Potting material

Fig. 4. Schematic of a hemodialyzer. The design of a dialyzer is close to that of a sheU and tube heat exchanger. Blood enters through an inlet manifold, is distributed to a parallel bundle of fibers, and exits into a coUection manifold. Dialysate flows countercurrent in an external chamber the blood and dialysate are separated from the fibers by a polyurethane potting material. Housings are typically prepared from acrylate or polycarbonate. Production volume is...

Mewtonian andMon-Mewtonian Materials. A Newtonian material s viscosity is shear-independent, whereas non-Newtonian materials are shear-dependent (Eig. 7). Eor most potting materials, a Newtonian material is preferred because the material is required to flow under all electronic components, but not be susceptible to shear. However, when flowable material is used for conformal coating appHcations, a non-Newtonian material with thixotropy agent added is desired since the material should flow on the electronic substrate but stop at the edge without creeping or mnover at the circuitry. 

Vigorous magnetic stirring of the pot material prevents excessive foaming during the distillation. 

The pot material in this distillation is rather viscous and tends to bump, so good stirring and extra care should be employed to avoid this problem. A low-boiling fraction (0.67-0.78 g, 95-133°C, 0.2 mm) is collected that is mostly a mixture of hydrocarbons and ethyl 1 -naphthylacetate (ca. 1% yield). More than 90% of the product distils at 134-138°C, 0.2 mm. For the final few drops of product the bath temperature must be raised by 15-20°C, resulting in a slight rise in product boiling... 

Epoxy resins find a large number of uses because of their remarkable chemical resistance and good adhesion. Epoxy resins are excellent structural adhesives. When properly cured, epoxy resins can yield very tough materials. They are used in industrial floorings, foams, potting materials for electrical insulations, etc. One of the principal constituents in many of the Fibre-reinforced plastics (FRP) is an epoxy polymer. 

Research effort at Albany International Research Co. has developed unit processes necessary for pilot scale production of several species of reverse osmosis hollow fiber composite membranes. These processes include spin-dope preparation, a proprietary apparatus for dry-jet wet-spinning of microporous polysul-fone hollow fibers, coating of these fibers with a variety of permselective materials, bundle winding using multifilament yarns and module assembly. Modules of the membrane identified as Quantro II are in field trial against brackish and seawater feeds. Brackish water rejections of 94+% at a flux of 5-7 gfd at 400 psi have been measured. Seawater rejections of 99+% at 1-2 gfd at 1000 psi have been measured. Membrane use requires sealing of some portion of the fiber bundle for installation in a pressure shell. Much effort has been devoted to identification of potting materials which exhibit satisfactory adhesion to the fiber while... 

Encapsulonts, Unconventional. Epoxies and other potting materials conventionally used for electronic assemblies are so difficult to dissolve that they are useless in R D (Research Development) applications. The search for temporary encapsulanes has led to several household items paraffin wax, soapstone, rice and brown sugar Refs 1) Sandia Science News 6(3). Sept 1971. Sandia Laboratories, Albuquerque, New Mexico, 87115... 

Polyurethanes are not suited as an insulation material in mains voltage situations due to the ability of the polyurethane to absorb moisture and lower its resistivity. Polyurethanes alone or in a combination with an epoxy can be used as a potting material. 

Refractories for the glass industry are made, as a rule, from a mixture of calcined clay, consisting partly of crushed old pot material, carefully cleaned, and plastic bond clay. The proportion of calcined (grog) to plastic clay usually is between 1 1 to 3 2. In some glass plants no clay but the Grossalmerode material and pot shell was used in others the plastic clay from Missouri was introduced, and, again, in some cases a smaller amount of raw flint clay was added. Some of these mixtures are as follows ... 

As any feed mixture will contain organic components at high concentration, mostly at elevated temperatures, chemical stability of all module components, such as spacer and potting material and glues is critical. So far two types of modules are most widely used. 

To provide raw material for this comparative study of untreated and heat-treated oils, asphaltenes from Cold Lake crude (crude asphaltenes) and from Cold Lake vacuum residuum (residuum asphaltenes) were prepared by n-heptane precipitation as described in the Experimental section. The Cold Lake residuum fraction was prepared by Imperial Oil Enterprises, Ltd. at Sarnia, Ontario, Canada. The distillation history of this bottoms fraction indicates that the pot material was subjected to temperatures as high as 314-318°C during atmospheric and vacuum distillation. The length of time at 300°C or higher was about two hours. This is well in excess of what would be experienced in a pipestill and should have provided ample time for any decomposition. It should be noted, however, that since it was possible to maintain the system vacuum at 0.35 mm, the maximum temperature experienced by the residuum was not quite as high as it might be during refinery distillation (e.g. ca 350°C). 

This is disadvantageous when potting the hollow fibers in a header. The potting material (usually epoxy) will not penetrate into the wall of the fiber resulting in a poor bond and a possible leak path for the feed stream through the cross section of the fiber wall and out into the permeate, by-passing the internal skin. 

The potting material must have a glass transition tenperature below the lowest temperature extreme the PV module might experience, which Is - -40°C. The material must r aln rubbery In order to damp Impacts and vibration of the fragile cells. 

Hollow fibers or capillary modules have not yet found an industrial application in pervaporation or vapor-permeation processes. A few data have been reported where organic capillary structures with an outside diameter of 0.5 to 1 mm have been coated with silicon and used in organophilic separation. With the flow on the shell side permeate pressure losses inside the bore of the fiber control the process. For specific organophilic applications, these pressure losses may be tolerable. For hydrophilic processes, however, the useful length of a module would be of the order of 20 to 30 cm only, even at an inner diameter of the capillary of 1 mm. Such a module, including housing and connection in any industrial application, is more costly than a plate module. So far no potting material is available that combines the necessary chemical and mechanical stability at the operation temperature and pressure of a dehydration plant. 

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