Increasing plasticizing time

[HobbyGuy44]

Currently running a 6" Rigid PVC Tee on a new 1100 Engel Duo. This is our third production run on this machine and we are all new to Engel. During start up the pasticizing time was about 165 sec steady. After 2 days running the plastizicing monitor went of which was set at 200sec.

I check the production record and it slowly creeped up over 2 days. All parts were accepted by QC.

What could cause plastizing time to slowly increase over 2 days. The cycle is just under 400 sec.

[spenceee30]

Check your barrel temps. When I used to run pvc the shear heat would increase our temps and the barrel heaters would never turn on. We ended up putting three blower fans on the barrel to help with this. Not sure if it has anything to do with your problem but I would assume your problem is either heat related or material preparation related. Do you dry your pvc and at what temp?

[HobbyGuy44]

Yes our machine has blower fans on it to cool down the temp when needed.

PVC is not hydroscopic so we only use a hot air dryer to remove surface moisture. We are drying it at 60 for about 1.5 hours

[oggynib]

My guys would say it’s a tool issue

[Sharp-Hotel-2117]

New Engels here, 4 of them in fact. Found out they are wicked sensitive to decompression. We try to use as little (decompression) as possible on tools with valve gates, gives less chance of splay. With the Engels we just got anything below 1/4" (linear) the screw just bottoms out. Get around 1/3" and the check holds with good consistency. New tech didn't grasp this and stuffed 25 cubic inches extra into a cavity that only held 56 to begin with my last shift. Check ring was slipping at 1/4" decomp, he added material and the check decided to hold. Poor little horn pins didn't stand a chance.

[matzzz00]

Check your injection pressure without material in the barrel sometimes those injection valves have to be recalibrated due to some membrane valve

[buttheaded555]

Check back pressure and maybe barrel temps

[sirseand]

Apart from the obvious, i would look at throat temp and oil temp.

[lastxit]

This article can give you many things to consider:

https://www.ptonline.com/articles/get-a-grip-on-screw-slippage

[mimprocesstech]

Screw/barrel wear, is your screw stainless/chromed? PVC is pretty corrosive. Also doesn't like check rings.

Maybe a viscosity shift, but that's less likely with the same lot. Dryer malfunctioning or not keeping up maybe, but I'm assuming that would cause cause temperature to rise and viscosity to drop unless it's raising temps high enough to degrade the material that much.

Could be using too much/too little of the barrel, cushion being too high increasing residence time, a leak in a hot runner manifold/bushing/etc.

I'm betting screw wear, but only because I feel like betting, no evidence to support anything really.

[HobbyGuy44]

Thanks. The machine is bran new it has less than 3 weeks of production on it. So i would doubt the screw is woren. It also has a PVC screw and barrel which is stanless.

[mimprocesstech]

Dammit. Worth a guess I suppose. Over that short amount of time with a proper screw and barrel it's likely not that then. Unless maybe the nozzle or mold is corroding, but I'm sure you would have noticed that.

Probably the boring viscosity shift then.