Grain dryers run axial or centrifugal fans continuously for weeks during harvest, moving heated air through a grain column. The impeller hub locks the blade roots, transmits motor torque to the blade set and holds the assembly true on the shaft taper or shaft bore. It is a rotating part, so balance, bore concentricity and freedom from casting defects matter more than raw strength: a hub that is out of balance or cracked at a blade root puts vibration into the fan housing, the bearings and the dryer structure. Dryer OEMs and service companies stock these hubs because a failed fan during harvest stops the whole intake line, so availability before the season is worth more than unit price.
Specifications
| Parameter | Value |
|---|---|
| Material | ductile iron |
| Casting process | Silica sol lost wax investment casting |
| Dimensional tolerance | ISO 8062-3 CT6 to CT7 |
| Machined tolerance | ISO IT7 |
| Surface treatment | Shot blast |
| Documentation | EN 10204 3.1 material certificate; PPAP / FAIR on request |
Material and process
Still, EN-GJS-450-10 is a ferritic ductile iron with 450 MPa tensile strength, 310 MPa proof strength and 10% minimum elongation. The high elongation and fully ferritic matrix give excellent toughness and vibration damping at the blade roots, which see cyclic bending from air load and blade-passing excitation. It is also the easiest of the ductile grades to machine, which matters on a hub with a bored taper, keyway and several blade-root faces. Castings are produced by silica sol lost wax investment casting, which holds the blade root slots and the hub web geometry as cast, and are annealed to the ferritic condition specified in the standard.
Casting and CNC route
The route is wax injection, shell build, dewax, pour, knock-out, cut-off, shot blast, then ferritising anneal. CNC turning bores the shaft taper or cylindrical bore and faces the hub in one chucking so the bore-to-face relationship is controlled; the keyway is then broached or machined on a machining centre, and the blade root slots are finish milled with a dedicated fixture that indexes each slot to the same datum. Because all blade roots are generated from one datum, the assembled blade set is symmetrical, which keeps the residual unbalance low and shortens the buyer’s balancing operation.
Tolerances and inspection
Generally, we quote casting tolerances to ISO 8062-3 CT6 to CT7. We machine the shaft bore or taper to the drawing, typically ISO IT7, with runout and concentricity controls to the blade root datum so the running assembly stays true. Slot pitch, slot width and radial position are checked on CMM or with a purpose-built gauge, since uneven pitch is the usual cause of fan unbalance. Surface roughness is verified on the bore and taper contact area, and a balance check on a mandrel is offered as an option before packing. Additionally, we report hardness per heat lot.
Quality & compliance
Blade root radii and the hub-to-web transitions are magnetic particle inspected, because those radii carry the cyclic bending load and are where a rotating part fails first. In general, dye penetrant inspection covers as-cast surfaces that cannot be magnetised. We offer ultrasonic testing on the hub boss section where geometry allows. Additionally, EN 10204 3.1 certificates give chemical analysis, tensile results and hardness, with metallographic verification of nodularity and ferritic matrix. Where the buyer requires it, we pack balance records with the inspection report. In addition, PPAP or FAIR documentation is available on request.
Packaging and logistics
We clean hubs, the bore protected with a cap or VCI liner, bagged and boxed with dividers so machined faces do not touch. Overall, cartons are palletised, strapped and stretch-wrapped for container shipment. Grain dryer programmes are strongly seasonal, so Ningbo Ruican builds to a rolling forecast and holds finished stock for release before the harvest, with split shipments available to OEM plants and to service depots.
CTA
- 3D model and drawing with shaft bore or taper, keyway and blade root slot geometry
- Grade: EN-GJS-450-10, ferritic condition, hardness band
- Blade count, slot pitch tolerance and radial position tolerance
- Balance requirement and whether balancing is done by the buyer or the supplier
- Machining scope: bore, taper, keyway, slot faces
- NDT scope and acceptance criteria
- Certification: EN 10204 3.1, PPAP or FAIR
- Stocking agreement and pre-season release schedule
- Contact Wendy She – sales@cnsandcasting.com – WhatsApp +86-13777124360
FAQ
Why is EN-GJS-450-10 chosen over a stronger grade?
A fan hub is governed by toughness, damping and machinability rather than ultimate strength; 10% elongation and a ferritic matrix resist crack growth at the blade roots.
Can you help reduce fan unbalance?
Yes. We machine all blade root slots from a single datum on a dedicated fixture, which keeps pitch and radial position consistent and lowers residual unbalance.
Is balancing included?
A balance check on a mandrel can be included before packing, with the record attached to the inspection report; final rotor balancing is usually done by the buyer after blade assembly.
Can stock be held for the harvest season?
Yes. At the same time, we build finished hubs to a rolling forecast and released against pre-agreed seasonal call-offs.
