Parison dimensions

M. R. Kamal, V. Tan, and D. Kalyon, Measurement and Calculation of Parison Dimensions and Bottle Thickness Distribution during Blow Molding, Polym. Eng. Sci., 21, 331-338 (1981). 

Three problems with outcome of blow molding axe related to rheology, including sharkskin, die swell, and parison dimensions (sag). These can be related to the influence of the above mechanisms of lubrication. Sharkskin is a surface roughness introduced by slip-stick effect between melt resin and metal surface. Melts are non-Newtonian hquids and shear rate is expressed usually by a power law ... 

Extrusion blow molded parts must meet strict dimension distribution requirements to provide the necessary strength and rigidity with minimum material usage. The final part dimension distributions are directly influenced by parison dimensions [4]. 

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... 

This expression therefore enables the thickness of the moulded article to be calculated from a knowledge of the die dimensions, the swelling ratio and the mould diameter. The following example illustrates the use of this analysis. A further example on blow moulding may be found towards the end of Chapter 5 where there is also an example to illustrate how the amount of sagging of the parison may be estimated. 

Another inventionl l has described a method of producing a laminated composite for use as intravascular catheters such as angioplasty catheters (Fig. 6.60). In the first step, a parison was formed in a coextmsion of a multilayer sheet through a die. The parison was heated in a mold and drawn to several times its original length. Next, the parison was expanded radially to the desired dimension and strength. The exterior of the expander was coated... 

A different problem occurs when the bottle has vertical rather than horizontal asymmetries, such as bottles with narrow waists or wide shoulders. In such cases, a one-time change in the die dimensions cannot produce even wall thickness. The solution is to provide the ability to change the die dimensions as the parison is being produced, so that a thicker profile is produced for the part of the parison that forms the wider part of the bottle, and a thinner profile where the bottle is thinner. This technique is called parison programming. 

The neck-ring insert is used in the bottle cavity in a manner similar to its use in the parison cavity, although they are not identical. The thread diameter dimensions in the bottle cavity are 0.05-0.25 mm larger than in the parison cavity. 

The weight and diameter of the parison is controlled by the geometry of the annular die opening and the resin being extruded. As the molten polymer is extruded through the die, it swells to a thickness and diameter that is greater than the dimensions of the die opening. The amount of swell is dictated by a complex relationship between the internal shape of the die and the viscoelastic properties of the polymer. 

Drawdown m (1) A film of ink deposited on paper by a smooth edged blade to evaluate the undertone and masstone of the ink. Syn Pulldown. (2) A thin film of even thickness on base material cast by means of a drawdown bar. Syn Casting. (3) In extrusion, the process of pulling the extmdate away from the die at a lineal speed greater than the average velocity of the melt in the die, thus reducing extrudate s cross-sectional dimensions. The term is also used by blow molders to denote the decrease in parison diameter and wall thickness due to gravity. 

A controlled parison is one in which the dimensions are partially controlled through tension (i.e., the rotary wheel, the falling neck ring, etc.)... 

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