Resin flow molding

Many modifiers and additives have been described for use with nylon composites, but generally a small amount, 0.05—1 wt %, of a lubricity aid, such as sodium or 2inc stearate (4) is added to enhance both resin flow during processing and removal from the mold after consoHdation. 

The cure of thermoset resins involves the transformation of a liquid resin, first with an increase in viscosity to a gel state (rubber consistency), and finally to a hard solid. In chemical terms, the liquid is a mixture of molecules that reacts and successively forms a solid network polymer. In practice the resin is catalyzed and mixed before it is injected into the mold thus, the curing process will be initialized at this point. The resin cure must therefore proceed in such a way that the curing reaction is slow or inhibited in a time period that is dictated by the mold fill time plus a safety factor otherwise, the increase in viscosity will reduce the resin flow rate and prevent a successful mold fill. On completion of the mold filling the rate of cure should ideally accelerate and reach a complete cure in a short time period. There are limitations, however, on how fast the curing can proceed set by the resin itself, and by heat transfer rates to and from the composite part. 

Melt Flow Index (MFI) — The amount in grams of a thermoplastic resin flowing through a standard orifice at a specified temperature in 10 minutes. The higher the value, the easier the resin flows in extrusion or injection molding. 

Flow within molds in processes such as IM and resin transfer molding (RTM), or through dies in the extrusion process, can orient the molecules of the resin as well as short or long fibers. This orientation can result in the designed properties desired or, if not properly processed, can result in inferior properties which may become evident in the form of reduced resistance to crazing, low impact strength, lowered creep rupture strength, etc. 

All corners and edges must be generously rounded (minimum radius 2 mm) to avoid stress concentration in the molded liner. Fitting liners that contain sharp comers may fail at these locations in chemical service after multiple temperature cycling. Unrounded liners may fail because of stress concentration that occurs by the hindrance of resin flow during the transfer operation and subsequent shrinkage during the cool-down. 

The fabric s unidirectional fibers are constructed in a way that increases resin flow during molding, and wet-out is up to 40% faster than with other products. So that molders don not have to modify their existing laminate designs, the fabrics are based on traditional knitted fabric technology and have comparable properties. Channels are built into the fabric structure to ensure a fast, even resin distribution. The faster flow rate can lead to higher production and mold turnover and because there is no need for local resin distribution media, the fabric can potentially decrease molding costs. A continuous filament mat version of the fabric is said to offer even faster surface flow. 

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