Parison forming

Fig. 14.15 Schematic representation of the blow molding process, (a) The extruder head with the blowing pin and open mold (b) the extrusion of the parison (c) the mold closed with the parison pinched in the bottom and sealed at the top (d) the inflated parison forming a bottle.

Fig. 14.24 Detailed cross-sectional representation of the die exit and the parison formed in the blow molding process, with the key design variables and the thickness and outer diameter swell.

In extrusion stretch blow moulding the first stage is similar to the first stage of extrusion blown, but the parison formed is conditioned to a specific temperature prior to stretching initially by a descending rod and then by compressed air (Figure 7.9). 

CLOSED LOOP CONTROL OF PARISON FORMING - PLUNGER UP CONTROL Background... 

In 1950, Continental Can Company received the first patent for a continuous extrusion blow molding machine. The term continuous applies to the constant extrusion of the parison as compared to an intermittent parison forming process. Plax Company and Continental Can Company owned a strong patent position on the blow molding process imtil about 1960. After the patents expired, Zam Company pioneered the first HOPE milk bottle for Borden Dairy in North Carolina using Uniloy machines [29]. 

FIGURE 1.161 Principle of parison forming for dip blow molding... 

As the parison is extmded, the melt is free to swell and sag. The process requires a viscous resin with consistent swell and sag melt properties. For a large container the machine is usually equipped with a cylinder and a piston called an accumulator. The accumulator is filled with melt from the extmder and emptied at a much faster rate to form a large parison this minimises the sag of the molten tube. 

Basically the BM lines have an extruder with a die or an injection machine with a mold to form the parison or preform, respectively. In turn the hot parison or preform is located in a mold. Air pressure through a tubular pin-type device located usually at the parting line of the mold will expand the parison or preform to fit snugly inside their respective mold... 

They are then forced through a narrow die to form a hollow tube called a parison. A chilled mold is then clamped around the parison and inflated from the inside by air. The air pressure presses the parison against the mold, and it hardens in the shape of the mold. The mold then opens and ejects the HDPE bottle. The bottle is then trimmed and conveyed to the milk filling station. The waste plastic is ground for reuse. GHG emissions associated with the embodied energy of the packaging machinery may be calculated but typically fall near the 1% cutoff line and can be excluded (Cashman et ah, 2009). 

The extrusion blow molding cycle is illustrated in Fig. 14.2. The extrusion component of the cycle is normally continuous. As soon as one length of parison has been captured by the mold, another length starts to form. To allow room for a new length of parison to emerge from the die, the mold moves aside as soon it has captured a parison and the knife has severed it. The mold is rapidly translated to a remote blowing station where inflation takes place. After the product is ejected, the open mold moves back under the die where it surrounds and captures another length of parison. 

As already stated, for aseptic BFS, the container is filled in a localized air shower provided with sterile filtered air. However, there is a short period of time between container formation and filling, when the open container is transferred from the par-ison formation position to the filling position and exposed to the clean room environment. During this shuttling period, there is a possibility for contaminants from the room environment to enter the container. The air used to form the parison (parison support air) is typically sterile filtered air. If this is not the case, it is also possible for nonsterile air to enter the parison during parison formation. 

The major difference between injection and extrusion blow molding is the way the soft hollow tube (called a preform or parison) is made. In injection blow molding, two different molds are used. One mold forms the preform and the other mold is used in the actual blow-molding operation to give the final shaped article. In the molding process, the softened material preform, from the preform mold, is introduced into the blowing mold and blow-molded to... 

Blowing methods work best for deep products and it frequently trust be used for thin-walled items, A common procedure, called the blow and hluw. involves two steps, of which the first is shaping the glass charge into a form called a blank or parison. Gob-fed machines receive the gob in the parison mold, where it is shaped inlo a cylinder ahoul iwo-lhirds the... 

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. 

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. 

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