Dongying (Suzhou Dongying Electronic Technology Co., Ltd.) is a mold maker and injection molder in Suzhou, China. We build molds and molded parts for electronics cooling and automotive components, including fan impellers, fan frames and bases. For the wider process, see our guide to cooling fan impeller injection molding.
PBT, PA66-GF and LCP for impellers at a glance
Short answer: PBT is the steady all-rounder, PA66-GF is the tough option that needs moisture planning, and LCP is the specialist for very thin, stiff blades.
| General trend (grade-dependent) | Glass-filled PBT | PA66-GF | LCP |
|---|---|---|---|
| Moisture uptake after molding | Low | High; part swells and softens | Very low |
| Hot, humid service | Hydrolysis risk at elevated temperature unless an HR grade is used | Holds heat well; properties shift with moisture | Good |
| Filling thin blades | Good | Good | Very good |
| Orientation effects | Glass orientation drives warpage | Glass orientation drives warpage | Strong flow orientation; weak weld lines |
| Drying before molding | Required | Required | Required, to very low moisture |
| Relative material cost | Lower | Lower to mid | Higher |
These are general trends; check the datasheets of the exact grades you shortlist.
Glass-filled PBT: steady dimensions, but watch humid heat
Short answer: PBT suits impellers that need stable dimensions in ordinary indoor air; hot and humid duty calls for a hydrolysis-resistant grade.
PBT absorbs little water, so blade dimensions and balance do not drift much with the seasons. Its weak point is hydrolysis. BASF explains that moisture, particularly at higher temperatures, damages PBT and changes its properties, which is why many automotive specifications test at 85 °C and 85% relative humidity (BASF). LANXESS states that standard PBT is resistant enough up to about 60 °C, and that above this, non-stabilized grades can lose impact strength and elongation (LANXESS). Hydrolysis-resistant (HR) grades are made for this duty.
In the mold, glass fibers align with the flow, so the part shrinks less along the flow than across it. Distributor guidance on glass-filled PBT names this as the main cause of warpage (Sales Plastics). On an impeller, it shows up as blade pitch and plane variation.
PA66-GF: tough and heat-resistant, but plan for moisture
Short answer: PA66-GF gives tough, heat-resistant blades, but the part keeps absorbing water after molding, so its size and stiffness change over time.
DuPont data show unreinforced PA66 reaching about 2.5% water at 23 °C and 50% RH, and about 7.5% when immersed (DuPont Zytel guide). DuPont's design information adds that this moisture enlarges PA66 parts by about 0.6% at 50% RH, lowers stiffness and strength, and raises toughness. The change is slow and reversible (DuPont design module). Glass fiber reduces it but does not remove it.
A dry-as-molded impeller measured on day one is not the impeller in the field. Agree whether dimensions and balance are checked dry-as-molded, after conditioning, or both. ISO 1110 describes accelerated conditioning of polyamide test specimens at 70 °C and 62% RH, giving moisture close to the 23 °C / 50% RH equilibrium (ISO).
LCP: very thin, stiff blades, if the mold is designed for it
Short answer: LCP fills very thin sections and barely absorbs water, but its strength depends heavily on flow direction and weld lines.
Celanese's Vectra design guide describes LCP as keeping an ordered molecular structure in both melt and solid. That gives high stiffness along the flow, low moisture absorption, low thermal expansion and inherent flame resistance. It fills very thin walls at lower injection pressure than conventional semi-crystalline resins, without a strong tendency to flash (Celanese).
Properties are much higher along the flow than across it, although glass or mineral fillers reduce the difference. Weld lines are weak points; Celanese recommends very fast injection to improve weld line strength. For an impeller, that means gating so melt runs from root to tip along each blade and keeping weld lines away from blade roots. It also costs more, so use it where thin, stiff blades are really needed.
How the material choice changes the mold
Short answer: shrinkage, gating, mold temperature and venting all depend on the material, so freeze the grade before the mold is designed.
| Mold item | Why the material matters |
|---|---|
| Shrinkage allowance in the cavity | Each grade shrinks differently, and differently along and across the flow. A later switch can mean steel rework. |
| Gate position and type | Sets fiber or molecular orientation in the blades and decides where weld lines fall. |
| Mold temperature control | Affects crystallinity, surface and warpage; each grade has its own recommended range. |
| Venting at blade tips | Fast-filling grades such as LCP need good venting to avoid burns and short shots. |
| Drying and material handling | Wet PBT or PA66 degrades in the barrel; LCP needs very low residual moisture. |
Run mold-flow analysis with the actual grade. If two materials are still open, decide before steel is cut.
