One fan, ten stations: the in-house build chain a trader can't show you

A trader shows you a datasheet. An assembler shows you a fan bolted together from parts bought in from wherever. Neither can show you the thing that actually decides whether your fan hits its duty point and stays quiet in year three — the run of stations between a steel plate and a tested machine, each with a check that has to pass before the part is allowed to move. That chain is what in-house fan manufacturing means, and it is the one thing a middleman structurally cannot put in front of you. As a custom centrifugal fan manufacturer, every critical operation and its inspection happens under our own roof — so the fan that ships is the fan that was engineered, not a close-enough approximation of it.

Here is one fan, followed from laser cut to factory acceptance test.

Station	What happens	The gate that must pass
1 · Laser	Fibre-laser plate cutting — every part and its ID are created here	First piece checked to the drawing before the batch cuts
2 · Rolling	Scroll strips, inlet rings, shrouds and cones rolled, cylindrical and conical (roughly 1–8 mm plate)	Radius, diameter and full cone geometry checked to drawing
3 · Bending	CNC press-brake bending of blades and plates	First-bend check of every dimension before the batch runs
4 · Impeller	Back plate, hub, blades and shroud built and welded out	Blade / notch direction confirmed to drawing before the first tack
5 · Balancing	Dynamic two-plane balancing on the machine	Residual unbalance at or below the calculated limit for the grade
6 · Casing	Scroll / volute, pedestal and inlet fabricated	Right angles at every tack, so the two casing halves actually close
7 · Assembly	Rotor on shaft, inlet and cone set; direct or belt / coupling drive	Free rotation by hand; final tightening by torque wrench, tapers dry
8 · Cone gap	Inlet cone tacked into position, running clearance set	Gap equal all round, 0.5–1.5% of wheel diameter per GA
9 · FAT	Mechanical run test, then works performance test	Vibration in ISO 20816 Zone A/B; duty met after density correction
10 · Finish	Cone welded, final paint, documentation pack	Signed FAT report travels with the fan as dispatch documentation

Cutting and forming: where the fan's identity is set

The laser is the first operation and the one that quietly governs everything after it — dimensional accuracy and part identity are both created here. A first-piece approval against the drawing, before the rest of the batch is committed, scraps one part instead of a whole sheet: the cheapest quality check in the shop. Every part is then deburred before it moves on, because a burr becomes a crack or a bad fit two stations downstream. Rolling and CNC bending follow the same discipline — parallel rollers so a cylinder does not come off as a cone, and a first-bend check of every dimension before the batch. Tilt welded in is tilt forever.

The impeller: the check that prevents the most expensive mistake

The impeller is the rotating heart of the fan and its most safety-critical part, so it carries the hardest rule on the floor: blade or notch direction is confirmed against the drawing before a single tack is laid. A reversed impeller is the most expensive direction mistake possible — it moves air backwards and looks perfectly normal doing it. Every blade radius is checked against a template, not by eye; an off-template blade changes the mass distribution blade-to-blade, and the wheel then arrives at the balancing machine already heavy on one side. Right angles between blade and back plate are verified, spatter is removed (trapped spatter is tomorrow's mystery noise), and only then does it weld out.

Balance to a number, not a feel

Every impeller goes to dynamic balancing — no exceptions — and anything reworked on a rotor goes back through balancing before it can move on. The permissible residual unbalance is calculated from the ISO 1940-1 / ISO 21940-11 method against rotor mass and service speed, to a stated grade (typically G6.3, or G2.5 where the duty demands it) — never judged by feel. A non-conforming wheel is quarantined and routed back, not shipped “close enough”. The full logic of grades and residual limits is in our note on balancing grade G2.5 and API 673. It matters more the harder the wheel works — abrasive and hot duties add wear protection and hardfacing to the same wheel without giving up the balance grade.

The cone gap, and the discipline of test-then-weld

At assembly the inlet cone sets the fan's running clearance: the cone-to-impeller gap must be equal all the way round and held to roughly 0.5–1.5% of impeller diameter per the GA — biased to the low end, with allowance for thermal growth on hot fans. This is performance, not cosmetics; an unequal gap is a measurable duty deviation. Which is why the cone is only tacked at assembly. The fan is tested first, and the cone is full-welded only after the test passes. Weld the cone before testing and you lock in whatever gap error the test would have revealed. It is a small piece of sequencing discipline that is invisible on a finished fan — and impossible to retrofit onto one you did not build.

The FAT: proof before dispatch

Before anything ships it runs a Factory Acceptance Test. The mechanical run test holds at rated speed and logs bearing temperatures, vibration velocity at both ends in three axes, and motor current on all phases; acceptance is ISO 20816 Zone A/B, and a new fan is expected to sit at Zone A (≤ 2.3 mm/s RMS). The works performance test is run to the IS 4894 / AMCA 210 method — Pitot-traverse flow, static pressure and shaft power, corrected to the contracted density basis by the fan laws and judged along the system line. That is an honest description of a works test; it is not a laboratory certified-ratings seal, and we do not dress it up as one. For petroleum, chemical and gas service the run test follows the API 673 method the contract names. Across the range we serve — up to 2,00,000 CMH, 2,000 mmWC and 400 HP, in materials rated to 600 °C — the signed FAT pack travels with the fan. Our works bench is rated to 400 HP; above it we test at reduced speed and convert by the fan laws, declaring the basis rather than leaving it silent. The quality system itself is ISO 9001:2015 certified — the one third-party certification in this story. Everything else named here is a method we test to, not a badge.

What a trader can't show you

Every arrow in that ten-station chain is a check that gates the next operation, and every one of them happens in our shop. A trader or assembler starts at station seven with parts someone else cut, formed and balanced — the gates that decide flow, pressure and vibration have already been passed or skipped, out of sight, before the fan reaches them. That is the difference you are actually buying. If you want to see it against your own duty — a dust-extraction wheel, a hot process fan, a high-static blower — start with the fan, and we will show you the chain behind it. Browse the product range and the applications we build for.

Talk to us about in-house fan manufacturing →

Jitamitra Electro Engineering · Fan-engineering notes, written for the engineer.