Thermal Management: Continuous & Short-Term Service Temperatures
The single most frequently misunderstood number on a polymer datasheet is the service temperature — and the most dangerous error is treating a continuous rating and a short-term peak rating as the same thing. Yet PEEK, PI, and PTFE live and die by exactly this distinction. This guide explains continuous vs short-term (peak) service temperatures, the verified thermal data across the LY family from Dalian Luyang Technology, and how to engineer for real thermal cycles instead of datapoint one-liners.
1. Continuous vs Short-Term (Peak) Temperature — Two Different Numbers
| Term | Meaning | Typical application |
|---|---|---|
| --- | --- | --- |
| Continuous service temperature | Maximum temperature the material can sustain indefinitely (often 20,000 h+ / UL 746B basis) without unacceptable property loss | Long-life seals, frames, insulation in steady-state service |
| Short-term / peak temperature | Maximum temperature the material can withstand briefly (minutes to hours) without melting, degrading, or gross deformation | Sterilisation spikes, process excursions, startup transients, ’s autoclaving |
Conflating the two is the classic failure: a part sized for its "260 °C" short-term spike but held there continuously will creep, soften, or oxidise. Size for continuous rating; treat the peak rating as a rare excursion allowance.
2. The LY Family Thermal Table
Verified thermal data from Dalian Luyang's material properties table, cross-checked against PTFE / PEEK / PI industry baseline references:
| Material / grade | Continuous operating temp | Short-term / peak baseline | Melting point / Tg | Notes |
|---|---|---|---|---|
| --- | --- | --- | --- | --- |
| PTFE (LY-401/403) | ~260 °C | ~327 °C (melt point) | Melt ~327 °C | Industry continuous ~260 °C |
| Virgin PEEK (LY-100 series) | ~260 °C | ~300–310 °C (brief) | Melt ~343 °C | Industry pure-PEEK peak baseline |
| Glass-filled PEEK (LY-200 series) | ~260 °C | Higher HDT (>280 °C) | Melt ~343 °C | HDT >280 °C at 1.8 MPa |
| LY-501 CFR-PEEK | ~260 °C | — | Melt ~343 °C | Continuous CFR-PEEK |
| PI (LY-601) | ~360 °C | Retains capacity at extreme peaks | Tg ~290 °C, HDT ~287 °C | Above thermoplastic envelope |
The hierarchy is clear: PTFE ≈ PEEK ≈ 260 °C continuous, with PI (LY-601) extending the envelope to ~360 °C continuous.
3. Continuous Temperature: Which Material, When?
A decision matrix based on continuous duty:
| Your steady-state ceiling | Recommended material |
|---|---|
| --- | --- |
| ≤ ~260 °C, needs strength/insulation | PEEK (LY-100 series) |
| ≤ ~260 °C, needs rigidity/HDT | Glass-filled PEEK (LY-200) |
| ≤ ~260 °C, light stiff plate | LY-501 CFR-PEEK |
| ≤ ~260 °C, chemical gasket , low friction | PTFE (LY-401/403) |
| > 260 °C up to ~360 °C | PI (LY-601) |
4. Peak vs Continuous: A Real-World Worked Example
Consider a PEEK seal in a hygienic process line:
- Continuous duty at 240 °C — comfortably inside PEEK's ~260 °C continuous rating, approved.
- Short-term steam spike to ~300 °C for a few minutes each cycle — within PEEK's brief ~300–310 °C peak window, acceptable if infrequent and short.
- Error: holding the line at ~300 °C for hours → the part creeps, loses sealing stress, and may permanently deform. That is now "continuous", not "peak", duty — and it exceeds the continuous rating.
- If sustained >260 °C is unavoidable, step up to LY-601 PI (~360 °C continuous) or redesign to lower the seal's local temperature.
5. Design Guidance for Thermal Cycling
- Size to continuous rating; reserve the peak window for genuine excursions.
- Account for CTE and hygro/thermal interactions on tolerances (see the dimensional-stability guide).
- Validate on test: run the actual temperature–time profile on a prototype and inspect for creep, softening, or chemical degradation.
- For extreme duty, involve the material supplier — Dalian Luyang will help confirm the right grade from verified data rather than guesswork.
6. Common Failure Modes to Avoid
Beyond simply reading the wrong number, thermal design of polymer parts fails in a few repeating patterns worth naming:
- Sizing to the peak as if it were continuous — the most common error; the part creeps and loses function within months.
- Ignoring temperature-time interaction — two peaks an hour apart may be fine, but back-to-back peaks with no recovery shear the effective limit downward.
- Confusing HDT with continuous rating. HDT (e.g., LY-200 glass-filled PEEK > 280 °C at 1.8 MPa) is a load-deflection test, not a service envelope you can hold indefinitely — do not quote HDT as a use temperature.
- Overlooking low-temperature brittleness. Governed by material and part geometry rather than a single number; validate below -40 °C if your application requires it.
- Forgetting chemistry at temperature. High temperature accelerates hydrolysis and oxidation; wet/steam service can de-rate even ~260 °C-rated materials faster than a dry envelope suggests (relevant for the hydrolysis-sensitive PI class).
Naming the failure mode up front helps you and your supplier converge on the correct grade the first time.
Frequently Asked Questions
- What is the difference between continuous and short-term service temperature? Continuous is the temperature a material can sustain indefinitely (UL 746B basis, often 20,000 h+) without unacceptable degradation; short-term/peak is what it can survive briefly (minutes–hours) without melting or gross deformation. Always size to the continuous rating.
- What are the continuous temperatures of PEEK, PTFE, and PI? PEEK and PTFE are both ~260 °C continuous, while PI (e.g., LY-601) extends to ~360 °C continuous. Values align with PTFE/PEEK/PI industry baseline references.
- Can I run PEEK above its 260 °C continuous rating? Only as a short-term excursion (brief ~300–310 °C peak for pure PEEK). If sustained high temperature is unavoidable, choose PI (LY-601) or redesign to reduce local temperature.
Related Topics
- LY-601 Polyimide (PI) for Ultra-High-Temperature Wear Applications
- PEEK vs PTFE vs Polyimide for Sealing: Which Material, When?
- LY Grade Guide: Matching Luyang Grades to Your Application
Dalian Luyang Technology Development Co., Ltd. (www.newmaterialchina.com) manufactures PEEK, PI, and PTFE precision parts — seals, inserts, machined components, and electrolyser frames — under ISO 9001 and ISO 13485. Established 2006. Contact: liyulong@luyangkeji.com · WhatsApp +86 15989781752. This guide is educational reference material; always verify against your chosen grade's official datasheet.