Glass fiber processing requirements

In the spray-up process a reinforcement, usuaHy glass fiber, is substituted for the mat and a special spray gun simultaneously chops the glass fiber and appHes it with catalyzed resin to the mold surface. Hand rolling techniques then consoHdate the fiber and resin to conform to the mold surface contours. The shorter chopped fibers aHow for more intricate design detaHs than do mats. Both processes rely heavily on the operators skiHs for product quahty. These two processes require the least capital investment and have the largest product size capabHity of aH the processes. A single-surface mold produces a part with one controHed (usuaHy the visible) surface. 

Reinforced Thermoplastic Sheet. This process uses precombined sheets of thermoplastic resin and glass fiber reinforcement, cut into blanks to fit the weight and size requirements of the part to be molded. The blanks, preheated to a specified temperature, are loaded into the metal mold and the material flows under mol ding pressure to fiU the mold. The mold is kept closed under pressure until the temperature of the part has been reduced, the resin solidified, and demolding is possible. Cycle time, as with thermosetting resins, depends on the thickness of the part and the heat distortion temperature of the resin. Mol ding pressures are similar to SMC, 10—21 MPa (1500—3000 psi), depending on the size and complexity of the part. 

Some of the common types of plastics that ate used ate thermoplastics, such as poly(phenylene sulfide) (PPS) (see Polymers containing sulfur), nylons, Hquid crystal polymer (LCP), the polyesters (qv) such as polyesters that ate 30% glass-fiber reinforced, and poly(ethylene terephthalate) (PET), and polyetherimide (PEI) and thermosets such as diaHyl phthalate and phenoHc resins (qv). Because of the wide variety of manufacturing processes and usage requirements, these materials ate available in several variations which have a range of physical properties. 

Microfiber glass fleece mats are typically produced from a blend of 20 - 30 percent glass microfibers <1 //m in diameter, with the balance of the glass fibers thicker (3 - 10 //m) and longer (cf. Fig. 1), on a specialized paper machine (Fou-drinier), since this is the only way of achieving the desired tensile strength without binder. The material is supplied in roll form, even though it is normally not processed into pockets, which are not required due to the absence of free electrolyte. The classification here as a leaf separator should be seen in this sense. 

These generally defined requirements are met quite comprehensively by microfiber glass fleeces. These are blends of C-glass fibers of various diameter, which are processed in the usual way on a Foudrinier paper machine into a voluminous glass mat. The blending ratio gains special importance since cost aspects have to be balanced against technical properties. The... 

Glass fibers and most other reinforcements require special surface treatment to ensure the bonding and compatibility of the fibers to the plastic in order to maximize performances. Treatments are also used to protect individual filaments during handling and processing (7,14). 

For certain products, skill is required to estimate a product s performance under steady-state heat-flow conditions, especially those made of RPs (Fig. 7-19). The method and repeatability of the processing technique can have a significant effect. In general, thermal conductivity is low for plastics and the plastic s structure does not alter its value significantly. To increase it the usual approach is to add metallic fillers, glass fibers, or electrically insulating fillers such as alumina. Foaming can be used to decrease thermal conductivity. 

Processing. The process requires a monofilament carbon-fiber core which is heated resistively in a tubular glass reactor shown schematically in Fig. 19.1. PI A carbon monofilament is pre-coated with a 1 pm layer of pyrolytic graphite to insure a smooth deposition surface and a constant resistivity. 1 1 SiC is then deposited by the reaction of silane and a hydrocarbon. Other precursors such as SiCl4, and CH3SiCl3 are also being investigated. A fiber cross-section is shown in Fig. 19.2.P1... 

Fibers can be added to a gelation solution [1212,1213]. Fibers that will not interfere with the gelation process and will provide adequate reinforcement must be chosen. In addition, they should not adversely affect the ability of the solution to be pumped and injected. In particular, glass fibers and cellulosic fibers meet the requirements as reinforcing fibers for plugging solutions. 

The NIR region is of great interest for pharmaceutical applications. NIRS is fast, nondestructive, and cost effective. Samples require no preparation and can be measured as such, intact and available for further analysis. NIRS can be performed in-, on-, and offline. Also, glass fiber optics can be used to perform remote analysis, thus bringing radiation directly to the sample. Many more advantages can be cited when considering the practical use of NIR in a pharmaceutical process, depending on the particular objective. 

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