Melt Temperature in Injection Molding: Reference Ranges by Material

Getting melt temperature injection molding parameters wrong costs you parts. Burn marks, splay, short shots, and degraded mechanical properties all trace back to running outside the resin manufacturer’s recommended melt window. The table below covers 20 common resins. Bookmark it, print it, tape it to the press. We reference it daily in our shops when qualifying offshore tools built to SPI Class 101 through 104 standards.

How to Read This Melt Temperature Table

Every value listed reflects the melt temperature at the nozzle tip, not the rear barrel zone. The nozzle reading is your real-time confirmation that material is processing correctly. Rear barrel zones run cooler by design to prevent premature melting and feed-zone bridging.

The “Typical Melt Range” column gives you the working window. The “Minimum Safe Melt” is the floor below which fill pressure climbs, weld lines weaken, and cosmetic defects increase. The “Degradation Onset” column is the ceiling. Cross it and you risk molecular chain scission, off-gassing, color shift, and a reduction in tensile strength that can exceed 15% according to material data sheets from BASF and Sabic.

Shrinkage values are listed because melt temperature directly affects volumetric shrinkage. Running 20°F above the nominal target can reduce shrinkage by 0.1 to 0.2% on semi-crystalline resins, shifting your part dimensions outside tolerance without changing the mold steel.

Melt Temperature Injection Molding Reference Table by Resin

Resin	Grade Examples	Typical Melt Range (°F)	Min Safe Melt (°F)	Degradation Onset (°F)	Typical Shrinkage (%)	Notes
ABS	Cycolac MG47, Lustran 348	410 to 500	390	520	0.4 to 0.7	Moisture-sensitive; dry 4 hrs at 180°F
Acetal (POM)	Delrin 100, Celcon M90	380 to 430	360	450	1.9 to 2.3	Narrow window; off-gassing of formaldehyde above 450°F
Nylon 6 (PA6)	Ultramid B3S, Zytel 73G30	460 to 510	440	540	0.6 to 1.4	Hygroscopic; dry to below 0.2% moisture
Nylon 66 (PA66)	Zytel 101, Vydyne 21SPC	500 to 550	480	570	0.8 to 1.5	Higher crystallinity than PA6; sharper freeze-off
PC (Polycarbonate)	Lexan 141, Makrolon 2805	540 to 610	520	640	0.5 to 0.7	Dry 4 hrs at 250°F; hydrolytic degradation if wet
PC/ABS Blend	Cycoloy C1200, Bayblend T65	480 to 540	460	560	0.5 to 0.7	Balance thermal stability of PC with flow of ABS
HDPE	Marlex HHM 5502, Hostalen GM 5010	380 to 480	360	500	1.5 to 3.0	Wide window; high shrinkage demands cooling
LDPE	Petrothene NA952, Escorene LD251	320 to 430	300	460	1.5 to 3.5	Low viscosity; watch flash on worn parting lines
PP Homopolymer	Moplen HP500N, Braskem H110-02N	400 to 480	375	500	1.2 to 2.2	High shrinkage; warp common in non-uniform walls
PP Copolymer	Moplen EP548R, Asylon 7823	400 to 480	375	500	1.0 to 2.0	Better impact than homopolymer; similar processing
PET	Rynite 530, Valox DR48	500 to 560	480	580	0.2 to 0.8	Dry aggressively; IV drop above 570°F
PBT	Celanex 2002, Valox 315	460 to 510	440	530	0.9 to 1.8	Fast crystallization; short cycle times possible
PPS	Ryton R-4, Fortron 1140L4	590 to 650	570	680	0.2 to 1.0	Requires H13 or hardened tool steel; aggressive on tooling
PEEK	Victrex 450G, Ketaspire KT-820	680 to 760	660	800	0.9 to 1.5	Barrel and nozzle must reach setpoint before shooting
PVC (Rigid)	Geon 87444, Vinnolit S4170	320 to 380	300	400	0.2 to 0.6	HCl release above 400°F; purge aggressively on shutdown
PMMA (Acrylic)	Plexiglas V825, Altuglas V920	430 to 500	410	530	0.2 to 0.8	Dry 4 hrs at 190°F; streaks indicate moisture or overheating
GPPS	Styron 685D, Total 1340	380 to 480	360	500	0.4 to 0.7	Brittle above Tg; watch gate vestige on cosmetic surfaces
HIPS	Styron 478, Edistir RG1500	380 to 480	360	500	0.4 to 0.7	Rubber modifier reduces flow; increase melt temp 10 to 20°F vs GPPS
TPU	Estane 58300, Pellethane 2103	380 to 430	350	450	0.5 to 2.0	Shear-sensitive; avoid high back pressure
TPE / TPV	Santoprene 101-64, Hytrel 4056	350 to 430	330	460	1.0 to 3.0	Grades vary widely; confirm with resin supplier datasheet

Setting Your Barrel Temperature Profile for Injection Molding Processing Temperature

A barrel temperature profile is not a flat line. You set zones from rear to front, then add the nozzle. A typical ascending profile runs the rear zone 30 to 50°F cooler than the front zone, with the nozzle at or 10°F above the front zone target. This prevents feed bridging at the rear while delivering fully plasticized melt at the gate.

For a standard PA66 run targeting 520°F nozzle temperature, a four-zone profile might look like this: Zone 1 (rear) at 460°F, Zone 2 at 480°F, Zone 3 at 500°F, Zone 4 (front) at 510°F, nozzle at 520°F. Verify with a pyrometer or thermocouple probe at the nozzle tip before the first shot. Controller displays are not ground truth. We have seen controller readings run 15 to 25°F high on older Asian machines with thermocouple drift.

