𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : What Common Issues Does Blow Molding Experience?

𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

What Common Issues Does Blow Molding Experience?

Now that you know how blow molding works to create the desired shape and some of its common products, it’s time to look at some of the issues that can be experienced during the blow molding process and what causes them

𝟭. 𝗟𝗲𝗮𝗸𝗮𝗴𝗲

Leakage occurs in the blow molding process when the gap between the blow pin nozzle and the mold is too wide. It doesn’t allow the blow pin to push enough material inside the mold, creating leaks. Leaks can also be caused by a tear in the product’s wall, contaminated plastic resin, or poor welding of the molding plastic. To prevent leakage, be sure that your blow molding manufacturer must make the blow pin nozzle and the mold a perfect match.

𝟐. 𝐑𝐨𝐜𝐤𝐞𝐫 𝐁𝐨𝐭𝐭𝐨𝐦𝐬

Rocker bottoms occur when producing bottles in the blow molding process. All bottles have a feature on the bottom known as the push-up, where the center of the bottle curves inward at various degrees. This feature helps ensure plastic bottles, especially those for carbonated beverages, sit on the base's outer rim (feet). A rocker bottom occurs when the plastic products are too hot after molding. The plastic then protrudes outward instead of inward and causes the bottle to rock instead of standing straight.

Rocker bottom can also occur, though rarely, when the residual air pressure inside the bottle pushes the center of the bottom out. To prevent rocker bottom, ensure you allow for adequate exhaust and cooling time, your blow molding vent is clean, the melt temperature is not too hot, and the cycle time is not too fast.

𝟯. 𝗦𝘂𝗿𝗳𝗮𝗰𝗲 𝗪𝗮𝗹𝗹 𝗗𝗲𝗳𝗲𝗰𝘁𝘀

Sometimes the defects on the surface wall of the molded product are barely noticeable, like tiny black spots. Other times, it’s quite obvious: horizontal ring-like lines, vertical streaking lines, and bubbles. These defects can be caused by foreign matter, recycled resin, old resin stuck inside the extruder die head, excess moisture, the parison thickness controller moving the die too fast, or the parison wall coming in contact with the cold mold surface twice instead of once.

𝟰. 𝗨𝗻𝗲𝘃𝗲𝗻 𝗪𝗮𝗹𝗹 𝗧𝗵𝗶𝗰𝗸𝗻𝗲𝘀𝘀

Uneven wall thickness happens when one part of the preform begins to stretch first, making it harder for the rest of the product to stretch to the same thickness. This problem can occur because of an off-center gate, uneven heating and cooling, and small stretch ratios.

source : Stoner Molding Solutions