Mold-cavity surface

The Battenfeld Airmould Contour process provides a gas-assist alternative when it is not possible to inject gas directly into the molten plastic, or where moldings with gas channel openings are not desirable. It can be used where parts only require one smooth or high gloss surface with different wall thickness or complex geometry on the other side. The process has gas entering between the melt and mold cavity surface where external pressure is applied to the melt. The gas can be applied within specific part sections. 

Having defined the boundary integral equations, next step is to discretize the integral equations and find solutions. Let us use Eq. 7.40 as an example. After substituting the boundary conditions on the mold cavity surface (Fp), the cooling channel surface (F ) and the external surface (F ), respectively, the equation can... 

Before the preform is placed in the mold cavity, a release agent is sprayed or brushed on the mold cavity surface to prevent sticking of the composite part to the mold during the demolding. 

The two-part mold opens, and the core pins carry the hot plastic to the second-stage blow-mold station. Upon the mold s closing, air is introduced via the core pin, and the plastic blows out and contacts the mold cavity surface. Controlled chilled water circulates through predesigned mold channels around the mold cavity (usually 4-21 C, 40-50°F), and solidifies the hot plastic. 

Orange peel, mold So called mold orange peel occurs when a mold cavity surface cannot be cooled below the dew point of the ambient air that causes moisture condensation and a cosmetic defect on the molded product s surface when the moisture flashes to steam when it contacts the plastic melt. This is different from polishing orange peel. 

The uniformity of the cavity temperature thus improves with larger distance A of the cooling channels to the mold cavity surface and with a smaller distance B from cooling channel to cooling channel (Figure 2.81). 

For the development of design surface, a distinction between the pre-and posttreatment of mold cavity surface and pure pre-treatment for coating (e.g., eroded mold surfaces) has to be done. For the design development, processes such as micro-radiation, mat-down treatment, or micro mat can be used. Depending on the technology used, as shown in Figure 2.110, paint-like or very dull surfaces can be established. 

Well-designed molds are vented, as entrapped air in the mold prevents good contact between the parison and the mold cavity surface. When air entrapment occurs, the surface of the blown part is rough and pitted in appearance. A rough surface on a shampoo bottle, for example, is undesirable because it can interfere with the quality of decoloration and can detract from the overall appearance. Molds are easily vented by means of their parting line, with core vents and with small holes. A typical mold parting line venting system is shown in Fig. 13.23. 

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