PET Mold Solutions

I collected a shot and found positions 1, 47, 64, 67, and 78 have long gates. Some process adjustments were made, and the system went into production. About 5 minutes later I checked another shot and found the following cavities making long gates 40, 49, 57, 64, 75, and 78. Two cavities (64 and 78) are repeat offenders, and the others are intermittent.

Since most cavities are intermittently involved, I decided to look at the mold services.

I checked the air pressure at the machine, it was good at 120PSI. I checked the air valves at the back of the machine and found, instead of a quick clean exhaust to atmosphere (less than 0.5 seconds), it was a long slow air release. I removed the two mufflers and found that they were completely plugged, preventing the compressed air from quickly exhausting to atmosphere. Both mufflers were removed and replaced with new. I checked two shots and found the long gates were resolved. The mold went back into production.

The brown degraded resin I found in the muffler, strongly suggests plastic has found its way under the valve gate piston and may be preventing the piston from reaching its fully forward position. It ran the rest of the day without issue.

The VG close was fighting the air on the VG open side of the piston, causing sluggish stem movement.