within poly(ethylene oxide) fibers using electrospinning. The sensitivity characteristics of the indicator to UV-activation and oxygen detection were investigated. The color recovery rate of the electrospun indicator related negatively to the UV exposure time and to the TiO2 fraction in formulation, possibly due to the ratio of higher free electrons to methylene blue concentration. The indicator can potentially be used as a method to analyze heat seal integrity in modified atmosphere packaging applications. / Natural Sciences and Engineering Research Council (NSERC) of Canada and E.I. Du Pont Canada Co.

The purpose of this study is to investigate the possibility of using the Bleached Kraft wastewater sludges as a sealant to a permeable soil structure which could contain these liquids. The sludges used are either self-contained in wastewater, produced from treatment processes, or from the addition of chemical coagulant to the wastewater. / The mechanisms of the sludge sealing phenomena which were investigated individually are divided into physical, physico-chemical, biophysical and bio-physico-chemical types of seals. Coarse sand #24 was found suitable for this sealing study as a particle size cut. Among the types of sealings studied, the bio-physical type of seals is the most effective. The physico-chemical type of seals is effective in the initial stage of sealing. The coefficient of the permeability is reduced from an average of 6.4 x 10('-2) cm/sec to 1.0 x 10('-6) cm/sec in a period of 24 hours, with a risk of leakage of less than 1% of the total effluent. / A long-term stability of using sludges as a liner to the wastewater pond has become a substantial issue. Alum was originally chosen as an effective coagulant for forming a layer of sludge for physico-chemical types of sealing. However, after the stability analyses, one finds that alum sludge is not a stable material under commonly-found hydrostatic pressures and high pH ranges. The results of the research shows that one of the alumino-silicate sludges is much more stable than that of alum sludge. The relatively stable alumino-silicate sludge was obtained from one of the coprecipitations of sodium-silicate and sodium aluminate in a BKME solution. / The economic impact of using alumino-silicate sludge is significant. The cost comparison study shows a cost ratio in the range of up to 1:10 as compared to conventional lining material. The results can be used for the implementation of field work in sludge sealing practice. In addition, this investigation could form an excellent foundation for further studies on other effluents with different parameters.

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No description available.