This study aims to understand the behaviour of a novel elastomer where hollow microspheres are used as a particulate filler. The behaviour of elastomers filled with rigid particles, is fairly well understood, where the stiffness increases as the amount of filler material is increased, alternatively, foamed elastomers which are usually produced with either closed cells or open cells, have been shown to become softer as the volume of the voids are increased. When traditional foam materials are compressed they exhibit non-linear behaviour in three distinct phases, the cell walls firstly bend, then they buckle and this is followed by densification. To understand the overall physical behaviour of the material, tensile tests of the elastomer material were conducted using unfilled materials and filled with a range of the hollow sphere filler volume fractions. Compression tests were also conducted on small cylinders, again using unfilled and filled rubbers with a range of filler volume fractions. The physical tests showed that increasing the filler volume fraction increased the reinforcing effect at low strains with an associated increase in stiffness, but the material then became increasingly less stiff at higher strains. To understand the behaviour of the bulk material, the mechanical behaviour of single hollow spheres under strain were investigated, both as a standalone material and then also embedded in an elastomer. To examine the mechanical behaviour of a single hollow plastic sphere a single microsphere was compressed using nano-indentation, the tests were then replicated at a larger scale using model table tennis balls. FEA software was used to model the behaviour of both types of hollow sphere, as well as a wide range of other spheres to better understand their buckling behaviour, to help predict the behaviour of microspheres with different ratios of wall thickness to diameters. To examine the behaviour of hollow spheres in a rubber matrix, simple cylindrical unit cells were made with a single hollow plastic sphere embedded within them. These model cylinders were produced with a translucent elastomer containing a single table tennis ball. Their behaviour in compression and in tension and that of a single hollow plastic sphere embedded in an elastomer was also modelled using FEA software, the effects of debonding and buckling were determined for small and large strains and were used to examine the more complex behaviour of the filled composite. A comparison between the measured behaviour and the various models indicates that the bulk behaviour of the microsphere filled elastomers is primarily determined by a progressive dewetting process of the rubber away from the microsphere in tension and by buckling phenomena of the hollow spheres in compression.

The degree of carbon black dispersion is a very important consideration in the manufacture of rubber both in quality control and basic research. A study has been made of various aspects of assessing dispersion and the dispersion process of carbon black in rubber. The main objectives of this work were: (1) To investigate the relationship between the light scattered at a fixed angle from the rubber surface and carbon black dispersion and hence develop and evaluate a new dispersion assessment system. (2) To determine the normal variations of industrial rubber mixing installations, and (3) To study the effect of internal mixing variables on black dispersion and other properties of rubber. To achieve these goals a carbon black dispersion assessment system based on an inverted Dark Field Reflected Light (D.F.R.L.) microscope was developed in three versions and successfully tested. The three versions differed in their degree of sophistication and automation and would be expected to find application ranging from routine quality control to research. The basic principle was that a rubber sample (cured or uncured) was cut with a new razor blade and the surface observed in a D.F.R.L. microscope. The light beam from the sample surface is sensed by a photometer and its intensity was shown to be related to black dispersion. In version III an automatic stage driven by two stepper motors was designed and fitted to the microscope to perform object plane scanning. The photometer and the stage were interfaced with an Apple II microcomputer providing the following functions; stage control, photometer control, data acquisition, statistical analysis, data storage and results output. The system was evaluated by taking measurements on several identically formulated compounds differing only in black dispersion. A general rubber goods and a tyre manufacturing installation were studied. Several production batches were sampled at various mixing stages and subjected to black dispersion assessment, cure and vulcanisate properties measurement. Analysis of variance of the results was accomplished with a statistical computer package designated GENSTAT Version 4.03. Factorial experimental designs and multivariate regression analysis techniques were used in studying the effect of mixing variables on black dispersion and other properties. The results are presented in the form of response equations and contour graphs are used to enable second order interactions to be readily identified.

No description available.

