Uniform mold filling

Injection pressure is a fimction of flow length, wall thickness, and melt rheology, and it is calculated to achieve uniform mold filling. The Arnitel injection pressure range is <5000 to >20,000 Ib/in (<34 to >137 MPa). Thermoplastic elastomers may not require back pressure, and when back pressure is applied, it is much lower than for thermoplastics that are not elastomeric. Back pressure for Amitel is about 44 to 87 Ib/in (0.3 to 0.6 MPa). Back pressure is used to ensure a homogeneous melt with no bubbles. 

A computer prt ram for the design of flow channels has also been developed to get uniform mold filling. This program is known as runner and gate variaticm (RGV). The resin melt can fills all the cavities at almost the same velosity. The program compu-... 

The planar reinforcement was coated and cured in a continuous production process as depicted in Fig. 5. The fabric was driven through a mold filled with epoxy resin. Excessive resin was squeezed out between rollers, so that a uniform application of the resin as well as a nearly saturated roving was achieved. Immediately after coating, the textile was cured in a heating tower at a maximum temperature of 160°C and coiled up to a roll. 

Sozer, E. M., Effect of preform non-uniformity on mold filling in RTM process . In 33rd International SAMPE Technical Conference -Advancing Affordable Materials Technology, Seattle, WA, 5-8 November 2001, pp. 176-189. 

Due to the flexible vacuum bagging system used in VARTM, a composite part manufactured by VARTM could have a thickness non-uniformity issue. Generally, better thickness control (i.e., preform compaction relaxation) can be achieved during the post-mold filling process if one allows enough time for the excess resin to be completely vented out from the resin saturated fiber preform with all resin inflow gates closed. Under such a scenario, the whole fiber preform could be uniformly compacted to its compaction limit (or fiber volume fraction limit) under the pressure difference between the environmental pressure and the vacuum pressure. The preform compaction relaxation can either be measured from experiments or predicted by numerical simulation tools. 

An example of the multilayered structures common in polyacetals is shown in the polarized light micrographs (Fig. 5.35). They depict a uniformly nucleated crystalline structure formed due to mold filling and variations in the rate of cooling of the melt. The skin surface in the microtomed section (top in Fig. 5.35A) is birefringent, non-spherulitic and highly oriented. The molecular chains are oriented parallel to the injection direction. The central portion of the bar consists of a core (bottom Fig. 5.35A) with randomly oriented spherulites (Fig. 5.35C). It has no preferred molecular or lamellae orientation. There are usually one or more layers between the skin and core that are transitional shear zones with intermediate... 

To convert solid pellet feed into uniform melt, moderate screws with some shallow flights are recommended. Melt flow is kept uniform in the mold with small gates (which maximize shear), large vents, and large sprues for smooth mold filling. Runners should be balanced and radiused for smooth, uniform melt flow. Recommendations, such as bal-... 

Improving the flow properties of the injection material and thus improved mold filling, and thus less warping through uniform cooling in thin-walled parts ... 

An example of the multilayered structures common in polyacetals is shown in the polarized light micrographs (Fig. 5.62) that depict a uniformly nucleated crystalline structure formed due to mold filling and variations in the... 

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