ABS, PP, PE, PC, Nylon: Recommended Mold Temperatures for Common Plastics

Introduction

Mold temperature is one of the most influential variables in injection molding and plastic processing. Set it correctly, and you get glossy surfaces, proper dimensional stability, and consistent part quality. Set it wrong, and you get sink marks, warping, short shots, and surface defects that render parts worthless.

Different plastics have dramatically different temperature requirements. Polypropylene wants to be kept relatively cool to prevent warping. Polycarbonate needs significant heat to flow properly into thin-wall sections. Nylon absorbs moisture from the air and needs careful drying and stable temperature control to avoid splay and blistering.

This reference guide provides recommended mold temperatures for the most common industrial plastics — PP, PE, ABS, PC, PA, PVC, PMMA, PBT, and POM — along with the reasoning behind each recommendation. Bookmark this page: it is the most-searched reference table in the plastic processing industry.

Why Mold Temperature Matters

The mold surface temperature directly controls:

• Surface finish quality — Higher mold temperatures produce glossier, more complete surface replication. Low temperatures cause weld lines, flow marks, and poor surface finish on Class-A visible components.
• Dimensional accuracy — Plastics shrink as they cool. Inconsistent mold temperature causes uneven shrinkage, leading to翘曲(warpage), dimensional variation between cavities, and out-of-spec parts.
• Material flow — Higher temperature reduces melt viscosity, improving flow into thin sections and reducing injection pressure requirements.
• Residual stress — Non-uniform cooling from uneven mold temperatures introduces molecular orientation and stress that manifests as warpage after ejection.

The mold temperature controller (MTC) is the tool that maintains these temperatures. ZILLION offers water-type MTCs (ZLW series, max 120°C) for standard applications and oil-type MTCs (ZLO series, max 180°C) for high-temperature engineering plastics.

Mold Temperature Reference Table: Common Plastics

Understanding the Relationship Between Melt Temp and Mold Temp

Mold temperature and melt temperature are two separate variables, though they interact. The melt temperature is the temperature of the plastic as it enters the mold (typically 20-40°C above the mold surface temperature for most materials). The mold surface temperature is what the MTC actually controls.

General rule: the mold should be hot enough to allow the material to fill the cavity completely without freezing off, but cool enough to solidify the part within a reasonable cycle time. Increasing mold temperature generally:

• Improves surface finish
• Reduces internal stress and warpage
• Extends flow length (reduces injection pressure)
• Increases cycle time (slower cooling)

Water Type vs Oil Type MTC: Which Do You Need?

Most standard plastics (PP, PE, ABS, PS) process perfectly well with water-type mold temperature controllers (ZILLION ZLW series, max 120°C). For engineering plastics and high-temperature applications, an oil-type MTC (ZILLION ZLO series, max 180°C) is required:

The Critical Role of Temperature Stability

Having the right target temperature is only part of the equation. Temperature stability — the MTC's ability to hold the setpoint consistently — matters equally. A mold that swings between 55°C and 65°C (a ±5°C variation) will produce parts with inconsistent dimensions and surface quality, even if the average temperature is correct.

Key factors affecting temperature stability:

• MTC P.I.D. tuning — Run auto-tune when changing molds or target temperatures. Factory defaults rarely match specific mold thermal dynamics.
• Cooling channel design — Poorly designed mold cooling circuits with dead zones, restricted flow, or uneven channel spacing cause temperature gradients across the cavity.
• Water flow rate — Insufficient flow (below MTC specification) means the heat picked up from the mold cannot be removed fast enough, causing the MTC to hunt and oscillate.
• Mold thermal mass — Large, thick molds require more stable heating systems. A small MTC controlling a large mold will struggle to maintain temperature during the first shots after a cold start.

Moisture Sensitivity: Why Drying Matters

Several of the most temperature-demanding plastics are also highly moisture-sensitive. Attempting to process them without proper drying causes immediate quality problems:

Use a hopper dryer for continuous drying during production. Never allow hygroscopic materials to sit exposed to ambient air — they reabsorb moisture within 30-60 minutes.

Troubleshooting: Temperature-Related Defects

Frequently Asked Questions

Q: Can I use a water MTC for polycarbonate?
A: For PC parts requiring mold temperatures up to 120°C, a water MTC (ZILLION ZLW series) is technically sufficient. However, above 90-100°C, water MTCs experience higher pressure and boiling risk. For PC applications above 100°C mold temperature, an oil MTC (ZLO series, max 180°C) is strongly recommended for safety and stability.

Q: How do I know if my mold temperature is actually correct?
A: The most reliable method is to use a contact or infrared thermometer to measure the mold surface temperature directly at the cavity during a production run. Compare this to your target setpoint. If there is a consistent gap (e.g., setpoint 60°C but mold surface reads 52°C), your MTC may be undersized, or there may be a flow restriction in the cooling circuit.

Q: What happens if mold temperature is too high?
A: Excessive mold temperature causes sink marks (especially in thick sections), flash at the parting line, extended cycle times, and in extreme cases, material degradation. It can also cause part ejection difficulties if the surface becomes too sticky.

Q: What is the most common mold temperature mistake?
A: Running the mold too cold. Operators often err on the side of low mold temperatures to reduce cycle time, but this causes a cascade of quality problems — warpage, short shots, poor surface finish, and dimensional inconsistency — that are more costly than the cycle time saved.

Q: Should mold temperature be the same for both halves of the mold?
A: Ideally yes — but in practice, many molds have different cooling requirements for the core and cavity sides. A temperature difference of up to 10-15°C between core and cavity is sometimes intentional to control differential shrinkage in specific part geometries. Document your stable operating temperatures once established.

Conclusion

Getting mold temperatures right is fundamental to quality plastic processing. This guide covers the recommended temperatures for the most common industrial plastics — but these are starting points. Your specific grade, part geometry, tooling, and quality requirements may require fine-tuning.

The key principles to remember: match your MTC type to your temperature requirement (water vs oil), dry hygroscopic materials properly, run P.I.D. auto-tune when changing molds, and measure actual mold surface temperature rather than relying solely on the MTC display.

ZILLION offers a complete range of mold temperature controllers — water type (ZLW, max 120°C) and oil type (ZLO, max 180°C) — plus hopper dryers for material drying. Contact our technical team for MTC sizing and application support for your specific material and part requirements.