Some resins call for a descending or flat profile. Rigid PVC runs nearly flat across all zones to minimize residence time at any single point. PEEK requires the entire barrel to reach 680°F minimum before injection begins, or you risk an incomplete melt plug that damages the screw and check ring.

Resin Melt Temperature vs. Mold Temperature: Don’t Confuse Them

Resin melt temperature and mold temperature are separate variables. Melt temp is the material condition entering the cavity. Mold temperature is the steel surface condition receiving it. Both control part quality, but through different mechanisms.

Mold temperature drives crystallinity in semi-crystalline resins. Running PA66 at a 520°F melt into a 160°F mold produces different crystallinity and shrinkage than running the same melt into a 200°F mold. The injection molding processing temperature you set on the barrel controls viscosity, flow length, and shear heat. The mold temperature controls skin formation rate and dimensional stability.

Mixing up the two is one of the most common setup errors we see on first articles from new offshore suppliers. A quoted “process temperature” from a Chinese molder sometimes means mold temperature, sometimes melt temp, and occasionally neither. Always request a full process data sheet that lists all five barrel zones, nozzle setpoint, mold coolant temperature in and out, and cycle time.

Thermal Degradation Risks and How to Catch Them Early

Every resin in this table has a degradation onset temperature. Cross it and you trigger one or more failure modes: hydrolysis in PC and PET, formaldehyde off-gassing in acetal, HCl release in PVC, chain scission in PA66 that reduces tensile strength. These are not recoverable with downstream processing.

The injection molding melt temp by material matters most during purging, startups, and extended downtime. A 10-minute screw-stall at 570°F in an acetal run can char enough material to contaminate the next 50 shots. Residence time in the barrel amplifies the risk. ISO 20457 specifies shot size selection in terms of barrel utilization; a good rule from that standard is keeping shot size between 20% and 80% of barrel capacity to control residence time and avoid excessive resin dwell at processing temperatures.

Watch for these early warning signs of degradation:

• Discoloration on purge shots, especially brown or black streaks
• Small bubbles or splay on the part surface not explained by moisture
• Unexplained drop in part weight from shot to shot
• Gas burning at the last-fill location in the cavity
• Odor changes at the press, particularly sharp or acrid smells

Worked Example: Setting Up a PC/ABS Run After a Tool Ships from China

Your H13 core-insert tool for a 6 oz PC/ABS structural cover arrives from Shenzhen. The supplier processed it on a 200-ton machine at “520°C,” which you correctly interpret as 520°F, not Celsius. Good. That falls inside the 480 to 540°F window from the table above.

You set your barrel temperature profile on your 220-ton press: Zone 1 at 460°F, Zone 2 at 490°F, Zone 3 at 510°F, Zone 4 at 520°F, nozzle at 530°F. You verify nozzle temp with a contact pyrometer. Measured reading is 512°F, 18°F below the controller setpoint. You adjust the controller to 548°F to hit 530°F measured. You run a short-shot study to confirm fill. Weld line location matches the simulation. First-article dimensional results pass on critical features. That is the correct workflow.

If the supplier had run 480°F barrel temperatures and the part filled only because of excessive injection pressure (above 18,000 psi on a thin 2.5mm wall), that is a setup that will cause inconsistency at volume. Melt temperature and injection pressure are traded against each other. Optimizing melt temp properly reduces required injection pressure and improves long-term part consistency.

Frequently Asked Questions

What is the difference between melt temperature and processing temperature in injection molding?

Melt temperature is the actual temperature of the molten plastic as measured at or near the nozzle tip. Processing temperature is a broader term that can refer to barrel setpoints, nozzle setpoint, or mold temperature depending on who uses it. Always clarify which variable is being referenced when exchanging process data with a supplier.

Why does my actual nozzle temperature differ from the controller setpoint?

Thermocouple drift, heater band degradation, and poor contact between the heater band and the nozzle body all cause setpoint-to-actual gaps. On machines over five years old, gaps of 15 to 30°F are common. Verify with a calibrated contact pyrometer at the start of every new material run and after any maintenance that involves the nozzle or barrel heaters.

How does melt temperature affect shrinkage in semi-crystalline resins?

Higher melt temperatures increase molecular mobility and reduce viscosity, which allows more complete packing but also affects the crystallization rate as the part cools. Running a semi-crystalline resin like PP or PA66 at the high end of the melt window typically reduces shrinkage by 0.1 to 0.2% compared to the low end of the window, because higher melt temperatures reduce back-pressure in the cavity and allow more packing. Tight-tolerance parts require you to lock in melt temp as tightly as plus or minus 5°F.

What tool steel should I specify for high-temperature resins like PPS or PEEK?

PPS and PEEK both require H13 tool steel hardened to 46 to 52 HRC minimum for core and cavity inserts. P20 is too soft and will show wear at the gate, parting line, and ejector pin bores within 50,000 cycles on an abrasive glass-filled PPS grade. For PEEK with 30% carbon fiber filler, some shops upgrade to powder-metallurgy steel like CPM 10V for critical wear surfaces.

How do I handle a resin with a narrow melt window like acetal during offshore tooling trials?

Request that your Chinese tool shop use a dedicated acetal machine that has been thoroughly purged with HDPE before trials begin. Acetal has a 70°F usable window between minimum safe melt (360°F) and degradation onset (450°F). Any contamination from a higher-temperature resin sitting in the barrel will push the acetal past its degradation point and generate formaldehyde gas. Insist on a process data sheet with time-stamped barrel readings from the actual trial, not default machine settings.

Use our clamp force calculator and injection molding consulting services to validate your full process window before approving first articles on any offshore tool. A process review at qualification costs a fraction of a $24,000 tool rework after production release.