Polypropylene
- Tough, light, and easy to fill in thin sections
- Suits fans that run near room temperature
- Softens and creeps sooner as air gets warmer
Molded part guide: fan blades
Injection Molded Fan Blades
A fan blade is a long, thin, twisted surface that has to hold its shape while air pushes back on it. The angle it leaves the tool with is not always the angle it keeps, and a blade that flattens a little moves less air and makes more noise. Holding the shape is most of the job.
Thin and twisted
A blade only works at the angle it was designed for
Axial cooling fans, ventilation fans, condenser fans, and blower wheels.
A blade is thin near its tip and thicker near its root, and it twists along its length. That shape is set by how the air has to meet it. A blade that is even a little flatter than intended pushes less air, draws less power, and makes a different noise, so the shape that comes out of the tool matters more here than the surface finish does.
Thin, twisted sections cool unevenly, and the blade relaxes as it cools. The hotter side pulls more than the cooler one and the blade untwists a little. Balanced cooling on both faces, a feed position that sends melt along the blade rather than across it, and a fixture that holds the fan while it finishes shrinking all keep the angle where it was drawn.
Then service takes over. Plastic under a steady load creeps, meaning it slowly changes shape and does not fully come back. A fan running warm all day, with air pressure on the blades, creeps most at the root where the bending is highest. Filled resins creep far less than unfilled ones, which is why warm-running fans usually use a filled grade.
Noise is set at the tip. The gap between the blade tip and the shroud is one of the strongest noise drivers in a fan, and a blade that has crept or warped changes that gap around the circle. So the blade shape, the fan stiffness, and the shroud fit are decided together, not one after the other.
Features
Blade areas and what each one controls
Shape, stiffness, and clearance all matter more than finish.
| Feature | Purpose | Design note |
|---|---|---|
| Blade angle | How much air moves | Must survive cooling and service |
| Blade root | Highest bending | Thicker section with a generous fillet |
| Blade tip | Sets noise with the shroud | Even gap around the circle |
| Hub | Drives the fan | Balanced feed and a positive shaft drive |
| Section along the blade | Fills a long thin part | Thins toward the tip without stopping the flow |
Creep
A warm fan slowly changes shape
Plastic under steady load creeps, and a blade root carries load all day.
- Steady air pressure plus warm air makes the blade slowly bend and stay bent
- Creep is worst at the root, where bending is highest
- Filled grades creep far less than unfilled ones at the same temperature
- A crept blade changes the tip gap, which is heard as a change in noise
Resin
Polypropylene blades or filled nylon blades
Room temperature fans and warm running fans pull in different directions.
Filled nylon
- Stiff and holds its shape when warm
- Keeps the blade angle over a long service life
- Needs more care to fill a long thin blade evenly
Drawing
What to send with a fan
Air performance and temperature drive the resin and the shape.
Fan CAD with blade profiles and hub
Speed, airflow, and pressure targets
Air temperature and how long the fan runs
Shroud and the tip gap you expect
Noise target, if you have one
Expected annual volume
Keep reading
Related guides
Rotating parts, filled resins, and why thin parts change shape.
Impellers
Pump wheels and balance.
ImpellersDucting
What the fan blows through.
DuctingMotor housings
What drives the fan.
Motor housingsSafety guards
Grilles in front of a fan.
Safety guardsWarpage
Blades that leave the tool twisted.
WarpageThin wall design
Filling long thin sections.
Thin wall designPolypropylene
A common blade resin.
PolypropyleneIndustrial and transportation
How we support industrial programs.
Industrial and transportationMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded fan blades
Why does the fan move less air than the design predicted?
The blade angle has usually flattened, either as the part cooled or later in service. Balanced cooling, a feed that runs along the blade, and a holding fixture recover most of the loss. Measuring the blade angle on parts taken straight from the press, and again after a day, separates cooling from creep.
Why did the fan get noisier after months of running?
Creep at the blade roots changes the tip gap around the circle. A filled grade, a slightly thicker root, or a lower service temperature all slow it down. Running a fan hot for an extended period and remeasuring the tip gap is the practical way to see how much creep to expect.
Can a fan be molded in one piece with its hub?
Usually yes, and one piece keeps the fan balanced. Very large fans are sometimes molded as a hub and separate blades that are assembled, which lets a broken blade be replaced.
How thin can a blade tip be?
It depends on the resin and how far the melt has to travel from the hub. We check the fill early and suggest where the section has to stay thicker so the tip does not fall short.
Next step
Quote a fan with its duty point
Upload the fan and tell us the speed, air temperature, and shroud. DFM feedback covers feed position, blade angle control, and resin choice.