Pressure-assisted resin injection

Problems associated with the use of prepreg for composite fabrication included a high bulk factor and difficulties in obtaining an optimum resin pre-cure to ensure correct consolidation. One approach was to use pressure assisted resin injection, where a fiber preform contained in a mold was evacuated and a fairly mobile resin pumped in under pressure [64]. To help maintain the accurate alignment of the fiber in the perform, it was held in place by a resin binder made of about 4% polysulfone applied as a solution in methylene chloride, drying to remove solvent and then followed by a short treatment at 320° C to fuse the polysulfone onto the fiber. Next, a laminate of primed sheets was prepared, which was about 2.5 times the bulk volume of the finished composite (i.e., when compressed at 0.65 f/). Two techniques were used to consolidate a preform. 

Pressure-assisted resin injection processes are used in iarge scale productions. Optimized flow rate numbers, high fiber volume contents, and reproducible surface... 

This technology is characterized by prc lacement of dry reinforcement in the mold bef(ne the mold is closed and resin is injected (Fig. 17). Normally a low viscosity resin is used and either low pressure or low vacuum employed to assist resin flow and w ut of reintocement. Complex preform sluqies are generated by shying of mats... 

Occasionally, fibers or tows are inserted or laid into a shape as a preform, and the whole preform is subjected to the injection of the resin system under pressure, such as resin transfer molding (RTM) vacuum-assisted resin transfer molding (VaRTM) or even partial injection of the resin or part of the resin system, with the same qualified resin transfer molding (SqRTM) process. In every case, there is the real possibility of fibers moving under the influence of the injected resin, producing considerable doubt as to the final formal structure, position, or integrity of the fibers after molding. 

Setup of the injection and double vacuum-assisted resin transfer Molding (IDVARTM) process proposed by Fan ef a/.The IDVARTM setup controls the preform porosity, compaction and the pressure inside the preform during the resin infusion process by changing the chamber vacuum pressure.The capillary flow effect and the Darcy s flow effect are both utilized in the IDVARTM process to infuse the MWCNTs enhanced epoxy into the glass fiber preform. (This original schematic Is created based on the work reported in reference 38.)... 

A variant of low-pressure moulding is catalysed resin injection into matched moulds in which the reinforcement has been preplaced prior to mould closure vacuum applied before resin injection assists mould filling. All these techniques depend on the easy flow of the prepolymer and good wetting of the reinforcement, but preclude the addition of much cheap particulate filler. 

Resin transfer molding With vacuum assisted RTM, this process can be called infusion molding. RTM usually uses liquid TS plastics that is transferred or injected into an enclosed mold usually at low pressures of about 60 psi (410 kPa) in which reinforcement... 

The liquid resin is then injected into the mould, typically from the bottom mould, assisted by pressure and vacuum to aid in providing an even resin distribution and achieving the removal of voids. A key processing consideration here is that the resin flow should match the wetting out and impregnation of the reinforcement. 

Resin Transfer Molding (RTM) is accomplished with the use of a reinforcement system that has been preshaped to fit the mold cavity and a low-pressure resin in liquid form that is injected into a closed mold. The injection process can be assisted with the use of a vacuum system to provide for evacuation of any volatiles and to gain molded density. 

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