Causes of Uneven Wall Thickness:

• Parison Core Deviation: The gap between the mandrel and die in the blow molding machine‘s die head is uneven.
• Mold Misalignment: The mold is misaligned with the die head center.
• Parison Control Issues: For machines with a “wall thickness control system,” improper program settings or a servo valve malfunction may occur.
• Raw Material Issues: Insufficient melt strength causes the parison to sag and stretch unevenly due to its own weight.

When encountering uneven wall thickness, follow these troubleshooting steps:

Step 1: Static Parison Inspection

• Allow the extrusion blow molding machine to extrude the parison normally, but without closing the mold or blowing air.

• Observation: Is the parison round? Is there any noticeable deviation to one side? Measure the circumferential thickness of the parison by hand or with a gauge.
• Conclusion: If the parison is uneven at rest, the problem is 100% with the die head (concentricity, temperature, or blockage).

Step 2: Check the Wall Thickness Control Curve

If the parison is uniform at rest, but the wall thickness of the product is uneven,

• Action: Check the curve set in the wall thickness control program for accuracy. Try running a “flat” curve (i.e., no control) to see if the part’s wall thickness becomes uniform (although the axial distribution may be incorrect).
• Conclusion: If the part is uniform circumferentially under a flat curve but has poor axial distribution, the problem lies with parison sagging or the wall thickness curve. If circumferential unevenness persists under a flat curve, the problem may lie with mold alignment or the inflation process.

Step 3: Check the Mold and Blowing Process

• Check the mold alignment.
• Check the blow needle for correct positioning to avoid scraping the parison and causing thinning.
• Observe the mold closing and blowing process to see if the parison is distorted.

Step 4: Check the Raw Materials and Process

• Verify that the raw materials are dry and clean.
• Verify that the processing temperature is within the recommended range to avoid excessive temperatures.

About Suzhou Bestar Blow Molding Machinery Co., Ltd:

Beier Group and Bestar company are same owner And Bestar has been established for more than 19years. Bestar provides customers high efficiency, innovative, energy saving blow molding machinery solutions. Bestar blow molding machines sold to more than 60 countries.

Series blow molding machine is used for blowing 100ml-1250L HDPE PE PP products like milk bottles, daily chemical packaging bottles, jerry cans, pesticide bottles / medicine bottles and stacking barrels.

Please write your machine inquire Email, Phone Number and Company Name here, we will respond within 12h. Or you can directly contact us: Email: sales@bestarmachinery.com or at Whatsapp/Wechat +86 18862609888.