Two 8-metre poles can be quoted 400 and 800 RMB apart, and the difference hides in the process. A pole looks simple — a tapered steel tube — but it passes through five processes before it stands on a road. Skip one or thin one out, and the service life drops by years. We have built multiple township lighting projects in Shanxi; here is the sequence in production order.
Process 1: Cutting the blank
Poles are rolled from Q235 carbon steel plate, typically 3.0–4.0 mm thick. The flat plate is sheared into the developed shape calculated from the top diameter, bottom diameter and taper. The critical detail is taper calculation: an 8 m pole commonly uses 1:100 (about 10 mm of taper per metre). If the developed outline is cut off-angle, the rolled pole comes out twisted.
Process 2: Bending and rolling
A large press brake bends the plate into arc segments section by section, then a plate rolling machine closes them into a round. Quality shows in two places: whether the curvature is continuous (over-pressed sections leave visible ridges on the pole face), and how tight the seam closes — a wide gap concentrates weld stress, and the pole can crack along the seam after a few years standing.
Process 3: Welding and straightening
The seam is closed with one automatic straight-seam weld pass, then the flange, door frame and cap are welded on. Welds should be full and even, without slag or porosity, and the whole pole is straightened afterwards. At acceptance, check that welds are ground smooth and that straightness deviation stays within 1/1000 of the pole length — stretch a chord line and a bent pole is obvious at a glance.
Process 4: Hot-dip galvanizing
This is the process that decides the lifespan. After pickling, the whole pole is dipped into ~450 °C molten zinc, forming a metallurgical zinc-iron alloy layer. Project specifications require an average coating of ≥ 80 µm (GB/T 3091 and transportation-industry practice); coastal and high-wind sites should specify 85 µm or more plus a second powder coat. A proper coating keeps the pole rust-free for 15+ years outdoors; a spec-cut one weeps rust in three to five. See hot-dip vs cold galvanizing for acceptance criteria.
Process 5: Powder coating
Electrostatic powder coating adds the final weathering and finish layer over the zinc, most commonly in white, grey or dark green. Outdoor powder should hold colour and gloss for 7+ years without chalking. Note that the zinc surface must be phosphated or passivated before coating — powder sprayed directly onto zinc has poor adhesion and peels within a year or two.
How to inspect a pole at procurement
Three checks: ask for wall thickness in writing with the right to spot-check with callipers; ask for galvanizing data — coating thickness readings or an on-site gauge test; and examine the small parts — flange thickness, number of stiffening ribs, the rain lip over the access door. The small details are where a cutting corners shows first.