Blown parison

When the parison exits the die and reaches a preset length, a split cavity mold closes around it and pinches one end of it. Usually a blow pin is located opposite the pinched end of the tube. Compressed air inflates the parison against the female cavity of the mold surfaces. Upon contact with the relatively cool mold surface, the blown parison cools and solidifies to the part shape. Next the mold opens, ejects the part, and then repeats the cycle by again closing around the parison, shaping it, and so on. 

Pock mark n. An imperfection on the surface of a blow-molded article, an irregular indentation caused by inadequate contact of the blown parison with the mold surface. Contributory factors are insufficient blowing pressure, air entrapment, and condensation of moisture on the mold surface. 

Figure 10.42 Placo process for 3D blow molding. Key A= mold begins to close on pre-pinched and pre-blown parison, B = mold fully closed with core forward and side walls hinged in, C = mold open and core retracted. ...

Ame. Consider both the cooling of the interior and exterior walls of the blown parison. Tap water at 12 °C is available for cooling the mold and air as eool as 12 °C or as hot as 100 °C can be used on the interior. The temperature of the parison as it contacts the mold wall is 220 °C. The thickness of the parison as it contacts the mold is 0.635 cm with one-Afth of the thickness being nylon 6. In order for the nylon to act as an effective barrier to gasoline it must reach 75% of its maximum degree of crystallinity, and the HDPE should reach 100% of its maximum degree of crystallinity to have adequate impact properAes. 

In blow and blow operations, the gob of glass (parison) is deUvered from the feeder to the blank mold. The gob drops through a guide funnel iato the blank mold ia the iaverted position. Air is appHed to settie the gob iato the finish, and air is blown ia to complete the parison shape. 

Horizontal rotary machines employ multiple molds in a horizontal plane on a rotary turret. As each mold approaches the extmder die exit, it opens to accept the parison and then closes. The parison is then blown into the bottle shape. The extmder must extmde on an intermittent basis or be intermittently withdrawn to provide a parison for each passing mold. 

In injection blow mol ding, a parison is injection molded onto a core pin the parison is then rapidly transferred via the core pin to a blow mold, where it is blown by air into an article. This process is appHed to smad and intricate bottles. 

Many articles, bottles and containers in particular, are made by blow moulding techniques of which there are many variations. In one typical process a hollow tube is extruded vertically downwards on to a spigot. Two mould halves close on to the extrudate (known in this context as the parison ) and air is blown through the spigot to inflate the parison so that it takes up the shape of the mould. As in injection moulding, polymers of low, intermediate and high density each find use according to the flexibility required of the finished product. 

Extrusion blow moulding (the simplest), in which the parison is an extruded tube that is blown with air. Various types of machinery are marketed shuttle, reciprocating and wheel machines. 

Injection blow moulding, in which the parison is injected into a first mould and then blown in a second mould having the shape of the final recipient. This process is more expensive and the cycle time is a longer. The aspect and dimensional quality are better compared to extrusion blow moulding. 

Reheat and blow moulding in which parisons are bought from an external furnisher and are blown on an in-house machine. 

Parison cooling significantly impacts the cycle time only when the final parison thickness is large. In thin blown articles the mold is opened when the pinched-off parts have solidified so that they can be easily stripped off thus they are the rate-controlling element in the cooling process. For fast blow molding of even very thin articles, the crystallization rate must be fast. For this reason, HDPF, which crystallizes rapidly, is ideally suited for blow molding, as are amorphous polymers that do not crystallize at all. 

The Owens protest employs vacuum to charge the glass into the blank or purison mold, Here, a blank mold dips into a shallow pot of molten glass, a vacuum is applied, and a charge of viscous glass is pulled into the hlank mold. The finish is formed simultaneously at the top of the blank. This blank or parison is subsequently Iransfcrred inlo the blow mold, where the bottle is blown into its final form. Sec Fig. 7. 

Fig, 7. Owens process Left Blank mold is dipped into the surface of molten glass, where it is tilted by a vacuum suction. As the mold is lified from the glass, a knife cuis ott rhe glass and doses ihc mold, Right The blank mold opens, and a puff ol air is introduced lo shape the parison before transferring it to the blow mold, where it is blown 1, iis final shape... 

Blown film is made similarly to blow-molded articles the molten resin is extruded continuously as a parison, which is blown to form a continuous film cylinder. This cylinder can be rolled up as a two-layer structure or slit to form one large or two smaller single layers. 

Extrusion blow molding. In extrusion blow molding, a parison or tubular profile is extruded and inflated into a cavity with a specified geometry. The blown article is held inside the cavity until it is sufficiently cool. Figure 3.56 [25] presents a schematic of the... 

Tubes and blown Aims can be produced as multilayer structures by employing multiple extruders and coextrusion manifolds and dies. Figure 12.44 is a schematic representative of a conventional and new spiral coextrusion die. The designs can be used for both blown-film and blown-molding parison dies. In the extrusion of tubes, such as rigid PVC or PE pipe, the extrudate passes over a water-cooled mandrel and enters a cold-water bath whose length depends on the tube thickness the tube leaves the bath well below its Tm (if it is crystalline) or Tg (if it is amorphous) and is sectioned to the desired lengths. 

An an alternative to printing the bottles or to affixing labels subsequently it is possible to apply the label at the moulding stage. Paper or thermoplastic film labels are printed in advance and are placed in the moulds before parisons are collected, being held in position by vacuum adhesion of the label takes place when the blown material fills the mould. 

Technologies, such as coextrusion and coinjection, allow PET and other plastics to package foods and other products.225 226> 227 Care must be taken to control the process so that the melt when blown will not have micro-voids in the container walls or will delaminate. Coextrusion and coinjection (or multilayer processes) are essential technique in the production of high performance BM products (Chapters 4 and 5). The parison or preform is coextruded with a number of different layers, each of which contributes an important property to the finished product. Increasingly, a mid layer may consist of recycled material which is encapsulated between inner and outer layers of virgin plastics. 

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