Blowing the Bottles

Sometimes, there are imperfections due either to crystallinity in the preform or due to crystallinity allowed to form during the reheat process. These imperfections show up as haze (pearlescence). This is due to microcracks in the PET induced by the stresses during blowing. This is different from the white color around the gate area of the preform, which is due to thermal crystallization. 

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Injection blow molded bottles are generally blown on the same machine as the one that makes the preforms. It is a multistation machine, where the first station does the injection molding, the second station blows the bottle, and the third station ejects the finished bottle from the machine. The process is often arranged on a horizontal table, as shown in Fig. 12.10. Multiple cavity preform molds and bottle molds can be used in the process. However, the cavitation (the number of cavities) is limited by the size of the rotary table. 

My first approach was to "cold" blow the bottle to produce an oriented small neck container with a bottom. 

This method is slow because of the multiple operations on a shuttle machine. The heat of extmsion sterilizes the bottle, which is not readily achieved after molding. Blow-mold/fill/seal systems are used commercially for beverages and for pharmaceutical packaging. 

Example 4.4 A blow moulding die has an outside diameter of 30 mm and an inside diameter of 27 mm. The parison is inflated with a pressure of 0.4 MN/m to produce a plastic bottle of diameter 50 mm. If the extrusion rate used causes a thickness swelling ratio of 2, estimate the wall thickness of the bottle. Comment on the suitability of the production conditions if melt fracture occurs at a stress of 6 MN/m. ... 

The steps in the process are illustrated in Fig. 4.48. Initially a preform is injection moulded. This is subsequently inflated in a blow mould in order to produce the bottle shape. In most cases the second stage inflation step occurs immediately after the injection moulding step but in some cases the preforms are removed from the injection moulding machine and subsequently re-heated for inflation. 

During extrusion blow moulding of 60 nun diameter bottles the extruder output rate is 46 X 10 m /s. If the die diameter is 30 mm and the die gap is 1.5 mm calculate the wall thickness of the bottles which are produced. The flow curves in Fig. 5.3 should be used. 

During the blow moulding of polypropylene bottles, the parison is extruded at a temperature of 230°C and the mould temperature is 50°C. If the wall thickness of the bottle is I mm and the bottles can be ejected at a temperature of I20°C estimate the cooling time in the mould. 

Flame treatment is predominantly used with articles of relatively thick section, such as blow moulded bottles, although it has been applied to polyolefin films as well. The most important variables in the process are the air-gas ratio and their rate of flow, the nature of the gas, the separation between burner and surface, and the exposure time. 

There are also bellows-style collapsible plastic containers such as blow molded bottles (jars) that are foldable. As shown in Figs. 3-16 and 3-17, the technology of foldable... 

A similar problem is presented by vehicle tires and certain blow molded bottles, which must be virtually impermeable to air and other gases. An example of the use of a very impermeable elastomers is butyl rubber. Because of its impermeability to gases, butyl rubber is used as a roof coating. With plastic bottles, different layers of both coinjected and coextruded plastics (Chapter 8) can be used to fabricate the bottle to make it impermeable to different vapors and gases depending on the barrier plastic included. 

An early problem was that the blowing process as originally developed produced rounded bases, and so the bottles could not be stacked upright on shelves. Initially, bottles were equipped with separately moulded base cups, usually made from polyolefin and readily attached by a snap-on or glue-on process. The Continental Group then introduced in the USA a bottle with a shaped multilobal bottom that did not require a base cup, and further designs have followed [64],... 

A significant fraction, more than 25%, of the low-density polyethylene (LDPE) (Sec. 3-14a) produced by radical polymerization consists of various copolymers of ethylene. LDPE has come under increasing economic pressure in recent years because of a combination of factors [Doak, 1986]. High-density polyethylene (HDPE) has displaced LDPE in applications such as blow-molded bottles and thin films where the increased strength of HDPE is preferred over the clarity of LDPE. Linear low-density polyethylene (LLDPE) (Sec. 8-1 lc) competes effectively with LDPE in terms of both cost and properties. New producers of ethylene have entered the LDPE market because of a lack of alternatives for their feedstocks. Many LDPE producers use copolymerization as a strategy to obtain products more resistant to displacement by HDPE and LLDPE. 

To get the egg out, it wouldn t make sense to suck on the bottle s mouth. The pressure inside the bottle is the same as atmospheric pressure. Extracting more air would just lower the pressure inside the bottle even further. To get the egg out, you have to increase the pressure inside the bottle so that it is higher than the atmospheric pressure. This is accomplished by blowing into the bottle. Give the bottle a good blow and out slides the egg. It may take a little practice, but you should be able to get the egg out with a good blow. 

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