It seems that the extrusion flash is only a one-time phenomenon in the molding process. However, the way the flash is designed is critical to maintaining the integrity of the Pet Preform. Here are some things that might go wrong:
The flash bag did not fill up enough space, so the pressure to push the plastic back into the container was too small to properly weld the gap. This condition is characterized by a “v” shaped notch at the pinch, indicating that the seam may be weak where the seam may crack.
The flash pocket is not large enough to hold all of the flash material, which creates excessive pressure towards the container. This creates a very thick plastic bump at the pinch. Depending on the characteristics of the plastic, the cooling rate and other processing factors, this extra thickness may cool at different speeds, move the volume, and cracks may occur.
If the processing conditions or mold pinch-off geometry is incorrect for any reason, it may have a negative impact on the integrity of the parison bond in the pinch-off area where the edges of the two molds are joined together.
After molding, the flash is removed manually or mechanically. Care must be taken, otherwise the container/part may be damaged, just like any post-forming process.
Flash can affect the appearance and function of plastic containers or components. Rough or excessive flash is visually unattractive. Excessive flash around the bottle neck can interfere with proper operation of the lid or cap.
Good extrusion blow molding design and engineering repair flash
Many adjustments can be made to solve the flash and pinch-off problems. This is mainly science – there is still a little art.
Pay special attention to the pinch-off area on the mold to ensure proper clearance. When the part is removed from the mold, too small gaps and flash edges will fall into the molded assembly. The gap is too big, it is difficult to trim, and it looks bad. Check the mold regularly to make sure the pinched land is in good shape.
Changing the parison thickness and clamping speed helps to adjust the amount of plastic that is pressed back into the container.
Changing the viscosity of the parison can adjust how much material will flow back into the container.
Control the duration and pressure of air blown into the mold. Make sure the process provides proper ventilation.
Test different flash pocket shapes. Adding a baffle or channel changes the speed at which the plastic is pushed back into the container and also affects the cooling rate.
Jilian Plastics has continuously adjusted the design and crafts of China Pet Bottle. We have also won the love and praise of many customers and determined to become a better reputation in the market.