Short glass fibers injection molding

Thermoplastic RPs (RTPs), even with their relatively lower properties when compared to thermoset RPs (RTSs), consume about 55wt% of all RP products. Practically all of the RTPs are injection molded with very fast cycles using short glass fiber producing highly automated and high performance products. 

Fakirov, S. and Fakirova, C., Direct determination of the orientation of short glass fibers in an injection-molded polyethylene terephthalate) system, Polym. Composites, 6, 41 (1985). 

Fig. 6.8. Fracture toughness, K, of short glass fiber-thermoplastics injection molded composites as a function of weight fraction of fiber, fVr. (O) and (A) polyethylene terephthalate (PET) matrix ( ) and (A) polycarbonate (PC) matrix. Notches made transverse (O, ) and parallel (A, A) to the mold fill direction,...

Fig. 6.9. Normalized fracture toughness, (Kc - AKQ)/K. of short glass fiber-thermoplastics injection molded composites as a function of reinforcing effectiveness parameter, ft (O) polyetheretherketone (PEEK) matrix (K = 6.5 MPa m) (A) polytetrafluoroethylene (PTFE) matrix (K = 1.9 MPaym).

To meet fabricated dimensional tolerances different approaches are used. They include use of specific fillers and reinforcements and process control (Chapter 3). Popular filler used is short glass fibers (Chapter 15). Over 50wt% of all types of glass fibers used with different plastics and by different processes are used in injection molding compounds. Table 2.2 shows the shrinkage of different unreinforced plastics ad glass fiber reinforced plastics based on ASTM testing procedures. 

In injection molded composites of polypropylene containing short glass fibers, the fiber orientation depended on the flow pattern (which, in turn, is related to mold thickness, the position of the gate, and flow rate)." Substantial variation was detected along the thickness of the sample. Crystallites followed a pattern of fiber distribution but they grew in a direction perpendicular to the direction of the fiber and specimen surface. The direction of spherulite growth was different in neat resin where crystallites grew parallel to the surface of the mold (specimen). 

Plastic lumber is recycled plastics processed such as commingled plastic, polyethylene plastic, and polypropylene plastic. To improve their performances different developments have been used such as specialty additives (lubricants, deoxidizers, etc.). An example is by adding as low as 10 wt% of short glass fiber to these recycled plastics can double their strength. Other fibers used include hemp, flax, and sisal. They are principally extruded other processes are used such as injection and compression molding, to produce products competitive to wood lumber on land and in the water. Compression molding allows for a deep-molded grain and a much more dense board. The density also helps the product resist moisture absorption and improves weatherability. 

For example, in direct injection molding of lid-like, thin-walled structural components (e.g., headlight reflectors), pronounced circular orientations of the short glass fibers are observed in the BMC (bulk molding compound) UP resins around the sprue gate. The solution is usually ICM or push-pull injection molding. 

The reinforcement of thermoplastics, notably polypropylene (PP) and polyamide (PA), with short glass fibers is a classical method to improve polymer mechanical properties. Fibers are dispersed more or less homogeneously in the polymer by melt compounding techniques such as twin screw extrusion to produce compounds ready for injection molding. Molded parts benefit from the better mechanical properties of the reinforcing fibers as the fibers bear a considerable part of the load applied to the composite structure. 

Z.A. Mohd Ishak, A. Arifl n, and R. Senawi Effects of hygrothermal aging and a silane coupling agent on the tensile properties of injection molded short glass fiber reinforced poly (butylene terephthalate) composites. Eur. Polym. J. 37, 1635-1647 (2001). 

Crowson, R.J. and Folkes, M.J. (1980) Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding. II. The effect of material parameters. Pdym. Eng. Sd.. 20 (14), 934-940. 

Here we introduce some commonly seen molding defects in injection molded short glass fiber reinforced parts. Solutions for other defects not described in this chapter can be found in Rubin (1972). ... 

Solomon S, Abu Bakar A, Ishak Z A, Leong Y W, Ishiaku U S and Hamada H (2007) Drop weight impact properties of (CO) injection molded short glass fiber/short carbon fiber/polyamide 6 hybrid composites, J Reinf Plast Comps 26 405-418. 

Figure 11.8. Tensile modulus (a), and tensile strength (b) of injection molded samples from recycled PET (bottles) and LDPE as compared to neat LDPE and LDPE reinforced by short-glass fibers (GF) or glass spheres (GSph)...

Figure 3.438. Schematic of the injection-molded rectangular plaque of a short-glass-fiber-reinforced thermoplastic with geometry and positions of specimens for mechanical tests. Also shown are position cross-sections (A and D) for fiber-orientation determination. The letters denote MFD) mold-fill L) longitudinal T) transverse x,y,z) coordinates [1256].

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