Blow Molding Pet Preform Design Principles

Update:08 Jul 2019
Summary:

1. "Closed channel" blows molding Pet Preform design pr […]

1. "Closed channel" blows molding Pet Preform design principle
(1) The cross section of the blow molded product is preferably round or nearly round, avoiding sharp corners and adopting a large rounded transition.
(2) When a rectangular cross section is used, the air passage is usually elliptical. In order to ensure the uniformity of gas penetration, b ≤ (3-5) h should be satisfied.
(3) The airway turning parts should have a sufficiently large fillet radius, and the difference in wall thickness between the inner and outer corners should be avoided.
(4) The airway cross-sectional dimension should change smoothly.
(5) The airway inlet should not be placed on the design surface or the workpiece is subjected to mechanical external forces.
(6) The airway inlet should be close to the gate to ensure that the gas is in the same direction as the melt.
2, "open channel" PET preform design principles
(1) When designing the ribs, avoid designing thin and dense ribs. If the size is too small, it will not provide a good passage of the gas, and there will be a “bubbling” phenomenon, which can be improved on a thicker and less stiff rib. However, if the size is too large, local melt accumulation will occur, and surface depression will be formed after cool shrinkage. The recommended values ​​for the geometry of the airway is given.
(2) The thickness of the flat plate should not exceed 4mm, otherwise it will easily produce a “fingerprint effect”—the gas will break into the flat part and reduce the strength of the part.
(3) When the workpiece has only one introduction port and a plurality of reinforcing ribs are to be formed, the air passage cannot form a loop. Because of the formation of weld lines of the melt intersection of the front end of the branch, a "radial" channels or a "manifold" channel can be used.
(4) The airway should be evenly arranged and extended as far as possible to the end of the PET preform. Because the gas is non-viscous, the pressure distribution of the entire airway space from the inlet to the end is completely uniform, so the higher the gas penetration, the more uniform the pressure distribution of the PET preforms, and the smaller the residual stress after cool the mold, the warpage The tendency to deform is smaller.



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