In-mold operation

Many plastic parts formed in molding operations will have some excess material, called flash, at the parting lines and on molded-in inserts. Gates are also excess resin material resulting from the flow path of the plastic into the mold. It is usually necessary to remove this excess material for cosmetic or functional reasons. 

Only when appreciation of its value in molding operations occurred did "TEFLON" PFA begin to justify the effort and cost of its development. 

Equation (10.48) is particularly useful for studies of crack healing, welding time in molding operations, and film formation from latexes (21). Alternately, equations (10.47) and (10.48) can be cast in the form. 

If a delay in molding operation should occur, the machine should be purged at 2-min intervals to prevent degradation. If the delay is of some length, it is suggested that temperatures be lowered and the machine purged. 

Aniline is sometimes added to resole resin preparations to slow the condensation reaction and thereby give products with improved rheological properties, which are of value in molding operations [46]. 

The structure of CBCF is shown in the SEM micrograph in Fig. 4. The crenellated surface of the rayon derived carbon fibers is clearly visible, as is the phenolic derived carbon binder. The preferred orientation of the fibers (resulting from the slurry molding operation) is obvious in Fig. 4, and imparts considerable anisotropy to the material. The molding direction is perpendicular to the plane of the carbon fibers in Fig. 4. 

This process is carried out at low pressure and at ambient temperature. The fiber is placed in the tool in the form of a mat and the resin is poured in. The mold is closed, and the resin spreads through the reinforcement thereby impregnating and fully wetting out the fiber strands. The process is done on an hydraulic press. Pressure levels required for molding are typically around 10 MPa. Gel coat can be applied to the mold faces before the molding operation commences. 

The operating pressures and shear rates in the extrusion process are considerably lower than they are in molding. As it exits the die, but not necessarily when it leaves the process, the material is in an essentially stress-free condition. Depending on the wall thickness of the material and the particular material, there is orientation of the plastic to a greater or lesser controllable degree. Thin walls produce higher orientation in materials such as PP, that is a highly crystalline polyolefin, and which orients much more than materials such as PVC. 

The typical TP encapsulation process is an insert injection molding or liquid injection molding operation. The insert, a coil, or an integrated circuit, for example, is placed in a mold equipped with either fixed spider type supports or retractable pins or other features to support it when molten TP is injected. 

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