Mold-flow direction

MED mold-flow direction MMC metal matrix composite... 

To obtain dumbbell-shaped test specimens having edges that are minimally perturbed by the cutting technique, a Dewes-Gumbs die DGD expulsion press was used to punch out sections of dumbbell-shaped type I ASTM tensile specimens along the longitudinal mold flow direction (7) and transverse (X) direction. Photographs in Fig. 12.23, a and b, show the apparatus used and how dumbbellshaped specimens were obtained. 

Test Procedure. In all tests, the upper and lower specimens were the same material and surface texture. The specimens were washed with a mild detergent, rinsed with water and air dried prior to installation in the test s paratus. The two specimens were placed in contact and the normal load was applied for 3 min. Previous studies (4,6) have shown that the increase of static friction with time of static loading before applying the tangential motion was constant after 5 min. The actuator speed for all tests in this study was 0.5 cm/s. The actuator was moved in a direction which put the isolators in tension. This eliminated the possibility of buckling of the stack of isolators if the reverse direction had been used. At least four replicates were tested at normal loads of 10.8 and 20.7 N. The sliding direction was the same as the mold flow direction. 

Similar to prepared metallographic samples, the injection molded samples were cut along the flow direction, smoothed, and polished in order to expose their internal surface. After proper etching, the treated surfaces of the flank cross-section were photographed using a polarized light optical microscopy. Based on the color differences between the TLCP and matrix, volume fraction and aspect ratio of the TLCP fibers were measured [23]. 

Anisotropic material In an anisotropic material the properties vary, depending on the direction in which they are measured. There are various degrees of anisotropy, using different terms such as orthotropic or unidirectional, bidirectional, heterogeneous, and so on (Fig. 3-19). For example, cast plastics or metals tend to be reasonably isotropic. However, plastics that are extruded, injection molded, and rolled plastics and metals tend to develop an orientation in the processing flow direction (machined direction). Thus, they have different properties in the machine and transverse directions, particularly in the case of extruded or rolled materials (plastics, steels, etc.). 

Regarding this relationship, when designing the mold it is necessary to know the flow direction. To obtain this information, a simple flow pattern construction can be used (Fig. 3-28) via computer analysis. However, the flow direction is not constant. In some cases the flow direction in the filling phase differs from that in the holding phase. Here the question arises of whether this must be considered using superposition. 

In this method, NWs can be aligned by passing a suspension of NWs through microfluidic channel structures, for example, formed between a poly(dimethylsiloxane) (PDMS) mold 49 and a flat substrate (Fig. 11.3a). Images of NWs assembled on substrate surfaces (Fig. 11.3b) within micro-fluidic flows demonstrate that virtually all NWs are aligned along the flow direction. This alignment readily extends over hundreds of micrometers, and... 

Figure 11.35 Photomicrograph of the silver-colored defect in a clear PS injection-molded packaging part. The flow direction was from the upper left to the lower right...

This reactor contains at least two solid phases, two Hquid phases, and a gas phase. The flows are largely driven by gravity caused by the density differences of the soHd and Hquid phases. Taconite and coke are admitted at the top of the reactor and O2 at the bottom. Liquid Fe and slag are withdrawn at the bottom of the reactor. The Hquid iron is either cast into ingots in molds or directly passed from the reactor through rolling mills to process it into sheets. 

Figure 13.13 shows such a distribution measured by Menges and Wiibken (30) for amorphous PS. They measured the shrinkage of microtomed molded samples at elevated temperatures. Figure 13.13(a) shows the longitudinal (flow direction) orientation distribution at two injection rates. The characteristic features of the orientation distribution are a maximum orientation at the wall that vanishes at the center with a local maximum near the wall. In Fig. 13.13(b), the longitudinal orientation at the wall and secondary maximum orientation are in close proximity, and the transverse orientation drops continuously from a maximum value at the surface. 

The thermoset (TS) plastics and reinforced thermosets (RTSs) are more suitable to meet tight tolerances. With amorphous and crystalline thermoplastics (Chapter 1) reinforced thermoplastics (RTPs), and particularly unreinforced thermoplastics (UTPs) can be more complicated tolerance-wise if the fabricator does not understand their behavior. Crystalline plastics generally have different rates of shrinkage in the longitudinal (melt flow direction) and transverse directions when injection molded. 

As indicated in Figure 7b and 8b, the outer skin layers were fibrillar microstructures in nature and were oriented parallel to the flow direction. The high orientation observed could be attributed to the elongational flows that seem to predominate nearthe surface of the mold. The skin layers were approximately 20-50 pm in thickness. 

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