Parison formation

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. 

Fig. 14.26 Diameter (SD, thickness (S7), and weight (Sw) swell of a parison extrudate from a commercial blow-molding machine equipped with CCD camera equipment and parison pinch-off mold based on the design of Shepak and Beyer (69). (a) A chain extended multibranched polyamide-6 resin (b) the former with 12% glass fiber of 10 pm diameter 60 1 L/D and (c) polyolefin modified polyamide-6 with some carbon black. [Reprinted by permission from A. H. Wagner and D. Kalyon, Parison Formation and Inflation Behavior pf Polyamide-6 During Extrusion Blow Molding, Polym. Eng. Sci., 36, 1897-1906 (1996).]...

A. H. Wagner and D. Kalyon, Parison Formation and Inflation Behavior of Polyamide-6 during Extrusion Blow Molding, AIChE J., 36, 1897-1906 (1996). 

S. Tanue, T. Kajiwara, K. Funatsu, K. Terada, andM. Yamabe, Numerical Simulation of Blow Molding - Prediction of Parison Diameter and Thickness Distribution in the Parison Formation Process, Polym. Eng. Sci., 36, 2008-2017 (1996). 

Air used to form the parison (parison support air) is typically sterile filtered air. If this is not the case, non-sterile air may be able to enter the parison during parison formation. 

Two basic methods are used in this process to deliver material to the processing units. These are extrusion and injection. In the next step, the preformed material is expanded to form parison. There are many commercial variations on this basic technique some of which include continuous-extrusion-blow-molding, coextrusion-and-sequential-blow-molding, and injection-stretch-blow-molding. Both extrusion and injection molding are the subjects of later discussions below, we will concentrate here on the parison formation, its processing, and the related effects. 

The blow molding process therefore involves essentially two properly synchronized operations parison formation from the plastic material and blowing the parison into the shape of the desired part. There are two techniques for plasticizing the resin for parison formation. These are extrusion blow molding (which is the most common method and which is characterized by scrap production) and injection blow molding. The latter process is versatile and scrap free and is beginning to be more understood and accepted by processors. 

Parison thickness control was achieved by adjusting the die annulus using the moving core technique (see PST 6). At the commencement of parison formation the core diameter was 145 mm and the die 150 mm diameter giving a 2.5 mm wide annulus. Actual diameter of the parison was approximately 190 mm. 

Extrusion blow molding is a continuous process capable of high production rates. This process (Figure 8.1) involves three main stages parison formation, parison inflation, and part solidification. It has a number of... 

Engineering thermoplastic blowmolding developments are gaining, such as the three-dimensional blow-molded automotive coolant ducting, and higher-MW, higher-melt-strength BPS for parison formation [16]. 

Fig. 22. Swelling behavior of viscoelastic material in parison formation.

Figure 6.21 Extrusion blow molding machine and parison formation. Reprinted from [28] with permission from Carl Hanser Verlag Munich.

Annular extrudate swell is important for parison formation in blow molding. Finite element calculations and comparison to experiment, together with calculations and measurements of blown bottle thickness, are in... 

Figure 6.12 Extrusion blow moulding. Step 1 Parison formation...

Another key parameter in extrusion blow molding is extrudate swell a.k.a die swell. Parison formation depends enormously on die swell since it dictates its final dimensions. However, since it cannot be predicted from molecular structure and is very dependent on processing conditions and die geometry (see equation 2)... 

NUMERICAL SIMULATION AND EXPERIMENTAL INVESTIGATION ON PARISON FORMATION FROM A VARYING DIE GAP IN EXTRUSION BLOW... 

The use of simulation software to predict the process of blow molding can save considerable time and money in the product development and is becoming more widespread. However, for parison formation simulation, the current finite element (FE) software is suitable only for the situation where the die gap is fixed. In this work, a new method was proposed to apply the FE simulation to the varying die gap parison formation. In order to evaluate the availability of the new method, the predicted parison thickness distributions were compared with the experimental results. It is demonstrated that the new method has certain accuracy and reliability in predicting the parison thickness from a varying die gap. 

Numerical simulations on the parison formation can minimize machine setup times and tooling costs. Several research teams modeled the parison formation stage to predict the parison dimensions [1-6]. The results showed that the finite-element-based numerical simulation method can predict the parison dimensions with certain precision. Huang et al. [7, 8] utilized the artifieial neural networks (ANN) method to predict the diameter and thickness swell of the parison and showed that the ANN method can predict the parison dimensions with a high degree of precision. However, the parison formation simulations and... 

ANN predictions in these researches are in the situation where the die gap is fixed. Until now, little work has been done in the field of varying die gap parison formation simulation. 

The parison formation process can be considered as an annular extrudate swell and sag problems of viscoelastic fluids. The parison swell and sag have competing effects on the parison thickness parison swell results in a thicker parison whereas parison sag results in a longer and thinner parison. 

Key Words Blow molding, Parison formation, Finite element simulation. 

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