This work addresses the problem of tyre tread pattern design for optimum wet grip performance. A mathematical model of tyre behaviour on wet roads has been developed. This utilizes the finite element method in the representation of tread pattern geometry. The performance of a particular tread pattern is found in terms of the fluid pressures and film thicknesses existing within the contact patch, under wet conditions. Many modern tread patterns are based on 'blocks', and a computer model has been developed specifically to assist the tyre designer in the design of these blocks for improved wet grip. Numerical results are presented both for complete contact patches and for individual tread blocks. To allow the use of the computer models by the tyre designer, with no specialist knowledge of the finite element method, special purpose mesh generation and plotting programs have been developed. Experiments have been undertaken whereby the fluid pressures and film thicknesses existing in the tyre contact patch have been measured under high speed conditions in the wet. These measure- ments were made on an indoor testing machine, and the techniques developed can be used in the routine evaluation of tyre wet grip performance. Some results of experiments performed on plain and simple patterned tyres are presented. The main purpose of this work was the development of the mathematical models which can be used for future research into, and design of, tyres for improved wet grip. However, some conclusions are made as to possible features which could be utilized in future tyre designs.

The research is concerned with· exploration of the utility of fractal methods for characterising the mixing treatment applied to a rubber compound and also for characterising the microstructure developed during mixing (filler dispersion). Fractal analysis is also used for characterisation of the fracture surfaces generated during tensile testing of vulcanised samples. For these purposes, Maximum Entropy Method and Box Counting Method are developed and they are applied to analyse the mixing treatment and the filler dispersion, respectively. These methods are effectively used and it is found that fractal dimensions of mixer-power-traces and fracture surfaces of vulcanised rubber decrease with the evolution of mixing time while the fractal dimension of the state-of-mix (filler dispersion) also decreases. The relationship of the fractal dimensions thus determined with conventional properties, such as viscosity, tensile strength and heat transfer coefficient are then explored For example, a series of thennal measurements are carried out during vulcanisation process and the data are analysed for determining the heat transfer coefficient Nuclear Magnetic Resonance is used to obtain the properties of bound rubber and a quantitative analysis is also carried out and possible mechanisms for the relationships between the parameters are discussed based on existing interpretations. Fmally, the utility of the fractal methods for establishing mixing-microstructureproperty relationships is compared with more conventional and well established methods. For this purpose, the fractal dimension of the state-of-mix is compared to conventional methods such as the Payne Effect, electrical conductivity and carbon black dispersion (ASTM D2663 Method C). It is found that the characterisation by the fractal concept agrees with the conclusions from these conventional methods. In addition, it becomes possible to interpret the relationships between these conventional methods with the help of the fractal concept.

The current work was initiated to develop, understand and optimise a novel computer controlled, automated, flexible compression moulding system primarily for the production of fluid seals. A prototype moulding system was designed and built for the study. It was used to process a range of rubber compounds for process evaluation.

No description available.

Quantitative design of extruder dies for rubber compounds and thermoplastics requires a knowledge of the pumping performance of the extruder, for an appropriate extruder-die interaction. The dies are generally formed from a succession of convergent, circular or noncircular ducts with axial varying geometrical dimensions. The design and operation of dies of these types is then a matter of sufficient importance to justify a detailed analysis of the factors involved.

No description available.

The purpose of this study is to identify and quantify factors governing extrudate swell and melt fracture. In the first part, the factors which control the extrudate swell of carbon black (N330) filled styrene-butadiene rubber (SBR) compounds at various states-of-mix were investigated. State-of-mix is quantified by effective filler volume fraction (EFVF), based on an estimate of the amount of rubber immobilised in the carbon black agglomerates. Extrudate swell was found to be dominated by recoverable strain and relaxation time, which are controlled by EFVF. In contrast, shear rate and the rubber-carbon black tridimensional transient network were not found to influence extrudate swell significantly. In the second part, melt fracture of the rubber compounds was investigated in terms of surface texture wavelength. The longer the wavelength, the greater the severity of the surface disruption. It was found that wavelength was controlled strongly by state-of mix (or by EFVF). In addition, a mechanism for melt fracture of the compounds studied has been proposed, based on average energy at the extrudate surface (t.E). Lastly, the influences of additives; paraffinic processing oil, stearic acid or a mixture of predominantly calcium fatty acid soaps on extrudate swell and melt fracture were investigated. For the rubber compounds with paraffinic processing oil or stearic acid, EFVF was found to play an important role in extrudate swell. The mixture of fatty acid soaps was shown to reduce significantly extrudate swell due to the presence of wall slip. The influence of the fatty acid soaps on extrudate swell is more noticeable for extrudates obtained from long dies, in which flow is dominated by shear. The major factors shown to exert a significant influence on melt fracture for the compounds with paraffinic processing oil or stearic acid are EFVF and green strength of the extrudate. Wall slip, promoted by a mixture of fatty acid soaps, was also found to decrease the melt fracture severity, particularly for long dies in which shear stresses are dominant.