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 cooling fan frames and housings, impellers and fan bases.
What a server fan frame has to do
Short answer: the frame is the reference part of the fan, so its stiffness, flatness and bore position decide how well the whole fan assembles and runs.
| Frame feature | Function | What it means for the mold |
|---|---|---|
| Bearing tube or hub seat | Holds the motor and bearings on the fan axis | Often a metal insert; position relative to the venturi is critical |
| Struts (spokes) | Connect the hub to the outer frame | Thin, loaded features; weld lines and fiber orientation matter |
| Venturi (inner shroud) | Surrounds the impeller tips | Roundness and concentricity set the tip clearance |
| Mounting flanges and holes | Fix the fan in the chassis or fan tray | Flatness and hole position; may need side actions |
| Wire channel and clips | Route and hold the lead wires | Small undercuts, usually slides or lifters |
Choosing the frame material
Short answer: glass-filled PBT, PA66 and PPS are the usual choices, and the decision depends on temperature, moisture behavior and any flame rating your product requires.
| General trend (grade-dependent) | PBT-GF | PA66-GF | PPS-GF |
|---|---|---|---|
| Stiffness at elevated temperature | Good | Good | Very good |
| Moisture effect on dimensions | Low | Noticeable; part grows as it absorbs water | Very low |
| Flame resistance | Needs an FR grade | Needs an FR grade | Many grades inherently flame resistant |
| Mold temperature | Moderate | Moderate | High, for full crystallinity |
| Abrasion on the mold | Moderate | Moderate | High with glass or mineral fill |
| Relative material cost | Lower | Lower to mid | Higher |
These are general trends; check the datasheets of the exact grades you shortlist. If your product needs a UL 94 rating, note that UL rates a material at a tested thickness, so compare the grade with the thinnest wall of your frame (UL Solutions). Our fan impeller material comparison covers PA66 moisture and PBT hydrolysis in more detail.
Molding in the bearing tube
Short answer: a molded-in metal bearing tube usually gives a stronger, better-located hub than pressing a sleeve in later, but the insert has to be defined and supplied correctly.
Solvay's Ryton PPS design guide notes that molded-in inserts are generally preferred over interference fits for larger components such as hubs or bearings, and that the insert should be designed so the load is carried through the metal rather than the plastic (Solvay). For a fan frame, that usually means a knurled or grooved metal tube held on a locating pin in the mold.
Points to agree early:
- Who supplies the insert, and its drawing and revision.
- How it is located in the mold, and which datum the bore position is measured from.
- Whether the bore is used as molded or finished afterwards.
See also our insert molding inputs.
Struts, weld lines and flatness
Short answer: gate position decides where weld lines fall and how glass fibers line up, which in turn sets strut strength and frame warpage.
Melt has to split around the hub and the venturi and meet again, so weld lines are unavoidable somewhere. The Ryton guide explains that weld lines are resin-rich because glass fiber does not cross the interface, which lowers strength; it recommends placing them in low-load areas and designing for rapid injection, thorough packing and good venting at the weld (Solvay). The same guide notes that glass-filled PPS is stronger along the flow than across it.
In practice, keep weld lines off strut roots and loaded mounting holes, run flow along the struts where possible, and balance filling between the four corners so the mounting faces stay flat. Compare gate options with mold-flow analysis on the actual grade before steel is cut; fixing warpage later usually means process changes or steel rework.
Tip clearance and venturi roundness
Short answer: the gap between impeller tips and the venturi affects pressure and efficiency, so venturi roundness and its position relative to the bearing tube deserve their own inspection point.
Research on axial fans shows that leakage through the tip clearance forms a vortex that reduces efficiency, and that the effect grows as the fan works against higher pressure (Pelz and Karstadt, TU Darmstadt). Server fans often run at such high-pressure points. A venturi that is oval or off-center from the bearing tube forces a larger nominal gap to avoid rubbing.
In the mold, roundness depends on uniform walls, even cooling around the shroud and stable core alignment. On the drawing, give the venturi and bore a shared datum scheme, so the frame and the impeller are checked against the same reference.
Mold construction for glass-filled frames
Short answer: glass-filled frame materials wear molds, so steel selection, replaceable gate inserts and mold temperature control should match the expected production life.
