No description available.

No description available.

In the electrostatic powder coating industry an increase in deposition efficiency and a controlled decrease in film thickness are constantly strived for. If adjustments to the size distribution of powders are made in order to improve the process in any way it is important that the excellent physical properties of the coating are not sacrificed. The aim of this study is to gain an understanding of the effects of particle size on the packing and final film properties of electrostatically sprayed coatings so that-recommendations can be made to increase the effectiveness of the process. Experimental studies involved the production of stoved sample coatings of various thicknesses obtained by spraying narrow size ranges of a commercial powder using a reproducible coating method. A testing programme was developed to assess the effect of particle size on the physical properties of the films produced. A three way comparison of physical property, size of sprayed powder and coating thickness has been compiled and results are discussed. It was observed that particle size had no significant physical effect on film properties. A method for determining a spreading factor, representative of the flow characteristics of a given powder, was developed. Observations from these stoving experiments suggested that the excellent flow properties of the powder used in earlier experiments accounted for the small variations in those results. However photomicrographs of typical coatings showed that large particles were dominant in the upper layers of packings. A loss of fines was identified from size analysis of various powders on coated plates compared to the original feed materials. Computer plots simulating the packing of particles on a substrate showed similar trends. Integration of the trajectory equation for individual particles, represented by means of a force balance, was carried out with consideration of all interparticulate electrostatic forces of the packed layer together with field and aerodynamic forces. Simulations of packings of monosized and size distributed powders sprayed at various transport air velocities show that, as a packing increases in thickness, various sizes behave differently. The results from these theoretical experiments give indications for the explanation of previous results.

No description available.

No description available.

No description available.

No description available.

The fumes evolved from hot rubber vulcanisates have concerned industrial hygienists for the last three decades. Analyses of such fumes reveal components as diverse in nature as the chemistry required to yield the finished article.

The present work forms part of a larger programme concerned with the interaction between the processing, structure and properties of rigid PVC compounds.

High quality silicon nitride ceramics have shown some advantages for rolling element bearing applications. In particular hybrid bearings (silicon nitride rolling elements and steel races) have the ability to withstand high loads, severe environments and high speeds. However, the difficulties of both sintering and machining the material may result in surfacedefects,such as surface ring cracks. It is difficult to detect surface ring cracks during high volume production processes and hence it is crucially important to understand their influence and the fundamental mechanism of the failures they cause. The purpose of this study is to examine the contact fatigue failure modes of silicon nitride rolling elements with surface ring crack defects. In this study, new experimental and computational techniques are developed to measure and model the interaction of the surface with pre-existing crack defects. A rolling contact fatigue test method is devised for positioning the ring crack in the contact path. Rolling contact fatigue tests are conducted using a modified four-ball machine in a hybrid ceramic/steel combination. A three-dimensional boundary element model is used to determine the stress intensity factors and to carry out the crack face contact analysis. Research shows that the RCF life performance of silicon nitride bearing elements is dependent upon the crack location and fatigue spall happens only at a few crack orientations. The spalling fatigue failure is not only influenced by the original ring crack propagation but also strongly influenced by the subsequent crack face contact. Secondary surface cracks play an important role in the forination of a fatigue spall. The crack gap and crack face friction coefficients significantly affect the formation of secondary surface cracks. Numerical calculation results are consistent with the experimental observations. A quantitative three-dimensional boundary element model has been developed, which can be used to determine the geometry of acceptable surfacering cracks.