Why the Drawing Comes Before the Quote
For a custom impeller OEM project, the drawing is the contract. It defines the aerodynamic duty, the mechanical interface, the material, the balance class and the inspection criteria. When those items are complete, an impeller manufacturer in China can quote and start production without a round of clarification emails. When they are missing, both sides lose time. The checklist below covers what SINDFAN needs in order to review a fan impeller drawing and confirm feasibility.
1. Duty Point and Operating Conditions
- Required airflow and static or total pressure at the duty point.
- Operating speed (rpm) and whether the impeller is belt-driven, direct-driven or motor-mounted.
- Gas temperature, density, humidity, and whether the air stream is clean, dusty or corrosive.
- Continuous or intermittent duty, and the direction of rotation viewed from the drive side.
- Any site altitude or system effect that changes air density.
These inputs set blade angles, blade count and the resulting diameter. Without them, a drawing can be geometrically correct and still fail to perform.
2. Geometry and Interface Dimensions
- Outside diameter — SINDFAN produces custom impellers from Ø150 mm to Ø3150 mm.
- Bore diameter, keyway or taper-lock bushing, and shaft tolerance.
- Hub length, hub position and overall width, including any overhang past the inlet.
- Blade form: forward-curved, backward-curved, radial or paddle, with inlet and outlet angles if fixed.
- Inlet cone or orifice geometry, clearance to the inlet ring, and shroud profile.
- Mounting holes, bolt circle, pilot diameter, and any balancing holes or balancing plane locations.
Where an impeller replaces an existing unit, include the measured shaft diameter and the actual housing clearance. Nominal drawing dimensions are not enough for a drop-in fit.
3. Material and Construction
State the required material and the environment it must survive. SINDFAN works in four build routes:
- Aluminium die-cast — LM6 / A356, for volume production and low weight.
- GRP — hand-lay and RTM, including large, low-speed decorative impellers where a GRP skin is laid over a welded steel frame.
- Nylon 66 injection — small, high-volume impellers.
- Fabricated steel — welded assemblies for larger diameters and higher temperatures.
The material choice drives tooling cost and lead time, so it belongs on the drawing, not in a side conversation.
4. Balance Class and Tolerances
Balance is frequently omitted from incoming drawings and is one of the most common causes of vibration complaints at commissioning. SINDFAN balances to ISO 1940-1 G6.3 as standard, with G4.0 available where lower residual unbalance is required. The drawing should state the balance grade, the balancing planes, the correction method permitted (drilling, washers, weld), and the maximum residual unbalance if it is tighter than the standard.
5. Documentation Set
A drawing alone is often not enough for a first article. Send the full set:
- A dimensioned 2D drawing with tolerances and a revision block.
- A 3D model (STEP or IGES) where the impeller fits an existing housing.
- Material specification and any surface treatment.
- Inspection requirements: dimensional report, balance report, runout limits.
- Packing, marking and shipping terms.
From Drawing Approval to Delivery
Once a drawing is approved, SINDFAN moves from prototype to series production on the same tooling, so the approved sample and the production parts match. Typical lead time is 2–4 weeks after drawing approval, depending on material and quantity. In a recent export order, an overseas sheet-metal manufacturer ordered five impeller types from Ø300 mm to Ø790 mm, shipped FCA Tianjin in June 2026.
Send the Drawing, Get a Real Answer
Contact SINDFAN on WhatsApp +852 9524 8434 or email info@sind-tech.com with your duty point, drawing or 3D model. Include airflow, pressure, speed, temperature and material preference, and we will confirm diameter, construction route, balance class and lead time against your application.