Solvay states that glass and mineral fillers in PPS are abrasive, recommends hardened tool steels for long-run production molds, and notes that replaceable gate blocks are often used because wear is highest at the gates (Solvay). The same guide stresses that mold temperature strongly affects PPS crystallinity and dimensional stability. Glass-filled PBT and PA66 also wear gate and high-flow areas over long runs. Side holes and wire clips add slides or lifters, and even cooling around the venturi helps roundness and flatness.
What to put in your RFQ
Short answer: send the geometry, the material requirement and the inspection method, not only the frame size.
- 3D model and drawing with revision, including the datum scheme for bore, venturi and mounting holes.
- Material grade or approved alternates, color, and any flame rating your product standard requires.
- Bearing tube or other insert drawings, and who supplies them.
- Critical features: bore position, venturi roundness, mounting-face flatness, hole positions.
- How parts are measured, for example dry-as-molded or conditioned for PA66.
- Annual volume and expected mold life.
- Whether the mold will be handed over to you or kept at Dongying with part supply; see tooling and supply scope.
Read how we handle inspection and approval and mold making.
FAQ
What is a fan frame mold?
A fan frame mold is the injection mold that produces the plastic housing of an axial cooling fan: the outer frame, mounting flanges, struts, venturi and hub or bearing-tube seat. For server fans it often includes a metal bearing tube molded in place, side actions for holes and wire clips, and a gate layout chosen to control weld lines, warpage and the roundness of the venturi around the impeller.
Which material is best for a server fan frame?
There is no single best material. Glass-filled PBT is a common, cost-effective choice with low moisture uptake. Glass-filled PA66 is tough but changes size as it absorbs water. Glass-filled PPS keeps its stiffness at higher temperatures, absorbs very little water and many grades are inherently flame resistant, but it costs more and needs a hotter mold. Choose against your temperature, flame rating and dimensional requirements, confirmed by your own tests.
Should the bearing tube be molded in or pressed in?
For most server fan frames, a molded-in metal bearing tube is the stronger option. Material suppliers such as Solvay note that molded-in inserts are generally preferred over interference fits for hubs and bearings. Pressing in later can work, but it adds a step and can stress the plastic around the bore. Either way, define the insert drawing, who supplies it and how its position is measured.
Why do fan frames warp after molding?
Warpage usually comes from uneven shrinkage. Glass fibers align with the flow, so the material shrinks differently along and across it, and a frame that fills unevenly from corner to corner tends to twist. Uneven cooling and thick sections near the hub add to it. Gate layout, balanced filling, uniform walls and even cooling, checked with mold-flow analysis before steel is cut, are the main tools to control it.
How does the frame affect fan performance?
The frame sets the gap between the impeller tips and the venturi. Studies on axial fans show that leakage through this tip clearance reduces efficiency, especially when the fan works against high pressure, as server fans often do. A venturi that is oval or off-center from the bearing tube forces a larger gap. Frame stiffness, mounting-face flatness and strut design also influence how the fan behaves in the system.
What should I send to discuss a fan frame mold?
Send the 3D model and drawing with revision and datums, the preferred or approved material grades, any flame rating your product requires, insert drawings and supply responsibility, critical features such as bore position and venturi roundness, the measurement method, annual volume and expected mold life. Also say whether you want the mold handed over or kept at Dongying with part supply. With these inputs we can discuss the tooling approach.
Related pages
Sources
- Solvay Specialty Polymers, Ryton PPS Design Guide (weld lines, fiber orientation, molded-in inserts, tool steels, mold temperature; PDF hosted by Drake Plastics): https://drakeplastics.com/wp-content/uploads/2020/01/Ryton-PPS-Design-Guide.pdf
- UL Solutions, Combustion (Fire) Tests for Plastics (UL 94 classifications): https://www.ul.com/services/combustion-fire-tests-plastics
- UL Standards & Engagement, UL 94 Tests for Flammability of Plastic Materials for Parts in Devices and Appliances: https://www.shopulstandards.com/ProductDetail.aspx?productId=UL94
- Pelz, P. F. and Karstadt, S., "Tip Clearance Losses – A Physical Based Scaling Method", International Journal of Fluid Machinery and Systems: https://www.jstage.jst.go.jp/article/ijfms/3/4/3_4_279/_pdf/-char/ja