Structuring in injection molding

It is seen that ultrasonic techniques have two major advantages high accuracy and the ability to determine the complete set of elastic constants for a sample of small size. As a result of these capabilities, all five independent stiffness constants have been obtained for extruded rods of PLC of high draw ratio (2 = 15) and small diameter (0.8 mm). Moreover, it has been possible to study the skin-core structure in injection molded PLC by monitoring the variation in stiffness with position. For blends of a PLC and a thermoplastic or glass fiber-reinforced PLC, successful correlation has been obtained between the modulus data and the orientation of the PLC fibrils or glass fibers. 

Arlo UR, Kjaer EM (2001) Transcription of small surface structures in injection molding - an experimental study. In Heim HP, Potente H (eds) Specialized molding techniques, plastic design library. Norwich, New York... 

M. Vincent, Flow induced fiber micro-structure in injection molding of fiber reinforced materials. In M. Kamal, A. I. Isayev and S. J. Liu (eds.). Injection molding Technology and fundamentals. Munich Hanser Publishers, 2009, pp. 253-272. 

Suppression of skin-core structure in injection molded polymer parts via in situ microfibrils... 

Zhong G J, Li L B, Mendes E, Byelov D, Fu Q and Li Z M (2006) Suppression of skin-core structure in injection-molded polymer parts by in situ incorporation of a microfibrillar network. Macromolecules 39 6771-6775. 

C. F. Johnson, Resin Transfer Molding and Structural Reaction Injection Molding in Engineering Materials Handbook, Vol. 2, ASM, International, USA (1988). 

Fujiyama M (1995) Higher order structure of injection molded polypropylene. In Karger- Kocsis J (ed) Polypropylene structure, blends and composites, vol 1. Chapman Hall, London, chap 6, p 168... 

Structural Foams. Structural foams are usually produced as fabricated articles in injection molding or extrusion processes. The optimum product and process match differs for each fabricated article, so there are no standard commercial products for one to characterize. Rather there are a number of foams with varying properties. The properties of typical structural foams of different compositions are reported in Table 4. The most important structural variables are again polymer composition, density, and cell size and shape. 

Figure 4.52. Structure of the flow stream in injection molding during filling of a plane cavity.

In extrusion, when the hot melt exits from the die, the compressed gas expands and foams the extrudate. In injection molding, the hot melt is injected into the mold, but the quantity is reduced ( short shot ) so that there is not enough melt to fill the mold the compressed gas expands, and the melt foams and fills the mold. Either way, the foamed melt cools and solidifies, producing a product with a solid skin and a somewhat expanded internal foam structure. It looks like a solid product, but it is lighter in weight and offers a number of advantages. 

The latest trend in foamed composites is automotive structural parts produced by the SRIM (structural reaction-injection-molding) process. The SRIM process is a method of the reactive liquid injection molding (i.e., LIM). LIM includes RIM (reaction injection molding), RRIM (reinforced RIM) and RTM (resin transfer molding). IX M (Liquid Composite Molding) is a relatively new technical term which includes SRIM, RRIM and RTM (Resin Transfer Molding). 

Processing. Relatively little has been published on the processing of thermotropic LCPs. The morphology of melt-processed articles is dependent on the deformation and thermal histories. Extensional flows produce fibrillar structures with high orientation in the machine direction. Flows with complicated stress distributions and temperature gradients, such as encountered in injection molding, yield complicated morphologies. 

Studies of the orientation phenomena in injection molding have shown that irrespective of the molding conditions and type of thermoplastic, molecular orientation is higher near the walls and decreases toward the interior. " " Low crystallinity and flow-induced structures have been observed near the walls for injection molded isotactic polypropylene parts. " High modulus materials have also been obtained with some injection molding techniques. " ... 

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