Polypropylene (PP) is commonly injected at a melt temperature of 190–240°C (374–464°F). That range is a useful starting point, not a fixed production recipe. The best PP injection molding temperature depends on the grade, melt-flow rate, part wall thickness, color masterbatch, mould cooling and the actual performance of the injection unit.
For a new mould or a new PP grade, start within the resin supplier’s recommended processing window. Then adjust one variable at a time while checking fill balance, surface finish, shrinkage, cycle time and part weight. This approach produces a more stable process than raising barrel temperatures simply to cure a short shot.
What temperature is PP material injected at?
For general-purpose homopolymer and copolymer PP, many moulders begin with a rear-to-nozzle profile that gradually rises toward the front of the barrel. The target melt should be hot enough to fill the cavity without excessive injection pressure, but not so hot that the material degrades, flashes or creates excessive shrinkage.
| Process area | Practical starting range | What to watch |
|---|---|---|
| Rear barrel zone | 180–200°C | Stable conveying and plasticizing |
| Middle barrel zones | 190–220°C | Uniform melt and recovery time |
| Front barrel / nozzle | 200–230°C | Flow into sprue without drool or hesitation |
| Measured melt temperature | 190–240°C | Actual melt condition, not only controller setpoints |
| Mould temperature | 20–60°C | Surface appearance, shrinkage and cooling consistency |
Thin-wall parts, long flow lengths and heavily filled grades often need a warmer melt or mould than thick, simple parts. High-flow PP may fill easily at lower temperatures. Talc-filled, glass-filled, impact-modified or recycled PP should always be set from the grade data sheet first.
Set barrel temperature as a profile, not one number
PP should melt progressively through the barrel. A profile that rises from the feed zone toward the nozzle usually gives better control than setting every zone to the same temperature. Keep the rear zone moderate enough to prevent bridging or premature softening at the feed throat. Use the front zone and nozzle to maintain flow at the point of injection.
Do not rely only on the display temperature. A worn heater band, loose thermocouple, damaged wiring or poor barrel contact can make the actual steel temperature different from the setpoint. If the process changes from shift to shift with the same recipe, verify heater zones and temperature feedback before changing the moulding parameters.
How mould temperature changes PP parts
Mould temperature is closely tied to PP crystallinity, surface finish, shrinkage and cycle time. A cooler mould can shorten the cycle, but it may make flow marks, weld lines or internal stress more visible. A warmer mould can improve the appearance and fill of a demanding part, but it can increase cooling time.
For many commodity PP parts, start around 30–40°C and adjust according to the part. Keep both halves of the mould and all cooling circuits consistent. Uneven circuit flow can look like a material problem even when the melt temperature is correct.
Common PP molding symptoms and the temperature checks that matter
| Symptom | Temperature-related cause to check | First practical action |
|---|---|---|
| Short shot or hesitation | Melt or mould is too cold; nozzle restriction; slow fill speed | Confirm actual melt temperature, then increase in small steps before raising pressure |
| Flash at the parting line | Melt is too hot; excessive packing; mould or clamp issue | Reduce melt or hold settings only after checking clamp force and mould condition |
| Splay or silver streaks | Moisture or volatiles; excessive melt temperature; contamination | Check resin storage, regrind quality and residence time |
| Sink marks and high shrinkage | Low packing effectiveness; hot core area; insufficient cooling | Review gate freeze, hold profile and cooling balance before increasing barrel heat |
| Burn marks or brittle parts | Air trapped in the cavity; overheating; long residence time | Check venting and shot size, then reduce exposure to high melt temperature |
A practical setup sequence for a new PP part
- Confirm the PP grade, melt-flow rate, filler content and supplier processing range.
- Start in the middle of the recommended melt range with a gradual barrel profile.
- Set a moderate mould temperature and confirm coolant flow on each circuit.
- Use a short-shot study to understand the fill pattern before increasing packing pressure.
- Adjust temperature, speed, hold pressure and cooling one at a time. Record part weight and visual result for each stable setting.
- When the process is stable, lock the approved window into the machine recipe and train operators to monitor the critical limits.
PP is normally not highly moisture-sensitive in the same way as materials such as PET or nylon. However, poor storage, wet colorant, excessive regrind or long residence time can still introduce defects. Drying may be needed when the material supplier or the actual condition of the resin calls for it.
When temperature instability is really a machine issue
A barrel profile cannot compensate for failing electrical or mechanical components. If one temperature zone cycles widely, check the heater band, thermocouple, SSR/contactor, wiring and controller output. If recovery time changes, inspect screw and barrel condition, back pressure, hopper feed and the material path. For an older machine, keeping critical electrical and wear parts in stock reduces the time required to return a stable process.
Daya Machinery supplies injection molding machines and machine parts and consumables for production teams that need support with process stability, replacement components or machine selection.
Information to prepare before asking for a PP molding solution
A useful technical discussion starts with the part drawing or sample, part weight, wall thickness range, PP grade, target hourly output, mould cavity count, current machine tonnage, defect photos and the current process sheet. These details help determine whether the priority is temperature control, mould cooling, injection capacity, clamp force or a specific replacement part.
Frequently asked questions
Is 220°C too hot for PP injection molding?
Not necessarily. Around 220°C is within the normal processing range for many PP grades. Confirm the exact grade data sheet, actual melt temperature and residence time before deciding whether it is suitable.
What mould temperature should I use for PP?
Many PP parts start around 30–40°C, with a broader practical range of 20–60°C. The final setting depends on surface quality, shrinkage control, wall thickness and the cooling capacity of the mould.
Why does PP flash after I increase temperature?
Hotter PP flows more easily. If the mould is already near its limit, higher melt temperature can make flash more visible. Check clamp force, parting-line condition, venting and packing settings together rather than treating temperature as the only cause.
Need help selecting an injection molding machine or diagnosing a PP process issue? Send your part information, resin grade and current process conditions to the Daya Machinery team. We can help identify the machine capacity, temperature-control components or spare parts that best match the application.