Parison Swell

A very important factor in BM is the effective diameter swell of the parison. Ideally, the diameter swell is directly related to the weight swell and would require no further consideration. In actual practice, the existence of gravity, the finite parison drop time, and the anisotropic aspects (the parison has directional properties) of the BM operation prevent reliable prediction of parison diameter swell directly with the weight swell. After leaving the die, the melt—which has been under shear pressure—undergoes relaxation that causes cross-sectional deformation or swell. 

The diameter swell is an important processing parameter that must be controlled for BM of unsymmetrical containers and particularly with blown side-handle products. Resins with an excessively high diameter swell could experience curtaining and stripping (adherence to mold cavity) problems. An inadequate diameter swell contributes to an increase in rejects for defective handles. 

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Parison swell, 20 172 Paritane, molecular formula and structure, 5 156t... 

M. R. Kamal and D. M. Kalyon, An Experimental Investigation of Capillary Extradate Swell in Relation to Parison Swell Behavior in Blow Molding, Polym. Eng. Sci., 26,508-516 (1986). 

FIGURE 70 Defective milk bottles resulting from the incorrect parison swell during blow molding. 

Cocatalysts can affect the polymer s melt elasticity in two ways by broadening the MW distribution and by increasing its LCB content (Table 25). Together, these properties control the parison swell in... 

FIGURE 211 The influence of cocatalyst concentration on the amount of parison swell with the polymer during the blow molding of 4-L milk bottles. 

Table 4-3. Average Parison Swell for Some Commonly Used Plastics.

Parison swell is the ratio of the cross-sectional area of the parison to the cross-sectional area of the die opening. Parison swell is caused by the tendency of the parsion to enlarge as it emerges from the die. 

Another important characteristic of blow-molding resins is the degree of parison swell and die swell. The former is the extent to which the molten tube tends to flare out during the extrusion step. An excessively high degree of flare can cause the tube to extend beyond the mold cavity, while too little flare can sometimes cause incomplete filling of the mold structure. Die swell is a measure of how much the tube wall expands as it exits the die under high pressure. The die gap must be adjusted to take die swell into accoimt in order to produce the desired wall thickness. Molders prefer to set this parameter midway and not have to... 

Blasrohling, Blasschlauch parison swell/ die swell/jet swell Strangaufweitung... 

Excessive parison swell 1. Increase material temperature 2. Increase die temperature 3. Decrease extrusion speed 4. Increase melt index 5. Reduce die size... 

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. 

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