Techniquesfor screw pullsInjection molding machine
fast, safe and machine-gentle
Screw pull is among maintenance heaviest jobs. This page packs standard steps, correct pull temperatures, ASACLEAN grade choice, and purge routines that stretch yourpull intervals further.
Why over-frequent screw pulls cost more than you think
When carbon and specks pile to crisis, most plants stop to pull and scrub screws — but true pull cost is never technician wages alone.
Whole-shift downtime lost
Traditional pull-scrub-reassemble runs 4-12 hours a time with zero output throughout, often spilling into delivery plans.
Screw and barrel damage
Cold-set plastic gripping the screw demands huge pull force, risking flight-edge and barrel-wall scoring; torching residue (Torching) alters metal structure — screws may bend or lose surface hardness.
Safety risks
Technicians handle parts hotter than 200°C — molten-plastic burns, plastic-fume inhalation, and injuries from long hard-residue scrubbing.
Why purging with PP or PE before pulls does not help
Low-viscosity PP and PE with no mechanical scrubbing power channels past carbon (Channeling), Channeling flowing past residue while cooling PP and PE shrink-grips screw flights — a lock making pulls harder than before.
See the difference in ten seconds of real video
Two identically run screws — differing only in purging-compound purge before pulling.
Screw pull after ASACLEAN purge
Compound layer wrapping flights hand-peels in long sheets with carbon coming along — no torching, no chiseling.
Peels like a bananaScrew pull with no pre-purge
Baked burn fills every flight; point-by-point steel picking, carbon debris scattering, many times longer.
Pick and scrub every flightASACLEAN Purging Compound demos — real site results depend on resin type, build-up level and machine settings.
Mechanism — why purging compound eases screw pulls
Mechanical purging compound works two ways at once: scrubbing residue off metal, and wrapping that residue in its own body to carry out together.
Micro scrub brushes
Glass Fiber grades act like countless tiny scrub brushes, cracking baked carbon in flights and around check rings (Check Ring) with no metal-scraping tools.
Peels in sheets
Low metal adhesion — cooled into the pull window, the compound grips tacky but never the steel, sliding screws out easier and hand or plier-peeling layers with residue in long sheets.
Never harms base metal
No torching, no wire brushes or chisels — screw and barrel walls unharmed, flight-to-barrel gaps stay in original spec, directly shaping next rounds melt quality.
4-step screw-pull SOP
Sequence built for speed and safety. The most-missed point is step 3 — pulling too fast while still too hot.
Step 1 Prep the system, drain old resin
Air-shot production resin out of the barrel, then bring barrel temperature into the running grade purge range. If old resin is low-heat-tolerant (below 220°C e.g. PVC, EVA, TPE), purge it out first with a low-temp grade, then climb temperature.
- Drain production plastic from the barrel fully.
- Set barrel temperature into the purge range per next-section table.
- Remove the Screen Pack first on extruders running Glass Fiber grades.
- Ready heat gloves, pliers and screw-support gear before starting.
Step 2 High-shear scrubbing
Feed purging compound, then raise Back Pressure and screw speed to the highest machine-safe levels — shear is what truly scrubs mechanically; set too low, compound flows past like PP and PE.
- Highest machine-tolerated Back Pressure and screw speed.
- Purge continuously until discharge runs clean with no specks or debris.
- Re-inject barrel-held compound fully once more before next step.
- For setting details see Back Pressure and Screw Speed
Step 3 Cool to the pull window
The result-deciding step. Switch off all heaters and wait for barrel temperature to fall evenly into the running grade pull range — pull too hot and compound stays runny and gooey, unpeelable; let it overcool and compound hardens into a stiff pull.
- Switch off every barrel heater zone.
- Wait until ALL zones sit evenly in the pull window, not just the front.
- Glass Fiber grades pull around 220-240°C; non-Glass-Fiber grades lower.
- While waiting, ready the screw-laydown area and lifting gear.
Step 4 Pull the screw and peel residue
Pull while still warm — friction runs far below cold-gripped plastic pulls. Then in heat gloves peel the compound layer in sheets; carbon comes along.
- Pull continuously without jerking, never levering against barrel walls.
- Hand or plier-peel layers while warm — easiest then.
- Inspect flight edges and check ring; log against next pull.
- Never torch or wire-brush screw surfaces needlessly.
