Pet Preform Defects And Their Prevention

Update:03 Oct 2018

In the process of making Pet Preform , even operators w […]

In the process of making Pet Preform , even operators with experience and knowledge are inevitable. There are many reasons for defects in preforms, standard process tolerances, differences between batches of materials, changes in machine calibration after repair or maintenance, environmental factors, and so on. Next, we will introduce the most common pet preform defects and some methods of prevention and repair.
1. Flow mark: Usually a band of discoloration or wavy discoloration occurs near the intersection of the mold.
The reason for this is because the cooling time is not accurate or the flow rate is not uniform.
The solution is that the prevention strategy is to prevent premature, inaccurate cooling of the material. These can include increasing the injection rate and pressure, increasing the temperature of the mold (to hold the material in a liquid state for a longer period of time), and increasing the injection temperature of the nozzle (thus increasing the material). Increasing the width or diameter of the narrow features, as well as the fillet, as the design requirements allow, can promote more uniform flow rates and cooling times.
2. Short Forming: The preform has an incomplete part and the mold is not completely filled with material, resulting in significant cost impact.
The reason for the occurrence: the material is cooled for too short, the mold is not completely filled, and gas or bubbles may appear.
Solution: Make sure the mold is completely filled throughout the process to ensure that the material flows through the mold. There is also the need to do a good job of mold maintenance.
3. Burn marks: The appearance of rust and blackening usually occurs near the edges.
Cause: The material is overheated due to trapped air, mold, nozzles and excessive injection temperatures.
Solution: The first is to reduce the injection speed, so that the mold and material can be more evenly cooled, reducing the temperature of the material to the point of combustion. It is also necessary to shorten the cycle time so that the air and gas in the mold can be cooled quickly. Finally, we must do a good job of cleaning the mold. Burn marks do not necessarily impair the structural integrity of the part and do not automatically result in scrapped parts. However, the integrity of the part with minor burn marks should be checked to ensure that the material remains intact.

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