Injection blow molding process

Describe both the extrusion blow molding and injection blow molding processes. Why would one method be chosen over the other ... 

Blow molding is rather difficult and limited to the direct blow molding process, because of the rheologic characteristics. For the same reason the injection blow molding process does not work. Tradenames appearing in the references are shown in Table 4.8. 

In the injection blow molding process, the parison is formed by injection molding of the preshaped parison onto a steel rod, as shown in Fig. 14.18. The rod with the molded thread already completed is moved to the blowing station, where the article is inflated free of scrap. The parison thickness distribution is determined in the injection mold without the need of further control. Some axial orientation is introduced during injection, resulting in an article with partial biaxial orientation. 

Future advances for the injection blow molding process are in tooling for bottles with special tabs, the use of process control to profile the melt injection pressure, and the use of microprocessor control when the volume of machines on the market makes it economical. 

FIGURE 2.34 Sketch of injection-blow-molding process. 

Coca-Cola bottle Acrylonitrile-styrene (AN) plastic was used in 1958 to produce the first commercial stretched Coca-Cola carbonated beverage bottles (two-liters). The glass pinch bottle debuted in 1915 was resurrected out of plastics. Production was by Monsanto Co. using Barex plastic from Sohia of BP Chemical International and DuPont s stretched injection blow-molding process. After production started in about eight plants on the East Coast, AN was banned by the U.S. Food and Dmg Administration because of possible food contamination, even though... 

Injecting preform Blow molding and ejection Fig. 4-8. Basic injection blow molding process. 

FIGURE 1.40 Extrasion and injection blow molding processes. ... 

Applicable materials for the injection blow molding process include high-density polyethylene (HOPE), low-density polyethylene (LDPE), polystyrene (PS), styrene acrylonitrile (SAN), ethylene vinyl acetate (EVA), polypropylene (PP), polycarbonate (PC), and polyurethane (PU). Polyethylene terephthalate (PET) and polyacrylonitrile (PAN) are less commonly used in the injection blow molding processes. 

Although the injection blow molding process is not suited to handleware bottles, it is rapidly gaining favor over extrusion blow molding for bottles up to 1.5 liters and... 

Below is a list of items or problems that are some-what common in the injection blow-molding process with possible solutions to the happening. The list is a... 

Injection stretch blow molding is a two-step blow molding process that is used to produce plastic bottles. Figure C.4 provides an illustration of the injection blow molding process. Multi-cavity injection molding dies are used to produce multiple preforms of plastic. The preforms are heated and stretched in a series of stations. After appropriate time, the... 

Figure 13.27 The injection blow molding process. (Courtesy of Johnson Controls, Inc.).

Basic credit is given to Piotrowsky for developing the first true injection blow molding process. Others followed as Farkus, Moslo, and Gussoni, with the industry once having Piotrowksy s principle adopted the Gussoni method as the simplest method to use in a production machine (Fig. 13.28). 

The injection blow molding process has a number of advantages. The preform can be injection molded in a profiled shape that corresponds to the requirements of the blow mold form. The neck form is molded in its entirety at the injection stage, resulting in a quality and precision that is superior to a blow-molded neck. There is no pinch-off scrap to be removed and recycled and no bottom seam. There are some drawbacks too. The process is difficult to use with high melt viscosity materials. Integral handles, view stripes, and multi-wall constructions are all impractical. 

Fig 19.40. Basic injection blow molding process (1) injection molding the preform (2) blow molding and part ejection. (Reprinted from Biow Molding Handbook. Rosato and Rosato. Eds., by courtesy of Cart Hanser Veriag.)... 

The principal steps of the injection blow molding process are illustrated in Figure 18. The initial step is the injection molding of an inflatable preform. This simultaneously creates a bottle neck with well-defined dimensions and a tube of polymer sealed at one end that will later be inflated. The preform is then transferred to an oven, where the tube is reheated to its softening temperature. The softened preform is then transported to a conventional blow mold, and compressed air is introduced to inflate it. 

The injection blow molding process involves two stages. In the first stage, a plastic part called a preform is made, using a traditional injection molding process. The preform is a precise shape, with precise wall thicknesses. This preform is then transferred to a blow molding station, where it is placed in another mold and held in place by specific features of the preform that mate with the blow mold cavity. Compressed air is then injected into the center of the part, forcing the unsupported walls of the preform tube to stretch and expand outward, until they hit the walls of the second mold. Once the material cools and solidifies, the mold is opened and the part is removed. 

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