Fan wheels are the widest workpiece family any balancing machine has to cover. A ventilation wheel is 400 mm across and weighs 8 kg; a process fan impeller is 2,000 mm and 400 kg. Both come off the same welding jig, both carry weld distortion, and both need correction before they leave the shop. In practice, buying a balancing machine for centrifugal fan impeller 1500 mm diameter wheels means buying a bed that spans the whole family — weight envelope, support spacing and belt width all set by your largest wheel, while the small ones still have to measure repeatably. This guide covers the sizing numbers, the bearing-type decision, and the post-weld step most fan builders underestimate.
1. Start With the Wheel, Not the Machine: Sizing for 400–2,000 mm
Sizing a fan impeller machine is driven by four numbers: wheel weight, outside diameter, service speed and correction method. Width matters less than on a lathe spindle, because a fabricated fan wheel is a wide disc — but the shaft overhang and bearing span decide how much bed length you need. Shenke engineers size these machines as follows:
✅ Weight envelope: largest wheel plus about 30% headroom, since a repaired impeller can come back heavier than the original drawing.
✅ Diameter and swing: the wheel must rotate clear of the bed and hood at full speed — check swing radius, not just diameter.
✅ Speed: a fan at 1,000–1,500 rpm sits at grade G6.3 per ISO 21940-11; high-pressure and high-speed fans often specify G2.5.
✅ Correction: welded balance weights inside the rim, or drilled holes in the backplate — decide before the machine is built, because it changes fixture access.
The arithmetic explains why fabrication tolerances matter so much. Permissible residual unbalance is U = 9549 × G × m / n. A 120 kg wheel at 1,200 rpm at G6.3 allows U = 9549 × 6.3 × 120 / 1200 ≈ 6,016 g·mm. At a 700 mm correction radius, that is only 8.6 grams of material — roughly one weld bead. Unless the wheel is measured after welding, that tolerance is gone before the fan is assembled. This is the single most common reason a balancing machine for centrifugal fan impeller 1500 mm diameter wheels ends up being specified with a wider weight range than the buyer first expected.
✅ Bottom line: Size on weight + swing + speed with 30% headroom; at G6.3 a 1,200 rpm fan wheel tolerates only grams, so measure after welding, not before.
2. Hard Bearing vs Soft Bearing: What Fits a Welded Fan Wheel?
For fabricated industrial fan wheels, hard-bearing machines are the better choice; soft-bearing machines remain the right tool for light, flexible rotors and laboratory work. This is the practical answer to the question hard bearing vs soft bearing balancing machine which is better — it depends entirely on rotor stiffness and production volume, not on brand preference.
✅ Hard bearing: rigid supports, force sensors, permanently calibrated. No calibration runs with trial weights, so a batch of wheels is measured in minutes each. Repeatability is stable across shifts, and the machine is far less sensitive to foundation and floor vibration.
✅ Soft bearing: compliant supports, displacement sensors, calibrated with trial weights on every new rotor type. Excellent for rotors that deflect at speed, and for R&D where rotor behaviour itself is being studied — but slower per part and more operator-dependent.
✅ For a fan shop: a welded wheel is a stiff, heavy disc-type rotor at moderate speed — exactly the profile hard-bearing measurement handles best. Belt drive adds the second benefit: no coupling error and no clamp marks on painted or machined surfaces.
A belt-drive horizontal machine from Shenke, built on the same heavy-duty bed design used for the YYQ-500 large-rotor machine, handles the disc-type family well; the full belt-drive range and swing capacities are listed in the product center. Two-plane correction is standard above roughly 0.5 width-to-diameter ratio, which covers most industrial fans; narrow ventilation wheels can often be corrected in one plane.
✅ Bottom line: Hard bearing wins for production fan wheels — no trial weights, stable repeatability, less floor sensitivity; choose soft bearing only for flexible or experimental rotors.
3. After Welding: Why the Wheel Changes and When to Re-Balance
Buying a balancing machine for blower wheel after welding is not a detail — it is the reason the machine exists. Welding pulls metal as it cools: the backplate dishes, blade pitch drifts by a degree or two, and the weld beads themselves are unevenly distributed. A wheel that was dimensionally perfect on the jig comes off the fixture with a couple unbalance that grows with diameter. At 1,500 mm, a 2 mm displacement of 300 g of blade material is already 600 g·mm — a tenth of the entire allowance at G6.3.
Re-balance at three points in the life of the wheel:
✅ After welding and stress relief, before painting — correction is easiest on bare steel.
✅ After any blade replacement, wear-plate rebuild or shaft repair, because mass distribution has changed.
✅ After field service that required removing the impeller from the fan casing, since re-mounting rarely repeats the original angular position.
Correction itself is straightforward on a fabricated wheel: weld small weights inside the rim on the light side, or drill on the heavy side of the backplate. Shenke supplies the fixture set and the measuring system — including the SK-780 readout — so the operator sees magnitude and angle in polar form and corrects in one pass instead of three.
✅ Bottom line: Balance after welding, after rebuilds and after re-mounting — weld distortion at 1,500 mm can consume a tenth of the G6.3 allowance before the fan ever runs.
Frequently Asked Questions
Q: What balance grade do centrifugal fan impellers need?
A: G6.3 per ISO 21940-11 is standard for general ventilation and process fans, calculated at the fan's service speed. High-pressure fans, direct-drive high-speed wheels and impellers above roughly 3,000 rpm usually specify G2.5. Do not use the balancing machine's speed in the calculation — the allowance follows the speed the wheel actually runs at.
Q: Is a hard-bearing machine less accurate than a soft-bearing one?
A: No — for production rotors it is usually more repeatable. When engineers ask hard bearing vs soft bearing balancing machine which is better in terms of resolution, the honest answer is that both reach the sensitivity a fan wheel needs; the difference shows up in cycle time, calibration effort and immunity to floor vibration. Soft bearing earns its place on flexible rotors that bend near service speed, not on welded steel wheels.
Q: Can one machine handle 400 mm and 2,000 mm wheels?
A: Yes, if you size on the largest wheel and confirm the small ones still measure repeatably. A balancing machine for centrifugal fan impeller 1500 mm diameter wheels typically also covers 400–800 mm ventilation wheels with the same saddles, provided the smallest rotor is heavy enough for the sensor range. Where the spread is extreme, Shenke supplies interchangeable saddle sets and, if needed, two capacity classes rather than one oversized compromise.
Q: Do you build custom machines for fan manufacturers?
A: Yes. As an OEM/ODM balancing machine manufacturer in China, Shenke builds beds, saddle spacing, belt width and fixtures around the wheel family you actually produce, and ships with installation, commissioning and operator training. Fan builders ordering a balancing machine for blower wheel after welding duty usually specify a fixture that locates on the shaft taper and a swing radius checked against their largest casing.
Ready to size a machine for your fan wheels? Send the largest and smallest wheel drawings — weight, diameter, service speed and correction method — and Shenke engineers will return a sizing proposal, fixture layout and factory-direct quotation within 24 hours.
Published: November 2026 | By Shenke Engineering Team
Fabricated 1,500 mm fan wheel on a heavy belt-drive balancing bed, with measuring cabinet alongside.
www.skbalancing.com
Shanghai Shenke Dynamic Balancing Machine Manufacturing Co., Ltd.