Part size limits: what fits the press, the galvanising bath and the powder-coating oven

Where the size limit comes from

The size of a part does not come from one place. The sheet is limited by the cutting table, the bend length is set by the press, and the finished part is checked against the galvanising bath and the oven chamber, so the tightest of these limits applies. The mistake shows up late: the drawing is approved, the sections are welded, and then the flange does not go into the bath or the pole does not fit the oven.

The numbers below are the limit sizes in the shop of POLYGONAL. Hanging in the bath, tooling and tolerances take part of the margin, so a part that sits right at a limit is always checked against the drawing, not by arithmetic alone.

Operation, limit, sizes: summary table

All sizes are for carbon steel parts unless stated otherwise. For other grades we confirm the maximum thickness for the order.

The sizes of the bath, the chamber and the press are production data of POLYGONAL, not a standard. For your part the final answer comes from reviewing the drawing.

A part must pass every operation

A part goes through several operations in a row, so its size is checked against all the limits, not just the one you started with. The table below shows conditional parts checked against the limits of the first table; each verdict is final only after the drawing is reviewed.

The sizes are conditional. The three sizes of a part are written in ascending order: the smallest is compared with the width of the bath or chamber, the largest with the length.

Cutting: what fits on the table

The laser takes a 2 × 12 m sheet, the plasma machine 2 × 6 m. Two practical points follow: a trapezoid blank for a long pole is no longer than 12 m, and a wide development that goes beyond 2 m is cut from several parts that are welded afterwards. It is better to put such a split into the shop drawings than to invent it in the shop.

Thickness is a separate limit: up to 25 mm on the laser and up to 50 mm on the plasma machine for carbon steel. For other grades we state the maximum thickness for your order, so send a sketch with the thickness and the sheet size.

After thermal cutting the edge keeps a hard layer and an oxide film. Before galvanising and coating the edge is brought to clean metal and sharp corners are rounded. In the zone of a future bend, burrs and the spot of raised hardness are ground off, since a crack can start there. Details are in the article on laser cutting price factors.

Bending on the press: length, thickness, throat

The press has a bend length of 12,000 mm and a force of 2000 t. Sheet up to 25 mm thick and up to 12 m long is bent in one pass, with no welded joints in the middle. The throat of the press is 2000 mm: this is how deep the part reaches past the bend line, so long flanges and large widths are checked separately.

Length and thickness of the sheet are looked at together with the force. A 25 mm sheet 2 m wide and 12 m long formally passes by size, and whether the force is enough for the needed angle and radius is shown by the bending force calculation.

The bend radius depends on the grade, the thickness and the rolling direction, and in long parts the bend line usually runs along the rolling direction, so the radius is larger. For parts to be galvanised take a radius with a margin over the minimum: the article on designing for galvanising gives not less than three thicknesses as a practical guide. More on the requirements for sheet and drawing is in the article on bending on the 2000 t press.

The size after bending does not match the size of the sheet. The finished part is what goes into the bath and the oven, so the request states both the development and the part dimensions after bending.

Galvanizing: what fits the bath

The bath measures 13,000 × 1,600 × 3,200 mm (length × width × depth). To check a part, write its three sizes in ascending order: the smallest must fit in 1,600 mm, the middle one in 3,200 mm and the largest in 13,000 mm. The sizes are taken together with protrusions: flanges, brackets, lifting lugs.

The allowance for hanging is not included in these numbers. The part is fixed in the bath and its exact position depends on its shape, so a part at the limit of all three sizes is checked against the drawing. The mass of one part for galvanising is up to 7 t; it is still stated in the request, because the hanging method depends on it.

In long hollow sections (over 6 m) the vent and drain holes are made larger or more numerous. Holes at both ends are placed diagonally, at the top and bottom points. The rules for holes, lap joints and cut corners are collected in the article on designing for hot-dip galvanising, and the checklist before dispatch in the article on preparation for galvanising.

The sizes are conditional, the final answer comes after the drawing is reviewed. Dimensions and mass can be estimated quickly in the galvanising cost calculator.

Powder coating: the 6 × 1 × 1.8 m chamber

The working chamber of the oven is 6 m long, 1 m wide and 1.8 m high. This is the tightest limit of all: it is less than half the length of the bath and narrower than it. Long lighting poles and masts of 8–12 m cannot be coated whole, but a section or part that fits in the chamber can.

