Venting at the Parting Line

When a parison or preform is inflated, it displaces the air around it within the mold. If no provision is made to vent the mold, compression of the air around the parison or preform can raise its temperature to such an extent that it can scorch the surface of the product. To avoid this problem, we equip blow molds with vents. These can consist of slit vents at the parting line between mold halves, porous plugs of sintered metal, or small holes drilled into the cavity walls. 

Venting at the parting line is no problem therefore, a surface ending there caa always be well vented using simple methods well known to die mold designer. (Unfortunately, the me cannot be said about venting for ribs, hubs, etc. this will be covered later.)... 

Up to a rib height of about H = stols, there is usually no problem with filling, even without provision for venting. Any deeper ribs will need venting. If the rib ends at the wall at the parting line, or if there are ejector pins pushing at the crest of the ribs, there are usually... 

To give up color when in contact with water or a solvent. Also a migration, tuidesired movement of additives in a plastic (e.g., plasticizers in PVC) to the surface of the finished article or into an adjacent material. The term is also used to describe a passage at the parting line of a mold (such as a vent, but deeper) that makes it possible for the material to escape or bleed. 

Bleed (1) n. An escape passage at the parting line of a mold, similar to an air vent but deeper, serving to allow material to escape or bleed out. (2) The spreading or running of a pigment color by the action of a solvent. 

Outgassing in transfer molding is accomplished by venting the mold. This is done by using orifices at the parting line of the mold. A typical size is 0.64 cm wide and 0.0025-0.0075 cm deep. 

If the rib ends in an outside wall, the air can usually escape through the parting line vents (Fig. 437). However, if the ribdoes not end at outside wall. 

Cavity venting—machined-in passages at one or more locations along the parting line or along ejector pins— is vital to obtaining complete cavity fill in the shortest possible time. Air in the cavity must have a... 

The vent should be located, if possible, directly opposite a gate, or at least at the point of a corner, etc. Typical vents on one mold half are 0.25-0.50 in. wide and 0.002-0.005 in. deep. In some cases the vent need be no more than a scratch made on the parting line surface of the mold using a diamond-pointed tool. 

Many injection molded products will influence the final product s performance, dimensions, and other characteristics. The mold includes the cavity shape, gating, parting line, vents, undercuts, ribs, hinges, and so on (Table 3-17). The mold designer must take all these factors into account to eliminate problems. At times, to provide the best design... 

Failure of bellows can be detected by medium leaking via the bonnet vent. As this is not always evident and detection systems not always very reliable, people have become very inventive in trying to detect bellows failure by putting whistles on the bonnet vent in order to detect leakages from the bonnet vent. The bottom line, however, is that bellows are a very vulnerable but, for its correct operation, very critical part of a spring-operated SRV. Bellow balanced valves need more frequent maintenance or at least checking in order to assure proper operation. The system might have an SRV installed but with the bellows invisibly ruptured, the SRV has no purpose whatsoever. 

The venting arrangement is an integral part of a loading or unloading system. Figure 9.37 shows a connection at the pump and two at the loading spot, near the flexible connections. Each vent line contains a trap with liquid detection to keep liquid out of the vent scrubber and chlorine recovety systems. 

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