What to put in your RFQ for impeller material
Short answer: give the operating conditions and the acceptance method, not just a material name.
- Operating temperature and humidity, including any hot-humid test in your specification.
- Maximum speed, the balance requirement, and whether it is checked dry or conditioned.
- Preferred grade or approved alternates (brand and grade), color, and any flame rating your product standard requires.
- Blade thickness at root and tip, and any insert such as a shaft or metal hub.
- Critical dimensions and the moisture state in which they are measured.
- Annual volume, and whether you want the mold handed over to you or kept at Dongying with part supply.
Browse our cooling impeller examples and fan frames and covers, and read how we handle inspection and approval.
FAQ
What is the best material for a fan impeller?
There is no single best fan impeller material. Glass-filled PBT suits indoor electronics fans that need stable dimensions. PA66-GF suits blades that need toughness and heat resistance, provided moisture-related size change is planned for. LCP suits very thin, stiff blades where the higher material cost is justified. The right grade comes from your temperature, humidity, speed and balance requirements, confirmed by your own test plan.
Is PBT or PA66-GF better for an impeller in humid conditions?
It depends on temperature. PBT absorbs little water, so dimensions stay steadier in humid air, but standard PBT can hydrolyze when heat and humidity combine, which is why hydrolysis-resistant grades exist. PA66-GF does not hydrolyze the same way but absorbs water, which enlarges the part and lowers stiffness. Compare both against your actual humidity and temperature test conditions.
Why choose an LCP impeller?
An LCP impeller makes sense when blades must be very thin and stiff. LCP fills thin sections easily, absorbs very little moisture and has low thermal expansion. The trade-offs are higher material cost, strong flow-direction effects and weak weld lines. The mold must be gated so flow runs along the blades, and weld lines must be kept away from blade roots.
Does PA66 moisture absorption affect impeller balance?
It can. As PA66 absorbs water, the part grows slightly and its stiffness drops, and the change is slow and reversible. An impeller balanced dry-as-molded may therefore differ after weeks in humid air. Agree with your supplier whether balance and critical dimensions are checked dry, after conditioning, or both, and write that condition into the drawing or inspection plan.
Can I change the impeller material after the mold is built?
Sometimes, but it carries risk. The cavity is cut with a shrinkage allowance for one material, and other grades shrink by different amounts and in different directions. Gates, venting and cooling may also suit one material better than another. A switch can mean trials, process changes or steel rework, so it is best to fix the grade, or at least the shrinkage family, before tooling.
What should I send to discuss impeller material and tooling?
Send the 3D model and drawing, the operating temperature and humidity, maximum speed, balance requirement and how it is measured, any preferred or approved grades, flame rating needs, inserts, critical dimensions, and annual volume. Also say whether you want the mold handed over or kept at Dongying with part supply. With these inputs we can comment on moldability and the tooling approach.
Related pages
Sources
- BASF, "Avoiding Moisture Damage" (PBT hydrolysis): https://download.basf.com/p1/8a8081c57fd4b609017fdf6da526231c/en/Avoiding_Moisture_Damage
- LANXESS, "Pocan HR – Improved Hydrolysis Resistance" (PDF hosted by ALBIS): https://www.albis.com/dam/jcr:daeb9e72-d470-4abd-8029-fd05fb5f37a0/LANXESS_-_Pocan_HR_%E2%80%93_Improved_Hydrolysis_Resistance_-_LXS-HPM-072EN_-_2017-10.pdf
- Sales Plastics, "PBT Injection Molding: Preventing Warpage in 30% GF": https://salesplastics.com/pbt-injection-molding-preventing-warpage-30-gf/
- DuPont, Zytel and Minlon processing guide: https://dupont.materialdatacenter.com/links/processing/Zytel.pdf
- DuPont, Minlon and Zytel Design Information, Module II (PDF hosted by Distrupol): https://www.distrupol.com/Minlon_Zytel_Design__Info_Module_2.pdf
- ISO 1110:2019, Plastics — Polyamides — Accelerated conditioning of test specimens: https://www.iso.org/standard/76395.html
- Celanese, Vectra LCP Design Guide: https://www.celanese.com/-/media/Engineered%20Materials/Files/Product%20Technical%20Guides/LCP-027_VectraLCPDesignGuideTG_AM_0613.pdf