Post-mixing processes

A brief description of the extrusion of a rubber compound is given with emphasis on the uniformity of the operation. One source of non-uniformity is that originating from the mixing and the other is caused by the extrusion itself. Only the former is related to mixing, but both cases are described here, because they may not be clearly separable in the actual extrusion operation. The purpose of extrusion is to fabricate a continuous object with a precisely defined cross-sectional geometry, i.e., a profile. It follows that the material must be uniform in every part over the cross-section as well as in the machine direction. The material, being viscoelastic, carries deformational memory. Therefore, the nniformity of the memory as well as that of the composition must be concerned with the recovery or else the memory will distort the profile. 

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In order to understand mixing of rubber one has to have a breadth and depth of knowledge, including polymerisation processes and post-mixing processes such as extrusion and injection moulding. 

In the post-dispersion process, the soHd phenoHc resin is added to a mixture of water, cosolvent, and dispersant at high shear mixing, possibly with heating. The cosolvent, frequently an alcohol or glycol ether, and heat soften the resin and permit small particles to form. On cooling, the resin particles, stabilized by dispersant and perhaps thickener, harden and resist settling and agglomeration. Both resole and novolak resins have been made by this process (25). 

Abstract world class unconformity-related U deposits occur in the Proterozoic McArthur Basin (Northern Territory, Australia) and Athabasca Basin (Saskatchewan, Canada). Widespread pre-to post-ore silicifications in the vicinity of the deposits, allow proper observation of paragenetically well-characterized fluid inclusions. We used a combination of microthermometry, Raman microspectroscopy and Laser Induced Breakdown Spectroscopy (LIBS), to establish the physical-chemical characteristics of the main fluids having circulated at the time of U mineralization. The deduced salinities, cation ratios (Na/Ca, Na/Mg) and P-T conditions, led to the detailed characterization of a NaCI-rich brine, a CaCl2-rich brine and a low-salinity fluid, and to the identification of mixing processes that appear to be key factors for U mineralization. 

Brown G. H., Tranter M., Sharp M. J., and GumeU A. M. (1993a) The impact of post-mixing chemical reactions on the major ion chemistry of bulk meltwaters draining the Haut Glacier d Arolla, Valais, Switzerland. Hydrol. Process. 8,465-480. 

The Dranco process (Dry anaerobic composting) (De Baere and Six, 1988) also utilises the segregated organic fraction of MSW. This is mixed with recycled effluent, and fed to the reactor. The retention time is 18 days, and after post-fermentation processing, dewatering, and drying, the final product is marketed... 

The blending process can be carried out in a variety of equipment in batch or continuous mode. For liquid blends a filtration step can be done post-mixing to... 

Multi-scale processing may be done for reasons other than to control exothermic reactions, e.g. for staged post-mixing, to have different process parameter levels along the reaction path (stage-wise change of temperature, pressure, etc.) or to combine various unit operations with different demands on process... 

In the CBP it is necessary to create a dispersed bubble structure in the dough during mixing for subsequent inflation by yeast fermentation and thermal expansion. This bubble structure must be substantially retained through post-mixer processing. 

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