If a part is galvanised and coated (duplex), both limits must be passed: the bath and the chamber. Coating is agreed before galvanising, because passivation against white rust worsens powder adhesion. About the coating system see the article powder coating: what the price depends on and the service page powder coating.

Powder settles poorly inside a tube or pole, so there the zinc protects, and the outside coating is agreed by size. Threads, bolt holes, earthing points and contact surfaces are closed with plugs or heat-resistant tape: mark them on the drawing.

How to split long members

A shipping element of a pole is usually not longer than 12 m: it is easy to transport and it passes through the sheet, the press and the bath. A pole up to 12 m inclusive goes in one section, a taller one consists of several. The mass of a shipping pack is not more than 5 t unless the contract says otherwise, and this also affects the split: see the technical requirements for poles.

Sections are joined by flanges or by a telescopic joint. In a flange joint the section lengths add up to the pole height. In a telescopic joint the sections enter one another, the joint length is taken at about 1.8 of the mean diameter, and its tolerance is 10–12 % of the joint length, so the sum of section lengths exceeds the height by the length of the joints. A conditional example: mean diameter in the joint zone 0.4 m, joint length 1.8 × 0.4 = 0.72 m, largest section 12 m.

An example with assumed values (0.72 m joint for all joints, section up to 12 m). The actual split comes from the calculation and the KM and KMD drawings. About the joints themselves see the article on multisided pole joints.

Not only poles: beams, chords, frames

A beam or chord longer than the bath or the transport is split into shipping elements and joined with bolts. Bolted joints are better assembled after galvanising, so the splice goes into the KMD at once, together with bolt holes sized for the coating: zinc reduces the hole diameter. Where exactly to put the splice is decided by the calculation, not by the length of the bath.

Galvanising in two dips

If a part is longer than the bath or does not pass by width, it is sometimes galvanised in two dips, turned over between them. This happens more rarely, makes the work harder, may affect the cost, and the method is agreed separately. So in the KMD the starting option is better a split into sections, and two dips are left as a separate decision agreed before fabrication.

What to state in the KMD and in the request

Sizes are checked at the drawing stage, when a change costs a pencil stroke, not a rework. State in the KMD and in the request:

• the three overall sizes of each shipping element together with flanges, brackets and lugs, and the mass of the element;
• the development and the part dimensions after bending, the steel grade and thickness;
• which operations wait for the part: cutting, bending, welding, galvanising, coating. If galvanising and coating go together, write about duplex separately;
• where the cut into sections goes and which joint is there: flange, telescopic or bolted;
• holes for air and zinc drainage in hollow members, cut corners of ribs;
• places that are not coated: threads, earthing, contact surfaces.

If there are no drawings, send a sketch: we prepare KM and KMD drawings and fabricate steel structures to the customer’s drawings (KM and KMD design, steel fabrication). The rules of presentation are in the articles on KMD drawings and how to order. Erection is done by a partner construction company.

Where mistakes are most common

• only the length is checked and the width is forgotten: the bath is 13 m long but only 1.6 m wide, and the oven is 1 m wide;
• the size is taken without flanges and brackets, and with them the part no longer goes into the bath;
• the sheet width is counted without the development: a 2 × 12 m sheet is too small if the development after bending comes out wider;
• coating of a 12 m section is planned without knowing that the chamber is only 6 m;
• a closed cavity is left without holes: in the bath it becomes dangerous;
• the galvanizer is not told that the part will be coated, and passivation spoils the adhesion of the powder;
• a pole is split into sections so that the flange of the bottom section does not go into the bath by diameter.

Standards and validity

The sizes of the press, the bath and the chamber are not a standard but production data of POLYGONAL, valid on the date of publication. Requirements for hot-dip galvanising of articles after fabrication are set out in DSTU EN ISO 1461:2024 (current). Guidance for the designer on articles to be galvanised is given in ISO 14713-2:2019 (in the European edition EN ISO 14713-2:2020, the latest edition); we have not confirmed the validity of a Ukrainian equivalent, so we refer to the international document.

The design and detailing of steel structures, including section joints, is done under DBN V.2.6-198:2014 «Steel structures. Design standards» (current, with Amendment No. 1). The figures in this article are for orientation: the split into sections and the joint sizes in a project are set by the calculation.