Closed-Mold Filling Method

TABLE 1.3 Cycle Time Comparison for Filling of a Dash Board Using the Open- and the Closed-Mold Filling Method... 

Closed-mold filling method Open-mold filling method... 

The used PUR systems in the closed-mold filling method have a shorter cure time, which can lead to a shorter cycle time. Therefore, the number of required molds can be reduced. However, after having finished the mold, changing the runner and gate position to produce perfect parts is very expensive. 

When the open cavity is filled, slowly foaming mixtures are used because the mold has to have enough time to close. In the past, the so-called closing time was brought down to less than four seconds due to the use of constantly improving motion drives. Neverless, the cure times are longer than the cures time for the closed mold injection method of PUR systems. 

This method, like extrusion, requires a molten polymer. The equipment is schematically illustrated in Fig. 3.5a. In this method, polymer granules are fed into a hopper and a screw transports the polymer through a barrel where the polymer is heated to make it flow, and the polymer melt is forced through a nozzle into a closed mold. The mold is cooled after it is filled, and the molded part ejected, and the equipment readied for the next shot. Injection molding is thus a semi-continuous batch process and is usually used for large-scale production, where high throughput and reproducibility are important. The process is economical. The method is commonly used for thermoplastics. E.g. PLA, PGA and copolymers. Some... 

The closures of BFS containers are formed within the automated process by the head mold set which closes around the top of the severed section of parison following filling. The integrity of the container and closure is generally tested by a manual or automated method of leak detection performed outside of the filling environment following removal of excess plastic (deflashing) from the filled product units. 

In ICM, the predosed, preplasticized mass is injected into the opened mold. When the mold is closed, the flowing mass fills the mold cavity. Items with large surface areas such as flat packing, membranes, and flat product trays are suited to the ICM method. 

In order to overcome MIMIC limitations, some authors have proposed the use of a closely related technique that is called microtransfer molding (pTM)(Figure 4.5b). In this case, a drop of liquid pre-polymer is poured over the patterned surface ofa PDMS mold, thus letting the liquid fill the mold cavities. Then, the excess of pre-polymer is removed and the filled PDMS is placed on top of a substrate, where the pre-polymer solidifies inside the mold. Zhao et al. [12] have shown that is possible to fabricate structures with 100 nm in lateral dimension by this method, although a thin polymer layer remained on the substrate. This method can be adapted for creating structures on curved surfaces and for the fabrication of multilayered structures. 

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