Both architectures can make food-grade PET. They fail differently. Use this when choosing among SI-85-44-950, XSI-PET-PLA, and LSI-PET-PLA.
| Twin-screw | Single-screw + crystallizer | |
|---|---|---|
| Predry | Often reduced or eliminated with vacuum | Typically 4–6 h crystallize + dry |
| Energy (industry ranges) | 0.18–0.28 kWh/kg | 0.25–0.35 kWh/kg including dryer |
| Capital | Higher (often +30–50%) | Lower |
| Flake / PCR | Preferred | Only dry, stable IV flake |
| Maintenance | Modular screws, more skill | Simpler gearbox and inventory |
IV and output bands
Put an IV target in the RFQ. Moisture and extra heat cut viscosity; cups then crack at the rim even if the former is new. Twin-screw helps when flake IV varies batch to batch because vacuum and mixing even the melt. Single-screw is fine when every gaylord is the same virgin grade.
Vendor guides often band twin-screw PET sheet at 500–3,000 kg/h and single-screw at 300–1,500 kg/h. Your cup line probably lives in the 350–800 kg/h band — buy the vent and dryer, not a pipe-line extruder you will never fill.
When we refuse a single-screw quote
RFQ says “70% washed flake” and no vacuum vent. We steer you to twin-screw. Cloudy sheet plus wasted resin beats the upgrade price. Send flake photos, IV target, and width — we mark one machine on the PET/PLA list.
Fault map — what the line is telling you
| Symptom | Likely cause | First check |
|---|---|---|
| Single-screw quote on 70% flake, no vent | Capital saving that becomes haze | We refuse this RFQ path — specify SI/XSI + vacuum |
| IV swings batch to batch on virgin-looking pellet | Flake mixed in without a target | Write IV and wash quality in the same sentence as the screw |
| Dryer runs 6 h and sheet is still cloudy | Flake load the crystallizer cannot finish | Twin-screw vacuum, or lower flake % |
| Pipe-line 2,000 kg/h machine sits at 400 kg/h | Bought vendor’s top band, not the cup line | Size 350–800 kg/h for most cup plants |
| Agent says “no drying” on a single-screw | Slogan copied from a vented twin | Single-screw lives on a real dryer |
RFQ checklist — send this in one email
Fill what you know; blank is better than a guess. Attach it on Get a Quote with photos of resin or flake.
- Expected flake % (0 / 15 / 40 / 70) and wash method
- IV target and whether batches will mix sources
- Width and kg/h of the cup program (not a pipe-line number)
- Dryer already on site? Dew-point log if you have one
- PLA share if any — dedicated or purged line
Frequently asked questions
Can twin-screw run 100% rPET flake?
Some vendor lines claim it. We specify flake quality, wash, and IV in the same sentence as the screw. Do not buy on the slogan alone.
Is single-screw dead for PET?
No. Virgin or PLA with a real dryer on LSI is a sound plant.
What is IV and why do I care?
Intrinsic viscosity. Moisture and heat cut it; cups go brittle. Flake lines need a target in the RFQ.
PLA on which screw?
Either if purged and dry. Dirty PP screws ruin PLA — use a dedicated or carefully cleaned line.