Blow Molding
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Uneven Wall Thickness of Polypropylene Blow-Molded Products
Problem Phenomenon
The wall thickness of various parts of the blow-molded product differs greatly; the thin-wall parts have insufficient strength and are easy to break, and the thick-wall parts waste material.
Uneven wall thickness affects the use performance and appearance of the product, and is common in bottle and barrel products.
Cause Analysis
(1) The parison wall thickness is uneven, and it sags and becomes thinner when the parison is extruded
(2) The blow-up ratio is too large, causing uneven deformation of the parison
(3) The mold temperature is uneven, and the cooling rates of various parts differ
(4) The blowing pressure is insufficient or uneven
(5) The parison control system (AWDS) is not enabled or is set improperly
Solution
(1) Enable the parison wall thickness control system (AWDS) and set a reasonable wall thickness distribution curve
(2) Appropriately reduce the extrusion temperature to a reasonable value within the range of 200-280°C to increase melt strength and reduce sagging
(3) Optimize the blow-up ratio, generally controlled at 1.5-3.0
(4) Control the mold temperature to be uniform, with the temperature difference of each part not exceeding 5°C
(5) Adjust the blowing pressure and blowing rate to ensure uniform blowing
Key Takeaway
Uneven wall thickness is caused by parison sagging and uneven blowing, and needs to be solved through parison control and process optimization.
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