Purge-temperature and pull-temperature table
Pull temperature varies results most. Ranges below are site starting points — always tune to old resin and real machine state.
| Grade group used | Old resin in machine | Purging temperature range | Screw-pull temperature range | Notes |
|---|---|---|---|---|
| NewEX / YG (Glass Fiber reinforced) | PP, PE, PS, ABS and general engineering plastics | 240–260°C | 220–240°C | Standard screw-pull range; compound body just right for peeling. |
| PX2 (Glass Fiber reinforced, heat-tolerant) | PPS, PEEK, LCP and high-temp resins | 300–380°C | 280–300°C | For old resin above 300°C; grade range 280-420°C. |
| Non-Glass-Fiber grades (RU, RE) | Jobs banning glass fiber, or limited machines | 200–240°C | 195–205°C | Lower scrubbing; fits mild residue or Hot Runner machines. |
| Special case: Low-heat-tolerant old resin (PVC, EVA, TPE below 220°C) — purge old resin first with a low-temp grade at 200-220°C, then switch to the screw-pull grade and climb into the table purge range. Never rush temperature while PVC still sits in the barrel. | ||||
For TDS or machine-matched values, contact CSC technicians for documents and site-specific advice.
Pick grades for screw-pull jobs
Screw-pull jobs need high mechanical scrubbing — purpose-built grades carry Glass Fiber, trading limits you must know first.
ASACLEAN NewEX
200–330°CThe main screw-pull grade for heavy carbon, specks and black spots in non-Hot-Runner injection machines, plus compounding and profile extrusion.
ASACLEAN YG
200–330°CThe value alternative for carbon, specks and screw-pull jobs where site terms allow.
ASACLEAN PX2
280–420°CFor high-temp resins like PPS, PEEK and LCP beyond standard-grade reach.
The best screw pull is needing fewer of them
The SOP above makes one pull single faster and safer — but bigger money comes from fewer pulls and that is routine purging job. Carbon never forms in a day; it layers from held resin in dead spots under repeated heat. Break that cycle early and screws never reach scrub-out state.
Routine Purging
Purge with compound every color or resin-grade change instead of production-plastic chasing, sweeping degrading old resin from dead spots before carbon layers.
Routine purging principlesPeriodic Purging
Long same-material runs still build residue; schedule mid-production purges, e.g. weekly, resetting barrel cleanliness before specks seed.
See purging stepsMachine Sealing
Before overnight, weekend or long-holiday stops, hold a sealing-capable purging grade in the barrel against oxygen reacting with leftover resin, cutting both burn and startup scrap.
How to seal machinesPurge at first signs
At first part specks, purge at once with a high-power grade while residue has not fully hardened; most cases finish at the machine with no screw pull.
Black-speck handlingReactive working
Chase with production plastic, no scheduled purges, no stop sealing.
- Barrel residuelayers continuously.
- Part specksrecur, denser.
- Reason for pullsmachine face cannot fix it.
- Pull-state workhardened residue needing torch and chisel.
Pull frequency
Proactive working
Purge every color change, periodic purges, seal before every stop.
- Barrel residueswept before carbon.
- Part specksfall and stay controlled.
- Reason for pullsfollow the maintenance plan, not emergencies.
- Pull-state workpeelable residue, no torching.
Pull frequency
Case study: m-PPE (Xyron) injection jobs
A plant running routine purging with pre-weekend sealing reported contamination-and-speck scrap falling from 3.0 percent to 0.3 percent with pull intervals stretched significantly since residue never reaches crisis. Figures are a single-case result; each plant outcome depends on resin, production rhythm and routine discipline.
Reclaimable yearly time and money
Enter your plant figures to value reclaimable time when per-pull time falls to about 1.5 hours.
Defaults are assumed values for preliminary estimates only.
Assumes post-compound pulls take about 1.5 hours a time; excludes falling scrap value, longer screw life, and fewer pulls from the above routines.
Shop-floor FAQ
Why does purging with PP or PE before pulls not work?
Is soaking NewEX in the machine truly banned?
Must Screen Packs come out before Glass Fiber grades?
What happens pulling too hot?
With purging compound, are pulls still needed?
Can Hot Runner machines use screw-pull grades?
Read more
Want screw pulls done in one shift?
Send machine, resins used, running temperature and pull frequency for CSC technicians to sequence work and pick site-fit grades, with trial samples available.