Loss core molding

This technology is also called fusible core molding, soluble core technology (SCT), lost-wax molding, loss core molding, etc. This technique is a take off and similar to the lost wax molding process used... 

Time, pressure, and temperature controls indicate whether the performance requirements of a molded product are being met. The time factors include the rate of injection, duration of ram pressure, time of cooling, time of piastication, and screw RPM. Pressure requirement factors relate to injection high and low pressure cycles, back pressure on the extruder screw, and pressure loss before the plastic enters the cavity which can be caused by a variety of restrictions in the mold. The temperature control factors are in the mold (cavity and core), barrel, and nozzle, as well as the melt temperature from back pressure, screw speed, frictional heat, and so on in the plasticator. 

Light wave technologies provide a number of special challenges for polymeric materials. Polymer fibers offer the best potential for optical communications in local area network (LAN) applications, because their large core size makes it relatively cheap to attach connectors to them. There is a need for polymer fibers that have low losses and that can transmit the bandwidths needed for LAN applications the aciylate and methacrylate polymers now under study have poor loss and bandwidth performance. Research on monomer purification, polymerization to precise molecular-size distributions, and weU-controlled drawing processes is relevant here. There is also a need for precision plastic molding processes for mass prodnction of optical fiber connectors and splice hardware. A tenfold reduction in the cost of fiber and related devices is necessaiy to make the utilization of optical fiber and related devices economical for local area networks and tlie telecommunications loop. 

Openings in the part that are not to be cut into it require the use of cores. When the melt encounters a core, it divides and passes around it. Therefore, there is always a knit line around a hole or boss on the side opposite from the direction of flow. For relatively simple parts, that would be the direction of the gate. It is also difficult for fillers to reach these same areas and they may contain little or no filler—a condition known as resin rich. If knit lines or lack of filler result in a loss of strength beyond what the application can withstand, it may be advisable to cut the holes instead, even though the cost is higher. With the proper equipment, machining the holes can also be more precise than molding them. 

Figure 7 shows that the micro-injection molded polyethylene parts exhibit typical skin-core morphology similar to that observed for conventional injection molding parts. While the interface between the skin layer and the transitional shear zone is apparent, the interface between the transitional shear zone and the spherulitic core is hard to locate. The skin layer probably has shish-kebab structural characteristics. The Kebabs , which are crystalline lamellae, fill the crystalhzed space. Fibrous crystals, or the Shishs , are ahgned parallel to the injection direction. They penetrate those lamellae. The fibrillar structure follows the direction of the flow, as shown in Figure 7. The transitional shear zone may be thought of as crystalline ribbons that branch and fill crystallized space with some loss of orientation. Crystallization occurring at the sites of both the skin layer and the transitional shear zone is significantly influenced by shear or elongational stress history. On the other hand, the influence of shear on the crystalhzation occurring in the spherulitic core is negligible. The crystalline structure...

---