Plastic PET Preform Injection Molding Troubleshooting
PET preform injection molding troubleshooting is very important during the whole PET bottles making process. As the PET preforms`s quality affects a lot in the following step PET preform blowing process. It may cause failed to bottle blowing if there are pet preform defects like the moisture not match the requirement(PET heating temperature is not collect). And will will waste lots of raw material if the preforms getting yellow (over melted or burned ).
Below table list is the PET preform injection molding troubleshooting guide for your further information:
| Defects / Problems | Cause / Reasons | Remedies / Solution for reference |
|---|---|---|
| Bottom whitening of PET preform | Too low temperature of nozzle of hot runner; Too low temperature of plastic material. |
Improve the insulation; Increase the nozzle temperature; Increase the PET material heating temperature; Increase the injection speed; Lower the packing pressure; Lower down the cooling water speed. |
| Opaque pet preform body | Poor material drying; Insufficient material plasticizion; Too thick wall and poor cooling; Foreign material mixed; Too low material temperature. |
ensure 4+ hrs drying; Increase material temperature; Increase the rotation speed of screw; Verify the drying temperature and shot volume, drying temperature 165 ℃ and moisture<0.02%; Improve the cooling and make the wall thinner |
| Pet preform from transparency to Opaque | Ejection temperature is too high | Improve cooling Set it longer for the cooling time Improve injection time |
| Haze on the one side of the preform | Too high hold pressure eccentric gate | Lower the hold pressure fix the PET preform mold |
| Sliver streaking or yellowing of PET preform | Plastic decomposition | Lower drying temperature and prelong drying time; Change the injection speed Lower the material temperature Lower nozzle temperature |
| Voids in Pet preform | Insufficient drying | Improve the drying; Increase the material temperature; Lower the rotation speed of the screw; |
| Uneven ring groove on the inner wall | Vapor condensation in the core and cavity | Improve the workshop drying; Increase the cooling water temperature; Drain the PET preform mold; |
| Breakage on the gate of the PET preform | Misalignment of hot runner nozzle and gate Undercut on the gate Gate temperature is too hot |
Fix the PET preform mold; Fix the gate; Set it longer for the cooling time; Increase the injection speed or prelong the injection time; Improve the insulation of the gate. |
| Short fill or welt line on the neck of PET preform | Poor venting; eccentric gate position. |
Enlarge the venting groove; Clean the screw neck; Lower the injection speed; Fix the gate |
| Uneven wall thickness of PET preform | Poor quality of PET preform mold; Eccentric gate orifice; Too high injection pressure; Eccentric core. |
Fix the PET preform mold; Increase the material temperature; Lower down the pressure; Improve the accuracy and use adjustable core and cavity. |
| Surface dent of the PET preform. | Too high material temperature; Too short injection time too short hold time; Too quick injection speed; Insufficient cooling. |
Lower the material temperature; Prelong the injection time; Increase the hold pressure; Lower the injection speed; Increase the cooling water pressure. |
| Nozzle drooling | Poor insulation; Insufficient cooling; Too much pressure on the melt; Poor non-return on screw head; Too low hold pressure. |
Secure the gate insulation; Improve the cooling clean the screw increase the hold pressure |
| PET preform bend after ejection | Eccentric gate orifice uneven cooling | Fix the PET preform mold; Lower hold pressure increase the injection speed; Pre-long the cooling time clean the cooling line; Increase the cooling water pressure |
| PET preform bend after heating | Eccentric core; Eccentric temperature adjust orifice uneven density of PET preform; |
Fix the PET preform mold fix temperature adjust base; Lower the temperature,especially on the bend section. |
| PET preform local whitening | Insufficient PET preform heating temperature | Increase the PET preform heating temperature and even the all body temperature |
| Insufficient expanding of PET preform | Insufficient air pressure; Insufficient heating temperature injection fault of PET preform |
Increase the air pressure and air; Increase the temperature of the PET preform; Verify the PET preform even soften by 100 C water. |
| Crack of the preform bottom | Too high preform bottom temperature too low preform temperature severe decomposition | Adjust the preform temperature; Check and change the preform and material,improve the drying |
| PET preform eccentricity | Too early blowing too high air pressure; Misalignment of blow pin the bottle bottom; Severe eccentricity; Too low speed of blow pin; Distance between blow pin and bottle bottom over 1.5 mm; Too high PET preform bottom temperature. |
Delay the blowing time; Lower down the air pressure; Check and fix the installment; Check the PET preform; Adjust the air cylinder pressure; Adjust the distance between blow pin and bottle bottom to be 1.5mm or smaller; Lower the preform bottom heating temperature. |
| Preform body insufficient extending on the vertical direction | Too high heating temperature local cold slug; Insufficient air pressure and air volume poor venting of blow mold; Too high blow mold temperature; Too thin wall; Bottle insufficient vertical draw ratio. |
Adjust the PET preform temperature increase the air pressure and air; Improve the blow mold venting; improve the blow mold cooling fix the blow mold; Increase the vertical draw ratio |
| Bottle circumferential uneven wall thickness. | PET preform eccentricity; Uneven heating temperature; Poor venting. |
Fix the PET preform mold; Improve the heating appratus; Lower the problem section temperature improve the venting |
| Protrusion on the bottom | Low temperature of PET preform bottom | Blow earlier and adjust the heating temperature |
| Bottle local whitening | Local insufficient heating temperature too much local draw ratio | Increase the PET preform temperature; Check the design of PET preform |
| Bottle poor vertical loading | Uneven wall thickness; Too high PET preform heating; Poor bottle profile. |
Make the wall thickness uniform; Try low temperature and high pressure molding; Improve the design of bottle |
| Bottle ease of broken after falling | Unsufficient draw of bottom of preform decomposition after over heating | Improve the draw raio of preform bottom; Improve the material drying before pet preform injection molding; Lower the blowing temperature. |
| Pitting and whitening on the bottle body | unclean air; Too much moisture. |
Install the air filter dehumidification of compressed air. |
| Too soft bottle body | Poor design; Too high blowing temperature |
Improve the design; Try low temperature and high pressure blowing. |
| Burning and odour smell after blowing. | Too high blowing temperature; Poor quality of compressed air poor quality of material. |
Lower the blowing temperature; Fix the air compressor and filter; Sse the good quality material |
| The water taste changed after filling. | Too much aldehyde content; Bad quality material. |
Low temperature of injection and blowing check the aldehyde content and expel bad material. |
Above PET preform injection molding defects and remedies are base on our experience in the last 16 years. Please feel free to contact us or leave a comment below if you had meet any other problems we don`t listed. We will try our best the work out a solution once we saw your message.
