Graded preform

Extrusion. Extmsion techniques are used in the preparation of tubing, hose, O-ring cord, preforms and shaped gaskets. Typical extmsion conditions are 70 to 85°C for the barrel temperature and 95 to 110°C for the head temperature. The extmded forms are normally cured in a steam autoclave at 150 to 165°C. Some special grades of peroxide curable fluorocarbon elastomers can be hot air vulcanized. 

Type 95 15-cm (150-mm) AP-HE Proj was filled with two preformed blocks of high grade TNT used in Type 4-Year, Type 38 Type 96 Hows and in Type 45, Type 7-Year, Type 90 Type 89 (bag chge) Guns (p 366)... 

We have done most of our studies on granular PTFE by compacting it into a preform and sintering to make a shape matching ASTM D-1708-66 for tensile testing. Orientation measurements by IR dichroism require thinner specimens, and for this purpose we used dispersion-grade material, commercially cast and processed into film (Dilectrix Corp., Farmingdale, NY). These films were used as received without further heat treatment. ... 

The level of crystallinity plays an important part in the level of heat stability of a PET bottle. Again, the evolution of preform designs and grades of material has increased the level of heat stability. In order to extend this stability to the temperatures used for hot-filling (typically 85°C), additional methods have... 

Liquid-phase infiltration of preforms has emerged as an extremely useful method for the processing of composite materials. This process involves the use of low-viscosity liquids such as sols, metal- or polymer-melts. Using this infiltration process, it is possible to design new materials with unique microstructures (e.g. graded, multiphase, microporous) and unique thermomechanical properties (graded functions, designed residual strains and thermal shock). 

Figure 14b displays a graded index profile which was produced by the deposition of 2000 layers. Because of the thinness of the layers they can no longer be detected individually. For both preforms the germanium depletion in the center is obvious from the circular interference lines. 

Functionally graded materials by electrochemical modification of porous preforms... 

Pharmaceutical containers can be produced by a number of moulding processes, and this may be carried out by a supplier or set up in-house to produce either a preformed container or one which can be formed, filled and sealed as a continuous operation. Often different moulding processes involve different grades of polymer. 

Reduction ratio, the ratio of the cross sectional surface areas of the preform and the extrudate, is an important variable in paste extrusion. For a given extruder barrel, the smaller the cross section of the final product, the higher the reduction ratio. The size of the preform can be varied in a fairly limited range, therefore, resins must be able to undergo the reduction during extmsion. Different fine powder grades have been developed by suppliers to accommodate the wide range of reduction ratios of commercial operations. 

Further experimentation showed that no complex formed when dispersed sodium was added to dimethoxyethane that had been carefully dried and purified by distillation from a sodium-naphthalene addition compound, yet ferric chloride was reduced almost as readily as when the so-called complex had been preformed (12). This was taken as evidence that the ether was acting also as a solvent for the ferric chloride and that the complex must have been dependent on impurities in the commercial-grade ether, which either reacted with sodium or acted as a catalyst for complex formation. Nevertheless, the ether was used as the medium for all iron powder runs because of its solvent action for ferric chloride and the smaller particle sizes which were obtained as a result of its use. 

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